The method of thermal imagery is considered to be one of the most modern and effective methods of scanning terrestrial objects. For successful detec­tion and identification of the UGE-controlled objects, such imagery requires knowledge of the spectral characteristics of radiation, weakening of the pathway of the working range of wavelengths, as well as the characteristics and capabilities of equipment in the temperature and spatial resolution of a UGE. Efficiency of detection of thermal anomalies from space can be increased by multispectral imaging including the use of the visible spectrum that provides a higher quality of decoding images and binds heat-radiating objects to the terrain. Low-orbiting satellites or space stations may be used as carriers of the recording apparatus. Although satellites and space stations both have long orbital paths of observation, the long-term survival of thermal anomalies allows them to receive and store information on the same site area due to the lack of restrictions in the number of times they can review the UGE sites.

Transfer of infrared radiation on the ‘Earth-Space’ tracks took place in the spectral range from 8 to 14 microns (comparative assessments in some cases took into account the adjacent region of the spectrum). The radiation detector was focused on the thermal anomaly, with an ideal spectral char­acteristic in the range of wavelengths, located at the altitude of the space­craft orbit equal to 300 km. The zenith angle of sight ranged from 0° to 80°. The distributions of basic meteorological parameters are used to character­ize the atmospheric conditions in cloud-free atmosphere within their natural variability in the warm and cold periods of the year (McClatchey et al., 1972). Gas models include vertical profiles of pressure, temperature, density, and the amount of water vapor, carbon dioxide and ozone as meteorological parameters, to a greater degree of influence on the transfer of radiant energy in this spectral range. Aerosol atmospheric models include a set of basic types of aerosol particles (dust, water soluble, water-dust, soot parti­cles, acid aerosols, volcanic dust), the vertical distribution of their concen­trations, the spectral values of volume extinction a, the scattering в, and absorption 8 coefficients for local and continental aerosol types.

A quantity that must be determined is the extinction coefficient E (flux density of radiation from a source of unit power) as a function of orbital altitude H, the zenith angle of sight v, complex of meteorological parame­ters M, the spectral range ДА and calculated as a linear functional:

E(v, ДА) = TM (v, ДА) • TM (v, ДА) • Teax (v, M, ДА) • Tg (H, v), [27.1]

where TC is the attenuation due to the weakening of the molecular scattering of radiation, T^b is the weakening due to molecular (gas) absorp­tion of radiation, TO is the radiation attenuation due to scattering and absorption by aerosol and Tg is the radiation attenuation due to geometrical factors.

The function in Eq. [27.1] is calculated from the following relations:

Here z is the current height above the Earth, РДА is the transmission func­tion of the atmospheric gases, Ao = 0.55 micrometers, H is the ceiling of the
atmosphere equal to 80 km, and R is a distance from the source to the receiver.

The greatest difficulty in calculating the factors given in Eqs [27.2-27.5] is the calculation of the transmission functions in Eq. [27.3]. The methodol­ogy for calculating the transmission functions is chosen in accordance with the work of McClatchey et al. (1972) and allows determination of the attenuation due to a selective absorption of atmospheric gases and water vapor continuum absorption. Calculations of extinction coefficient are pre­sented in Fig. 27.7 as the E function of the zenith angle of sight v. The figure shows that the influence of aerosol extinction and molecular scattering is much weaker than the gas absorption. This explains the higher values of spectral transmittance in the cold season compared to the warm. From the graphs it follows also that a change in viewing angle from 0° to 80° for all weather conditions and satellite altitudes can be incorporated in a single change to the extinction coefficient E.

The energy flux density value of the extinction coefficient E should be multiplied by the flux of the intrinsic radiation source in the corresponding intervals. Self-radiation of the UGE thermal anomaly can be approximately estimated as gray-body radiation with a surface area equal to the square of light, which manifests itself in the thermal image. Assuming that the emis­sive capacity FAX(T) of the thermal anomaly is constant throughout the area, for typical sizes and temperatures, radiation flux density on orbit with a height of 300 km is in the spectral range 8-14 micrometers which is quite high for the infrared radiation quantity of about 10-9W cm-2.

It should be borne in mind that detection of thermal anomalies against the background of the outgoing radiation from the Earth and the atmos­phere depends on the response of the radiometer receiving element to temperature change, i. e. on the temperature contrast AT = T — Tbg or to change in the radiation flux density, i. e. on the energy contrast

27.7 Extinction coefficient depending on sight angle for high (a) and low (b) transparency of atmosphere: 1, AX = 4-5 micrometers; 2, 8-10 micrometers; 3, 10-12 micrometers.

K = (Ф — Ф6?)/(Ф + ФЬе). Here T and Tbg are the temperature of the thermal anomaly and background, and Ф and Ф^ are the relevant flux density in the orbit of the satellite/space station, provided that the spatial resolution of the detectors is close enough to the size of the thermal anomaly. Modern infrared receivers have a temperature coefficient of resistance, reaching tens of percent at 1°C. The typical thermal anomalies in the temperature contrast is AT = 10°C. Energy contrast reaches values of 0.07-0.09, if the pixel size does not exceed the size of the thermal anomaly, and decreases linearly with the increase of the former. Minimum resolvable contrast to existing energy equipment is 0.4% and corresponds to the range of varia­tion ratio of the characteristic size of thermal anomaly and a pixel in the range from 0.03 to 0.3, i. e. spatial resolution can substantially exceed the size of the thermal anomaly.

In addition to the spatial resolution, an important quantity for assessing the quality of the thermal and optical system is the probability of detecting thermal radiation from the object depending on signal/noise ratio, where the noise means temperature threshold of detection or, alternatively, tem­perature noise equivalent. The noise value is defined experimentally for specific optical systems and receives the equations of heat background light and varies from 0.1 to 0.2°C.

The method described provides a consistent and effective way if imple­menting operation related to decoding of information from the thermal anomaly as well as identifying its location and parameters. In this case, we consider the temperature field of the study area, mapped character images obtained under various shooting conditions, and analyze their dynamics with regard to the influence of all other factors. If the interpretation of thermal images is performed in conjunction with the data from visible or multispectral photography, it will facilitate recognition of terrain objects and allow the exclusion of anomalies of topographical nature, e. g. sun — warmed rock outcrops.

[1] Romuvaara (Kuhmo Municipality)

• Veitsivaara (Hyrynsalmi Municipality)

• Kivetty (Konginkangas Municipality)

• Syyry (Sievi Municipality)

• Olkiluoto (Eurajoki Municipality).

In 1992, TVO published a summary of the results from the site investiga­tions. After this phase in the siting process, Veitsivaara and Syyry were discarded, since they were considered less suitable than the remaining three sites.

[2] requirements for waste packages (e. g., surface dose rates, surface con­tamination, mass, leak tightness);

• requirements for waste forms (e. g., radionuclides content, composition and parameters of waste matrix and solidified waste, encapsulation material);

[3] 159 Member States (as of February 2013).

[4] In February 2013: Australia, Austria, Belgium, Canada, Czech Rep., Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Luxemburg, Mexico, Netherlands, Norway, Poland, Portugal, Rep. of Korea, Russian Federation, Slovak Rep., Slovenia, Spain, Sweden, Switzerland, Turkey, United Kingdom and the United States of America.

[5] The European Commission (EC) establishes policies, directives, regula­tions and recommendations in the field of nuclear energy, including the safe management of spent fuel and radioactive waste. In 2007, following a decision of the EC, the European Nuclear Safety Regulators Group (ENSREG) was established as an independent, authoritative expert body. Its aim is to help to establish the conditions for continuous improvement and to reach a common understanding in the areas of nuclear safety and radioactive waste management. It is composed of senior officials from the national nuclear safety, RAW safety or radiation protection regulatory authorities from all 27 Member States in the European Union and representatives of the EC [22]. Recently the European Commission approved a new Directive on the management of spent fuel and radioactive waste [23].

• Regulatory associations (networks) in Africa (Forum of Regulatory Bodies in Africa — FNRBA [24]), Europe (WENRA — Western Euro­pean Nuclear Regulators Association [25]), Latin America (Latin American Forum of Nuclear and Radiological Regulatory Organisa­tions — FORO [26]), Arab countries — ANNuR (Arab Network for Nuclear Regulators [27]), Asia — Asian Nuclear Safety Network (ANSN

[6]The standard is entitled ‘Radiation Protection and Safety of Radiation Sources — Interna­tional Basic Safety Standards’, but is commonly referred to as the Basic Safety Standards or

BSS.

[7] Category 1 sources, if not safely managed or securely protected, would be likely to cause permanent injury to a person who handled them, or were otherwise in contact with them, for more than a few minutes. It would probably be fatal to be close to this amount of unshielded material for a period of a few minutes to an hour. These sources are typically used in practices such as radiothermal generators, irradiators and radiation teletherapy [50].

[8] Category 2 sources, if not safely managed or securely protected, could cause permanent injury to a person who handled them, or were otherwise in contact with them, for a short time (minutes to hours). It could possibly be fatal to be close to this amount of unshielded radioac­tive material for a period of hours to days. These sources are typically used in practices such as industrial gamma radiography, high dose rate brachytherapy and medium dose rate brachy — therapy [50].

[9] Classification of Radioactive Waste, No. GSG-1 [3] that substitutes the previous waste classification No. 111-G-1.1 of 1994 [64];

• Management of Low and Intermediate Level Waste, No. WS-G-2.5 [65];

• Management of High Level Waste, No. WS-G-2.6 [66] ;

[10] 1 Tera-Becquerel (TBq) = 1012 atoms decaying per second or transmutations per second.

*1996-June 2012.

[11]1996-2002 — mission complete.

* 1991 to April 2012 at 142 L glass per canister and an assumed glass density of 2.75g/cc (390kg glass per container).

** Maximum total is 10,000 (capacity of vitrified product store), of which -2,200 will be returned to overseas customers. Actual total is expected to be less depending on post-operation clean-out strategy.

‘ 1989-2011.

11978-2008.

51985-1991.

"1995-2012.

“acidic waste loadings comprise fission products and minor actinides; corrosion products and alkali are not included as for neutralized wastes. a From [163]. bFrom [204]. cFrom [205].

dCaterine Veyer of AREVA, personal communication (2012). sSeiichiro Mitsui of JAEA, personal communication (2010). fP. P. Poluektor, personal communication (2010).

[12] single-phase (homogeneous) glasses

• multi-phase glass composite materials (GCMs; heterogeneous glasses)

• single-phase crystalline ceramic/mineral analogs

• multi-phase crystalline ceramic/mineral assemblages

• bitumen

• metals

• cements

• geopolymers (inorganic) and organic polymers

• hydroceramics

• ceramicretes.

[13]SRO: radius of influence -1.6-3 A around a central atom, e. g. polyhedra such as tetrahedral and octahedral structural units.

[14] MRO: radius of influence -3-6 A encompasses second — and third-neighbor environments around a central atom. The more highly ordered regions, referred to as clusters or quasicrystals, often have atomic arrangements that approach those of crystals.

[15] LRO extends beyond third-neighbor environments and gives crystalline ceramic/mineral structures their crystallographic periodicity.

[16] Supercalcines were the high temperature silicate-based ‘natural mineral’ assemblages proposed for HLW waste stabilization in the United States (1973-1985).

Adapted from [11].

[17] Phosphate glasses (aluminophosphates and iron phosphates) are not used commercially as frequently as the borosilicates and hence are not as well studied in HLW stabilization applications.

[18]This is not the baseline AJHM process that will produce a homogeneous glass with minimal crystallization.

substituted phase

These types of crystal-chemical substitutions have been studied in (1) Synroc (Synthetic rock) titanate phases such as zirconolite (CaZrTi2O7), perovskite (CaTiO3), and hollandites (nominally Ba(Al, Ti)2Ti6O16) [90], and (2) in high alumina tailored ceramic phases such as magnetoplumbites (Table 6.8). The magnetoplumbites (discussed below) are also found as a minor component in Synroc when the waste being stabilized is high in Al [91].

In the Synroc phase assemblages, the hollandite phase is the Cs+ host phase. The structure can be written as BaxCsy(Al, Fe)2x+yTi8-2x-yO16 where x + y must be <2 [92] [ There are two types of octahedral sites. One accommo­dates trivalent cations like Ah+, TrA and FeA while the other accommo­dates Ti4+ . The Cs+ is accommodated in tunnels that normally accommodate the Ba[+ cation. The Cs-Ba lattice sites are VIII-fold coordinated [90, 92] [ 7 Note that the number of lattice sites have to be equivalent on the left-hand side and right — hand sides of the equation.

[20] Saltstone contains 5 wt% cement, 25 wt% flyash, 25 wt% blast furnace slag, and 45 wt% salt solution.

[21] Conditions affecting dissolution, solubility of actinides. Environmental conditions such as reducing aqueous groundwater result in very low dissolution rates of fission products and low solubility of actinides in SNF dissolution. This limits the radionuclide release into the biosphere.

[22] —

[23] evaluation of the severity of the problem in terms of radionuclide con­centration or dose levels to determine whether there is a need to remediate;

• evaluation of the remediation alternatives including the feasibility, cost, waste generation and management, and risk reduction;

[24] De-licensing is taken to mean ‘ending of the period of responsibility under the Nuclear Installations Act’ and happens when the HSE gives notice in writing to the operator that in its opinion there has ‘ceased to be any danger from ionizing radiations’.

• Any residual radioactivity, above natural background levels, which can be satisfactorily demonstrated to pose a risk less than one in a million per year (of the order of 10 microsieverts or less per year) for any reasonably foreseeable land use is taken to be broadly acceptable.

• Additionally, the operator should demonstrate that risk has been reduced to levels as low as reasonably achievable and should take into account the views of relevant regulators in respect of non-radiological contamination issues.

• All risks are taken to be additional to natural background levels for the area, including an allowance for impacts from authorized discharges and artificial background from worldwide sources.

• The IAEA safety guide on the application of the concept of exclusion, exemption and clearance (RS-G-1.7) (IAEA, 2004) contains radionu­clide specific values that should be used to demonstrate achievement of

[25] repeated grouting using highly penetrating biocide cement composi­tions of cemented solidified RAW;

• creation of an anti-filtration screen in the soil on the perimeter of the repository;

• formation of a barrow from the natural materials on the surface of the repository;

• piling and welding sheets of the geo-membrane Carbofol (1.0-2.0 mm thick);

The main characteristics of the ‘Shelter’ object (SO) RAW are given in Table 11.7. The total waste activity of the SO as of the beginning of 2005 is approximately 4.1 x 1017Bq, and the waste volume (according to different estimates) is between 530,000 and 1,730,000 m3.

The volume of waste concentrated in RWDP and the main RWTSP of the ChEZ is approximately 2 million m3, and the total activity is estimated at 7.7 x 1015Bq. It should also be noted that the same amount of radionu­clides is again contained in natural objects (vegetation, soils, bottom

[27] In Ukraine, activities to create a deep geological repository have been carried out since 1993. They are performed by Institutes of the National Academy of Sciences of Ukraine and the enterprises of the State Geological Survey. This activity refers to the early stages of a siting and conceptual repository design. It is assumed that the most promising host rocks in which to locate a geological repository are Archaean and Proterozoic crystalline rocks of the Cher­nobyl Exclusion Zone and its vicinity. Two possible options for the repository design are considered: a mine (KBS-3 concept, Sweden) and a borehole one (VDH concept, Sweden). Further information can be found in Shestopalov et al. (2005,2008).

[28]The London Convention subdivided radioactive waste into high and low level waste, with definitions of high and low level waste that were derived specifically for disposals at sea.

[29] The policy is enabling to allow waste managers, regulators, facility owners and the NDA to take decisions on the long-term management of HAW.

• The policy is not prescriptive and it is the responsibility of HAW manag­ers to decide on HAW management methods on a case-by-case basis in accordance with the policy framework.

• An implementation strategy for the policy will be developed by the Scottish government.

• Long-term storage is the primary long-term management option.

• The waste hierarchy should be applied and HAW can be managed by treatment, storage or disposal.

[30] Defense waste is mainly characterized as radioactive material in a very diluted form, whereas civilian waste is mainly generated in a concen­trated form.

[31] CANDU® is a registered trademark of Atomic Energy of Canada Limited.

[32]Till or glacial till is unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. Its content may vary from clays to mixtures of clay, sand, gravel and boulders.

[33] Although no medium depth (higher confinement) repositories cur­rently exist in South Africa (still in the planning phase), waste needs to be classed in terms of general criteria for effective pre-disposal man­agement. Waste characterized in terms of general criteria will be con­sidered in the long-term safety assessments that are necessary for the authorization of such repositories. Taking a retrospective approach, the design of repositories will have to be suitable for waste that has been processed and is in compliance with specific long-term safety-related criteria.

• The long-term safety of the national near-surface repository for LILW at Vaalputs in the Northern Cape is demonstrated and is currently authorized in terms of specific criteria. The long-term safety assessment of Vaalputs needs to be reviewed in terms of specific criteria prior to the authorization of receipt of waste from different generators. This is necessary to evaluate the suitability of the disposal system at Vaalputs for specific waste streams and additional inventories.

[34] waste treatment and volume reduction technology

• low-level waste vitrification technology

[35] safety concerns about the disposal facility,

• lack of transparency and fairness during project implementation,

• lack of social consensus among the stakeholders.

In February 2004, the Ministry of Knowledge Economy (MKE) announced new site selection procedures, and MKE/KHNP made various efforts to enhance the acceptance by local residents of disposal facilities. As a result,

[36] groundwater infiltration rate into silos: re-estimation of the groundwa­ter infiltration rate into the concrete

• silos during the post-closure phase, in combination with justification of the human intrusion scenarios

• quality control of geochemical data: reconfirmation of the representa­tiveness of empirically determined site-specific geochemical data (e. g. sorption coefficients, diffusion coefficients, etc.)

• long-term management of uncertainties in geochemical data

• seismic safety and design: verification of the geological structure model and tectonic activity of the site

• structural stability of the rock caverns and silos.

The above KTIs were resolved through regulatory dialogues and requests for more detailed information along with the applicant ’s amendments to the license application documents, reflecting the results of further supple­mentary site surveys, safety assessments, and design changes, which occurred during the review process.

[37] control of waste transfers to prevent contamination,

• maintenance of normal operations of the waste treatment system to reduce generation of secondary waste,

• minimization of the entry of materials into controlled areas, and

[38] replacing dismantling notification by licensee, to approval of the licen­see’s decommissioning plan by the regulatory body,

• implementation of decommissioning as approved in the decommission­ing plan,

• completion of decommissioning is confirmed by the regulatory body and after confirmation of the completion of decommissioning, the operating licence becomes ineffective,

• the regulatory activities during the decommissioning process should be changed in accordance with the changes of functions of facilities and safety operation activities as the decommissioning proceeds.

Source: Used with permission of the Ministry of Economy, Trade and Industry (METI).

maximum at the end of March, and it gradually decreased to 100 Bq/L in May.

The release of volatile radioactive nuclides into the atmosphere from the three units is considered to have occurred mainly after March 14, while the hydrogen explosions of units 1 and 3 occurred on March 12 and on the morning of March 14, respectively. These large releases after the night of March 14, along with the unfortunate climate conditions of wind and rain/ snow at that time, have probably caused contamination over a wide region of the Fukushima Prefecture in a north-easterly direction. Along with the varying climate conditions, particularly of wind direction, some of the

Investigation of residual effects from peaceful explosions is a laborious and expensive task, requiring the creation of special missions with the appropri­ate hardware and monitoring equipment including vehicles, staffed by highly qualified scientific and technical personnel. For example, to study the thermal fields, among other things, requires manned aircraft. It is consider­ably more convenient to study the geophysical implications and methods of their control at test ranges where a developed technological infrastruc­ture and trained personnel with the necessary qualifications exist to ensure that the results of these studies for relevant peaceful uses of nuclear explo­sions are adequate. Therefore, a significant part of the material in this section is based on the results of experiments conducted at the Semipalat — insk nuclear proving ground.

The majority of the surveyed explosions took place at the Degelen moun­tain range, located near the Kalba-Chingiz deep fault. This complex, mostly granite, volcanic and volcanic-sedimentary rocks, forms a large structure with a diameter of about 30 km. Intrusive rocks are interspersed in the form of individual granite-like bodies of relatively small size. A smaller part of the surveyed explosions were in the area of the test site Balapan located close to the eastern border of the landfill. Geologically, much of it is placed in the Zaisan folded region. A latitudinal piece of the Kalba-Chingiz deep fault, which separates this area from Chingiz-Tarbagatai, runs almost along the southern border of the latter. The depth of the water table is 200-400 m. The entire area is characterized by a homogeneous filler surface, folded eluvial sands of 4-6 m, or dense clays (Busygin and Andreev 2004).

Climatic conditions at Semipalatinsk are sharply continental with an average temperature of about +1°C. Summer is hot and dry with tempera­tures up to +40°C. Autumn and spring are cloudy and cold with average temperatures not higher than +7°C. The exception is May, when it is warm and clear. Winter is cold with little snow and with temperatures as low as -40°C. These geological and climatic characteristics of the area determine the conditions of conservation of thermal lesions in the rocks, the formation of thermal anomalies on the ground surface, and the possibility of their detection.

The first results of the thermal regime created by the underground explo­sions (UGE) on the ground surface were obtained in the late 1980s and were published in a series of papers by Busygin et al. (1999) and Busygin and Andreev (2004). First ring-shaped forms were discovered covering the cleavage zone of the UGE as they were luminous in the infrared spectrum. The physics of these phenomena remains unclear. The formulation and solution of rigorous mathematical tasks was required to describe the proc­esses of heat transfer and gas flow. However, a comprehensive package of initial data and a set of direct measurements of temperature and air flow in the cavity and the Earth ’s surface, made in a wide range of temporary, geometric, and meteorological conditions, was also required.

Review of materials on the sprung hole of a UGE shows that for many years they have a high internal temperature, slowly decreasing over time (Israel, 1974’ Taylar, 1973). Results for the domestic UGE show that the average air temperature in the boiler cavities of the explosion conducted more than 10 years before, is 30-50°C, i. e., the boiler cavities of UGEs are long-term sources of heat.

It follows from Section 27.2 that the boiler cavity after the UGE is not absolutely airtight. The presence of anthropogenic influences, fracture zones, column collapses and other tectonic features makes the contents of the boiler cavity available for air transport and, consequently, for the removal of heat and gases present in the cavity to come to the surface. To control the intensity and configuration of thermal anomalies on the ground surface, the method of heat shot is employed from onboard aircraft, using the ‘Volcano’ thermal imaging equipment which is modified with a unit controlling the film transport rate, which requires a flight height range of 200-3,500 m above the surface. The method of optical-and-mechanical scan­ning was used in the direction perpendicular to the direction of travel of the thermal imager in the aircraft. The flights carried out tasks over the examined area, and the height of the flight was supposed to provide the required coverage.

The optical part of the recording apparatus was a cooled infrared radi­ometer with a sensitivity of 8-14 microns. The sensitive nature of the equip­ment required that it be placed in a hanging gondola on the outer side of the fuselage of the carrier, which eliminated the effects of the aircraft glass windows. Along with the heat-sensing aerial photography conducted in the visible spectrum which allowed detailed information about the surrounding landscape to be obtained, there was a need to decrypt the thermal images and a need to accurately reference the area of the thermal objects. In this way (Busygin and Andreev, 2004), more than 50 UGE were examined during the period from 1 to 26 after the date of the initial measurement.

Almost all of the surveys performed on the ground surface in the epicentral area were observed to be ring-shaped or curved thermal structures, cover­ing the cleavage zone of the explosion. The typical form of these structures is shown in Fig. 27.1.

To validate the existence of thermal anomalies, as long-term residual processes occurring in boiler UGE cavities, investigations were carried out in two directions. The first set of investigations was connected with the hypothesis of uneven solar heating of the soil due to the different solar exposure of mountain slopes and micro-relief. To this end, a loop of night and pre-dawn measurements in autumn and winter under cloudy conditions with zero duration of sunshine and little difference in day and night values of air temperature were performed. The results confirmed the presence of ring-shaped thermal anomalies. Indirectly, the role of solar warming from the thermal anomalies is refuted, as solar radiation during the cold season could ‘warm up’ only one side of the failure cone and warming was found in these ring-shaped patterns.

The second set of investigations was conducted to test the binding of thermal anomalies on the ground surface to a picture of the local actions of UGE. The problem was solved using ground-temperature well-logging methods in the area of the thermal anomaly tied to the locality on the thermal image. Measurements of ground surface temperature were made with copper wire resistance thermocouples (temperature sensors); the standard error did not exceed 0.2-0.4°C. For the measurements of each thermal anomaly, one or two measurement lines were created. Not less than 20 sensors were placed along a cable line at a distance of about 5 m from each other (Fig. 27.2). Measurement lines were located on the ground around the diameters of circles covering a cleavage zone. The sensors are protected from direct solar radiation by special shields. The true value of the measured temperature T was calculated for each sensor separately after adjusting for the actual impedance of the line. Each cycle of measurements was carried out for three days with interval readings after 2 hours. The duration of one data point on one line does not exceed 10 minutes.

Figure 27.3 shows the typical spatial distribution of temperature for the autumn-winter period for the profile of the location of temperature sensors

shown in Fig. 27.2 . Distances between sensors are marked as the abscissa on a proportional scale. It is evident that sensors located in a highlighted strip correspond to higher values of ground temperature compared with background values of temperature (about -9°C). The excess temperature reaches 8-10°C.

Figure 27.3 also shows that the gases exiting to the Earth’s surface have a temperature lower than the rock at the charge depth (6-8°C throughout the year). This has two causes. First, the cold-season air passing through an explosion cavity that is 20-40°C did not have sufficient time to warm up due to the high velocities of the air masses. Second, due to a lack of integrity arising from formation of a large number of deep cracks, there is deeper cooling of the rocks in the array, which significantly increases the contact area of the exhaust air from the cooled rock. To confirm the fact that the removal of heated air instead of air at the natural temperature of the boiler at the depth of the cavity was examined, a peaceful UGE was conducted in Kalmykia (Russia) in the warm season, i. e. at a background temperature of 21-23°C (Granberg et al. , 1997). Temperature thermal anomalies for it reached 28-34°C, which certainly indicates the presence of an artificial heat source from the UGE.

In parallel with the temperature well logging, estimates of the geometric dimensions of thermal anomalies were made. It was shown that a suffi­ciently broad energy spectrum at the depths of the UGE gives the maximum radius of the thermal anomalies which varies from 80 to 250 m, while the width of the thermal ring varies from 20 to 60 m. It was not possible to establish the full duration of thermal anomalies, as over a nearly ten-year period, their thermal anomalies remained virtually unchanged. For the UGE held in galleries, the largest fixed term for thermal anomalies at the time they could be observed was 25-26 years and for UGEs conducted in wells it was 16-18 years.

It is certainly interesting to study daily and seasonal measurements of the thermal effects of UGEs at individual sites. Diurnal temperature vari­ation, obtained by simultaneous measurements on a strip heater removed from the UGE and from the undamaged section of the Earth ’s surface, averaged over 48 experiments (October-November), is shown in Fig. 27.4 (here t0c = local time). It can be seen that the thermal effect at the UGE site was observed continuously for days in the field, according to the thermal image, due to removal of heat from the air cavity (line 1). Characteristically, the temperature fluctuations during a day in the field of thermal anomalies are about 1°C, while for the damaged portion of the UGE, site surface peak-temperature reaches 4°C.

Significant differences are observed in the form of plots of temperature versus time for undisturbed and disturbed UGE sites. For undisturbed sites, the temperature dependence is very ordinary, without thermal anomalies in the afternoon heating and only minimum temperature anomalies at 7-8 a. m. All this also suggests that the observed thermal anomalies are not the result of solar heating of the Earth ’s surface and that the surface albedo changes under the influence of the UGE.

Seasonal temperature variation, in contrast to the daily temperature vari­ation, was studied the least. In particular, during the warmer months there have been instances when the UGEs conducted in groups decreased by 2-3°C in the cleavage zone compared with the background temperature. To explain such phenomena, a phenomenological model for the formation and dynamics of thermal anomalies based on the principles of ‘heating effect’ was proposed. Its essence lies in the fact that the movement of air through the heated boiler cavity occurs by gas convection, and the direction of motion can be either from the portal tunnel up through tectonic faults in the epicentral area, or vice versa. From the equation for the depression

thrust air he = A(tB — tH), where A isa coefficient for atmospheric parameters and channel exhalation of air; tH is outside air temperature; and tB is aver­aged over the profile of raising the air temperature inside the rock, it is evident that the magnitude of depression is proportional to the temperature difference outside and passing along the tectonic disturbance of air, and the direction of motion is determined by the sign of this difference. If the tem­perature tB is calculated by using the empirical formula tB = 1.1(tp — 6)/H + 6 (Busygin et al, 1999), where tp is air temperature in the boiler cavity, and H is the reduced depth of the UGE, we can obtain approximate values of the external temperature of a UGE site, for which one should observe a positive depression (he > 0). For example, for an explosion with the yield 1 kt, warhead detonation depth H = 100 m, a positive depression is observed when the outside temperature does not exceed 16°C if the air temperature in the cavity is 100°C. If the temperature in the cavity decreases to 20°C, the boundary outside temperature decreases to 7-7.5°C.

The estimates given are quite approximate until a full-scale experiment can be carried out with monitored directions of transport and air flow to the outside air temperature. It should be noted that the direct measurement of air movements is possible only in the portal tunnel. In the area of the cleavage phenomena, as mentioned above, anemometric measurements are difficult due to the complexity of micro-relief areas and the inability to visu­ally determine the position of the majority of cracks, which serve as conduits to move the air.

Air mass velocity was measured using an anemometer at a distance of 40-50 m from the tunnel portal. The direction of air mass movement is determined by the deviation of the flame or the direction of motion of smoke from burning smoke grenades (at speeds below 0.2 m/s). The meas­urements were performed at two points located at the ‘top’ and ‘bottom’ gallery. In each session, measurements of velocity were carried out at least three times for a duration of 10 s. By measuring the mean values taken for air velocity at the point of measurement, the air flow can be calculated. Results are summarized in Table 27.1 which indicate the following:

The experimental results qualitatively confirm the adequacy of the pro­posed model to real processes. It should be noted that in wells, a high temperature persists for much longer than in galleries because the heat loss occurs only due to natural convection (i. e., there is no is ‘stove’ effect). According to field measurements at Semipalatinsk site, the temperatures in the wells have decreased to 42-45°C some 6 years after the explosion, while in the galleries the temperature has been observed for 1.5-2 years.

Along with air, radionuclide products are transported to the Earth’s surface. Direct measurements of the exposure dose on the profile of thermal anomalies have shown that in this case the radiation levels are 3-5 times higher than natural background levels (Fig. 27.6). Comparison of tempera­ture and gamma-radiation curves indicates a high degree of correlation of these two processes. The distribution of activity and concentration of radon behaves similarly. In the location of the thermal anomaly, the volume of radon activity is 80-100 Bq/m3. At the same time over the epicenter of the explosion, the natural background of ionizing radiation remains: 5-10 micro — R/h for gamma-rays and 30-40 Bq/m3 for radon.

During surveys of the territories of Semipalatinsk nuclear test site by Amer­ican satellites NOAA-14 and NOAA-15, experts at the National Nuclear Centre of Kazakhstan detected large-scale surface temperature changes (Zakarin et al., 1997; Sultangazov et al., 1997). Their findings indicated the presence of a regional thermal anomaly with a surplus temperature of about 10°C in an area which was over 20,000 km2, i. e., the entire area of the landfill including the sites of Degelen and Balapan. The presence of such a thermal anomaly was assured to be associated with increased activity of the earth surface and the active mechanism of ‘smoldering’ reactions of nuclear fission. It is hypothesized that, under the influence of gamma radiation in the atmospheric boundary layer, reactions occur that result in a certain part of the oxygen being converted into ozone (Melent’ev and Velikhanov, 2003). Since ozone is heavier than air, it is concentrated at the surface of the Earth and, having been an active oxygenator, produces detrimental effects on biological systems. This effect is confirmed by the images obtained from satellites: there is practically no vegetation in the places that experi­enced these higher temperatures. Publications on this issue are the subject of much scientific debate. It is clear that the parts of the Earth’ s surface exposed to nuclear explosions should be looked at in more detail to examine the structure of the thermal field at the landfill, in order to draw attention to the complex combination of natural conditions and radiation effects, taking into account the low spatial resolution of the apparatus of NOAA satellites.

In addition, these influences are manifested at the ground surface (under certain conditions they can be observed visually, such as when snow melts in the warmer parts of the area). However, all processes associated prima­rily with the underground migration of radioactive products in the aqueous and hydrocarbon layers (including the partitioning of radioactive products in the area of the boiler cavity from a melt solution, and their contamination of surface and groundwater) and changes in the hydrological regime of aquifers are hidden from the naked eye.

The articles by Kiryukhina and Shahidzhanov (2003) and Bakharev et al. ( 2002 ) specifically note the possible effects of long-term exposure of ele­ments of the cavity to radionuclides and the post-explosion collapse of aquifers after different times. In this case, additional man-made caverns and aquifers contaminated with radionuclides may produce an ever-expanding contaminated area in concert with the natural aquifer system. It is noted that the radiation risk can increase substantially if the boiler starts to accu­mulate karst cavities or other water, that interacts with calcium oxide which can serve as a basis for the formation of liquid radioactive brine (calcium hydroxide), which is able to penetrate sufficiently large distances, up to the upper layers of aquifers. With technological processes occurring near such cavities, the removal of radioactive material to the surface should not be excluded. In limestone-containing rocks, these processes can be exacer­bated by the fact that it is likely that the crushed pile containing calcium oxide and carbon dioxide will expand and will be distributed through per­meable systems and brought to the surface through increased fracturing.

Observations on the migration of radioactive products from underground nuclear explosions carried out in permafrost conditions have been described by Golubov et al. (2003) and Kozhukhov and Kukushkin (2003). The distri­bution of radon, tritium, strontium and other radionuclide contents in the water, and gamma radiation in the vicinity of the explosion ‘Crystal’, carried out in 1974 in Yakutia near the diamond-mining quarry known as ‘Udachnyi’, were studied. Measurements were carried out from the epicenter to the quarry (about 5 km) and showed the following:

1. The level of gamma radiation ranged from 9 to 14 micro-R/h, i. e. it did not exceed natural background levels when the whole area was surveyed.

2. The volume of the radon activity in the epicenter, at a distance of 2.5 km, ranged from 400-500 to 1,300-1,400 Bq/m3.

3. In the area of the quarry, the radon content was 200-700 Bq/m3, suggest­ing that the rate of migration of radon in the local soil is low.

4. There is increased concentration of tritium to 220 Bq/l in the epicenter of the explosion.

5. Concentrations of radioactive carbon and strontium in the drained brines on the side quarry of ‘Udachnyi’ are on average 2-3 times higher than the corresponding concentrations in groundwater from technologi­cal wells close to the background level.

6. It cannot be excluded that the permeability of permafrost rocks in this area caused the working quarry horizons to drop to a much greater depth than that of the cavity created by the nuclear explosion, thereby promoting the drainage of underground brines in the vicinity of the cavity wall of a quarry with the formation of the network of flooded cracks with dissolved radioactive products.

Thus, according to Bakharev et al. (2002), each underground nuclear explo­sion site creates a self-generating uncontrolled dumping of radioactive products into the environment that can have a permanent impact on nature and mankind and, therefore, should be regarded as a functioning ‘radiation — dangerous’ object. Evaluation of radiation and ecological safety in this case is connected with the prediction of the secondary impacts of the residual effects of an explosion on the environment and should be based analysis of situations that could lead to further dissemination and redistribution of the radioactive products.

When a camouflet explosion occurs under high temperature (over a million degrees Kelvin) and high pressure (order of several million atmospheres), evaporation and melting of rock occurs in the region where the charge was laid, resulting in a boiler chamber having a shape similar to a three­dimensional ellipsoid. The effective radius of this cavity is 10-40 m. The cavity wall thickness is several tens of centimeters, composed of sintered layers of rock. The mass of the melt reaches 400 m at 1 kiloton of explosive power. Behind the wall cavity, as a result of the shock wave, is crushed rock. At large distances behind the wall cavity, is a region of increased fracturing. A truncated cylinder shape is formed with the upper limit in the cleavage zone impacting the surface of the Earth above the boiler cavity zone where increased fracturing occurs (Israel, 1974).

Over time, gravity causes the melt to flow down from the top and side walls of the cavity to its lower part, forming a lens of melt. After a further decrease in temperature, the melt passes into a solid phase and is partially or completely embedded with fragments of rock up to a height of a few meters from the bottom of the cavity. In this case, the bottom layer of the fractured rock pile covers the lens of melt. The array of the rock above the boiler cavity has been destroyed and eventually starts to sink down to form a pillar collapse. This process partially reverses the expansion of soil and rock mechanical faults caused by the shock wave, but also lowers the gas pressure in the cavity that was formed. Since the diameter of the column collapses the diameter of the boiler cavity, the cave only partially fills the cavity, forming one or more hollow zones located closer to the surface. The pillar collapse has very high moisture and gas permeability. The associated, filtration coefficient is hundreds of meters per day, and the coefficient of loosening of pillar collapses, defined by the ratio of porosity before and after the explosion, reaches 0.73-0.85. At the same time, the lateral border pillar collapses and is clearly separated from the solid undisturbed rock. At the point of contact, the lateral border pillar collapses along with the adja­cent undisturbed rock to form a peeled zone with permeability greater than the permeability of the collapsed column. At the ground surface above the explosion zone epicenter cleavage phenomena were observed. These took the form of swelling or rock subsidence depending on the exact nature of the explosion. Often crushed rocks are observed on the rock — similar arrays in the cleavage zone.

Because of the complexity of nuclear processes, a range of radionuclides are released in the explosion, which are deposited mainly in the cavity of the explosion. High-melting products are concentrated mainly in the lens of the melt and are mostly fissile nuclides of uranium and plutonium, fission fragments and neutron-activated elements of the charger and breeder. In the column collapse and fracture zone, volatile compounds such as pluto­nium and polonium are concentrated, as well as the radionuclides stron­tium, cesium, lanthanum, etc. (Israel, 1974).

V. P. B U S Y GIN, Defence Department, Russia

DOI: 10.1533/9780857097446.3.833

Abstract: This chapter reviews and discusses the effects of residual features on the long-term geothermal activity in the epicentral zone of underground nuclear explosions (UGE). The thermal anomaly parameters and their connection to carrying out thermal surveys and surface thermal logging on the present day surface are determined. A remote method of measuring the thermal anomalies is proposed.

Key words: underground nuclear explosion, radioactive waste, thermal radiation, monitoring, epicentral zone.

27.1 Introduction

Worldwide, 2,054 nuclear explosions have been conducted since 1945, including 1,524 underground explosions (many explosions were carried out in groups) (Kochran et al., 1992; Mikhailov, 1992, 2001). The last 1,373 explo­sions were performed at special nuclear test sites:

• 333 explosions at Semipalatinsk and West Kazakhstan (former Soviet territory, at present the territory of the Republic of Kazakhstan),

• 39 explosions at Novaya Zemlya (Russia),

• 781 explosions in the US (Nevada),

• 3 explosions in the USA on the Island of Amchitka (Alaska) landfills,

• 13 explosions in Algeria (District Hoggar),

• 147 explosions on the islands of Mururoa and Fangataufa (France)

• 24 explosions at the Nevada test site in the US were performed by the United Kingdom,

• 24 explosions were performed at the Lop Nor test site in China,

• Miscellaneous test explosions were carried out by India (3), Pakistan (2), and North Korea (2) (Mikhailov, 2001).

Other underground nuclear explosions were carried out underground at various test sites or on the surface, but with the purpose of applying the technology of nuclear explosions for peaceful solutions of a variety of tech­nical problems (Mikhailov, 2001; Logachev et al., 2001).

In the Soviet Union from 1961 to 1987, in accordance with Programme No 7 ‘Nuclear explosions for the national economy,’ 124 industrial com­plexes experienced an explosion, of which a number were carried out at the Semipalatinsk test site. Outside the territory of the present-day Russia, 80 explosions were carried out in the Republic of Kazakhstan (outside the polygon), 32 in the Ukraine, two in Uzbekistan, and two in Turkmenistan. The majority of the explosions were carried out in camouflet option, i. e. without a breakthrough cavern explosion into the atmosphere, and were aimed at solving problems: seismic sensing (39), creation of industrial con­tainers for food storage (26), working out the technology and scientific experiments (22), intensification of oil fields (21), eliminating emergency fountain (5), creating reservoirs (4), waste disposal in deep horizons (2), crushing ore (2), prevention of gas emission in coal seams (1), creating channels (1), and tailings dams (1) (Mikhailov, 2001; Israel, 1974).

Most of the explosions were carried out under difficult physical and geological conditions: in permafrost, semi-deserts, mountains, and salt for­mations in mining areas. Together with the explosion parameters and the monitoring information, these conditions determine the nature of residual geophysical phenomena, i. e. cleavage zones, zones of increased fracturing, changes in the permeability induced by electric and magnetic fields, thermal effects, and possible contamination with radioisotopes, which are precursors of volatile radioactive elements, increased release of radioactive radon gas, and changes in the environmental performance of the natural environment, etc.

This chapter describes the features and control areas of underground nuclear explosions and potential changes over long time periods, which allow evaluation of the state of the environment, i. e. the outward manifesta­tion of certain physical fields on the surface.

Section 27.2 describes the basic mechanisms of the boiler cavity, pillar collapses, and the cleavage phenomena on the surface, while also summariz­ing the classification and spatial distribution of radioactive waste. Section 27.3 examines the long-term problematic situations that arise at the surface, in aquifers and hydrocarbon horizons in the zone of underground nuclear explosions. There are cases that require regular monitoring. Section 27.4 is devoted to describing the results of thermal imagery and ground tempera­ture well logging in areas of underground nuclear explosions. A phenom­enological model of formation and dynamics of thermal anomalies is developed. Links are made between thermal anomalies, the level of gamma background radiation, and radon releases. In Section 27.5 we propose a method using monitoring by spacecraft to measure thermal anomalies. The prospects of applying this method for global monitoring of the effects of underground nuclear explosions are determined.

These final sections overview the results of flow and transport modeling studies and assessments of uncertainty for the Frenchman Flat CAU, the most developed of the CAU studies on the NNSS. There are three dominant features of all conceptual models of the Frenchman Flat basin (Fig. 26.4):

1. the high hydraulic heads in the CP basin northwest of Frenchman Flat (over 100 m higher heads than the Frenchman Flat basin; see Fig. 26.4),

2. the semi-perched condition of groundwater in the alluvial and volcanic aquifers with higher heads in these aquifers than the regional LCA,

3. the southeastward thinning of the volcanic section beneath the basin across Frenchman Flat.

These combined features support two inferential observations for the basin. First, groundwater flow in the alluvial and volcanic aquifers is likely hori­zontal across the basin from northwest to southeast (NNES, 2010a, b). Second, there is increased leakage downward into the LCA from the allu­vial and volcanic aquifers as the basal volcanic confining unit thins to the southeast and/or is offset by faults associated with the Rock Valley fault system. Particle track studies originating at locations of underground tests show southeast flow through the alluvial and volcanic aquifers changing to southwestward flow in the LCA following surface and subsurface faults associated with the basin structure (Bechtel Nevada, 2005; SNJV, 2006; NNES, 2010a, b). These observations are consistent with groundwater flow converging into and following faults of the Rock Valley fault system in southern Frenchman Flat (Fig. 26.8).

Modeling studies for the Frenchman Flat CAU combine steady state and transient source term studies, multiple alternative representations of the groundwater flow system, and probabilistic transport simulations. Source term models of radionuclide releases into groundwater were developed for

26.8 Satellite photograph of the Frenchman Flat basin on the southeast edge of the NNSS showing the major structural features of the basin and directions of groundwater flow (large black arrows: regional flow system; large gray arrow: local flow in the alluvial and volcanic aquifers). The Rock Valley fault zone is a zone of echelon faults that form the Rock Valley fault system. The asterisks mark the location of ten underground nuclear tests; three in central Frenchman Flat and seven in the north part of the basin. The solid gray lines outline the edges of contaminated groundwater defined by the 95th percentile of exceeding the radiological standards of the Safe Drinking Water Act over 1,000 years. These contaminant boundaries are small (<500 m length and for some tests in alluvium, the contaminant boundaries are smaller than the asterisk symbol marking the test locations); the contaminant boundaries are larger for two tests where the underground cavity was in or near fractured volcanic rocks (two tests in the northern area) or where a 17-year radionuclide pumping experiment discharged contaminated groundwater on the surface (one test in the central area).

two settings. First, the radiological source term for underground tests in alluvium were calibrated, for both steady-state and transient models, to observed breakthrough of radionuclides at a pumping well located 91 m from the CAMBRIC test in the water table in alluvium (Tompson et al., 1999; Carle et al., 2007). Second, two underground tests in northern French­man Flat were conducted above the water table in or near fractured vol­canic rock, where the rock permeability and porosity is inferred to be enhanced from the effects of the test detonation (IAEA, 1998). Simplified source term models were developed for these tests that account for unsatu­rated and saturated flow and transport and test-induced changes in rock properties (NNES, 2010a, b).

Multiple steady state groundwater flow models were developed for the Frenchman Flat CAU (SNJV, 2006) that are calibrated to hydraulic heads and permeability data for hydrostratigraphic rock units, and attempt to account for conceptual model uncertainty. The evaluated components of conceptual (structural) model uncertainty include variability in boundary conditions and boundary fluxes, permissible alternative hydrogeological frameworks for the basin, including structure (faults and basin features), stratigraphic units within the basin, and alternative recharge models. The goal in developing flow models was not to identify a best-fit calibration or a best predictor flow model but instead to distinguish a range of alternative flow models that capture the range of variation in flow fields from paramet­ric and structural uncertainty. This range in groundwater flow was then used in transport simulations. Statistical metrics of goodness of fit of alternative groundwater calibrations did not provide useful information for discrimi­nating or screening groundwater flow models. Two alternative sets of data did provide useful information for categorizing results for calibrated flow models (SNJV, 2006). These include variability in particle track results, and variability in groundwater velocity and direction at test cavity locations using linear predictive uncertainty analysis from parameter estimation soft­ware (PEST; Doherty, 2007).

Monte Carlo transport simulations were conducted for underground tests at the two testing areas in Frenchman Flat (Fig. 26.4). Four flow models were combined with alternative sets of boundary conditions (boundary fluxes, hydrostratigraphic frameworks and recharge) to represent the vari­ability in the groundwater flow field (velocity and direction of flow at the test cavity). These flow conditions were established at the underground test cavities as the initial conditions for transport simulations sampling stochas­tic transport parameters using a streamline-based convolution transport code (Robinson et al., 2011). Radionuclide concentrations for 1,000 years of transport were post-processed to develop probabilistic forecasts of exceeding the radiological requirements of the SDWA (Fig. 26.8); the boundary of this representation denotes the limits of contaminated groundwater (contaminant boundary) defined as a 5% chance or less of exceeding the SDWA. There are two categories of contaminant boundaries: (1) small boundaries (<500 m maximum lateral distance) where the test cavity and transport are in the alluvial aquifer and (2) larger boundaries (>1600 m) where the source term and/or transport is in fractured volcanic rock. For the latter category (two underground tests), the contaminant boundaries extend slightly off the NNSS boundaries into adjacent Federal land (Fig. 26.8).

The contaminant boundaries of the central testing area of Frenchman Flat (Fig. 26.8) are complicated by two factors. First, the long-term pumping test for the CAMBRIC test discharged contaminated groundwater on the surface into a ditch that drained into the Frenchman Flat playa. Second, the discharged contaminated water in the drainage ditch infiltrated to the water table in concentrations that exceed the SDWA. This required transient models to account for the 17 years of continuous aquifer pumping and surface discharge of contaminated water and significantly extended the contaminant boundaries of the central testing area.

The contaminant boundaries depicted in Fig. 26.8 will be used for two regulatory decisions. First, the boundary geometries will be used to desig­nate surface use restriction areas where institutional controls will be imposed to restrict all drilling to potentially contaminated groundwater. Second, the contaminant boundaries and results of subsequent monitoring studies will be used by NDEP to identify a regulatory boundary designed to protect the public and environment from exposure to contaminated groundwater. The NNSA/NSO will be required to develop a plan to miti­gate potential impacts on the public, if radionuclides are detected at the regulatory boundary. The regulatory boundary has tentatively been identi­fied as the Rock Valley fault zone at the southern end of Frenchman Flat, the expected migration pathway to public access to groundwater south of the southern boundary of the NNSS.

The transport model for the Frenchman Flat CAU was accepted by NDEP following successful external peer review of the CAU studies (Navarro-Intera, 2010). This marks the first successful completion of the model development stage under the UGTA strategy and the initiation of the model evaluation stage for the Frenchman Flat CAU (USDOE, 2011).

26.4 Acknowledgments

This chapter is a snapshot of ongoing work for UGTA. This work is a multi­disciplinary cooperative effort conducted by scientists at the Desert Research Institute, the Lawrence Livermore National Laboratory, the Los Alamos National Laboratory, National Security Technologies, Navarro — Intera and the US Geological Survey. The chapter was improved through review comments provided by Bimal Mukhopadhyay, Joe Fenelon and Susan Krenzien. Nathan Bryant and Joe Fenelon assisted in the develop­ment of the chapter figures.

A risk-informed perspective was added to the revised UGTA strategy, recognizing the twofold nature of the project goals. The first essential goal is to complete a sufficient level of characterization and modeling studies to establish a fundamental understanding of the processes of release and transport of test-produced radionuclides in groundwater. Second, this knowledge is applied to each CAU to identify the risk of radionuclide contamination to the public. Risk in this context is the likelihood and consequences of public exposure to contaminated groundwater and is mitigated by two factors. The first is natural attenuation or intrinsic reme­diation, the operation of natural processes that can reduce the concentra­tion of a contaminant in groundwater (National Research Council, 2007a). For groundwater flow at the NNSS, natural attenuation relies on the processes of dispersion, dilution, radionuclide retardation and radioac­tive decay to reduce the concentration of radionuclides in groundwater from their concentrations near test cavities. Second, access to contaminated groundwater is required to complete the pathway to public exposure sce­narios, the consequences portion of the risk definition. Public access to groundwater on the NNSS is restricted by the current institutional control policies. Assuming continuity of these policies, the likelihood of public access to contaminated groundwater is greatest where there is the potential for migration of radionuclides beyond the NNSS boundaries.

As noted previously, the approach to assessing the likelihood of the hazard part of the risk definition for radionuclide contamination of ground­water is developing probabilistic maps of exceeding the SDWA as specified in the FFACO agreement. The consequences of groundwater contamina­tion from underground testing are currently controlled through implemen­tation of worker safety protocols with respect to accessing contaminated groundwater and maintaining restrictions on public access to the NNSS. The uncertainties in these controls are the effectiveness and duration of active institutional control of the NNSS and the ability of NNSA/NSO to establish and maintain institutional controls for areas of groundwater contamination that extend off the boundaries of the NNSS.

Fig. 26.3 shows the location of sites of past underground testing on the NNSS for the major CAUs, and the expected directions of groundwater flow and radionuclide transport are shown in Fig. 26.2. The highest source term by activity in Curies is the Pahute Mesa CAU which contains less than 10% of the underground tests but more than 60% of the radiological source term (8.0 x 107 curies). The Yucca Flat CAU includes about 82% of the underground tests and 37% of the radiological inventory (5.1 x 107 curies). Slightly over 7% of the underground tests on the NNSS were conducted at the Rainier Mesa/Shoshone Mountain CAU which includes 0.7% of the radiological source term (8.9 x 105 curies). Finally, 10 underground tests were detonated at the Frenchman Flat CAU and these tests equal about

0. 14% of the radiological source term (1.9 x 105 curies).

Comparison of Fig. 26.3 and the above cited distributions of the radiologi­cal source term by CAU provide important risk perspectives. The Pahute Mesa CAU contains the highest underground inventory and the greatest potential for contaminant migration off of the NNSS. As noted previously, tritium contamination has already been detected in groundwater just south of the NNSS boundaries in western Pahute Mesa. By virtue of the high inventory and high likelihood of migration off of the NNSS, the Pahute Mesa CAU provides the greatest risk to the public. The Frenchman Flat CAU has the lowest inventory of the UGTA CAUs but the results of the transport modeling indicate a fair potential for offsite migration of radio­nuclides at the southeast boundary of the NNSS (Fig. 26.4). The Yucca Flat CAU includes the highest number of underground tests and a relatively high inventory, but sites of underground testing are more than 40 km away from the southern boundaries of the NNSS. Finally, the Rainier Mesa/ Shoshone Mountain CAU has both a relatively small inventory and a very long expected distance of transport of radionuclides to the southern boundary of the NNSS. From a risk perspective, it is the least hazardous of the testing areas on the NNSS.