The average resonance parameters recommended for RIPL-2 were prepared on the basis of the evaluations performed by the Obninsk group, taking into account the analysis of discrepancies between similar evaluations of other groups. Good agreement was found for Г7 among the three RIPL-1 files (Obninsk, Mughabghab and Beijing) [5]. However, the comparison is less fa­vorable for the neutron strength functions, especially for those cases with a large number of resonances. The revised average resonance parameters were obtained for 20 additional nuclei for which the data on resolved resonance parameters are available in the Sukhoruchkin compilation [9], bringing the total number of D05S in RIPL-2 to 301. Generally, the accuracy of these additional data is rather poor due to the low number of resonances available for analysis. New evaluations of the average parameters for p-wave neutron resonances, prepared by the Obninsk group, have been included in the up­dated version of the RIPL-2 file. These resonances provide a good check of consistency since they are known to be about a factor of 3 smaller than the s-wave spacings, which is particularly relevant for magic nuclei.

Careful attention was paid to the estimation of uncertainties for the recommended parameters, based on experienced guesswork of systematic errors beside statistical uncertainties.

5.5.1. Nuclear structure

A number of teams around the world are engaged in the co-ordinated evaluation and compilation of nuclear structure data, under the auspices of the International Atomic Energy Agency. This International Network for Nuclear Structure Data Evaluation generates updated Evaluated Nuclear Structure Data Files (ENSDF), and is responsible for the evaluation of all the mass-chains on a regular basis (NNDC, 1987; Bhat, 1992). The resulting files are maintained by the National Nuclear Data Centre at Brookhaven National Laboratory, along with other services (Dunford, 1994; Kinsey et al, 1994). Available databases include ENSDF, atomic masses, NuDat (basic nuclear data extracted from ENSDF, including radionuclidic decay data), RADLST (calculated decay parameters from ENSDF), CSISRS (experimental cross­section data) and ENDF-6 (evaluated nuclear reaction and decay data in ENDF-6 format for applications in the nuclear industry). Details of the methods of data retrieval from NNDC are given in Appendix A, including access to the ENDF-6 files (Dunford, 1992). Theoretical decay data have been incorporated into this library for a number of important short-lived fission products, including delayed-neutron data and continuum spectra (Brady and England, 1989).

NUBASE is a database that contains the main nuclear and decay properties of nuclides in their ground and isomeric states (Audi et al, 1996 and 1997). These data have been primarily derived from ENSDF and the atomic mass evaluation of Audi and Wapstra (1995). Experimentally-measured nuclear parameters have been compiled for virtually all known nuclides, with some values estimated by systematic extrapolation. Recommended data are listed for mass excess, excitation energy of isomeric states, half-life, spin and parity, decay modes and branching fractions, as well as isotopic abundances for the stable nuclei and a list of relevant references.

The Table of Isotopes has a long and respected history, culminating in the release of the eighth edition in 1996 (Firestone et al, 1996). A CD-ROM is also included that contains all of the recommended decay-scheme data, and this vehicle will be preferentially used to communicate updates (Firestone et al, 1998). The main table is initially ordered by mass number and then by atomic number, with abbreviated mass — chain decay schemes that give the adopted half-lives, spin-parity and Q-values. Data are listed for each ground state and isomer with half-lives > 1 sec. ENSDF evaluations have been adopted whenever the authors judged this data source to be appropriate. Significant amounts of nuclear data are contained within this immense document/file, and the reader is referred to the original publication for greater detail. Other specialised decay-data compilations have been published (e. g., Reus and Westmeier, 1983; Westmeier and Merklin, 1985; Rytz, 1991; Nichols, 1996), but few appear to have been maintained in the same rigorous manner as ENSDF and the Table of Isotopes. Both are comprehensive and contain decay data for approximately 2500 radionuclides, effectively covering all nuclides that have been observed and characterised to some degree. The ability to inspect and use these data via a CD — ROM and the World Wide Web adds considerable strength to their commonality of use.

In this method Methane (CH4), a main component of natural gas, and water react at temperatures of 600 — 800 C to produce hydrogen and carbon monoxide and dioxide. The steam reforming system can be easily coupled to a HTGR, which can provide the necessary heat and high temperature. Considerable R&D work has been carried out in Germany for the steam reforming of methane including performing experiments in a pilot plant, EVA-I and EVA-II. Currently work is in progress in JAERI for the HTTR14, in China for the HTR-1015 and in Russia.

A. CO2 Reforming of Methane

The basic CH4 and CO2 reaction for this process (with no addition of steam) produces CO and hydrogen. The reforming process requires high temperature (800 — 900 C) and high energy input, both of which can be provided by HTGRs. The generated CO and H2 mixture (syngas) can be used directly as fuel for electricity generation (e. g., by fuel cells).

One of the main missions of the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy, founded in 1964, is to foster the growth of advanced studies and scientific research in developing countries. To this end, the Centre organizes a number of schools and workshops in a variety of physical and mathematical disciplines.

Since unpublished material presented at the meetings might prove to be of interest also to scientists who did not take part in the schools and work­shops, the Centre has decided to make it available through a new publication series entitled ICTP Lecture Notes. It is hoped that this formally structured pedagogical material on advanced topics will be helpful to young students and seasoned researchers alike.

The Centre is grateful to all lecturers and editors who kindly authorize the ICTP to publish their notes in this series.

Since the initiative is new, comments and suggestions are most welcome and greatly appreciated. Information regarding this series can be obtained from the Publications Section or by e-mail to “pub_off@ictp. it”. The series is published in-house and is also made available on-line via the ICTP web site: “http://www. ictp. it/~pub_off/lectures/”.

Katepalli R. Sreenivasan, Director Abdus Salam Honorary Professor

Nuclear data files are normally based on statistical analyses and evaluations of all relevant measured data reported in the open literature. Unfortunately, there may be omissions in the resulting data libraries that need to be filled to avoid serious impact on the ability to undertake the desired calculations with confidence. Setting this issue aside until Sections 4 and 5, some consideration is given below to data uncertainties and the value of sensitivity studies in identifying the main parameters to be improved in order to increase the accuracy and reliability of decay-heat calculations.

NEA Data Bank has developed and released the JEF-PC program, in co-operation with CSNSM-Orsay and the University of Birmingham. This jointly-developed program generates a “Chart of the Nuclides” format for the display of data from a number of evaluated libraries, including the Joint Evaluated File (JEF-2.2), ENDF/B — VI.4 and JENDL-3.2 supplied on CD-ROM as part of the package. Three internal modules are devoted to radioactive decay, fission product yields and cross-section data (Konieczny et al., 1997). Evaluated and experimental cross-section data can also be plotted and compared.

JANIS (JAva Nuclear data Information System) is in the process of being developed by the NEA Data Bank on the basis of user feed-back from JEF-PC. All earlier features of JEF-PC have been reproduced, along with several others (e. g., energy and angular distribution, and display of resonance parameters). This new software is more flexible and user-friendly, and is undergoing preliminary tests (Nouri et al., 2001).

Contact the NEA Nuclear Data Service Section for further information:

Mark A Kellett or Ali Nouri:

Address: OECD Nuclear Energy Agency Le Seine St-Germain 12, boulevard des Iles 92130 Issy-les-Moulineaux France

Tel: +33 1 4524 1085 +33 1 4524 1084

Fax: +33 1 4524 1110 +33 1 4524 1110

E-mail: kellett@nea. fr nouri@nea. fr

NEA Data Bank Website: http://www. nea. fr/html/databank/

More information on JANIS is available on the Web at: http://www. nea. fr/html/dbdata/

From what has been seen, NPP’s decommissioning appears to be a mature technology. However, while it is certainly true that we have today available all or most technologies needed to dismantle a NPP and return the site to essentially the initial, undisturbed condition, large margins exist for the process optimization in terms of efficiency, waste generation, occupational doses and especially costs. Specific areas that can be mentioned are:

— decontamination technologies : chemical, electrical, mechanical, ultrasonic…

— dismantling technologies;

— improvement of waste volume minimisation ;

— non-metallic material recycling ;

— control and measurement techniques ;

— remote operations.

In this field the role of the universities may be limited, since the matter is more related to an industrial development in many cases at competitive levels among suppliers, but it is anyway important, in the advanced and high technology fields (advanced chemical decontamination, waste treatment such as vitrification, robotization, waste stream characterization), as well as in computer codes for dose or environmental impact calculations.

As discussed below eq. (2.41), all integrals are of short range, therefore the Coulomb functions, fi(r) and gi(r), see eq. (2.3), can be expanded in terms of the functions xv, eq. (2.5), or rv, eq. (2.15), in an appropriately chosen finite interval A. Since fi and gi are solutions to the point Coulomb Hamiltonian, A has to cover the range of the interactions folded with the size of the fragments. In addition to that, the range where gi(r) deviates from gi (r) due to the regularisation factor Ti(r), eq. (2.3), has to be considered.

The starting point is to minimize the integral

The function fL is calculated numerically according to ref. [15]. The ex­pansion functions xkL are given in eq. (2.5). Two sets of width parameters вк are given in [26]. The variational parameters Ck are determined from a system of linear equations. The weight function Wi(x) is chosen in such a way that the internal region dominates and the total interval becomes finite. A typical expression is

Wl(x) = x-(L+1> e-x (4.3)

with є w 0.01fm-2.

Thus a typical expansion interval is of the order of 20 — 50 fm. The parameter є is numerically very critical: If it is chosen too large the interval will become too small and the small width parameter ek are strongly suppressed. On the other hand if є is too small, then the expansion interval will become larger and it gets numerically very difficult to reproduce the oscillating function fL by a finite number of Gaussians centered around the origin. Increasing the number of Gaussian width parameters may lead to numerical dependencies, due to the non-orthogonality of these functions, especially as one set of parameters is used irrespective of the orbital angular momentum L.

The expansion can be improved, if in addition to the functional eq. (4.2) also the derivative of fL is included in an obvious way. Outside the interval de­termined by the weight function WL the values of the sum must not become too large. Modifications of this type are discussed in [31]. An analogous procedure is used for gi.

Depending on the kinetic energy of the fragments we found up to 100 MeV

15 to 20 width parameters sufficient to obtain a good representation of the

Coulomb functions. The choice of parameters fik is not critical to scattering calculations. We can easily omit some of them without changing the results. Changing the parameter во of the regularisation factor, eq. (2.4), in a wide range does not modify the final results either, as long as TL approaches unity outside the interaction range.

The fission-yield data sets in the most recent evaluations are listed in Table 7. Thermal (T) yields cover all measurements at 0.025 eV, or in well-moderated thermal reactor spectra. Fast (F) yields include all measurements in fast reactor spectra (mean neutron energies of 150-500 keV) and fission neutron spectra (mean energies around 1 MeV and above). H means neutron energies around 14-15 MeV, while S stands for spontaneous fission.

Measurements of the energy dependence of fission yields are too scarce to derive systematic trends and develop a semi-empirical model for obtaining reliable predictions; many more systematic measurements are required before a reliable model can be developed. Therefore, ‘thermal’, ‘fast’ and ‘high’ (around 14 MeV) yields continue to be evaluated for data files and are used in applied calculations.

(a) The US evaluation has increased from 10 to 60 yield sets, each yield set consisting of cumulative and independent yields (total of about 132,000 yield values and their uncertainties). Corrections have been applied, models have been used to estimate unmeasured yields, and adjustments have been made to all yield sets in ENDF-6 format (England and Rider, 1994).

(b) UKFY2 includes 39 yield sets (UKFY3 is in the process of being assembled, and also contains 39 sets of cumulative and independent yields). Both UKFY2 and UKFY3 are in ENDF-6 format (James et al, 1991a, 1991b and 1991c; Mills, 1995), and have been adopted as the fission yield files for different versions of the NEA — OECD Joint Evaluated File (NEA-OECD, 2000). A number of important short-lived fission products are absent from the decay data files (with greater than 10% of the yield in some mass chains of specific fissioning systems) — while assembling this library for JEF-2.2, correction terms were applied to adjust the independent yields for each mass, so that calculations gave the recommended chain yield values. An improved method of calculation of the correction terms has subsequently been developed for UKFY3, and decay-data evaluations have been undertaken for the most significant missing fission products in order to avoid this problem.

(c) The Chinese fission yield file was released in 1987 as part of the CENDL library (Wang Dao and Zhang Dongming, 1987); a new evaluation is in progress that will be converted into ENDF-6 format.

Fission yields adopted in other applications files have been taken from these sources (for example, the Japanese JENDL library and the French files have adopted US ENDF/B-VI fission yields).

The facilitating role of a recent IAEA-CRP on the compilation and evaluation of fission yield nuclear data should be noted and acknowledged (IAEA-CRP, 2000); specific facets of this work are described below. Co-operation has been established between internationally-respected fission yield experts, and resulted in considerable improvements to the evaluation process (e. g., cleanup of data bases, analyses of experimental data, model development, and evaluation procedures). A PC-based program has also been written and made available through the Internet to calculate mass yields, fractional independent and cumulative yields for 12 fission reactions [YCALC (Gromes, Kling and Denschlag), based on the studies of Wahl, 1988; see also IAEA-CRP, 2000]:

252Cf(sf), 229Th(T), 233U(T), 235U(T), 238Np(T), 239Pu(T), 241Pu(T), 242Am(T),

249Cf(T), 232Th(F), 238U(F) and 238U(H);

sf, T, F and H refer to spontaneous fission, thermal, fast and 14 MeV neutron — induced fission, respectively. Results can be displayed and down-loaded in graphic and tabulated forms via LINKS on the University of Mainz Website

http://www. kernchemie. uni-mainz. de

Empirical models are available for mass and charge distributions and for ternary fission yields that allow the reliable derivation of fission yields for neutron energies from thermal to 15 MeV. Computer programs have also been developed for the introduction of correlations and covariance matrices in future fission yield evaluations.

South Africa, Japan, China and a consortium of US, Russia, France and Japan are developing small gas-cooled reactor designs and technologies. Coated fuel particles are used in these reactors and they retain fission gases even under accident conditions. Modularization, inherent safety characteristics, direct cycle, and high temperature applications have generated renewed interest in High Temperature Gas — cooled Reactors (HTGR). Japan and China have made the most recent progress in the technology development as they have already constructed and are operating two research reactors; South Africa and the above-mentioned consortium are developing innovative power reactor designs with direct cycle gas turbine for power conversion.

China: The 10 MWe helium-cooled, pebble bed reactor (HTR-10) reached criticality in December 2000. It will initially have steam turbine for phase 1 and later helium turbine for phase 2. Preliminary design of the helium turbine is in progress. It will deliver He at 950 C for electricity generation and for heat applications for coal gasification/liquefaction.

Japan: A High Temperature Engineering Test Reactor (HTTR) with prismatic fuel elements has reached full power this year. This 30 MWth reactor will be the first of its kind to be connected to a high temperature process heat utilization system with an outlet temperature of 850 C. The system will operate as a test and irradiation facility, and be utilized to establish the basic technology for advanced HTGR designs for nuclear process heat applications.

Russian Federation: MINATOM, General Atomics, Framatome and Fuji Electric have combined their efforts to develop the Gas Turbine Modular Helium

Reactor (GT-MHR). This plant features a 600 MW(th) helium cooled reactor as the energy source coupled to a closed cycle gas turbine power conversion system. This is under consideration for the purposes of burning weapon grade plutonium and for commercial deployment. The net efficiency of this advanced nuclear power concept is expected to be 47%. Substantial progress in the development of components such as magnetic bearings and fin-plate recuperators makes this type of HTGR plant a feasible alternative for commercial production of electricity.

South Africa: S. Africa is developing a Pebble Bed Modular Reactor (PBMR) based on technology developed in Germany. The design is a single loop direct gas cycle system that utilizes a helium cooled and graphite-moderated nuclear core as a heat source. The coolant gas transfers heat from the core directly to the power conversion system consisting of gas turbo-machinery, a generator, gas coolers and heat exchangers. The reactor has a thermal power of 268 MW with an electrical output of 110 MW. Improvements of the design are underway to increase the electrical output. The inlet and outlet Helium coolant temperatures are approximately 500 °C and 900 °С, respectively. The important design feature of PBMR is its tennis ball sized pebbles containing the silicon carbide coated HTGR fuel particles, which is expected to contain all fission products for the PBMR13 during all accident conditions, and hence requires no separate containment building.