The evolution of the various decay-data libraries for nuclear applications has resulted in programmes of intensive testing to re-assure users that the recommended data sets are reliable and comprehensive. During the course of these benchmark exercises, errors and inadequacies have inevitably been discovered. Many can be dealt with rapidly, but some problems have proved more difficult to overcome without a significant amount of additional work. Although the assessments given below are not comprehensive, a number of important discrepancies are noted, along with known efforts to improve the contents of the decay-data libraries. Sometimes the analyses required to highlight and identify the culprit radionuclide(s) can be as taxing as subsequent attempts to correct the problematic data. Furthermore, attempts to improve the quality of the recommended decay data in this manner may be seriously undermined by the increasing lack of expertise available to undertake such work.

After much consultation and debate in the mid-1990s, a number of important radionuclides were judged to be inadequately characterised for various applications (ranging from estimates of radiotoxicity and input data for reprocessing flowsheets, to nuclides that undergo delayed-neutron emission). A set of 27 fission products (plus short-lived daughters and related metastable/ground states) was identified as important for various thermal reactor studies, including decay-heat calculations (Table 15). The majority of these radionuclides are short-lived fission products with half-lives significantly less than 3 hours. Considerable improvements were made in their recommended decay data as a consequence of including a number of relatively recent measurements in the evaluations, although the complexity of many of the decay schemes may still pose mean energy problems (Nichols, 1998; Nichols et al, 1999a).

Various decay parameters and continuum spectra have also been theoretically derived for 35 neuton-rich nuclides deemed to be important at short cooling times in decay-heat calculations (Table 16). While each of these fission products contributes significantly to the decay heat of irradiated fuel (>0.01 of the fractional cumulative yield), they have proved extremely difficult (if not impossible) to prepare, isolate and study experimentally, and are not included in the JEF-2.2 decay-data library. The US ENDF/B-VI decay-data library contains files of theoretical data for 33 of these nuclides, and they were considered as possible candidates for incorporation into the JEFF library, with supportive data from Takahashi et al (1973) and Audi et al (1997).

The precise content of any data library for decay-heat calculations is based on subjective judgements, although the desire for completeness can overcome many constraints. While the nuclides contained within Appendix B provide a reasonably comprehensive set of fission products and actinides for this type of study, changes can always be made to improve and expand the data base (Storrer, 1994). The addition of further isomeric states is a particular good example of this form of improvement; recent experimental studies have furnished evaluators with evidence for further short-lived radionuclides of this type that could be incorporated into the decay-data (and fission yield) libraries:

117mPd. 107mAg 119mAg ^^Ag 122mAg. 123mCd 125mCd* 120nIn 122nIn 126mIn 130m,130nIn 131m,131nIn. 114mSn 128mSn* 129mSb* 132mp 132mXe* 144mCs* 146mLa* 148mP^ 153mSm* 155mGd

While the postulated decay schemes for many of these radionuclides are simple (e. g., 107mAg, 113mPd and 128mSn), others are relatively complex (e. g., 112mRh, 122nIn, 125mCd and 146mLa). Their decay data can be found in ENSDF, and could be assessed and transferred to nuclear applications libraries.

Additional short-lived daughter and related metastable/ground state radionuclides are in parentheses, and were also evaluated.

*Beta-decay mode only.

An interesting piece of detective work has been carried out by Yoshida et al (1997 and 1999) to offer some explanation for the discrepancy between experiments and calculations of the gamma component of decay heat over cooling times between 300 and 3000 sec (Fig. 31, instantaneous fission burst for 239Pu). Experimental data measured by Dickens et al (1980 and 1981), Akiyama and An (1983), and Nguyen et al (1997) were combined and compared with decay-heat calculations using the JNDC-FP-V2 library (adoption of either fast-neutron or thermal-neutron fission yields had little impact on the resulting curves). Yoshida et al introduced a gamma — ray emission that is effectively missing from the decay-data files, and was postulated to belong to an ill-defined fission product (half-life of ~1000 sec). An additional P — decay chain was artificially added to the JNDC data base (as two radionuclides) on the basis of this proposed omission.

An energy release of 1.5 MeV per decay was assumed to occur (e. g., 104Mo (half-life of 60 sec) ^ 104Tc (half-life of 1092 sec) represents a suitable candidate for such an emission). The results of these artificial calculations are shown in Fig. 32 for, , U and Pu in comparison with the measurements of Akiyama and An (1983): the discrepancies between 300 and 3000 sec disappeared for all four sets of data. Fig. 33 shows the impact on the beta-energy component for the fission burst of 239Pu; there is some decrease against the original calculation, but this change falls well within the error bars of the measurements. Re-assessments have been made of beta-strength functions to identify possible candidates, including 102Tc, 104Tc and 105Tc. Overall, the proposal of Yoshida et al would appear to be a reasonable suggestion.

The incorrect assignments of ground and metastable states may also play an important role in explaining some of the discrepancy in the gamma component between 300 to 3000 sec. Fig. 34 compares experimental data with decay-heat calculations for 239Pu; improvements can be achieved by adjusting the decay data for Rh. The ground and metastable states of Rh are assigned half-lives of 17 sec and 6 min respectively in JNDC-V2 (labelled ‘JNDC-V2 original’ in Fig. 34), while these assignments are reversed in JEF-2.2 (labelled ‘Rh108-JEF2.2’ in Fig. 34). Adoption of the JEF-2.2 data increases the half-life of 108gRh by a factor of ~ 20, leading to a considerable rise in decay heat around 1000 sec. Another feature is worthy of note: a lack of gamma-ray transition energy in the 102Tc decay-data file of JEF-2.2 gives rise to a collapse in the gamma energy component (labelled ‘Tc102- JEF2.2’ in Fig. 34), implying that this radionuclide represents a suitable candidate for the missing gamma energy (as noted earlier). These studies demonstrate that adjustments to the decay-data of only one nuclide can dramatically change the decay — heat predictions, and that beta branching ratios to the ground and metastable states need to be measured with good accuracy in order to define the situation correctly.

All power plants, coal, gas and nuclear, have a finite life beyond which it is no longer economical to operate them. Generally speaking, Nuclear Power Plants (NPP’s) were designed for a life of about 30 years, though some have proved capable of continuing well beyond this term. Newer plants are designed for a 40 to 60 years operating life. To date, 70 commercial power reactors, over 250 research reactors and a number of fuel cycle facilities, have been retired from operation. Some of these have been fully dismantled. Assuming an average of about 25-years lifespan, almost 300 nuclear power plants would have to be decommissioned by the year 2010. By appropriate refurbishment, replacement or upgrading of some equipment, operations at many of these plants can probably be extended well beyond this conservative estimate.

However, ultimately it becomes either technically or economically advantageous to retire a facility from operation and, if necessary, replace it with a new plant.

In Italy 4 Nuclear Power Plants have been prematurely definitely shutdown and are now in different stages of decommissioning. They were operated by the National Electrical Utility ENEL, now partially privatized. In figure 1, the names and location of these plants are reported. The responsibility of carrying out the decommissioning projects and to manage the spent fuel has passed in the 1999 to SOGIN Company (which includes all nuclear competences of ENEL), which is now completely owned by the Italian Government (Ministry of Treasury). In Table 1 the main characteristics of these plants are summarized.

In this section I briefly review potential scattering following along the lines of ref. [4]. Let us consider for simplicity first the scattering of a spinless particle off a fixed potential. The wave function ф can then be expanded in partial waves

V(r) = £ u-NlY, m(i) (2.1)

Here, as everywhere vectors are bold faced and unit vectors carry addition­ally a hat. We use for the asymptotic scattering wave function ul(r) a linear combination of regular fi(r) and irregular gi(r) solutions of the free Hamil­tonian, so that all wave functions are real, thus simplifying the numerical calculations. The wavefunction ui is normalized to a ^-function in the energy by using the ansatz

Mr) = + ai 91 (r) + Ь"1 Xui (r)

Here M denotes the mass of the particle. The momentum k is related to the energy by E = h2k2/2M. For the variational principle ui (r) has to be regular at the origin, therefore gi(r) is the irregular solution gi regularized via

gi(r) = Ti(r)gi(r) with Ti(r) ^ r2l+l and Ti(r) 1 (2.3)

The regularisation factor Ti should approach 1 just outside the interaction region. A convenient choice is

where the limiting values are apparent in the different representations. A typical value for во is 1.1 fm-1. The calculation is rather insensitive to this parameter, see, however, the discussion below eq. (4.6).

The last term in eq. (2.2) accounts for the difference of the true solution of the scattering problem and the asymptotic form. Furthermore, in the region where Ti differs from this term one has to compensate the difference between gi(r) and gi(r). Since this term is different from zero only in a finite region, just somewhat larger than the interaction region, it can be well approximated by a finite number of square integrable terms. We will choose the terms in the form

Xvi(r) = ri+1e-e r (2.5)

where ви is an appropriately chosen set of parameters (see discussions in chapters 4.2 and 4.3).

Since fi and gl are not square integrable, we have to use Kohn’s variational principle [6] to determine the variational parameters ai and bvi via

where Hi denotes the Hamiltonian for the partial wave of angular momentum

l. It is easy to show [2], that all integrals in eq. (2.6) are well behaved if and only if the functions fi and gi are solutions of the free Hamiltonian to the energy E. See also the discussion in [5].

Most experimental measurements of nuclear structure and decay-scheme data focus on the emission of discrete gamma-rays. This type of spectral measurement dominates fission-product decay-scheme studies because of the difficulties and scarcity of facilities throughout the world to measure the corresponding beta — transition energies and emission probabilities accurately. However, the inability to detect weak high-energy gamma-ray emissions satisfactorily has been noted by Hardy et al (1977), and this problem impacts on the P — decay data calculated from such measurements. A generalised assessment was made of a radionuclide with a complex decay scheme (labelled “pandemonium”): approximately 20% of the gamma-ray emissions above 1.7 MeV were estimated to remain undetected within the background, and would be omitted from the proposed decay scheme. Under these conditions, every complex p — decay scheme derived through gamma-ray studies must be regarded with some doubt — the recommended P—decay scheme may be inaccurate (Fig. 1), and might explain anomalies that sometimes occur between calculated and measured decay heat.

The P — decay of 87Br represents a good example of the problems faced by evaluators of complex decay schemes (Reich, 1987). This nuclide has a half-life of 55.7 sec, and an extremely thorough study by Raman et al (1983) has revealed the existence of 126 bound levels and 12 levels in the unbound region. Approximately 220 gamma rays were detected in a series of singles and coincidence measurements, and P-
emission probabilities were calculated from the measured gamma-ray intensities: 160 beta branches were defined, with evidence of broad resonance-like structure in the overall beta-strength distribution. These measurements have resulted in significant changes in the mean beta and gamma energies for this radionuclide. Unfortunately, few short-lived fission products with such complex decay schemes are likely to be studied in such a comprehensive manner. Many short-lived fission products are very poorly characterised because their gamma-ray spectra have been incompletely measured or remain undetermined; under these circumstances, theoretical models have been adopted to calculate mean beta and gamma energies (and half-lives).

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The 4He atomic nucleus is one of the best studied few-body systems, both experimentally and theoretically, as summarized in the recent A = 4 com­pilation [37]. Besides the many textbook examples of gross structure, there are subtle points yielding large effects that are only qualitatively understood. Except for [38] none of the existing calculations aims at a complete under­standing of the many features of 4He, which is not surprising in view of the number of different phenomena studied so far [37]. Here we are interested

in the 3He (n, p) reaction, which connects the two lowest fragmentations in energy.

To use the above described techniques, the potentials must also be given in terms of Gaussians. Here we use realistic nucleon-nucleon forces, suitably parametrized, the Bonn [40] and the Argonne AV18 potential [39] and even a three-nucleon interaction (TNI) Urbana IX [41]. The inclusion of the additional TN1 requires almost two orders of magnitude more computing power than the realistic NN-forces alone.

In the 4He system we use a model space with six two-fragment channels, namely the p-3H, the n-3He, the 2H-2H, the singlet deuteron and deuteron d -2H, the d — d, and the (nn)- (pp) channels. The last three are an ap­proximation to the three — and four-body breakup channels that cannot in practice be treated within the RGM. The 4He is taken as four clusters in the framework of the RGM to allow for the required internal orbital angular momenta of 3He, 3H or 2H.

For the scattering calculation we include S, P, and D wave contributions to the Jn = 0+, 1+, 2+, 0“, 1“, 2- channels. From the R-matrix analysis these channels are known to give essentially the experimental data. The full wave-functions for these channels contain over 200 different spin and orbital angular momentum configurations, hence, they are too complicated to be given in detail. For the deuteron we use a type similar to that given in [38]

yielding the binding energy of — 1.921 MeV, whereas for 3He and triton, we use an analogue to [42] for two model spaces, 29 and 35 dimensional, called small and large, respectively. For the triton AV18 yields -7.068 and -7.413 MeV binding energy, respectively, falling short of the experimental datum of -8.481 MeV. Adding the TNI improves the binding energies to -7.586 MeV and -8.241 MeV respectively, see table 1. The binding energy of the deuteron could be easily improved, but then the threshold energies deteriorate and thus yield worse results. All the Gaussian width parameters were obtained by a non-linear optimization using a genetic algorithm [43] for the combination of AV18 and Urbana IX. The model space described above (consisting of four to ten physical scattering channels for each Jf) is by no means sufficient to find reasonable results. So-called distortion or pseudo­inelastic channels [3] have to be added to improve the description of the wave function within the interaction region. Accordingly, the distortion channels have no asymptotic part. For practical purposes it is obvious to re-use some of the already calculated matrix elements as additional distortion channels. In that way we include all the positive parity states of the three-nucleon subsystems with Jf < 5/2+ in our calculation. However, it was recently pointed out by A. Fonseca [44] that states having a negative parity J3 in the
three-nucleon fragment increase the n-3H cross section noteably. Therefore we also added the appropriate distortion channels in a similar complexity as in the J+ case to our calculation, thereby roughly doubling the size of the model space.

In fig. 3 we compare the standard 3He(n, p) cross section as given in the ENDF/B-VI evaluation [36] with various calculations using the AV18 po­tential alone. The calculation using the smallest model space reproduces the data surprisingly well. (The kink in the calculated curves below 10 keV is due to a loss in precision of the energy.) Since the threshold energy is almost 70 keV too low, this result should not be overestimated. Especially as the calculated 0+ triton-proton phase shifts close to threshold and be­low demonstrate large differencies between themselves and to the R-matrix analysis, see fig. 4.

120

(/)

<L>

<D

D)

0)

■o 90

60 30

0 0.2 0.4 0.6 0.8 MeV

Figure 4: Comparison of the 0+ triton-proton phase shifts from the R-matrix analysis (crosses) and calculations employing AV18 in the small model space (av18), adding neg­ative parity distortion channels (av18n), for the large model space (av18-l) and adding negative parity distortion channels (av18n-l).

The corresponding figure 5 including three-nucleon forces reveals a much better agreement, also for the threshold energies, see table 1. Unfortunately the 3He(n, p) cross sections including TNI are not yet available, due to the large amount of CPU time necessary.

Figure 5: As fig. 4, but R-matrix results (crosses) are compared to the full NN-calculation (av18), adding UIX (av18u) and adding V3 (av18uv).

Since the 3He(n, p) data at higher energy are usually deduced via detailed balance from the more easily accessible 3H(p, n) reaction we display in the following the results of a few calculations. In fig. 6 the results for the Bonn potential and a semi-realistic one, which will be used later on on the 6Li(n, t) reaction, are compared to data and the R-matrix analysis. At forward and backward angles large discrepancies between data and calculation are visible. In fig. 7 we change from using the Bonn potential to the Argonne AV18. Obviously the calculations reproduce the data much better. Again the cal­culation employing the smallest model space is by far the best, missing the data only close to the minimum around 90 degrees. Additional three-nucleon forces do not improve the situation. Considering the fact that the calcula­tions start ab initio from NN — and NNN-potentials the agreement between data, R-matrix analysis, and microscopic calculation is remarkably good. At the time being, any extension to heavier nuclei using the above forces fails due to lack of computing power.

Decay-data requirements for decay-heat calculations are parametrically limited to half-lives (through the decay constants, Лі (t>/2 = ln2/A,)) and the mean alpha, beta and gamma energy releases per disintegration of the nuclides (Ea, Ep and Er) . Ideally, the mean energies are systematically determined from the discrete alpha, beta and gamma transitions and other relevant emissions, which extends the decay-data needs dramatically.

(a) The mean alpha energy is the mean energy of all heavy particles (alpha particles, recoil nuclei, protons, neutrons, and spontaneous fission fragments):

all a all recoil all protons all neutrons fission frag

Ea = X Ea"Pa, + X ERjPRj + X Epk Ppk + X Enl Pnl + X EFm Pf

i j k l m

where Ea,, Erj, Epk, Eni and EFm are the mean alpha, recoil nucleus, proton, neutron and fission fragment energies of the ith, jth, kth, lth and mth component of each type respectively, and Pa, PR, Pft, Рщ and PF^ are the corresponding

absolute emission probabilities per disintegration.

(b) The mean beta energy is the mean energy of all electron emissions:

all в all в+ all Auger all conversion

E в= X EP РвГ + X ‘Ев+ Pfi+ + X EAkPAk + X Ece. pce,

i j k l

where Eв — , Eв+ , EAk, and Ecel are the mean negatron, positron, Auger electron and conversion-electron energies of the ith, jth, kth and lth transition of each type respectively, and P, P„+ , PA and Pce are the corresponding

Pi вj k l

absolute emission probabilities per disintegration.

(c) The mean gamma energy includes all the electromagnetic radiation such as gamma rays, x-rays, annihilation radiation and bremsstrahlung:

where E7i and Ex, are the mean gamma and x-ray energies of the ith and jth transition of each type respectively, and PY and PX are the corresponding
emission probabilities per disintegration; E pt is the mean internal bremsstrahlung energy of the 1th beta transition with absolute emission probability, and P^+ is the absolute emission probability of positron

transition k.

Data files containing these nuclear parameters have been assembled over many years to assist analysts and spectroscopists to identify and quantify radionuclides. As the emissions from nuclides have been characterised in greater detail and their decay — scheme data defined with increased confidence, extended libraries of nuclear data have been compiled in agreed formats for use by the nuclear industry. These libraries are also used in decay-heat calculations, and are updated at regular intervals through either international consensus, or more localised efforts based on specific national needs.

The contents of a decay-data library need to be complete and consistent in order to model decay heat with confidence. The normal procedure would be to evaluate and prepare individual files of decay data that have been internally tested for consistency between the various decay-scheme parameters (i. e., a, P and у transitions), and to validate the complete library against benchmark experiments.

Evaluated decay-data libraries are used for many different purposes, as well as decay-heat calculations. Files of discrete decay data can aid in the measurement and quantification of the radionuclidic composition of a sample, and provide spectroscopists with the necessary high-quality standards data for detector efficiency calibration. Ideally, a comprehensive set of such data files should encompass all of the important fission products, actinides and their decay-chain nuclides, and provide the user with the necessary half-lives, mean energies and isomeric branching ratios to carry out decay-heat calculations with confidence. Unfortunately, this requirement cannot be realised because of the difficulty of measuring comprehensively the discrete data for the many short-lived fission products, along with the added complications that occur when studying some of the more complex decay schemes (pandemonium (Hardy et al, 1977)).

A lot of attention has been given in recent years on the subject of partitioning and transmutation of the actinides and some long-lived fission products contained in the spent fuel as it has the potential of easing operational and safety requirements of a repository. Some would even like this to become an important alternative to direct disposal of spent fuel. Separation of the long-lived isotopes and transmutation of these into less hazardous materials have several advantages. It allows a reduction of the volume, toxicity, and fissile content of waste and supports a simpler repository. The issues related to long-term disposal of spent nuclear fuel is attributable to only ~1% of its content, namely plutonium, neptunium, americium, and curium (the transuranic elements) and long-lived isotopes of iodine and technetium. When transuranics are removed, the toxic nature of the spent fuel drops below that of natural uranium ore within a period of several hundred years. The removal of neptunium, technetium, and iodine also makes the waste safer for the biosphere. Removal of plutonium eliminates the relevance of the waste from the point of view of nuclear proliferation. Thus if the nuclear waste can be partitioned and transmuted economically to more benign materials, the waste can be disposed of in controlled environments having time scales of a few centuries rather than millenniums.

Partitioning and transmutation requires advanced reactor and fuel cycle technologies, including multiple recycle strategies. That is the spent fuel must be reprocessed. Partitioning of waste can be accomplished by both aqueous and non­aqueous methods. The Argonne National laboratory in the US has developed an electrometallurgical non-aqueous process that can separate fissile material from fission products. This process can be used for both metallic and oxide fuels. For transmutation, both accelerator driven systems (ADS) and fast reactors are being considered for actinide burning. The ADS has the potential of providing both plutonium and minor actinide utilization, and enhanced safety of sub-critical operation. It has been recognized that a pure accelerator driven system for transmutation of waste is too costly, and hence a dual concept of power production and transmutation is being envisioned. This option combines the accelerator and fission reactor technologies; neutrons are generated by directing a beam of high — energy protons from an accelerator against a heavy target such as lead or lead — bismuth eutectic and these neutrons are then used in a surrounding blanket to fission the actinides and transmute the long-lived fission products. Unlike a conventional reactor the blanket is sub-critical and cannot sustain a chain reaction without the

accelerator generated neutrons. Power is generated from this sub-critical facility while transmuting the waste.

Various ADS schemes are being studied in several countries: the OMEGA (Option Making Extra Gain from Actinides) project in Japan, Advanced Accelerator Applications (AAA) program in the US, HYPER (Hybrid Power Extraction Reactor) project in the Republic of Korea, European Industrial Partnership and other projects at CERN, and CEA, France, and China. Russia is also participating in international collaboration activities. Carlo Rubbia’s “Energy Amplifier” is one ADS design that provided a strong, early impetus in developing a system to generate more energy than needed for the accelerator.

There are many technical problems to be solved; ADS is only at the beginning stage of investigation. It is very likely that the best results in terms of high level waste radio-toxicity reduction will be achieved by symbiotic systems, including critical fast reactors and hybrid systems (e. g., accelerator driven concepts).

6. CURRENT ISSUES

Although fuel diversity and energy security are important items for a country, economic competitiveness with alternate sources of electricity has been recognized as the critical element for the survival of nuclear power. Hence consorted efforts are being made with design, construction, operation and maintenance of new nuclear power plants to reduce its capital and operation costs. Currently nuclear production costs (fuel and O&M) of existing plants are low, approaching 1 cent/KW-hr; hence the critical issue is capital cost for new plants. Also, investors expect a short-term payback of capital costs such as within 20 years of operation. It appears that capital costs in the range of $1000 — 1200 per KWe are needed for competition with natural gas. In this regard, construction of large nuclear power plants, if allowed by the infrastructure of a country, provides an advantage. At the same time, new generation of small, innovative plants are needed for specific markets and especially for developing countries.

Non-proliferation and physical protection have become more important for nuclear power plants since the September 11, 2001 terrorist event in New York. In spite of the demonstrated effectiveness of the international safeguards regime, the risk of proliferation of nuclear weapons remains a social and political concern. A significant deployment of nuclear power would lead to building a large number of reactors in many different countries and sites, and there may not be sufficient resources to safeguard all reactors. Therefore, gaining acceptance will require specific efforts of designers to enhance the proliferation resistance characteristics, particularly for the SMRs. It has also been argued that since no country has made nuclear weapons from the civilian nuclear power program and we surely have the international, scientific and regulatory mechanisms to handle the proliferation question, we should move forward as rapidly as possible to build nuclear power where it can meet human and environmental needs. In any case, the world must remain vigilant and the suppliers, verifiers, and buyers must assure safeguarding of nuclear materials.

The September 11, 2001 event has highlighted the importance of protecting nuclear facilities from sabotage and stealing of nuclear material by terrorist organizations. Even if the actual impact of a potential terrorist activity is very minimal, the occurrence of such an event will create havoc from the public perception point of view; hence nuclear facilities including spent fuel storage facilities must be secured. An issue here is how to achieve this in a cost-effective manner and how much security effort is good enough.

Disposition of spent fuel is a challenge and a roadblock for nuclear power. However, great progress has been made this year when the governments of Finland and USA have approved the construction of geologic repositories in Olkiluoto in Eurajoki, Finland and at Yucca Mountain, Utah, USA. Finland is now set to become the first country in the world to build a final repository for spent fuel from nuclear power plants. Sweden and the US are also well ahead with similar plans.

This segment contains parameters that quantify Giant Resonances, experi­mental 7-strength functions and methods for calculating 7-emission in sta­tistical model codes.

The experimental Giant Dipole Resonance parameters were provided by the Chinese group, as represented by Lorentzian fits to the total photo­neutron cross sections for 102 nuclides ranging from 51V to 239Pu as compiled by Dietrich and Berman [13]. Additional data for 12C, 14N, 16O, 27Al and 28Si were estimated by Liu Jianfeng and Su Zongdi in 1995 [14].

New compilations of calculated GDR widths and energies for about 6000 nuclei with 14 < Z < 110 lying between the proton and the neutron driplines have been provided by Goriely. The table gives the predicted GDR energies [15] with a renormalized np-interaction of strength derived from a least-square fit to the experimental GDR energies [16]. The expression for the shell-dependent GDR width is taken from [17] using the newly — determined GDR energies and the ETFSI shell correction energies. Such predictions include the shell-dependent GDR broadening due to the cou­pling between the dipole oscillations and the quadrupole surface vibrations.

Theoretical predictions of the E1-strength functions for 3317 nuclei with 8<Z<84 lying between the proton and the neutron drip-lines have been sup­plied by Goriely [18, 19]. These strength functions were determined within the QRPA model based on the SLy4 Skyrme force. The ground state was consistently calculated within the Hartree-Fock+BCS model based on the same SLy4 force. QRPA equations were solved in the configuration space so as to exhaust the energy weighted sum rule. All QRPA calculations are performed in the spherical approximation. A folding procedure is applied to the QRPA strength distribution to take the damping of the collective motion into account. In the case of deformed nuclei, a phenomenological splitting of the QRPA resonance strength is performed in the folding procedure. The resulting E1-strength function is found to be in close agreement with photo­absorption data as well as the available experimental E1 strength at low energies.

A theory-supported practical approach, based on a micro-canonical de­scription of initial states (modified Lorentzian (MLO)) for the calculation of the dipole radiative strength function, was compared with experimental data as well as with the SLO end EGLO models, and included in the library. The strength functions for other multi-polarities will be carried over from RIPL-1.

Estimates of decay heat can only be calculated with confidence if the neutron cross sections, fission yields and radionuclidic decay data are known with confidence, and extensive data libraries have been assembled at both the national and international levels in an agreed format (ENDF-6) to achieve this objective. All data in these libraries are subjected to comprehensive checking procedures and some form of validation before they are released for general use. Their adoption in decay-heat calculations has shown measurement-based files to be inadequate, and therefore efforts continue to improve and extend their contents (particularly isomeric fission yields and the decay data of short-lived fission products), as requested by users.

Systematic fitting procedures, gross energy measurements and theoretical data have played important roles in addressing the problem of non-existent (unmeasured) fission-yield and decay data. Along with evaluations of measured discrete data, these approaches will continue to be used in order to extend the contents of the data libraries, and so improve decay-heat calculations and increase operational confidence in the results.

Acknowledgments

The author wishes to thank the following for their assistance in formulating specific features of this article:

C. J. Dean (AEA Technology, Winfrith),

M. A. Kellett (NEA Data Bank),

M. Lammer (IAEA Nuclear Data Section),

F. Storrer (CEN Cadarache),

E. B. Webster (AEA Technology, Winfrith).

cooling time t (s)

References