Journal

of NUCLEAR SCIENCE and

JENDL-3

TECHNOLOGY,

29[3],

pp. 195~213

Fission Product

(March

Nuclear

1992).

195

Data Library

Masayoshi KAWAIt1, Shungo IIJIMAt1,a, Tsuneo NAKAGAWAtt2, Yutaka NAKAJIMAt2, Teruo SUGIt2, Takashi WATANABEIt3, Hiroyuki MATSUNOBUt4, Makoto SASAKIt5 and Atsushi ZUKERANt6 Fission Product

Nuclear

Data Working Group,

Japanese Nuclear Data Committee, Japan Atomic Energy Research Institute* Received September 30, 1991 Neutron nuclear data in the energy range between 10-5eV and 20 MeV have been evaluated for 172 nuclides from 75As to 159Tb in the fission product mass region to provide data for the JENDL-3 fission product nuclear data library. Evaluation was made on the basis of recent experimental data reported up to 1988and the nuclear model calculations. Resonance parameters have been evaluated on the basis of measured data set and a REPSTOR system developed in JAERI. The spherical optical model and statistical theory were applied to calculation of the total, capture, elastic and inelastic scattering cross sections, and the multistep evaporation model and pre-equilibrium theory were used for threshold reaction cross section calculations. For the even-even nuclides around fission yield peaks, direct inelastic scattering cross sections were calculated with the distorted wave Born approximation. Nuclear model parameters, such as optical model parameters, level density parameters, r-ray strength functions and Kalbach constant of the pre-equilibrium model were determined so as to give a good agreement between the calculated and measured cross sections. The parameter systematics were obtained as a function of nuclear mass or atomic number. For thermal capture cross sections, a simple relation between measured and calculated cross sections was found as a function of level spacing. The evaluated results were compiled in the ENDF-5 format. KEYWORDS: neutrons, cross sections, JENDL-3, fission products, evaluation, nuclear model parameter, optical model parameter, level density parameter, gamma-ray strength function, resonance parameter

I. Neutron

libraries containing FP cross sections, such as JENDL-2(2) in Japan, ENDF/B-V(3), -VI(4) in the United States and JEF-2(5) in Western Europe and Japan. The data in the FP nuclear data file of ENDF/B-VI are the same as that of ENDF/B-V, except for 34 nuclides including such nuclides as Zr, Nb, Ag and Gd isotopes which are contained in the general

INTRODUCTION

cross sections

of fission

product

(FP) nuclides are important to predict burnup performance of fission reactors. Additionally, data on the various kinds of reaction cross sections of the nuclides in the FP mass region are needed for activation analysis and estimation of gas production for structural materials in reactors, radiation damage estimation and assessment of noble gas contents used for reactor diagnostics of fuel failure detection with tagging gas method. In the WRENDA(1), required accuracy is reported to be smaller than 5% for capture cross sections of important nuclides and a few tens of percent for those of the other nuclides. There are several evaluated nuclear data

purpose file of ENDF/B- V and were not released. The JENDL-2 FP cross section library *

Tokai-mura , Ibaraki-ken 319-11. Nuclear Engineering Laboratory, t1 Toshiba Corp. a Deseased November 14 , 1990. 2 Japan Atomic Energy Research t Institute . 3 Nuclear System Division , Kawasaki Heavyt Industries, Ltd. 4 Sumitomo t Atomic Energy Industries , Ltd. 5 Water Reactor Division , Mitsubishi t Atomic Power Industries, Inc. 6 Energy Research t Laboratory , Hitachi Ltd.

1

I. Nucl. Sci. Technol.,

196

contains the data for 100 nuclides. It covers 99.6 % capture and 195% cumulative yields for the 239Pu fission, but it is insufficient for thermal reactors and high conversion light water reactors (HCLWR), because of the lack of important FP nuclides such as 105Rh, and 148mPm. ENDF/B and JEF-2 contain the data for a larger number of nuclides than JENDL-2. However, after the evaluations for these libraries, new measurements on cross sections for FP nuclides have been made at JAERI, ORNL, NIR in USSR, KfK and so on. Large differences in the capture cross sections are observed between the evaluations and the recent experimental data. Besides, accuracy of the capture cross sections of the available libraries was not always sufficient to satisfy the required accuracy. The sensitivity study(6) on HCLWR fuel burnup

reactor burnup calculations but also for more general purposes as mentioned above. The number of nuclides was extended to 172 covering nuclides ranging from 75As to 159Tb, by adding As, Se, Br, Sn and Te isotopes and some short lived nuclides to JENDL-2. They contain constituent stable isotopes of natural elements in the FP mass region as well as FP nuclides which cover about 200 % of cumulative fission yields. Much effort was concentrated to obtain complete sets of resonance parameters. Threshold reaction cross sections were newly evaluated. For the nuclear model calculation, parameters and their systematics were investigated. This paper describes methods used in the present evaluation in Chap. II Chapters III, IV and V are devoted to description of the nuclear model parameters, resonance parameters and capture cross sections, respectively. Evaluations of scattering and threshold reaction cross sections are described in Chaps. VI and VII.

performance showed high sensitivities to capture cross sections of FP nuclides, particularly, those in the resonance energy range. Therefore, it is important to evaluate the resonance parameters as accurately as possible. An integral test on the JENDL-2 FP nuclear data, using sample reactivities measured in the STEK reactor(7), showed large discrepancies between the calculations and the measurements for nuclides with small absorption cross section(8). It was pointed out that these discrepancies depended on a scattering component of the reactivity worth, and particularly came from inelastic scattering cross sections(9). In order to overcome these discrepancies, an evaluation based on the recent experimental data and more refined nuclear models is necessary for resolved resonance parameters and cross sections. The integral test of JENDL-2 also suggested the necessity for re-evaluation of data for several isotopes, such as 132Xe, Xe, 152Eu and 154Eu, which had no 134 experimental data. The JENDL-2 integral test results on the capture cross section were reflected on the cross section revision for these nuclides"". In the present work, the evaluation of the FP nuclear data has been made for JENDL-3, on the basis of experiments made up to 1988. It was intended to provide data, not only for

II.

EVALUATION

METHODS

1, General The multi-level Breit-Wigner formula was used for resolved resonances. Unresolved resonance parameters were determined in the energy range below 100 keV using the ASREP code(11). Above 100 keV, the spherical optical model and the statistical theory code CASTHY(12) were used to calculate the total, capture, elastic and inelastic scattering cross sections. Direct and semi-direct capture cross sections, calculated according to the BenziReffo's formula(13), were added to the CASTHY results in the higher neutron energy range above 1 MeV. For even mass nuclides around the fission yield peaks, i.e. Ru, Pd, Cd, Ba, Ce, Nd and L"Sm, contributions of direct inelastic scattering were calculated with the DWUCK-4 code(14), based on the distorted wave Born approximation theory. Cross sections of (n, 2n), (n, 3n), (n, p), (n, a), (n, np), (n, na), (n, t), (n, d), (n, nd), (n, nt), (n, 2p) and (n, 3He) reactions were calculated with a pre-equilibrium PEGASUS(15). 2

and multistep

evaporation

code

Vol.

29, No. 3 (Mar.

1992)

197

2. Development of Computer Codes In order to make numerous computation of cross sections and to process the massive amount of data for 172 nuclides, various kinds of computer programs were developed and integrated into an evaluation system, as shown in Fig. 1. The REPSTOR is a code for processing resolved resonance parameters, i.e. it has

of ENSDFRET, LVLPLOT and LEVDENS were developed to retrieve the level scheme data from the Evaluated Nuclear Structural Data File, ENSDF(16), to make a staircase plot of levels and to evaluate level density parameters, respectively. The code JOBSETTER and its extensive data file, containing the level density parameters and inverse cross sections for neutrons and charged particles, were prepared for massive computation of CASTHY.

functions of storage-and-retrieval and modification of parameters, counting statistics and making a file in the ENDF format. Programs

Fig.

III .

NUCLEAR

MODEL

1

Auxiliary

evaluation

programs

flow

the computer code NDES(19), and the most recent experimental data of total cross sections, scattering radii and neutron strength functions. The results are summarized in Table 1. Potential forms are as follows :

PARAMETERS

1. Optical Model Parameters The neutron spherical optical

and data

potential

parameters used in JENDL-2 were evaluated elementwise so as to reproduce measured neutron total cross sections in the energy region between 1 keV and 10 MeV within 5% uncertainty, and neutron strength functions and scattering radius taken from BNL-325 3rd edition(18) within 20 % uncertainty. However, extension of the number of the nuclides to be evaluated and the requirement of accuracy of calculations in the high energy region forced the authors to revise the potential parameters. The re-evaluation was made with

(1) where

(derivative 3

(Woods-Saxon

type),

Woods-Saxon

type),

198

J. Nucl. Sci. Technol.,

4

Vol.

29, No. 3 (Mar.

1992)

199

ments(21)~(26) is excellent at various incident neutron energies : 1~14.6 MeV in the figure, except for the cross section minima, which are thought to be probably smeared to a certain extent in the experiments because of finite resolution of the detector system. For calculations of threshold reactions with PEGASUS, inverse cross sections were calculated with ELIESE-3(27), using the global optical model parameters of Perey"" for

=exp{-[(r-R)/b]2)} (Gaussian), and R is the nuclear radius, mp the mass of c the light velocity, s the nuclear spin and l the orbital angular momentum. The Gaussian type surface absorption was applied to Moldauer's potential(20). The parameters were revised for most of the elements, except for Sr-Mo, La-Ce and Nd, to which the same parameters as used for JENDL-2 FPs were adopted. The validity of the parameters was checked by comparing the calculated angular distributions of the elastic scattering cross section with the experimental data. Figure 2 shows the angular distributions elastically scattered by 114Cd and Cd. Agreement between the calculations and the measure-

proton, Huizenga & Igo(29) for a-particle, Lohr & Haeberli(30) for deuteron, and Bechetti & Greenlees(31) for triton and 'He. 2. Level Scheme Data and Level Density Parameters Level scheme data for newly added nuclides for JENDL-3 were taken from ENSDF(16) and the Nuclear Data Sheets. However, those for nuclides contained in JENDL-2 were used in the present evaluation without any change. The level density parameters for the Gilbert-Cameron's composite formula(32) were determined according to the procedure reported by lijima et al.(33) so as to reproduce the number of low-lying levels and the observed resonance level spacings for 320 nuclides, which were composed of the 172 target nuclides and their compound and daughter nuclides of the (n, 2n), (n, p) and (n, a) reactions. From the results, the following mass dependence was found for constant nuclear temperature T (in MeV) : T=65/A =0 .65-0.00242(A-100)

A100,

(2 )

where A is the nuclear mass number. The systematics are depicted in Fig. 3. The level density parameters 'a' is dependent on the neutron number of nuclei, as shown in Fig. 4. This dependence was expressed in several separate following formula :

Fig.

2

regions

by the

(3)

Comparison of differential elastic scattering cross section calculated for 114Cd with experimental data which are for Cd except for 114Cd data reported by Golrov et al,

where N: Neutron number C1,C2: Fitting coefficients N1,N2: Lower and upper boundaries of neutron number. 5

—

J.

200

Fig.

Fig.

4

3

Mass

Neutron

number

number

dependence

dependence

of nuclear

of

Since the level density parameter 'a' shows a shell effect, the authors took neutron numbers of closed neutron shell or subshell nuclides as N, and N2. Table 2 shows the coefficients of Eq. ( 2 ). For the nuclides whose parameters 'a' and T were not available, these

level

temperature

density

parameter

Nucl.

Sci.

Technol.

T

'a'

systematics were used to estimate the parameters. 3. Gamma-ray Strength Functions The r-ray strength functions were adjusted to fit the capture cross sections calculated with the statistical model to the measured 6

Vol.

29, No. 3 (Mar.

Table

2

201

1992)

Systematics parameter

of ' a'

level

density

for FP

nuclides

values

for

of

the r-ray

on

the

of

by

were

It

shape ized

Fig.

5

Neutron nuclide

seen

of strength by

dips

the the

the

that

curves magic

function for other nuclides

(a)

values neutron

strength

figure

function near

strength

using 5 shows

the

and the

the

compi-

et al.(18)(34)(35)

of the r-ray

of the r-ray from

number dependence of r-ray strength with even Z and even mass and (b)

7 —

Mughabghab

Figure

dependence is

from

value

estimated,

width

taken

investigated,

initial was

radiation

systematics

determined.

An

function

spacing

reported

tion

region.

the

level

The

ber

keV strength

basis

resonance lation

the

functhus num-

functions. the

global

is characternumbers

of

50

J.

202

,

(4 )

where g is the single particle level density and A the mass number of the compound nucleus. The estimation is based on the expression of two-body interaction in nuclear matter, given by Kikuchi & Kawai"'). The K values of the Ce, Nd and Sm isotopes were adjusted to reproduce the measured (n, 2n) reaction cross sections. IV.

RESONANCE THERMAL

PARAMETERS CROSS

Sci.

Technol.,

and resonance integral. The unassigned value of the neutron orbital angular momentum of the resonance level was determined with the method reported by Bollinger & Thomas(38), using the Bayesian theorem. The total spin J' was also statistically determined for the levels whose total spin was not experimentally assigned. An examination was made to ascertain that the evaluated resonance parameters reproduce the measured thermal cross sections at 2,200 m/s and resonance integrals which were mainly taken from the compilation of Mughabghab et al. When a discrepancy between calculated and measured values were found, the parameters for low-lying levels were modified, using NDES(19). No resolved resonance parameter was given for 31 nuclides whose resolved resonance parameters have not been measured. For these nuclides, the 1/v shape capture cross section consistent with the measured thermal cross section was assumed. The elastic scattering cross section was assumed to be constant in the low energy region, and the value was calculated from scattering radius obtained from the optical model calculation. The thermal capture cross section was unknown for 10 nuclides. Its elementwise systematics were investigated and the following relation was obtained from the observation that thermal capture cross section a.hermat was very sensitive to the level density :

and 82, and by local oscillations corresponding to even or odd neutron numbers. The systematics of the r-ray strength functions can be used for the nuclides whose capture cross section has not been measured. 4. Kalbach's Constants Kalbach's constant K(36), which represents the strength of the pre-equilibrium transition rate, was estimated, with an accuracy of about 50%, as K=0.1/(g/A)3

Nucl.

AND

SECTIONS

The resonance self-shielding effect plays an important role in predicting the capture rates in the reactors. Therefore, the resonance parameters were given in the energy region below 100 keV. 1. Resolved Resonance Parameters and Thermal Cross Sections The resonance parameters for 65 nuclides were essentially taken from JENDL-2. Those for 57 nuclides were determined on the basis of the recent experimental data and Mughabghab's compilation(34)(35), by checking the conservation of the measured capture area. Particularly, for 18 nuclides of 75As, 82Se, 79Br, Br, 82Kr, 86Kr, 91Zr, 93Zr, 107Pd, 81 110mAg, 122sn, 121 Sb, 123Sb, 136Xe, 140Ce, 148Sm, 152Gd and 154Gd, a lot ofexperimental data were reported from JAERI, ORNL, NIR in USSR, after Mughabghab's compilation. The evaluation for these nuclides was made by using these new experimental data. For "'Rh, which is important in the thermal reactors but whose resonance parameters have not been measured, artificial negative and positive resonance levels were given so as to reproduce the experimental values of thermal capture cross section

hermalc/sCASTHYC=C0 D obs-b.

st (5)

where sCASTHYcis the cross section calculated with CASTHY at 1 eV, Dobs the resonance level spacing estimated from the level density parameters, and Co and b are fitting parameters. For example, the result for the Cs isotopes is shown in Fig. 6. In the figure, a dotted line was fitted to the measured values and it gave the thermal capture cross section of 13 barns for 136Cs. Equation ( 5 ) is well adoptable to most of the cross sections which have 1/v-energy dependence. For elements containing non-1/v absorber, such as Eu, the thermal capture cross sections were determined by taking into consideration the data 8

Vol.

29, No . 3 (Mar.

1992)

203

JENDL-2 and ENDF/B-V, for 40 nuclides in the order of importance(6) i.e. in the order of fractional absorption rate of fission product in HCLWR. For the 11 most important nuclides, agreement between the resonance integrals for JENDL-3 and other files is good. For the other nuclides, however, the integral is discrepant from Mughabghab's compilation (values mainly calculated from the resonance parameters) or ENDF/B-V. It should be noted that the values calculated from the newly evaluated resonance parameters for 93Zr, 107Pd,148Sm and 154 Gd show large discrepancy. In order to reproduce the resonance integral for several nuclides, ENDF/B-V gives an unnatural cross section shape, as shown in Fig. 7. In the

Fig.

for

6

Correlation between the measured-to-calculated cross section ratio and observed resonance level spacing for Cs isotopes

neighboring

elements.

thermal

capture

for

10 nuclides.

the Table

Table

cross

and of

the

infinite

capture

5 compares

nance

integrals et

of

to

the

al.

together

evaluated

resonance

for

all the

values

the

estimated

thermal

dilution

ratios

3 lists

thus

calculated

reaction

Table

Mughabghab

Table

sections

Thermal cross sections from systematics

4 gives

sections grals

3

present evaluation, the authors used methods to adjust evaluated (or in a few cases, artificial) resonance parameters or to adjust the boundary energy between epithermal region characterized by the 1/v-shape of capture cross section and unresolved resonance region for nuclides whose resolved resonance parameters were not available. Figure 7 shows capture cross section for Zr. ENDF/B- V gives a broad cross sec93 tion peak at 100 eV. On the other hand, JENDL-3 contains 139 resonances up to 21 keV ; an upper boundary of the resolved resonance region was determined to be 17 keV, considering the missing levels. As for the resonance integral, Walker(39) recommended it to be 22 barns. The value of 18.2 barns of JENDL-3 is closer to this value than ENDF/ B-V and JENDL-2. Moreover, Walker's recommendation was based on the unpublished ORNL data of single resonance at 110 eV. Reliability of the resonance parameter of

the

cross inte-

172

present compiled with

JENDL-3 is higher than that of the old ORNL data. For 142Nd, as shown in Fig. 8, JENDL-2 shows deep dips at several hundred eV. These dips caused a problem of underestimation of the resonance integral : JENDL-2 gives 6.45 barns, while Gryntakis et al.(40) recommended 8.5+-1.0 barns. The value of 34+-11 barns by Mughabghab can be considered to be too large,

those

FPs. resoby

judging from the cross section shape culated from the resonance parameters.

of 9

calIn

204

J.

Table

4

Calculated integrals

thermal of capture

cross

sections

reaction

JENDL-3, energy of the negative resonance was moved from -20 eV to -1 keV and the resonance parameters were adjusted so as to reproduce the thermal capture cross section of 18.7+-0.7 barns. The final values are 18.4 barns for the thermal capture cross section and 8.78 barns for the resonance integral. Similar modification of the resonance parameters was made for the nuclides whose neg-

for

and

infinite

dilution

Nucl.

Sci.

Technol.,

resonance

172 FP nuclides

ative resonance was too close to zero energy and the resonance integral was underestimated . 2. Unresolved Resonance Parameters Below 100 keV, the unresolved resonance parameters were determined with the ASREP code(10). The neutron strength functions were taken from the compilation of Mughabghab et al. whenever experimental data were existing. Otherwise, values calculated with the 10 —

Vol.

29, No. 3 (Mar.

205

1992)

Table

4

(Continued)

V.

spherical optical model were adopted. Average radiation widths were also adopted from Mughabghab's compilation or its systematics. Nuclear radius R' was determined to reproduce the total cross section at 100 keV. Energy dependent resonance level spacing was determined by fixing other parameters, so as to fit to the average capture cross sections which were calculated with CASTHY or determined from experimental data.

CAPTURE CROSS SECTIONS

The capture cross sections of FP nuclides are important for the burnup calculations. Their values above the resolved resonance region were mainly evaluated with the spherical optical model and the statistical model calculation using the parameters described in Chap. H. The calculation was carried out with CASTHY, by considering the competing process of the threshold reactions such as (n, 2n), (n, p), (n, a) etc., whose cross sections were calculated with PEGASUS as is described in Chap. VII. For several nuclides such as "Tc, the structure for the capture cross sections was reproduced by tracing the experimental data with an eye-guide technique. In the MeV neutron energy region, direct and semidirect capture cross sections were also taken into account by using the formula given by Benzi & Reffo(13). For 132Xe, 134Xe, 152Eu and Eu whose experimental capture cross section 154 data were not available, the results of the cross section adjustment for JENDL-2 FP were reflected in the evaluation(10). The evaluated results are compared with those in JENDL-2 and ENDF/B- V , and the measured data for typical cases. Figure 9 shows the result for 81Br. It is found in the 11 —

J.

206

Table

5

Ratio

of evaluated

to value

compiled

capture

resonance

by Mughabghab

12 —

integral et al.

Nucl.

Sci.

Technal.,

Vol.

29, No. 3 (Mar.

1992)

207

Fig.

7

Comparison of evaluated capture for 98Zr with JENDL-2, ENDF/B-

cross section and resonance V and experimental data

integral

Fig.

8

Comparison of evaluated for 142Nd with JENDL-2,

capture cross section and resonance ENDF/B-V and experimental data

integral

13 —

J. Nucl. Sci. Technol.,

208

figure

that

JENDL-3

measured by overestimated gives than

agrees

with

Macklino(41), while it by 20~50%

the

data

about 250 eV. A similar extension of resonance energy is made for 18 nuclides of 76As, Se, 79Br, 81Br, 82Kr, 86Kr, 91Zr, 93Zr, 82 107Pd, 110mAg, 122 Sn,121Sb, 128Sb, 136Xe, 140Ce, 148Sm, 2Gd and 154Gd. 15

ENDF/B-V JENDL-3

a wider resonance region, up to 13 keV, ENDF/B-V which covers only up to

Fig.

9

Comparison for 81Br

with

of evaluated ENDF/B-V

capture

cross

and

experimental

For 93Zr shown in Fig. 7, the evaluated data agree well with the data measured by Macklin". Above 5 MeV, JENDL-3 shows direct and semi-direct capture effects. VI.

INELASTIC CROSS

SCATTERING

SECTIONS

Neutron moderation due to the inelastic scattering cross section of the FP nuclides is larger than that for the elastic scattering. Accordingly, it may affect the sample reactivity in a reactor core, particularly for weak neutron-absorbers. The discrepancy in the weak-neutron-absorbing oxide sample worth, between the measurements in the STEK core(7) and calculations, were interpreted by Gruppelaar(9) as an effect of neglecting direct inelastic components although Iijima(43) pointed out that inadequate correction for the slowing

section

and

resonance

integral

data

down effect due to oxygen was more serious. Either way, reliable data should be provided, including both components of compound and direct inelastic scattering processes. The former was calculated with CASTHY and the latter with DWUCK-4(14) for 28 nuclei with even atomic number and even mass number around the fission yield peaks. Deformation parameters for the DWUCK-4 calculation were mainly taken from Refs. (44) and (45) . Figure 10 compares the evaluated data with the data measured by Coope et al .(46) and by Haouat et al.(47) for 144Nd. The dashed line curve displays the compound inelastic scattering and the dotted line curve indi cates the direct component. It was found that the present results agree well with the two experimental data and that the direct compo _ nent becomes dominant at energies higher 14 —

Vol.

29, No. 3 (Mar.

Fig.

1992)

10

209

Comparison excited

state

of excitation between

function JENDL-3

than 4 MeV. VII.

THRESHOLD CROSS

REACTION

SECTIONS

The authors calculated the cross sections for (n, 2n), (n, 3n), (n, p), (n, np), (n, a), (n, na), (n, 2p), (n, d), (n, nd), (n, t), (n, nt) and (n, 3He) reactions for all the 172 FP nuclides by using PEGASUS. Figure 11(a) and (b) give the experiment-to-calculation ratios for the (n, 2n) and (n, p) cross sections at 14.5 MeV. The (n, 2n) cross sections are predicted fairly well About 80% of all the points are in the range from 0.7 to 1.5. On the other hand, the prediction for (n, p) and (n, a) reaction cross sections is rather poor. In the final data file, the calculated results were normalized to the data at around 14 MeV recommended by Bychkov et al.(48) for the (n, 2n) reaction and by Forrest(49) for the (n, p) and (n, a) reactions or to the 14.5 MeV systematics. The 14.5 MeV systematics are given by Wen Den Lu et al.(50) for the (n, 2n) reaction, and by Forrest for the (n, p) and (n, a) reactions. The value of the Kalbach constant K was adjusted to reproduce the measured (n, 2n)

of inelastic

scattering

to first

data

for 144Nd

and experimental

reaction cross sections for 15 nuclides 1,4Ce ,144Nd, 146Nd, 148Nd, 150Nd,147~154Sm

of 142Ce, and

because large discrepancies were observed between cross section shapes of calculations and measurements. As an example of the threshold reaction cross section, Fig. 12 compares the evaluated (n, 2n) cross sections for 104Ru. The calculations with PEGASUS were taken as a final result and are in good agreement with the experimental data reported by Temperley(51), Lu(52), Bormann(53)and Qaim(54). The calculation for the Nd isotopes was carried out by adjusting the Kalbach constant as mentioned above and gives an overall agreement with the measured data, as shown in Fig. 13. Figure 14 shows the result for the (n, p) cross section for "Mo. The present evaluation is in marked agreement with the recent experimental data(55)~(58). 160Gd,

VIII.

CONCLUSION

In the present work, the neutron nuclear data for the 172 fission product nuclides have been evaluated in the energy region from 10-5 eV to 20 MeV, on the basis of the experi15 —

J. Nucl.

210

Fig.

11(a),(b)

Ratio

of experiments

(n, 2n) and

(n, p)

to calculations reactions

16 —

cross

with section

PEGASUS at 14.5 MeV

for

Sci.

Technol.,

Vol.

29, No. 3 (Mar.

Fig.

12

1992)

Comparison

211

of evaluated

(n, 2n) cross

section

with

experimental

data

for 104Ru

mental data published up to 1988 and compiled into the JENDL-3 FP nuclear data file in the ENDF-5 format. Considering that the other FP nuclear data files, such as ENDF/B-VI, are mainly based on older evaluations, the present results are considered to be very valuable. The new evaluation for the resolved resonance parameters was made as well as the re-evaluation for the nuclides contained in JENDL-2. These results might improve the prediction of the reactor performance, particularly for HCLWR. The nuclear model parameters were determined and the systematics were found for the level density parameters, nuclear temperatures, r-ray strength functions and Kalbach constants. The systematics will be useful for calculation of cross sections of unstable nuclei and profitable for use in calculations based on a simplified model. The applicability of the present file to reactor burnup calculation will be verified by integral tests planned for near future in which Fig.

13

Comparison

of

evaluated

(n, 2n)

cross section with experimental data for 144Nd, 146Nd, 148Nd and 150Nd 17

J.

212

Fig.

14

Comparison

of evaluated

(n, p)

cross

the data for STEK, EBR II, CFRMF and the other experiments with the mock-up FP samples illw be analyzed using the present file. The authors also prepare a data book(59) presenting cross section curves and tables of group cross sections

for the 172 FP nuclides.

ACKNOWLEDGMENT This work was carried out as one of the activities in Japanese Nuclear Data Committee in Japan Atomic Energy Research Institute. The authors are very thankful to Dr. Y. Kikuchi and the JNDC members for their encouraging and meaningful discussions. REFERENCES (1) WANG, D. H. (ed.): WRENDA 87/88, World Request List for Nuclear Data, INDC(SEC)095/URSF, (1988). (2) AOKl, T., at al.: Proc. Int. Conf. on Nuclear Data for Basic and Applied Science, Santa Fe, Vol. 2, p. 1627 (1985). (3) ENGLAND, T.R., et al.: NP-2345 (ENDF-322), (1984). (4) DUNFORD, C. L. : Evaluated nuclear data file, ENDF/B-VI, Presented at Int. Conf. Nuclear Data for Science and Technology, 13~17 May 1991, Juelich, IP12.

section

with

experimental

Nucl.

data

Sci.

Technol.,

for 96Mo

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