BNL-98708-2012-IR

Release of the ENDF/B-VII.1 Evaluated Nuclear Data File

David Brown

Presented at the 2012 ANS Winter Meeting Town & Country Hotel & Resort

San Diego, CA November 11-15, 2012

National Nuclear Data Center Brookhaven National Laboratory

P.O. Box 5000 Upton, NY 11973-5000

www.nndc.bnl.gov

U.S. Department of Energy Office of Science, Office of Nuclear Physics

Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. This preprint is intended for publication in a journal or proceedings. Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.

DISCLAIMER

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Release of the ENDF/B-VII.1 Evaluated Nuclear Data File

David Brown

National Nuclear Data Center, Blg. 197D, Brookhaven National Laboratory, Upton, NY, 11973, email: dbrown@bnl.gov

For the Cross Section Evaluation Working Group and all of the contributors to ENDF/B-VII.1:M. B. Chadwick, M. Herman, P. Oblozinsky, M. E. Dunn, Y. Danon, A. C. Kahler, D. L. Smith, B. Pritychenko, G. Arbanas,

R. Arcilla, R. Brewer, D. A. Brown, R. Capote, A. D. Carlson, Y. S. Cho, H. Derrien, K. Guber, G. M. Hale, S. Hoblit, S. Holloway, T. D. Johnson, T. Kawano, B. C. Kiedrowski, H. Kim, S. Kunieda, N. M. Larson, L. Leal, J. P. Lestone, R. C. Little, E. A. McCutchan, R. E. MacFarlane, M. MacInnes, C. M. Mattoon, R. D. McKnight, S. F. Mughabghab, G. P. A.

Nobre, G. Palmiotti, A. Palumbo, M. T. Pigni, V. G. Pronyaev, R. O. Sayer, A. A. Sonzogni, N. C. Summers, P. Talou, I. J. Thompson, A. Trkov, R. L. Vogt, S. C. van der Marck, A. Wallner, M. C. White, D. Wiarda, and P. G. Young

INTRODUCTION

The Cross Section Evaluation Working Group (CSEWG) released the ENDF/B-VII.1 library on December 22, 2011. The ENDF/B-VII.1 library is CSEWG's latest recommended evaluated nuclear data file for use in nuclear science and technology applications, and incorporates advances made in the five years since the release of ENDF/B-VII.0, including: many new evaluation in the neutron sublibrary (423 in all and over 190 of these contain covariances), new fission product yields and a greatly improved decay data sublibrary.

In this summary, I will highlight some of the changes. The full list of major changes includes: • Many more evaluations in the neutron sublibrary

(ENDF/B-VII.0 contained 393 isotopes, ENDF/B-VII.1 contains 423);

• Extensive nuclear reaction data on uncertainties (covariance data evaluations) for 190 isotopes;

• All minor actinide cross section evaluations improved, including new U, Np, Pu and Am evaluations and the use of the JENDL-4 library for Cm, Bk, Cf, Es, Fm and others;

• Structural material evaluations have been advanced through use of recent resolved and unresolved resonance analyses of new measured data;

• New light nucleus R-matrix evaluations have been developed for the nuclides 3He, 9Be, and 6Li.

• Modifications to thermal neutron reactions on fission products (isotopes of Mo, Tc, Rh, Ag, Cs, Nd, Sm, Eu) and neutron absorber materials (Cd, Gd);

• Fission energy release evaluations; • Fission product yield advances for fission-spectrum

neutrons and 14 MeV neutrons incident on 239Pu, including details of the neutron energy dependence over the fast neutron range from 0.5 - 2.0 MeV; and

• A new decay data sublibrary.All of these are detailed in Ref. [1] and the rest of the December 2011 issue of Nuclear Data Sheets.

0.9750

0.9800

0.9850

0.9900

0.9950

1.0000

1.0050

1.0100

1.0150

1.0200

1.0250

k eff C

/E

HMF1 (Godiva)

HMF28 (Flattop -25)

IMF7d (Big-10)

PMF1 (Jezebel)

PMF2 (Jezebel -240)

PMF6 (Flattop -Pu)

PMF8 (Thor)

UMF1 (Jezebel -23)

UMF6 (Flattop -23)

Fig. 1. ICSBEP benchmarks from Los Alamos’s FAST suite, demonstrating the continuing excellent agreement of ENDF/B-VII.1 with integral experiments.

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

C/E

LANL

IPPE-Russia

COSMOS (CEA)

Fig. 2. Fission reaction spectral index C/E values for selected actinides from LANL (Flattop-25), PROFIL and FUND-IPPE-FR-MULT-RRR-001 assemblies. The spectral index ratio is usually made to 235U(n,f), but some of the LANL ratios are to 239Pu(n,f).

The ENDF/B-VII.1 library is the most extensively tested ENDF release and many new benchmark tests were added since the release of ENDF/B-VII.0 (see Ref

mailto:dbrown@bnl.govmailto:dbrown@bnl.gov

[2]). Although the library has undergone substantial revision since ENDF/B-VII.0, we have preserved the excellent agreement with key benchmarks as one can see in the selection of FAST critical assembly simulations from Los Alamos National Laboratory in Fig. 1. In Fig. 2 we show some results from new benchmark tests, namely spectral index measurements. In this type of test, one irradiates a small sample of a material and then radiochemically assays it after irradiation. This allows one to target specific reactions in a material for testing. As one can see in Fig. 2, we have overall good agreement at the 2 sigma level.

In the remainder of this summary, I will focus on changes that directly impact reactor simulations, namely: improvements to Zr (as Zr is used in reactor cladding), the new decay library (as it determines decay heat) and the expanded suite of data covariance. Finally, I will present some thoughts on the future of the ENDF library.

LIBRARY HIGHLIGHTS

Sample of new evaluations: Zirconium isotopes

Zr is used in fuel rod cladding due to its corrosion-resistance and low thermal neutron absorption cross section. These properties also make it an attractive material for advanced reactor design either as a moderator in the form of zirconium hydride or an inert matrix fuel material. The ENDF/B-VI.8 evaluations from the 1970‘s relied on fits to experimental data and lacked double differential outgoing particle distributions and gamma production data. These evaluations were replaced in the ENDF/B-VII.0 library with complete, but theory based, evaluations. Testing by KAPL and Bettis demonstrated a drop in reactivity in various proprietary benchmarks in the transition from ENDF/B-VI.8 to ENDF/B-VII.0. Sensitivity studies revealed that these deficiencies can be remedied by adjusting the elastic cross section as was done in ENDF/B-VI.8 (see Fig. 3).ENDF/B-VII.1 Nuclear Data ... NUCLEAR DATA SHEETS M.B. Chadwick et al.

Incident Energy (MeV)

Cro

ss

Se

cti

on

(b

arn

s)

1 10

5

10

15

ENDF/B-VII.1 (BNL)ENDF/B-VI.8JENDL-4.0ENDF/B-VII.040-Zr-0(N,TOT),SIG

FIG. 45: natZr(n,tot) cross section. The ENDF/B-VII.1 eval-uation preserves the data-driven fluctuations present in theolder ENDF/B-VI.8 evaluation.

components. We took the energy-dependence of thelevel spacing to be the Gilbert-Cameron level densityformula with associated parameters from Mughabghab[35, 126]. Further, we took the energy-dependence ofcapture widths to be the generalized Fermi liquid model[126] with associated parameters from [35]. We use aneffective scattering radius of 7.2 fm in the URR.

Fast neutron regionBecause the Zr isotopes are so close to a closed shell, thetotal and elastic cross sections exhibit pronounced fluctu-ations up to nearly 1 MeV. To preserve these fluctuations,which were present in the original ENDF/B-VII.8 eval-uation and integral testing suggests are important, weused EMPIRE’s ability to tune cross sections to data tomatch natZr(n,tot) (see Fig. 45). Total cross sectionsin all of the Zr isotopes were tuned with the same fac-tors while elastic cross sections were obtained subtract-ing non-elastic channels from the total. Whilst strictlyspeaking this is not correct, it preserves the transportcross section for natZr while leaving the activation crosssections for the individual isotopes unchanged. Modelcalculations in the fast energy range were based on nu-clear model calculations using the EMPIRE code [82].Starting values for nuclear model parameters were takenfrom the RIPL recommendations [85]. A dispersive OMP(RIPL 609) [85] based on soft rotor couplings was usedto describe the incident channel on even-even targets; thesame potential with rigid-rotor couplings (RIPL 611) wasemployed to describe the incident channel for even-oddisotopes. The optical model calculations for the incidentchannel of even-even Zr isotopes were performed withthe OPTMAN code [149], which is capable of includingsoft-rotor couplings. All other optical model calculationswere performed with the ECIS code [87] that is incor-porated into the EMPIRE system. TUL multistep di-rect and the Heidelberg multistep compound models wereemployed to describe the preequilibrium neutron emis-sion; proton, gamma and cluster pre-equilibrium emis-

Angle (deg)

dσ

/dΩ

(b/s

r)

0 50 100 150

10-1

1

ENDF/B-VI.8ENDF/B-VII.0JENDL-4ENDF/B-VII.140-Zr-0(N,EL),DA

FIG. 46: natZr(n,el) double differential cross section for neu-trons with incident energy 3.6 MeV. The ENDF/B-VII.1 eval-uation tracks the shape of JENDL-4.0, but with the normal-ization controlled by the fluctuations in Fig. 45.

sion was calculated using a one-component exciton model(PCROSS). Hauser-Feshbach [88] and Hofmann-Richert-Tepel-Weidenmüller [89] versions of the statistical modelwere used for the compound nucleus cross section calcula-tions. Both approaches account for the multiple-particleemission and the full gamma-cascade. Level densitieswere described by the (semi)-microscopic parity depen-dent Hartree-Fock-Bogoliubov level densities [85].

Extensive comparison of the calculated elastic angulardistributions with the wealthy amount of experimentaldata (about 150 plots) demonstrated that JENDL-4.0using the Walter-Guss OMP below 6 MeV, and Koning-Delaroche OMP above 6 MeV describes measurementsbetter, especially at low incident energies. Since KAPLsensitivity studies indicated that elastic angular dis-tributions might be of importance for their integraltesting we adopted the (n,el) angular distributions fromJENDL-4.0. A sample angular distribution is givenin Fig. 46. It can be seen that our tuning of theelastic cross sections slightly improves agreement withthe experimental data. Benchmarking performed withthe suite of 22 integral experiments (see accompanyingvalidation paper [8]) confirmed that switching to theJENDL angular distributions reduces over predictionof the TRIGA 132 and 133 reactivities by 50% bring-ing our results well within the experimental uncertainties.

Covariance dataWe added the Zr point-wise covariance data whichwere used to produce group-wise COMMARA-2.0 [150]library to the evaluations. In the thermal and resolvedresonance region we made use of the covariance formal-ism based on the kernel approximation along with datain the Atlas of Neutron Resonances. In the fast neu-tron region covariance estimates were calculated using

2929

Fig. 3. The natZr total cross section. In the ENDF/B-VII.1 evaluations, (n,el) cross sections were adjusted so that the (n,tot) cross section matches experimental data and the legacy ENDF/B-VI.8 evaluation.

-1000

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-250

0

250

500

750

1000

k(ca

lc) -

k(b

ench

mar

k), p

cm ENDF/B-VI.8

ENDF/B-VII.0 ENDF/B-VII.1

Fig. 4. ICSBEP benchmarks containing significant amounts of Zr either in the form of control rods or reflectors. The new ENDF/B-VII.1 evaluations demonstrate a substantial improvement over older releases, especially in TRIGA and ZPPR benchmarks.

The new ENDF/B-VII.1 evaluations detailed in Ref. [1] contain several improvements, including new resonance regions for 90,91Zr, new fast evaluations created using a new dispersive soft-rotor optical model potential and covariance data from the COMMARA-2.0 project. The (n,el) cross sections in the Zr evaluations were tuned to match (n,tot) data in the fast region, enabling the new evaluations to capture the best features of the ENDF/B-VII.0 and ENDF/B-VI.8 evaluations. In Fig. 4, we show benchmark simulation results for a variety of critical assemblies which contain significant amounts of Zr, either in the form of control rods or reflectors. One can clearly see the improvement in the ZPPR and TRIGA benchmarks (Ref. [2]).

Decay sublibrary

The new ENDF/B-VII.1 decay sublibrary is a substantial improvement over the previous ENDF/B-VII.0 release. The new sublibrary consists of 3817 materials, each one corresponding to the ground state, a long-lived state or an isomer of a nucleus. 19 poorly known materials in ENDF/B-VII.0 were dropped. This sublibrary is based mainly on the decay data in the Evaluated Nuclear Structure Data File (ENSDF), with some crucial additions: incomplete data were supplemented using the Nuclear Wallet Cards (2011), Q-values were computed from the Audi-Wapstra 2003 mass tables and atomic data was taken from Lawrence Livermore National Laboratory’s Evaluated Atomic Data Library [1]. The sublibrary was improved further with beta-decay modeling using the Cascading Gamma Multiplicity (CGM) model and by comparing to Total Absorption Gamma-ray Spectroscopy (TAGS) data. In Ref. [1], it is noted that the TAGS comparison is directly responsible for the excellent agreement with experiment shown in Fig. 5.

ENDF/B-VII.1 Nuclear Data ... NUCLEAR DATA SHEETS M.B. Chadwick et al.

In addition to the incorporation of new and updateddata from ENSDF, the new ENDF/B-VII.1 contains anumber of modifications, additions and error resolutions,compared with ENDF/B-VII.0. These include a morethorough treatment of the atomic radiation, improvedQ value information, recent theoretical calculations ofthe continuous spectrum from beta-delayed neutron emit-ters, and new TAGS (Total Absorption Gamma-ray Spec-troscopy) data.

Atomic radiation, X-rays and Auger electrons, are pro-duced from the filling of atomic vacancies created in elec-tron capture and electron conversion. A detailed de-scription of these processes is important for nuclides forwhich the main decay mode is electron capture. It isalso relevant in heavy deformed nuclei where gamma-raytransitions are strongly converted, as well as in the de-formed actinides where the gamma-ray transition energyis smaller than the K binding energy. In ENDF/B-VII.0,the atomic data included fluorescence yields, energies andintensities taken from the 8th edition of the Table of Iso-topes [259].

In the new ENDF/B-VII.1, the atomic data from theEvaluated Atomic Data Library [260] developed by LLNLwas used, in a similar way to the calculations describedby Stepanek [261]. All the K-L, K-M and K-N as wellas the Lα, Lβ and Lγ X-rays are included. In addition,the KLL, KLX, KXY, LLX, LMM, LMX, LXY, MMX,and MXY average Auger electrons are also listed. Theelectron conversion to atomic sub-shells was calculatedwith the code BRICC [262].

An essential component of any decay process is thetotal energy available for the decay (Q value). The pre-vious ENDF/B-VII.0 makes use of the 2003 Audi massevaluation [263]. Since then, with the advent of multi-ple Penning traps around the world, numerous massesof both neutron and proton rich nuclei have been mea-sured with very high precision. These are incorporatedinto the 2009 and 2011 updates of the mass evaluationand have been used in creating the ENDF/B-VII.1 decaysublibrary. Changes in the overall Q value for a decay im-pact the values of energy for electromagnetic radiation,light particles, and heavy particles.

In some neutron rich nuclei, beta-decay followed byneutron emission is an energetically favored decay mode.The resulting neutron spectrum is very difficult to mea-sure experimentally and data are available for only a se-lect few cases. As this decay mode has particular rel-evance for energy applications, ENDF/B-VII.1 includesnew theoretical calculations using the Cascading GammaMultiplicity (CGM) model of continuous gamma, beta,and neutron spectra [264]. The calculations were per-formed for beta-delayed neutron emitters which comprisethe thermal neutron fission fragment yield of 235U and239Pu. The previous ENDF/B-VII.0 modeled the neu-tron spectrum using Gross theory whereas in the presentcalculations, a micro-macroscopic (QRPA) theory of thebeta-decay strength function is coupled with a statisticalmodeling of the levels and continuum in the daughter nu-

FIG. 102: Decay heat multiplied by time for a single fissionevent for 235U(n,f) at neutron thermal energy. Shown are theelectromagnetic (blue) and light particle (red) components ofthe decay heat. ENDF/B-VII.1 values are compared withexperimental data [267].

cleus. Depending on the known available data, differenttypes of files were generated. For those nuclei where thecomplete neutron spectrum is known, the neutron datafrom ENDF/B-VI.8 was combined with the beta-decaydata in ENSDF, as in 136I. In cases where only a portionof the neutron spectrum is measured, the neutron datafrom ENDF/B-VI.8 were merged with the CGM calcu-lations to provide a complete neutron spectrum up tothe available Q value. For those nuclei where no neutrondata are available, but detailed gamma and beta radia-tion have been determined, the information from ENSDFwas combined with the neutron spectrum from the CGMcalculations. Finally, for those nuclei where no measure-ments have been performed, the theoretical calculationsprovided the gamma, beta, and neutron spectra. Thevalues of Pn (delayed neutron emission probability) weretaken from ENSDF when experimentally known; other-wise, the values from the CGM calculations were used.Lifetimes were also taken from ENSDF when experimen-tally known, otherwise the systematic values provided byPfeiffer et al. [265], were adopted.

Total Absorption Gamma-ray Spectrometry (TAGS) issensitive to the total beta-decay population of all nuclearlevels, rather than to individual, discrete gamma-rays.Particularly in cases where the Q value is quite large, dis-crete gamma rays can be missed, and the TAGS method ispreferred for an accurate measurement of the total beta-decay strength. The values of energy of electromagneticradiation and energy of light particles from the recentlypublished TAGS data for 105Mo, 104,105,106,107Tc [266],were included in ENDF/B-VII.1.

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Fig. 5. Decay heat times the time for a single neutron induced fission event on 235U at thermal neutron energies, broken out into electromagnetic and light particle components.

Covariance data

The ENDF/B-VII.1 library contains over 190 neutron evaluations with covariances, more than any previous ENDF library. A summary of these covariances is provided in Table I. Notable is the substantial increase of covariance data for structural materials and minor actinides (see Ref. [4]). Although the mean values of all quantities in the major actinides were unchanged, covariances for Prompt Fission Neutron Spectrum (PFNS) were added (see Ref. [5]). Sample plots of these covariances are shown in Figs. 6 and 7.

Table I. Summary of neutron cross section covariance data sets in ENDF/B-VII.1.Table I. Summary of neutron cross section covariance data sets in ENDF/B-VII.1.Table I. Summary of neutron cross section covariance data sets in ENDF/B-VII.1.Category Materials CommentLight nuclei

12 6 evaluated by R-matrix; 6 low fidelity estimates

Structural + FP

105 38 evaluated for COMMARA-2.0; 40 updated low fidelity estimates; 15 for criticality safety programs; 12 for other purposes

Priority Actinides

20 13 evaluated for COMMARA-2.0; 1 from ENDF/B-VII.0; 6 from JENDL-4.0

Minor Actinides

53 All from JENDL-4.0

0.2

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1

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0.01 0.1 1 10

Rat

io to

Max

wel

lian

(T=1

.42

MeV

)

Outgoing Neutron Energy (MeV)

n(0.5MeV)+239Pu PFNS

Knitter, 1975 (0.215 MeV)Staples, 1995 (0.5 MeV)

Lajtai, 1985 (thermal)Bojcov, 1983 (thermal)

ENDF/B-VII.0present work

1 bandJENDL-Actinoid, 2008

Fig. 6. 239Pu Prompt Fission Neutron Spectrum (PFNS) for 0.5 MeV incident neutrons, in ratio to a Maxwellian spectrum. The mean value of the PFNS in ENDF/B-VII.1 is the same as ENDF/B-VII.0, but the covariance data is new.

-1 -0.5 0 0.5 1

10-3 10-2 10-1 100 10110-3

10-2

10-1

100

101

Outgoing Energy (M

eV)

Outgoing Energy (MeV)

Fig. 7. The newly evaluated covariance for 239Pu PFNS for 0.5 MeV incident neutrons.

RESULTS

This summary barely touches on the five years’ worth of advances present in the ENDF/B-VII.1 library. We expect that these changes will lead to improved integral performance in reactors and other applications. Furthermore, the expansion of covariance data in this release will allow for better uncertainty quantification, reducing design margins and costs.

The ENDF library is an ongoing and evolving effort. Currently, the ENDF data community embarking on several parallel efforts to improve library management:

• The adoption of a continuous integration system to provide evaluators “instant” feedback on the quality of

their evaluations and to provide data users with working “beta” quality libraries in between major releases.

• The transition to new hierarchical data format: the Generalized Nuclear Data (GND) format. We expect GND to enable new kinds of evaluated data which cannot be accommodated in the legacy ENDF format.

• The development of data assimilation and uncertainty propagation techniques to enable the consistent use of integral experimental data in the evaluation process.

REFERENCES

1. M.B. CHADWICK, et al., “ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields and Decay Data,” Nucl. Data Sheets, 112, 2887 (2011).2. A.C. KAHLER, et al., “ENDF/B-VII.1 Neutron Cross Section Data Testing with Critical Assembly Benchmarks and Reactor Experiments,” Nucl. Data Sheets, 112, 2997 (2011).3. J.P. LESTONE, “Energy dependence of Plutonium Fission-Product Yields,” Nucl. Data Sheets, 112, 3120 (2011); M. MACINNES, M.B. Chadwick, T. Kawano “Fission Product Yields for 14 MeV Neutrons on 235U, 238U and 239Pu,” Nucl. Data Sheets, 112, 3135 (2011).4. D.L. SMITH, “Evaluated Nuclear Data Covariances: The Journey From ENDF/B-VII.0 to ENDF/B-VII.1,” Nucl. Data Sheets, 112, 3037 (2011); S. HOBLIT, et al., “Neutron Cross Section Covariances for Structural Materials and Fission Products,” Nucl. Data Sheets, 112, 3075 (2011); A. TRKOV, et al. “Covariances of Evaluated Nuclear Cross Section Data for 232Th, 180, 182, 183, 184, 186W and 55Mn,” Nucl. Data Sheets, 112, 3098 (2011).5. P. TALOU, et al., “Quantification of Uncertainties for Evaluated Neutron-Induced Reactions on Actinides in the Fast Energy Range,” Nucl. Data Sheets, 112, 3054 (2011).