A.C. Kahler

• PhD, University of Tennessee
• Los Alamos National Laboratory

We demonstrate how machine learning (ML) techniques can be used as an auxiliary tool for nuclear data validation analysis. The output of the ML analysis can inform evaluators and validators on the quality, or lack thereof, of specific nuclear data and benchmark experiments with respect to simulating these experimental benchmark values. To this end,...

High quality nuclear data is the most fundamental underpinning for all neutron metrology applications. This paper describes the release of version II of the International Reactor Dosimetry and Fusion File (IRDFF-II) that contains a consistent set of nuclear data for fission and fusion neutron metrology applications up to 60 MeV neutron energy. The...

High quality nuclear data is the most fundamental underpinning for all neutron metrology applications. This paper describes the release of version II of the International Reactor Dosimetry and Fusion File (\mbox{IRDFF-II}) that contains a consistent set of nuclear data for fission and fusion neutron metrology applications up to 60~MeV neutron energ...

The energy spectra of neutrons emitted promptly in the neutron-induced fission reactions of ²³⁵U and ²³⁹Pu were re-evaluated for ENDF/B-VIII.0. These evaluations are based on a careful modeling of all relevant physics processes, an extensive analysis of experimental data and a detailed quantification of pertinent uncertainties. Energy spectra of ne...

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 235,238U, 239Pu, 56Fe, 16O and 1H - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Wor...

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on ¹H, ¹⁶O, ⁵⁶Fe, ²³⁵U, ²³⁸U and ²³⁹Pu described in companion papers in the present issue of Nu...

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies – 16O, 56Fe, 235,8U and 239Pu – with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working P...

NJOY is a well respected code for nuclear data processing throughout the world. It was first publicly released in 1977 as a successor to MINX and has continuously improved its capabilities ever since. The latest release of NJOY is NJOY2012 and was released in December 2012 with its latest update coming in February 2015. A new effort has begun at Lo...

We present an evaluation of the 235U prompt fission neutron spectrum (PFNS) induced by thermal to 20-MeV neutrons. Experimental data and associated covariances were analyzed in detail. The incident energy dependence of the PFNS was modeled with an extended Los Alamos model combined with the Hauser-Feshbach and the exciton models. These models descr...

This paper presents a number of refinements to the original Los Alamos model of the prompt fission neutron spectrum and average prompt neutron multiplicity as derived in 1982. The four refinements are due to new measurements of the spectrum and related fission observables many of which were not available in 1982. They are also due to a number of de...

The results of validation of the latest release of International Reactor Dosimetry and Fusion File, IRDFF-1.03, in the standard 252Cf(s.f.) and reference 235U(nth,f) neutron benchmark fields are presented. The spectrum-averaged cross sections were shown to confirm IRDFF-1.03 in the 252Cf standard spontaneous fission spectrum; that was not the case...

Starting in the 1950s and continuing into the early 1970s, a number of foil irradiations and fission chamber measurements were made in a variety of Fast critical assemblies at Los Alamos National Laboratory. These include (i) Godiva, a bare HEU spherical assembly; (ii) Flattop-25, a spherical assembly consisting of an HEU core and a natural uranium...

We present a new evaluation of the 239Pu prompt fission neutron spectrum (PFNS) induced by thermal to 30 MeV neutrons. Compared to the ENDF/B-VII.1 evaluation, this one includes recently published experimental data as well as an improved and extended model description to predict PFNS. For instance, the pre-equilibrium neutron emission component to...

Nuclear criticality safety analysis using computational methods such as a Monte Carlo method must establish, for a defined area of applicability, an upper subcritical limit (USL), which is a calculated multiplication factor k that can be treated as actually subcritical and is derived from a calculational margin (combination of bias and bias uncerta...

We present evaluations of the prompt fission neutron spectrum (PFNS) of 239Pu induced by 500 keV neutrons, and associated covariances. In a previous evaluation by Talou et al. 2010, surprisingly low evaluated uncertainties were obtained, partly due to simplifying assumptions in the quantification of uncertainties from experiment and model. Therefor...

The International Reactor Physics Experiment Evaluation Project (IRPhEP) and the International Criticality Safety Benchmark Evaluation Project (ICSBEP) provide evaluated integral benchmark data that may be used for validation of reactor physics/nuclear criticality safety analytical methods and data, nuclear data testing, advanced modeling and simul...

In December 2011, the National Nuclear Data Center released ENDFIB-VII.1, the "latest recommended evaluated nuclear data file for use in nuclear science and technology applications." The data were released in the standard Evaluated Nuclear Data Format (ENDF). This release represents the advances made in nuclear data during the 5 years since the rel...

The OECD Nuclear Energy Agency (NEA) organizes cooperation between the major nuclear data evaluation projects in the world. The NEA Working Party on International Nuclear Data Evaluation Cooperation (WPEC) was established to promote the exchange of information on nuclear data evaluation, measurement, nuclear model calculation, validation, and relat...

Analyses of thermal plutonium solution critical benchmark systems have indicated a deficiency in the Pu-239 resonance evaluation. To investigate possible solutions to this issue, the Organisation for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) Working Party for Evaluation Cooperation (WPEC) established Subgroup 34 to fo...

In the frame of a US-DOE sponsored project, ANL, BNL, INL and LANL have performed a joint multidisciplinary research activity in order to explore the combined use of integral experiments and covariance data with the objective to both give quantitative indications on possible improvements of the ENDF evaluated data files and to reduce at the same ti...

This report has been issued by the WPEC Subgroup 34 with a view to solving a general discrepancy when calculating criticality benchmarks with plutonium, using the most recent evaluated data libraries. This international effort enabled the delivery of a single set of resonance parameters up to 2.5 keV. The large fluctuations of the prompt neutron mu...

We review the results of ENDF/B-VII.1 cross section data testing with International Criticality Safety Benchmark Evaluation Project (ICSBEP) benchmark assemblies. Comparisons with the previous, ENDF/B-VII.0, file are made, noting where the new data perform better and also noting areas of continuing weakness that require further experimental and the...

In summary, we have provided a brief overview of recent Los Alamos accomplishments in support of the various program elements of the Nuclear Criticality Safety Program. Los Alamos appreciates the support from DOE to enable these exciting projects.

We review the results of the DOE's Nuclear Criticality Safety Program sponsored data evaluation and data testing work at performed at LANL in support of ENDF/B-VII.1.

The ENDF/B-VII.1 library is the latest revision to the United States Evaluated Nuclear Data File (ENDF). The ENDF library is currently in its seventh generation, with ENDF/B-VII.0 being released in 2006. This revision expands upon that library, including the addition of new evaluated files (was 393 neutron files previously, now 423 including replac...

The ENDF/B-VII.1 library is our 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. These advances focus on neutron cross sections, covariances, fission product yields and decay data, and represent work by the US Cr...

This report was issued by WPEC Subgroup 32, which investigates the methodologies used in the unresolved resonance region (URR) for cross-section and covariance representation. The objectives of the subgroup were (i) to investigate the use of the Single-level Breit-Wigner formalism in the URR for fissile and fertile isotopes; (ii) to investigate URR...

In this work we report the methodology and the results of an evaluation carried out for 48 Ti in the resolved resonance region for applications in criticality safety calculations. The evaluation was performed using the computer code SAMMY with the reduced R-matrix Reich-Moore formalism. The Bayes' scheme was utilized for fitting the experimental da...

Neutron cross section covariance library has been under development by BNL-LANL collaborative effort over the last three years. The primary purpose of the library is to provide covariances for the Advanced Fuel Cycle Initiative (AFCI) data adjustment project, which is focusing on the needs of fast advanced burner reactors. The covariances refer to...

The NJOY Nuclear Data Processing System is widely used to convert evaluations in the Evaluated Nuclear Data Files (ENDF) format into forms useful for practical applications such as fission and fusion reactor analysis, stockpile stewardship calculations, criticality safety, radiation shielding, nuclear waste management, nuclear medicine procedures,...

We describe a new cumulated fission product yield (FPY) evaluation for fission spectrum neutrons on plutonium that updates the ENDF/B-VI evaluation by England and Rider, for the forthcoming ENDF/B-VII.1 database release.11We intend to release the ENDF/B-VII.1 database in December 2011, and all released data are subject to CSEWG approval. It is poss...

Uncertainties associated with the prompt fission neutron spectrum (PFNS) of n(0.5 MeV)+$^{239}$Pu evaluated for the ENDF/B-VII.0 library are estimated using known experimental information and model parameter uncertainties in the framework of the Madland-Nix model. The model parameters used for the ENDF/B-VII.0 evaluation are also used in the presen...

Following the release of ENDF/B-VH.O evaluations, an ACE-formatted continuous-energy neutron data library called ENDF70 for MCNP has been produced at Los Alamos National Laboratory. This new library contains data for 387 isotopes and three elements at five temperatures: 293.6, 600, 900, 1200, and 2500 K. It can be obtained as part of the MCNP5 1.50...

Improved neutron cross section covariances were produced for 110 materials including 12 light nuclei (coolants and moderators), 78 structural materials and fission products, and 20 actinides. Improved covariances were organized into AFCI-1.2 covariance library in 33-energy groups, from 10{sup -5} eV to 19.6 MeV. BNL contributed improved covariance...

With the growing demand for multigroup covariances, the National Nuclear Data Center (NNDC) has been experiencing an upsurge in its covariance data processing activities using the two US codes NJOY-99 (LANL) and PUFF-IV (ORNL). The code NJOY-99 was upgraded by incorporating the new module ERRORJ-2.3, while the NNDC served as the active user and pro...

Continuous energy Monte Carlo eigenvalue calculations have been performed for several hundred critical benchmarks described in the International Handbook of Evaluated Criticality Safety Benchmark Experiments. These calculations were performed with MCNP5 using either ENDF/B-VI.8 or ENDF/B-VII.0 cross sections. ENDF/B-VII cross section data files yie...

Up to date publication reference details: http://orcid.org/0000-0002-2201-6703. We describe the next generation general purpose Evaluated Nuclear Data File, ENDF/B-VII.0, of recommended nuclear data for advanced nuclear science and technology applications. The library, released by the U.S. Cross Section Evaluation Working Group (CSEWG) in December...

WPEC Subgroup 22 was established to investigate a systematic reactivity under-prediction of thermal light water reactors fuelled with low-enriched uranium. The keff discrepancy (~ -500 pcm) was demonstrated with accurate Monte Carlo transport codes and the most recent nuclear data libraries (ENDF/B-VI.8, JENDL-3.3 and JEFF-3.0) available at that ti...

Continuous-energy Monte Carlo eigenvalue calculations have been performed for a selection of HEU-MET-FAST, IEU-MET-FAST, HEU-SOL-THERM, LEU-COMP-THERM, and LEU-SOL-THERM benchmarks using ENDF/B (primarily VI.8), JEFF-3.0, and JENDL-3.3 cross sections. These benchmarks allow for testing the cross-section data for both common reactor nuclides such as...

This report was issued by a WPEC Subgroup investigating a problem with the early releases of the ENDF/B-VI evaluated neutron cross-sections for 235U (6.0, 6.1 and 6.2). Despite the high quality of the fits to a variety of accurate differential data, thermal benchmarks and other soft-spectrum critical facilities were not well calculated. It appeared...

The revised ENDF/B-VI data set is discussed. The low capture resonance integral is primarily responsible for the large eigenvalue trend with epithermal fission rate, and a modification of the uranium 235 evaluation will yield a significantly improved evaluated data set.

Several clean critical experiments were analyzed with ENDF/B-VI data to assess the adequacy of the data for U{sup 235}, U{sup 238} and oxygen. These experiments were (1) a set of homogeneous U{sup 235}-H{sub 2}O assemblies spanning a wide range of hydrogen/uranium ratio, and (2) TRX-1, a simple, H{sub 2}O-moderated Bettis lattice of slightly-enrich...

High spin states of 189Tl have been populated through the fusion-evaporation reactions 169[24Mg(125 MeV),4n], 165[28Si(140 MeV),4n], and 175[20Ne(128 MeV),6n] and its subsequent decay studied by in-beam γ-ray spectroscopy techniques. Among the firmly established features there are two band structures resulting from the coupling of the h(9/2 and i(1...

The light water breeder reactor (LWBR) was developed by the Bettis Atomic Power Laboratory under the technical direction of the Office of Naval Reactors, U.S. Department of Energy. The LWBR operated successfully in the Shippingport Atomic Power Station from 1977 to 1982, producing more than 29,000 equivalent full-power hours. Because of the small b...

The first three moments of the ..gamma..-ray multiplicity distribution were measured for individual ..cap alpha..xn exit channels of the reactions 85-MeV /sup 12/C+ /sup 154/Sm, 109-MeV /sup 12/C+ /sup 154/Sm, and 115-MeV /sup 14/N+ /sup 159/Tb, in which massive transfer had been studied previously. The average ..gamma.. multiplicity (first moment)...

With the use of a helium gas-jet transport system the isotopes 145Tb and 144Tb were identified in a series of 10B+144Sm irradiations. Nuclidic assignments were based on yields as a function of bombarding energy, gamma-ray coincidences with gadolinium K x rays, and comparisons with data from in-beam gamma-ray studies. Thirteen transitions were obser...

High-spin states in Er164 have been studied by using the Nd150(O18,4n) and Dy164(±,4n) reactions and by multiple Coulomb excitation with Xe136 ions. Several positive-parity bands are excited, and two negative-parity bands have been identified. The previously reported backbending behavior of the yrast sequence is demonstrated to result from the inte...

Fast, forward-peaked protons, deuterons, and tritons observed in the reactions of 135-and 165-MeV 14N ions with 152,154Sm and 166-MeV 19F ions with 148Nd are shown to originate in massive-transfer reactions. These reactions are also demonstrated to have merit as probes of angular momentum space in nuclei at very high spin.

Particle-γ coincidence experiments have been performed to study heavy-ion-induced reactions at 6-9 MeV/nucleon which lead to fast α particles. Experimental evidence is presented that the α particles are emitted in a new class of reaction called "massive transfer" which involves fusion of the remaining projectile mass. Such reactions are shown to oc...

We report the first experimental evidence for Coulomb-nuclear interference in the excitation of high-spin states by very heavy projectiles. The data are intepreted with use of a model described previously, and the feasibility of using this method to study the deformed nuclear surface is demonstrated.

Members of the ground-state band of 150Nd to spin 8+ have been Coulomb excited with 149-MeV 40Ar ions, and the lifetimes of these states have been measured by the Doppler-shift recoil distance method. The half-lives of the 2+, 4+, 6+, and 8+ states are 1.44+/-0.07 ns, 63.0+/-3.2 ps, 12.4+/-1.1 ps, and 4.0+/-0.4 ps, respectively. The observed enhanc...

Members of the ground-state band of /sup 150/Nd to spin 8/sup +/ have been Coulomb excited with 149-MeV /sup 40/Ar ions, and the lifetimes of these states have been measured by the Doppler-shift recoil distance method. The half-lives of the 2/sup +/, 4/sup +/, 6/sup +/, and 8/sup +/ states are 1.44 +- 0.07 ns, 63.0 +- 3.2 ps, 12.4 +- 1.1 ps, and 4....

High-spin states in 185Au have been populated via the 169Tm(20Ne, 4ngamma) and 175Lu(16O, 6ngamma) reactions. We observe two aligned bands built on rapidly downsloping h9/2 and i13/2 proton orbitals. This permits one to examine for the first time the role of these and other orbitals in backbending, free from deformation effects. The i13/2 band is o...

High-spin states in 164Er have been studied by using the 150Nd(18O,4nγ) and 164Dy(α,4nγ) reactions and by multiple Coulomb excitation with 136Xe ions. Several positive-parity bands are excited, and two negative-parity bands have been identified. The previously reported backbending behavior of the yrast sequence is demonstrated to result from the in...

We review MCNP eigenvalue calculations from a suite of International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook evaluations with the recently distributed ENDF/B-VII.1 cross section library.

We discuss how to use critical benchmarks from the International Handbook of Evaluated Criticality Safety Benchmark Experiments to determine the applicability of specific cross sections to the end-user's problem of interest. Particular attention is paid to making sure the selected suite of benchmarks includes the user's range of applicability (ROA)...

The light water breeder reactor (LWBR), a pressurized water reactor fueled with ²³³UOâ and ²³²ThOâ in Zircaloy-clad fuel rods, was designed and built by the Bettis Atomic Power Laboratory (BAPL) under the technical direction of the US Dept. of Energy's Office of Naval Reactors. The LWBR objective was to demonstrate that breeders can be operat...

Members of the ground-state band of ¹⁵°Nd to spin 8/sup +/ have been Coulomb excited with 149-MeV ⁴°Ar ions, and the lifetimes of these states have been measured by the Doppler-shift recoil distance method. The half-lives of the 2/sup +/, 4/sup +/, 6/sup +/, and 8/sup +/ states are 1.44 +- 0.07 ns, 63.0 +- 3.2 ps, 12.4 +- 1.1 ps, and 4.0 +-...

This paper summarizes some early data testing of ENDF/B-VI by members of the Cross Section Evaluation Working Group (CSEWG) Thermal Reactor Data Testing Subcommittee. Projections of ENDF/B-VI performance in thermal benchmark calculations are beginning to be available; and in some cases the calculations were performed with only a portion of the cros...

Proof of self-sustaining breeding in the light water breeder reactor (LWBR) would mean that this proven pressurized water reactor (PWR) could provide our nation with an energy option from plentiful thorium about 50 times larger than that provided by current commercial reactions. Assay measurements to date of expended fuel elements from the LWBR ind...

A production-irradiated fuel assay gauge (PIFAG) has been developed with the capability of determine, nondestructively, the total fissile fuel content (loading) of an irradiated fuel rod with a precision of 0.5% or better. This gauge was developed by the Bettis Atomic Power Laboratory under the technical direction of the US Department of Energy's O...

In this work we report the methodology and the results of an evaluation carried out for 48Ti in the resolved resonance region for applications in criticality safety calculations. The evaluation was performed using the computer code SAMMY with the reduced R-matrix Reich-Moore formalism. The Bayes scheme was utilized for fitting the experimental data...

The cross section covariance library has been under development by BNL-LANL collaborative effort over the last three years. The project builds on two covariance libraries developed earlier, with considerable input from BNL and LANL. In 2006, international effort under WPEC Subgroup 26 produced BOLNA covariance library by putting together data, ofte...

A gauge has been designed and constructed to measure, nondestructively, the fissile content of spent fuel rods from the Light Water Breeder Reactor (LWBR) Core. This gauge, called the Production Irradiated Fuel Assay Gauge (PIFAG) uses the method of active neutron interrogation and delayed neutron detection. A set of calibration rods fabricated wit...

With the use of a helium gas-jet transport system the isotopes ¹⁴⁵Tb and ¹⁴⁴Tb were identified in a series of ¹°B+¹⁴⁴Sm irradiations. Nuclidic assignments were based on yields as a function of bombarding energy, ..gamma..-ray coincidences with gadolinium K x rays and comparisons with data from in-beam ..gamma..-ray studies. Thirtee...