Shedding light on the 239Pu fission source term with new high-precision experiments and advanced fission modeling

Neudecker, Denise; Lovell, A. E.; Kelly, K. J.; Marini, P.; Snyder, L.; White, Morgan Curtis; Talou, P.; Devlin, M.; Taïeb, J.; Chadwick, M.B.

doi:10.3389/fphy.2022.1056324

Cited by 6 publications

(4 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A final, and more detailed, documentation of the combined evaluation work on νp , PFNS, and (n,f) cross sections is published in Ref. [17]. This demonstration that CGMF can produce evaluation quality νp consistent with reasonable Y(A), and average total kinetic energy is an important step towards evaluating fission quantities consistently with each other.…”

Section: Summary Conclusion and Outlookmentioning

confidence: 98%

Producing Evaluation-quality ²³⁹Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

2023

Self Cite

View full text Add to dashboard Cite

An evaluation of the average prompt fission neutron multiplicity, ν¯ p, of 239Pu(n,f) is shown. This evaluation includes (a) the correlated fission model CGMF, and (b) a detailed analysis of past and recently published experimental data. Using CGMF-calculated ν¯ pas prior enables to link, through the use of evaluated model input parameters, ν¯ p to other fission observables such as the prompt fission neutron spectrum (PFNS), pre-neutron emission fission yields as a function of mass, and the average total kinetic energy of the fragments. These evaluated parameters produce realistic predictions of many fission observables, while the evaluated ν¯ p agrees well (χ2 ≈ 1) with data. Moreover, with the new evaluated ν¯ p, the effective neutron multiplication factor of fast Pu ICSBEP critical assemblies are predicted with a mean bias of 58 pcm compared to 18 pcm with ENDF/B-VIII.0, when paired with a new 239Pu PFNS and fission cross section. Due to these encouraging validation results, the evaluated ν¯ p is currently part of a release candidate for the 239Pu ENDF/B-VIII.1 file. Hence, a correlated fission model was used for the first time for evaluating ν¯ p that is of evaluation quality. This is an important step towards consistent evaluations of prompt fission observables.

show abstract

Section: Summary Conclusion and Outlookmentioning

confidence: 98%

Producing Evaluation-quality ²³⁹Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

2023

Self Cite

View full text Add to dashboard Cite

show abstract

“…The rest of the present paper is devoted to describing the PFNS research during that period, as well as during the first post-war decade, in a bit more detail. Companion papers in this special issue provide a summary of recent Los Alamos PFNS work in experiment [6] and in modeling and ENDF evaluation [7].…”

Section: Figurementioning

confidence: 99%

Manhattan Project 1940s research on the prompt fission neutron spectrum

Chadwick

Capote²

2023

Front. Phys.

View full text Add to dashboard Cite

We describe how the prompt fission neutron spectrum (PFNS) was determined for the Manhattan Project at Los Alamos. Early work before World War II at American and British universities is described, together with theoretical work by Feather at Cambridge and Bethe at Los Alamos. As the Manhattan Project was being planned in 1942, two experiments on natural uranium were commissioned that proved to be influential: 1) An integral experiment at Chicago by Christy and Manley that accurately determined the average PFNS spectrum energy, 2.2 ± 0.2 MeV; 2) Bloch and Staub’s Stanford cyclotron measurement of the PFNS spectrum, which obtained an average energy of 1.70 ± 0.34 MeV. These two papers, previously unavailable outside of Los Alamos, are reproduced in the Supplementary Appendix. From these data, at the beginning of the project in 1943 Serber estimated an average 235U PFNS energy of 2 MeV, and indeed this agrees with today’s best estimate. The challenges facing the scientists involved both the availability of only very small samples of enriched uranium and plutonium targets, and fast neutron detection technologies. During the project, 235U and 239Pu PFNS were measured by Nicodemus and Staub. These also proved to be quite accurate and gave an average spectrum energy of 2 MeV for 235U. [This is not reproduced in the Appendix because it was published after the war in Physical Review 89, 1288 (1953)]. New methods were developed to enable more accurate measurements, and this paper describes how the PFNS was determined surprisingly well by 1945. We end by describing the post-war measurements in the 50s, including the PFNS data used by Ford and Wheeler in their simulations in 1951, the Bonner 1952 data, the seminal 1952 Watt paper with a new empirical parametrization of the PFNS, and the accurate PFNS measurement undertaken at Los Alamos by Cranberg et al. in 1956. We compare the measurements with our best understanding today as embodied in the Evaluated Nuclear Data File ENDF/B-VIII.0. Some images from historical documents in our Los Alamos National Security Research Center (NSRC) archives are shown.

show abstract

“…In step four, one could exclude those observables related to bias where changes in the nuclear data within differential experimental data do not significantly impact the simulation of C. However, it is a well-known fact that small changes in the nuclear data of the observables in the top of Fig. 3, let alone changes within the spread of existing experimental data, significantly impact the simulation of k eff [23]. Hence, all seven 239 Pu observables in the top of Fig.…”

Section: The 239 Pu Examplementioning

confidence: 99%

Uncovering Where Compensating Errors Could Hide in ENDF/B-VIII.0

et al. 2023

View full text Add to dashboard Cite

Unconstrained physics spaces between two or more nuclear data observables in a library occur when their values can be simultaneously adjusted without violating the uncertainties in either differential information or simulations of relevant integral experiments. Differential data are often too imprecise to fully bound all nuclear data observables of interest for application simulations. Integral data are simulated with combinations of nuclear data so that an error in one observable may be hidden by a counterbalancing error in another. In this manner compensating errors may lurk within nuclear data libraries and these errors have the potential to undermine the predictive power of neutron transport simulations, particularly in situations where there is no conclusive validation experiment that resembles the application of interest. The EUCLID project (Experiments Underpinned by Computational Learning for Improvements in Nuclear Data) developed a preliminary workflow to identify these unconstrained physics spaces by bringing together results from a large collection of integral experiments with their simulated counter-parts as well as differential information that have a one-to-one correspondence to nuclear data. This wealth of information is processed by machine learning tools for subsequent refinement by human experts. Here, we show how the EUCLID work-flow is executed by applying it first to 239Pu and then to 9Be nuclear data in ENDF/B-VIII.0.

show abstract

Shedding light on the 239Pu fission source term with new high-precision experiments and advanced fission modeling

Cited by 6 publications

References 63 publications

Producing Evaluation-quality ²³⁹Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

Producing Evaluation-quality ²³⁹Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

Manhattan Project 1940s research on the prompt fission neutron spectrum

Uncovering Where Compensating Errors Could Hide in ENDF/B-VIII.0

Contact Info

Product

Resources

About

Shedding light on the 239Pu fission source term with new high-precision experiments and advanced fission modeling

Cited by 6 publications

References 63 publications

Producing Evaluation-quality 239Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

Producing Evaluation-quality 239Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

Manhattan Project 1940s research on the prompt fission neutron spectrum

Uncovering Where Compensating Errors Could Hide in ENDF/B-VIII.0

Contact Info

Product

Resources

About

Producing Evaluation-quality ²³⁹Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model

Producing Evaluation-quality ²³⁹Pu Average Prompt Fission Neutron Multiplicities using a Correlated Fission Model