Evaluation of the 239 Pu prompt fission neutron spectrum induced by neutrons of 500 keV and associated covariances

Abstract We present evaluations of the prompt fission neutron spectrum (PFNS) of 239 Pu 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. Therefore, special emphasis is placed here on a thorough uncertainty quantification of experimental data and of the Los Alamos model predicted values entering the evaluation. In addition, the Los Alamos model was extended and an evaluation technique was employed that takes into account the qualitative differences between normalized model predicted values and experimental shape data. These improvements lead to changes in the evaluated PFNS and overall larger evaluated uncertainties than in the previous work. However, these evaluated uncertainties are still smaller than those obtained in a statistical analysis using experimental information only, due to strong model correlations. Hence, suggestions to estimate model defect uncertainties are presented, which lead to more reasonable evaluated uncertainties. The calculated k eff of selected criticality benchmarks obtained with these new evaluations agree with each other within their uncertainties despite the different approaches to estimate model defect uncertainties. The k eff one standard deviations overlap with some of those obtained using ENDF/B-VII.1, albeit their mean values are further away from unity. Spectral indexes for the Jezebel critical assembly calculated with the newly evaluated PFNS agree with the experimental data for selected (n, γ ) and (n,f) reactions, and show improvements for high-energy threshold (n,2n) reactions compared to ENDF/B-VII.1.

[1]  R. Capote,et al.  Random Sampling of Correlated Parameters – a Consistent Solution for Unfavourable Conditions , 2015 .

[2]  J. Terrell.  Fission Neutron Spectra and Nuclear Temperatures , 1959 .

[3]  Patrick Talou,et al.  Prompt Fission Neutron Spectrum Uncertainty Propagation Using Polynomial Chaos Expansion , 2013 .

[4]  Said F. Mughabghab,et al.  Atlas of Neutron Resonances: Resonance Parameters and Thermal Cross Sections. Z=1-100 , 2006 .

[5]  R. Haight,et al.  Preliminary Evaluation and Uncertainty Quantification of the Prompt Fission Neutron Spectrum of 239Pu , 2014 .

[6]  F. D. Becchetti,et al.  NUCLEON--NUCLEUS OPTICAL MODEL PARAMETERS, A > 40, E < 50 MeV. , 1969 .

[7]  T. Ohsawa,et al.  Multimodal analysis of prompt neutron spectra for (sf), (sf), (sf) and (n,f) , 2000 .

[8]  Patrick Talou,et al.  Evaluation and Uncertainty Quantification of Prompt Fission Neutron Spectra of Uranium and Plutonium Isotopes , 2013 .

[9]  J. Fréhaut,et al.  Mesure de {\bar \nu _p} et Ēγ Pour la Fission de 232Th, 235U et 237Np Induite par des Neutrons D’Energie Comprise Entre 1 et 15 MeV , 1983 .

[10]  P. P. Dyachenko,et al.  Energy spectrum measurements of neutrons for energies 30 keV - 4 meV from thermal fission of main fuel elements , 1986 .

[11]  Arjan J. Koning,et al.  Local and global nucleon optical models from 1 keV to 200 MeV , 2003 .

[12]  S. Wender,et al.  Multiple-scattering Corrections to Measurements of the Prompt Fission Neutron Spectrum , 2015 .

[13]  Patrick Talou,et al.  Monte Carlo Hauser-Feshbach predictions of prompt fission γ rays: Application to n th + 235 U, n th + 239 Pu, and 252 Cf (sf) , 2013 .

[14]  D. Madland,et al.  Prompt fission neutron spectra and average prompt neutron multiplicities , 1982 .

[15]  S. Kailas,et al.  RIPL – Reference Input Parameter Library for Calculation of Nuclear Reactions and Nuclear Data Evaluations , 2009 .

[16]  F. Hambsch,et al.  Prompt Fission Neutron Spectrum Evaluation for 252Cf(SF) in the Frame of the Multi-Modal Fission Model. , 2005 .

[17]  Patrick Talou,et al.  Monte Carlo Simulation for Particle and γ-Ray Emissions in Statistical Hauser-Feshbach Model , 2010 .

[18]  F. Hambsch,et al.  Neutron emission in fission , 2007 .

[19]  R. Capote,et al.  Evaluation and use of the prompt fission neutron spectrum and spectra covariance matrices in criticality and shielding , 2009 .

[20]  R. Vogt,et al.  Event-by-event study of prompt neutrons from 239Pu(n,f) , 2009, 0907.5045.

[21]  R.E. MacFarlane,et al.  The NJOY Nu-clear Data Processing System Version 91 , 1994 .

[22]  Boris Pritychenko,et al.  The CIELO Collaboration: Neutron Reactions on 1H, 16O, 56Fe, 235,238U, and 239Pu , 2014 .

[23]  D. V. Nikolaev,et al.  Basic results of investigations of scission neutrons in nuclear fission at low excitation energies , 2008 .

[24]  N. M. Larson,et al.  ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields and Decay Data , 2011 .

[25]  R. Haight,et al.  Measurement of prompt neutron spectra from the 239 Pu(n,f) fission reaction for incident neutron energies from 1 to 200 MeV , 2014 .

[26]  R. Mcknight,et al.  Note on the prompt-fission-neutron spectra of uranium-233 and -235 and plutonium-239 and -240 relative to that of californium-252 , 1980 .

[27]  Naohiko Otuka,et al.  Experimental Nuclear Reaction Data Uncertainties: Basic Concepts and Documentation , 2012 .

[28]  O. Serot,et al.  Investigation of phenomenological models for the Monte Carlo simulation of the prompt fission neutron and γ emission , 2010 .

[29]  R. Capote,et al.  Current Issues in Nuclear Data Evaluation Methodology: 235U Prompt Fission Neutron Spectra and Multiplicity for Thermal Neutrons , 2015 .

[30]  R. Capote,et al.  Impact of the Normalization Condition and Model Information on Evaluated Prompt Fission Neutron Spectra and Associated Uncertainties , 2015 .

[32]  R. A. Forster,et al.  Initial MCNP6 Release Overview - MCNP6 version 1.0 , 2013 .

[33]  Gunter H. R. Kegel,et al.  Prompt fission neutron energy spectra induced by fast neutrons , 1995 .

[34]  R. Macfarlane,et al.  The NJOY Nuclear Data Processing System , 2008 .

[35]  R. Little,et al.  Uncertainty Quantification of Prompt Fission Neutron Spectrum for n(0.5 MeV) + 239Pu , 2010 .

[36]  Total prompt energy release in the neutron-induced fission of 235 U, 238 U, and 239 Pu , 2006, nucl-th/0603071.

[37]  Tadashi Yoshida,et al.  Simultaneous Evaluation of Fission Cross Sections of Uranium and Plutonium Isotopes for JENDL-3.3 , 2000 .

[38]  B. Kiedrowski.  MCNP6.1 k-Eigenvalue Sensitivity Capability: A User’s Guide , 2013 .

[39]  Cyriel Wagemans,et al.  The Nuclear Fission Process , 1991 .