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LA-UR-15-24551 Approved for public release; distribution is unlimited. Title: Introducing Nuclear Data Evaluations of Prompt Fission Neutron Spectra Author(s): Neudecker, Denise Intended for: T-2 (T-Division) Seminar at LANL on 2015-06-23 Issued: 2015-06-17

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Introducing Nuclear Data Evaluations of Prompt Fission Neutron Spectra T-2 Seminar 6/23/2015 D. Neudecker XCP-5, XCP Division, LANL, work performed in T-2 Thanks to: P. Talou, T. Kawano, A.C. Kahler (T-2) M.C. White, M.E. Rising, J.P. Lestone, D. Vaughan (XCP) R.C. Haight, T.N. Taddeucci, H.Y. Lee (P-27) T. Burr (CCS-6), R. Capote (IAEA), D.L. Smith (ANL) U N C L A S S I F I E D Slide 1 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Abstract Nuclear data evaluations provide recommended data sets for nuclear data applications such as reactor physics, stockpile stewardship or nuclear medicine. The evaluated data are often based on information from multiple experimental data sets and nuclear theory using statistical methods. Therefore, they are collaborative efforts of evaluators, theoreticians, experimentalists, benchmark experts, statisticians and application area scientists. In this talk, an introductions is given to the field of nuclear data evaluation at the specific example of a recent evaluation of the outgoing neutron energy spectrum emitted promptly after fission from 239 Pu and induced by neutrons from thermal to 30 MeV. U N C L A S S I F I E D Slide 2 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Evaluation of the 239 Pu Prompt Fission Neutron Spectrum and Covariances  Introduction ➢ What is nuclear data evaluation? ➢ What is a PFNS?  The 239 Pu PFNS evaluation ➢ Experimental information … ➢ Model information …  Summary and Future Activities U N C L A S S I F I E D Slide 3 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Introduction a Reactor t a d r a e Physics l c u n ' s i t a h W ? ' n o i t a u l a v e Stockpile Stewardship ... W h a t i s a p r o m f i p s t s i o n n e u t r o n s p e c t r u m ( P F N S ) ? W h y d o w e n e e d i t ? U N C L A S S I F I E D Slide 4 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Introduction a t a d r a e l c u n ' s i t a h W ? ' n o i t a u l a v e U N C L A S S I F I E D Slide 5 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Nuclear data evaluations provide recommended data for nuclear applications. Reactor Physics Stockpile Stewardship ... U N C L A S S I F I E D Slide 6 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Nuclear data evaluations often contain model and experimental information. P-27, XCP-3, XCP-5 Reactor Physics Stockpile Stewardship T-2, ... T-2, XCP-5, XCP-3 CCS-6 U N C L A S S I F I E D Slide 7 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Nuclear data evaluations combine model predictions and experimental information. Prior (Theoretical) Input Experimental Input Experimental data Model predicted data (PFNS, <TKE>, cross (PFNS, <TKE>, cross sections, etc.) sections, etc.) Statistical Methods Parameter Experimental Uncertainties Evaluated Evaluated covariances data & data & covariances covariances Model Defects U N C L A S S I F I E D Slide 8 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Nuclear data evaluations combine model predictions and experimental information. Prior (Theoretical) Input Experimental Input Experimental data Model predicted data (PFNS, <TKE>, cross (PFNS, <TKE>, cross sections, etc.) sections, etc.) Statistical Methods Parameter Experimental Uncertainties Evaluated Evaluated covariances data & data & covariances covariances Model Defects D. Neudecker, R. Capote, H. Leeb, NIMA 723 , 163 (2013). U N C L A S S I F I E D Slide 9 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Often Generalized Least Squares algorithms are used for the evaluation. Statistical This is a standard statistical algorithm … but it assumes: Methods ? ➢ Experimental data are normally distributed. ➢ Model data are normally distributed. U N C L A S S I F I E D Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Benchmark tests compare computed benchmarks to integral experiments. Reactor Physics Stockpile Stewardship XCP-5, ... T-2, XCP-3 U N C L A S S I F I E D Slide 11 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

The effective multiplication factor of critical assemblies - good benchmark for 239 Pu PFNS. The Jezebel critical assembly consists of two 239 Pu half spheres and is used to study the effective multiplication factor k effective multiplication factor k eff eff : k eff = 1 → critical k eff < 1 → sub-critical k eff > 1 → super-critical The Boltzmann Eqs. simulate this assembly using nuclear data. These simulations help us benchmark nuclear data relative to measured values of k eff . U N C L A S S I F I E D Slide 12 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Introduction What is a prompt fission neutron spectrum (PFNS)? Why do we need it? U N C L A S S I F I E D Slide 13 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

A PFNS gives the energy distrib. of neutrons emitted after scission & before β -decay U N C L A S S I F I E D Slide 14 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

A PFNS covers many orders of magnitudes. Maxw ∝ √ E exp (− E / T ) U N C L A S S I F I E D Slide 15 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

The 239 Pu PFNS Evaluation w e n a y h W 239 Pu PFNS ? n o i t a u l a v e U N C L A S S I F I E D Slide 16 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

A new 239 Pu PFNS evaluation was undertaken due to new exp. & model info. P. Talou et al., Nucl. Science Eng. 166, 254 (2010) provided an evaluation for E inc = 500 keV with covariances, since then: Experiment Model 2014 ➢ Not all physics processes considered for higher E inc in current library. ➢ New parametrizations of important model parameters are available. U N C L A S S I F I E D Slide 17 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Improved 239 Pu PFNS for follow-up of ENDF/B- VII.1, IAEA CRP & CIELO → applications: ➢ Development of innovative nuclear reactors (Generation IV- reactors, small and modular reactors) ➢ Dosimetry ➢ Global Security ➢ Stockpile stewardship ➢ Non-proliferation … Not only mean values but also covariance matrices are needed! U N C L A S S I F I E D Slide 18 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

The 239 Pu PFNS Evaluation: Experimental Data and Uncertainties n i k o o l e w d d i d n a y h a t W a d . p x e n i l i a t e d ? s e i t n i a t r e c n u D o e s a n i m p r o U v Q e d m e a x t p t e . r ? U N C L A S S I F I E D Slide 19 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

The 239 Pu PFNS Evaluation: Experimental Data and Uncertainties n i k o o l e w d d i d n a y h a t W a d . p x e n i l i a t e d ? s e i t n i a t r e c n u U N C L A S S I F I E D Slide 20 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Differential experimental data show discrepancies, which are partly larger than 1 σ error bars! Taken from P. Talou et al. LA-UR-19-00646, published in NSE 166, 254 (2010). U N C L A S S I F I E D Slide 21 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA