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Title: Plutonium Critical Mass Curve Comparison to Mass at Upper Subcritical Limit (USL) Using Whisper

Abstract

Whisper is computational software designed to assist the nuclear criticality safety analyst with validation studies with the MCNP ® Monte Carlo radiation transport package. Standard approaches to validation rely on the selection of benchmarks based upon expert judgment. Whisper uses sensitivity/uncertainty (S/U) methods to select relevant benchmarks to a particular application or set of applications being analyzed. Using these benchmarks, Whisper computes a calculational margin. Whisper attempts to quantify the margin of subcriticality (MOS) from errors in software and uncertainties in nuclear data. The combination of the Whisper-derived calculational margin and MOS comprise the baseline upper subcritical limit (USL), to which an additional margin may be applied by the nuclear criticality safety analyst as appropriate to ensure subcriticality. A series of critical mass curves for plutonium, similar to those found in Figure 31 of LA-10860-MS, have been generated using MCNP6.1.1 and the iterative parameter study software, WORM_Solver. The baseline USL for each of the data points of the curves was then computed using Whisper 1.1. The USL was then used to determine the equivalent mass for plutonium metal-water system. ANSI/ANS-8.1 states that it is acceptable to use handbook data, such as the data directly from the LA-10860-MS, as it ismore » already considered validated (Section 4.3 4) “Use of subcritical limit data provided in ANSI/ANS standards or accepted reference publications does not require further validation.”). This paper attempts to take a novel approach to visualize traditional critical mass curves and allows comparison with the amount of mass for which the k eff is equal to the USL (calculational margin + margin of subcriticality). However, the intent is to plot the critical mass data along with USL, not to suggest that already accepted handbook data should have new and more rigorous requirements for validation.« less

Authors:
 [1];  [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Monte Carlo Codes
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Nuclear Criticality Safety Division
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1329543
Report Number(s):
LA-UR-16-27371
TRN: US1700382
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 42 ENGINEERING; 97 MATHEMATICS AND COMPUTING; PLUTONIUM; CRITICAL MASS; DIAGRAMS; VALIDATION; COMPARATIVE EVALUATIONS; CRITICALITY; W CODES; M CODES; DATA VISUALIZATION; BENCHMARKS; MONTE CARLO METHOD; ITERATIVE METHODS; SAFETY; STANDARDS; WATER; RADIATION TRANSPORT; DATA COVARIANCES; SENSITIVITY ANALYSIS

Citation Formats

Alwin, Jennifer Louise, and Zhang, Ning. Plutonium Critical Mass Curve Comparison to Mass at Upper Subcritical Limit (USL) Using Whisper. United States: N. p., 2016. Web. doi:10.2172/1329543.
Alwin, Jennifer Louise, & Zhang, Ning. Plutonium Critical Mass Curve Comparison to Mass at Upper Subcritical Limit (USL) Using Whisper. United States. doi:10.2172/1329543.
Alwin, Jennifer Louise, and Zhang, Ning. 2016. "Plutonium Critical Mass Curve Comparison to Mass at Upper Subcritical Limit (USL) Using Whisper". United States. doi:10.2172/1329543. https://www.osti.gov/servlets/purl/1329543.
@article{osti_1329543,
title = {Plutonium Critical Mass Curve Comparison to Mass at Upper Subcritical Limit (USL) Using Whisper},
author = {Alwin, Jennifer Louise and Zhang, Ning},
abstractNote = {Whisper is computational software designed to assist the nuclear criticality safety analyst with validation studies with the MCNP® Monte Carlo radiation transport package. Standard approaches to validation rely on the selection of benchmarks based upon expert judgment. Whisper uses sensitivity/uncertainty (S/U) methods to select relevant benchmarks to a particular application or set of applications being analyzed. Using these benchmarks, Whisper computes a calculational margin. Whisper attempts to quantify the margin of subcriticality (MOS) from errors in software and uncertainties in nuclear data. The combination of the Whisper-derived calculational margin and MOS comprise the baseline upper subcritical limit (USL), to which an additional margin may be applied by the nuclear criticality safety analyst as appropriate to ensure subcriticality. A series of critical mass curves for plutonium, similar to those found in Figure 31 of LA-10860-MS, have been generated using MCNP6.1.1 and the iterative parameter study software, WORM_Solver. The baseline USL for each of the data points of the curves was then computed using Whisper 1.1. The USL was then used to determine the equivalent mass for plutonium metal-water system. ANSI/ANS-8.1 states that it is acceptable to use handbook data, such as the data directly from the LA-10860-MS, as it is already considered validated (Section 4.3 4) “Use of subcritical limit data provided in ANSI/ANS standards or accepted reference publications does not require further validation.”). This paper attempts to take a novel approach to visualize traditional critical mass curves and allows comparison with the amount of mass for which the keff is equal to the USL (calculational margin + margin of subcriticality). However, the intent is to plot the critical mass data along with USL, not to suggest that already accepted handbook data should have new and more rigorous requirements for validation.},
doi = {10.2172/1329543},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 9
}

Technical Report:

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  • An intensive program of critical and subcritical experiments and associated calculations was conducted on highly enriched, hydrogen-moderated systems. Interest was centered on overall effects such as reactivity, prompt neutron decay constants, and region-wide spectra, and experiments were performed as a function of fuel density, core size, metal to water ratio, and temperature. The effects of theoretical improvements on the agreement between calculations and experiments were studied. The experiments were carried out in the Solid Homogeneous Assembly, Pressurized Test Reactor, pulsed subcritical systems, and a series of subcritical lattices having a volume of 1 cubic foot. The results showed a consistentmore » discrepancy between calculation and experiment in the clean critical experiments, with the calculated reproduction constants being 1 to 3% high. Good agreement was obtained between calculated and measured low-energy spectra in weakly absorbing media but not in highly absorbing media. No consistert discrepancy was observed in the pulsed measurements, but the accuracy was poor. (D.L.C.)« less
  • The range-energy relation for 0.2 to 3.0 Mev tritons moving through helium was obtained experimentally and was used to evaluate the mass of the neutrino in the interaction mu /sup -/ + He/sup 3/ -- H/sup 3/ + v as 6 Mev/c/ sup 2/. (D.C.W.)
  • Training classes for nuclear criticality safety, MCNP documentation. The need for, and problems surrounding, validation of computer codes and data area considered first. Then some background for MCNP & Whisper is given--best practices for Monte Carlo criticality calculations, neutron spectra, S(α,β) thermal neutron scattering data, nuclear data sensitivities, covariance data, and correlation coefficients. Whisper is computational software designed to assist the nuclear criticality safety analyst with validation studies with the Monte Carlo radiation transport package MCNP. Whisper's methodology (benchmark selection – C k's, weights; extreme value theory – bias, bias uncertainty; MOS for nuclear data uncertainty – GLLS) and usagemore » are discussed.« less
  • An upper limit of less than 4 mg TNT equivalent fission energy release from the HOLOG experiment was determined using a germanium {gamma}-ray detector to measure the ratio of selected fission-product and plutonium {gamma} rays. Only three hours of {gamma}-ray data collected immediately after the zero-time were analyzed to calculate the above limit. We found no peaks corresponding to the {sup 97} Zr - {sup 97} Nb fission product pair at the gamma-ray energies of E{sub {gamma}} = 743 keV and E{sub {gamma}} = 658 keV, respectively. No information on the plutonium isotopic ratios is revealed because {gamma}-ray peaks inmore » the energy region below 100 keV are not observed due to the high absorption in the containment barrier. The measurement is relatively easy to perform and is not subject to false-positive results because specific fission product and plutonium {gamma} ray energies need to be detected.« less