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

Technical Report · Tue Sep 27 04:00:00 EDT 2016

DOI:https://doi.org/10.2172/1329543· OSTI ID:1329543

Alwin, Jennifer Louise ^[1]; Zhang, Ning ^[2]

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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

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 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.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1329543
• Report Number(s): LA-UR--16-27371
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
42 ENGINEERING
97 MATHEMATICS AND COMPUTING
BENCHMARKS
COMPARATIVE EVALUATIONS
CRITICAL MASS
CRITICALITY
DATA COVARIANCES
DATA VISUALIZATION
DIAGRAMS
ITERATIVE METHODS
M CODES
MONTE CARLO METHOD
PLUTONIUM
RADIATION TRANSPORT
SAFETY
SENSITIVITY ANALYSIS
STANDARDS
VALIDATION
W CODES
WATER