Monte Carlo Source Convergence and the Whitesides Problem

Conference · Thu May 11 04:00:00 EDT 2000

OSTI ID:752868

Blomquist, Roger N. ^[1]

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1. Argonne National Lab. (ANL), Argonne, IL (United States)

The issue of fission source convergence in Monte Carlo eigenvalue calculations is of interest because of the potential consequences of erroneous criticality safety calculations. In this work, the authors compare two different techniques to improve the source convergence behavior of standard Monte Carlo calculations applied to challenging source convergence problems. The first method, super-history powering, attempts to avoid discarding important fission sites between generations by delaying stochastic sampling of the fission site bank until after several generations of multiplication. The second method, stratified sampling of the fission site bank, explicitly keeps the important sites even if conventional sampling would have eliminated them. The test problems are variants of Whitesides' "Criticality of the World" problem, in which the fission site phase space was intentionally undersampled in order to induce marginally intolerable variability in local fission site populations. Three variants of the problem were studied, each with a different degree of coupling between fissionable pieces. Both the superhistory powering method and the stratified sampling method were shown to improve convergence behavior, although stratified sampling is more robust for the extreme case of no coupling. Neither algorithm completely eliminates the loss of the most important fissionable piece, and if coupling is absent, the lost piece cannot be recovered unless its sites from earlier generations have been retained. Finally, criteria for measuring source convergence reliability are proposed and applied to the test problems.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP); USDOE Office of Environmental Management (EM)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 752868
• Report Number(s): ANL/RA/CP-100164
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
97 MATHEMATICS AND COMPUTING
CONVERGENCE
CRITICALITY
Criticality of the World Problem
EIGENVALUES
Eigenvalue
FISSION
Fission Site Algorithm
MONK
MONTE CARLO METHOD
Nuclear Criticality Safety Program (NCSP)
RADIATION SOURCES
SAFETY ANALYSIS
Stratified Sampling Method
Superhistory Powering Method
VIM-A
WIMS Library