Criticality Calculations for Step-2 GPHS Modules

Journal Article · Mon Jan 21 04:00:00 EST 2008 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2845002· OSTI ID:21049473

Lipinski, Ronald J ^[1]; Hensen, Danielle L ^[2]

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1. Advanced Nuclear Concepts Department, Sandia National Laboratories, P.O Box 5800, Albuquerque, NM 87185 (United States)
2. Risk and Reliability Department Sandia National Laboratories, P.O Box 5800, Albuquerque, NM 87185 (United States)

The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) will use an improved version of the General Purpose Heat Source (GPHS) module as its source of thermal power. This new version, referred to as the Step-2 GPHS Module, has additional and thicker layers of carbon fiber material (Fine Weaved Pierced Fabric) for increased strength over the original GPHS module. The GPHS uses alpha decay of {sup 238}Pu in the oxide form as the primary source of heat, and small amounts of other actinides are also present in the oxide fuel. Criticality calculations have been performed by previous researchers on the original version of the GPHS module (Step 0). This paper presents criticality calculations for the present Step-2 version. The Monte Carlo N-Particle eXtended code (MCNPX) was used for these calculations. Numerous configurations of GPHS module arrays surrounded by wet sand and other materials (to reflect the neutrons back into the stack with minimal absorption) were modeled. For geometries with eight GPHS modules (from a single MMRTG) surrounded by wet sand, the configuration is extremely sub-critical; k{sub eff} is about 0.3. It requires about 1000 GPHS modules (from 125 MMRTGs) in a close-spaced stack to approach criticality (k{sub eff} = 1.0) when surrounded by wet sand. The effect of beryllium in the MMRTG was found to be relatively small.

• OSTI ID: 21049473
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 969; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ABSORPTION
ACTINIDES
ALPHA DECAY
BERYLLIUM
CARBON FIBERS
CRITICALITY
FISSION
HEAT SOURCES
LAYERS
MONTE CARLO METHOD
NESDPS Office of Nuclear Energy Space and Defense Power Systems
NEUTRONS
OXIDES
PLUTONIUM 238
POWER GENERATION
THERMOELECTRIC GENERATORS