Preliminary Flattop-25 Reevaluation Results

Journal Article · Wed Jun 15 04:00:00 EDT 2016 · Transactions of the American Nuclear Society

OSTI ID:22991947

Favorite, Jeffrey A. ^[1]

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1. XCP-3, MS F663, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

This paper is a preliminary status report on a reevaluation of the Flattop-25 criticality benchmark that is under way. Flattop-25 consists of a nearly spherical oralloy (Oy) core reflected by a nearly spherical tuballoy (Tu) or natural uranium reflector. In the International Criticality Safety Benchmark Evaluation Project (ICSBEP), the Flattop-25 benchmark is HEU-METFAST- 028 Rev. 1. A simplified one-dimensional spherical version of Flattop-25 was given in LA-4208 in 1969. The handbook evaluation presented the LA- 4208 model with material definitions slightly modified from the Cross Section Evaluation Working Group (CSEWG) benchmark. The reevaluation will include a detailed three-dimensional model of a specific Flattop-25 configuration. The k{sub eff} calculated using MCNP6 for the preliminary Flattop-25 detailed three-dimensional benchmark model is 0.00632 larger than the measured k{sub eff}. The preliminary uncertainty is ±0.00157, and the uncertainty in the uncertainty is estimated to be +100%/-0%. The largest driver of the k{sub eff} uncertainty and its uncertainty is the uncertain mass and density of the Tu reflector parts. Validating the geometry and mass of the Tu reflector parts is work for the near future. The benchmark model uranium part masses are generally going to be smaller than those in the preliminary model, but we do not yet know how much smaller. (author)

• OSTI ID: 22991947
• Journal Information: Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Journal Issue: 1 Vol. 114; ISSN 0003-018X
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
CRITICALITY
CROSS SECTIONS
DENSITY
NATURAL URANIUM
SAFETY
SPHERICAL CONFIGURATION
THREE-DIMENSIONAL LATTICES