Subcritical measurements for a HEU storage vault at the Y-12 Plant using the {sup 252}Cf-source-driven frequency-analysis method
- Oak Ridge National Lab., TN (United States). Instrumentation and Controls Div.
The tube vaults at the Oak Ridge Y-12 Plant were constructed in 1975 out of massive amounts of concrete to safely store large quantities of highly enriched uranium (HEU) metal. At the time of construction, criticality safety specialists were concerned about the concrete drying out over time. The difference between dry and wet concrete is the absence of unbound water, which results in a change in the hydrogen content of the concrete by a factor of 2. For this system, dry concrete increases the neutron interaction between the uranium metal castings in the array. With the development of the {sup 252}Cf-source-driven frequency-analysis method for the determination of subcriticality, it became feasible to perform a more sensitive, meaningful, and relevant subcriticality measurement of this vault configuration with HEU. For this vault loading, the average mass of the castings was 18.75 kg of uranium, and the {sup 235}U enrichment was 93.2 wt %. These measurements are interpreted with a general Monte Carlo model rather than limited-point kinetics models that were used in previous measurements. This measurement and analysis shows how the {sup 252}Cf-source-driven frequency-analysis method with MCNP-DSP can be used to obtain the subcritical neutron multiplication factor and the bias in calculational methods for criticality safety for an in-plant configuration of fissile material. The determination of the neutron multiplication factor from the measured data did not depend on knowing the condition of the vault concrete. The use of a more general Monte Carlo model in place of the limited-point kinetics models extends the application of this method.
- OSTI ID:
- 642363
- Journal Information:
- Nuclear Safety, Journal Name: Nuclear Safety Journal Issue: 1 Vol. 38; ISSN 0029-5604; ISSN NUSAAZ
- Country of Publication:
- United States
- Language:
- English
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