Effect of a detailed radial core expansion reactivity feedback model on ATWS calculations using SASSYS/SAS4A

Conference · Wed Jan 01 04:00:00 EST 1986 · Trans. Am. Nucl. Soc.; (United States)

OSTI ID:6951815

Wigeland, R A

The present emphasis on inherent safety and inherently safe designs for liquid-metal reactors has resulted in a need to represent the various reactivity feedback mechanisms as accurately as possible. In particular, the reactivity feedback from radial core expansion has been found to provide the dominant negative feedback contribution in postulated anticipated transient without scram (ATWS) events. Review of the existing modeling in the SASSYS/SAS4A computer code system revealed that while the modeling may be adequate for the early phases of various unprotected transients, the accuracy would be less than desirable for the extended transients which typically occur for inherently safe designs. The existing model for calculating the reactivity feedback from radial core expansion uses a feedback from radial core expansion uses a feedback coefficient in conjunction with changes in the temperatures of the grid support plate and the above-core load pad. The accuracy of this approach is determined partly by the conditions used in deriving the feedback coefficient, and their relevance to the transient being investigated. Accuracy is also affected by the need to include effects other than those that could be directly related to changes in the grid plate and above-core load pad temperatures, such as subassembly bowing and the potential for clearances to occur between subassemblies in the above-core load pad region. As a result, a detailed model was developed in an attempt to account for these and other effects in a more mechanistic form.

• Research Organization: Argonne National Lab., IL
• OSTI ID: 6951815
• Report Number(s): CONF-861102-
• Conference Information: Journal Name: Trans. Am. Nucl. Soc.; (United States) Journal Volume: 53
• Country of Publication: United States
• Language: English

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