Electric Generation Expansion Analysis System a progress report on RPI 1529

Abstract

The long and short term behavior of light water reactor stainless steel clad fuel has been investigated in order to establish more adequate or applicable operation/design criteria. The performance record of stainless steel clad fuel used in both the Connecticut Yankee and San Onofre 1 power stations has remained essentially unmarred until the recent past. While the San Onofre 1 plant has maintained this record, the Connecticut Yankee station has experienced a number of fuel element failures since 1977. Consequently, emphasis has been placed on cladding behavior for anomalous operation experienced by the Connecticut Yankee reactor prior to its first observed coolant activity increase.

In order to predict cladding behavior, a fuel performance code (STRESS) has been developed with the capabilities of analyzing long term cladding creepdown behavior, cladding conditioning, and behavior during up-power ramping and power maneuvers. The effects of varied fill gas pressure and cladding creep rate on the stress/deformation behavior of stainless steel cladding for these performance areas have been investigated. Similar calculations are also performed for Zircaloy clad fuel so that a comparison can be made between these materials. Code limitations are discussed and some methods which compensate for insufficient modeling are reviewed.

Fuel element design and reactor operation recommendations are made for Connecticut Yankee (and San Onofre 1) stainless steel clad fuel. These include fill gas pressurization level, up-power ramp rate limitations, and possible cladding material preference. These recommendations are based on the results of the STRESS code and the trends which may be inferred from them.