Evaluation of breach characteristics of fast reactor fuel pins during steady state irradiation

Oka, Hiroshi   ; Ikusawa, Yoshihisa   ; Otsuka, Satoshi   ; Kaito, Takeji 

In the fast reactor fuel pin design analysis, the cumulative damage fraction (CDF) is applied to predict the fuel pin breach. The objective of this study is to evaluate the reliability of CDF analysis for the prediction of the fuel pin breach. For this objective, the relationship between the CDF analysis and actual occurrence of the fuel pin breach during steady state irradiation was investigated. Six in-reactor fuel pin breaches (20% cold worked D9 steel) have been obtained in the run-to-cladding-breach testing program that was performed in EBR-II. The CDF of each breached pin was calculated by using the in-reactor creep rupture data of D9 steel, the irradiation history of cladding temperature, and gas pressure induced hoop stress. The evaluated CDFs of the breached fuel pins were in the range of 0.7 to 1.4 at the occurrence of the breach. This confirms that the fuel pin breach occurs when the CDF approaches "1".