Evaluation on rapid heating rupture behavior in heavily irradiated PNC316 fuel claddings

Yoshitake, Tsunemitsu ; Omori, Tsuyoshi; Sakamoto, Naoki ; Ukai, Shigeharu  

The estimation of the life of fuel claddings at thermal transient event is important for evaluating of the fuel claddings validity under the loss of coolant flow (LOF) accident. In order to estimate the life time of the fuel claddings corresponding to any temperature rising condition, the instrumental technique was first improved in the post-irradiation examination and the temperature-transient-to-burst tests were extensively conducted on PNC316 claddings which were irradiated in JOYO as a fuel test assembly PFC030M and a driver fuel assembly PFD304. The life time evaluation of the irradiated PNC316 fuel claddings was carried out, based on these test results. The results obtained in this work are as follows; (1) As a result of the improvement in the temperature-transient-to-burst testing, the diametral change data and higher hoop stress data were obtained. And the highly accurate measurement of rupture temperature was also achieved. (2) The temperature-transient-to-burst test results showed that the rupture temperature of the irradiated PNC316 cladding was equal to that of unirradiated one up to present neutron fluence in LOF stress condition. It was indicated that the temperature-transient-to-burst property of PNC316 was not influenced by irradiation in lower hoop stress region. (3) The life time of the irradiated PNC316 cladding at any thermal transient condition was evaluated by means of LMP-Life Fraction Rule method. Consequently, the result of estimation for failure temperature of heavily irradiated PNC316 showed the possibility for rising the design limit of the cladding highest temperature for MONJU.