Behaviour under off-normal conditions

Power and/or temperature transients may occur during reactor operations which could lead to excessive fuel pin loads, life limiting features or even fiiel pin frilures. Extensive R D programmes to investigate oxide fuel pin behaviour during and after such transient conditions have been carried out on irradiated fiiel pins  

Comparison of measured maximum FCCI depths in FFTF irradiated Juel pins with EBR II based design correlation at the 95% confidence level. 

In the ORT programme, the irradiation tests combined steady-state irradiation with a range of operational (duty cycle) and overpower transients various cladding materials were or will be tested (20% CW type 316, D9, PNC 316, PNC-FMS, PNC 1520, PNC-ODS). Some fuel pins were tested in transients at high exposure levels (up to 17 at % and 90 dpa for PNC 316 clad pins). These programmes provided an extensive data base and led to the demonstration of 

To sum-up, the accumulated experience has demonstrated conclusively that breaches are benign events and has provided the data base for reactor operators to define their own criteria for managing such events depending on their specific circumstances. However, these optimistic considerations have to be confirmed for the highest target bum-up and exposure levels, taking into account the potential embrittlement of cladding materials as dose increases. 

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