Experience in monitoring the BWR fuel behaviour and fission product releases during off-normal conditions

Tarapur Atomic Power Station has accumulated over 33 reactor years of operating experience in monitoring Boiling Water Reactor fuel behaviour. The sudden and sharp increases in the fission product releases were experienced in the earlier years due to gross fuel failures caused by mechanical damage (lifting of certain core internals) or due to certain operating practices and transients. Data on fission product releases under such gross fuel failure conditions is presented and discussed with evaluation of the incident and corrective actions taken. An apparent correlation observed in incidents of fuel failures and certain operating system transients are discussed. Conventionally for the BWRs sum of six fission gas release rate measured at Steam Jet Air Ejectors is correlated with fission gas radiation monitor reading to work out alarm and trip settings - modifications are suggested to improve reliability and effectiveness in monitoring of fission gas release rates. Appropriate data for fission product deposition and characterisation of coolant crud long lived fission products is also presented. (author). 6 refs, 15 figs, 9 tabs