A technique for detection of fuel failures by the activity of XE radionuclides during WWER reactor operation
Fuel failures during operation of Nuclear Power Plants (NPPs) may lead to substantial economic losses. Negative effects of reactor operation with leaking fuel in the core may be reduced if fuel failures are detected in timely manner.
Currently, the value of the ratio of normalized release rates for 131I and 134I is used for detecting fuel failures during steady state operation of WWER reactors. However, unequivocally establishing fuel failure based on the activity of iodine radionuclides is not possible in all possible cases. Such situation may occur in the case of small defects of fuel cladding of the leaking fuel rod or under high fuel burnup if the defect is overlapped by the surface of the fuel pellet. If such case fuel holdups can make the dominant contribution in iodine radionuclide activity, and the fuel cladding failure may be indistinguishable against the background activity level.
The technique for detection of fuel failures at WWER reactors by activity of radioactive noble gases in the primary coolant is suggested in the present paper. It is shown that radioactive noble gases may serve as the indicator of fuel failures more sensitive than the activity of reference iodine radionuclides. The suggested criterion for detection of fuel failures is based on monitoring the ratio between 133Xe and 135Xe activities. Some examples of practical applications of the developed methodology are given.
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