An Estimation Method for Off-Gas Sources in a Boiling Water Reactor with Nondefective Fuel

A new method for off-gas source estimation in plants with nondefective fuel is proposed. This method based on the activity ratio between 138Xe and 88Kr is able to directly estimate the off-gas source using only measurement data. The 138Xe to 88Kr activity ratio is decided on the basis of the fissile irradiation with the different neutron spectrum in the core region and the fission fragment emission rate into coolant. This method was applied to actual plant data, and it was demonstrated that the dominant source of off-gas in a plant with nondefective fuel is Pu produced by the burnup of uranium impurities in the core structure. The concentration of uranium impurities in cladding estimated by this method is consistent with the result of neutron activation analysis.