PURPOSE: To prevent the corrosion by iodine at the time of starting and stopping of an off-gas treating device by supplying a gas essentially consisting of NO2 to a retreatment off-gas in such a manner that the concn. of the NO2 in the gas attains ≥0.5% when the concn. of the NO2 in the gas is low.
CONSTITUTION: The respective devices in the system from a pre-condenser 5 to a blower 15 of the off-gas treating device are started so that the treating device is ready to operate. A dissolution tank 4 is heated up to a temp. T1 simultaneously with dissolution of nuclear fuel and further, a nitric acid NO2 generator 19 is heated up to a prescribed temp. T2. The nitric acid vapor, steam and gaseous NO2 from the dissolution tank 4 and the nitric acid NO2 generator 19 are then supplied to the off-gas system. The shearing and dissolution of the fuel are executed by supplying the nitric acid vapor, steam and gaseous NO2 to the off-gas system for the prescribed time t1 so that the concn. of the NO2 in the gas attains ≥0.5%.
TSUKAGAMI YASOJI
NAKAO MOTOROKU
NISHIMURA YASUYUKI
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