A Method for Detecting Fuel Cladding Penetration in LMFBRs by Monitoring the Sodium Coolant for Iodine-135

Abstract

Work has been completed to demonstrate the feasibility of a new cladding- failure monitoring technique based on determination of the /sup 135/I content of the primary sodium coolant of Liquid Metal Fast Breeder Reactors (LMFBRs). The method was devised to aid in detecting the penetration of fuel element cladding by sodium coolant. The method consists of isolating a small volume of primary sodium, sparging it with an inert gas to strip out dissolved gases which are discarded, further sparging the sample to strip /sup 135m/Xe produced by /sup 135/ I decay, and calculating the /sup 135/I content of the sodi um from the /sup 135m/ Xe content of the second sparge. A sparging monitor was built and tested to determine the time required to sparge dissolved radioxenon (/sup 133/Xe) from molten sodium. This time varied from approximates 1 to 1.5 min, depending on experimental conditions. For the calculated background level of /sup 135/I in the primary sodium of Experimental Breeder Reactor II, a counting time of approximates 2 min would be required to determine the amount of /sup 135m/Xe removed by the second sparging to a 1 sigma counting precision of plus or minus 4%. A shorter counting time wouldmore » be required for higher /sup 135m/Xe levels that would occur during fuel failure. A system with automatic controls was designed for monitoring /sup 135/I in the primary sodium of an LMFBR. (auth)« less