Work has been completed to demonstrate the feasibility of a new cladding-failure monitoring technique based on determination of the 135I 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 135mXe produced by 135I decay, and calculating the 135I content of the sodium from the 135mXe content of the second sparge. A sparging monitor was built and tested to determine the time required to sparge dissolved radioxenon (133Xe) from molten sodium. This time varied from ∼1 to 1.5 min, depending on experimental conditions. For the calculated background level of 135I in the primary sodium of Experimental Breeder Reactor II, a counting time of ∼2 min would be required to determine the amount of 135mXe removed by the second sparging to a 1σ counting precision of ±4%. A shorter counting time would be required for higher 135mXe levels that would occur during fuel failure. A system with automatic controls was designed for monitoring 135I in the primary sodium of an LMFBR.