FISSION-PRODUCT MONITORING IN EBR-I, MARK IV

A description is given of the development and testing of a monitoring system which announces and analyzes the seriousness of a fuel cladding failure. The system is based on the method of passing the cover gas of the NaK coolant system through an electrostatic precipitation unit, passing the wire carrying the neutralized daughters of the rare gas fission products through a Hg trap gas seal into some water, and counting the resulting radioactive water. Since /sup 41/K, the daughter of /sup 41/Ar, is inactive, the water activity is almost exclusively that of the various Rb and Cs fission products. The equipment is described, and results are reported of some experimental tests. The discrimination against /sup 41/Ar was found to be satisfactory, and essentially all the water activity was due to /sup 88/Rb, /sup 89/Rb, and /sup 138/Cs. The background components were separated and compared, and the ratio of the normal Rb-- Cs activity to the other background components is 0.58. Results of a failure simulation experiment using unclad enriched U foils indicated that the failure of a Mark-IV fuel rod cladding would be detectable. (D.L.C.