Fission-Product Releases to the Primary System of EBR-II, January 1974-March 1975

Seven releases of fission products occurred in EBR-II from January 1974 to March 1975 - - five from mixed-oxide elements and two from sodium-bonded driver-fuel elements. Four releases were from elements that contained a xenon tag, which aided considerably in locating three of the elements; data from the fourth element allowed estimation of changes of tag composition with reactor exposure. Rapid release of fission from two breached mixed-oxide elements caused the reactor to trip because of increased delayed-neutron activity, the first time such behavior has been observed. Identification of a subassembly of Mark-1A driver-fuel elements was complicated by multiple failure of its untagged elements during the diagnosis period. Several of these elements had some exposed fuel in the core, which was the likely cause of increasing delayed-neutron signals from the subassembly.