Failure of triga fuel cladding at the Berkeley Research Reactor

On September 16, 1985, following a long maintenance shutdown, unusually high concentrations of radioisotopes were detected in the reactor-room air on a Constant Air Monitor (CAM) after two and a half hours of full power operation. It was thought that the activity could be coming from some contamination in the pool water. Thus the water was cleaned and the water conductivity was reduced fourfold. However, a full-power operation again showed high count rates on the CAM. A third test was conducted with a germanium detector. Following two hours of operation, three fission-product gasses were identified in the reactor-room air; Kr85, Kr37 and Kr88. Once again no unusual activities could be detected on the CAM filter, in the pool water, or in the demineralizer resins. It was concluded that the gasses must be coming from a leaking fuel element. Three old, instrumented elements with defective thermocouples were selected to be the first ones isolated from the core. After removing the elements, the reactor was operated at full-power for two hours with no abnormal activities detected. New standard elements were loaded and the reactor was again operated at full-power to confirm that no leaking element remained in the core. Since then, the reactor has been operated, with no abnormal activities detected. (Nogami, K.)