Diver

The accident at Three Mile Island Unit 2 (TMI-2) in March 1979 caused extensive contamination of the plant structure. During the accident, the rupture disk (overpressure relief) of the reactor coolant drain tank burst and released primary coolant containing up to 200 μCi.ml of Cs-137 to the reactor building basement. The 700,000 gallons of contaminated water that were released reached a depth of eight feet from the basement floor and carried contaminants into all submerged areas. The concrete surfaces in the reactor building basement-the enclosed stairwell block wall, the 3000- and 5000-psi walls, and the 3000-psi floor fill slab-were all heavily contaminated. Activity concentrations on these surfaces prior to decontamination ranged from a few μCi/cm2 to well over 10 mCi/vm2, and exposure rates exceeded 40 R/h in much of the basement. This paper describes a modified Eberline HP-220A directional GM probe which has been used successfully at Three Mile Island Unit 2 to characterize the high contamination levels on concrete walls and floors in the reactor building basement