Evaluation of radiation monitor effectiveness for the detection of 85Kr.
As part of the preparations for the purging of TMI Unit-2, the 85Kr sensitivity of 12 radiation detector systems or system combinations was determined. Eleven of these were evaluated using a cube-shaped polyethylene-walled room containing a volume of 5.6 m3 (200 ft3). Krypton-85 gas was added to produce a concentration of 6.7 x 10(-6) muCi/ml in the test room. It was found that none of the ion chambers and scintillation detector systems were able to detect this concentration of 85Kr. Detectors employing thin window GM pancake probes were found to be sensitive enough to monitor this gas down to the unrestrictive area maximum permissible concentration level (MPC) of 3 x 10(-5) muCi/ml, while a large window gas flow proportional counter was found to be sensitive enough to monitor down to about 09.1 MPC. At the end of this experiment, 2.3 m3 (80 ft3) of the gas in the test room was pumped into a compressed air cylinder (scuba bottle) and was used to calibrate The Pennsylvania State University (PSU) Noble Gas Monitor. The sensitivity of this system, which employs gas compression and Ge(Li) spectroscopy, was demonstrated to be between 0.1 and 0.03 times MPC, depending on the counting time employed.
D000396:Air Pollutants, Radioactive / Q000032:analysis; D005069:Evaluation Studies as Topic; D007726:Krypton / Q000032:analysis*; D008452:Maximum Allowable Concentration; D009688:Nuclear Reactors; D011834:Radiation Monitoring / Q000379:methods*; D011868:Radioisotopes / Q000032:analysis*
D000396:Air Pollutants, Radioactive; D011868:Radioisotopes; D007726:Krypton