Development of a Process Flowsheet for the Elution of Radiocesium from the TMI-2 (Three Mile Island Nuclear Power Station, Unit 2) Makeup and Purification Demineralizers

摘要

A process was developed for removing radiocesium from the two makeup and purification demineralizers at TMI-2 which had been highly contaminated as a result of the accident in 1979. Process conditions were established in hot-cell experiments using relatively small samples of the contaminated and degraded resins from the TMI-2 demineralizers. The process was designed to elute the radiocesium from the demineralizer resins and then resorb it onto the zeolite ion exchangers contained in the Submerged Demineralizer System (SDS). It was also required to limit the maximum cesium activities in the resin eluates (SDS feeds) so that the radiation field surrounding the pipelines would not be excessive. The process consisted of 17 stages of batch elution. In the initial stage, the resin was contacted with 0.18 M boric acid. Subsequent stages subjected the resin to increasing concentrations of sodium in NaH sub 2 BO sub 3 -H sub 3 BO sub 3 solution (total boron = 0.35 M; and 1 M sodium hydroxide in the final stages). Simulated SDS tests with small zeolite beds (2 mL) showed that the eluates were compatible with SDS processing. Cesium was effectively sorbed (99.99%), and bed performance was unaffected by the presence of relatively small quantities of soluble organic resin degradation products (100 to 200 ppM total C) in the eluates. Also included in this report are radionuclide, elemental, and fissile isotopic analyses of the demineralizer samples, which may be of interest to investigators concerned with the phenomenological aspects of the TMI-2 accidents. 6 refs., 11 figs., 14 tabs. (ERA citation 12:020733)