Phase 1 task of chemical decontamination of the clean-up system of Unit - 2 of Tarapur Atomic Power Station

The essential pre-requisites for carrying out the chemical decontamination of clean-up system of TAPS boiling water reactors (BWRs) are: i) raising the system temperature of the decontamination solution to 363 -368 K from about 300 K and ii) bringing down its dissolved oxygen (DO) to < 100 ppb from about 6-7 ppm. The achievability of these two critical parameters is demonstrated in the Phase-l run of this project. The paper describes the details of decontamination circuit established with the C/U system, the effectiveness of the limpet vessel design coupled with the steam heating using an electrode boiler, the hydrazine sorbing nature of the oxide bearing system surfaces and the effectiveness of the hydrazine dosing method of DO control. The successful run of Phase-1 is the key for Phase-2 of this project that would see the actual decontamination of the system. Preparations are underway for Phase-2. (author)