Full system chemical decontamination of Pressurized Heavy Water Reactors (PHWRs)

Pressurized Heavy Water Reactors (PHWRs) are the main stay of the Indian Nuclear Energy Program. Unlike the PWRs and BWRs, the PHWRs are of tube type reactors. The primary heavy water (D2O) coolant passes through zircaloy fuel channels and takes the heat to steam generator through carbon steel feeders and headers. Radiation field in the primary heat transport (PHT) system of PHWRs builds up over a period of time. Dilute chemical decontamination processes that employ various chemical formulations are being applied to reactor coolant system components and sub systems all over the world to get savings in MAN-REM. However, full reactor coolant system chemical decontamination is difficult to implement especially in vessel type reactors. The Primary Heat Transport (PHT) System of Pressurized Heavy Water Reactors is amenable for full system chemical decontamination. An Nitrilo Tri Acetic Acid (NTA) based chemical process has been developed to decontaminate the entire coolant system. This process works on the regenerative Dilute Chemical Decontamination (DCD) principle and is applied to the full primary coolant system when the reactor is under shutdown. The decontaminating chemicals are added to the heavy water coolant without significant downgrading of the heavy water. Also, the decontamination is carried out with the fuel in the core