Tritium buildup in calandria vault and end shield cooling system

Tritium activity buildup in Pressurized Heavy Water Reactor (PHWR) is mainly due to activation of deuterium present in heavy water used in coolant and moderator. But Tritium activity buildup in shield cooling systems namely Calandria Vault Cooling System (CVCS) and End Shield Cooling System (ESCS) is not due to activation of deuterium. It is found that activity buildup is mainly due to activation of Lithium-6 present in lithium hydroxide, which is added to maintain chemistry. Practical values obtained during the study period are in agreement with theoretically computed values of tritium concentration. This paper discusses the activity buildup mode and trend with reactor operation in detail. (author)