Computer modelling in automation of water chemistry control in pressurised heavy water reactors

In pressurised heavy water reactors, the secondary system consists of a light water steam raising circuit with morpholine and hydrazine as alkalising and deoxygenating agents respectively. The steam is condensed by either sea water or lake/river water. In either case, condenser tube leak results in the ingress of contaminants like NaCl or Ca2+ and Mg2+ salts. Blowdown, saw-dust addition and phosphate dosing are temporary measures adopted to increase the time available for the reactor operators to act in a planned manner. Condensate polishing which was the prerogative of neutral water chemistry regime is being considered for maintaining good chemistry in the secondary circuits of PHWR cooled by sea water. However, the presence of the alkalising agents create problems and require optimisation of blowdown and condensate polishing flow rates. In order to effectively implement this scheme and to computerise it totally, modelling of the secondary system is a pre-requisite to define the roll of containments and flow rates. An interactive software code 'BOIL' presented in this paper simulates the buildup of chloride in various parts of the secondary circuit of PHWR subsequent to the onset of seawater leak in the condenser. It is possible to establish the leak rate by just measuring the chloride concentration successively twice over a period of time in boiler water circuit and feeding that data to the code. (author)