This report indicates the problems associated with the maintenance of the purity of the D2O in a pressurized heavy water power reactor and how these problems are handled.
In a pressurized water power reactor, impurities will be introduced into the coolant and moderator from the corrosion of the steel system. These impurities are mainly particulate and colloidal in nature. They must be kept to a minimum since when circulated through the reactor they become activated by the neutron flux and when deposited throughout the system they make accessibility for maintenance difficult. Impurities may also be introduced into the water from fuel element ruptures. These also create maintenance problems since they are intensely radioactive.
Heavy water systems require a constant guard against the introduction of light water which would degrade the D2O and make the operation of the reactor inefficient or perhaps impossible. The isotopic content of the heavy water must be checked constantly. Upgrading may be required periodically or continuously.
The general purity of the water in the reactor is maintained by passing a fraction of the main circulating volume through a by-pass containing a filter and a mixed bed ion exchange resin column. This column serves to remove ionic impurities as well as acting as an efficient filter itself. It is also used to maintain the pH of the water at the desired level whether neutral or alkaline. In the case of heavy water systems the resin must be deuterized before use to prevent degrading the D2O.