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PWR Coolant Chemistry Loop (PCCL)

The PCCL was designed as an approximately 1/3 scale model of a single flow channel in a PWR, Its components included a core section of Zircaloy 4 tubing representative of the flow channel between fuel pins in a PWR core, a steam generator section of Inconel tubing representative of a single steam generator tube, and connecting sections representative of the recirculation piping. PWR coolant was circulated in the loop at representative velocities by a seal-less, magnetic drive pump. In-core heating was provided by an electric resistance heater coupled to the loop tubing by a lead bath that was predominantly liquid at operating temperature. Full operating temperature and pressure for the loop were maintained independent of the reactor power and the loop was designed to run for periods of up to 3 months at constant conditions.

An important feature of the loop was that the bulk of the tubing was replaced for each run. This facilitated the performance of a series of closely controlled experiments where only the pH of the coolant was changed from run-to-run. The initial conditions for each run were virtually identical; there was no need to decontaminate the tubing between runs and the tubing itself was available for analysis after each run. Coolant chemistry was maintained at a constant boric acid and lithium hydroxide level for each run, with feed and bleed to the loop set at a rate proportional to the total loop volume. Inlet dissolved hydrogen levels were controlled and monitored as was the inlet dissolved oxygen content of the coolant.



Schematic of the PCCL showing major components both in and out of core.