Numerical Simulation on Effect of Methanol Addition on Coolant Radiolysis in Pressurized Water Reactor

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The addition of alcohol into the primary coolant of pressurized water reactors (PWRs) was proposed as an alternative of hydrogen addition. The radiolysis of the coolant in the presence of methanol was simulated, assuming a batch system and changing dose rate. At 300°C, the addition of 4.0 ppm methanol shows an equivalent scavenging capacity toward the OH radical to a typical dissolved hydrogen concentration in Japanese PWR plants. At low dose rate, the addition of 1.0 ppm methanol suppresses considerably the radiolysis of the coolant. At high dose rate, the addition of at least 10 ppm methanol is necessary to lower concentrations of the radiolytic oxidizing products. Concentrations of the radiolytic oxidizing products are determined not only by the scavenging of the OH radical but also by secondary reactions. In the presence of fast neutron irradiation, methanol acts to decompose the radiolytic oxidizing products. The fact that steady-state concentrations of the final organic products depend on dose rate means that complicated secondary reactions contribute to the decomposition of methanol. The major final organic product is formed through a reaction of ethylene glycol with OH. Methanol addition may have the same effect as ethylene glycol addition, and radiation chemical reactions of ethylene glycol systems should be elucidated in future.