Zinc ion injection passivation technique is being used in BWRs in order to reduce the radiation field build-up around the reactor coolant system. In the case of PWRs and PHWRs, the chemistry of the primary coolant system and the materials of construction are different from those of BWRs. In the present paper, the results of studies on the effect of magnesium ion in modifying the oxide layers formed under PHWR chemistry conditions are reported. The experiments carried out at room temperature and at 265'C are described. Electron spectroscopy for chemical analysis (ESCA) of the materials autoclaved at 265 "C in magnesium containing solution has also been reported.
Zinc ion injection passivation technique is being used in BWRs in order to reduce the radiation field build-up around the reactor coolant system. In the case of PWRs and PHWRs, the chemistry of the primary coolant system and the materials of construction are different from those of BWRs. In the present paper, the results of studies on the effect of magnesium ion in modifying the oxide layers formed under PHWR chemistry conditions are reported. The experiments carried out at room temperature and at 265'C are described. Electron spectroscopy for chemical analysis (ESCA) of the materials autoclaved at 265 "C in magnesium containing solution has also been reported.
Gadolinium is used as neutron poison in Pressurized HeavyWater Reactors (PHWR) at 15 ppm concentration during emergency shut down and at 2 ppm during start up of the reactor. The pH a range of 5-5.5 is recommended based on the acidity requirement for maintaining gadolinium in the solution and to minimize corrosion of moderator system structural materials and radiolysis. Gadolinium has to be progressively removed as the reactor goes to power. It has been observed that gadolinium precipitates in the purification system consisting of ion exchange columns. Experimental investigations were carried out to understand the phenomenon of precipitation of gadolinium in the weak base ion exchange resin. Attempts were made to selectively cap the strong base groups in weak base resin with nitrate to prevent precipitation of gadolinium. Based on studies carried out on gadolinium pick-up and radiation decomposition of weak base anion exchange resins, a simple mixed resin column consisting of nitrate treated poly acrylic based macroporous weak base resin and a strong acid cation exchange resin has been recommended for the removal of gadolinium. It does not precipitate gadolinium and gives optimum chemistry parameters in the outlet.
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