General Electric Company

Chien-Chang Lin

Robert James Law

Robert L Cowan, Ii

Carl P Ruiz

James Leon Simpson

Dragomir Duitna

A pre-oxidation treatment for decreasing the amount of chromium deposited on out-of-core surfaces such as the internal surfaces of recirculation piping. Hydrogen peroxide is injected into the reactor coolant through the recirculation line during reactor shutdown after H.sub.2 addition has been terminated. A dilute acid solution (e.g., nitric acid) is also injected into the loop to serve as a catalyst to accelerate the oxidation reactions. An appropriate water pH (e.g., in the range of 5-6) is maintained by acid injection. The coolant temperature during shutdown is maintained at approximately 150.degree. C. or lower. The peroxide concentration in the recirculation piping is maintained at approximately 1 ppm or higher as needed. The oxidation process should be allowed to take effect in the proposed temperature range with the recirculation pump in operation for at least a few hours to 24 hours, depending on the temperature and the oxide film thickness. The Cr-enriched oxides can be readily oxidized by the hydrogen peroxide to a soluble chromate under proper conditions. Some of the radioactivities associated with the oxides will then be released into the coolant and consequently removed by the reactor water cleanup system.

Pre-oxidation of oxide film for chemical decontamination of

A method and apparatus decrease the release of volatile radioactive iodine from a nuclear reactor pressure vessel containing a reactor core having fuel rods submerged in water. The method includes monitoring the pressure vessel to determine an accident condition and then injecting into the pressure vessel a stable iodide in liquid solution to mix with the reactor water for decreasing vaporization of volatile radioactive iodine discharged from the fuel rods. A reservoir initially stores the stable iodide in the liquid solution and is operatively joined to the pressure vessel through a supply conduit and a normally closed valve which is selectively opened following the accident condition to inject the stored iodide liquid solution into the pressure vessel to mix with the water therein.

Method and apparatus to decrease radioactive iodine release

In a boiling water reactor nuclear plant, hydrogen is injected into the feed water to neutralize radiolysis which causes stress corrosion in stainless steel components. It has been discovered that by inhibiting volatile ammonia, and other gaseous nitrogen compounds from leaving the liquid phase portions of the plant to the steam phase portions of the plant, radiation is reduced to acceptable levels. Formation of ammonia is inhibited chemically, by altering the reaction paths for volatile nitrogen species with trace additives in the parts per billion range, suitable additives include nitrous oxide, copper, zinc, carbon dioxide, and other components. It has also been found that by manipulating the pH, the formation of the voltage nitrogen compounds, especially ammonia, is decreased. Similarly, by physically altering plant operating conditions to reduce sparging or scrubbing of the gases from areas of high radiation, confinement of the N-16 within the liquid phase of the plant within the reactor vessel occurs. It is further found that by decreasing the total hydrogen concentration in the core region, the N-16 volatility can be limited. This includes alternate hydrogen injection points and enhancement of the hydrogen-oxygen recombination reaction by e.g., catalysis by radiation or by surfaces. The possibility of increasing the N-16 holdup time in the steam phase is also considered. Finally, the concept of operating at a higher electrochemical potential which requires a lower hydrogen concentration and hence less N-16 converted to the volatile form is also described.

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Fremont, CA, United States of America

Chien-Chang Lin