Behavior of Radioactive Iodine Isotopes in the Multiple Forced Circulation Loop in an RBMK Reactor

Abstract

The flow of iodine, including 131I, into the coolant water in a nuclear power plant with an RBMK-1000 reactor under normal operating conditions and during transient regimes is analyzed. It is shown that under normal operating conditions the specific activity of 131I in the coolant is correlated with the iron concentration. During shutdown, its content increases by factors of 30–200. The emission of 131I into the coolant can be decreased by factors of 10–15 and the degree of unsealing of fuel elements can be decreased if before shutdown the reactor is held for 2–5 days at 50% of the nominal power level. Recommendations are made for decreasing 131I emissions into the atmosphere. The adoption of these recommendations at the Leningrad nuclear power plant has reduced the 131I emissions into the atomsphere by a factor of 17.