Inhibiting radioactive substances from eluting into cooling water of a nuclear plant.

摘要

When a new fuel rod is loaded into the reactor of a nuclear plant, a layer of NiO or CoO may be formed on the fuel cladding surfaces. This then causes the release of radioactive <5><8>Co or <6><0>Co into the cooling water of the plant. To prevent this, iron is injected into the cooling water to form an iron oxide layer on the fuel cladding surfaces to a covering rate of 100%. That layer then prevents the formation of a NiO or CoO layer. Subsequently the rate of iron injection is controlled so that the Fe/Ni molar concentration ratio in the cooling water is between 2 and 10, to maintain the oxide layer without allowing excessive amounts of iron to be present. To control the iron injection, the iron, nickel and cobalt levels in the cooling water are monitored using a suitable detector (13). The results are fed to an evaluation means (14), which controls the iron injector (6,7). Measurement occurs between a feed water heater (9,11) and the reaction vessel (15), and injection occurs downstream of a water purifying unit (4,5) acting on water condensed by a condenser (2) from a turbine (1).