1. Field of the Invention
This invention relates generally to nuclear reactor power plants and more particularly to the removal of radioactive contaminants from the coolant of a liquid metal-cooled fast breeder nuclear reactor.
2. Description of the Prior Art
In a nuclear reactor power plant electricity is generated from heat which is produced by fission of fissile materials. In an initial phase of this process a reactor coolant, such as liquid sodium, is used to remove the heat from fuel elements which contain the fissile materials. The reactor coolant circulates through a closed flow system known as the primary system which is made up of a main coolant circulating pump, either a heat exchanger or a steam generator, reactor vessel, and connecting piping arranged in series flow connection. The primary system is closed in the interest of safety since a closed system prevents the release, to the environment, of radioactive particles should the primary system become contaminated. One way that the contamination may occur is by release of radioactive fission products from failed fuel elements. Another way is from the use of vented fuel elements which operate by purposely allowing the release of fission products rather than trying to keep them contained.
In the past, the radioactive contamination was removed, although not effectively, by a cold trapping technique which operates by lowering the temperature of a diverted portion of the reactor coolant causing the contamination to precipitate out of solution. Recently, however, major advances were made in the art by using the cold trapping technique in conjunction with adding certain chemicals or reactants to the hot reactor coolant to enhance the precipitation of the contamination. That is, high concentrations of reacting chemicals or isotopic diluents are mixed with a diverted stream of reactor coolant and the radioactive contamination, in the form of isotopically exchanged or insoluble compounds, are precipitated out of solution in a cold trap. The addition of non-radioactive iodine for example, to hot liquid sodium removes as much as 99.9% of the radioactive isotopes, iodine-131 and iodine-125. Also, the addition of hydrogen to hot liquid sodium removes essentially all of the tritium, cesium-137 and iodine-131 from the reactor coolant. Even these recently employed methods, however, have certain disadvantages. A principal disadvantage is that the amount of radioactive contamination removed is quite small relative to the amount of reactants or additives used. This means that the precipitant in the cold trap consists primarily of unreacted chemicals and unexchanged isotopic diluents. Consequently, the cold trap must be large and must either be replaced or cleaned on a frequent basis. This severely limits the availability of the plant for the production of electrical energy. The present invention eliminates this highly undesirable feature of the prior art.