Patent Number: 048204773
Section: summary

TECHNICAL FIELD This invention relates to the art of nuclear reactors, particularly the art of light-water cooled nuclear power plants. BACKGROUND ART The known fission nuclear reactor employs a fuel, such as uranium, to produce heat which is transferred to a generating apparatus, typically a turbine driven generator. A known uranium fuel is enriched uranium-235. A coolant medium is circulated through the reactor to absorb heat produced by the nuclear reaction to create steam much as in oil or gas steam-generating processes. The steam is directed to a turbine to drive a generator, and the steam is then condensed and reintroduced to the coolant stream as a liquid. U.S. Pat. No. 3,222,255 (Maldague) teaches a circuit for a nuclear reactor wherein a distillation column is used for removing substances which are suspended or in solution in the coolant circuit. The coolant intentionally contains a substantial amount of heavy water. It is known to use either light water (H.sub.2 O) or heavy water (D.sub.2 O) as the coolant medium. Light water is used because of its good heat transfer and abundance. A reactor using light water as a coolant is commonly known as a light-water reactor. A significant problem with the known nuclear reactor is that the coolant medium becomes radioactive because of bombardment of the medium with neutrons produced by the nuclear reaction. When water is used as the coolant medium, the bombardment with neutrons produces tritium which is highly radioactive and dangerous. The production of tritium is a two-step process. First, light hydrogen accepts one neutron to produce deuterium (heavy hydrogen). Second, the heavy hydrogen accepts another neutron to become the heaviest known hydrogen, which is called tritium. The second reaction is much slower than the first. The major technique of preventing escape of tritium is to seal the coolant medium so as to prevent its escape. It is impossible, however, to fully prevent escape of the coolant medium since there must be a pressure relief valve for those instances when the coolant medium becomes overheated. It is a major safety hazard for the reactor to overheat thus causing the pressure relief valve of the coolant circuit to open and release tritium into the atmosphere. SUMMARY OF THE INVENTION The invention prevents a safety hazard caused by the presence of tritium in a coolant medium of a light-water reactor by removing deuterium from the coolant. According to the invention, deuterium is continuously removed from the coolant medium, and formation of tritium is accordingly reduced or prevented. Thus, when a reactor overheats and the pressure relief valve is opened, exiting steam will not present a safety hazard because it will contain an extremely small amount of tritium. Deuterium formed in the coolant medium combines with oxygen and either hydrogen or deuterium to form intermediate weight water or heavy water. Intermediate weight water and heavy water may be separated from light water by known apparatus. Since the difference in boiling points of the intermediate weight and light weight water is about one-half degree Celsius while that of the heavy water and the light water is about one degree Celsius, a preferred apparatus for separating these materials is a distillation column having about one hundred plates. The distillation column has one advantage that heat from the circulating coolant may be used to boil the material in the distillation column, and a second advantage that heat removed by the column's condenser can be used to preheat a coolant used in a secondary circuit. In accordance with the invention, only a portion of the circulating coolant stream is subjected to removal of deuterium or heavy water. It has been determined that if approximately a one-percent bleed sample is taken continuously from the coolant medium, enough deuterium, or heavy and intermediate water, will be removed to diminish the level of deuterium progressively from 1 part per 6,400 parts to 1 part per 10,000 parts or as far as it is determined practical to go. This will prevent formation of an unsafe level of tritium. It is an object of this invention to provide increased safety in a nuclear reactor. It is a further object of this invention to prevent the formation of an unsafe level of tritium in a coolant medium for a nuclear reactor. It is a still further object of this invention to continuously remove deuterium from the coolant medium of a nuclear reactor.