The Heavy Water Reactor

While the coolant void coefficient is normally positive, the degree of subdivision of the piping allows any power excursion arising from a loss of coolant accident to be easily terminated by the control rods. An added advantage is that, with on-load refueling, the excess reactivity of the core can be maintained at a much lower level than is required for a light water reactor. 

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Because early Canadian reactors used heavy water, and because it is also fundamentally the most efficient moderator, Canada naturally adopted the heavy water reactor for the development of a nuclear power system. By using heavy water both as moderator and as coolant, and by refuelling with the reactor at power, it was possible to develop the CANDU system to operate efficiently and economically with natural uranium fuel. This in turn resulted in the simplest possible fuel cycle. 

Under some conditions it is economically attractive or environmentally preferable to reprocess spent fuel in order to (1) recover uranium to be recycled to provide part of the enriched uranium used in subsequent lots of fuel, (2) recover plutonium, and (3) reduce radioactive wastes to more compact form. In part II of Fig. 1.11 the recovered 0.83 percent enriched uranium is recycled and the 244 kg of plutonium recovered per year is stored for later use in either a light-water reactor or a fast-breeder reactor. This recycle of uranium to the isotope separation plant reduces the annual UaOg feed rate to 220 short tons, still appreciably greater than for the heavy-water reactor. 

In part III of Fig. 1.11, the recovered uranium is recycled and reenriched and the recovered plutonium is recycled to provide part of the fissile material in the reactor fuel assemblies. Two kinds of fuel assemblies are used. One kind is the same as used in cases I and II, which consist of UO2 enriched to 3.3 w/o The annual feed rate of these assemblies is 18.3 MT of enriched uranium. The other kind consists of mixed uranium and plutonium dioxides, in which the uranium is in the form of natural UO2. Their annual feed rate is 8.9 MT of heavy metal (uranium plus plutonium), including 445 kg of recycle plutonium. The total annual UjOg feed rate is 160 short tons, which is less than for the heavy-water reactor of Fig. 1.10. 

The heavy-water reactor can probably increase its utilization of fuel... 

GE-HAPO). The PRTR achieved criticality on November 21, 1960. Since that date a considerable amount ct zero-power testing has been performed. The following results are among those of particular interest in the heavy water reactor field a complete description of all tests is also available. ... 

Use of well-proven special heavy-water equipment and systems from the heavy-water reactor power plants MZFR (multi-purpose-research reactor, Karlsruhe, FRG, 58 MW) and Atucha I (Argentina, 367 MW(e)). 

The heavy water reactor was developed in Canada and is known as the CANDU reactor. The D2O is used as both coolant and moderator. The relative moderating efficiency of various materials is given in Table 7.11. Because of the superior moderating property of D2O, it is possible to use natural uranium as the fuel in the form of UO2 pellets in zircaloy tubes. This makes the CANDU one of the best designed reactors in the world. The coolant cycle and the moderator are separate flow circuits shown in Fig. 7.6. The fuel elements in the pressure tubes and the D2O flow is shown in Fig. 7.7 where the coolant is at about 293°C and 100 atm pressure. The moderator is at lower temperature. The efficiency is rated at 29%. ... 

Because of its good neutron economy, the heavy water reactor is an obvious candidate for the role of thermal near-breeder or advanced converter, using the fuel cycle. The value of the cycle depends on... 

The concept of a passive-safety reactor KAMADO (in Japanese a Japanese traditional kitchen range for cooking with firewood) was proposed in 2001 by the Central Research Institute of Electric Power Industry (CRIEPI), Japan. The KAMADO concept is based on a synthesis of the design approaches used in light water reactors, the heavy water reactor FUGEN [Xni-1] and pool type research reactors. 

For example, the heavy water inventory monitoring was a special interest at the heavy water reactor DHRUVA. 

In some calculations the heavy water reactors in this combination were replaced by high temperature reactors (HTR + FB). 

Without the introduction of breeders in future nuclear programs, some savings in fuel requirements could also be expected from the utilization of advanced converters, like the heavy water reactor, instead... 

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