Heavy water reactors moderator

One of the technical problems of ranoval of tritium is its low concentration in technological and waste streams. In heavy water reactor moderator (pressurized heavy water reactor [PHWR]), the ratio of DTO to D2O is 10 , and in water... 

There are various types of nuclear power reactors, including boiling water reactors (BWR) and pressurized water reactors (PLWR or LWR), which are both light-water reactor (LWR) designs and are cooled and moderated by water. There also are pressurized heavy-water reactor (PHWR or HWR) designs. 

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. 

CANDU power reactors are characterized by the combination of heavy water as moderator and pressure tubes to contain the fuel and coolant. Their excellent neutron economy provides the simplicity and low costs... 

Heavy-water reactors utilize heavy water (D2O) as a moderator. They can be operated with natural uranium, since the capture cross-section for the thermal neutrons, necessary for controlling nuclear chain reactions, is very low for D2O compared with H2O. Enrichment of U is therefore not necessary. The high price of heavy water (only present as 0.015% in natural water) is, however, a disadvantage. The resulting higher investment costs... 

Use (Nonradioactive.) Preparation of heavy water to moderate nuclear reactors. (Radioactive.) Tracers in biochemical, metallurgical, and medical research in geochemical and archeological research (14C) irradiation source for polymerization, sterilization, etc. therapeutic agents in various diseases (iodine, sodium, gold, etc.) electric power generation. 

In the CANDU heavy-water reactor the dominant source of tritium is the deuterium activation reaction of Eq. (8.53). The data given in Prob. 3.3 for the Douglas Point Nuclear Power Station provide a basis for estimating the rate of production of tritium in the heavy-water moderator and coolant ... 

Of the three moderators that make possible a fission chain reaction in natural uranium, heavy water, graphite, or beryllium, heavy water has become the preferred material. It is used both as coolant and moderataor in heavy-water reactors, which are the exclusive source of nuclear power in Canada, Argentina, and Pakistan, are being used in India, and are being considered in other countries wishing to have a nuclear power system not dependent on a source of enriched uranium. 

The old proposed heavy water—moderated reactor had a core volume almost ten times greater than the present one, while the total power output, 3 10 kw, and virgin—neutron mean free path was the same. Its average virgin flux was thus smaller by a factor of 10. A comparison of the slow, resonance, and fast flux in these light water and heavy water reactors is given in Table 4. 2.A. 

Many countries have developed prototype reactors similar to CANDU using heavy water as moderator but with light water as the coolant, for example FUGEN (Japan) and CIRENE (Italy). A 100MW(e) British version has been running since 1969 at the UKAEA s Winfritb establishment. 

The CERNAVODA NPP Unit 1 is a CANDU 600 reactor which uses heavy water as moderator and coolant. The fuel is natural uranium supplied in the form of bundles loaded into, and removed from, the reactor during on-power operation. 

One very satisfactory method of determining critical size is to measure the Lapladan (A) in an exponential pile, i. e., a structure that is similar in all respects to the full size reactor contemplated, but is considerably smaller than that size required to m e the reaction seff-sustain-ing. A detailed discussion of how this is done can be found in the United States Patent of Enrico Fermi et al.. No. 2,708,656. In case the reactor is to be built in the form of a spherical structure employing uranium bodies of any shape or size imbedded in a heavy water (DsO) moderator, the following formula gives the critical overall radius ... 

In the arrangement of FIGS. 3 and 4, the uranium compound is dissolved in bismuth in a ratio of about 1 gram to 25 cubic centimeters. The solution is circulated through the tubes 70 which passes as above described through the heavy water neutron moderator in the tank 80 to define therewith a neutronic reactor in which neutron losses are reduced to a minimum as above described. 

A heavy water reactor uses D2O ( H20 or heavy water) as the moderator rather than H2O. Deuterium absorbs neutrons much less efficiently than ordinary hydrogen. Because fewer neutrons are absorbed, the reactor is more efficient and does not require enriched uranium. On the other hand, more neutrons leak out of the reactor, too, though this is not a serious disadvantage. 

Includes gas-cooled, heavy water, graphite-moderated light water, and liquid metal-cooled fast-breeder reactors. Includes reactors of all types planned or under construction. 

Uranium used in light water reactors must first be enriched by increasing the relative amount of U-235 in the material to be used as fuel in a light water moderated reactor. Heavy water reactors can operate using natural uranium. The enrichment process is described in Chapter 11. In Chapter 12, the processes used to manufacture the enriched uranium into usable nuclear fuel are discussed. The subsequent chapters discuss other processes related to the fuel after it is removed from the reactor, including storage (Chapter 13) and reprocessing (Chapter 14). The recycle of reprocessed fuel is discussed in Chapter 15. 

Other types of reactor fuels that are fabricated include heavy water reactor fuels, research reactor fuels, navel fuels, and mixed oxide (MOX) fuels. Heavy water reactor fuels fabrication is much the same as light water fuels with the exception that the assembly configuration is different and the uranium can be of natural enrichment due to the increased moderation provided by the heavy water. Navel fuel fabrication and configuration processes are classified, although it is generally understood that the fuel is metallic and highly enriched, similar to some research reactors. 

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