Heavy water reactors experience with

Most proposed MSR designs call for the use of enriched lithium-7 and/or beryllium such as in the 70.7%T ,iF-17%BeF2-12%ThF4-0.3%UF4 fuel salt of the 1970s MSBR program. This carrier salt is often termed FLiBe. The presence of either Li or Be leads to significant production of tritium, on par with production levels in heavy water reactors such as CANada Deuterium Uranium (CANDU). For example in the 1970s, the 1000 MWe MSBR projected 2420 curies per day (ORNL 4541,1971), 98.3% from lithium and beryllium, and the remainder of 0.4% from fluorine and 1.2% from ternary fissions. For comparison, CANDU operations typically experience a tritium release rate of less than 24 curies per day (CNSC INFO-0793,2009). 

A notable exception is provided by national experience of India, a developing country that is successfully ongoing with operation and construction of new nuclear power plants with the domestically produced pressurized heavy water reactors of 209 and 490 MW(e) net capacity. 

The success of the CANDU reactor depends on maintaining heavy-water losses at a low level. Experience (64) at Pickering and Bruce confirms that losses can be kept to less than 1% of the total inventory per year. Elaborate recovery systems are provided to deal with heavy-water leakage. Most important has been the development of large reliable and eflBcient molecular sieve drying systems to recover heavy-water vapor from the air in various parts of the reactor building (65). 

The design and construction of the apparatus for these experiments were carried out by members of the Technical Division (of Clinton Laboratories). The reactor was a vertical welded stainless steel cylindrical tank 140 cm in diameter and built to be filled to a depth of 144 cm with heavy water. The top of the tank was covered by a perforated stainless steel tube sheet which was bolted and gasketed on the rim of the tank proper (Fig A1,A). "Fuel tubes" containing U could be lowered through the tube sheet into the heavy water and thus a lattice could be built up by adding fuel tubes until the assembly became critical. The perforations in the tube sheet and the amount of in the fuel tubes were arranged so that if contiguous holes were... 

Clustering Experiments with ThOi-UO, Fuel In 0,0, W, C.Redmm and J.A. Beideltnan (ANL, The program of critical experiments with lattices of thoria-urania fuel in heavy water has been extended from a study of uniform lattices to the determination of properties of clustered fuel arrangements. Such data are of interest for the design of hdavy tvater power reactors. The fuel, contained in 5/16-in.-OD aluminum tubes, has a diameter of 0.23 in., a density of 8.4 gm/cm and a thorium to atom ratio of 25. 

The leakage of heavy water from hot, pressurized reactor circuits presents problems both on account of the economic penalty and the associated escape of radioactive tritium which is formed by neutron capture in the deuterium. Early experience with the Douglas Point CANDU reactor, for example, indicated the need foi sealing of building volumes around the coolant circuit, and the extraction and recovery of the D2O vapor which had leaked into them. 

W. B. Lewis and J. S. Foster, Canadian Operating Experience with Heavy Water Power Reactors, AECL-3569 (1971), available from Atomic Energy of Canada Limited, Chalk River, Ontario. 

Very good experience has been obtained in many countries over many years In the use of heavy water as moderator In experimental but quite high power (5 MW to 200 MW thermal) reactors. Little If any more difficulty is anticipated with the heavy water moderator In power reactors. It is true that maintenance operations become more difficult the higher the level of the tritium that builds up In the moderator, but exposure of open surfaces of heavy... 

Canadian Deuterium-Uranium Reactor (CANDU). The CANDU reactor is interesting because it can mn continuously and be fueled online. With a capacity factor near 100%, the CANDU bums plutonium the quickest. Online fueling would also be very useful for putting the entire inventory through one reactor rapidly to self-protect the fuel. Because plutonium provides excess core reactivity, the core could be cooled and moderated with light water instead of heavy water. The large core also allows low power densities. However, this modified CANDU concept could have positive temperature coefficients of reactivity. Lack of experience with this concept is the main reason that it has not been studied further. 

Deuterium is used primarily in the form of heavy water as a moderator for nuclear reactors with high power outputs. Deuterium is also used in certain bubble chambers and in nuclear fusion experiments. Natural hydrogen contains about 0.015% deuterium by volume, but is combined with hydrogen in the form of diatomic HD. Thus, natural hydrogen contains about 0.032% HD by volume. Separation of hydrogen and deuterium is feasible if the HD is concentrated. 

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