CANDU power reactor

Balakrishnan, P.V., Lister, D.H. "The Chemistry of the Water Circuits in CANDU Power Reactors" Paper E26 Chemistry for Energy Symposium, Chemical Institute of Canada, Winnipeg,1978... 

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... 

In early radiation processing work, cobalt-60 was the principal source of radiation, but now it has been displaced by machine-produced electrons wherever possible. Cobalt-60 is commercially available from the Canadian CANDU power reactors. 

ATOMIC ENERGY CONTROL BOARD, Overpressure Protection Requirements for Primary Heat Transport Systems in CANDU Power Reactors Fitted with Two Shutdown Systems, AECB Regulatory Policy Statement R-77, AECB, Ottawa (1987). 

The GANDU Reactors. The Canadian deuterium uranium (CANDU) reactors are unique among power reactors in several respects. Heavy water is used as moderator natural uranium having 235u... 

CANDU-9 is the next generation of CANDUs. It is a larger version of the CANDU producing 870 MWe, the CANDU-9 to complement the mid-size CANDU-6 with updated proven technology, a modified CANDU-6 station layout, improved construction methods and operational features. Standardization, a feature of CANDU reactors, is emphasized in CANDU-9 in the key components (steam generators, coolant pumps, pressure tubes, etc.) being the same design as those proven in service at CANDU power stations. 

Fanjoy, G.R., Bain, A.S. "CANDU Fuel - Fifteen Years of Power Reactor Experience" AECL-5711, 1977... 

All over the world, 432 nuclear power reactors are under operation and more than 36 GW of electricity could be produced as of December 31, 2001. There are several types of reactors such as boiling water reactor (BWR), pressurized water reactor (PWR), Canada deuterium uranium (CANDU), and others. In these reactors, light water is normally used not only as a coolant, but also as a moderator. On the contrary, in CANDU reactors, heavy water is taken. It is widely known that the quality control of coolant water, the so-called water chemistry, is inevitably important for keeping the integrity of the plant. 

Fig. 25. Series of towers comprising part of the heavy water production plant at Ontario Hydro s Bruce nuclear power complex near Tiverton on the shores of Lake Huron. Heavy water is a clear, colorless liquid that looks and tastes like ordinary water. It occurs naturally in ordinary water in the proportion of approximately one part heavy water to 7000 parts of ordinary water. While ordinary water is a combination of hydrogen and oxygen (H20), heavy water (D.-1.0) is made of up of deuterium—a form, or isotope, of hydrogen—and oxygen. Deuterium is heavier than hydrogen in that it has an extra neutron in its atomic nucleus, so heavy water weighs about 10% more than ordinary water. It also has different freezing and boiling points. It is the extra neutron that makes heavy water more suitable than ordinary water for use in CANDU nuclear reactors as both a moderator and a heat transport medium. (Ontario Hydro, Toronto, Ontario, Canada)...

CANDU Reactor A pressurized heavy-water, natural-uranium power reactor designed by a consortium of Canadian government and private industry participants. CANDU utilizes natural, unenriched uranium oxide as fuel. Because unenriched uranium is cheaper, this kind of reactor is attractive to developing countries. The fuel is contained in hundreds of tubes that are pressure resistant. This means that a tube can be refueled while the reactor is operating. CANDU is a registered trademark of the CANDU consortium. 

For a 1000-MWe CANDU power plant with the same reactor lattice and with the same ratio of... 

Extensive studies (57, 58, 59) defined the controlling processes for activity transport in the power reactors. These are oxide solubility, particle deposition, difiusion through oxide films, and rates of crystallization. Detailed models for activity production in-core and surface activation out-core have been developed (60) that successfully predict the growth of corrosion product fields in each of the CANDU reactors. 

Heavy fuel deposits were expected in boiling systems, and therefore the initial studies of deposition and activity transport for power reactors concentrated on the CANDU-BLW concept until the fields at Douglas Point became a concern. The deposit thickness was proportional to iron concentration in the coolant and to the square of the heat flux (69) deposition was reversible and quickly reached a steady value set by the local conditions. The corrosion products initially deposit by hydrodynamic and electrostatic effects then boiling accelerates deposition by drawing water and its contained iron into the deposit to replace the steam that leaves. Local alkalinity gradients within the deposit determine whether iron crystallizes to cement the deposit or dissolves to weaken it, and erosion processes then define the equilibrium thickness (70), This model works well in explaining deposition under boiling conditions. 

This section provides a comparison of power reactors built in the UK with the Soviet RBMK. But it is worth recollecting that, elsewhere in the world, other types of power reactors are in use. The most widely built reactor is the Pressurised Water Reactor (PWR) but the second is the Boiling Water Reactor (BWR), a light water reactor in which, like the RBMK, steam is generated in the core and passed to the turbines in a direct cycle. Light (i.e. ordinary) water is used as coolant and moderator. The Canadian industry has developed the CANDU series of reactors, with limited export to India, etc., which have many pressure tubes to retain the coolant, as in the British SCHWR and Soviet RBMK, but are heavy-water-cooled and moderated. 

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. 

Not all commercial power reactors require the uranium fuel to be enriched. A small number of reactors, notably the Canadian CANDU reactors, can operate using natural uranium because they use heavy water (D2O) rather than light water (H2O) as the neutron moderator. Additionally, some early British gas-cooled reactors do not require enriched uranium. 

Reactor vendors have achieved success with very small reactors, for example SLOWPOKE, TRIGA, PULSTAR and MAPLE-X, and with large power reactors, for example CANDU, PWR, and BWR. They have however failed to produce commercially viable small reactors (say in the 10 to 1000 MWth range). This is because the very small reactor technology is not amiable to... 

The pressure in the PHTS of a CANDU 6 reactor is controlled by a pressurizer connected to the outlet headers at one end of the reactor. Pressure in the pressurizer is controlled by heaters in the pressurizer and by steam bleed. Heavy water in the pressurizer is heated electrically to pressurize the vapor space above the liquid. The volume of the vapor space is designed to cushion pressure transients, without allowing excessively high or low pressures to be generated in the HTS. (Nuclear power plants that do not allow the coolant to boil in the channels, do not use a pressurizer, and rely on the feed-and-bleed system for control.)... 

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