CANDU Reactor Canada

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. 

The loss of neutrons to non-fissile absorption represents a significant problem for the reactor designer, particularly near the end of the reactor run, when the fuel is starting to become used up. While very careful attention to neutron economy may allow a reactor to be designed to run on natural uranium (e.g. the UK s Magnox and Canada s CANDU reactors), most commercial reactors use enriched uranium as the fuel. 

There are three essential nuclear materials for the CANDU reactor uranium, heavy water, and zirconium. The latter material has involved little chemical engineering activity in Canada and will not be considered further in this review. 

Pressurized heavy water reactor "CANDU" (PHWR) Canada 33 18 Natural UO2 Heavy water Heavy water... 

Table 15.2 shows the cumulative bundle defect rate over a 10-year period to 1996 for 37-element fuel bundles discharged from the 14 large CANDU reactors in Canada. 

Boczar, P.G., P.S.W. Chan, R.J. ElUs, G.R. Dyck, J.D. Sullivan, P. Taylor, and R.T. Jones. 1998. A Fresh Look at Thorium Fuel Cycles in CANDU Reactors, Proceedings of the 11th Pacific Basin Nuclear Conference, May 3-7, Banff, Canada. 

Milgram, M.S. 1982. Once Through Thorium Cycles in CANDU Reactors, Atomic Energy of Canada Limited Report, AECL-7516. 

Mr. Allan further noted that presently spent Candu-fiiel contains half the amount of plutonium as could be separated from LWR fuel and would, if separated, be significantly more expensive than freshly mined uranium. However, the Candu reactor system is flexible direct recycle of LWR fuel and LWR plutonium is possible. If Canada should at some future date begin to reprocess spent fuel, it could even decide to retrieve Candu fuel from the rq)ository and convert its strategy to high-level waste di sal. The in rtant point fix>m waste management perspective is that both options exist, both are feasible and both meet the objective of protecting human health and die environment. 

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%. ... 

Fig. 5.2. Uranium oxide fuel bundle for CANDU reactor (photo by courtesy of Atomic Energy of Canada Limited).

Fig. 10.4. Fuel bundle for CANDU reactor (courtesy of Atomic Energy of Canada Limited). 1, Zircaloy bearing pads 2, Zircaloy fuel sheath 3, Zircaloy end cap 4, Zircaloy end support plate 5, uranium dioxide pellets 6, canlub graphite interlayer 7, interelement spacers 8, pressure tube.

Figure A1.26 Simplified flow diagram of SIS-MW, CANDU reactor NPP (Pickering Power Plant, Ontario, Canada) (AECL Report, 1969) these 515-MWei CANDU reactors are the smallest ones in Canada, and first two of them were put into operation in 1971. 

CANDU (Canada) The exiting CANDU reactors as well as the proposed new designs rely to varying degrees on heat removal processes driven by natural circulation. Passive heat sinks based on NC, are utilized in current CANDU reactors, which are able to mitigate the accident progression for more than 24 hours. The passive heat sink consists of the heavy water moderator, which is contained within a low-pressure vessel, called a calandria. The calandria vessel is in turn contained in a calandria vault filled with light water, which provides a second... 

Niobium is also important in nonferrous metallurgy. Addition of niobium to tirconium reduces the corrosion resistance somewhat but increases the mechanical strength. Because niobium has a low thermal-neutron cross section, it can be alloyed with tirconium for use in the cladding of nuclear fuel rods. A Zr—l%Nb [11107-78-1] alloy has been used as primary cladding in the countries of the former USSR and in Canada. A Zr—2.5 wt % Nb alloy has been used to replace Zircaloy-2 as the cladding in Candu-PHW (pressurized hot water) reactors and has resulted in a 20% reduction in wall thickness of cladding (63) (see Nuclear reactors). 

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. 

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... 

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)...

The initial surface composition of boiler tubing, prior to its installation will have an important impact on the amount and type of activated corrosion products in an aqueous reactor coolant. Consequently, the type of thermal pre-treatment the tubing undergoes, for example, for mechanical stress release,will affect the surface oxide film, and ultimately, the corrosion behavior. This particular work has been directed toward characterization of surface oxide films which form on Inconel 600 (nominal composition 77% Ni, 16% Cr, 7% Fe, — a tradename of Inco Metals Ltd., Toronto Canada) and Incoloy 800 (nominal composition 31% Ni, 19% Cr, 48% Fe 2% other, — a tradename of Inco Metals Ltd., Toronto, Canada) heated to temperatures of 500-600°C for periods of up to 1 minute in flowing argon. These are conditions equivalent to those experi enced by CANDU(CANadian Deuterium Uranium)ractor boiler hairpins during in situ stress relief. 

The technetium isotope of interest for nuclear fuel waste disposal is Tc. It is a pure 3-emitter (E = 0.293 MeV) with a half-life of 2.13x10 years. Its high fission yield of 6% accounts for the relatively high concentration 0.02% by weight) (1) in fuel discharged from a CANDU (CANada Deuterium Uranium) reactor (burnup 650 GJ/kg U). 

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