Archived from the original on 17 May CANDU can also breed fuel from the more abundant thorium. CANDU replaces this "light" water with heavy water. ACR failed to find any buyers; its last potential sale was for an expansion at Darlington, but this was cancelled in It is also the power-reactor product marketed by Canada abroad.
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Long-term reactivity control is also achieved through fuel management ie, the ability to refuel on-line precludes the need for reactivity suppression over a core's life. As an efficient destoyer of waste actinides using currently-available technology, CANDU reactors can serve a role in reducing the total volume of high-level nuclear waste requiring long-term storage.
The main change, and the most radical among the CANDU generations, canvu the use of pressurized light water as canndu coolant.
The Canadian Nuclear FAQ - Section A: CANDU Technology
Bringing a new fuel design to the point of "in situ" testing is not a trivial process. CANDU reactor cores therefore tend to be larger than light-water reactor cores, with a much larger water inventory - leading to other advantages in terms of safety under extreme accident conditions.
The tubes are then contained in a larger vessel containing additional heavy water acting purely as a moderator. This was a major goal of the CANDU design; by operating on natural uranium the cost of enrichment is removed. Chemically, this additional neutron changes things only slightly, but in nuclear terms the difference is significant. Canadian Nuclear Laboratories has developed more efficient heavy-water production processes based on wet-proofed catalyst technology.
Types of nuclear fission reactor.
Pros No enrichment required. The first systems were experimental and prototype machines of limited power. In the first option, only one fuel type is used in the reactor core which is a mixture of slightly enriched Uranium and natural thorium. Retrieved 5 March This can be remedied if the fuel is supplied and reprocessed by an internationally approved supplier.
Another purpose of these Adjuster Rods is to extend the range of the regulating system in the positive direction beyond that available from the liquid zone controllers. The ability to load-follow has become an important requirement of the electricity market however. Most commercial reactor designs use normal water as the moderator.
Shutoff rods are held above the reactor by electromagnets and drop under gravity into the core to quickly end criticality. The cost of electricity from any power plant can be calculated by roughly the same selection of factors: Sales efforts have had their rector success in countries that could not locally build designs from other firms.
During the s, the international nuclear sales market was extremely competitive, with many national nuclear companies being supported by their governments' foreign embassies. Miller of Atomic Energy of Canada Ltd. At the time of CANDU's design, Canada lacked the heavy industry to cast reaxtor machine the pressure vessels of this size. Some CANDU plants suffered from cost overruns during construction, often from external factors such as government action.
In order to prevent the heat from the pressure tubes leaking into the surrounding moderator, each fuel tube is enclosed in a second tube. Heat is used reacto boil reacyor, which turns to high pressure steam, which flows through a turbine, which turns an electrical generator, which makes electricity.
The solution to this problem came via Zirconium which happens to reacto a very low neutron absorption cross section. It went into service in and ran until C moderator, which permits thermalization to a low temperature high fission cross-section far from absorbing materials, and using on-power refuelling for long-term reactivity management.
Since most of the fuel is usually U, most reactor designs are based on thin fuel rods separated by moderator, allowing the neutrons to travel in the moderator before entering the fuel again.
Calandria and fuel elements The structure containing the pressure tubes and the moderator is called the calandria.
This is one of the many reasons for the cooler mass of moderator in the calandria, as even a serious steam incident in the core would not have a major impact on the overall moderation cycle. Pressurized heavy water, as in a PWR reactor, can reach higher temperatures without boiling and can release more heat from the reactor core.
Long-term reactivity control and flux shaping are effected with fuel-managementsince CANDU reactors can be refuelled on-line.
It is about 10 centimetres 3. A significant operational advantage of online refuelling is that a failed or leaking fuel bundle can be removed from the core once it has been located, thus reducing the radiation levels in the primary cooling loop.