CANDU reactor
| 1 | Fuel assembly | 8th | Fuel element changing machine |
| 2 | Moderator tank (Calandria) (pressureless) | 9 | Heavy water as a moderator |
| 3 | Control rods | 10 | Pressure tube |
| 4th | Heavy water reservoir for the primary circuit | 11 | Secondary circuit steam |
| 5 | Steam generator | 12 | Cold water return from the turbine |
| 6th | Circulation pump for secondary circuit (light water) | 13 | Containment |
| 7th | Circulation pump for the primary circuit |
The CANDU reactor ( CAN ada D euterium U ranium) is a heavy water reactor type that was developed by the Canadian company Atomic Energy of Canada Limited .
features
The main features are:
- the moderation with heavy water (D 2 O), which enables the use of natural uranium as fuel. The CANDU reactor can therefore be operated as a natural uranium reactor . Heavy water is also used as the cooling medium in the existing systems, but light water can in principle also be used;
- the construction as a pressure tube reactor . It technically facilitates the construction of such reactors and at the same time allows a relatively simple extraction of weapons plutonium .
Together, these features make the reactor type particularly interesting for emerging and developing countries, but also result in an increased risk of the proliferation of nuclear weapons .
technical description
In contrast to a normal light water reactor , a pressure tube reactor has separate moderator and coolant circuits. The moderator D 2 O is used in the CANDU practically without pressure and at low temperatures (approx. 70 ° C), which contributes to better moderation. Heavy water as a moderator enables the use of natural uranium or only slightly enriched uranium (around 2%) as fuel, because the neutrons are less absorbed in heavy water than in normal water. The uranium dioxide fuel pellets are in a zircaloy -Brennstabhülle.
Horizontal pressure tubes , in which the fuel rod bundles ( fuel assemblies ) are located, run through the moderator tank . These are about 1 m long and have a circular cross-section. Several bundles are arranged one behind the other in each pressure pipe. The pressurized coolant is heated when it flows around the fuel elements and transfers the heat in the steam generator to a water-steam system that works with normal (light) water to generate electricity.
The fuel assemblies can be changed individually during operation if the relevant pressure pipe is separated from the cooling circuit by closing valves. A shutdown of the reactor to change the fuel element, such. B. in light water reactors is not required. In principle, this makes it possible to replace fuel elements after a short dwell time while generating electricity and to obtain relatively pure plutonium- 239 , which is also suitable for nuclear weapons .
In 2010, attempts were first started in China to reuse spent fuel from normal light water reactors in CANDU reactors. For this purpose, the old fuel, which still contains sufficient 235 U, is blended with depleted uranium to produce fuel that corresponds to natural uranium. The tests take place in the Qinshan 3-1 reactor with the collaboration of the Canadian CANDU developer Atomic Energy of Canada Ltd. (AECL).
distribution
The reactor type is used in many countries, especially Canada (a total of 22 reactors, of which 18 are in operation) and India (12 reactors in operation, 6 under construction). Further CANDU reactors are operated in Argentina (1 reactor), China (2 reactors), Pakistan (1 reactor), Romania (2 reactors) and South Korea (4 reactors).
At the beginning of its civil nuclear program, India was supplied by the USA with the two light water power plants from Tarapur . However, the USA later imposed a total freeze on deliveries because India did not appear to be militarily trustworthy to them. Canada jumped into the void with the CANDU reactors out of commercial interests. An agreement was concluded which stipulated purely civilian use. However, this was broken by India; the country built its nuclear weapons arsenal with CANDU know-how and technology .
Advanced CANDU Reactor
The Advanced CANDU Reactor ( ACR for short ) is a further development of the CANDU reactors. He also uses heavy water as a moderator, but ordinary water (light water) as a coolant and weakly enriched uranium (1 to 2% 235 U) as fuel . It is designed for an electrical output of 1200 MW. The construction was classified in the reactor generation III +, so it is comparable with z. B. EPR type reactors . An ACR has not yet been built (as of August 2017).
Improvements over the older CANDU reactors include:
- Newly designed fuel assembly with fuel rods of two different diameters, thus more even power distribution,
- 50% higher performance with the same size of the reactor core,
- higher burnup , so that less used nuclear fuel is produced,
- negative vapor bubble coefficient , achieved by the neutron absorber built into the fuel element,
- improved thermal efficiency through higher working temperature and higher steam pressure at the turbine,
- two independent emergency shutdown systems,
- Containment made of prestressed concrete with a wall thickness of 1.8 m with steel lining.
See also
Web links
Individual evidence
- ^ J. Whitlock: Canadian Nuclear FAQ , Section D.3
- ↑ CANDU Owners Group Inc. ( Memento of the original from February 25, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ J. Whitlock: Canadian Nuclear FAQ , Section A.2
- ↑ Chinese Candu reactor trials uranium reuse
- ↑ Swiss Energy Foundation : Energy and Environment , 1987
- ↑ a b J. Whitlock: Canadian Nuclear FAQ , Section A.13
- ↑ Candu Energy Inc .: ACR-1000 ( Memento of the original from August 1, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
