KS 150

KS 150 (also known as A-1) is a heavy water gas cooled reactor (HWGCR) nuclear reactor. Single unit was used in the power plant A-1 in Jaslovské Bohunice, Czechoslovakia. The power plant suffered a series of accidents, the worst being the accident from February 22, 1977 rated INES-4. Since 1979 the plant is in decommission process.

History

Decision to build a nuclear power plant in Czechoslovakia was made in 1956. The construction of the plant (A-1) in Jaslovské Bohunice (western Slovakia) started in 1958 and unexpectedly took 16 years. A-1 was opened on October 24, 1972.

The KS 150 reactor was designed in the Soviet Union and completely built in Czechoslovakia by Škoda Works. This type of reactor was never deployed before. One advantage of the design was to be able to use the unenriched uranium mined in Czechoslovakia, similarly to the CANDU reactor.

Because of its experimental design the power plant suffered from accidents resulting in over 30 unplanned shutdowns. On January 5, 1976 two workers were killed due to leak of carbon dioxide used as a coolant. The most serious accident from 1977 was rated INES-4. The damage could have been repaired with a large investment but on May 17, 1979 the government, dissatisfied with the costs, low performance and accidents, decided to decommission the plant. Plan to build the second reactor block A-2 was canceled.

The accidents were kept in secret although wild stories had circulated among the public.

The decommissioning, decontamination and dismantling of the plant still continues, see [http://www.iaea.org/inis/aws/htgr/abstracts/abst_29059905.html 1997 report] for the schedule.

Technical details

KS 150 is a heavy water moderated, gas cooled reactor (HWGCR) able to refuel during operation.

Active zone

Translated from [http://proatom.luksoft.cz/jaderneelektrarny/index.php?akce=reaktor&idtypbloku=6] : Metal uranium in form of a thin string is covered by compound of magnesium and beryllium. Around 70 strings form a fuel rod. The reactor vessel is a cylinder made from an aluminum compound filled by heavy water used as a moderator. The fuel channels are vertical, each containing single fuel rod cooled by flow of carbon dioxide. The active zone is placed in a pressurized vessel which allows refuelling during operation. The heavy water is cooled in a separate circuit.

The gas used as a primary coolant is forced to flow around the fuel rods, is heated by them and then piped to six steam generators. The water steam powers three turbines with electricity generators.

Parameters

* Fuel: unenriched metal uranium, 23.1 tons in the reactor.
* Active zone: diameter 3.56 m, height 4 m.
* The coolant gas on the output from reactor: pressure 5.4 MPa, temperature 426°C.
* Conversion efficiency: 18.5%.
* Moderating heavy water: temperature 65°C
* Capacity: 143 MWe.

1977 accident

On February 22, 1977, during fuel change, a combination of human mistake and design problem caused the worst nuclear accident in Czechoslovakia. Part of fuel rods were placed while the reactor was active. Humidity absorbers covering the rods were not removed causing local overheating of the fuel (transmission of heat to the coolant gas was reduced). The active zone was damaged, heavy water got in contact with the coolant and both primary and secondary circuits were contaminated.

The accident was rated as level 4 on International Nuclear Event Scale (for comparison, the Three Mile Island accident was rated level 5).

External links

* [http://www.javys.sk/en/index.php?page=vyradovanie-jadrovoenergetickych-zariadeni/vyradovanie-jadrovej-elektrarne-a1/technologia/reaktor-ks-150 Detailed schematics of the KS-150 reactor] (Adobe Flash required)
* [http://www.javys.sk/en/index.php?page=vyradovanie-jadrovoenergetickych-zariadeni/vyradovanie-jadrovej-elektrarne-a1/technologia Detailed schematics of the A-1 nuclear power plant] (Adobe Flash required)
* [http://proatom.luksoft.cz/jaderneelektrarny/index.php?akce=reaktor&idtypbloku=6 Short description, schema] (in Czech)
* [http://www.iaea.org/inis/aws/htgr/abstracts/abst_29059905.html Decommissioning of the reactor] ( [http://www.iaea.org/inis/aws/htgr/fulltext/29059905.pdf detailed report] , PDF)