KS 150 is a gas-cooled reactor using heavy water as a moderator (GCHWR) nuclear reactor design. A single example, A-1, was constructed at the Bohunice Nuclear Power Plant in Jaslovské Bohunice, Czechoslovakia. The power plant suffered a series of accidents, the worst being an accident on February 22, 1977, rated INES-4. Since 1979 the plant has been undergoing decommissioning.

The decision to build a nuclear power plant in Czechoslovakia was made in 1956. Construction of A-1 in Jaslovské Bohunice (western Slovakia) started in 1958 and took an unexpected 16 years. A-1 was commissioned on October 24, 1972.

The KS 150 reactor was built entirely in Czechoslovakia, designed together with USSR, built by Škoda Works. One advantage of the design was its ability to use unenriched uranium mined in Czechoslovakia, similar to a 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 a leak of carbon dioxide, which was used as a coolant. A 'technical' (mechanical?) failure occurred during refuelling and a fresh fuel assembly was shot off the reactor into the reactor's hall. The most serious accident from 1977 (see below) was rated INES-4. The damage could have been repaired with a large investment but on May 17, 1979, the government, dissatisfied with high costs, low performance and accidents, decided to decommission the plant. Plans to build the second reactor block A-2 were canceled.

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

A1 Nuclear Power Plant was in operation for 19,261 hours altogether, it generated 1,464 GWh and supplied 916 GWh to the network. Maximum output achieved was 127 MW.

Decommissioning, decontamination and dismantling of the plant still continues and is expected to be completed in 2033.

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