The Halden Reactor was a 25MW (thermal) nuclear reactor located in Halden, Norway and dedicated for research. Construction started 1955 and the reactor became operative in 1958 and was operated by the Institute for Energy Technology (IFE). The reactor was built into bedrock at 100 metres (330 ft) depth. The Halden Reactor was operational 1958–2018. The Halden Reactor was transferred to the state agency Norwegian Nuclear Decommissioning on 1 April 2025, for decommissioning.