Water leakage in reactor hall during dismantling of research reactor


VTT's FiR 1 research reactor in Otaniemi, Espoo, has been dismantled since June 2023. Fortum acts as the main contractor in the project and is responsible for the work, waste treatment and final disposal. The work has progressed according to schedule, and the aim is to finish in the first half of 2024. All decommissioning measures are carried out under the supervision of the Radiation and Nuclear Safety Authority (STUK).

On Wednesday, 9 August, there was a water leak in connection with the dismantling work. About 3 cubic meters of water leaked on the floor of the reactor hall. Based on the samples measured on 9 August and 10 August, it contained small amounts of radioactive substances. Due to the low level of radioactivity, none of those present was exposed to abnormal radiation and no radiation or water was released from the controlled area. The hall is prepared for various emergency situations, including water leakage. All the water was collected during the same day. The hall is designed so that under no circumstances can water get outside. The dismantling was interrupted to investigate the abnormal event. There was no accident or environmental risk.

All deviations affecting nuclear safety are classified according to the International Nuclear Event Scale (INES). VTT as a licence holder makes the classification with the support of Fortum's expertise. Based on the assessment, the safety significance of the event is low, in which case the severity on an eight-step scale (0-7) is 0 "Deviation". STUK will also assess the classification.

The dismantling of the reactor has progressed to the intermediate-level reactor structures. These structures (concrete radiation shielding, aluminium pool and core structures, cooling circuits and instrumentation) are dismantled in stages. The demolition waste generated includes a few dozen cubic metres of low and intermediate level concrete, steel, aluminium, graphite and Fluental neutron moderator material used in the radiation therapy facility.

In addition to the dismantling work, Fortum also takes care of the final disposal of the waste. The reactor of United States Geological Survey (USGS) in Denver, CO, United States, received the used nuclear fuel from the research reactor in January 2021.

After the dismantling, the surfaces of the reactor building are cleaned, the cleanliness of the building is ensured with precise radiation measurements, and it can be released for other uses.

The research reactor was in operation between 1962 and 2015, and it is the first nuclear facility to be dismantled in Finland. Further information on the history of the research reactor: https://www.vttresearch.com/en/ourservices/decommissioning-fir-1-nuclear-reactor 

Further information:

Petri Kotiluoto, Vice President, Nuclear Energy, VTT 
[email protected], tel. +358 40 573 3867

Pauliina Vuosio, Vice President, Corporate Relations Nuclear, Fortum 
[email protected], tel. +358 50 453 2383 


Petri Kotiluoto
Petri Kotiluoto
Research Team Leader
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