Nuclear Installation Event at OLKILUOTO-2

Print View Posted on: 11 December 2020

Event Date: 10 December 2020 Event Type: Power Reactor
Event Location: Finland, OLKILUOTO-2 INES Rating: 0 (Final)

The INES classification is the same INES 0. This is just update of the event description.

Situation at the Olkiluoto unit 2 was initiated 10-12-2020 10:22 UTC when hotter than normal water entered primary circuit water treatment system during maintenance work. The hot water caused breakdown of filter resin, which was carried in primary circuit through the reactor core into main steam pipes.

The resin material caused alarm of high radiation levels in the main steam pipes. This triggered reactor scram and main steam line isolation by plant protection automation. High radiation levels in the main steam pipes is criteria for Site Area Emergency due to it being possible indication of fuel damage.

The plant was taken to hot shutdown. Activity in the main steam pipes returned to normal after a short time. Primary circuit water chemical analysis confirmed that there are no fuel damage.

The plant is being taken into cold shutdown 11-12-2020. The NPP organization is preparing plan of work needed to return the plant operational.

All safety systems worked as planned during the incident. There has been no releases of radioactivity into environment. The plant personnel have neither been exposed to radiation.

STUK has stood down its emergency organization and continues to follow the situation with its normal safety oversight function.

INES Rating: 0 - Below scale (Final) as per 10 December 2020
Release beyond authorized limits? No
Overexposure of a member of the public? No
Overexposure of a worker? No

Contamination spread within the facility? No
Damage to radiological barriers (incl. fuel damage) within the facility? No

Degradation of Defence In-Depth No

Person injured physically or casualty? No
Is there a continuing problem? No

Tomi Koskiniemi
Radiation and Nuclear Safety Authority (STUK)
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