8 Jul (NucNet): Unit 2 of the Temelín nuclear power station in the Czech Republic will be back online at the end of July after a refuelling and maintenance outage was extended due to a leak in one of the four steam generators, operator ČEZ has said.
According to the country’s nuclear regulator, SÚJB, the leak occurred during the reactor’s start-up procedure when the scheduled outage was in its final stages on 26 June. The reactor was shut down and remains in a cold shut-down state.
The leak was caused by “a small defect” in a tube of the steam generator venting system. The leakage rate from the primary to the secondary reactor circuit was estimated at between two and three cubic metres per hour, SÚJB said.
An unspecified amount of radioactive material leaked into the secondary circuit and systems of the unit. The systems are being cleaned and treated by “standard procedure”, SÚJB said. There was no release of radioactivity outside the unit, ČEZ said.
During the draining of the steam generator on 26 June, radiation dose rates were measured of between 0.25 and five microsievert per hour – roughly equivalent to dose rates on long-haul flights.
Contaminated water leaked into the unit’s cooling water system and a small amount was transferred into the rainwater collection safety tank. The water contained tritium with a radioactivity of 272 becquerels per litre (Bq/ℓ) on 27 June, which decreased to 105 Bq/ℓ on 2 July.
The water from the safety tank flows through several intermediate systems and then into the nearby Hněvkovice reservoir, where tritium radioactivity remained at the standard environmental background level of about 2 Bq/ℓ.
The provisional rating of the event on the International Nuclear and Radiological Event Scale (INES) is Level 1 of 7. INES Level 1 is an “anomoly”.
Temelín-2 began a scheduled refuelling and maintenance outage in April 2015. During the shutdown, technicians replaced one-quarter of the fuel, modernised the turbine and made adjustments stemming from European Union stress tests after the March 2011 Fukushima-Daiichi accident.
As part of the extended outage of Temelín-2, an inspection of the remaining three steam generators will take place, ČEZ said.
Unit 1 is scheduled to begin a refuelling and maintenance outage on 10 July and will be offline until the end of August.
