“At 09:20 AM on January 10th, 2010, Reactor Unit 1 of the Volgodonsk [Nuclear Power Plant] was shut down for ongoing maintenance. The preliminary cause has been determined as leakiness in the piping of the steam generator. The repairs are estimated to take four days,” said an official statement by Concern Rosenergoatom, the operator company that runs Russia’s ten nuclear power plants. The statement has been posted in Russian on the company’s site.
The emergency shutdown at Volgodonsk made headlines throughout major news outlets, including twice in news programmes of the second most popular Russian TV channel NTV, as well as in reports posted by news agencies. It immediately ranked among the top news stories on the Russian national online search portal Yandex – the Russian analogue of Google. This was unusually broad coverage for an incident of this kind: According to the federal nuclear regulatory agency Rostekhnadzor, around 40 scram events take place at Russian nuclear power plants year in, year out, but media organisations with federal coverage rarely report on these incidents.
The January 10th episode, however, is cause for more serious concerns than the one that occurred at Volgodonsk two weeks ago, which had resulted from problems with electric insulation. A steam generator is a heat exchanger, where the primary coolant loop, which becomes radioactive from its exposure to the reactor core, transfers heat to the secondary, uncontaminated, loop. Because of leaks occurring through loss of seal in the steam generating system, radionuclides contained in the primary loop’s coolant water may escape into the secondary loop or into the nuclear power plant’s premises. Furthermore, failures in the core cooling system, which includes the steam generator, can lead to failures in reactor core heat removal and to a core melt. This alone introduces the possibility of a severe accident.
According to the Russian news agency Interfax, the recent emergency shutdown at Volgodonsk was caused by an increase in radioactivity levels detected in the secondary loop’s steam lines. No information is available on the scale of contamination in the secondary circuit: The exact levels will have to be determined during the repairs. If radioactive substances that leaked into the secondary loop because of loss of seal in the steam generator’s tubes caused serious contamination not only in the steam generator, but also the steam lines and the turbine, these repairs could take longer than anticipated at this time.
In any case, leakiness in a steam generator system means degradation of one of the safety barriers that prevent dangerous artificial radionuclides from escaping into the surrounding environment.
This contradicts Rosenergoatom’s official statement that says: “The limits and conditions of safe operation of the equipment have not been violated.”
Rosenergoatom continues to say that levels of “background radiation at Volgodonsk [Nuclear Power Plant] and in the surrounding area [correspond to those of] standard-mode reactor operation and do not exceed natural background radiation values.” However, the statement does not give any specific data to support the claim. Bellona’s attempts to obtain comments from Volgodonsk NPP or Rosenergoatom have been unsuccessful as, just as it was two weeks ago, calls failed to go through to the press service of either organisation.
The incident of December 26th 2009 happened on account of failures in the current lead, whereupon the reactor was taken off the grid. Two days later, it was plugged back in. Leakiness in the steam generator’s pipe system may have well been caused by the reduction of power as part of the trip event and the ensuing rise to power as the reactor was being taken back online: It is exactly such transitions from one operating mode to another that place an increased load on the plant’s systems, causing incidents of varying degrees of emergency.
Volgodonsk’s head Alexander Palamarchuk asserts there is no connection between the two incidents: “These are two completely different situations. In the fist case, the cause was failures in the generator [in the electrical circuit]; what we’ve had now is a thermomechanical [failure],” Palamarchuk was quoted by the news agency RIA Novosti as saying. He added that a situation where two foul-ups happen at a nuclear power plant in the course of such a short period of time does not yet warrant serious concerns.
For the next several days, however, Volgodonsk is expected to remain in an unstable condition and will be unable to function at design capacity.