Second reactor block shut down at Leningrad Nuclear Power Plant

The entry to the Leningrad Nuclear Power Plant.
ERC Bellona

Publish date: June 4, 2007

Written by: Vera Ponomareva

Translated by: Charles Digges

ST. PETERSBURG – The second reactor unit at the Leningrad Nuclear Power Plant – 70 kilometres to St. Petersburg’s west – was shut down Monday after a failure in its cooling system – the latest in a series of mishaps that have led to serious incidents at the station.

The cooling system of any reactor is the primary safety mechanism that keeps the core of the unit within manageable limits, and without which nuclear meltdowns occur.

“Considering that the reactor is old, its engineered life span has been extended, that there are questions about its integrity, such in stoppages are cause for worry,” said Alexander Nikitin, who heads Bellona’s St. Petersburg office.

The Leningrad NPP’s four reactors are all of the fatally flawed Chernobyl RBMK-1000 type. RBMK reactors in Europe are being decommissioned – several former Soviet bloc nations had employed them. In Russia, however, the engineered life-span of such reactors is actually being prolonged, allowing them in many cases to run as long as 15 years beyond their period of safe usage – drastically increasing the chances for a serious incident in the near future.

“This time we were lucky: all the (alert) systems worked as they should. However, this new incident bears witness to the fact that we cannot rule out such events,” said Oleg Bodrov of Green World in Sosnovy Bor, the town in which the Leningrad NPP is located.

“Water exchange with the Baltic Sea (on the shore of which the Leningrad NPP is located) is very limited and any such incident could turn into a catastrophe for the entire region.”

Frighteningly, Bodrov’s words here refer to an earlier incident at one of the Leningrad NPP’s reactors – proving Monday’s inicident was in no way isolated.

On Monday, Leningrad NPP spokesman Sergei Averyanov confirmed in a telephone interview with Bellona Web that the plant’s second reactor unit had experienced problems with its cooling system.

“The automatic systems controlling the water input parameters worked,” said Averyanov.

He said that the reasons behind the deviation will be examined by specialist. At present, the reactor is shut down and unplugged from the power grid and will remain so for some two days. Background radiation measurements in the surrounded area taken after the incidents were normal, said Averyanov.

Environmentalists pointed out that the cooling system of RBMK’s reactors have always been a weak point in their design, and can list several similar incidents at the Leningrad NPP.

“The fact is, the reactor is cooled by 1,693 water canals, through which water is funneled upward,” said Bodrov. “There have been occasions when the delivery of distilled water stopped causing crises in the heat exchange, which can lead to incineration of heat generating (fuel) elements.”

Bad reactors, good safety systems
The Leningrad NPP’s No. 2 unit is one of the oldest in Russia. Brought online in 1975, it is of the first generation series of reactors, which European governments have been pressuring Russia to shut down.

Despite the fact that it’s 30-year engineered life span has come to an end, the reactor was granted a 15-year working extension by Russian nuclear authorities in 2006. Earlier, nuclear authorities had given the same 15-year new lease on life to the Leningrad NPP’s exhausted reactor block No. 1.

Before receiving engineering life span extensions, reactors undergo modernisation. Safety systems are upgraded by expanding and diversifying control equipment. Yet the reactor is the same reactor and incidents continue to occur.

“Stoppages happen on average about one to two time a year because we are monitoring many parameters, many automated systems,” said Averyanov. “If any parameter deviates from the norm, the load on the reactor is reduced to a certain output or is stopped. This is a normal state of affairs for specialists.”

The mechanism in question, said Averyanov is comparable to any electrical device: if a short circuit occurs in a lamp for instance, then a fuse shuts it down to prevent a fire.

Incidents at the Leningrad NPP
The most serious incident involving the dehydration of a technical cooling canal at the Leningrad NPP happened in November 1975. On that occasion damage occurred to fuel elements in the plant’s reactor block No. 1. Over the course of a month, radioactivity was released into the atmosphere. According to varying estimates, some 137,000 to 1.5 million Curies of radioactive material feel on the surrounding area, including the city of St. Petersburg and its 5 million residents. Tons of radioactive waste were emptied into the Baltic Sea.

Information about this accident still remains in the shadows – Rosatom as Russia’s Federal Atomic Energy Agency, steers clear of answering inquiries from environmentalists about the consequences of this incident.

History repeated itself in 1992 when radioactive steam, measuring some 4000 Curies of inert gasses and 2.5 million Curies of iodine, spilled into a Leningrad NPP reactor’s ventilation system and consequently was released into the atmosphere.

In May 2000, during repairs of the No. 1 reactor at the Leningrad NPP, a piece of rubber was left behind in one of the technical cooling canals causing a sharp drop in the amount of water pumping in to cool the reactor. But as the reactor was only just being powered up, the error was caught in time, avoiding the 1972 and 1992 accident scenarios.

A similar incident occurred in 1993 when a simple piece of metal fell into one of the canals when they were being changed in the Leningrad NPP’s reactor No. 1.