Construction workers at the LNPP shut down reactor by tripping emergency shut-down switch

Publish date: June 2, 2004

Written by: Rashid Alimov

A minor storm of fear and contradictory reports resulted from the unexpected shut-down of Reactor Block No.4 at the Leningrad Nuclear Power Plant, or LNPP, on May 20th at two minutes to five in the afternoon. Much information about the incident indicates that the reactor’s emergency shut-down switch, located near a ladder being used by repairmen, was accidentally tripped by a construction worker.

LNPP chief spokesman Sergei Averyanov told the Rosbalt Russian news agency that the installation ceased operation because emergency shut-down switch AZ-5 was unwittingly pushed.

“This is our problem—as far as the public is concerned, nothing has happened at the station,” Averyanov said, according to Rosbalt.

But experts have acknowledged that such abrupt shut-downs can have deleterious effects on a reactor, causing damage to fuel cladding and prematurely exhausting fuel assemblies. Frequent abrupt shut-downs only increase the chances of such damage. Reactor block No.4 experienced two emergency shut-down three years ago—once because of a false alarm, and another because of a problem with its turbine system.

The situation for the LNPP is even more delicate, given the age and type of reactors it runs on—four flawed Chernobyl style RBMK-1000.

Other such break-screeching stops—not counting reactor block No. 4’s—have occurred four times over the past three years—once at reactor block No. 2 and three at reactor block No.2.

The emergency shut-down switch
According to Alexander Nikitin, Chairman of Bellona’s St. Petersburg branch, using the emergency shut-down switch in a reactor is “an extreme measure.”

“One is only allowed to use it in exceptional circumstances, when all other means of controlling a nuclear reactor will not work,” said Nikitin, who has worked as a reactor safety inspector for the Russian Ministry of Defence’s nuclear safety regulatory body.

As a rule, one emergency shut-down key is located on the reactor’s control board, and another in a central position within the reactor control room.

Reasons behind the shutdown
“Most likely, there will be an under-production of electrical energy, but the reactor block poses no danger,” said Averyanov. Vestnik LAES, the LNPP’s official newspaper, reported that the accidental shutdown cost the plant approximately $3.5 m.

According to Rosbalt, cosmetic repair work was underway in the reactor block and after the workers left, a shift in the electrical control unit occurred. Vestnik LAES, explained the shutdown as “an unsanctioned activation of the emergency shut-down switch by a reactor operator.”

”We don’t know where Rosbalt found out about the repair ladder—we won’t comment on that,” said a staffer with the LNPP public information office. “We can only say that an accidental movement against the emergency shut-down switch occurred. There were no technical prerequisites for it the shut-down to occur.”

According to one LNPP worker, who spoke with Bellona on the condition of anonymity, it is as yet unknown who pushed the emergency shut-down switch. “We could assume some kind of diversion,” said the source. “There is foundation to think that a member of the personnel did this out of frustration over management’s recent refusal to grant pay raises. But there is no concrete suspect yet.”

In August 2001, scaffolding was erected inside reactor block No. 4 that covered the ceiling of the reactor control hall’s block shield. According to Vestnik LAES, because of the scaffolding, “workers on duty are forced to work ‘in a haze’ with only local lighting, which, however, has no effect on the fulfillment of their duties.”

“One version is that one of the construction workers, while moving their ladder, accidentally broke the glass covering emergency shut-down switch AZ, and thus stopped the entire reactor block.”

According to one LNPP engineer, who himself has not been given total access to the information surrounding the incident, nonetheless said that the Rosenergoatom—the giant conglomerate that owns all 10 of Russia’s nuclear power stations—was feeding the public “a version that is profitable to itself.”

The LNPP press office offered that “as far as the button is concerned, it is there to stop the block—and it worked properly.”

According to the St. Petersburg daily newspaper Smena, the shut-down of the block was accompanied by a release of radioactive steam into the atmosphere. This version of events could not be independently confirmed.

Checks will be carried out
The LNPP has carried out its own checks as a result of the incident, however the surprise shutdown will likely draw the closer scrutiny of Rosenergoatom, which took control of the LNPP on April 1st 2002. The LNPP will therefore get a Moscow-style going-over.

“Without the assistance of Moscow, we won’t get anywhere. Gosatomnazor the former name of Russia’s nuclear regulatory service will be present,” said a representative of the LNPP public information office.


“In the given circumstances, irresponsibility and weak control along the vertical chain of command are evident,” LNPP Director Valery Lebedev was quoted as saying in Vestnik LAES.

The LNPP information service said that the shut-down occurred as it should have, “without notice—all equipment and all systems worked as per regulation, reliably.” On the international scale of nuclear incidents, called INES, the event rated a zero—the lowest possible rating on the INES scale.

The dangers of abrupt shut-downs But are they really so rare?
The same reactor—No, 4 — was last stopped with the emergency switch on October 15, 2001. The automatic AZ-5 shut-down switch reacted to a false signal along the chain of the apparatus’ functioning.

On April 20 this year, due to human error, turbine generator No.2 in reactor block No.2 was shut down.

Prior to that, on June 28st 2002, reactor block No. 2 was shut down because of a defect in the electrical system. On January 21st 2002, an emergency shut-down system stopped reactor block No. 1 because of an electronic defect. That same reactor experiences a shut down the previous year on June 28th, and reactor block No. 4 was stopped by the emergency shut-down system because of a fault in its turbine section.


There have been other instances preceding these. In 1992, after a canal replacement operation in reactor block No. 2, a plug fitting weighting about 50 grams was left behind by workers. The plant had to shut the reactor down to extract it. In 2000, a piece of rubber was discovered in the technological canal of reactor block No. 1. and, the block had to be shut down. In 2003 following major repairs on reactor block No. 3, a number of odd items, such as light-bulbs, shavings, and pieces of plastic were discovered in the block’s technological canal. The FSB is investigating the latest of these instances.

Reactor shut-downs that occur because of a sharp pressure and temperature drops happen because of multiple rush-job equipment switches, which have a negative impact on the functioning of the apparatuses in question.

“In similarly acute situations, personnel transfer equipment while inside the first zone of the reactor. “During normal routines, that zone, which is highly irradiated, is not entered by personnel. Therefore, because of such shut-downs, people get unplanned irradiation.”

Up and running—for now
After reactor block No. 4 was shut-down, checks of all systems’ equipment were carried out as per regulation, and on May 23rd at 7:42 a.m., re-powering the reactor commenced. By the next day, the reactor was operating at normal capacity.

At present, the LNPP’s reactor blocks No.1 and No. 2 are undergoing repairs.

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