Accident Possibilities at #Gentilly2 and Other #CANDU Reactors

BACKGROUND INFORMATION ~ AUGUST 1995

by Gordon Edwards, Ph.D., President, Canadian Coalition for #Nuclear Responsibility

"When Gentilly-2 was built, nobody thought about the possibility that an accident could kill everybody in the control room of the nuclear reactor, possibly resulting in a catastrophic accident. (Even if the reactor is shut down, the heat still has to be removed from the core to prevent a catastrophe -- and that cannot be guaranteed if the operators are dead.) A few years ago, AECB discovered that a sudden break in one of the steam pipes passing over the roof of the control room could, in fact, kill everyone inside and make the control room unusable. Obviously, this improbable situation could be extremely hazardous for the population at large.

"At first, AECB wanted Hydro-Quebec to relocate the steam pipes, but Hydro-Quebec argued that this would be too expensive. Instead they offered to make some substantial alterations to the interior design of the building so as to minimize the effects of such a break in the steam pipes, and to carefully monitor the pipes so as to detect any weakening which might (or might not) occur before such a break would happen. Those corrective actions are still being carried out. Whether they are adequate to eliminate the possibility of a catastrophic accident caused by a steam pipe rupture is a matter of judgment.

"One of the most serious kinds of accidents in any nuclear reactor is a Loss of Coolant Accident, or LOCA. It is caused by a pipe break or an open valve, allowing the water normally used to remove the heat from the core of the reactor to escape. Without adequate cooling, the core of the reactor will overheat and fission products will be released from the damaged fuel, many of them in the form of radioactive gases and vapours. If these materials escape into the environment in large enough quantities, a nuclear catastrophe will result.

"Every CANDU reactor has an Emergency Core Cooling System (ECCS) which is supposed to flood the core of the reactor with ordinary water in case of a large LOCA to prevent it from overheating. Sometimes, however, the ECCS is not available. The AECB allows the ECCS to be unavailable for up to eight hours in any given year, and in some cases it is unavailable for a much longer period of time. If a large LOCA were to happen at such a time, serious core damage could occur and a nuclear catastrophe could result.

"The first LOCA in a Canadian nuclear generating station was at Pickering, just outside of Toronto, in 1983, when a pressure tube burst without warning in the core of the reactor. A few years earlier, nuclear experts had insisted that a pressure tube could not burst suddenly, because it would begin to leak long before it would break, giving the operators enough time to shut the reactor down and correct the situation. But the experts were wrong.

"Fortunately, it was not a very large LOCA, and the ECCS was not needed to keep the fuel from overheating. Most of the fuel remained undamaged and so not much radioactivity was released. However, repairs to the core of the Pickering reactor took four years and cost more than 500 million dollars. All of the pressure tubes had to be replaced, since many of them were showing signs of serious deterioration and some were developing blisters. If several pressure tubes had burst at the same time, a much more frightening situation would have to be dealt with.

"All CANDU reactors have pressure tubes, and all of them deteriorate with time. But the cost of replacing all the pressure tubes is so great that Ontario Hydro has decided to shut down some of its reactors permanently rather than spend the money needed to repair them. At Gentilly-2, until recently, Hydro-Quebec was also planning to replace all the pressure tubes; but now, to save money, they have decided to try something less expensive -- to re-adjust the "garter springs" which support the pressure tubes inside the core of the reactor, so they will not sag as much and, hopefully, will not develop the same kind of blisters that were seen in the pressure tubes at Pickering. This approach does not halt or reverse the deterioration of the pressure tubes, but it will perhaps slow it down.

"In December, 1994, a second LOCA occurred at a Canadian nuclear reactor. This time, it was not a pressure tube, but a relief valve that broke at Pickering.As the superheated mixture of water and steam escaped through the broken valve, a powerful vibration shook the pipe so hard that it broke, resulting in a large LOCA that required -- for the first time in Canadian history -- the use of the ECCS to prevent damage to the nuclear fuel. Similarly accidents involving broken relief valves in CANDU reactors have also occurred in #SouthKorea, and -- in May 1995 -- at one of the Bruce reactors in #Ontario. In these situations, however, the vibrations did not result in broken pipes.

"In June 1995, the AECB made public its analysis of these accidents. They have concluded that a similar accident could occur at any time at Gentilly-2, and that the resulting vibrations would very likely result in either broken pipes or damage to other valves, thus resulting in a serious LOCA. Hydro-Quebec has made no statement about the situation, and may not agree with the AECB as to the possibility of such an accident or the necessity of undertaking the necessary repair work which would involve redesigning that portion of the pressure relief system."

http://www.ccnr.org/Gentilly_Safety.html

#NuclearPlants #Canada #WaterIsLife #RenewablesNow

#HydroQuébec considers reopening #Gentilly2 #nuclear power station

by Philip Authier, August 10, 2023

QUEBEC – "Hydro-Québec is currently studying the possibility of reopening the mothballed Gentilly-2 nuclear plant in #Bécancour to boost #Quebec’s available power resources in the face of soaring demand.

"On Thursday, Hydro officials confirmed the news, first reported by the Journal de Montréal .

"'Concerning the Gentilly-2 station, an evaluation on the current state of the station is underway, to evaluate our options and to feed our reflection on Quebec’s future energy offering,' the utility said in a statement to the Montreal Gazette.

"The new CEO of Hydro-Québec, #MichaelSabia, is already on the record saying he has 'an open mind (on future options) given the context of a strong increase in demand,' the statement added.

"'We are evaluating different possible options to increase the production of clean electricity. It would be irresponsible at this time to exclude certain energy sectors.'

"In 2012, the #PartiQuébécois government endorsed a recommendation from Hydro-Québec to close Gentilly-2, a #CANDU reactor, mainly owing to the high costs of upgrading the installation. It cost Hydro-Québec $80 million to shut down the plant.

"With a capacity of 675 megawatts, the Gentilly-2 reactor started producing power in 1981."

Source:
https://www.msn.com/en-ca/news/canada/hydro-qu%C3%A9bec-considers-reopening-gentilly-2-nuclear-power-station/ar-AA1f6m1M

#NuclearPlants #Environment #WaterIsLife #NuclearWaste

#HydroQuébec étudie la possibilité de réactiver la centrale nucléaire #Gentilly2

« Hydro-Québec confirme que l'état des lieux a été demandé récemment, soit depuis l'arrivée de son nouveau PDG, #MichaelSabia qui est entré en fonction le 1er août. »

https://ici.radio-canada.ca/nouvelle/2002412/energie-nucleaire-quebec-gentilly-2

#ÉnergieQC #CAQ #PolQC