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Are Canada’s nuclear power plants ready in case of disaster?

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The CANDU Bruce Nuclear Generating Station is ...
The CANDU Bruce Nuclear Generating Station is the second largest nuclear power plant in the world. (Photo credit: Wikipedia)

Background:                        July 19, 2015

 
It is becoming increasingly clear that the Canadian nuclear establishment is turning a blind eye to serious unresolved safety issues. If uncorrected, these defects will affect adversely affect the behaviour of Ontario‘s CANDU reactors under severe accident conditions, likely leading to far greater radioactivity releases than those currently anticipated. 
 
According to testimony given at the recent Bruce licensing hearings by a nuclear engineer well-versed in CANDU technology, Sunil Nijhawan, there are about forty serious safety problems that are unacknowledged by OPG experts or by CNSC staff.
 
Example: Hydrogen Gas Explosions
 
One particular problem has to do with the generation of explosive hydrogen gas if there is a loss of regular cooling and emergency cooling to the reactor core.  Even if the reactor is totally shut down, the intense radioactivity in the irradiated fuel will drive the temperature upwards beyond 1000 degrees C in the absence of cooling. 
 
At such temperatures, the hot steam (H2O) reacts very rapidly with zirconium metal (Zr) to produce zirconium oxide (ZrO) and hydrogen gas (H2).  Since all nuclear power reactors use zirconium metal as a “cladding” for the uranium fuel, there is a rapid buildup of hydrogen gas mixed with radioactive gases and vapours from the damaged fuel (because the cladding is shot).
 
Many readers will recall the three violent explosions that occurred at the Fukushima Dai-ichi nuclear reactors in 2011, blowing the outer shells of three of the six nuclear reactors to kingdom come, and releasing radioactive gases and vapours into the atmosphere.  If such violent explosions were to occur in an Ontario CANDU reactor, causing similar damage to the outer containment structures, the radioactive releases offsite will be considerably greater than those from Fukushima becuae of the fact that the CANDUs do not possess an inner pressure-resistant containment structure such as the Fukushima reactors had.
 
Accordingly, CANDU reactors have “hydrogen gas recombiners” inside the reactor buildings. These devices are supposed to reduce the explosion potential by recombining hydrogen gas (H2) with oxygen gas (O2) to produce non-explosive water (H2O). If these devices work as intended, the explosion potential should be averted and the reactor structure should be safe.
 
But CANDU reactors have far more zirconium in the core of the reactor than other reactor types, so the hydrogen gas generation will be correspondingly greater.  Not only is the fuel cladding made of zirconium metal, but also the hundreds of pressure tubes and the thousands of fuel bundles inside the core.  The pressure tubes are connected to “feeder pipes” made of carbon steel, and at high temperatures there is even more hydrogen gas generated by the oxidation of the carbon steel feeders than there is by oxidization of the zirconium metal in the core.  
 
Mr. Nijhawan has performed these calculations and has demonstrated that Canada‘s nuclear experts have not provided adequate protection against the enormous quantity of hydrogen gas that can be generated under severe accident conditions — a situation far worse than that at Fukushima.  The existing hydrogen recombiners are not only inadequate to the task, but they become so hot in the course of operation that they may well provide the spark that will trigger the very hydrogen gas explosion that they are supposed to prevent.
 
Such a situation must never be allowed to develop, because there is no adequate recovery strategy after such a massive explosion.  Mr. Nijhawan has pointed out the need for more and larger hydrogen recombiners, much better positioning of the recombiners to prevent the accumulation of hydrogen gas near the roof of the plant, and a reliable external cooling system to prevent the recombiners themselves from overheating.
 
So far, Ontario Power Generation (OPG) and the Canadian Nuclear Safety Commission (CNSC) have refused to take these concerns into account.  They stubbornly insist that they have done enough to make the plant safe and will go no further.
 
This is only one item in a list of dozens of other  equally serious safety concerns that Mr. Nijhawan has identified.  Instead of treating him as a welcome contributor the industry seems determined to ignore his concerns because, in their opinion, Ontario’s reactors are already safe enough and need not be made any safer.  Mr. Nijhawan’s concerns have received a more positive response from CANDU owners in some other countries, notably China and South Korea.
 
Gordon Edwards.
————————————-
 
Are Canada’s nuclear power 
plants ready in case of disaster?
 
Meltdown at Fukushima forced nuclear facilities 
across the country to review their fail-safe measures, 
but the modifications being put in place might still be inadequate.
 
By Kevin Bissett, Canadian Press via Toronto Star, Jul 18 2015
 
 
 
 

The Pickering Nuclear Generating Station -- Pi...
The Pickering Nuclear Generating Station — Pickering, Ontario, Canada — 2008 April (Photo credit: Wikipedia)

The meltdown of three nuclear reactors at the Fukushima facility in Japan following an earthquake 

 

and tsunami in 2011 should be a warning to power plant operators that “new, more extreme weather 

events” must be a part of their disaster-mitigation capabilities.

 
FREDERICTON—More than four years after an earthquake and tsunami triggered a meltdown of three nuclear reactors in Japan, lessons learned are still being put into place at nuclear power plants in Canada.
 
But one critic is questioning whether the industry and the Canadian Nuclear Safety Commission have gone far enough in preparing for potential disasters, particularly in light of climate change.
 
Shawn-Patrick Stensil, a nuclear industry observer with Greenpeace, said that, while the technical changes mandated by the commission are good, there also needs to be a new mindset in the nuclear industry after what happened at the Fukushima Dai-ichi facility.
 
Using a recent licence-renewal hearing for the Bruce nuclear plants in Ontario as an example, he said discussions on tornado strengths were inadequate and more severe weather must be considered as a result of climate change.
 
“Fukushima should be a warning that we should be looking at these new, more extreme weather events in the risk assessments of all plants globally, and we haven’t done that yet,” Stensil added.
 
Ramzi Jammal, executive vice-president of the commission, said it launched a review of Canadian nuclear power plants shortly after the March 2011 accident at Fukushima. Two years later, it produced a report and identified changes that must be completed by the end of this year.
 
“We need to expect the unexpected,” he said.
 
Before Fukushima, Jammal said the emphasis in the nuclear industry was on design and prevention, but now it’s on prevention and mitigation.
 
“Now we’re saying accidents are going to occur. We are going to design and put into place emergency measures to deal with off-site consequences,” he said.
 
The effort is to make nuclear power plants completely self-sufficient in situations that would stress a facility beyond most reasonable and probable scenarios, Jammal said.
 
He said that means making each facility able to provide its own backup power, cooling water and other key safety measures to protect a reactor in the event of earthquakes, tornadoes, blackouts and even terrorism. They need to be self-sufficient for three days to a week, depending on how remote the facility is located.
 
At New Brunswick’s Point Lepreau nuclear power plant, it has meant a number of measures including increasing the number of diesel generators to four from two, adding a new building for emergency equipment, installing a large diesel storage tank, and adding pumps and hoses to ensure a supply of water to maintain cooling of radioactive fuel.
 
NB Power president Gaetan Thomas said many of the changes began before Fukushima when Point Lepreau was going through a major refurbishment to extend its lifespan by at least another 25 years.
 
“We were able to do tens of millions (of dollars worth of work) in the refurbishment, specifically in response to some potential beyond-design-basis accidents, before Fukushima occurred,” he said.
 
That work included seismic upgrades to make sure piping and other equipment would be able to survive a strong earthquake.
Thomas said they’ve tried to take into account everything that could affect the facility.
 
“What would be the highest waves that could be generated on a tsunami at Point Lepreau? We look at wind. We look at a combination of events. We look at loss of power supply,” he said.
 
Jammal said similar reviews and work have been done at nuclear facilities across Canada and they’ve worked to standardize equipment, such as the fittings for water hoses so that crews from one plant can assist other facilities and have the right gear.
 
The investigation into the Fukushima accident determined that the direct causes were all foreseeable and that the plant was not capable of withstanding the earthquake and tsunami.
 
Stensil said the industry in Canada must not dismiss possible events because they have a low probability of happening.
 
There has also been little examination by the nuclear safety commission of an accident involving multiple reactors, said Stensil, who is based in Toronto.
 
“We have 10 reactors in the GTA (Greater Toronto Area). They’ve never provided data on whether emergency planning can cope with that scale of accident,” he said.
 
The commission will present a report on Canada’s nuclear power plants in August, which includes status updates on each facility.
 
Point Lepreau is planning a major emergency-preparedness exercise in November that will be monitored by more than 30 departments and agencies.
 
“We will be testing a lot of these response capabilities and out of that, there will be some lessons learned and improvements that we will implement and also share with our partners in the industry,” Thomas said.
Schematic Diagram of a CANDU reactor: The prim...
Schematic Diagram of a CANDU reactor: The primary heavy-water loop is in yellow and orange, the secondary light-water loop in blue and red. The cool heavy water moderator in the calandria can be seen in pink, along with partially inserted adjuster rods. { (Photo credit: Wikipedia)