By Ryan McGreal
Published March 14, 2011
I'm not a fan of nuclear power, for a variety of reasons; but the disaster management at the Fukushima I Nuclear Power Plant in Japan has been a breathtaking accomplishment of engineering-for-safety before a disaster and competent management during a disaster in which nearly everything that could go wrong went wrong.
Perhaps surprisingly, watching the horrible events play out at Fukushima I has actually somewhat increased my confidence in the capacity of sound engineering and competent crisis management to mitigate the inherent risks.
The 8.9 magnitude earthquake that struck Japan on Friday, March 11 was several times more powerful than the plant was designed to withstand. Nevertheless, the plant withstood it and the reactors survived intact - even though the facility is 40 years old.
The first crisis came with the earthquake. As planned, the reactors immediately went into shutdown, meaning that control rods were fully inserted into the reactor cores to absorb neutrons and stop the nuclear chain reaction.
(Note: in pressurized water reactors like the CANDU design, the control rods are suspended electromagnetically above the reactor and automatically drop down when power is disrupted. Fukushima I is a boiling water reactor, in which the control rods are held below the reactor using high pressure hydraulic accumulators and are raised automatically when power is disrupted.)
However, fuel rods continue to produce residual heat for several days after the fission chain reaction has stopped and require ongoing cooling - essentially, pumps circulating cold water to absorb and remove decay heat.
This brings us to the second crisis: the power supply to the cooling systems was disrupted when the earthquake damaged the electricity grid. As planned, the backup diesel generators kicked in to power the pumps.
An hour later, the third crisis hit: the tsunami roared down the coast from Sendai and washed out the diesel generators. As planned, the secondary backup batteries kicked in. As the batteries discharged, mobile generators were brought to bear to continue providing power.
However, these methods provided insufficient power to properly cool the reactors. The officials realized the potential existed for a partial or complete nuclear meltdown, in which the fuel rods get so hot that they literally melt the reactor and release dangerous levels of radiation into the environment. They evacuated some 170,000-200,000 people from the surrounding area as a precaution.
The operators had to step in and carefully manage the heat and pressure inside the reactors. One method of doing this was to release some of the steam inside the reactors to reduce the pressure to safer levels. This resulted in three explosions - on March 12, 13 and 15 respectively - that partially destroyed the buildings housing the Unit 1, 3 and 2 reactors.
Before and after images of the explosion at Fukushima I Unit 1 reactor (Image Credit: Wikipedia)
The explosions appear to have been caused by hydrogen formed inside the reactors due to high pressure and falling water levels. The hydrogen reacted explosively after the engineers vented the reactors and released it. They also released some radiation, resulting in elevated levels outside the reactors and the evacuation of 800 staff.
The first two explosions did not compromise the reactors themselves. The third explosion, caused when the explosion at Unit 3 damaged the pumping system for Unit 2 and left the fuel rods dangerously exposed for several hours, may have damaged the Unit 2 reactor.
Reports suggest that the explosion occurred at the bottom of the unit in the pressure system and may have breached the reactor itself, resulting in a radiation leak.
A fourth explosion just took place in Unit 4, which was not in operation when the earthquake struck but is being used to house spent fuel rods. A fire in the reactor seems to have triggered the release of hydrogen.
Operators have been pumping sea water and boric acid into all the reactors to maintain cooling and prevent meltdowns, though periodic aftershocks have at times disrupted their efforts.
So far, 15 plant personnel have been injured in the explosions and up to 190 people have been exposed to elevated radiation levels. No major radiation leaks have been reported to date - the radiation released through venting has been mild and short-lived.
The situation is now probably under control, though the corrosiveness and impurity of the sea water means the reactors will likely never operate again.
Prime Minister Naoto Kan just announced that the evacuation has been extended to a 20 km radius around the plant and that people between 20 and 30 km from the plant should stay indoors. He added that there is a "very high risk of further radioactive material coming out" of the reactor.
Essentially, a multiple-event disaster that far exceeded the design specifications of a 40 year old plant has at worst possibly produced a partial meltdown in which the radiation has been almost entirely contained.
Here we have an example of an incredibly fault-tolerant system that survived multiple simultaneous catastrophic failures with no loss of life (so far) and ongoing containment of radioactive material.
Assuming the situation holds, this will have been achieved through a dazzling combination of engineering for safety, multiple redundant backups, and careful crisis management during a volatile and unpredictable series of disasters.
Of course there are a number of possible interpretations and conclusions we can draw from these events, and I'm sympathetic to all of them.
For many people, the mere possibility of a catastrophic meltdown renders nuclear power an unacceptable risk. The fact that the risk of a meltdown must be actively managed and mitigated for several days after automatic shutdown means the system is not inherently safe no matter how you spin things.
Others will point out that, next to the appalling devastation of the earthquake and tsunami, which may have killed 10,000 people, the situation at Fukushima is almost benign by comparison.
I don't pretend to know enough about Japanese culture and politics to have any idea what the long-term political consequences will be from this incident.
Will the Japanese people turn decisively away from nuclear power? If so, will mounting public opposition be enough to pressure the government into decommissioning the 53 functioning nuclear plants that currently provide a quarter of Japan's electricity, and/or cancelling plans in the works to build additional reactors?
As fossil fuels availability goes into decline, these issues are going to come up again and again. The questions remain: how much risk is acceptable in exchange for enough electricity to power a modern economy, particularly in an earthquake-prone region; and what technology, policy and oversight options are available to mitigate that risk?
Worldwide, after a long decline in popularity starting in the 1980s, policy interest in nuclear power has increased in recent years in response to high oil prices. Supporters have touted modern nuclear reactors as a panacea that will allow us to transition away from fossil fuels. Will this disaster reverse the global trend toward accepting nuclear power?
Canada has 18 active CANDU reactors operating at five sites, most of them in Ontario, that produce 15 percent of Canada's electricity (and 50% of Ontario's electricity). The Province of Ontario is planning to build another reactor, either at Bruce Nuclear Station or Darlington Nuclear Station.
I grew up in sight of the Pickering Nuclear Station. We used to wade up Duffin's Creek and fish in Frenchman's Bay. In winter, we used to toboggan on the hills at Brock Rd. and Montgomery Park Rd. in front of the reactors.
I must admit to a visceral aversion to nuclear power, doubtless spurred in part by a childhood in the paranoid 1980s at the height of hostilities between the USA and the USSR. Still, I try to make policy decisions based on a sound understanding of the facts rather than blind fear.
Again, I'm surprised to find myself somewhat heartened by how well the Fukushima I plant has survived the massive traumas to which it has been subjected. Canada's nuclear facilities, in contrast, are situated in geology that is orders of magnitude safer.
On the other hand, I'm left wondering whether we can trust our government officials to maintain the same obsessive commitment to safety engineering as their Japanese counterparts.
You must be logged in to comment.
There are no upcoming events right now.
Why not post one?