This is not to say that the people involved in the nuclear industry are careless or incompetent or corrupt, though sometimes, as is inevitable in any society, some are. But generally they do take great care and are very meticulous in following safety procedures, probably more so than in other hazardous industries. But nuclear technology is totally unforgiving. It does not allow for even a single error. And to err is human.
The story of the rise of
In the process of rebuilding the nation,
But ironically, in the very process of atomic destruction lay a gleam of achieving the elusive dream of energy security.
Large number of light water reactors of both the pressurised water (PWR) and the boiling water (BWR) kind were built in profusion (54 by the latest count). Reprocessing the spent fuel and creating a vast stockpile of plutonium was the key to elusive energy security. However, many a proverbial slip between the cup and the lip. The reprocessing spent fuel plant at Rokasho suffered series of 'teething troubles': just one damn problem after the other. Many problems still have not been fully overcome. As a stop-gap measure,
with potential catastrophes;
At this stage the reactor operators were confronted with two separate set of problems (amongst many others). One was to cool the reactor cores in reactors 1, 2, and 3 and the other was to provide cooling to the spent fuel pools of all the six reactors. Why was this cooling required if the nuclear chain reaction had successfully shut down? That is because, although the chain reaction has shut down the various radionuclide that it has spawned continue to produce heat (See Box 1) and in the absence of cooling, this would lead to a meltdown and dispersal of radioactivity to the surroundings.
The Boiling-water reactor (BWR) design has the spent fuel bundles tucked in a room just above though not directly above the reactor. While the reactor core is encased in a steel vessel inside the primary containment, (another defence in depth safety feature), the spent fuel is outside this containment. All that shields it from getting dispersed into the environment and becoming part of the food chain are the thick outer walls of the reactor building; the so called secondary containment. While the core cooling system has a lot of redundant safety (diesel generators and battery systems), the spent fuel cooling system does not have all these defence in depth features. All it has is lots of water. In normal operation, this water is kept below 250 C. The reasoning being that since spent fuel is not very hot to begin with, it would take many hours in the absence of cooling for all this water to boil off. This would give adequate time for remedial measures to be undertaken.
Two things need to be understood about spent fuel. First, there is a lot of it. (See
The second point is that spent fuel is potentially far more harmful to the environment than the material in the core. This is because all the short lived radio-isotopes have already decayed away and what is left are isotopes with long half-lives that will stay in the environment for centuries and millennia.
It is possible that by not having frequent venting, the containment pressures rose high enough to allow hydrogen and other gases to leak into the reactor building. If so, hydrogen could build up to an explosive mixture.
There were huge explosions that demolished the roofs of the reactor buildings at both unit 1 and later at unit 3. With an inevitability that resembled a Greek tragedy, unit 2 followed and there was a fire in the spent fuel pool of unit 4. At present, (22.3.'11) cooling has been restored to the pools at unit 5 and 6 and efforts are continuing to do the same at pools of reactor 1 and 2. The pools at units 3 and 4 are the cause of the greatest worry since the explosions have already damaged the buildings and in case there is any further fuel damage and radioactive gasses released, they will go directly into the environment.
The spent fuel in the pool at unit 4 is far hotter than the rest. This is because it was put in the pool in December 2010 during the refuelling outage at the plant. Therefore, a lot more water needs to be pumped into it to keep the bundles under water, than into others. The water not only evaporates due to the heat, but is also lost because there is probably a leak in the pool as has been reported. Unit 3 has special problems since it uses MOX fuel that has much greater proportion of plutonium and is thus a greater risk to human health if dispersed.
The restoration of power has led to a certain amelioration in the acute emergency nature of the calamity. It has certainly given the operators a little more time to think. But the emergency is not over and the situation can flare up again into a further disaster any time. Nuclear engineers say some of the most difficult and dangerous tasks are still ahead — and time is not necessarily on the side of the repair teams.
Some thoughts on “Defence in Depth.”
Japanese are leagues ahead of most others as far as technological sophistication is concerned. To have nuclear authorities in countries like
While nuclear power is on its way out there are some steps that need to be thought through immediately. The least this disaster should do is to raise questions against the wisdom of locating many reactors at one site. What we had in this case was a natural disaster that overwhelmed all the depth in the defence and then became a hydra-headed technological monster just because so many reactors were located together. Due to economies of scale, nuclear plants all over the world have a number of units together. In
While this accident was precipitated by an earthquake and tsunami, the direct cause seems to have been a loss of power supply and the inability to restore it quickly leading to a station blackout. There are many other types of initiating events that could cause such a situation, including war and terrorist attacks. Various regulatory agencies require plants to have the capability to cope with a station blackout for no more than four to eight hours. This needs to re-evaluated. The severity of problems encountered at Fukushima Daichi reactors has allowed the Japanese nuclear establishment to completely wash their hands of problems at other reactors, especially at Fukushima Daini, but also at Onigawa and Tokai plants. While these did escape without the serious consequences of the former, but at least at Fukushima Daini there was some problem that was characterized as level 3 on the INES scale of nuclear accidents. Complete silence on these other problems will not lead to a better understanding.
The INES scale of nuclear disasters has been shown to be a disaster in itself. It is another handle to confuse the public and the change in the characterization of the accident from a level 4 to a level (is it a 5 or is it a 6 or a ….) Again funny if not so tragic.
The storing and piling of spent fuel (high level nuclear waste) in pools at reactor sites requiring active cooling for safety has been shown to be the foolish idea that it is. Saying that eventually it would be reprocessed is not an acceptable solution. Humanity has been waiting since the dawn of the nuclear age for Godot to arrive and find some solution to the intractable problem of storing nuclear waste.
A well-known Indian anti-nuclear activist and physicist, Gadekar lives in the remote tribal village of Vedchhi near the Kakrapar atomic power plant in the western Indian state of Gujarat. There, with his wife, a physician, he runs a Gandhian school for young activists and monitors the Indian nuclear industry, conducting surveys of power plants, uranium mines, and nuclear-testing facilities to determine the effect on the public's health. In 1987, he founded Anumukti, a journal devoted to establishing a non-nuclear India.