This is an archived blog post from The Acorn.
All six reactors at Fukushima Daiichi 1 nuclear power station automatically shut down after the earthquake in North-east Japan on March 11th, 2011. Automatic shutdown, an important safety feature to prevent catastrophic leakage of radiation, involves the complete insertion of control rods into the fuel core to stop the nuclear fission reactions. Had reactors not been designed with this crucial safety feature, the potential tragedy would have been immediate and far worse. Therefore, even in the worst case, the radiation damage will be much lower than if this were not the case. [See David Ropeik’s post at Scientific American blogs]
The problems at Fukushima Daiichi 1 power station involve the malfunction and failure of post-shutdown safety systems. Fuel cores generate heat for some time even after the reactor is shut down, and need to be cooled using a circulation of water. The diesel generator & batteries that pump the coolant water into the reactors malfunctioned, either due to internal faults or due to the damage caused by the earthquake, resulting in the failure of the normal cooling mechanisms. Two of the six reactors at Fukushima suffered this problem. The nuclear plant authorities, assisted by Japanese armed forces, are attempting to ensure that the fuel core is cooled by pumping water through other means or by flooding the reactor cores with sea water.
The reactor core is enclosed in a thick steel & reinforced concrete containment vessel. Even if, in the worst case, the attempts to cool the reactor cores fail, causing the fuel rods to melt, radiation leakage will be limited to the extent that the containment vessel remains intact. [See this post at Atomic Insights]
Despite the boiling water reactor technology used in Fukushima Daiichi 1 being 40 years old, it has performed reasonably well given the intensity of the earthquake and tsunami. The automatic shutdown worked. Even if the post-shutdown safety systems malfunctioned, they did so in a manner that gave engineers and policymakers crucial time to plan emergency manoeuvres, make important decisions and evacuate the public. Modern reactor designs take into a account the historical experience since 1970 (when Fukushima’s first reactor came online), including technologies to make the post-shutdown cooling less dependent on diesel/batter-powered pumping. The Westinghouse AP1000 reactor, for instance, places the cooling unit above the reactor core, so that it would flow down naturally.
Fukushima’s managers might have thought that they could implement the cooling without having to use the final option of injecting seawater and permanently putting the reactors out of commission. There are three possibilities why they waited almost a whole day before taking this option (for Reactor 1). First, they might have estimated the risk of radiation leakage to be low enough to warrant attempting other options. Second, commercial imperatives caused them to try and save the reactor, even at the risk of a threat to the public. Third, relevant engineers, officials and policymakers couldn’t make an immediate decision for some reason. With the available information, and given the Japanese context, it is likely that it was the first of the three possibilities—that the risks of radiation was estimated to be low.
Japanese authorities have been both calm and prudent in responding to the situation. They have provided timely information (given that the nuclear emergency is taking place within a larger natural disaster situation), ordered the population in a 10km (and subsequently 20km) radius to evacuate, made arrangement for the distribution of iodine pills and generally called for calm. Prime Minister Naoto Kan himself visited Fukushima the day after the quake.
Nuclear energy remains a relatively safe, clean and secure way of generating power. It remains to be seen how Japanese engineers & policymakers handle the technical and policy challenges (not least involving release of radioactive vapour into the atmosphere). It is possible that attempts to cool the reactor will not succeed. Even so, the technological vintage, the age of the reactors, the unprecedented nature of the disaster and the relative safety performance of the Fukushima reactors must be seen in perspective while assessing the impact of this incident on the future of civilian nuclear power.
India is well-placed to benefit from a global nuclear renaissance. The international nuclear power industry was in the doldrums for the last three decades after a nuclear emergency in Three Mile Island in the United States and the disaster at Chernobyl in the Soviet Union. However, projected shortage of fossil fuels and environmental concerns have triggered a renewed interest in nuclear power in recent years. Unlike 30 years ago, neither is the Indian civilian nuclear sector closed to foreign investment nor is the Indian scientific establishment locked in by international sanctions. This presents a strategic opportunity for India to not only expand the use of nuclear energy to strengthen its energy security, but also for Indian companies to become international players in this sector. As such it is in India’s interests to debunk irrational, unjustified and motivated campaigns to discredit nuclear power.
© Copyright 2003-2024. Nitin Pai. All Rights Reserved.