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React on reactors

india Updated: Sep 10, 2011 19:38 IST
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As this article goes to press on Thursday, the Tokyo Electric Power Company was continuing with its unusual emergency procedure of pumping large amounts of sea-water into the Fukushima-Daiichi reactors.

The company hopes to cool the reactors and avert a complete core meltdown although the sea-water will corrode the plants, rendering them useless.

Meanwhile, the pools of water where radioactive spent fuel is stored have begun drying out resulting in fires due to hydrogen releases. Radiation levels have risen alarmingly and the workers involved in these operations themselves face significant health risks.

It is not necessary to paint worst case scenarios to point out that the situation is dire.

The tragedy in Japan should serve as a critical wake-up call for India, which has announced a vast expansion of its nuclear programme. A close examination of the events that led to the Fukushima accident holds important lessons.

The Fukushima plants are boiling water reactors - somewhat more advanced versions of the Tarapur I and II reactors near Mumbai. Even though the reactors were technically 'shut down' when the earthquake occurred, their cores continue to produce large quantities of heat. This will continue for weeks to come, and is a feature common to all nuclear reactors.

Although the reactors contained multiple cooling systems to remove this heat, the primary system collapsed when the earthquake led to a loss of electrical power. The emergency diesel generators, which provide back-up power, were flooded by the tsunami.

This resulted in a 'station blackout' and disabled the systems which provide cooling-water to the radioactive core. Station blackouts have occurred in the past, for example at the Narora 1 reactor in 1993, and are very dangerous.

The next stage of cooling depends on using the steam generated in the reactor itself to drive the cooling-water, but this requires DC power from emergency batteries for its controls to function.

When the emergency batteries ran out, the temperature in the reactor core started to rise causing chemical reactions that produced hydrogen - a highly inflammable gas - and eventually led to the multiple explosions of the past few days. The explosions at units 1 and 3 reportedly only breached the outer-wall of the reactor but the explosion at unit 2 appears to have damaged the containment enclosing the reactor core.

What lessons should we draw from these events?

First, no nuclear plant is completely immune to the possibility of a major accident. Multiple safety systems do not rule out accidents because they can be disabled by a single root cause, which in this case was the earthquake.

Redundancy may not help either: there were supposedly 13 diesel generators at unit 1 but none of them worked. Furthermore, new technology is not a panacea: the sophisticated electronics at Fukushima were of no use when the power supply failed.

Second, there were also a host of small failures, for example, release valves which did not work in the face of high pressure - precisely when their services were required. What could fail became evident only after the fact.

For example, replacement generators could not be used because the hook-up is done through electrical switching equipment that was in a flooded basement room. These small problems can, in some cases, combine to cause major failures. Such problems also make it clear that it is not possible to plan for all contingencies, and therefore protect against all possible accident pathways.

Third, the Indian government has argued that having multiple reactors at one site makes them cheaper and easier to build, but this comes with a safety penalty. Reports suggest that explosions at one reactor damaged spent fuel pools in co-located reactors. Moreover, the radiation leak from unit 2 made it difficult for emergency workers to approach the other units.

Fourth, the safety of all Indian nuclear facilities must immediately be reviewed in a thorough and transparent manner; all new reactor project plans must be suspended till this audit is completed and the detailed results are publicly available.

The prime minister has mentioned such an audit but it is imperative to involve independent experts from outside the atomic-energy establishment. In fact, the recent statement of the managing director of the Nuclear Power Corporation of India, who said that "there is no nuclear accident in Japan's Fukushima plants.

It is a well planned emergency preparedness programme", hardly inspires confidence in the ability of this body to conduct an impartial safety investigation.

The accident in Fukushima also vindicates the local people at Jaitapur who have been protesting against plans for six reactors, each nearly four times larger than Fukushima-Daiichi 1.

Jaitapur is also in a seismic zone and worse, its reactors are untested: not a single reactor of the Jaitapur design is in commercial operation anywhere in the world. After Fukushima, it would be sheer folly for the government to force this untested technology on the reluctant locals, who will bear the brunt of any accident.

The fable about the boy who cried wolf is often invoked when concerned citizens raise the possibility of accidents. It is worth remembering, though, that at the end of the fable, the wolf did come one day.

MV Ramana is a physicist with the Programme on Science and Global Security, Princeton University and is the author of a forthcoming book on nuclear power in India. Suvrat Raju is a fellow, Department of Physics, Harvard University. Both are with the Coalition for Nuclear Disarmament and Peace

The views expressed by the authors are personal