IT IS a tragic irony that the nuclear disaster at Fukushima occurred within weeks of the 25th anniversary of the catastrophe at Chernobyl in the former Soviet Union, the world’s worst nuclear accident.

When the scale 9.0 earthquake struck just off the coast of the Japanese city of Sendai on 11 March, the seismic shock was immediately registered by the sensors at the Fukushima One plant which is situated on the coast, south of the epicentre of the quake. This had the effect of shutting down the reactors as a precautionary measure. Initially, nearly all of the dozens of pro-nuclear experts who were asked to comment kept repeating that this showed that ‘everything was under control’.

However, after the control rods had been lowered into the reactor core to stop it functioning, it was vital that the cooling system kept operating, because the fuel rods continue producing significant amounts of heat due to the on-going nuclear reaction, for up to a week after shut-down (see diagram). If this was not done, the heat would boil off the water covering the reactor core, which could melt down, penetrate the containment structure and release radiation to the atmosphere. The quake had cut off the electric power supply to the cooling system, but the diesel powered back-up cut in as planned, so things still seemed to be under control.

The main problem arose when the earthquake was followed by a tsunami, which easily overcame the coastal defences around the plant and inundated the reactor buildings, putting the diesel generators out of action. All that was left was a third line of defence in the form of a room full of batteries. These lasted for only a few hours. John Gittins, former safety director of the UK Atomic Energy Authority, explained that the only option was to try to pump seawater into the reactors to cool them. This was difficult because, as the pressure in the core rose, it became ever more difficult to force the seawater into the vessel. Also, the heat was so great by then that the seawater was evaporating more quickly than it was being pumped in, and “that heat makes xenon and krypton gas inside the fuel rods exert a positive pressure, cracking some of the zirconium alloy fuel rod capsules”. (New Scientist)

Radioactive caesium and iodine fission products could then get out from the rods and into the steam, which was vented from the containment vessel to stop it exploding. This did not prevent the outer buildings surrounding the containment structures blowing up when the steam was vented, since highly explosive hydrogen was also generated by the conditions.

Part-used nuclear fuel, such as existed at Fukushima, contains several radioactive isotopes with different toxic effects. Iodine 131, released here – and in far greater quantities at Chernobyl – is absorbed by the thyroid gland and can cause cancer, particularly in children. Caesium 137 was also released in Japan and Chernobyl, but was not definitively linked to cancer at Chernobyl, although this may have been due to poor health data.

Fukushima One has six reactors, three of which were operational at the time. However, as it later emerged, just as much trouble arose with the stored spent fuel that is housed in the same buildings as the reactors. There was, it appears, a partial meltdown of the nuclear fuel in reactors one and two. In reactor two, there was also damage to the containment vessel which is meant to be virtually indestructible. This may have been responsible for the very high spikes of radiation that occurred early in the emergency. The buildings housing the reactors one and three were destroyed by hydrogen explosions, as steam was vented into these areas from the containment vessels.

The situation in the reactor four building was very serious, with a possible hydrogen explosion in the area storing spent fuel rods, leading to a fire. The spent fuel does not have a containment structure around it, so radiation from the ponds holding this fuel could be released directly into the atmosphere. There was a danger that, as these rods heated up they could go ‘critical’, starting a nuclear chain reaction, although a nuclear explosion was not possible. This scenario arose when it was revealed that the entire core of reactor four had been put into the storage ponds, creating a potentially critical mass. At the time of writing, there are reports that radioactive iodine has been found in food in the area around the plant and the government is considering banning food originating in the Fukashima prefecture.

There is still not enough information to draw out all the lessons of this disaster, partly because there was a scandalous lack of data made available by the private operator, the Tokyo Electric Power Company. In the late 1980s and 1990s, this organisation had been found to have systematically falsified records of safety problems at its nuclear reactors. It also admitted that it was unaware that its Kashiwazaki Kariwa facility was built directly above an active fault line where four tectonic plates converged. When an earthquake hit that nuclear plant in 2007, it was put out of action for two years.

Despite the continuing lack of information it is possible to reach some conclusions. Firstly, there are clear similarities with the catastrophe at Chernobyl in 1986, since design flaws played key roles in both disasters (see box). At Fukushima, the chief flaw was that the multiple backup safety systems should not have had causes of failure in common. The earthquake toppled the power lines that cut off electricity to the cooling system, and the resulting tsunami put the diesel backup power out of action. In other words, the failure of both systems had a common cause. Backup independence may have been achieved with higher walls protecting from a tsunami, or simply putting the backup power generators on high ground.

There were multiple design flaws in the Chernobyl reactor, the most serious being that the reactor core did not have a containment vessel around it at all. A similar situation was found at Fukushima. Here, the spent fuel storage area, where a fire started and radiation was emitted, also did not have any containment around it. However, at Chernobyl, the reactor itself had also been unprotected. So it is probably unlikely that similar amounts of radioactivity will be released in the Japanese plant, although the full facts are still not clear.

The key point is that it is very difficult to predict every possible situation that, in extremely rare circumstances, could lead to failure. But when these circumstances arise, as they have been seen to do, a catastrophe is possible. This is one of the fundamental problems with nuclear power. Japan is one of the most technologically advanced countries on earth. Theoretically, therefore, it should have been able to design out failure. The situation in some other countries using nuclear power will be even more dangerous. For instance, China is planning a crash programme of building new nuclear reactors, far outstripping all other nations. Despite strict environmental regulations on paper, laws are commonly flouted at local level in the wild-west capitalist atmosphere that exists there.

The safety of the plants is also only one aspect of the threat that nuclear power poses. No safe method has been devised for storing the spent nuclear fuel, which remains radioactive for more than 100,000 years.

So how are states around the world likely to react to this latest disaster? The strategy of the Con-Dem government, like the former New Labour administration and those in many other countries, is to expand nuclear energy. This is because it does not produce greenhouse gases and can therefore help in reaching targets on cutting global warming emissions. In the aftermath of the disaster in Japan, many governments have announced that they are reviewing the expansion of nuclear power. In most cases, this will probably be temporary, since they will not be willing to contemplate the relatively small, but greater expenditure on renewable energy compared to nuclear.

A movement needs to be built to challenge the nuclear policy of the bourgeois, yet again exposed as being reckless by this incident. But it will take a change in society to remove the threat permanently since, ultimately, the quest for profit comes first under capitalism, not human needs and safety.

Countdown to disaster at Chernobyl

25 April 1986

1am: Reactor four at the Chernobyl nuclear plant running at full power with normal operation. Slowly the operators begin to reduce power for a test. The purpose of the test is to observe the dynamics of the RMBK type reactor used at the plant with limited power flow, in order to permit repairs to be conducted in the future while it is operational.

2pm: Under the normal procedures of the test the reactor would have been reduced to 30% maximum power. The Soviet electricity authorities, however, refuse to allow this because of an apparent need for electricity elsewhere, so the reactor remains at 50% power for another nine hours.

26 April

12.28am: Chernobyl staff receive permission to resume the reactor power reduction. Instead of setting power at 30%, one of the operators sets a computer incorrectly which results in the power level eventually falling to 7% – too low for the test and potentially dangerous.

1-1.20am: In order to keep the reactor from automatically shutting down under these conditions, the emergency core cooling system and several of the automatic shutdown circuits are disconnected.

1.22am: The turbine is disabled to initiate the test despite the dangerously low power levels. This causes four of the eight recirculation pumps to switch off. This would have shut down the reactor if the automatic circuit to do this had not been disconnected.

1.23am: Reduced coolant flow linked to the turbine closure causes a rapid increase in boiling water because of the heat, producing huge quantities of steam. The operator, recognising an emergency, lowers all the control rods into the reactor core to shut it down but, due to a design problem and the abnormal operating conditions, instead causes power to surge to 100 times normal levels in four seconds. Because of the intense heat, the core begins to break down and the steam tubes burst, causing a huge explosion. Steam pressure blows the 1,000-ton steel and cement filled shield off the top of the reactor, destroying the roof of the reactor building and exposing the hot core to the atmosphere.

When the highly radioactive graphite control rods catch fire, a huge cloud is released which spreads across Ukraine, Belarus, Russia and much of Europe. Tonnes of radioactive strontium, caesium, iodine, and plutonium are blown across the globe, affecting millions of people.

27 April to 4 May

Most of the radiation is released in the first ten days. At first, south and south-east winds predominate. The first radioactive cloud goes high into the atmosphere and blows north-west away from Ukraine toward Sweden. Kiev is lucky in that the wind carries the radioactive cloud away rather than directly to the Ukrainian capital and its population of three million.

6 May

The first extensive report on the situation appears in Pravda, the official Russian Communist Party paper. Schools in nearby Gomel and Kiev are closed, all the children sent elsewhere. This brings the total number of people evacuated to half a million – 140,000 never return.

14 May

Russian president Mikhail Gorbachev speaks for the first time publicly about the accident on Vremya, a Russian TV news programme. He insists there was no cover-up: “The moment we received reliable data we gave it to the Soviet people and sent it abroad”.

15/16 May

New fires break out and more radiation is released.

1986 to 2000

New Scientist magazine estimates that 100,000 could eventually die due to cancers linked to radiation, although much lower figures were later put forward. However, it will never be possible to know exactly how many died, because the collapse of the Soviet Union in 1991 and the chaos that followed have made accurate assessments impossible. The Chernobyl nuclear power plant continued to be used until 2000.

Committee for a workers' International publications

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