Ten years after Fukushima

posted in: Energy | 0

What happened?

At 14.46 on 11 March 2011, the largest earthquake ever to hit Japan started in the Pacific Ocean about 72km (45 miles) from the Japanese coast. Occurring in fairly shallow waters, the earthquake caused a tsunami with a maximum height of 15m (49 ft.), which struck the coast about 50 minutes later with devastating effect. The combination of earthquake and tsunami led to over 15,000 deaths and over 127,000 buildings totally collapsed.

The tsunami overwhelmed the Fukushima Daiichi (*) nuclear power plant on Japan’s east coast. Three of the US-designed GE boiling water reactors were out of operation at the time of the earthquake. The other three were automatically shut down when the earthquake struck, in line with their design. The earthquake appears to have done little damage. External power was lost, as expected, so diesel generators automatically switched on to ensure the station could keep coolant flowing to the reactor cores.

But the tsunami, around 14m high, overwhelmed the protective sea wall around the station, which was only 10m high. A second tsunami arrived a few minutes later. The sudden flooding knocked out the sea water pumps and then the diesel generators which provided power to them.

A nuclear reactor core continues to produce heat even when the control rods are fully inserted, stopping any further nuclear fission. This heat must be taken away somehow or the reactor fuel will overheat and there will be a “meltdown”. All reactors have a backup system to cope with this.

At Fukushima Daiichi the diesel generators were supposed to supply power to keep seawater pumping through the reactors to take the heat safely out to sea. But, located below the reactors (against advice from GE engineers), the generators were flooded by the tsunami.

At about 5pm on March 11 a nuclear emergency was declared as it became clear that the three reactors would overheat with the likelihood of radiation emissions. An area of radius 2km from the plant was evacuated rapidly extended to 3km, then 10km and then 20km.

About an hour after the fission reaction had been shut down, the reactors were producing about 1.5% of their normal thermal heat. This is not a large percentage but still some 22MW of energy in reactor 1 and 33MW in reactors 2 and 3 (20MW is roughly the average power used by 4,000 UK homes). The heat turned the surrounding water to steam and a chemical reaction between the fuel cladding and the steam later produced hydrogen, along with yet more heat. The mixture of hydrogen and steam was released through safety valves to the outer section of the reactor containment vessel, steadily building up pressure.

The hydrogen in reactor 1 exploded on 12 March, blowing off the roof of part of the building. Venting of the gas from reactor 2 avoided a similar explosion. An even larger hydrogen explosion occurred at reactor 3, causing further damage. There was also an explosion at reactor 4, which was not operating and didn’t have any fuel in, probably from a flow of gas from reactor 3.

The venting and explosions released radioactive fission products to the atmosphere. Most of the fuel, though badly damaged by fire, remained in the reactors or in the concrete containment beneath them. Radioactive emissions continued until December when they returned to minimal levels, below background radiation, and the plant was put into “cold shutdown”.

Various inquiries concluded that this was an avoidable, human-made disaster. Contributory factors included locating the plant too close to sea-level, the seawall being too low, the position of the diesel generators and the failure to make changes that allowed the sister plant (Fukushima Daini), only 12km away, to shut down safely. Above all, the problem was, according to the official Japanese government inquiry: “collusion between the government, the regulators and TEPCO, and the lack of governance by said parties. They effectively betrayed the nation’s right to be safe from nuclear accidents.”

How bad was it?

Although Fukushima was given a seven, the highest score on the International Nuclear Event Scale, the same as the 1986 Chernobyl disaster, the amount of radiation was far smaller. The UN and WHO concluded that the direct health effects of the Fukushima nuclear accident were small but many people died as a result of the evacuation and disruption to their lives.

Radiation from Fukushima Daiichi contaminated areas of Japan near the plant, some of which are still not safe to return to. But the overall health damage of the radiation is estimated to be fairly small. One plant worker has died as a result of lung cancer. But in the population outside the plant, the estimated dose received was mostly small relative to normal background radiation (see table below).

The effect on health of relatively low exposure to radiation is poorly understood because it is hard to distinguish from the effects of natural and background radiation that we are all exposed to. Most of what is known about the harm to health from radiation comes from the cohort studies of survivors of the atomic bombs dropped on Japan in 1945. Those unlucky people were exposed to very high levels of radiation and it is not clear how far the results can be extrapolated to lower doses (using the officially recognised Linear No Threshold model). As authors in a 2015 article in The Lancet put it, “whether cancer risk is increased by acute low doses (0·1 Gy or lower) or low dose rates is unclear”.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) concluded that “a discernible increase in cancer incidence in this population that could be attributed to radiation exposure from the accident is not expected”. The WHO agreed that “The present results suggest that the increases in the incidence of human disease attributable to the additional radiation exposure from the Fukushima Daiichi NPP accident are likely to remain below detectable levels.”

That doesn’t mean that nobody will die earlier than they otherwise would have, but the numbers will be so small, and spread over decades, that no individual case of cancer could ever be definitively linked to Fukushima. Other authors have widely varying estimates of the additional premature deaths that would statistically be expected from higher radiation doses, ranging from 15 to several thousand. Against this, screening the local population for cancers may actually detect some cancers that would not otherwise have been found, thus preventing some future deaths.

The table below gives some idea of the risks, relative to the background radiation dose everybody on Earth already faces, using the standard measure of milliSieverts (mSv). Note that the higher average annual dose in the US is because of more frequent medical procedures, mainly CT scans. And Cornwall has a lot of naturally occurring radon gas. The annual maximum safe dose for nuclear power workers far exceeds the actual annual dose. The Japanese government used 20mSv as its criterion for evacuation.

Estimated Fukushima radiation doses and comparisons

Sources: https://en.wikipedia.org/wiki/Background_radiation; https://www.unscear.org/docs/GAreports/A-68-46_e_V1385727.pdf; https://www.gov.uk/government/publications/ionising-radiation-dose-comparisons/ionising-radiation-dose-comparisons

Fukushima prefecture estimates 2,268 disaster-related deaths from the earthquake and tsunami, many of which were caused by the evacuation. Most of these were older people, including some whose medical treatment was interrupted and others who were badly affected by stress, including the perception of radiation dangers (which even if mistaken is still a health risk), including a rise in suicides. In hindsight, some argue the evacuation was unnecessarily large, but trust in the government after the accident was already low and made worse by poor communications and alleged cover-ups of radiation data. A relatively orderly evacuation would probably have been replaced by a disorderly, unofficial one.

Is nuclear safe?

All energy sources have some drawback, even solar and wind energy which are intermittent and face severe recycling challenges at the end of their operating lives. Nuclear’s main advantages are that it operates continuously, emits virtually no greenhouse gases and takes up very little space (an important consideration in crowded island nations like the UK and Japan). As for safety, despite the very high profile disasters at Chernobyl and Fukushima, nuclear is relatively far safer than fossil fuels (see chart below).

Source: https://ourworldindata.org/safest-sources-of-energy

Note that brown coal (lignite) is the most dangerous source of energy because of the high level of air pollution it emits per unit of energy. This is relevant to the case of Germany (see below).

Nuclear unavoidably creates highly toxic waste which must be stored safely for thousands of years. No country has yet built long term storage but the problem is manageable and already with us; it doesn’t get much worse if we build new nuclear stations, which produce less waste than earlier reactors.

What were the consequences?

In the early part of the 21st century, there was much talk of a “nuclear renaissance” as new “Generation III” reactor types became available that promised to provide a safe, economic contribution to combatting climate change. That renaissance has not happened, with the limited exception of the UK, which, along with Finland, is the only advanced economy still actively seeking to build new nuclear power stations.

But the main reason is not a shift in public opinion following Fukushima, with attitudes remaining surprisingly favourable in the UK. The problem with new nuclear remains economic: it costs too much to build. Both Generation III designs, one American (the Westinghouse AP1000) and one European (Areva’s EPR), have proven complex to build and have cost many billions of dollars and euros over their budgets (though China has managed to build both of them, perhaps owing to China’s far greater recent experience in building nuclear power stations).

The disaster greatly damaged Japanese people’s confidence in their nuclear industry. Lacking natural energy resources, Japan built 54 nuclear reactors, which supplied about 30% of electrical energy before 2011. Since the Fukushima disaster, the government has tried to reopen some of the reactors since but there is great public resistance. Only 5 our of a remaining 42 reactors have so far reopened. Meanwhile Japan has to fill the energy gap with imported natural gas, which is luckily relatively cheap owing to the surge in US production in the last decade.

Meanwhile abundant natural gas resulting from the US shale revolution has kept gas-fired generation cheap in the US. Even with federal government subsidies, it is very unlikely that any further new nuclear plants will be built soon in the US.

The biggest impact on policy was in Germany, where a large fraction of the public has never been happy with nuclear power, despite its good safety and economic record. When the Green Party entered a national coalition government for the first time in 2000 it sponsored a law to phase out all German nuclear power by 2022. When Angela Merkel (who has a PhD in quantum chemistry) became Chancellor in 2010 she delayed the phase out till 2036. But after Fukushima, the pragmatic Merkel reverted to the original timetable.

Nuclear is now being phased out in Germany with a small part of the energy gap being filled by imports from France (most of which is nuclear generated) but the majority coming from additional burning of coal and brown coal. The effect of this is higher costs to German consumers, higher CO2 emissions and an estimated 1,100 extra German deaths a year from air pollution.

The UK will probably soon give approval to a second European designed reactor, Sizewell C, to be built in Suffolk, next to the UK’s last new nuclear power station, Sizewell B, which opened in 1995. If that goes ahead it will be because the government is willing to take the risk of cost over-runs; without that insurance, no private investment will be forthcoming.

Nuclear is still – just – in the game

The history of nuclear power is something of a rollercoaster from inflated claims and optimism to disillusionment, much of the ride influenced by the habitual secrecy of the nuclear industry. There is now a reaction to the disillusionment, with many environmentalists coming to see nuclear as part of the solution to climate change. The story is very well told in the film The Atom: A Love Affair (for which I was interviewed).

New types of small, modular nuclear reactor are now being offered as potentially cheaper options to the complex giant projects of the past. It remains to be seen if these can prove their worth in time to make a contribution to the urgent need to decarbonise electricity in the next two decades. The tragedy at Fukushima has, perhaps surprisingly, not fundamentally affected the case for new nuclear power as part of the fight against climate change.


(*) Daiichi (第一) means number one.

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