The huge earthquake off the Japanese coast on 11 March continues to send ripples across the globe - not least because of the accident that it caused at Japan's Fukushima Daiichi nuclear power plant. The worst nuclear accident since the 1986 Chernobyl catastrophe, it may ultimately prove even more damaging to the prospects for nuclear power, as countries from China to Germany now rethink their energy policies. Japan itself has just announced it will abandon current plans to expand its own nuclear industry and 'make efforts to further promote renewable energy'.
What happened?
At the time the magnitude 9.0 earthquake struck off the main Japanese island of Honshu, some 80 kilometres east of the city of Sendai, only three of the six reactor units at Fukushima Daiichi were operating; the others were shut down for routine maintenance. All three operating units 'scrammed' as designed, that is, control rods were automatically inserted into their cores to halt the fission chain reaction that generates energy.
However, even after shutdown, the reactors' highly radioactive cores continued to produce heat (as residual fission products decayed) and required cooling. After the earthquake knocked out both external power lines, back-up diesel generators continued to pump cooling water through the reactors. These generators were, however, destroyed by the approximately 14 metre-high tsunami that hit the plant less than an hour later.
Without power, boiling water in the inner reactor pressure vessels could not be replenished. As a result, the water level dropped and the steam pressure started to rise. This forced plant operators to vent slightly radioactive gas into the atmosphere. Over the following week, explosions (caused by a build-up of hydrogen) severely damaged the outer concrete containment structures of Reactors 1 and 3, leaving pools that were storing spent fuel exposed to the atmosphere. An explosion in Reactor 2 (possibly also caused by a hydrogen build-up) damaged a critical inner containment structure known as the primary containment vessel.
To avert a catastrophic meltdown, the plant operator Tokyo Electric Power Company (Tepco), and Japanese nuclear authorities began injecting first seawater and then fresh water, mixed with boric acid into the cores of Reactors 1 to 3 and into all reactors' spent-fuel pool. After abortive attempts to dump water from helicopters, the fuel pools have been sprayed using water cannons and, more recently, modified concrete pumping trucks. But increasing radiation levels created dangers for the 'Fukushima 50' group of workers involved, and residents within a progressively widening zone were evacuated.
Although external power had been reconnected to all of the crippled power station's reactors by 21 March, restarting the pumps themselves required extensive repair work. This work has been severely hampered by contaminated water that had been pumped into reactor vessels and was accumulating, in large quantities, in underground structures around the plant.
In early April, some of this water was discovered leaking into the Pacific Ocean, when radiation levels about 1,000 millisieverts an hour were detected at the surface of a trench leading from Reactor 2. A 20 centimetre crack in a pit connected to this trench - which may have been caused by the earthquake - was eventually plugged with 'liquid glass'. However to make room for the all the radioactive water created by cooling efforts, Tepco released 11,500 tonnes of less radioactive water into the sea.
There are now an estimated 70,000 tonnes of contaminated waste water at Fukushima and finding somewhere to store it will be a major challenge.
What next?
Efforts so far have averted the worst-case scenario of a complete meltdown of the reactor cores and the concomitant possibility of highly radioactive molten material burning through the pressure vessel into the containment building. Nonetheless, fuel in Reactors 1, 2 and 3 has undergone partial melting, and cooling efforts have not prevented significant releases of radiation into the environment. Although substantial progress has been made towards stabilising the plant, Tepco has announced that it expects to bring the crisis under full control only by the end of the year.
On 17 April, Tepco released a two-phase 'roadmap', for managing the accident. The goal of phase one, predicted to last about three months, is to significantly reduce external radiation doses and install a new cover over the reactor building. Phase two, expected to last a further three to six months, aims to bring Reactors 1, 2 and 3 into 'cold shutdown'.
From the perspective of bringing the accident fully under control, the most significant of the measures Tepco has proposed is a plan to flood the reactors' primary containment vessels with water, thereby completely immersing all the fuel. Tepco has begun to implement this plan at Reactor 1, but it is too early to gauge its success. Dealing with the damaged primary containment vessel in Reactor 2 could prove particularly challenging. Even if this operation is successfully completed, Tepco will have to restart the existing cooling system or install a new one before it can declare the crisis over.
Although the risk of further large releases of radioactivity is receding, it is not yet zero. Should cooling operations at the plant be interrupted for any reason, there remains the very slight possibility of a complete meltdown. Aftershocks pose a threat to the structural integrity of damaged buildings filled with water. Further releases of radioactive waste water into the ocean could also occur.
Once the reactors have been brought into cold shutdown, clean-up can begin in earnest. Extensive work will be required to ensure the reactors and spent fuel pools remain safe and stable before they can eventually be decommissioned. The entire process is likely to take decades. Remediation work, such as removing topsoil from schools near the plant, will also be required offsite.
Impact on Japan
Despite the significant quantity of radioactivity that has been released, radiation levels offsite have not been high enough to cause radiation sickness. However, around the plant they are high enough that anyone exposed to them for a prolonged period would have an increased probability of contracting a fatal cancer. In consequence, the Japanese government has imposed a 20km mandatory evacuation zone around the plant. It is also evacuating people from certain more distant towns and villages where there are radiation ‘hotspots'. As a result, the accident by itself has caused large-scale disruption, although the total number of fatalities resulting eventually from the Fukushima accident is likely to be small - especially by comparison with the more than 25,000 deaths estimated to have been caused by the earthquake and tsunami.
Radiation levels that exceed regulatory standards have been detected in milk, crops and fish from surrounding areas. The Japanese government has acted swiftly to prevent these foodstuffs from being consumed. Occasionally, tap water in certain prefectures has also contained unacceptably high levels of radiation. Most notably, for slightly over a day starting on March 23, radioactive iodine-131 levels in Tokyo tap water exceeded the regulatory limits set for infants.
Nuclear safety implications
Tepco has come in for much criticism for its response to the disaster, including from the country's equally embattled prime minister, Naoto Kan, whose nuclear adviser also recently resigned unhappy with the way the crisis was being handled. Tepco's president has publicly apologised, and the company is now looking to pay compensation. However, ultimately, the extent to which the disaster was exacerbated by poor operating practices or poor emergency management will only be answered by future official reviews.
The accident also raises questions about Japanese regulators. The disaster's root cause was that the plant was not designed to withstand the natural disaster that hit it. Although its back-up diesel generators did withstand a 9.0-magnitude earthquake, they were destroyed by a tsunami that was more than twice as high as the seawalls protecting it. A key question for investigating authorities is whether the accident was the result of an extremely low-probability event that could not reasonably have been anticipated or whether there are systematic flaws in Japanese regulator's approach to hazard prediction.
More generally, the safety of even the best-run, best-designed nuclear power plant cannot be guaranteed if it is struck by a disaster - man-made or natural - that is bigger than it is designed to withstand. As a result, Laurent Stricker, chairman of the World Association of Nuclear Operators, called on 15 March for a review of the 'design bases' for nuclear reactors worldwide.
The Fukushima accident also raises questions about the handling of spent fuel. In Japan, as in most countries with nuclear power, large quantities of spent fuel are stored in pools adjacent to the reactors. If the cooling of these pools is interrupted, a potentially serious accident can result. Indeed, apparently as a result of loss of coolant from its spent fuel pool, there were fires and an explosion at Reactor 4 on 15 March. These probably contributed to the release of radioactivity.
Against this background, a debate about whether spent fuel should be moved from pools to concrete 'dry casks' has already begun. Dry casks, which do not require an external power source for cooling, offer certain safety advantages compared to pools but there would be cost implications in moving fuel into them sooner.
Fukushima also provides a sobering lesson to all states that have or want to acquire nuclear reactors about the importance of being prepared to handle a major nuclear accident.
Nuclear power implications
Prior to the Fukushima accident, there was much talk of a 'nuclear renaissance', stimulated in large part by concern about climate change. The accident has inevitably led to a renewed debate about nuclear power's cost-benefit trade-off. To try to head off this debate, most states with nuclear reactors have now announced safety reviews. There have also been more ambitious calls for increased international cooperation on nuclear safety. French President Nicolas Sarkozy has suggested a G20 meeting on the subject. The success of such efforts could have significant implications for nuclear power's spread.
Particularly in Western Europe and North America, public acceptance is key to the feasibility of nuclear power. Fukushima has already reignited almost dormant public fears about nuclear safety. This has been seen most dramatically in Germany. In 2010, Chancellor Angela Merkel had reversed a 2001 decision to phase out nuclear power. But following the Fukushima accident, she announced a three-month moratorium on implementing her new policy and indicated that it may be reconsidered. She also ordered the immediate shutdown of Germany's seven oldest operating reactors for safety checks.
In spite of these actions, she has paid a high political price for her previous support of nuclear power. As a direct result of the Fukushima accident, her party lost power in its traditional stronghold of Baden-Württemberg in state elections on 27 March. This state, now with a Green-led government, is the site of one of Germany's most controversial nuclear power plants (GKN) and was the focus of a huge anti-nuclear demonstration the day after the accident.
In the United Kingdom, public acceptance is important to the feasibility of nuclear new build and public support for nuclear power appears to have dropped as a result of Fukushima. However, it may still be robust enough to allow the building of new power plants, although probably on a delayed schedule. Other European states, including Switzerland, Italy and Poland, have all announced they will suspend or rethink their plans to build new reactors.
In many states outside Western Europe and North America, public opinion is much less important in influencing energy policy. Although Indian prime minister Manmohan Singh announced a safety review of all his country's nuclear reactors in the wake of Fukushima, and China suspended the construction of new plants, most analysts expect nuclear demand to remain strong in these two countries, even if plans are ultimately implemented in a modified form.
Another key determinant for the future will be the availability of finance for new plants. The accident may have relatively little effect on the plans of countries which, like the United Arab Emirates, are planning to fund construction from the state's coffers. But, where private financing is the chosen mechanism, Fukushima could put plans for new nuclear plants on ice. Even before the accident, the capital markets viewed nuclear energy as a risky investment, particularly in the United States. On 19 April, for example, NRG Energy of the US announced the suspension of plans to build two new units in southern Texas because it could not 'justify to [its] shareholders any further financial participation in the development'. In the United States there are few concrete plans for new nuclear reactors - in spite of the offer of loan guarantees by the US government-because of insufficient financing. Fukushima may make raising capital even harder.
