What happened in Japan?

When nuclear plants are shut down, there is still a lot of heat to be dispersed for many hours afterwards. Normally this is easily dealt with by the cooling system pumps, but if grid electricity supplies to the pumps are interrupted, as happened in Japan on March 11th after the 8.9 magnitude earthquake, then emergency on-site backup generators start up.

Most of Japans nuclear plants successfully followed this pattern, but the plants at Fukushima 150 miles or so north of Tokyo were unfortunate in that the subsequent tsunami damaged the emergency generators, which went off-line.

Temperatures and pressures in one of the reactor cores rose, and there was a risk of a catastrophic fuel meltdown.   Local evacuation plans were initiated as a precaution. Mobile generators were hastily brought on site to maintain cooling, and some gasses were vented to reduce pressure, but on March 12^th a hydrogen gas explosion occurred, demolishing parts of the outer shell of the reactor building.

A similar fate engulfed a second reactor on the site, with an explosion there on March 14^th, and, as I write, the third reactor there is facing a possible full or partial  meltdown, with fuel rods said to be exposed.

Fortunately in each case so far, the reactor core containments have remained intact, and only relatively small, but not trivial, amounts of radioactive material seem to have escaped, although radiation levels outside the plant were said at one point to be above permitted levels.  Cooling operations continue, pumping in sea waster mixed with boron, and hopefully will successfully avoid further problems.

The immediate impacts are still unclear- and it is still an ongoing situation. But in addition to at least one death and some injuries from the first explosion, there have been reports that 160 people had been contaminated by radiation. 200,000 or so people were evacuated from a 20km zone around the plants and many evacuees are being monitored for contamination.

It can’t happen here

The ostensible cause of the Japanese nuclear accident was the earthquake and tsunami.  Surely that’s a unique event? Japan is certainly more prone to major earthquakes than most places.  The 7 reactor  Kashiwazaki-Kariwa complex in central Japan, was hit by a Richter scale 6.8 earthquake in July 2007, which fortunately only led to a relatively small  radioactive leak into the sea. But Japans Citizen’s Nuclear Information Center commented. ‘Japan is simply too quake bound to operate nuclear plants.’

There are reactors near fault lines in other places around the world e,g. in California, and even in  the UK- there was recently a small quake near the Sellafield nuclear facility in Cumbria, an area being considered for  Geological Repository for nuclear waste.

However, you don’t need an earthquake or tsunami to create a similar situation to that at Fukushima, as was demonstrated in Sweden in 2006 when a ‘common failure mode’ breakdown occurred with the emergency cooling system when grid power was cut off at the Forsmark nuclear plant. Fortunately a disaster was averted.

Major nuclear accidents are seen as potentially high impact but low probability events, and perhaps therefore as disproportionately expensive to avoid. Most of Japans reactors are only designed to withstand quakes of 6.5 magnitude.  A proposal some years ago to raise the quake proofing design standard for nuclear plants in Japan to magnitude 7.1 level was shelved because of the high costs.

Climate change is likely to introduce a new set of problems. As in Japan, nuclear plants are often located on the coast to get access to cooling water. However rising sea levels and increasing storm surges could lead to sudden flooding episodes, much as with the tsunami.

Some risks can be avoided by better design. Pretty clearly emergency cooling systems ought to be protected from floods. So lessons will be learnt. Certainly nuclear plant designers try hard to predict and protect against possible problems, and, even given the cost limits, they do very well in most cases.

In reality though nothing can be 100% safe, despite this being one area where we would like to think it can be. We nevertheless continue to hope that we can avoid or limit errors or failures, human or technical.  However, nuclear technology is unforgiving, and, Nature often shows us the error of our ways, as we have just seen.  And it may not only be malevolent nature we have to worry about. If you also add in the potential for terrorists action against nuclear facilities, including nuclear waste stores and shipments, then the risks begin to look even more worrying- and far from remote.

Do we need to face them? In the short term there seems likely to be a ‘dash for gas’- fuelled by the discovery of shale gas reserves.  But that’s no long-term solution to climate change and it has its own health and safety problems.  Long-term there is no climate friendly alternative we know of at present to a shift to renewable energy- reserves of uranium and thorium on this planet are inevitably finite, and using them will leave us with radioactive waste to deal with for many centuries after all the nuclear fuel has be exhausted. Some look to nuclear fusion as a long-term solution, but that is decades away and uncertain, with its own set of safety issues. Why try to build a sun on the earth when we get enough energy from the sun in the sky to meet all our needs?    Why not switch to technologies, available now, which can use some of this free energy and have none of the safety, security or fuel depletion problems, costs and risks associated with nuclear power?