16 March 2011
Thoughts on the Disaster in Japan

I've been following the harrowing news this week about the earthquake, tsunami and nuclear accident in Japan, triggered by the 9.0 magnitude earthquake which struck last Friday. I can't even begin to imagine how devastating it must be for those caught up in the disaster, particularly those who have lost loved ones or had their homes destroyed.

A series of photographs published by the New York Times really brought home the extent of the damage.

One question which has been bugging me regarding the Fukushima Daiichi nuclear power plant, is why the reactors are still getting hot, even though they were shut down within minutes of the earthquake?  When learning about nuclear power many years ago at school, I was taught that inserting the control rods stopped all nuclear reactions (which generate the heat to boil the water to drive the turbines to produce electricity).  Why then, are the authorities struggling to cool the reactor cores days after the earthquake?  This answer from Stack Exchange explains things nicely.  During normal operations, the uranium fuel produces other radioactive isotopes.  When the control rods are inserted, the uranium stops reacting, but these other secondary isotopes continue to undergo nuclear reactions themselves, creating heat.  Even with the rods inserted, the reactor continues to produce heat equivalent to about 3% of its full power level.  With a 460MW reactor such as those at Fukushima, this means that enough heat is still generated shortly after shutdown to boil 42 litres of water per second (from room temperature)!  That's still an awful lot of heat, and explains why massive cooling is still required following a shutdown.

I'm sure that everyone is quite capable of working out how they can donate to the relief efforts, but if not, here are a couple of links:

In the UK: please donate via or by phoning 08450 53 53 53.  Please note that fraudsters are claiming to act on behalf of the Red Cross, so please only donate via the official Red Cross website, and do not reply to emails soliciting donations.

In the US: you can donate via the American Red Cross at  Alternatively, you can donate $10 by texting REDCROSS to 90999 from your phone.

Please give what you can.