FUKUSHIMA DAIICHI NUCLEAR PLANT

Q.WHAT CAUSED THE FUEL TO OVERHEAT?
A.The failure of the electricity supply for the cooling pumps. At the first sign of a tremor, the reactor started to shut down by inserting the control rods and the reactor ceased to produce power. Even after the reactor has shut down, a nuclear power station still produces about 5-10 per cent of its heat. When the cooling water stops flowing the fuel dries out and the temperature rises extremely.

Q. WHAT CAUSED THE EXPLOSION?
A.It is possible that the nuclear fuel, once it has become uncovered, became sufficiently hot to separate the water and steam that is around into the separate components of oxygen and hydrogen. This mixture of hydrogen and oxygen exploded.

Q. HOW DOES THIS COMPARE TO PREVIOUS DISASTERS?
A.This scenario is far closer to the Three Mile Island accident in 1979, Pennsylvania –which did not cause any cases of cancer – than to Chernobyl in 1986. There is a containment holding the overheated core, which in the Three Mile Island case saved the day. At Chernobyl, the reactor did not have a containment, exposing the bare core to the atmosphere.

Q. WHAT ARE THE RISKS OF EXPOSURE TO THE RADIOACTIVE CORE?
A.We should take comfort from the fact that the Japanese authorities, are saying that the containment that sits around the reactor, which is a very strong structure of concrete and steel, is holding. That is important to stress.

• Answers from Dr William Nuttall, of Cambridge Judge Business School, a lecturer in technology policy and a lead academic at the Cambridge Nuclear Energy Centre