"The NHS will last as long as there are folk left with the faith to fight for it"
Aneurin Bevan

Friday, 18 March 2011

The 'N' and 'F' words

Nuclear, fission.

I bet you've started to feel a little unwell, just reading those words.

The problem is that because the most destructive weapons man has used (so far) have been nuclear and used a fission reaction people associate these two words with death.

In the mid-80s I started a physics degree at Nottingham and in the first year lab one of the experiments we had to do involved nuclear magnetic resonance. In short, each atom has a nucleus and you can make this vibrate with radio waves from an external source. As the nucleus vibrates it will also give off radio waves. If you do this in a magnetic field you can 'tune' the nucleus to produce radio waves of a particular frequency associated with the magnetic field strength and the atom's nucleus. This is a purely electro-magnetic technique: it does not use radioactivity, indeed, NMR works with non-radioactive materials.

The reason why undergraduate students had to do this experiment was because the department had a nuclear magnetic resonance research group. Three years later I started as a research student in the same department studying for my PhD in the semiconductor group. The NMR group had morphed into the MRI group. I asked the research students what had happened. The explanation was simple: they were developing techniques to scan people with nuclear magnetic resonance (for his work in this area the head of the group was made an FRS, then knighted and finally awarded a Nobel prize), but found that patients were reluctant to go near a machine with the 'n'-word in its name. So, like other groups studying the same technique, they dropped the 'n'-word and called it Magnetic Resonance Imaging.

The 'n--word is powerful. But so is the 'f'-word: fission.

Earlier this week, when the Fukushima spent rod pool was running dry the BBC "science" editor* quoted nuclear experts saying that without the moderating effects of the water there would be a fission chain reaction, and then he said, darkly, that this could spread nuclear materials many miles away from the power station site. I could not quite understand how the fission reaction would do this, after all, it happens all the time in the reactor core and not over the locality. Then I realised that the journalist was associating the fission chain reaction with nuclear bombs. He thought that a fission chain reaction in the spent rod pool was the same as the explosion that happens in a nuclear bomb. The 'f'-word has that effect on people.

[* that's an odd-job name if ever there is one: can he really be skilled in all aspects of every kind of science?]

Well, here's a clue for budding BBC science journalists: if it was that easy to create a nuclear bomb Iran would have had one years ago.

The 'f'-word and the 'n'-word are special, they make people invent new science.

Remember that the Fukushima reactors survived an M8.9 earthquake and a 5m tsunami. The cores remained contained even after these. The design also succeeded in that the control rods were placed between the reactor rods which stopped the fission reaction. "All" that had to be done now was to cool the core down from its operating temperature. The cooling system is normally powered by electricity generated by the power station, which had been shut down. The problem is that the tsunami also destroyed the backup diesel generators, so the operators flew in replacement generators . However, they found that they could not connect the generators to the pumps: they lacked a suitable connector.

So reflect on this: the failure at Fukushima is not in the reactor, it is not nuclear; the problem is electrical: they needed an electrical connector.

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