Nuclear Thread - 4

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[url="http://news.yahoo.com/s/nm/20110312/wl_nm/us_japan_quake_experts"]Factbox: Experts on explosion at Japan nuclear plant[/url]

– 2 hrs 26 mins ago

(Reuters) – Radiation was leaking from an unstable nuclear reactor north of Tokyo on Saturday, the Japanese government said, after an explosion blew the roof off the facility following a massive earthquake.

The development has led to fears of a disastrous meltdown. Here are comments from experts about what might have happened.

PROF PADDY REGAN, PROFESSOR OF NUCLEAR PHYSICS AT THE

UNIVERSITY OF SURREY

"It looks as if the coolant pumps had initially stopped working. They shut down automatically when the reactor shuts down, but there is a backup system running off a diesel generator -- it looks as though that's the bit that failed.

"As a result there is no way of pumping heat out of the reactor, so it has to cool naturally. If the reactor gets too hot, in principle this means the fuel rods can melt - but it looks unlikely this has happened to any great extent in this case.

"To reduce the pressure, you would have to release some steam into the atmosphere from the system. In that steam, there will be small but measurable amounts of radioactive nitrogen - nitrogen 16 (produced when neutrons hit water). This remains radioactive for only about 5 seconds, after which it decays to natural oxygen.

"But if any of the fuel rods have been compromised, there would be evidence of a small amount of other radioisotopes in the atmosphere called fission fragments (radio-caesium and radio-iodine).

"The amount that you measure would tell you to what degree the fuel rods have been compromised. Scientists in Japan should be able to establish this very quickly using gamma ray spectroscopy as the isotopes have characteristic decay signatures. Current reports seem consistent with a small leak to relieve pressure."

"But we still need to establish the cause and exact location of the explosion, which is a separate issue. So far it looks like it's not the reactor core that's affected which would be good news.

"We must remember that there are 55 reactors in Japan and this was a huge earthquake, and as a test of the resilience and robustness of nuclear plants it seems they have withstood the effects very well."