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Has the plutonium got out ?

So far it is clear that iodine-131 (some other related iodine / tellurium isotopes) and cesium has escaped from the stricken plant.

I have seen some suggestions on the web where it has been suggested that plutonium has escaped from the damaged plant. From what I have seen on the news so far I have seen no evidence to prove or disprove that plutonium has escaped from the plant. But I will stay that for an overheating reactor accident (LOCA) that plutonium if it was to escape would escape at a very late stage in the accident.

An accident in the used fuel ponds which scatters solid around might have the potential to release plutonium. It is hard to know what has happened to the fuel in the ponds which overheated.

Now I will admit that pure Pu-239 can be a living nightmare to detect and measure, it is an alpha emitter but it is a very weak gamma emitter. Now alpha contamination meters do exist in the world but they have some weaknesses

1. Price, they tend to be very expensive

2. Matrix, if the Pu is mixed into some forms then it will be hard to detect with the contamination meter. For example an aqeuous solution of Pu can not be measured with as much ease as a one atom thick layer on a stainless steel disc.

But there is some good news, in the case of reactor grade (and even bomb grade) plutonium which is more than a few years old then it is likely to contain some americium-241. This is a gamma emitter, while the gamma photons are quite low in energy they can be detected with gamma spectrometers and contamination meters.

The age of the plutonium is the time since it was last made pure by a chemical separation, due to the fact that the MOX fuel was made by BNFL, shipped to Japan and then stored for years before being used it is quite old so I would expect it to have some Am-241 in it.

The Pu which has been recently formed in the reactor might not contain any americium, this is Pu which is made by the neutron activation of uranium.

If the Pu is in a nuclear fuel which has recently been in a reactor which has been running (critical) then it will contain Zr-95, Ce-141 and Ce-144.

The zirconium forms a very high boiling point and high melting point solid in the nuclear fuel, the zirconium and the strontium/barium form a solid known as a perovskite (SrZrO3). Some plutonium can become part of the perovskite phase.

Even if we assume that the plutonium is stuck in the uranium dioxide in the form of a solid solution then this is in another high boiling point form which has a high melting point.

Then if the fuel is subject to some violent event like an explosion then the fuel fragments containing the plutonium which are flung out will also be likely to some of the perovskite which contains the Zr-95. Hence if a plutonium release occurs then it is likely that a zirconium release will also occur at the same time.

Likewise if some very super hot heating event was to occur which converted the plutonium in the fuel into a vapour or a plasma, then I would expect it to also make the zirconium boil into the gas phase along with the cerium. When the plutonium then condenses it will be likely to condense at the same time with the zirconium / cerium, as a result I would expect that these gamma emitting fission products will act as a tale tale for the plutonium.

So my advice is if you are worried about the plutonium escaping then look for zirconium-95, americium-241, cerium-141 and cerium-144.


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