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Monday, 7 September 2015

How ionising radiation gets into water

by Gordon Edwards, Ph.D.

(1) When nuclear fuel is used in a nuclear reactor or an atomic bomb, the atoms in the fuel are “split” (or “fissioned”) to produce energy.  The fission process is triggered by subatomic particles called neutrons.  In a nuclear reactor, when the neutrons are stopped, the fission process also stops.  This is called “shutting down the reactor.”

(2) But during the nuclear fission process, hundreds of new varieties of radioactive atoms are created that did not exist before.  These unwanted radioactive byproducts accumulate in the irradiated nuclear fuel — and they are, collectively, millions of times more radioactive than the original nuclear fuel.

(3) These newly created radioactive materials are classified as fission products, activation products, and transuranic elements.  Fission products — like iodine-131, cesium-137 and strontium-90 — are the broken pieces of atoms that have been split.  Activation products— like hydrogen-3 (“tritium”), carbon-14 and cobalt-60 — are the result of non-radioactive atoms being transformed into radioactive atoms after absorbing one or more stray neutrons.  Transuranic elements — like plutonium, neptunium, curium and americium — are created by transmutation after a massive uranium atom absorbs one or more neutrons to become an even more massive atom (hence “transuranic,” meaning “beyond uranium”).

(4) Because of these intensely radioactive byproducts, irradiated nuclear fuel continues to generate heat for years after the fission process has stopped.  This heat (“decay heat”) is caused by the ongoing atomic disintegration of the nuclear waste materials.  No one knows how to slow down or shut off the radioactive disintegration of these atoms, so the decay heat is literally unstoppable. But decay heat does gradually diminish over time, becoming much less intense after about 10 years.

(5) However, in the early years following a reactor shutdown, unless decay heat is continually removed as quickly as it is being produced, the temperature of the irradiated fuel can rise to dangerous levels — and radioactive gases, vapors and particles will be given off into the atmosphere at an unacceptable rate.

(6) The most common way to remove decay heat from irradiated fuel is to continually pour water on it. Tepco is doing this at the rate of about 400 tons a day. That water becomes contaminated with fission products, activation products and transuranic elements.  Since these waste materials are radiotoxic and harmful to all living things, the water cannot be released to the environment as long as it is contaminated.
(7) Besides the 400 tons of water used daily by Tepco to cool the melted cores of the three crippled reactors, another 400 tons of ground water is pouring into the damaged reactor buildings every day. This water is also becoming radioactively contaminated, so it too must be stored pending decontamination.

(8) Tepco is using an “Advanced Liquid Processing System” (ALPS) that is able to remove 62 different varieties of radioactive materials from the contaminated water — but the process is slow, removal is seldom 100 percent effective, and some varieties of radioactive materials are not removed at all.

(9) Tritium, for example, cannot be removed. Tritium is radioactive hydrogen, and when tritium atoms combine with oxygen atoms we get radioactive water molecules. No filtration system can remove the tritium from the water, because you can’t filter water from water. Released into the environment, tritium enters freely into all living things.

(10) Nuclear power is the ultimate example of the throwaway society. The irradiated fuel has to be sequestered from the environment of living things forever. The high-quality materials used to construct the core area of a nuclear reactor can never be recycled or reused but must be perpetually stored as radioactive waste.  Malfunctioning reactors cannot be completely shut off because the decay heat continues long after shutdown.  And efforts to cool a badly crippled reactor that has melted down result in enormous volumes of radioactively contaminated water that must be stored or dumped into the environment.  No wonder some have called nuclear power “the unforgiving technology.”……

Sources:
http://akiomatsumura.com/2013/06/experts-explain-effects-of-radioactive-water-at-fukushima.html
http://nuclear-news.net/2015/09/06/how-ionising-radiation-gets-into-water/
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