It is publicly known that even reactor-grade plutonium can be made into a bomb if done carefully. By avoiding plutonium altogether, thorium cycles are superior in this regard. Besides avoiding plutonium, Thorium has additional self-protection from the hard gamma rays emitted due to U as discussed above. This makes stealing Thorium based fuels more challenging. Also, the heat from these gammas makes weapon fabrication difficult, as it is hard to keep the weapon pit from melting due to its own heat.
Note, however, that the gammas come from the decay chain of U, not from U itself. This means that the contaminants could be chemically separated and the material would be much easier to work with. U has a 70 year half-life so it takes a long time for these gammas to come back. Then, it will decay directly to pure U By this challenging route, one could obtain weapons material. But Pa has a 27 day half-life, so once the waste is safe for a few times this, weapons are out of the question. So concerns over people stealing spent fuel are largely reduced by Th, but the possibility of the owner of a Th-U reactor obtaining bomb material is not.
Update: See our full page on Molten Salt Reactors for more info. In these, fuel is not cast into pellets, but is rather dissolved in a vat of liquid salt. The chain reaction heats the salt, which naturally convects through a heat exchanger to bring the heat out to a turbine and make electricity.
The U does not just sit idly by, however; it transmutes into other fissile elements. When an atom of U absorbs a neutron, it transmutes into short-lived U, which rapidly decays into neptunium and then into plutonium, that lovely, weaponizable byproduct. When the U content burns down to 0. This waste fuel is highly radioactive and the culprits — these high-mass isotopes — have half-lives of many thousands of years. As such, the waste has to be housed for up to 10, years, cloistered from the environment and from anyone who might want to get at the plutonium for nefarious reasons.
Thorium's advantages start from the moment it is mined and purified, in that all but a trace of naturally occurring thorium is Th, the isotope useful in nuclear reactors. Then there's the safety side of thorium reactions. Unlike U, thorium is not fissile. That means no matter how many thorium nuclei you pack together, they will not on their own start splitting apart and exploding. If you want to make thorium nuclei split apart, though, it's easy: you simply start throwing neutrons at them.
Then, when you need the reaction to stop, simply turn off the source of neutrons and the whole process shuts down, simple as pie. Here's how it works. When Th absorbs a neutron it becomes Th, which is unstable and decays into protactinium and then into U That's the same uranium isotope we use in reactors now as a nuclear fuel, the one that is fissile all on its own.
Thankfully, it is also relatively long lived, which means at this point in the cycle the irradiated fuel can be unloaded from the reactor and the U separated from the remaining thorium. The uranium is then fed into another reactor all on its own, to generate energy.
The U does its thing, splitting apart and releasing high-energy neutrons. But there isn't a pile of U sitting by. Remember, with uranium reactors it's the U, turned into U by absorbing some of those high-flying neutrons, that produces all the highly radioactive waste products. With thorium, the U is isolated and the result is far fewer highly radioactive, long-lived byproducts. Thorium nuclear waste only stays radioactive for years, instead of 10,, and there is 1, to 10, times less of it to start with.
And yet the nuclear industry itself is also sceptical, with none of the big players backing what should be — in PR terms and in a post-Fukushima world — its radioactive holy grail: safe reactors producing more energy for less and cheaper fuel.
In fact, a National Nuclear Laboratory NNL report PDF concluded the thorium fuel cycle 'does not currently have a role to play in the UK context [and] is likely to have only a limited role internationally for some years ahead' — in short, it concluded, the claims for thorium were 'overstated'. But even were its commercial viability established, given 's soaring greenhouse gas levels, thorium is one magic bullet that is years off target.
Those who support renewables say they will have come so far in cost and efficiency terms by the time the technology is perfected and upscaled that thorium reactors will already be uneconomic. Indeed, if renewables had a fraction of nuclear's current subsidies they could already be light years ahead. All other issues aside, thorium is still nuclear energy, say environmentalists, its reactors disgorging the same toxic byproducts and fissile waste with the same millennial half-lives.
Oliver Tickell, author of Kyoto2, says the fission materials produced from thorium are of a different spectrum to those from uranium, but 'include many dangerous-to-health alpha and beta emitters'. Tickell says thorium reactors would not reduce the volume of waste from uranium reactors.
Looked at in these terms, it's a way of multiplying the volume of radioactive waste humanity can create several times over. Nuclear New Projects Reactors. France to build new nuclear reactors to meet climate goals. Rolls-Royce secures funding for SMR nuclear technology. The role of small modular nuclear reactors in meeting climate goals.
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