Thorium for Singapore

Discussing the future of energy in Singapore

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Home Myths and Misconceptions

Myths and Misconceptions

 

Question : It’s Nuclear whachamathingy! It will blow up, Singapore will sink and we are all gonna DIE!

 

Answer : Modern nuclear reactors, even the regular Light Water Reactors (LWR) have substantially improved safety with technological advances, catastrophic accidents are highly unlikely now, however they still run the risk of meltdown under certain conditions. HOWEVER, the LFTR is not just ANY nuclear reactor.  Because of it’s design and liquid fuel form factor, even if the core is breached and everything goes to heck, the LFTR will just passively release it’s liquid fuel into a holding tank and there it will solidify. In addition it does NOT use high pressure steam to drive its’ generators, no KABOOM there….sorry.

 

 


 

Question : Ok, so it won’t blow up, but it will leak radiation and we will have mutated rats!

 

Answer : The LFTR is a closed system reactor there are no emissions from the plant. Also it is small enough (even massive 1-10GW plants) to be built underground….so, no…no mutated flying rats, sorry.

In fact non-nuclear systems like coal spew out worse pollutants. The emissions from those contain arsenic, mercury, lead and a whole host of radioactive materials like uranium, thorium and radium dumped directly into the environment at levels 100 to 400 times the level of nuclear plants!

 

 


 

Question : It will produce radioactive waste! We will pollute the whole earth!

 

Answer : A liquid-fluoride thorium reactor (LFTR) makes ~0.08% of the waste per GW-yr of a regular LWR and other traditional nuclear power plants.

First, most of the mined thorium is eventually fissioned. In contrast, natural Uranium for a light water reactor (LWR) is only 0.71% fuel. So, it starts with a 1/99.28 waste ratio. Depleted uranium is long-lived radioactive waste, so it counts... However, honestly, the real environmental advantage at this step is the hundred-fold reduction of mining damage to human populations and biomes.

Next, most LFTRs run at 650C or hotter, so with a gas turbine, they run at ~50% efficiency, rather than ~35% for LWR's steam cycle. So the thermal waste ratio is 50/65 in favor of LFTR. (so (50*1)/(65*99.29) = 1/129)

Basically all of the fissioned fuel turns into radioactive waste. However, not all waste is the same. Transuranic wastes are those nasty, long-lived elements, thousands of years, etc. Fission products, in contrast, decay in a few hundred years. 

However, a LFTR can produce about 1/10 of the TRUs per Gw/yr. Here's how that works. The Thorium fuel cycle breeds Th232 into Pa233, which then decays to U233, a fission fuel. 

In the case of U233, further transmutations tend to produce useful nuclear fuels rather than transuranic wastes. When U233 absorbs a neutron, it either fissions or becomes U234. It has about a 10/1 fission to capture ratio. U234 doesn't fission well. It usually captures a neutron and becomes U235, an excellent fuel with a 6:1 fission/capture ratio. After this point, only 1.7% of the LFTR waste becomes transuranic. U236 is also not a good fuel, and absorbs a neutron. The main reaction product is Neptunium 237. (These are approximations. There are other reactions, but with small quantities.)

In LWR waste, somewhat less than 1/6 of the U235 becomes TRUs, so, the TRU waste ratio compared to a LFTR is about .16/.017. I'm not even counting the U238 that becomes plutonium in a LWR; after all, most of that is potential future fuel, and some is fissioned in place.

As it happens, most odd-numbered TRUs are nuclear fuels. In a LFTR, it's reasonably practical to just put the Np237 and other TRUs back into the salt. Something like this is also possible with LWR waste. Areva separates plutonium from LWR waste, and manufactures MOX fuel. 

However, the even-numbered TRUs (like Plutonium 238) build-up, because most aren't good nuclear fuels. Even these can be disposed of. They can be put into fast-neutron breeder reactors and fissioned by force. However, with LFTRs, society can get by with about 1/10 as many fast-breeder waste disposal reactors.


 


 

 

Question : I H@TES teh Nu©L3aR!

 

Answer : Instead of calling yourself 'Anti-Nuclear' why not call yourself 'Pro-Thorium'? Other than that, I can't help ya there.... sorry.