Like any nuclear reactor, thorium reactors will be hot and radioactive, necessitating shielding. The amount of radioactivity scales with the size of the plant. It so happens that thorium itself is an excellent radiation shield, but lead and depleted uranium are also suitable.
Smaller plants (100 megawatts), such as the Department of Energy’s small, sealed, transportable, autonomous reactor (SSTAR) will be 15 meters tall, 3 meters wide and weigh 500 tonnes, using only a few cm of shielding.
Because thorium reactors present no proliferation risk, and because they solve the safety problems associated with earlier reactors, they will be able to use reasonable rather than obsessive standards for security and reliability. If we can reach the $145-in-1971-dollars/kW milestone experienced by Commonwealth Edison in 1971, we can decrease costs for a 1-gigawatt plant to at most $780 million, rather than the $1,100 million to build such a plant today. In fact, you might be able to go as low as $220 million or below, if 80% of reactor costs truly are attributable to expensive anti-meltdown measures. A thorium reactor does not, in fact, need a containment wall. Putting the reactor vessel in a standard industrial building is sufficient.
Because thorium reactors will make nuclear reactors more decentralized. Because of no risk of proliferation or meltdown, thorium reactors can be made of almost any size. A 500 ton, 100MW SSTAR-sized thorium reactor could fit in a large industrial room, require little maintenance, and only cost $25 million. A hypothetical 5 ton, truck-sized 1 MW thorium reactor might run for only $250,000 but would generate enough electricity for 1,000 people for the duration of its operating lifetime, using only 20 kg of thorium fuel per year, running almost automatically, and requiring safety checks as infrequently as once a year. That would be as little as $200/year after capital costs are paid off, for a thousand-persons worth of electricity! An annual visit by a safety inspector might add another $200 to the bill. A town of 1,000 could pool $250K for the reactor at the cost of $250 each, then pay $400/year collectively, or $0.40/year each for fuel and maintenance. These reactors could be built by the thousands, further driving down manufacturing costs.
