nuclear energy to go

Thorium | Lawrence Livermore, Los Alamos, and Argonne national laboratories are designing a self-contained nuclear reactor with tamper-resistant features. Called SSTAR (small, sealed, transportable, autonomous reactor), this next-generation reactor will produce 10 to 100 megawatts electric and can be safely transported on ship or by a heavy-haul transport truck. In this schematic of one conceptual design being considered, the reactor is enclosed in a transportation cask. SSTAR

Thorium reactors would be cheap. The primary cost in nuclear reactors traditionally is the huge safety requirements. Regarding meltdown in a thorium reactor, Rubbia writes, “Both the EA and MF can be effectively protected against military diversions and exhibit an extreme robustness against any conceivable accident, always with benign consequences. In particular the [beta]-decay heat is comparable in both cases and such that it can be passively dissipated in the environment, thus eliminating the risks of “melt-down”. Thorium reactors can breed uranium-233, which can theoretically be used for nuclear weapons. However, denaturing thorium with its isotope, ionium, eliminates the proliferation threat.

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.

Smaller reactors make power generation convenient in two ways: decreasing staffing costs by dropping them close to zero, and eliminating the bulky infrastructure required for larger plants. For this reason, it may be more likely that we see the construction of a million $40,000, 100 kW plants than 400 $300 million, 1GW plants. 100 kW plants would require minimal shielding and could be installed in private homes without fear of radiation poisoning. These small plants could be shielded so well that the level of radiation outside the shield is barely greater than the ambient level of radiation from traces of uranium in the environment. The only operating costs would be periodic safety checks, flouride salts, and thorium fuel. For a $40,000 reactor, and $1,000/year in operating costs, you get enough electricity for 100 people, which is enough to accomplish all sorts of antics, like running thousands of desktop nanofactories non-stop.