Thorium Reactor

SSTAR (small, sealed, transportable, autonomous reactor

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.

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