Pramod Dibble's Blog

Nuclear Power If it was a Nintendo game, it’d be called “Smash ‘em Smoosh ‘em”

22 Jul 2014 | by Pramod Dibble
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                I am a nuclear power enthusiast. In fact, if I ever sell an app to Facebook, or find out I’m the long-lost heir apparent of the King of Saudi Arabia, I’m almost certainly going to start a company that makes all kinds of nuclear reactors. Despite the scientific challenges and PR problems associated with nuclear power, I do believe it represents an integral part of a long-term, environmentally sustainable solution to growing energy consumption.

                Fission technology is the one with which most of us are familiar. All of the commercial reactors in operation are fission reactors of some type or another, and most of those are regular, light-water reactors using solid fuel. These reactors generate energy by smashing neutrons into very heavy, energy-rich molecules and harnessing the resulting kinetic energy as heat, much the same as a coal or natural gas power plant gathers heat from burning fuel. Radioactive decay and gamma radiation from the fission process contributes to the heat extracted from the process. These heavy molecules are usually uranium, which contains about 3 million times more energy than coal by volume. 

                The fission technology that interests me is breeder reactors, which generate more fissile material (fuel) than they consume. A conventional light water reactor (LWR) extracts less than 1% of the energy in uranium, while breeder reactors extract 100 times more. Breeder reactors accomplish this by dramatically increasing the degree to which neutrons knocked off fuel get picked up by other, fertile particles in the reactor, thus generating more fissile material to be used in the reaction. Since power output efficiency is roughly 100 times higher in a breeder reactor than in a LWR, they require about 100 times less fuel to generate the same power. Defining this input/output relationship, there appears to be sufficient fuel in the planet’s oceans to satisfy global energy demand for some 5 million years.

                Breeder reactors have the added advantage of being able to consume plutonium, the extremely hazardous molecule which is used to make nuclear weapons. In storage, plutonium takes roughly 24,000 years to decay to safe levels, while a breeder reactor is able to use it productively. This eliminates or alleviates many of the storage problems associated with radioactive waste from nuclear power plants, and lets these reactors actually use waste from older power plants as fuel. Additionally, breeder reactors are meltdown resistant; under the circumstances that cause catastrophic failure in a conventional LWR, the breeder reactor begins “leaking” neutrons, halting the chain reaction.

                Probably my favorite type of breeding reactor is the LFTR (liquid fluoride thorium reactor). These use mined thorium rather than uranium, which means that the breeding reaction produces Uranium 233 instead of hazardous plutonium which can be weapon-ized. LFTRs operate at atmospheric pressure, which allows their containment structures to be roughly 1/600th, the size (and cost!) of a LWR containment vessel, and achieve about 10% better heat to energy conversion than a LWR. LFTRs utilize a passive cooling system to control reactor failure; if the reactor loses power, the fuel simply drains into a safety vessel in which it is cooled. Because they use thorium instead of uranium, LFTR waste radiotoxicity is about 10,000 times less than that of a uranium/plutonium reactor, and they are able to consume nuclear waste in the startup and operation processes. Additionally, thorium is about 4 times as abundant in the Earth’s crust as Uranium, making fuel procurement far less costly.

                All of these fission reactors are practical given current technology, though many have yet to be proven commercially viable. They stand in contrast to nuclear fusion reactors, which are theoretically possible, but require a number of scientific breakthroughs which push their feasibility into the long term timeframe for even a proof-of-concept. Fusion is desirable over fission for a number of reasons. First and perhaps most importantly, the fuel is abundant. Fusion reactions have been demonstrated using deuterium molecules, hydrogen with an extra neutron. This fuel is naturally occurring, can be fabricated, and is non-radioactive. A fusion reactor accelerates the deuterium molecules along a magnetically confined loop, in a near vacuum, until their strong nuclear force pulling them together overcomes the electrostatic force pushing them apart, fusing them in a nuclear reaction. This reaction occurs at above 100 million degrees Celsius. It is possible to use any particle in this type of reaction, but the scientific challenges associated with fusing heavier molecules are probably outside the scope of our lifetimes.

                Fusion does not produce radioactive waste. The only radioactive element in a deuterium reactor would be tritium, which is both produced and consumed within the reactor itself, requiring no transportation or post-use storage. Even the reactor core itself would return to safe radiation levels after less than 100 years, a tiny fraction of the time it takes fission by-products to decay. There are no negative environmental impacts from fusion power whatsoever, the by-product of a deuterium reaction being helium. A fusion reactor is meltdown-proof, as any breach to the magnetic confinement field will terminate the reaction automatically (though it would cause near total destruction of the reactor as 100-million degree plasma leaves the confinement field).

                The first large-scale fusion reactor is currently under construction in France. The ITER (International Thermonuclear Experimental Reactor) proposes to demonstrate the scientific and commercial viability of fusion power for electricity generation. This project is sponsored by 7 nations, and is estimated to cost upwards of 20 billion dollars. This estimate is likely to be low, as the project has run into several complications already, and isn’t scheduled to begin operations until 2027, an 11-year delay. While this is clearly not optimal for either the project itself, or for popular perception of fusion for electricity, demonstrating a brand-new highly-complex technology like nuclear fusion is extremely difficult, and if successful, would certainly be counted amongst the most significant technological advancements our species has achieved. It would also fundamentally alter global energy markets.

                Nuclear energy, coupled with renewables like wind and solar, is the answer to meeting the growing global demand for energy in an environmentally sustainable, economically feasible manner. Fast-breeding fission reactors are already part of the grid, and if the ITER or another fusion project is successful, electricity generated by fusion will become main-stream in our lifetimes. Though coal scrubbers and fracked gas have a solid hold on the short-term, these technologies will become totally obsolete over the coming century, with nuclear and renewables coming to dominate the growing grid.