One of the frustrating and intriguing things about nuclear energy is that there is no standard design that is essential. For example, if you want to build a motorcar, you need to start with the idea that it will have four wheels; three is less effective, and two with gyroscopes is something else again. But when it comes to nuclear reactors, there are seemingly no limits. There are literally hundreds of reactor designs and possibilities. The moderator, which acts like a shock absorber to the reaction, varies too. It is nearly always water, but it can be gas, salt or a liquid metal. The end, though, is to use fission to produce power to turn a generator to make electricity or to propel a ship, like a submarine or aircraft carrier. So far, so good. But the limit is that the reactor only produces heat which then must be converted, through steam or some other medium, into shaft horsepower to make electricity or to drive the submarine. In my many years of writing about nuclear and chronicling its ups and downs, I have always been aware of the apparent weakness here: Huge, sophisticated power plants are only giant kettles; their purpose is to boil water, albeit very effectively. Periodically, scientists have tried to tackle this issue with thoughts on a direct conversion of heat to useful work in turning a drive shaft for whatever end use. There have been theoretical attempts to make the leap to the direct use of nuclear heat for work without a transfer agent. The great nuclear theorist Leo Szilard, according to his biographer William Lanouette, toyed with an idea but abandoned it. But there is a way, says Mark Adams, an MIT-educated physicist and former staff member at the Lawrence Livermore National Laboratory in Livermore, Calif. He has designed an engine which he calls an “internal” rotary engine, rather like the kind of Wankel engine which has been around since the 1950s. Instead of pistons going up and down, the engine has a rotor that rotates around a crank shaft.
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