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 California. He has designed an engine that he calls an “internal” rotary engine, rather like the kind of Wankel engine that has been around since the 1950s. Instead of pistons going up and down, the engine has a rotor that rotates around a crank shaft.
The rotary engine that Adams envisions looks diagrammatically very like a schematic of the rotatory engine that Mazda introduced to varying degrees of success in its cars in the 1970s.
It works like this: A small amount of gasified “nanofuel,” which contains nuclear material mixed with hydrogen, is ignited by a neutron source to set up a controlled fission reaction, creating heat and propelling the rotor forward and driving the crank shaft. The fuel can be derived from the transuranic parts of spent conventional nuclear fuel or can be created separately.
A company dedicated to energy innovation, Global Energy Research Associates (GERA), is working on design and raising money. The Department of Energy has held back.
Adams, 45, explains his engine this way, “Much like the way your car converts chemical energy into mechanical work, our engine converts nuclear energy directly and safely into useful mechanical work. This eliminates a lot of expensive reactor equipment and paves the way for low-cost nuclear power plants.”
He says his engine would produce 340 megawatts of electric power, if deployed in a combined-cycle configuration. The radioactive byproducts are only cesium and strontium with half-lives of about 30 years — a great improvement on the nuclear waste from conventional reactors. It would be a high-level waste burner as well as an energy source. Tests to prototype engine components are underway at the Idaho National Laboratory in Idaho Falls.
The nuclear engine would shut itself down automatically if things went wrong. A meltdown accident of the kind seen at Three Mile Island and Fukushima is not possible, according to GERA, which Adams formed to demonstrate and market the engine.
One must have, as one must with all futuristic, high-technology designs, a healthy skepticism and a lot of excitement.