On occasion, people write to Atomic Insights with questions whose answers might be beneficial to a number of other people. We will be sharing some of those questions and responses with you in the Ask Atomic section of the publication.
John Mahler holds an almost invisible, but extremely important job. He is in charge of the physical plant operations for a major California hospital. He and his team of workers keep the water running, the electricity flowing, and the air at a comfortable temperature. He has a detailed knowledge of practical thermodynamics and energy that is rarely approached by professors with a raft of advanced degrees and titles.
As a hobby, he designs steam powered automobiles.
I have a question relating to a statement in your page concerning the replacement of spent fuel and the containment of spent fuel pellets. It is probably from so great an uninformed level of comprehension, that it should be obvious to me. However, it is not obvious to me at all. The question is: “Why isn’t the residual thermal energy in the fuel pellets used constructively, instead of being contained?”
I remember, in the late 1950’s and early 1960’s that the French, who used nuclear reactors extensively at that time, removed spend fuel and mixed it with a high temperature silica, or glass substrate. The material remained thermally elevated for an estimated 200 years. The temperature was supposed to be in the range of 400 degrees Fahrenheit. They heated brine with the material and used a piping system to remove ice and snow from their roadways in winter. I do not know if that is currently being done.
From the Atomic Engines page: “After providing power for several years, the core materials will be replaced. The material that is removed will be stored in a licensed dry container system until the valuable byproducts of fission can be recycled. “
John Mahler comments: I know this also sounds uninformed. My further question is : “Can the public obtain any of the spent fuel to use experimentally? If it were bound in glass and the experimenter were licensed and credentialed as a knowledgeable experimenter, I think new lower temperature applications could be found for this residual energy, not suitable for reactor use. When the thermal temperature was too low for post reactor use, the pellets could be recycled
I am a steam car developer. I have long dreamed of using an energy source such as this. This could be the answer to the 21st Century need for permanent energy sources. It is non polluting if properly handled. Gasoline is far more dangerous today, because of its “taken for granted” handling by the public. I am sure that safe containment could be constructed that would shield the world from radiation in the event of mishap such as collision. The remaining oil supplies of the world would last indefinitely, if refined only for lubricants, resins and solvents. The pollution the world knows today would be eliminated by use of such “post reactor spent pellet” fueled low pressure boilers. If used in a cascade design, the make up water the engine would consume would not be irradiated to any kind of dangerous level. The brine cooling the spent fuel pellets would be totally contained in the containment vessel. I don’t believe the containment vessel would be as large as a conventional automobile engine. The power to weight ratio would be insignificant except for designers to engineer safe transportation with derivability and traffic handling characteristics.
If wide spread use of such pellets became possible, the price of refueling would be perhaps about the same cost as today’s lead acid automobile storage batteries. I suspect that motoring sized, post reactor fuel, steam generators would require refueling every 4 to 5 years. If that is the case, the generator could be replaced at competent facilities about as affordably as present automobile repairmen presently price repairs.
Also, if a vehicle were to be replaced every 4 to 5 years, the generator price could be prorated for the used car purchaser. Or, the vehicle could be turned in for a new car every 4 to 5 years on a lease basis. This would be preferable if affordable. This would remove poorly maintained vehicles from our roadways and keep the infrastructure in place which would manufacture the rest of the vehicle.
So, though these questions appear to be uninformed and without reasonable assumption, I hope I have convinced you that I have spent a great deal of time considering these issues. And, that you will be moved to answer me on these points.
Just knowing if the spent fuel has the thermal properties I think it has would be a big gain in my knowledge. The cost of procurement, the availability and standards of experimentation, the equipment and competency of the individuals, that would be required, would also help me decide to pursue this, or drop it. I look forward to your answer.
You have asked some key questions. You are being far too humble by calling yourself uniformed. You may not understand nuclear policies (neither do I), but your technical knowledge of heat sources is obviously extensive. You have also reminded me how easily humans can get into a thinking rut, where their problem solving ideas are limited to what has been done before.
Until your letter arrived, I never really thought about using isotope fuel for anything other than a conventional RTG with a solid state heat conversion system. (For a list of articles on RTGs visit the Nuclear Battery section of our Topical Index.) Active heat conversion systems never crossed my mind even though I was well aware of the extremely low efficiency of the solid state method and the limits that inefficiency imposes on isotope power supplies.
All radioactive materials release energy, and most of that energy can be easily be converted into heat or light by surrounding the material with shielding materials. The surface of a shielded material would get hot. The temperature it reaches depends on several variables including: the isotopes involved, the quantity of material, shield material characteristics, and the heat removal process. It is quite possible to imagine filling a container with a measured quantity of these shielded isotope fuel elements to make an easily controlled heat source. There are an infinite number of possible ways to use that heat; steam engines might be one of the best. A tight steam system operating at appropriate temperatures can easily achieve 30% thermal efficiency; five times as high as conventional solid state RTGs.
Your letter also pointed to the reason that there are no such devices in use today. An irrational set of laws makes it legally impossible for a thinker like you or me to obtain spent fuel for experimentation. The US Congress has declared that the federal government is the monopoly supplier of the service of disposing of spent nuclear fuel. There is essentially only one possible disposal method under study by government functionaries; they view the potentially valuable material as a waste product that requires an enormously expensive final repository.
Until the government is ready receive the material, the utilities that generated power from the fuel rods must carefully keep track of all fuel materials their plant has used. Woe be unto the utility that cannot do so. Northeast Utilities, the former owner of the Millstone reactors recently spent 9 million dollars in a lengthy investigation to find out exactly what happened to two individual rods that somehow got separated from their bundle. They finally narrowed down the location of the rods to one of several very safe locations, but there are still people that are not satisfied. The fact that the rods never hurt anyone seems immaterial to the regulators.
In my cynical heart of hearts, I blame the current restrictions on people that will do anything in their power to choke off atomic developments. These people often have a vested interest; creative use of atomic fuel can render chemical fuel supplies worthless. It is that much better as measured by cleanliness, concentration, and value. Just imagine how the executives of Exxon-Mobile or the King of Saudi Arabia would feel if as you said “the oil supplies of the world would last indefinitely, if refined only for lubricants, resins and solvents.” They would suddenly become quite poverty stricken.