Startup Deep Fission has found a new way to solve the economic and safety problems of nuclear power that is novel, to say the least. The idea is to build a reactor less than 76 centimeters wide and put it in a borehole 1.6 kilometers deep.
With its promise of unlimited energy through the decomposition of matter, nuclear energy was long considered a utopian promise for humanity. However, economic and safety concerns as well as political resistance slowed its development – especially in the countries that developed this technology.
The safety and economic factors are closely linked because the high cost of building nuclear power plants has little to do with the nuclear technology itself. Nuclear fuel, even when all processing costs are taken into account, costs only about $1,663 per kilogram (2.2 pounds). Because nuclear fuel has such an incredible energy density, that’s about 0.46 cents/kWh – and fuel costs continue to fall as the technology becomes more efficient.
The real cost comes from the massive construction work required to contain the nuclear reactor and protect the outside world in the event of a catastrophic accident. The reactor pressure vessel can be up to 2.4m thick made of stainless steel and the reinforced concrete containment shell can be up to 2m thick. Add in foundations, support equipment, pressurizers and cooling systems and the costs add up before any licensing fees are added up.
Deep nuclear fission
What Deep Fission is trying to do may seem crazy, but there is a certain elegance to the proposal. The idea is to build a small reactor based on a conventional pressurized water reactor (PWR) that fits into the borehole of a drilling rig. Like a PWR, the Deep Fission reactor would run at a pressure of 160 atmospheres and a temperature of 315 °C (600 °F).
The clever part is to simplify the design considerably and avoid the extremely expensive civil engineering work by lowering the reactor into a borehole 1 mile deep. A pair of pipes would be attached. One would carry water down and another to bring steam back from the reactor’s steam generator.
The result is a small reactor that uses the same type of fuel and many of the same components as a pressurized water reactor, but has almost no moving parts aside from the remotely operated control rods. Since the column of water is a mile high, it would pressurize the reactor by its weight alone, just as if it were a mile below sea level. So a pressurizer would not be needed and the cooling system would be completely passive.
Also, because the well is encased in solid rock deep below the water table, no containment system is required. If things get really bad, fill the well and plug it.
According to the company, if the reactor needs to be checked or serviced, it can be raised to the surface by cables in about one to two hours. The reactor is also designed to be self-limiting, so the nuclear reaction is automatically dampened if it overheats.
The concept still needs a lot of development, but Deep Fission has already begun the pre-application and application review process with the Department of Energy to discuss its plan for developing the system and finding the best geological location for a pilot plant.
If successful, this could give the term “geothermal energy” a whole new meaning.
Source: Deep Fission
