Reactivating Mothballed Nuclear Reactors by Using Electrolysis
Much of the world’s nuclear capacity is either mothballed or running at reduced capacity because of market factors and regulations requiring utilities to take wind and solar power when it is available, as was discussed in a recent Bloomberg story.
Nuclear power plants do not work well with changing their operating conditions, because their reactor cores are massive. Cycling the power level up and down necessarily creates thermal stresses in the reactor core which reduces the useful life of the reactor. This damage costs far more than any savings on nuclear fuel. If we are going to have nuclear power as part of the mix it is highly desirable for those reactors to run continuously.
The traditional way to deal with this need to run constantly is to link a nuclear reactor with an energy storage device or a large grid with multiple smaller generators that can be dispatched as needed such as gas turbine generators. That energy storage is almost always pumped storage, which is far lower cost than batteries for example. Recently though, these pump storage facilities have been repurposed to even out fluctuations in renewable energy.
Changing the nuclear reaction rate is a delicate and somewhat dangerous operation. Nuclear power should ideally be run at constant power output day and night. Providing an economic floor for the nuclear power which covers just the operating cost during the night or at any time where renewable energy supplies exceed demand, and using that power for electrolysis of water makes sense.
Electrolysis reactors are cheap enough to be made dispatchable and could cost-effectively absorb the excess power at lower total cost than pumped storage facilities (which typically cost about $1100 per kilowatt and at least $80 per kilowatt-hour) or batteries (which cost at least $4000 per kilowatt-hour).
Electrolysis facilities could be built for about $300 per kilowatt, comparable to the cost of simple gas turbines which are used for peak power production. Cost per kilowatt-hour for the entire system including storage of the gas would depend on the cost of underground storage in caverns or depleted natural gas seams for the hydrogen and oxygen.
It is not necessary to use the most efficient types of electrolysis devices which involve catalyst at the electrodes. I envision instead to use the simplest type of electrolysis unit based on a potassium hydroxide solution, which is about 80% thermodynamic efficiency. (Because at the anode the electrolysis reaction first creates potassium metal which then reacts with water to generate hydrogen gas.) The lower cost of production and maintenance of these units would be an important factor.
If government policy guaranteed or facilitated a market for this gas, this could be a big contributor to reducing greenhouse gas emissions. The hydrogen would primarily be used in place of natural gas in combustion turbines. Unlike the case with natural gas, this would lead to no greenhouse gas emissions.
The hydrogen gas would also be useful in oil refineries and chemical manufacturing. Gas turbines have the big advantage of being dispatchable, which is not true of nuclear power plants. Gas turbines are now up to about 60% thermodynamic efficiency, about the same efficiency that can be obtained from fuel cells, but with much lower capital cost.
The oxygen obtained from electrolysis is very pure compared to the oxygen obtained from cryogenic plants which is typically contaminated by argon. In fact, medical-grade oxygen is more expensive than the oxygen used in industrial processes specifically because of the cost of removing this argon.
The lack of dispatchability is the Achilles heel for nuclear power. During the phase that many nuclear power plants were built throughout the world, there were also in many cases energy storage facilities that were associated with the power plant. These pumped storage facilities were filled up at night and discharged as needed to provide extra power during the day.
More recently, government regulations have forced utilities to use much of this pumped storage capacity to level out the loads from various renewable energy sources such as wind and solar power. This has totally screwed up the economics of baseload generation, for example, by nuclear power. It has indirectly created a disincentive to using one of our most available potential ways to displace the use of fossil fuels.
Pumped storage works well but it does take quite a lot of real estate and there are large environmental impacts. Because the pumped storage reservoirs experience large changes in lake level on a daily cycle they do not constitute normal lake environments.
Making hydrogen and oxygen via electrolysis to absorb the excess power at night or whenever wind and solar power are not able to provide the needed electricity would have fewer environmental consequences than pumped storage. Providing an economic framework for optimizing the output of nuclear power plants would go a long way towards decarbonizing our economy.
