Per Peterson has a modular molten salt nuclear reactor design in the US and is also working with China’s molten salt nuclear reactor program

Per Peterson and his co-authors believe that the way forward for the US nuclear industry is to use new nuclear reactor designs with passive safety and modular construction. This will make nuclear power both cheaper and safer.

Per Peterson is an expert on molten salt nuclear reactors and other nuclear reactor designs and technology.

Per Peterson, the Floyd Professor of Nuclear Engineering at UC Berkeley, is working with America’s national energy laboratories on the development of breakthrough nuclear technologies that are safer, less expensive, and more efficient and flexible than current technologies. Peterson’s early research was critical to the development of passive safety systems adopted in new reactors currently being built in the United States and China, and he is a co-inventor of fluoride-salt cooled high-temperature reactor technology now being developed in the United States and China. Secretary of Energy Steven Chu appointed Peterson to the Blue Ribbon Commission on America’s Nuclear Future in 2010.

Per Peterson has a design for a molten salt-cooled reactor that couples to a conventional General Electric (GE) gas turbine. Our Mk1 reactor design can generate 100 megawatts (MWe) of baseload nuclear power, but can also be co-fired with gas to rapidly adjust power output between 100 MWe and 240 MWe. The ability to rapidly adjust power output helps balance variability in the grid and is thus attractive to grid operators. And because the turbine remains “hot and spinning,” efficiency losses to provide peaking and spinning reserve services are low. The thermal efficiency of our design in converting peaking fuel into electricity is 66 percent, compared to about 60 percent for today’s best combined-cycle natural gas-fired power plants. To top things off, our molten salt design is much more compact than other advanced reactor designs. We believe it offers one of the most cost-competitive alternatives to conventional water-cooled reactors.

The design has passive safety, and requires no electrical power to shut down and remove residual heat. The fuel, which is the same design as used in high-temperature gas-cooled reactors, is fully ceramic and cannot melt. Recent tests at the Idaho National Laboratory have shown that the most recent methods for fabricating these fuels make them even more robust, and that they can survive an amazing 1800°C (well above the melting temperature of steel) without releasing and significant amount of radioactive material. Moreover, the molten salt used in our reactor is good at absorbing and retaining fission products, meaning that any radioactive elements that did escape from fuel, perhaps if it were not manufactured correctly, would get caught in the salt. We recently held a workshop in Berkeley, California, where we asked expert participants to create scenarios where radioactive material would be released following an accident. We could not find a way that this would be physically plausible.

The major caveat with molten salt reactors (MSRs) is that, compared to pressurized water reactors (PWRs), they produce a lot of tritium, a radioactive isotope of hydrogen. PWRs produce small amounts of tritium that are released into the environment with very low risks. On the other hand, because MSRs produce relatively large amounts of tritium, we need to find ways to retain and recover it. Moreover, this key technical challenge needs to be solved in an affordable way.

There are two ways this is being addressed. The first is to reduce the amount of tritium that is released into the power conversion system. This is technically solvable if you replace traditional steam-based Rankine or an air-Brayton cycle with a closed gas power cycle (like helium or CO2), but these technologies are not yet mature. The second way, which is more desirable today, involves restricting the release of tritium and using a sink to collect the tritium. Our lab has found that the graphite surface on the fuel pellets that we use have a large capacity to absorb and retain the tritium. Massachusetts Institute of Technology has been doing tests with this graphite material and has found that less than 1 percent of the amount of tritium that is generated gets released. Thus, the retention of tritium appears to be solvable. We also need to study the design of heat exchangers that use barriers to reduce tritium release.

SMRs are small and modular, unlike large reactors (which typically have to be shipped by barge), they lend themselves to landlocked locations accessible by rail. They also lend themselves to sites where old coal power plants have been shut down. Rather than building many modules at a single site, single modules could be placed diffusely across a large grid, like today’s coal plants tend to be. Most coal sites are already equipped with transmission infrastructure and water for cooling, which would reduce installation costs of SMRs. Policy incentives to support this kind of development would go a long way, particularly since today’s low natural gas prices make it challenging for light-water reactor SMR vendors to recoup money spent on developing their reactors. But with the current very low natural gas prices in the US, compared to the rest of the world (due to shale-oil fracking, which produces natural gas as a byproduct), its also critical that US SMR vendors access international markets effectively, where gas prices are much higher, so that their development costs can be recovered. The most innovative US SMR designs are the most likely to be successful in reaching international markets.

There is an ongoing formal collaboration between the Chinese Academy of Sciences (CAS) and the US Department of Energy (DOE).

China has a huge nuclear program and is building almost every kind of reactor possible, including a number of experimental advanced reactors. Two years ago the Chinese Academy of Sciences decided to pursue a thorium liquid-fueled molten salt reactor, but first decided to build an intermediate reactor that uses a solid fuel with salt as coolant. (The choice to build a solid fuel reactor reduces the licensing risk without heavily compromising performance.) In 2015, China will be starting the construction of the 10 MW solid-fueled thorium molten salt test reactor. By 2017 they hope to have this reactor operating. And by 2022, they hope to have commissioned a 100 MW thorium molten salt commercial prototype reactor. Alongside this effort, the Chinese will be developing a 2 MW liquid-fueled reactor that will enter the final stages of testing in 2017.

You can attribute most of the increase in cost of nuclear power in the United States to the underutilization of skilled labor and specialized manufacturing capabilities. As the country started building fewer reactors in the 1980s and 1990s there was a surplus of skilled labor and specialized manufacturing, and much of it was used inefficiently, driving costs up. The airline industry is a good example of a similar, capital-intensive industry that has avoided this trap. Airplanes are extremely expensive to build and require a lot of specialized labor and manufacturing, but since today airlines manage to fill every seat (or nearly so), the price per seat is amazingly low (much different from a couple of decades ago). If you frame the nuclear cost issue as an efficiency of labor and specialized manufacturing issue, solutions begin to emerge. One good way to reduce the need for skilled labor and manufacturing would be to procure more nuclear components from pre-existing supply chains, where current quality levels can be very high compared to a couple of decades ago, and then test these components to certify them for nuclear use.

SOURCES – Energy Collective, Foreign Affairs

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