UC Berkeley's Per Peterson Pursues Radical New Design with Off-the-Shelf Technologies
What is the best design to make next generation nuclear reactors safer and cheaper? That’s the question everyone from Bill Gates to the Chinese government is asking. The US Department of Energy has recently bet that smaller will be cheaper, funding small modular reactors with passive safety features. But much of the action is on molten salt reactors, which are being pursued by Gates-backed Terrapower, Transatomic, and UC Berkeley Nuclear Engineering Professor Per Peterson.
Peterson is a Breakthrough Senior Fellow and came by the office to discuss his fluoride-salt-cooled design. The strategy to make it cheap is to use two off-the-shelf technologies: a modified combined-cycle gas turbine based on current natural gas technology, and high-temperature ceramic fuel that the US Department of Energy has developed, and that is also being used in China. This strategy reduces the huge construction costs behind the rise of the cost of building nuclear power plants.
The gas turbine also allows the reactor to have a conversion efficiency of 42 percent with nuclear heat, much higher than the 32 percent of current reactors. Equally interesting, the power can be boosted by injecting natural gas or hydrogen, and converted into peak electricity with an efficiency of 66 percent, even higher than the 60 percent for the very best natural gas combined cycle plants today. So these reactors could provide steady nuclear base load with almost zero carbon dioxide emissions, while also producing peaking power when needed with much lower carbon emissions than current peaking plant technology (and zero emissions if they use nuclear hydrogen as their fuel).
For the public, the most important design feature may be its inherent safety. The fuel pebbles and salt cooling, Peterson says, eliminates meltdown risk. “Our fuel pebbles are complete ceramic, and have been tested by the DOE up to 1800°C, far above the melting temperature of current fuels and even the melting temperature of steel, without releasing any radioactive material — the maximum temperatures that can occur in accidents is under 1000°C.”
The Shanghai Institute of Applied Physics is now designing a salt-cooled test reactor, which it plans to start operating in 2017. This achievement, says Peterson, could have important consequences for the commercialization of salt-cooled reactors in the United States and abroad. Paying close attention to what is happening in China – and encouraging international cooperation – will be essential for the large-scale deployment of nuclear, he says.
Tell us more about the advanced nuclear reactor that your team is working on.
We have 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.
How safe is your design? Is there a risk of meltdown?
Our 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.
Your molten salt design sounds foolproof. Are there any drawbacks?
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.
That sounds like a big challenge. How is it being addressed?
There are two ways. 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.
What about waste? Does your design generate any of that?
Yes, it’s still a once-through fuel cycle. No matter what, we’ll have to develop the capability to place nuclear waste into geologic disposal. Even integral fast reactors (IFRs), which recycle most of their waste, leave behind materials that have been contaminated by transuranic elements and so cannot avoid the need to develop deep geologic disposal. We’re already doing deep geologic disposal at a repository in New Mexico, 2000 feet below ground. Another option would be to store waste in very deep boreholes. There are many other options, so geologic disposal is a solvable problem.
I’ve heard a lot about small modular reactors (SMRs) these days. Is the US interested in those?
Yes. The US DOE is supporting the licensing of light-water small modular reactors (SMRs). If such SMRs are successfully licensed it could address a number of issues for advanced, next-generation reactors, whose first commercial designs will also be small and modular. Much of the onus of ensuring that such issues are addressed will fall on the engineering firms that receive the DOE grants. All in all, DOE support for SMRs could help create domestic markets for small, modular, advanced nuclear designs. The creation of such markets will require thinking about where small reactors make the most sense. DOE has had previous success with competitive grants for advanced nuclear designs. Its big success was the advanced light-water reactor program, which led to the development of reactors that incorporate passive safety features, such as General Electric’s advanced boiling water reactor and Westinghouse’s AP600/1000.
Where do SMRs make the most sense?
Because 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.
Could you tell us about NuScale?
NuScale Power is one of the companies that received a DOE grant, along with the firm Babcock and Wilcox. NuScale is a very unique business model; it’s very exciting. They’re a venture-capital funded company based on a new reactor design that was developed at Oregon State University in 2000. The company was granted a DOE contract to develop a reactor that had a sealed core and was transportable. Once they tested the initial design, an integral pressurized water reactor (IPWR), they realized it would have limited near-term appeal for developing countries. But the team realized that if you configured these reactors into multi-module, larger plants, utilities could finance their construction much more easily. In my opinion their design is very promising.
What are China’s plans for advanced molten salt nuclear reactors?
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.
Are you collaborating with the Chinese on this effort?
There is an ongoing formal collaboration between the Chinese Academy of Sciences (CAS) and the US Department of Energy (DOE). The DOE has a memorandum of understanding with the CAS. Under this formal umbrella, our research group has an informal relationship with the Shanghai Institute of Physics. There is also a cooperative research agreement being developed between China and Oak Ridge National Laboratory in Tennessee, which would provide funding for China’s thorium molten salt research effort.
Tell us more about US involvement in the Chinese effort to commercialize advanced nuclear technologies.
The US DOE has been reviewing the Chinese effort to build a molten salt reactor. The Chinese program has been using US expertise in reactor safety, and US experts have reviewed the early test reactor design and remain engaged. So far, China’s nuclear regulatory policy has been to adopt and follow the safety and licensing regulation of the exporting country. Russian-built reactors in China are have adopted a regulatory approach similar to that of Russia. Likewise, licensing for the Westinghouse AP1000s that are being built in China is following a US approach. There appears to be an emerging, consensus approach in the US and in China for safety for molten salt reactors as well.
How should the US participate in the commercialization of these reactors?
My view is that the United States needs to maintain the capability to independently develop advanced nuclear designs that are being studied and will be commercialized in China. Maintaining such capability could encourage US-China joint ventures, which could accelerate development and thus ensure that commercial designs are deployed at large scale as soon as possible. The United States has a lot of expertise in the areas of nuclear safety and licensing, and could bring such expertise to US-China partnerships. If new advanced nuclear designs are simultaneously licensed in both the US and China, the possibility for large-scale deployment increases.
Do you think such reverse engineering is possible? Isn’t China keeping their plans secret?
The Chinese Academy of Sciences has been remarkably open and transparent in their effort to build their thorium molten salt reactor. They’ve been doing a lot of international collaboration. All of the reports are published in an extraordinary level of detail. This collaboration is really important if we want to see this technology developed and deployed soon enough to make a real difference in helping reduce climate change. If China can stay on track to commission a 100 MW commercial scale reactor by 2022, it would be fantastic if this reactor could include substantial contribution by US industry as well. This kind of collaboration could lead to a joint venture effort that could result in more rapid and larger near-term deployment.
Is the DOE exploring molten salt reactor technologies, outside of its involvement with China?
The DOE is learning more about molten salt reactor technologies through university consortia, as well as targeted research in the US national laboratories. The US is investing far less in nuclear energy R&D than it should, but the current DOE program is well balanced to address all of the technical areas needed for US leadership, particularly high temperature fuels, graphite, high-temperature structural materials, advanced high-temperature power conversion methods, and licensing of multiple-module SMR facilities—the configuration that Generation IV technologies including molten salt technologies can most easily be deployed in.
What is being done to license advanced reactors in the United States?
Our research group and our collaborators have been working on the licensing framework for molten salt reactors in the United States. A year ago we petitioned to the American Nuclear Society (ANS) and were delegated to develop a safety standard for a fluoride-salt-cooled high temperature reactors (FHRs). Recently, the US DOE launched an effort to develop new “general design criteria” that can be applied to non-water-cooled reactors, which is expected to be completed by the end of summer. The Nuclear Regulatory Commission (NRC) will review that effort, and their response will reduce the future uncertainty in how to design new Gen IV systems so they can be licensed by the NRC.
How should the US contribute to an international advanced reactor industry?
If the US is going to lead in the innovation in developing new reactors, it should first try to facilitate a larger domestic market for small modular reactors. One way to do this would be to provide incentives for utilities to repower coal sites with nuclear SMRs instead of natural gas. We should also be thinking about how to gain better access to international markets. Our export control system makes it very time consuming to obtain the necessary approvals to sell anything into international markets. Export control approval takes over a year, compared to a few months in most other countries. This imbalance gives other countries incentives to procure nuclear components from Japan, Korea, Europe, and other places. The reason the US export process is so slow is because parts require multi-agency review. The Nuclear Energy Institute has been advocating for a more streamlined process. Instead of having to approve every component for export, it would be more efficient to approve an entire project.
Why did the costs of nuclear power increase in the United States?
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.
Do you foresee a global industry for advanced nuclear power?
Yes, we already see one emerging. The ongoing construction of AP1000 reactors in China has created a partnership between the Chinese State Nuclear Power Technology Corporation (SNPTC) and Westinghouse (and Toshiba, which owns Westinghouse). Toshiba just purchased land in the United Kingdom where AP1000s will be built. Bulgaria and Czech Republic may also build AP1000s. The best thing for nonproliferation is multinational ownership of nuclear fuel cycles and infrastructure, which creates a firm legal basis for international response if a national attempts to “nationalize” the fuel cycle and infrastructure, which in turn deters the political decision to misuse the fuel cycle for proliferaiton. A shift toward multinational reactor sale and construction, drawing resources from multiple nations, will give countries greater confidence that the nuclear infrastructure is being deployed for peaceful purposes. Thus, the formation of a joint venture between the Chinese SNPTC and Westinghouse to build AP1000s internationally is a positive development.
Still, the US has clear areas of policy disagreement with China. World powers during the Cold War also had fundamental disagreements, but were able to take actions in fundamental areas where the future of the world and humanity were in balance, such as in reaching agreements to stop the above-ground testing of nuclear weapons and to then greatly reduce their numbers.
Today the accelerating increase in the concentration of carbon dioxide in our atmosphere creates real risks that we will destroy the capacity of our climate to support water and food supply for our future world population. Nations with high population densities, such as China, are particularly vulnerable to the water and food disruption caused by major climate shifts, which we expect can happen in a few decades or less.
It is now 60 years since the US launched the first nuclear powered submarine, using a water-cooled reactor, and what is remarkable is how little the technology has changed during this six decades. For nuclear energy to make any major difference in the future, we must greatly accelerate our rate of innovation, and this will occur more rapidly if joint international efforts emerge and are successful to develop these next-generation technologies.
For a detailed look at how the US can reboot its nuclear industry, check out Per Peterson’s latest article in Foreign Affairs, “Nuclear Freeze,” coauthored with Mike Laufer and Edward D. Blandford.
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.