Tag Archives: Reprocessing

Per Peterson: various answers to reddit AMA questions to UCBNE faculty

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More from the reddit.com Science AMA Series with members of the UC Berkeley Department of Nuclear Engineering.

In this AMA the UCBNE faculty offers a volume of valuable information. Following are some fragments that I want to archive for reference.

Regarding waste: Prof. Per Peterson was a member of Obama’s Blue Ribbon Commission on America’s Nuclear Future. I consider him one of the best-informed sources regarding Spent Nuclear Fuel (SNF) which the anti-nuclear lobby calls Nuclear Waste. It is not “waste” it is an extremely valuable source of carbon-free energy. 

Q: One of the elephants in the room for nuclear power is the waste….

A: …Finland and Sweden have successfully sited and are building deep geologic repositories in granite, and France is very far along in developing its geologic repository in clay. The U.S. nuclear waste program is currently stopped and is in a state of disarray…

There are a wide range of opinions as water reactors (LWRs) is substantially more expensive than making new fuel from uranium, even if the plutonium is free. This is primarily because the plutonium must be handled as an oxide powder to make LWR fuel, and oxide powder is the most hazardous and difficult form to handle plutonium in. All of the Generation IV reactor technologies can use fuel forms that do not involve handling plutonium and minor actinides in the form of powders and that are much easier to fabricate using recycled material (e.g., metal, molten salt, sol-gel particles in either coated particle or vibropacked fuel forms).

In my personal opinion, the most sensible thing to do in the near term is to prioritize U.S. defense wastes for geologic disposal, and to use a combination of consolidated and on-site interim storage for most or all commercial spent fuel. Implementation of the Blue Ribbon Commission’s major recommendations, which include development of consolidated interim storage that would initially be prioritized to store fuel from shut down reactors, would put the U.S. on this path.

By using geologic disposal primarily for defense wastes first, and using primarily dry cask interim storage for commercial spent fuel, this will give a couple of decades for nuclear reactor technology to evolve further, and by then we will be in a better position to determine whether commercial spent fuel is a waste or a resource.

Nuclear innovation: Prof. Peterson replies

There are a number of factors which make innovation difficult in improving nuclear reactor technology, in particular the long operating life of nuclear power plants and their very large capital costs, which dissuade innovation. The trend toward designing larger and larger water-cooled reactors has increased these disincentives.

Given their lower capital cost and shorter construction times, innovation is much easier in small reactors. There will remain a role for large reactors, just as dinosaurs existed for millions of years alongside the new mammal species, but currently some of the most important policy issues for nuclear power involve creating an ecosystem where small reactors find customers. Smaller reactors, produced in larger numbers with most of the fabrication occurring in factories, would also use specialized manufacturing and skilled labor more efficiently. Imagine factories as being similar to airplanes, and the ability to keep more seats filled being really important to having low per-seat prices…

FHR (Fluoride Salt Cooled High Temperature Reactor), Where to take technical risk?

I will answer this question first indirectly, and then more directly.

A key question for innovation in developing new nuclear energy technology is where to take technical risk. SpaceX provides a good example of a highly successful risk management strategy. They focused on developing a highly reliable, relatively small rocket engine, that they tested in the Falcon 1, which uses an ancient rather than innovative fuel combination, kerosene and liquid oxygen. On the other hand, they chose to use aluminum-lithium alloy with friction stir welding for their fuel tanks, which is at the cutting edge of current technology. They have then used the approach of ganging together large numbers of these engines to create the Falcon 9, which is now successfully delivering cargo to the International Space Station.

Currently the most important barrier to deploying nuclear power is not the cost of the fuel, but instead is the capital cost of the plants, the need to assure that they can run with high reliability (which for current large reactor designs creates strong disincentives to innovate), and the relatively low electricity revenues one receives for producing base load power, particularly today in the U.S.

The primary reason that UCB, MIT, and UW, and the Chinese Academy of Sciences, are working on solid fuel, salt cooled reactor technology is because we have the ability to fabricate these fuels, and the technical difficulty of using molten salts is significantly lower when they do not have the very high activity levels associated with fluid fuels. The experience gained with component design, operation, and maintenance with clean salts makes it much easier to consider the subsequent use of liquid fuels, while gaining several key advantages from the ability to operate reactors at low pressure and deliver heat at higher temperature.

Q: Can I also ask what you think the safest way to transport the waste is?**

A: Per Peterson: There is a long record of safe transportation of nuclear waste, including spent fuel, world wide. The containers used to transport nuclear wastes are substantially more robust than those used to transport hazardous chemicals and fuels, which is why transportation accidents with chemicals generate significantly more risk.

This said, the transportation of nuclear wastes requires effective regulation, controls, and emergency response capabilities to be in place. The transportation system for the Waste Isolation Pilot Plant in New Mexico has logged over 12 million miles of safe transport, with none of the accidents involving the transportation trucks causing any release of radioactive materials.

One reason it is important to restore WIPP to service (it had an accident involving the release of radioactive material underground in late February, which had minimal surface consequence because the engineered safety systems to filter exhaust air were activated) is because the WIPP transportation system has developed a large base of practical experience and skilled personnel at the state and local levels who are familiar with how to manage nuclear waste transport. This provides a strong foundation for establishing a broader transportation system for commercial spent fuel and defense high level wastes in the future.

A commenter replied to Per’s hecklers, referring to WIPP:

Actually I work for this program and this is an understatement. Not only have there never been any accidents that caused a release of nuclear material, there have never been any accidents with a truck loaded with waste containers, ever. They’ve happened while empty, but never otherwise.