While the exact set of phenomena that unfold to release energy remains unclear, what was not debated at all was whether the potential to release heat was real. It clearly is, despite the extended difficulty scientists have had pinning down theory and practice. This issue seems entirely settled. Decades of work by hundreds of researchers reporting on their experiments and experiences of heat release “anomalies” have begun to provide a far more nuanced picture of the dynamics and the parametric guideposts that will eventually enable those studying them to narrow in on the controlling aspects. //

Given the potential value of this technology, it is no wonder that dozens of cash-strapped researchers and venture teams have soldiered on for decades. Now that ARPA-e has chosen to continue the work initiated by Google to identify a proof-of-concept design, there is new-found scientific integrity and rebranding to be done. There is also a greater awareness that what set cold fusion back and derailed early efforts was not scientific fraud but rather its far more complex sub-atomic transmutations, its multibody interactions combined with environmental factors such as temperature, pressure and light that varied by selection of component materials. These complexities still need to be sorted out but could potentially provide many viable options for sourcing and construction of systems and thus help to reduce manufacturing costs.

Uranium and thorium are two of nature’s most incredible clean energy storage assets. If completely fissioned, a handful of nuclear fuel weighing a kilogram contains more stored energy than 50 large tanker trucks filled with petroleum.

At the current diesel fuel price of $5.60 per gallon, 50 trucks can carry more than $3,000,000 worth of fuel. In contrast, nuclear power plant owners pay approximately $1,700 per kilogram of fuel in the form of finished assemblies.

The tiny waste production per unit energy released is an inherent aspect of concentrated fission reactions. Unlike combustion, all ingredients needed for fission are contained inside fission fuels. (Combustion needs an external source of oxygen in greater masses than the fuel itself.) The mass of fission wastes is slightly less than the mass of fission fuel; the mass of combustion wastes are about 2.5 times the mass of input fuel.

No fission product wastes need to be routinely removed to allow the reaction to continue operating for its design fuel cycle. None need to be discharged to the environment. Fission reactors are clean enough, safe enough and independent enough to operate inside sealed submarines carrying crews of several dozen people. Those submarines have gone to every part of every ocean on the planet.

Fission even works in the vacuum of deep space.

Those physical and economic facts almost beg power plant designers to think about building a wide variety of machines in order to use that amazing source of energy in as many parts of the diverse global energy markets as possible. Power systems using combustion fuels range in size from model trains to multi GWe power stations. Fission-based power systems need sufficient size to support a chain reaction, and to provide adequate shielding, but that still leaves a wide spectrum of potential applications and sizes. //

Larger units can successfully use the economy of scale to lower the cost per unit of output but it isn’t the only kind of scale that can drive down costs. Ever larger units can also run into diseconomies of scale that plague mega-projects in construction, mass transit, sports complexes, and airports.

The experience of the industry in building the Vogtle AP1000s shows that there is such a thing as too large. In contrast, the economies of scale that we believe will aid in the appeal of SMRs takes the form of mass production and is expected to enable the construction of SMRs to more closely follow the declining cost curves experienced by wind and solar projects.

One advantage of smaller systems is the improved ability to use factory manufacturing techniques. Of course, the components used in conventional large reactors are produced in factories, but then they are individually shipped to the site to be assembled into an operating plant. With reactors that have the size and complexity closer to that of large ships or commercial aircraft, it is possible to assemble and transport complete or nearly complete products.

Factory workforces have many advantages over site construction workforces. They can improve productivity by repeating similar tasks regularly, They can live and work in cities served by mass transit. They can implement quality assurance techniques and environmental consistence systems that are difficult to achieve at remote large plant assembly sites. //

…for a sodium-cooled reactor, for instance, that sodium coolant is likely to become low-level waste at the end of the reactor’s lifetime, because it becomes contaminated and activated during reactor operation. So, the “up to 30 times more waste” that’s been driving the headlines, it’s mostly the sodium coolant.

Diaz-Maurin,François Interview: Small modular reactors get a reality check about their waste, Bulletin of the Atomic Scientists, Jun 17, 2022 //

A Taxonomy of Access Control

My personal definition of a brilliant idea is one that is immediately obvious once it’s explained, but no one has thought of it before. I can’t believe that no one has described this taxonomy of access control before Ittay Eyal laid it out in this paper. The paper is about cryptocurrency wallet design, but the ideas are more general. Ittay points out that a key—or an account, or anything similar—can be in one of four states:

• loss No one has access,
• safe Only the user has access,
• leak Both the user and the adversary have access, or
• theft Only the adversary has access.
• [disclosed everybody has access]

Once you know these states, you can assign probabilities of transitioning from one state to another (someone hacks your account and locks you out, you forgot your own password, etc.) and then build optimal security and reliability to deal with it. It’s a truly elegant way of conceptualizing the problem.