Small is Beautiful, Even for Nuclear Fission Reactors

E. F. Schumacher published a book titled Small is Beautiful in 1973 that has become one of the reference sources for ecologists and people interested in living on a human scale. In part, that book was inspired by the steady trend in the post-war era in which Schumacher lived towards building bigger and bigger companies that produced more and more goods in factories and power plants that were more and more remote from where people lived.

There is a back story to Schumacher’s inspiration, however, that makes his vision slightly tarnished in my mind. From 1950-1970, Schumacher was employed by the UK’s National Coal Board, one of the largest organizations in the country at that time; in 1950 it employed approximately 700,000 people, most of whom were directly involved in extracting coal from Britain’s well endowed mines. During his tenure at the NCB, coal employment steadily dropped as the country closed less productive mines in an attempt to compete with oil and gas supplied by multinational firms and with the rapidly expanding nuclear energy industry. In part, Small is Beautiful came as a lament from a man who spent his career trying to stem the tide that was moving power generation out of cities and replacing coal stoves with piped natural gas.

Of course, most of his fans will dispute that characterization.

My own personal philosophy matches pretty well with the idea that smaller organizations, smaller products and smaller production facilities are better suited to human existence. Though I am employed by a larger organization than even Schumacher was, I have picked a specialty within that organization that resulted in me working with a small crew in an independent environment. When I was going to sea, it was with 150 people whose names I knew, not 5,000 people whose names I could never hope to learn. I like to spend my money on small gadgets, compact cars, and small boats (my favorite right now is a single seat kayak).

Long ago, I realized that part of the reason that many people shied away from nuclear energy is that they have developed the impression that nuclear equals enormous. Whenever they see photos or video of nuclear power plants, they see huge cooling tower structures. They know that the plants are owned by the electric utility company; often one of the largest companies in any given city or state. My image of nuclear energy has always been much more compact; the plants I learned to operate could be toured in just a few minutes and none of the components was large enough to be intimidating.

As far back as 1991, when I first started thinking carefully about how to produce nuclear plants that could be more successful in the market, I have aimed at conceiving plants that could serve niches ignored by the big boys. I have never been enamored with the often repeated phrase of “economy of scale” because I have seen many cases where bigger is simply more trouble and trouble equates to cost. I have spent enough time as a manufacturer to see for myself the economy that can result when you set up a system that allows you to learn a task well and then repeat it and refine it. Series production economy is just not possible when you produce something at a rate of one every 5-7 years, which is what a given construction crew might achieve in the nuclear world.

I have also studied enough thermodynamics and reactor physics to understand that it is simpler to provide sufficient cooling to lower power reactor cores to keep them from overheating in the case of a loss of forced cooling. When the core power density is below a certain level, it is possible to allow the natural effects of heat transfer to surrounding materials and moderate fluid flows driven by temperature variations and gravity to remove any heat that is generated by the radioactive decay of fission products.

Reactors that can demonstrate passive cooling are not any safer in the real world than those that need forced cooling. After all, how can you improve on a safety record like that developed by the US nuclear power plant operators over the past 50 years? Reactors that are small enough to be cooled passively under any loss of cooling flow scenario, however, are easier to produce because they do not need to have layer upon layer of redundant power supplies or back up forced cooling systems.

When cores operate at lower power levels, they have a smaller “source term” used in accident scenario computations. That can be an important part of demonstrating a need for much smaller exclusion zones. As a guy who got sealed up inside of a small ship for months at a time with a reactor, I have no trouble envisioning reactors that can be put into factory building basements to provide power, heat, air conditioning and fresh water.

There is a growing cadre of thinkers who have independently developed similar visions. Some of those thinkers have come together to work toward implementation of their ideas in products that can meet customer power needs in smaller chunks than can be supplied by the 1000 MWe class of nuclear power plants that most people, even those in the industry, think of when people like Al Gore accuse nuclear of only coming in one size – extra large.

Here is a brief summary of the small reactor projects that become visible so far.

Hyperion Power Generation has their uranium hydride reactor that produces about 75 MW of heat; it can be connected to a user provided heat engine to produce approximately 25 MW of electricity along with heat at a lower temperature. The Hyperion heat sources are often described as being about the size of a large hot tub and being transportable by a large truck, barge or rail car. The company describes a concept of complete replacement when the fuel runs out, preventing any need for customers to have fuel handling expertise or equipment.

NuScale Power has their 45 MWe natural circulation light water reactor that can be built as a complete module and shipped to a location for installation. Natural circulation means that there are no powered pumps, the fluid flow that is necessary to transfer heat from the reactor into the steam generator is driven by temperature and density differences. Each module comes complete with a turbine generator so it can produce electricity independently, but the company envisions that many customers will choose to build a plant with a larger total output by installing a number of modules on a single site and controlling them in a common control room.

B&W has developed a 125 MWe modular pressurized water reactor that has no external piping, but, in contrast to NuScale’s modules, B&W’s modules have internal pumps to force the primary water through the core and through the steam generators. The pumps are not needed to cool the core if it is shut down; there is enough natural circulation to provide passive cooling. Like NuScale, B&W expects that customers will build stations with larger power output by ganging together a number of modules. Both NuScale and B&W have designed systems that use what is essentially proven light water reactor fuel – the primary difference is that the tubes that make up the fuel assemblies are shorter.

The PBMR project out of South Africa is in the process of a redesign to a module that will provide approximately 200 MW of heat which may convert to 80 MW of electricity in an efficient steam plant. The pebble bed modules would be cooled by helium circulated with blowers through a steam generator; the pebbles themselves are billiard ball sized graphite spheres that contain about 9 grams of coated uranium dioxide particles enriched to about 9.8%. The pebbles are slowly circulated through the core, which resembles a tall bucket of balls.

The other thinkers who are active in this area include Tom Sanders at Sandia National Laboratory who has been promoting “right-sized” reactors for more than a decade. Sandia just recently issued a press release indicating that they are actively working with industrial partners to develop power production systems based on sodium cooled breeder reactor technology along the lines of the systems proven by the EBR I and EBR II. Charles Barton often writes about small reactors on both Nuclear Green and at Energy from Thorium.

On October 8 and 9, the U. S. Nuclear Regulatory Commission is hosting a public meeting on licensing small reactors at its headquarters in Rockville Maryland. I am taking some leave from my day job and planning to attend at least part of the meeting. It is sometimes convenient to live near the nation’s capital; keeps the travel cost and time down.

For a somewhat more “balanced” view of the potential for small reactor projects to change investor and customer minds about nuclear energy as a power source, you might be interested in reading Less Is More for Designers of “Right-Sized” Nuclear Reactors. The article is generally informative, but the author is evidently compelled to add balance by quoting people like Arjun Makhijani, who can always be relied upon to say something negative about nuclear energy. In this particular article, he demonstrates his preference for ignorance by worrying that spreading nuclear power to people who could never hope to afford or use 1000 MWe in a single unit would encourage too many people to become nuclear engineers.