How reactor safety is actually engineered

The United States has been operating small nuclear power plants continuously since the early 1950s. These reactors have been used for research and development, power generation, and ship propulsion. There have been tens of thousands of people associated with the design, development, manufacture and operation of these smaller reactors. The enterprise has accumulated an admirable…

The United States has been operating small nuclear power plants continuously since the early 1950s. These reactors have been used for research and development, power generation, and ship propulsion. There have been tens of thousands of people associated with the design, development, manufacture and operation of these smaller reactors.

The enterprise has accumulated an admirable safety and reliability record and is the basis for some of the optimism associated with the development of small modular reactors that can produce power in volumes that would be uneconomical if produced in the far larger nuclear plants that became the standard during a period when coal, oil and natural gas were extremely cheap. When nuclear power plant sizes ramped up from 60 MWe at Shippingport to the 1000 MWe class that became the standard, an abundance of fossil fuels were widely available in the US for well under 50 cents per million BTU. For comparison, current fuel prices range as high as $14 per million BTU. (Bulk residual oil that contains 135000 BTUs per gallon and sells for $80 per barrel costs $14.00 per million BTU.)

In the days of very cheap fossil fuels – those are in the past, by the way – and little concern about air pollution, nuclear plant designers decided to aim for “economy of scale” in order to compete. That decision was also influenced by the natural corporate tendency of GE and Westinghouse to emphasize their core competencies. At the time, those competencies included the industrial capacity to construct some of the largest turbines and pressure vessels in the world.

There ARE certain economies of scale that give companies that can build the specialized components required for very large systems a leg up on the competition – especially when they focus on a customer base like regulated utilities that like very large projects because of their access to cheap and patient capital.

Aside: Some day, I am going to put together the story of how General Electric pushed the American Locomotive Company (ALCO) out of the business of producing both locomotives and nuclear power plants as a way to increase its market dominance, but I need to make a trip to a library in New York where some of the archives are still on paper. End Aside.

The world has changed a great deal since those days in the 1960s and 1970s when American industrial giants dominated the nuclear energy scene, when fossil fuels were really cheap, when people ignored the environmental consequences of rapid fossil fuel consumption, and when designs were done using pencils, compasses, T-squares and slide rules. For one thing, our industrial might has been outsourced and our large steel forging capacity is in mothballs or has been sent overseas. The enormous turbine manufacturing facilities that once employed thousands in upstate New York are largely empty or destroyed.

A number of companies have determined that American nuclear opportunity now lies in the direction of smaller, simpler, more sophisticated designs that can make use of the economy of small. On this scale, designers and operators can take advantage of the natural safety features that come from having cores where the surface area to volume ratios are small enough to allow easier cooling – even from natural forces like the following:

• the driving head that can be generated by differences in water temperature
• the heat content capability of large pools of liquid metal
• the ability of molten salts to accept very high temperatures without boiling
• the ability of graphite and silicon carbide to resist damage at temperatures that will not be reached in an acceptably sized core that has some natural gas flow after shutdown

I am not at all surprised that there are naysayers who think that smaller nuclear power plants are a bad idea. After all, there are still some large industrial giants out there who can build the very large plants and think they can put together the very large project finance teams that are required for multi-billion dollar units. The supporters of very large systems do not really want their customers thinking that they might want to dip their toes in the water by going small first.

There is still a market for the extra large systems, though it looks to me like the market in the US is quite limited. We have a relatively well built out electrical power infrastructure, we have risk averse corporate leaders, and we have relatively small electric power producers. The relatively small size of our electrical generating corporations is due to our historical aversion to consolidation and “trusts” in an industry where monopolies seem to be a natural consequence of development.

There is also sniping against smaller nuclear power plants from organizations that have never met a nuclear reactor that they like. Arjun Makhijani, the nuclear fusion specialist who rarely misses any opportunity to spread FUD (fear, uncertainty and doubt) about the use of nuclear energy, has gotten together with the Physicians for Social Responsibility (the group initially formed by Helen Caldicott) to release a “study” claiming that small nuclear power plants are “no panacea” for the issues that they claim make nuclear energy a bad investment.

Not surprisingly, that study makes some bold assumptions and assertions. It asserts that there really is a waste issue, despite the fact that no one has ever been harmed by exposure to used nuclear fuel and despite the fact that storing the leftovers from reactor operation does not require much space and despite the fact that the stored leftovers represent a tremendous energy legacy for future generations.

If you really are worried about “the waste issue” associated with current nuclear power plants, then I suppose you will agree with the IEER/PSR study. I cannot deny its correct assertion that smaller nuclear plant operators will have similar responsibilities – and opportunities – associated with managing nuclear fuel left overs. I just do not believe that it is really a fatal blow when compared to the waste issues of the fossil fuel competitors.

Some of the other assertions that the study makes are simply red herrings. It implies that small nuclear plants cannot afford a secondary containment – that is simply not true. Even the small nuclear plants that the US has been operating for many years at sea have adequate secondary containments that form a barrier to fission product release. Containments do not have to be enormous concrete structures with thick walls of tensioned steel bars. Even if they are, they are not all that expensive. I fully expect that any small reactor licensed to operate in the US or in any market where we have much influence will have an adequate secondary containment system/

The IEEr/PSR study points to the failure of the South African PBMR project as evidence that SMRs are fatally flawed. The PBMR project failed for a number of reasons, but none of them included the fact that the reactor output was too small to be competitive. Similar sized pebble bed reactors are under construction in China today and will likely find a niche in the market as coal furnace replacements for some of their very new steam power plants.

There has been another worry about small nuclear plants expressed by people who are simply naturally worried about things. They point to the only fatal fission reactor accident in any US nuclear energy facility – the SL-1 tragedy that occurred in the wee hours of the morning hours January 3, 1961.

Most nuclear industry insiders dismiss that event as not being related to “commercial” nuclear power, and they are correct. The SL-1 was an electrical power generation system designed

to supply electricity and heat to remote radar stations that were designed to be part of the Defense Early Warning (DEW) line. Its relevance to the small reactor discussion is the fact that it was a tiny power plant with an expected customer – remote radar sites – that is not unlike some of the customers that Grizz Deal talks about when he is describing the 25 MWe Hyperion Power Module.

Aside from the fact that the SL-1 could only produce a few hundred kilowatts compared to the 25,000 kilowatts that the HPM will be able to generate, it is important to understand the other contributing factors that le