Small Reactors, Safety Culture, Safe Design, and Lessons Learned From SL-1

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 led up to the fatal explosion that impaled one operator in the reactor building ceiling and killed the other two operators with a fatal dose of radiation. (Please visit the July 1996 issue of Atomic Insights for a series of explanatory articles.)

Here is how I responded in a recent discussion thread on LinkedIn when someone made a comment implying that the accident was the result of a “love triangle”, and demonstrates just how easily a single person can cause damage in a small nuclear power facility. (That theory, by the way, has been floating around for nearly 50 years.)

Mark – I have studied the SL-1 accident in detail. I give little credence to the theory of the love triangle as the cause of the accident. From what I learned, the reactor designers and operators at a management level allowed a little plant to become less and less important in their daily decision making. Due to some design decisions – aluminum cladding, poison strips tack welded to the exterior of fuel rods in places where they could interfere with control rod motion, a very high reactivity central control rod, and a maintenance procedure that required control rods to be separated from their drive mechanisms and then reconnected with a VERY sketchy procedure, the plant was set up for problems.

The managers combined that carelessness in design with a culture that allowed operational casualness to the point where operators were routinely “getting it done” or “making it work” when the plant gave warning signs – like frequently sticking rods – that all was not well. The not particularly well trained operational staff started acting more like “git ‘er done” mechanics and put in “procedures” like exercising rods before operation to give them a better chance of working later. (That process was essentially rubbing off “crud” that had accumulated to make the rods sticky, but the operators did not understand that at least some of the “crud” was boron coming off of those tack welded and corroding poison strips I mentioned earlier.)

Finally, the culture allowed for some extremely light manning – just three people on an evening maintenance shift doing a procedure that a better trained crew with adequate supervision would have recognized as hazardous.

The specific act that most likely resulted in the accident occurred when one of the operators did what the “git ‘er done” folks had decided worked to prevent sticky rods – he “exercised” the central rod while it was still disconnected from its speed limiting drive mechanism. If all had been in a better initial condition, that would not have been such a tragic decision.

The operator most likely figured it would be quicker to move the rod by hand. It was a pretty small rod, weighing less than 100 pounds and needing just 20.7 inches of movement from full in to full out. He stood over the rod, braced himself and pulled. He might have even intended to pull slowly, but he probably had to use more force than expected because of the stickiness. When it broke free, it moved very quickly, adding both permanent and transient reactivity to a cold core.

(Of course, he might have been more careful if he had not been experiencing some of the personal life issues that you mentioned, but there is no evidence of a desire to break the plant or take anyone’s life.)

The core went critical and then supercritical, boiled off the water in the channel, ejected the rod completely and made at least one large penetration in the top of the core when the rod left and impaled the operator.

The real lessons are several. Correcting any one of the problem areas would have reduced the probabilities enough to break the chain of events that resulted in the tragedy.

Nuclear energy plants are safe if designed and operated with care. There is no need for perfection – if we needed perfection to prevent accidents there is NO WAY that we could have accumulated the safety record we have established over a 60 year history.

After all, there are a lot of machines and a lot of humans working 24 hours per day in the industry. Murphy happens, but there is a corollary to the law. As we all know, Murphy says “if something bad CAN happen, it probably WILL happen.” Here is my corollary “If something really bad happens only once or twice in 6 decades, then it most likely will only happen once or twice for the next 6 decades.” Compared to the accident rates of the competition, I find that to be an acceptable outcome. That is why I work in the industry.

I am a big fan of smaller nuclear power plants that can compete in markets that are currently unable to take advantage of atomic fission energy. There is no reason to force islands, ships, remote areas, mines, locomotives, or small towns to limit their energy sources to diesel engines, combustion gas turbines, or small coal plants – with possible supplements from unreliable and land consuming sources like wind and solar.

SMRs have a place in the market. With attention to detail and factory production techniques, they can eventually capture a substantial share. As anyone who reads Atomic Insights knows, I recognize that the competitive nature of the energy business makes SMRs targets for the establishment fuel and power business. You will hear plenty of negatives about SMRs, but please consider that at least some of those negatives will be coming from people who sell power systems that will have a harder time competing when small nuclear fission systems are available as a real option that can be installed with on a predictable cost and schedule.

Disclosure: I work for Babcock&Wilcox on the B&W mPower^TM small modular reactor project. I earn my current salary working in the field of developing smaller nuclear power systems. My words and thoughts about the general technology are my own; I do not represent the company where I work in public discussions. I have been writing about my support for small modular reactors for almost two decades.

Update: Atomic Energy Commission video describing the accident and its aftermath.

SL-1 The Accident: Phases I and II