Galena, Alaska has a problem that may be solved with an innovative application of nuclear power. The remote village in Western Alaska is a long way from the grid that supplies electricity to more densely populated regions. It is a fly-in village with only local roads. The energy supply is limited to fossil fuels transported on river barges, but the river is choked with ice 8-9 months per year.
The long winters without large volume transport requires the town to maintain very large fuel tanks – the total storage capacity is more than 3 million gallons between the town and the airport, which equates to more than 4,000 gallons for every resident. Fuel purchase, transportation, storage, and financing costs drive the cost of electricity to more than $0.30 per kilowatt-hour – making it more than 4 times as expensive as the electricity in my home area. The town leaders determined several years ago that this situation was harmful to the town’s existing and future population – and that was when the price of distillate fuel was about half of the current price.
Because electricity is so expensive, consumers avoid using it if possible. Electricity and tanked gas each supply less than 4% of the town’s heat, fuel oil or kerosene heaters supply 62% and wood supplies 31%. All of the heat sources have significants costs and limitations, but heat is vital for survival in this town where temperatures can sink as low as minus 60 Fahrenheit.
With the help of the state of Alaska, the town leaders commissioned a study to determine if there was any available technology that could meet their energy needs at a lower cost. The study looked at improved diesel engines, coal fired steam plants, windmills, solar panels, in stream hydro, and nuclear power. For the nuclear power option, the town focused on a plant offered by a partnership that includes Toshiba and the Central Research Institute of Electric Power Industry (CRIEPI) of Japan.
The study provided some logical conclusions. New diesel engines offered about 5-8% improvement in cost and environmental impact over the existing machines; coal would require large investments in mining, fuel transportation, and transmission wires and would have a negative effect on air and water quality; windmills were vulnerable to icing and required diesel engine back-up; solar panels would be useless for much of the winter; in-stream hydro was limited by the low available head (large but slow moving river) and by ice formation; and the nuclear option seemed worth further investigation.
As currently envisioned, the Toshiba 4S (Super Safe, Small and Simple) nuclear power system would be able to supply about 10 MW of electrical power for 30 years without any new fuel. It could be transported in modules by barge and installed in a building measuring 22 meters by 16 meters by 11 meters with an excavation for the reactor core and primary cooling system of about 30 meters deep. (Nishi Feb 2005) Compared to the alternatives, the small nuclear plant would almost disappear into the background and would have little effect on the environment. Depending on a variety of assumptions, the cost for power could range as low as 6 cents per kilowatt hour. Unfortunately, there are scenarios where the cost per kilowatt hour could approach infinity.
If all goes well, the Toshiba 4S could be providing Galena with abundant power by about 2012. Not only would it supply all of the electricity that the village needs, but there would be enough low cost energy capacity left over to produce hydrogen from water and district heat from the waste heat released from the plant. Galena could experience a mini-boom as it becomes a hub of regional energy and innovation. If certain hurdles are not overcome, however, a large amount of money and time can be consumed without producing any new power capacity at all.
Technical description of Toshiba 4S
The Toshiba 4S has been described in some promotional articles as a nuclear battery, but as attractive as the plant is, that is too simplistic a description. The plant is a small, sodium cooled fast reactor with a rather technologically advanced, compact steam turbine secondary system. Though it is based on sound engineering design work dating back to 1988, there are some areas where the designers and manufacturers will be pressing the edges of the known in terms of chemistry, materials, equipment reliability and fluid flow. If history is any guide, the system will require a significant number of design modifications and operating procedure refinements as more is learned by actual construction and operation. If there is sufficient patience and dedication, the system could prove to be a reliable power producer.
The core heat source for this plant is quite compact; it is only about 0.7 meters in diameter and about 2 meters tall. This section of the plant would be at the bottom of the 30 meter deep excavation inside a sealed cylinder, a location that helps to provide the driving force needed for natural circulation cooling and that provides an impressive level of nuclear material security. The active core material is a metallic alloy of uranium, plutonium and zirconium. The material has been extensively tested but it has not been commercially produced and used as a reactor fuel.
The 30 year lifetime for the core is achieved through a variety of mechanisms. The core is a metallic alloy cooled by sodium and the overall reactivity is controlled through the use of a moveable reflector instead of neutron absorbing control rods. Because of these features, which differ from those of conventional water cooled reactor technology, more of the neutrons that are released by fission either cause a fission or are absorbed by fertile materials like uranium 238. When fertile materials absorb neutrons, they become fissile and useful as fuel the next time that they are struck by a neutron. It is unclear from available technical materials whether or not the 4S actually produces more fuel than it uses – that is, whether or not it is a breeder reactor – but it is clear that the efficient use of neutrons for converting non fuel materials into fuel materials helps to increase its projected lifetime.
The safety of the plant is achieved by maintaining a negative temperature coefficient of reactivity throughout the life of the core, and by providing sufficient natural circulation and heat removal capabilities to prevent overheating the core. Though it is a long, technical sounding name that tends to make non techies respond with rolling eyeballs, the fact that the system has a “negative temperature coefficient of reactivity” simply means that an increase in core temperature will cause a decrease in core power. If the temperature increases too much, the core will shut down. However, a shutdown reactor still produces heat from the decay of radioactive materials, so there must be some mechanism provided to remove the generated heat. That is the job of the natural circulation and heat removal characteristics.
The use of sodium cooling contributes to the heat removal ability because it is a liquid over a wide range of temperatures, even if the cooling system is kept at atmospheric pressure. In water cooled reactors, which are often required to maintain pressures of 2000 PSI, a loss of pressure can be a problem because the cooling medium will change from a liquid to a gas, which has a much lower ability to remove heat. Since the major possible cause of a pressure loss is a cooling system leak, the hot high pressure water also implies the need for a very strong and pressure tight secondary containment system. The need to maintain a high pressure drives many of the design features and operating procedures for light water reactors; liquid metal cooling changes the equation and shifts some of the concern away from pressure maintenance.
Liquid sodium cooling also allows the 4S system to produce higher quality steam than is available in a light water reactor because higher coolant temperatures are readily achievable. The system will produce steam temperatures on the order of 500 C (932 F) which is considerably higher than the 260 C (500 F) temperatures available in conventional water cooled reactors. Higher temperature steam improves thermodynamic efficiency and allows the production of more power per unit size of machine.
Challenges Faced by Toshiba 4S
The major hurdles for the success of the Toshiba 4S are shared by any small nuclear power system using technology other than light water reactors. The fact is that the nuclear regulatory system currently in place in the United States assumes that all nuclear power plants will produce roughly 1000 MW of electrical power and they will all use similar light water reactor technology.
Smaller plants – especially those in the size category of the 4S – are severely handicapped by the fact that NRC licensing cost tables are computed on a per plant basis, without any discounting for reduced size or complexity. Innovative ideas are also handicapped by the fact that Nuclear Regulatory Commission expertise is decidedly specialized in light water reactors and the current approach is for any owner of a new idea to be responsible for paying NRC employees approximately $200 per hour each to learn something new.
The final major hurdle imposed by the NRC is the fact that their new, streamlined licensing timeline imposes a 42-60 month delay from the time that the application is filed until it is approved. Very few businesses can afford to finance projects that require almost five years of frequent government interaction – at an ever inflating rate of $200 per bureaucrat hour – before they are even allowed to break ground to build their revenue generation equipment. The only way that even enormous companies like General Electric or Westinghouse have been able to do it is to obtain Department of Energy grants to pay Nuclear Regulatory Commission fees.
Small reactor producers also face a prejudice that they will be vulnerable to attack and possible misappropriation for nefarious purposes. That is one reason why Toshiba is proposing to bury their reactor nearly 100 feet (30 meters) under ground in a sealed container that cannot be lifted by any equipment available in the local area. The reality is that even very small nuclear reactors will be surrounded by strong layers of steel, lead, and concrete in order to protect their operators from excessive radiation levels. These containers are at least as strong and certainly far better protected than most bank vaults. They are less likely to be attacked because, unlike a bank vault, they surround radioactive material that is quite good at protecting itself from human beings.
Small nuclear plants like the 4S certainly will contribute to nuclear proliferation of the very best kind. They will enable nuclear power benefits to reach a much larger and needy audience and they will not contribute to the uncontrolled spread of nuclear weapons. They are machines that Ike would like very much; they meet the objectives of his Atoms for Peace initiative rather nicely.
Small nuclear power plants can be terrific boons to the populations in remote areas, but I have some reservations about the specific technology proposed for Galena. (Disclosure: Adams Atomic Engines, Inc. the sponsor of this web site, has developed designs for closed cycle nuclear gas turbine systems that may someday compete in the same markets as the Toshiba 4S.)
Though sodium has some attractive characteristics as a reactor coolant, there are some tradeoffs that have limited its use to a very small portion of the world’s nuclear reactors. These include the challenge of keeping the material warm enough to be a liquid under all reactor conditions – including long term maintenance, the challenges posed by chemistry and materials, the challenges posed by neutron interactions with sodium, and the challenges posed by the need to pump a rather dense fluid reliably through a variety of heat exchangers.
Another obstacle limiting sodium’s use is the cost and availability of the material. Sodium is far more expensive than water, and it would experience significant price increases if there was a sudden large increase in sodium demand. The quantity of material needed for each reactor might be reasonably small, but the aggregate demand from filling the cooling systems of even a moderate number of the plants like the 4S could cause major market disruptions until sufficient production capacity is built. As is the case for all commodities, if there is more demand for the material than the market can supply, the price will increase substantially.
The 4S is a very nice reactor system, but my reading of all available materials indicate that only passing attention has been paid to the secondary (steam) side of the plant. As is common among plant design documents produced by nuclear engineers, there are dozens to hundreds of pages of details about the reactor system and a few paragraphs about the “balance of plant” (BoP). Though steam is an old and well understood technology, it is not particularly simple or cheap. There is a reason why there are few steam plants being produced today, the plants tend to be labor intensive, heavy, and relatively expensive compared to alternatives like diesel engines or gas turbines.
I spent a lot of time early in my career supervising the operation and maintenance of a steam plant that was almost exactly the same capacity as the one proposed for Galena. I will admit that it was a rather venerable and well worn system by the time I arrived, but I am pretty sure that many of the maintenance issues that made for some long days have not disappeared. Steel steam piping still rusts, packing around valves still wears out, condensers still need periodic cleaning and inspection, steam leaks are still potentially deadly for operators, steam generators still require careful chemistry control and monitoring, water purification systems are still a must, and turbine bearing lubrication oil systems still require careful attention.
Nothing in that list is earth shattering or really difficult; the main reason I point them out is to try to get them out into the open so that the customers are not disappointed when their “nuclear battery” requires more operators and more talent than they initially assumed. We might have been a bit overmanned, but the plants that I was associated with had a crew of about 20 people directly associated with the steam plant and associated electrical equipment.
The other consideration is the fact that the proposals floated so far mention only one 4S for the village and do not describe the backup power system that will be required during certain maintenance evolutions. There are plenty of nuclear steam plants that operate with limited back up in remote areas, but all of the ones that have been successful have the ability to come back into port so that the grid can provide power while they receive scheduled or corrective maintenance.
The 4S is a scaled down version of a 50 MWe power plant that has been on the drawing boards for a number of years, so it might be difficult to produce economically in even smaller sizes. If I lived in Galena, however, I would be more comfortable if the proposed nuclear installation had more redundancy and ability to produce partial load power while part of it was undergoing repair or maintenance. Keeping the existing diesel engines around for back up might work, but their ongoing maintenance costs and the cost of storing sufficient fuel should be included in the overall decision process.