The Keys to Lowering Reactor Cost: Some Siting Considerations

When I first saw Jim Holm's web page, I thoughts what a crazy Idea. Jim wants to convert coal burning power plants into pebble bed reactor sites. The more I think about Jim's idea, the more it makes sense to me. Jim has clearly thought a lot about the problem and siting is a big issue. Jim proposes that the pebble bed reactors be built under ground at these old power plant sites. 

At this point I need to digress to a disagreement I have with Kirk. Kirk wants to site reactors under water.  Actually there are actually quit a lot of moble reactors sited underwater already.  They provide the power for atomic submarines.  So there are no real technical problems with Kirks concept.  Kirk wants to place his under water reactors off shore.  Power would be sent to land by a submerged power cable.  Unlike atomic submarines the reactor would be unmanned.  Remote operators would perform whatever controlling functions would fall to the operators. As I have already noted human control is a major problem for nuclear safety.  Thus reactor safety ios best handled by the inherent safety features of the reactor.  

Underwater siting would work if for reactors located on he Atlantic, Pacific or Gulf Coasts and for reactors located on the Great Lakes, but It would not work for Utah! Thus even if we locate all our costal reactors under water we still need to build inland reactors, and there are siting issues. That is where undergrouns sits come in. I will talk more about them shortly.

The principle advantage of recycling old power plant sites is that it eliminates the grid hook up problems. Every power station needs to be connected to the grid. In some cases the grid may require significant and expensive modifications to accommodate power from a new power station.

To the extent possible, in a crash program to replace old power plants with nuclear generated power, we want to avoid secondary expenses related to the grid. Later on we might want to fix the grid, but the major goal is to stop producing CO2, and that is where the investment dollars should go. In addition the old power station is a site that is partially prepared. There maybe useful structures on the site, and the site is laid out for the generation of electricity.

We can see some of the important features in the pictures of TVA's Bull Run Steam plant.  I wanted my readers to notice the especially beautiful lake side setting.  There is a problem with that setting, however. If you intend to site a reactor or reactors underground, the first question you would have to ask is about the water table.   There is a lot of limestone in the area, and I suspect that you would not have to dig very deep to find water.  An under ground reactor that is underneath the Bull Run Steam Plant might end up  also being under water, but I do not think that is what Kirk has in mind for his under water reactor sites.  So right off we have a problem with the site, but note the adjacent ridge.  The inside of the ridge is also underground. Now the ridge may be above the water table, but there may still be a water problem.  The ridge is probably limestone, and water may be trickling through it when it rains.  It well may be that the Bull Run site is not suitable for underground construction, in witch case you might have to go with plan C.  That would be to build a massive containment structure or structures above ground.  The Bull Run plant is currently rated at 870 MW.  That means that the grid hookup could handle the power generated by up to 9 small 100 MW reactors.  Waterside settings for power plants are not at all unusual because even coal fired power plants require cooling water, and locations by rivers and lakes frequently means high water tables.     

Why then should we think about underground settings?   It was originally Edward Teller's idea, and Teller was very much a man of ideas.  Teller was truly a nuclear safety pioneer.    In the late 1940's Teller was the first chairman of the AEC's Reactor Safeguards Committee.  Teller was also concerned about global warming.  He warned the 1957 ACS meeting about the CO2/global warming problem.   The discovery of the natural underground reactors at Oklo, in Gabon, Africa interested Teller. Teller noted that the fission products produced by the Oklo natural reactors had not moved in over a billion years, and had long since ceased to be dangerous. Teller came to believe that underground siting was the ultimate answer to the problem of nuclear safety. He advocated that reactors be buried at least 200 meters under ground. He was not alone in holding this idea. Andrie Sakharov wrote in his Memoirs, "Plainly, mankind cannot renounce nuclear power, so we must find technical means to guarantee its absolute safety and exclude the possibility of another Chernobyl. The solution I favor would be to build reactors underground, deep enough so that even a worst case accident would not discharge radioactive substances into the atmosphere.”

Other research has shown that underground reactors protect against:
* Attacks by aircraft
* Other forms of terrorist attacks,
* Sabotage and vandalism
* Radiation release inthe event of an accident

Teller assumed a deep (200 meters) reactor setting. Research conducted during the 1970's, however concluded that there were cost penalties connected with deep reactors. This conclusion ought to be assessed in light of current construction costs. Wes Myers, and Ned Elkins suggested that past cost research had not evaluated siting in underground salt formations.

Myers and Elkins favored salt formation settings and noted some of the cost benefits:
* Decommissioning costs,through in-situ decommissioning and
disposal
• Transportation costs,through co-located storage/disposal facilities
• Excavation costs, which are ~$20/m3 in salt vs~$40 to $80/m3in
granite
• Facility costs,through elimination of the containment structure
• Reactor costs,through the use of modular reactor
• Site costs for successive reactors, due to the lack of constraints on
lateral expansion in the subsurface
• Security costs, because of the need for fewer guards and physical
protection measures
• Insurance costs,through reduced health and property risks

There would, of course be ways of indirectly recovering the cost of excavating granite. The mined granite could be processed for Thorium. The recovered thorium then run through LFTRs, and the power produced would more than pay the cost of mining, but this approach does not lower upfront costs, and for the near future there are less expensive ways to mine thorium.

It should be noted that Ralph Moir was able to talk Teller into a shallow underground setting for LFTRs, when they collaborated on Teller's last paper. (See Thorium fueled underground power plant based on molten salt technology, Ralph Moir and Edward Teller, Nuclear Technology 151 334-339 (2005)).

Underground siting does hold some promise for limiting siting costs.  However, problems such as the presence of ground water should be considered.  Siting in salt formations, and in old salt mines holds promise. Underground siting could provide superior protection against attacks by suicide aircraft, and other forms of terrorism.  In addition it could provide a means of containing radioactive materials in the event of reactor accidents.  Underground siting would be appropriate for smaller Generation IV reactor such as the PBR and the LFTR and has been proposed for both of them.   Underground siting then is an interesting and promising option for advanced reactors that requires further research,

The Keys to Lowering Reactor Cost: Labor Costs

Labor cost are of course a major source of reactor construction expenses. It was recently reported that the on site construction of AP-1000 reactors require from between from 16 to 20 million man hours to complete. The labor required for parts and module manufacture must be added to the cost. I have already suggested that as much work as possible be transfered to a factory where mass production techniques could be used. These techniques could include labor saving automation in the manufacture of standard reactor parts, and the extensive use of of robots in reactor assembly. These are standard well understood aspects of modern manufacturing and should not require further elaboration.

The work force in the reactor factory should be well trained and compensated accordingly. Assembly line workers should be understood to be part of the quality control, assembly technique and reactor design improvements teams, and both encouraged and motivated to make contributions to efforts of those teams.

In addition to the factory team there should be a site development team, whose task is to analyze site conditions, develop site plans, using as much as possible site design information stored in the sight development data base. Once the site conditions are understood, and a plan developed, the site would be quickly developed. The site development should be completed on the same day that the assembled reactor is shipped. The third stage would be reactor assembly and site completion. Again the highest possible degree of assembly automation should be used. Both of the onsite teams should be be part of the manufacturer's quality control, assembly technique and reactor design improvements teams, and both encouraged and motivated to make contributions to efforts of those teams.

The keys to controlling labor cost in reactor construction include using modern mass manuring techniques, carful organization of working activities, the organization of experience based data bases drawing on workers experience, from which best practices can be identified, and the inclusion of all workers as part of management teams. Labor practices should have an over all goal of creating a well-compensated, high morale workforce that is efficient, loyal, productive, and creative. That is an important part of lowering labor costs.

The Keys to Lowering Reactor Costs: Nuclear Waste

The problem of "nuclear waste" is one which is generated by nuclear technologies which fail to efficiently convert U-238 into nuclear fuel. The ultimate source of the problem is found in the uranium-plutonium fuel cycle, and in the use of reactor technology which fails to burn Pu-239 efficiently, and in fuel cycle technology which fails to efficiently, and cleanly reprocess nuclear fuel in a cost effective fashion. As a consequence of the systemic fuel inefficiencies, added facilities for the handling of used nuclear fuel must be added to reactor construction cost. The nuclear industry regards paying the added construction expenses as preferable to paying for fuel reprocessing, However, since we are taking the "full court press" in examining cost lowering measures to reactor construction, the cost of fuel storage facilities is certainly an issue.

In my previous "keys" postings, I found advantageous in both the PBR and the LFTR as far as cost savings are concerned.  But the LFTR has a major advantage in terms of a need for post-reactor fuel storage facility costs, and indeed in virtually every aspect of the fuel cycle. About 98% of the Thorium that enters a LFTR is burned up inside the reactor. The other 2% will come out as Neptunium 237, which has a use. In once through uranium cycle civilian reactors, Most of the original fuel charge remains unused when the fuel is withdrawn from the reactor. In addition significant amounts of the fissionable materials remain in the "spent" fuel, and their presence becomes an issue in post-reactor fuel handling. Post reactor fuel handling is a problem for LWRs and for PBRs. And if anything there are more problems in reprocessing post-reactor fuel from Pebble Bed Reactors, than in reprocessing fuel from LWRs. (Kirk Sorensen discussed LFTR fuel reprocessing here, and here.)

There are, however, added fuel handling expenses that come with LFTR technology. The fuel/carrier/coolant salts of the LFTR are in most designs subjected either continuous or periodic processing. The design requires that several sorts of processing should take place. Each process would require a separate processing unit. These fuel reprocessing units would add to the expense, and complexity of the LFTR. In addition they would create safety issues, and there would be significant problems with servicing and maintaining them.

There economics of fuel reprocessing with LFTR is, however, complex. The reprocessing of LFTR involves the extraction of fission products which are valuable minerals and metals. This in tern creates a second revenue stream from the LFTR, the sale of valuable fission byproducts. While it is doubtful that this revenue stream would by itself return all of the capitol costs involved in LFTR fuel reprocessing, it would at least produce a partial return on the capitol investment, beyond revenues produced by the generation of electrical power.

There are hidden advantages that effect reactor construction costs. By solving "the problem of nuclear waste," the LFTR would go a long way toward undercutting public opposition to nuclear power. If nuclear power is more acceptable to the public, investment risk diminishes. Diminished risk means lower capital costs. Hence the superior fuel processing features of the LFTR may in fact indirectly lower reactor construction costs. It would most certainly lower nuclear fuel cycle costs.  There is a public relations benefit to constructing what is perceived as being clean or at least cleaner nuclear power.  That benefit does have a cash value, even if it is not directly accounted in assessing the cost of reactor construction.  

The Keys to Lowering Reactor Costs: Inherent Safety

One of the Keys to lowering reactor cost is engineering high levels of inherent reactor safety into the reactor design. There are two ways to think about safety. The first way would be to examine reactor designs to identify inherent safety flaws. Once the flaws are identified, safety systems are designed to prevent those flaws from leading to serious accidents. The Light Water Reactor is an example of this approach. If the reactor looses its coolant water the nuclear fuel in the reactor core would overheat and eventually if it got hot enough it would melt. There are ways to prevent this. For example, inserting reactor control rods if the heat inside a reactor begins to rise. But sometimes a reactor operator might decide to do the wrong thing, and not insert the control rods. Human error is the biggest cause of accidents, so an inherently safe reactor has to be fool proof. That is no human error, no matter how serious can lead to an accident. The best way to do that is to build self regulation into the reactor design. If a reactor can regulate itself, then there is no need for a reactor operator. If you eliminate operators, you eliminate operator errors.

Simplicity is an important component of of reactor safety. The fewer parts there are in a reactor, the fewer parts there are to break. One way to build simplicity into a reactor is to rely on the laws of physics and chemistry as much as possible. For example the Westinghouse AP=1000 reactor relies on gravity to feed emergency cooling water into its core. Thus you do not need electricity to pump coolant water into the AP-1000 core, in the event it looses its normal coolant. This is what is called a passive safety feature. Operators do not need to turn on pumps, because as the core looses coolant water, an automatic process releases coolant water from an overhead tank. The water, powered only by gravity, flows into the reactor core, cooling it.

Of course even a gravity feed emergency cooling system costs money to build. Is there any way to save that money? Well if you could push the reactor fuel out of the reactor, you would not have to cool it inside the reactor. If for example your reactor was overheating because it had too much nuclear fuel in the reactor core, you could cool down the reactor by pushing some of the fuel out from the reactor core. Doing this would be difficult with a light water reactor, and doing it would more problems that would requite expensive solutions. So instead reactor designers take other approaches to controlling heat. One would be to increase coolant flow inside the reactor core. Increased coolant would remove heat from the core. Another method would be to insert reactor control rods into the reactor core. The reactor control rods would slow down the chain reaction. But this would lead to a decrease of reactor power output. Thus the reactor operator has a choice to make about how to deal with the increase in reactor heat. A wrong choice might lead to under production of power, or in the worse case it could lead to a serious accident. The history of nuclear accidents suggests that whenever you introduce the possibility of a human being making a bad choice you can count on that happening sooner or later. The best way to control accidents is to take the possibility of making bad choices away from the reactor operator.

The best way to remove bad choices from reactor operators is by designing reactors to operate in a stable fashion, to respond to increases in reactor temperature by automatically pushing fuel out of the reactor core. It would also be desirable if the reactor core got too hot to remove all of the reactor fuel to a place where no chain reaction would be taking place, and where its tempreture could be easily controlled. Impossible, you say? Not at all!

So we want to lower reactor cost by building a reactor with these safety features:

* Simple reactor structure

* Continuous removal of radioactive gases from the reactor fuel

* A strong tendency to push nuclear fuel out of the core as reactor temperature rises

* The reactor is both stable and be self-controlling

* No externally operated controls are required

* Safety features are all passive, are triggered automatically before unsafe reactor conditions arise, and rely on the basic laws of physics and chemistry

* Safety is inherent and safety features cannot be altered by tampering, and are thus fool proof

* Ultimate reactor shut-down can accomplished by moving nuclear fuel from the reactor core

* An automatic, passive feature and automatically feature is used as a means of both triggering the transport and actually removing fuel material from the core if the reactor reaches an undesirable heat level

* The force to empty the core of nuclear fuel solely uses only the power of gravity

* core melt down could never be a problem

* Emergency core cooling would not be required

* Coolant leaks would not lead to core melt down

* Escaping radioisotopes would be either chemically bonded to materials that are solid at sub reactor core temperatures, or is not bonded, encapsulated by solid materials outside of reactor.

* Radioactive gases are continuously removed from the reactor fuel, so that no fuel accident will cause the escape of large amounts of radioactive gases from the reactor core.

* The chemistry of escaped isotopes would facilitate their local and relatively low cost containment.

* The chemical bonding and encapsulation of escaping radioisotopes would facilitate their post-accident clean-up and recovery.

* Even terrorist attacks using large amounts of explosives or direct attacks with large aircraft, would not lead to widespread dispersal of core radioisotopes. Radiation and radioactive materials would be contained locally.

You might believe that it is impossible to build a reactor for which safety is not an added on at extra expense feature. But not only is it possible, but such reactors have already been built and tested. Why do we still have reactors that are expensive to make safe?

Greater inherent safety is can be the outcome of simplified reactor design, and thus lower reactor construction costs. Chemical and physical features of reactor fuel that prevents its dispersal in the event of an accident, in turn can lead to a lowering of containment costs. Stable operating reactors, and the elimination of operator choice, lowers the number of operators needed for safe reactor operation. A smaller staff means that less space is required for staff housing, less staff housing lowers construction and maintenance expenses for staff housing. A smaller staff means smaller staff compensation expenses. Hence greater safety saves on many fronts. It saves in reactor expenses, site construction expenses, and in reactor operations expenses.

Again if we examine what we understand about the cost saving advantages of inherently safe reactor design stand out. We can observe that light water reactor technology, as well as LMFBR technology have some significant inherent safety problems. In order to build a satisfactory level of safety into the design of these reactors, expensive safety features have to be added to the reactor design. Two Generation IV reactor concepts demonstrate superior inherent reactor safety. They are again the Pebble Bed Reactor and the LFTR.

Sea power

I was googling the words LFTR safety this morning, and I came up with something unexpected. The Navy Post Graduate School Foundation encourages Naval officers to study for graduate degrees. Listed under RESEARCH PROJECTS AT THE NAVAL POSTGRADUATE SCHOOL, I found:

CURRENT PROJECTS: Thorium Ship Power

Well, well well, I thought, and read further.

Project Objective: An NPS student design team is investigating the benefits of a liquid-fluoride thorium reactor (LFTR) as a ship power plant. The LFTR offers greater power system density, deep inherent safety, and a simple, closed nuclear fuel cycle using abundant thorium rather than uranium. Successful development of LFTR power plants enable future naval operations for any size vessel even if fossil fuel prices rise dramatically.

Operational Payoff:
The payoff for this work would be a fleet that could operate with impunity to fuel price/availability with a reactor design that is simpler, safer, and less expensive than today’s pressurized-water reactors. Unrestricted electrical power for propulsion, weapons, communications, and land support services (water desalination, electrical power, hydrogen or fuel production).

Design Advantages:

• Smaller systems volume
• Minimizes fissile inventory with no external fissile addition
• Immediate restart or shutdown
• Inherent load following without control rods
• Extraordinarily safe - high negative temperature coefficient / passive decay heat removal

Technical Objective:
High efficiency, safe, low-cost, compact naval nuclear power.

Technology Challenges:
• Thorium fuel requires continuous reprocessing to remove bred 233U from blanket to core.
• Optimized gas turbine machinery for closed-loop and wide temperature range operation.

Technical Approaches:
Online thorium blanket processing, graphite/BeF2 slurry moderator, spiral core design, multi-reheat helium gas-turbine power generators.

Quote: "Increased fuel costs could threaten future naval operations. US thorium reserves can
power us for thousands of years. Increased fuel costs could threaten future naval operations. US
thorium reserves can power us for thousands of years."

Someone has been reading Energy From Thorium!

Keys to Lowering Reactor Costs: Advanced Materials

The cost inflation that is effecting the price of all new electrical generating facilities all over the world is a matter of serious concern. If we assume that anthropogenic global warming is going to require the replacement of virtually every carbon based energy source in the world with a carbon-free energy sources that means that most of the world's generating capacity must be replaced during the next 40 years. The last thing that we need right now is run away inflation of new generator costs. Advocates of renewable energy must face the same inflationary prospects as advocates of nuclear power. The inflation problems of renewable generating system are in some respects worse than the problems of nuclear systems, because renewables use more of the materials that are rapidly increasing in price.

One of the keys to cost control is the substitution of low cost materials for higher costs materials. Lower cost does not mean lower quality, and the use of potential substitutes could in fact lead to improved reactor efficiency. Both silicon carbide (SiC/SiC) composites and Carbon-Carbon composites have potential for reactor use. Carbon-carbon composites are particularly interesting because there is an important history of their use in the aircraft industry. Carbon-carbons are known to be light, strong and fatigue resistant. Manufacturers like Boeing have a good understanding of manufacturing techniques for carbon-carbons parts. Materials and parts manufacture costs with carbon-carbons would be lower and less subject to inflation than with metals. Other advantages of carbon carbons include excellent heat transport properties, making them potential materials for heat exchange, and tolerance for both fluoride salts and helium. Carbon-carbon composites can also withstand any temperature likely to be encountered inside a reactor. Thus the use of carbon-carbon composites is consistent with greater thermal efficiencies than are possible with the use of metal in reactor construction.

Some forms of carbon-carbon composites do not tolerate neutron radiation well. Thus is by no means certain that carbon-carbons can be used for reactor core structures. Material scientists have by no means given up on carbon-carbons in high neutron environments, and research continues. At the very least carbon-carbons can be used for reactor coolant piping, pumps and heat exchanges in LFTRs. If material scientists can solve the radiation tolerance problem carbon-carbons could be used in reactor cores structure as well.

It should be noted that carbon-carbons are potentially ideally suited for LFTR's, but if their neutron radiation problem can be solved, they could also be used to build reactor core structures for PBRs as well. The neutron resistant qualities of SiC/SiC composites have been studied and it would appear that some forms of SiC/SiC are fairly neutron resistant. Exactly how resistant remains to be seen. I have yet to see a definitive statement on the compatibility of SiC/SiCs with fluoride salts, yes, but in discussions of their use with fluoride salts, that is usually assumed. I have seen a statement made some 10 years ago about manufacturing difficulties with SiC/SiCs, but I am not aware if the problem was due to a lack of experience, or if it reflected an underlying problem with SiC/SiCs. It is not clear to what extent use of SiC/SiCs would lower reactor-manufacturing costs. However, its use might still be justified even if it proved more expensive, because it could enable reactors to operate at higher temperatures than would be possible with metal components. Thus if SiC/SiCs proved to be relatively expensive to manufacture, their cost might be repaid many times over by the added electrical output produced by greater thermal efficiencies.

Thus carbon-carbon composites are very promising materials for reactor structures involving movement of liquid salts outside reactors, and for heat exchanges. There use in reactor core structures cannot be discounted, but more research and development are required. SiC/SiC composites are promising materials for reactor core structures, and of course, more research is needed. Thus there appears to be a high likelihood that the use of composites would lower the costs of some Generation IV reactor designs, and could prove advantageous for the PBR and could be highly advantageous for the LFTR. Carbon-carbon composites could also be expected to lower reactor costs, and increase transportability of large reactor modules or even complete small reactors, by lowering reactor weight.

It should be noted that that this discussion points to the compatibility of advance materials with generation IV reactors, and in some cases their incompatibility with other well regarded reactor designs. Thus an unexpected consequence of the potential advantages of advanced materials would be a preference for certain Generation IV reactors - the PBR and the LFTR - over LWRs, and LMFBRs.

I would like to express my appreciation to the participants in the Energy From Thorium Engineering Materials Forum for advancing my knowledge and stimulating my thinking about advanced materials. Of course, I picked up the ball and as usual ran with it in a different direction. The Forum members are not responsible for any fumble I might have incurred.

Robert Hargraves on the economic advantages of small reactors

Introduction: I cross-posted yesterday's post on "Energy From Thorium. Robert Hargraves responded to that post with a comment, and I thought it was worthwhile to reproduce his comment here:

I'm not a nuclear engineer, but here are my ignorant observations about the benefits of small sized nuclear power plants....

1. Small size enables mass production with more experience per unit produced, leading to the economies of production lines and smaller costs for errors.

2. Small size means lower capital investments at risk, with the opportunity to add to power plants as needed.

3. Small size means that low energy demand areas of the developing nations might be able to acquire nuclear power plants.

4. Small size means that power plants can be distributed closer to the points of power consumption, reducing transmission losses, reducing network management requirements, and enabling local control of production and consumption in emergencies. The "intelligent grid" concept flies in the face of the success of the distributed network control intelligence of the Internet.

My latest adventure in nuclear power is the course I gave and posted at http://rethinkingnuclearpower.googlepages.com

Afterword: Robert's blog is well worth looking at.  Robert probably started looking at the small reactor-mass production equation before I did.  However, Robert was thinking in terms of producing reactor construction kits here, which would still require considerable onsite  assembly. My view is that everything possible should be done in the factory, with the reactor shipped out in a few large modules, such as a core module, or a power generator module.  Local assembly of the modules should be like putting together "legos", simple and quick.   Robert advocates building Pebble Bed Reactors, and of course, the Pebble Bed concept has many attractive features, including a potential for high thermal efficiency, and inherent safety.    Of course the the LFTR matches the advantageous features of the PBR, and offers many attractive features which the PBR lacks.   But Robert's observations are correct for the manufacturing potential of both reactors.  Robert is a big picture thinker.