Wednesday, July 22, 2009

The Keys to Lowering Reactor Cost: Some Siting Considerations

Since I wrote this post, my thinking has turned to the use use of LFTRs to re[;ace natural gas fired turbines and combined cycle generators. David LeBlanc's suggestion which was also found in an old ORNL research report, was that stainless steel and other low cost materials could be used in the LFTR with a relatively modest performance penalty in exchange for a cost advantage. It occurred to me, that given the LFTR's already modest cost, that a low cost LFTR could easily replace natural gas generators as peak power producers. I called the Peak generation LFTR the "Big Lots" reactor, after my favorite bargain shopping haunt. The LFTR's negative co-efficiency of reactivity gives it the unique ability to shut off while at maximum coolant temperature. Thus the LFTR enters peak reserve ready to almost instantly spin its turbines to maximum output levels. Thus natural gas fired power plant sites would also be available for LFTR conversions. LFTRs and be air cooled, thus the availability of coolant water would not be an issue, and LFTR can generate electricity at a lower cost than natural gas generation system.

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.

There are, of course alternatives to underground siting. Kirk S. wants to site reactors under water. Actually there are actually quit a lot of mobile 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 is best handled by the inherent safety features of the LFTR.

Underwater siting would work if for reactors located on the 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 coastal reactors under water we still need to build inland reactors, and there are siting issues. That is where underground sites come in. I will talk more about them shortly.

One major 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. This is the case for new nuclear power plants as well as wind farms. Added grid capacity can be expensive, in some cases running to billions of dollars.

To the extent possible, in a crash program to replace old power plants with nuclear generated power, we might want to avoid secondary expenses related to the grid. Later on we might want to upgrade the grid, but the major goal is to stop producing CO2 as quickly as possible, 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 of the Bull Run plant, and I suspect that you would not have to dig very deep to find subsurface 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.

Aside from cost savings, why then should we think about underground settings? The use of underground reactor sites 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 in the 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
• Transportation costs,through co-located storage/disposal facilities
• Excavation costs, which are ~$20/m3 in salt vs~$40 to $80/m3in
• 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 recover 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,

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