Friday, November 12, 2010

The Cost Benefit of Molten Salt Nuclear Technology

Charles Forsberg was not alone in his views. In fact the concept of a salt cooled high temperature reactor had three fathers.
The AHTR, which could also be used to produce electricity, was conceived in 2001 by Forsberg, Paul S. Pickard of DOE's Sandia National Laboratories, and Per Peterson of the University of California at Berkeley. The AHTR is based on three technological feats: a molten-salt coolant developed at ORNL for the nuclear aircraft propulsion program of the 1950s and the molten salt breeder reactor program of the 1960s; fuel elements made of coated nuclear fuel particles embedded in a graphite matrix, developed in the 1970s at ORNL for the gas-cooled reactor program; and passive safety systems devised by industry for gas-cooled and liquid-metal reactors.
Packard was subsequently to not play a major role in the development of the AHTR concept, but Per Peterson, who is now a member of Energy Secretary Chu's Blue Ribbon Commission, worked out an analysis which showed that the Graphite embedded fuel, molten salt cooled reactor concept had a very significant potential to lower nuclear costs.

Per Peterson argues that Molten salt cooled reactors are more compact than traditional nuclear technology. Peterson argued that reactor costs are related to the total building volume which the reactor occupies. One GW Light Water reactors of the 1970's typically occupied 336 m(3) per MWe of rated generation capacity while Generation III+ reactors typically occupy from 422 to 486 M(3) per MWe of rated capacity. Larger building volume suggests higher costs, because they require more materials and more labor to build. However not all advanced reactors would save money on building costs. Peterson reported that the Pebble Bed Modular reactor occupies 1285 M(3) per MWe of rated capacity. This finding suggests that the PBMR is not cost competitive with traditional Light Water Reactors. Yet by turning the PBMR into a Molten Salt cooled reactor, Peterson calculated, its construction cost could be dramatically lowered.

Peterson worked to develop a hybrid Molten Salt cooled Pebble Bed Reactor. Pebble Bed Modular Reactors use Helium as a coolant. The heat removal capacity of helium is much smaller than the heat removal capacity of molten salts. Thus by switching coolants, reactor designers could decrease the reactor coolant volume. Decreased coolant volume means a smaller core and smaller heat exchanges. This in turn dramatically decreases reactor system housing volume. Peterson estimates that the building volume for a 410 MWe hybrid Pebble Bed-Molten salt cooled reactor (the PB-AHTR would be 260 M(3) per MWe of rated generating capacity.

Peterson's estimate is unprecedented and contradicts normal assumptions about nuclear power economies of scale. The usual assumption about economies of scale

Molten Salt Reactor researchers have consistently found that MS cooled and fueled reactors costs were equal to or less than the cost of Light Water Reactors. For example, ORNL researchers who were attempting to estimate the capitol cost of a Molten Salt Breeder Reactor design in 1972, attempted to compare the cost of the MSBR with the cost of a typical Pressurized Water Reactor (PWR) of the time wrote in ORNL 4541 (1972),
The capitalization costs for the two reactor types are not greatly different. In a broad sense this can be explained by the fact that only about one-third of the total cost is for reactor equipment, the remainder being for the heat-power system, general facilities, and indirect costs, which are expenses that are somewhat similar for all thermal power plants. Variations in reactor equipment costs are not of sufficient magnitude to cause striking differences in the overall capital requirement because there are rough similarities in costs of vessels, shielding, etc., and many of the differences that do exist are offsetting,
The cost competitiveness of the MSBR is remarkable for several reasons:
First the MSBR had superior performance features.
One of the distinguishing features of the MSBR station is the use of initial steam conditions of IO00°F and 3500 psia, with reheat to IO00°F. As shown in account '_.31,Table 15.1, a turbine-generator for these conditions has a relatively low first cost compared of the turbine-generator for a PWR. Good utilization of the available heat in the MSBR is reflected in the relatively low steam mass flow rates and amount of heat transfer surface needed. Although no credit was taken for it in the MSBR cost estimate, this factor could also, influence siting and environmental control costs in that the heat rejected to the MSBR condensing water is only about one-half that for the PWR.
Secondly, the MSBR required several safety and maintenance features not required by the PWR.
The alternate reactor vessel head assembly used to facilitate replacement of the core graphite in the MSBR is included in the first cost of the plant. The estimate also includes the special maintenance equipment used for the replacement operation. The MSBR does not consider a safeguards cooling system (account 223, Table 15.1) as such but does require a drain tank with afterheat-removal capability, as included in account 225, Table D. 1.
It should be pointed out that ORNL researchers had failed to capture the effects of inflation on LWR costs. During the decade of the 1970's PWR costs rose significantly faster than over all inflation. Some of those cost increases were due to over all inflationary pressure operating on the U
nited States economy, while other components of the inflation were due to the effects of regulation on nuclear costs improvements in reactor design also contributed to the increase in the cost of reactors, and eventually older nuclear plants were modified to reflect improved safety technology and other features, developed by the nuclear manufacturing industry. In many instances those changes and at least some of the other inflationary pressures operating on nuclear costs, would not have fallen equally on the MSBR.

It should also be noted that the MSBR was a very new technology then. MSBR designers in 1972 were unaware of issues related to nuclear costs, that are matters of concern in 2010. Reactor designers seeking to take advantage of Molten salt coolant/fuel carrier technology are much more concerned about lowering and/or controlling nuclear cost than Oak Ridge reactor designers were in 1972.

ORNL researchers had attempted to update MSR cost estimates in 1975, and that updating process continued to about 1980. However ORNL Molten Salt Technology cost estimates after 1972 were largely based on the 1972 ORNL-4541 study. The weakness of the MSBR/PWR comparisons were ignored, and the estimated cost of PWRs became unrealistically low with the passage of time. Thus I found that the ORNL staff had estimated the cost of PWRs to be $597 million in 1978, the cost was in fact probably closer to $1.5 billion.

In 2002, LLNL physicist Ralph Moir attempted to compare the cost of the cost of electricity from coal, conventional nuclear power and potential Molten Salt Reactors. Moir found,
We conclude that the cost of electricity generated by an MSR is competitive with other sources based on the old but comprehensive evaluations. Using the same methodology, the COE is 7% lower than that for water reactors and 9% lower than that for coal plants. The information in this note based on the three options as defined in 1978 does not include current safety, licensing, and environmental standards which will impact costs, as will CO2 sequestering and
increased HAP (Hazardous Air Pollutants) for coal. The low cost of electricity along with the MSR’s many other potential advantages suggests that stopping the development of the MSR might have been a mistake and that restarting the program should be considered. These advantages include: the ability to burn thorium, the ability to burn most of its own actinide wastes (and some wastes from other plants), the ability to continuously add fuel and remove fission products, and the ability to provide an alternative to the plutonium cycle with its association with nuclear weapons. The fuel cycle is near to being closed, and fuel is burned with high conversion efficiency (near breeder). Again, it is emphasized that the MSR is a conceptual design several decades old. A new evaluation of MSR is strongly recommended based on current safety, licensing and environmental standards and comparisons made to alternative power plants.
Moir's calculations, if anything, fell short of the cost savings potential of molten salt nuclear technology.
Dr. Furukawa's company, "International Thorium Energy & Molten-Salt Technology Inc." (IThEMS) has estimated the cost of the FUJI to be 30% less than the cost of conventional water cooled reactors. It should be noted that Dr. Furukawa's estimate is, if anything quite conservative. The 30% lower cost estimate, is entirely based on added efficiency, and does not take into account the cost savings derived from smaller coolant volume, the cost saving potential of small reactor factory production, interest savings contingent on shorter manufacturing time, and lower borrowing costs, related to diminished risks entailed in financing modest size nuclear projects. In short, Dr. Furukawa's FUJI reactor project, as well as Per Peterson's PB-AHTR are likely to create per storms of nuclear cost savings. Since most of the technology for both projects is already in the can, molten salt nuclear technology already potentially offers very large cost savings, rapid deployment, and a very significant shift away from carbon emitting fossil fuel technology, to a sustainable post carbon, nuclear based economy.


Martin Burkle said...

What are your thoughts on comparing the AP1000 containment vessel to the containment vessel for a molten salt reactor. As I understand the containment vessel for an AP1000, it is a silo about 2 inches thick with the diameter and height equal to about 1/2 of a football field. I think its major function is to contain the pressure of a reactor rupture. The bottom bowl is made of 50 some pieces that are welded together on site. The pieces for Vogle were made in Japan and shipped here. It will take about a year using special welding techniques to put the pieces together on a site specially built for this construction. The worlds largest crane is needed to move the bowl over to the reactor site. This sounds expensive to me.
Question: Does a molten salt reactor running at atmospheric pressure need a containment vessel? Would it need to be 2 inches thick and air tight? How much less would this cost?

Mike Swift said...

Martin, I believe the AP 1000 containment vessel design requires a differential pressure of 49 psi. Its size is determined by the engineering trade offs of room needed to contain all reactor components, to give a volume to keep the differential pressure down when all of the water in the plant is vented to the containment vessel, surface area required to allow passive cooling in an accident, and cost.
On a LFTR there would be no pressure rating requirement, OK maybe two or three psi, and little surface area for heat removal required. Only a meter or two of concrete for shielding, and intrusion protection.

Martin Burkle said...

Thanks, Mike, for the explanation.
I think Per Peterson did not include volume estimates for the AP1000 whose footprint is much smaller than 1970 style reactors. The volume of an AP1000 containment vessel is about 80,000 cubic meters or 80 cubic meters per MWe. Calculated from diameter of 40 meters and height of 65 meters. The molten salt reactor needs to be even smaller than the AP1000 to be cost competitive.
A lighter weight smaller containment vessel should save construction costs and reduce build time (think reduced interest cost).
Both plants (AP600 and AP1000) utilize a 39.6 meter (130 feet) diameter freestanding containment vessel. AP600 utilizes three ring sections and an upper and lower head. AP1000 has an additional ring section to provide additional free volume. The AP1000 containment design pressure has been increased from 3.10 bar (45 psig) to 4.07 bar (59 psig) through the use of a slightly thicker wall thickness 4.44 cm (1 3/4 in) and a stronger steel. The ring sections and vessel heads are constructed of steel plates pre-formed in an offsite fabrication facility and shipped to the site for assembly and installation using a large-capacity crane. The largest ring section includes the polar crane support and weighs approximately 658 metric tons (725 tons). Each of the two heads weighs approximately 500 metric tons (550 tons).

Westinghouse has signed off contracts for two more AP1000 containment vessels. Chicago Bridge & Iron (CB&I) will manufacture the two components, which each measure some 36 metres in diameter and 65 metres in height, for a fee of $150 million. CB&I said design work would begin immediately with construction to follow during next year, the first vessel being complete in 2015, the second in 2018. It was not revealed which planned nuclear units the components are destined for - CB&I narrowing it down only to "the southeastern US" where seven pairs of AP1000s are currently planned. An identical contract was announced in late October for deliveries in 2014 and 2015.

Martin Burkle said...

Thanks, Mike for the explanation.
I think Per Peterson did not include volume estimates for the AP1000 whose footprint is much smaller than 1970 style reactors. The volume of an AP1000 containment vessel is about 80,000 cubic meters or 80 cubic meters per MWe. Calculated from diameter of 40 meters and height of 65 meters. The molten salt reactor needs to be even smaller than the AP1000 to be cost competitive.
A lighter weight smaller containment vessel should save construction costs and reduce build time (think reduced interest cost).

Charles Barton said...

Martin, Per Peterson did include the materials use of the AP-1000 in his study. The Steel use of the AP-1000 is similar to the steel use of a 1970's Generation II reactor. In addition to materials, input, field labor plays a major role in reactor costs and on site construction of the AP-1000 requires between 12 and 20 million hours of labor.

Anonymous said...

The real comparison then is not a small LFTR for each m/MW but a LARGE one of comparible MW output to a AP1000. Comparing a 1150MW LFTR to the AP1000 would still give a huge savings based on reactor design. Size is irrelevant for the LFTR as it's directly scalable.


Ron Mylar said...

Nuclear technology is rising very fast. As you have shared each and every single step of the nuclear energy. And that is very beneficial.

Anonymous said...

I am looking for the 1972 Oak Ridge molten salt costing paper. This was referenced above as ORNL 4541 but that is not a costing paper. It is
F. W. Wiffen and E. E. Bloom
I've tried to find this paper several other places but no luck. Can you help me?

Charles Barton said...

Anonymous, you are asking about a well known document, which lays out the design of a single fluid Molten Salt Breeder Reactor.

here is a link:

If you have problems with the link the report can be found in the Energy from Thorium document archive.


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