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 United 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.