ORNL Offers a Brief Look at MSR/LFTR Economies

A recent ORNL report, Fast Spectrum Molten Salt Reactor Options, offers some insight into the cost lowering potential of MSR nuclear technology. Since Nuclear Green has always had an interest in the cost lowering potential of MSR technology, I intend to review the cost related information included in this report, while in some cases offering a context for that information.

The "Fast Spectrum" report does not offer and cost evaluation in terms of dollar costs, indeed this would not be possible. The report offers an overview of technical options, and no dollar cost evaluation is possible outside the context of a specific design project. The report acknowledges,

A confident assessment of the economic performance of an FS-MSR is not yet possible. Technology, regulatory requirements, and market conditions have changed significantly over the 40 years since the economic assessments accompanying the MSBR; therefore, the cost inferences drawn from the earlier work have such large error bands that they provide little guidance. Additionally, the neutron spectrum of the present evaluation alters the fuel cycle both in and outside the power plant site sufficiently that direct analogies to other reactor concepts are challenging. The most challenging aspect of reporting a cost for an FS-MSR, however, arises from the concept flexibility. A no-heavy-metal reprocessing design variant has a plant layout much different from that of a full-recycle plant intending to directly accept used LWR fuel as its fuel source. Similarly, a plant intending to produce gasoline as its primary product has an entirely different power cycle compared with an electricity generator.

Overall economic tendencies, however, can be estimated by comparing FS-MSR attributes with those of other nuclear power systems. A summary of FS-MSR attributes and their cost implications is provided in Table 2. A primary cost metric for any power plant is its thermal efficiency. FS-MSRs, as high- temperature power plants, are anticipated to have 45–48% thermal efficiencies, a 12–15% efficiency advantage over LWRs. As refueling for an FS-MSR would be performed on-line, the plant availability would be expected to eventually, once maintenance techniques were developed and matured, surpass that for an LWR.

Thus costs are evaluated in relationship to the cost of Light Water Reactor costs. For example, the absence of a fuel fabrication requirement would lower FMSR costs and indeed all MSR costs relative to LWRs

Other FMSR characteristics that would tend to lower capital costs noted by the Fast Spectrum report would include,

* No fuel handling equipment or pool storage facilities
* No irradiated cladding or matrix material in ultimate waste stream
* Large temperature reactivity coefficient
* No cladding- or matrix-based temperature limits in accident scenarios
* Safe shutdown possible through geometry control in accident scenarios
* Higher primary coolant volumetric heat capacity
* Visually transparent, low-pressure, chemically stable coolant

In addition to these cost lowering characteristics, the capacity of all MSRs to operate at a one atmosphere pressure offers a further and important cost lowering potential.

The ORNL Fast Spectrum report also noted characteristics of FMSRs that would lower electrical costs to customers, or increase utility revenue per unit of electricity generated. These include,

* No cladding-based burn up limits
* Higher operating temperature
* Flexible input fuel chemical form
* Flexible input fuel isotopic content

A number of FMSR characteristics that would raise capital costs include,

* No cladding as fission product barrier with a substitute fission product barrier
* Higher operating temperature
* Highly radioactive, fissile-bearing primary coolant
* Potential for safeguards concerns with separated material
* Material corrosion problems

In the case of materials corrosion, it should be noted that there is a low cost work around, if the designer is willing to accept a somewhat lower but still high by LWR operating temperature.

One MSR characteristics offer a mixed cost picture. This was:

* Continuous separation of fission products (and reduction of source term in accident scenarios)

Not only did continuous separation have potential to lower safety related manufacturing and construction costs, but it offered a potential for dramatically lowering regulatory costs. If gaseous and volatile fission products are removed from a reactor as they are produced by nuclear fission, then the motive for most aspects of nuclear regulation is disappears. Thus the cost of nuclear regulation can be lowered. In addition, if separated from the coolant salts, many fission products become salable, either immediately or after a laps of some time. Thus fission product separation can lead to a new revenue stream. Finally although fission product removal devices add to capital costs, their cost can be lowered if Molten Salt Reactors are mass-produced.

It should be noted that the capital cost raising and lowering picture is similar other forms of MSR, with factors such as coolant salt choice, core design including graphite use, and relative neutron speed (thermal, epithermal, and fast), effecting capital costs.

The Fast MSR offers a tool for managing the actinide content of nuclear waste. . In 1991, Uri Gat, and J. R. Engel of ORNL, and C. H. Dodds, of the University of Tennessee, proposed burning fissile fuel from dismantled nuclear weapons in LFTRs, as a means of nuclear deproliferation. That is the process of destroying the raw materials of nuclear weapons.

V. V. Ignatiev, S. A. Konakov, S. A. Subbotine, and R. Y. Zakirov of the Kurchatov Institute in Moscow, and K. Grebenkine proposed the use of Molten Salt Reactors as a means of disposing of nuclear waste. They noted that LFTRs had advantages over Liquid Metal reactors for nuclear waste disposal. The Russian research has lead to the development of the MOSART reactor design. The MOSART is a liquid salt fuel reactor concept intended to burn nuclear waste.
A similar proposal has come from Charles W. Forsberg of ORNL.

The integral Fast Reactor can perform a similar function. and while I have come to appreciate the IFR design, it still has safety problems that would not trouble a fast MSR design. In addition, fast reactors require very large start up charges, in comparison to MSR thermal thorium breeders. The large size of fast start up charges limits their scalability. Thus ten times as many LFTR can be started with the plutonium from nuclear waste, as IFRs or FMSRs. Fast reactors thus are an option for disposing of plutonium from nuclear waste. LFTRs can be started with Reactor grade plutonium (RGP), U-235 or U-233 if it is available. They can be started with a mixture of reactor fuels, or they can be started with all three. The current American stockpile of RGP is gig enough to start enough LFTRs to supply the entire American electrical demand and then some.

Some IFR advocates argue that high breeding ratio IFRs are rapidly scalable because they can produce a very large amount of nuclear fuel. But IFR design research and development has to date largely focused on IFRs capable of burning RGP with breeding ratios similar to those of thermal LFTR breeders. Higher IFR breeding ratios are undoubtedly possible, but they would require much R&D and would never be as safe as FMSRs. Thus RGP can be disposed of by fast reactors, but Lars Jorgensen has established that a fleet of thermal LFTRs can dispose of our entire stock of RGP in under 300 years. Thus if it is viewed as desirable to use the RGP found in "nuclear waste" to start thermal breeder LFTRs, it can be used to start hundreds of LFTRs. Since actinide disposal is the largest single problem associated with the so called nuclear waste issue, the thermal LFTR-RGP start option may well represent the best option for nuclear waste management.

At any rate ORNL FMSR report, offers further support for the contention that MSRs have the potential for lowering nuclear costs. The cost lowering features of the FMSR are all available in high scalable thermal spectrum LFTRs, as well as uranium fueled MSR designs. In addition small MSRs can be built in large numbers in factories. Factory produced small MSR/LFTR modules can be shipped by truck or by train to final assembly sites, or completely assembled in factories and shipped by barge. Not only can they be used to provide electrical power, but they can produce industrial heat, serve as the basis of combined heat and power systems, and even include bottom cycle desalinization. Thus the small MSR may prove to have not only a lower cost than conventional nuclear power plants, but superior versatility.

It is clear then that if breeder scalability and rapid manufacture is desirable, the thermal MSR/LFTR path holds significant advantages over the FMSR or IFR fast breeder approach.