In depth: Costs

Cost competitiveness should be a design goal

In his memoirs, Alvin Weinberg, director of Oak Ridge National Laboratory at the time of the Molten Salt Reactor Experiment, cites from his 1964 ‘State of the Lab’ year-end speech. “…extreme caution is necessary whenever one speaks of untried reactors”.

Weinberg’s words also apply to the subject of the cost of the power produced by future thorium MSR’s. Simply put, assertions made on the cost of MSR are inevitably speculative at the present time.

Nevertheless, some statements regarding the cost bandwidth of MSR’s are worth noting.

Some of these are historic, like the remark that Alvin Weinberg makes, a few lines after the reference to his 1964 speech: “I personally had concluded that the commercial success of nuclear power would have to await the development of the breeder” (in his memoirs, Weinberg uses the word ‘breeder’ when referring to thorium MSR’s).

Thorium-MSR’s higher efficiency is due to its higher operating temperature of around 700 °C. Higher temperatures are favourable for conversion of thermal to electrical energy, leading to conversion efficiencies of 45%-50% instead of the 33% typical for coal and traditional nuclear power plants. The high temperature also allows for excess heat to be used for powering other industrial processes such as hydrogen production and desalination.

Herbert MacPherson, who was in charge of the Molten Salt Reactor Experiment at the time, is even more specific in his cost estimation. In 1970 MSR was estimated to have 1% of capital cost compared to the LWR. However the cost of machining tools, remote maintenance of radioactive primary systems and decommissioning were still unsure at the time (MacPherson, 1985)(Weinberg, 1994).

The MIT study “The Future of Nuclear Power” puts capital costs for coal plants at $2,30 per watt and nuclear power at $4,00 per watt.

The above figures are the capital cost for LWR’s. An important reason for the higher costs of LWR’s is in the nuclear power plant construction. There are reasons to assume that construction costs of thorium-MSR-based power plants will be lower. One difference is that LWR designs need a large reinforced concrete dome constructed to accommodate for a possible steam explosion, in case of a pressure breach. In addition, the primary system is pressurized and primary system system failure is a severe safety accident, causing the primary steel components to be overdimensioned and constructed and tested following the highest quality standards available. A thorium-MSR operates at atmospheric pressure. It contains no super-heated pressurized water, and hence will not need this large dome. For a thorium-MSR a more closefitting structure will suffice. One concept is a hardened concrete facility below ground with a concrete lid on ground level to protect it from aircraft impact and other possible forms of assault.

A large share of the radioactive shielding in LWR systems is achieved by water in the primary system and around the reactor pressure vessel. In an MSR all shielding of the primary system will most likely be established by heavy and thick concrete to bring especially gamma radiation to acceptable levels. The concrete is mainly there for shielding, it has no pressure containment function, and hence quality requirements are more modest, but quite a lot will be needed.

In a light water reactor the fuel cost form a large share of the operating costs, but they hardly impact the electricity price, which is determined by capital costs, and infrastructure improvements enforced by ever changing regulations.

Other factors relevant to the cost profile are that a thorium-MSR can do without expensive emergency coolant injection systems, lower fuel costs (natural thorium instead of enriched uranium, no need for fuel element fabrication), simpler fuel handling (liquid fuel, no periodic shutdowns needed to replace solid fuel elements), smaller components, and a much higher energy efficiency.

Another factor relevant to the cost per kWh is that thorium-MSR’s are expected to perform with higher efficiency, due to their higher operating temperature of up to 700 °C. Higher temperatures are favourable for conversion of thermal to electrical energy, leading to conversion efficiencies of 45%-50% instead of the 33% typical for coal and traditional nuclear power plants. The high temperature also allows for excess heat to be used for powering other industrial processes such as hydrogen production and desalination.

On the other side, it is expected that a well-designed thorium MSR includes a unit that will perform inline cleaning of the salt mixture, a feature that as yet has to be developed and will add to the cost.

It has been suggested that based on its size and design, it may be feasible to produce 100 megawatt thorium-MSR’s factories for around $200 million apiece, similar to the way Boeing produces large aircraft in factories, which would come down to at $2,00 per watt, lower than the capital cost of a coal power plant.

Two of the present day start-up-companies developing MSR Technology, Terrestrial Energy and Thorcon Power, claim that their business case shows that their molten salt based power systems can produce energy cheaper than coal. As was stated above, it is impossible to either confirm or reject such claims where it concerns untried reactors. One might argue that an MSR prototype successfully operated from 1965-1969, which was indeed the case, but the present day licensing procedure has not yet taken place.

But some authors argue that construction cost only explains a modest part of the capital cost required for nuclear power: a substantial part of the capital cost for nuclear power plants to the mandatory licensing costs.

Another reason for high construction costs is that most of the existing nuclear power plants have their own design. This not only prevents cost savings based on standard designs, it also is a tremendous driver of licensing costs.

One of the companies mentioned above displays a cost philosophy that is not specific to any design. This philosophy basically states that cost is something that should be designed for from the outset. This philosophy is relevant for any effort to develop a power technology that aims for being cost competitive. Their approach to handling the high licensing cost of molten salt reactors is to basically license a single design, then stick to that design. This is comparable to car licensing: the license is granted to a type. Once in production, the authorities need only check if a specific car sticks to the design.

Standardized, modular designs will be crucial for developing cost competitive nuclear reactors, regardless of the technology used. This is relevant to the licencing cost, but also to deployment times. Mass produced thorium-MSR’s could even replace the power generation components in existing fossil fuel powered plants, integrating with the existing electrical distribution infrastructure which would also save large amounts of money (Deutch, et al., 2009, p. 6)(Juhasz, et al., 2009, p. 4)(Hargraves & Moir, 2010, pp. 310,311).

The challenge however will be to get past the initial cost. This will not only involve the designing and building the first thorium MSR, it will also involve setting up a proper licensing framework, which will be largely design specific, and requires the initiation of the thorium fuel cycle.