Leslie Dewan and Mark Massie, as Doctoral candidates in the nuclear department at MIT, produced a modified design of a reactor technology that first appeared many decades ago : the molten salt reactor, originally designed, built and tested at Oak Ridge Tennessee during the 1950’s 60’s and 70’s.
After her graduation, the two formed Transatomic Power in 2011, as a means of completing the design and commercializing their reactor design. Recently, they received a $2 million grant of venture capital from Founders Fund. The money will be used to test and verify the corrosion resistance of metals that their design employs in the reactor core and piping, as well as modeling the reactor design. One major purpose of the testing is to determine if the moderator’s lifespan (currently only vaguely estimated) will require periodic replacement, or will last throughout the reactor’s service lifespan. The answer to this question will not prove an obstacle to the design, only to the need for a design that provides for modulator access (for replacement).
Dewan believes one of the MSRs biggest advantage is the its ability to burn SNF (spent nuclear fuel – “nuclear wastes”) more or less completely, extracting 20 times more energy from uranium than a conventional reactor, producing a far smaller and far less radioactive final waste product, that will be much easier and cheaper to store, and will retain its radioactivity above background levels for only a few centuries rather than thousands of years. It also can be configured to burn Thorium, although that is not Dewan’s desired fuel, for several reasons : the greater perceived need to burn nuclear wastes, and the inferiority of a Thorium reactor’s proliferation safeguards, the lack of any need for an alternative to uranium fuel, as well as the current existence of a uranium fuel processing system.
The original Oak Ridge MSR design was modified in only a few ways : use of a different material for the moderator in place of the original space-consuming graphite, and slightly modifying the molten fuel salt (uranium dissolved in lithium flouride) being the most important. Together, these modifications allow for commercially competitive amounts of power to be generated, not possible from the experimental molten salt reactors built at Oak Ridge, and the ability to be powered by low level radioactive fuel, reducing proliferation concerns.
The Transatomic Power plant design has an estimated overnight build cost of $2 billion for a 520MWe unit. The lower costs are primarily due to the fact that no massive high pressure containment vessels or piping is needed for much of the plant, and also due to its higher efficiency output temps, which allow for smaller power turbines to be used. Power turbines constitute a major cost in any nuclear power plant design. With these build costs and the prospect of near zero fuel costs, there likely won’t be another power source that is cheaper, all things considered. Another advantage of the design is its ability to support load following – i.e. to alter power output quickly as demand changes. As of now only some fossil fueled and hydroelectric plants have such an ability.
This capability would allow for a larger percentage of nuclear power in any grid, which today only can exist as baseload power (although pumped storage does sometimes allow for nuclear power to be stored and then later available as hydroelectric, load following power). This plant would also likely reduce (realistically, probably eliminate) commercial prospects for the larger versions of small modular reactors, those that produce over 250 MWs. It achieves (actually, exceeds) the economies of scale of a conventional large reactor, something small modular reactors are totally incapable of. It also does not require shutdown for refueling – it is refueled at intervals and can be run continuously for decades, another cost advantage over conventional reactors.
Commercially, a $2 billion dollar 520MWe power plant can meet the needs of utilities facing only gradually increasing demand as well as those whose service area doesn’t require the 1000MW plus size of a conventional reactor, or those wanting to replace fossil-fueled load-following or baseload coal plants. Build time is estimated to be 36 months. The plant does not require any source of cooling water – the molten salt fuel liquid acts as its own coolant as it flows thru the primary loop, transmitting heat (but not radiation) to an intermediate loop. The lack of any requirement for cooling water dramatically increases the number of potential build sites. In fact, its inherent safety characteristics would allow for these reactors to be sited near large population centers, avoiding lengthy transmissions, reducing costs due to power losses and transmission line construction.
In considering the reactor’s characteristics with respect to safety, it’s hard to conceive of a situation that anyone would find threatening or dangerous. Every reactor state that one can reasonably imagine as conceivable, ends up with the reactor shutting down as the molten salt cools (slightly) and becomes a solid at which point no fission is possible (or heats up, reducing fission). No radioactive material (the molten fuel salt liquid) is ever subjected to anything other than slightly above atmospheric pressures, which essentially eliminates any radioactive blast issues, ( in fact, all pressures work towards forcing the radioactive material back into the reactor system), and no hydrogen emissions can develop to the point of posing an explosive danger.
The entire steam turbine system and its piping, which contains the only only material under significant pressure (water), is completely radiation free, meaning that any rupture in that system is, radioactivity speaking, a non-event. The fuel liquid operates at a much lower temperature than fuel rods in a conventional reactor and never contains the excessive reactivity potential possessed by a conventional reactor at the start of its two to three year run cycle.
The entire system is considered walk-away safe – no operator actions, or electricity, or pumps are ever needed in order for the system to shut down should an accident occur. The reactor will achieve a stable shutdown state in a fairly short time frame.
It’s hard to imagine anyone having any objections to this nuclear reactor design. For those attracted to the safety of Thorium reactors or concerned about future uranium fuel supplies (such as India) , this design is better all the way around. With its meager fuel requirements, uranium will be economically available from either SNF, terrestrial mining or ocean extractable uranium ( freely available to virtually every country) for many millennia, eliminating any conceivable concerns about future fuel sources. And, of course, it can burn Thorium as well, should anyone so desire.
The superior economics and flexibility and load following characteristics, lack of any need for refueling shutdown, elimination of any significant fuel cost increases, removal or reduction of nuclear waste storage requirements, a much lower build cost requirement and elimination of the economic danger of a multi-billion dollar nuclear accident, would certainly make these reactors the first choice for any grid operator. And the plants can easily be co-located with conventional nuclear plants without placing any additional water demands, and be located near the likely source of the SNF they will consume as fuel.
One finds it difficult to foresee any significant risks when buying into this reactor design, financial or otherwise. I see a real possibility for this reactor design to become not only the standard and universal nuclear reactor, but also the standard commercial power plant as well, rendering all others of this size and larger obsolete. It is everything one could reasonably ask for in a power plant.
A complete technical description, accompanied by economic and safety rationales can be found at the company’s website :