Molten Salt Reactor Safety Related Advantages

The molten salt reactor was not exactly intended although Ed Bettis and his associates were concerned with the safety of the original sodium cooled Aircraft reactor design. They just understood that the original reactor had a positive coefficient of reactivity, and that coupled with the sodium cooling was extremely bad news. Their calculations had shown that a fluoride salt cooled reactor would feature a negative coefficient of reactivity. Their choice of fluoride salts was not a fortuitous accident. They worked for the Oak Ridge K-25 plant, which was the largest industrial facility in the world that used chemical processes based on fluoride chemistry, and thus knew that their project would have in house access to chemists who understood fluoride chemistry.

But after the ANP shifted to ORNL in 1950' the scientists involved began to understand that Molten Salt Reactors offered exceptional nuclear safety characteristics. First, reactors are made less safe by dangerous things that you put into their core. Things like water and sodium Water is dangerous because under heat and pressure it turns to steam and can explode. Steam explosions are well known problems with the use of water as a heat to work transfer medium. The literature of the early age of steam features dozens of accounts of boiler explosions. Boiler explosions are not just a curiosity from the past, witness the 2003 boiler explosion aboard the cruse ship Norway while in port in Miami. Light and heavy water cooled reactors are basically boilers heated by nuclear reactors. In order to operate efficiently core coolant water is superheated and kept liquid by high pressure. The presence of critically heated water in the core of water cooled reactors is a fundamental safety issue, that requires special design features to manage. Those features cost money to design and implement.

In contrast Molten Salt Reactors, even while operating at high temperatures, do not produce more than a single atmosphere's pressure, and thus will not produce anything like a steam explosion. Thus MSRs are at a significant advantage as far as nuclear safety costs.

The MSR was designed to cope with a number of safety problems associated with a liquid sodium cooled reactor. While liquid sodium cooled reactors including sodium cooled fast breeders do not operate under high pressures, the chemical nature of sodium, as well as some particularities of sodium flow inside reactor cores, create some safety issues. Sodium is extremely chemically active and will burn in contact with air and water. Thus special care must be taken with sodium cooled reactors to maintain separation between between coolant sodium and air, as well as structural materials which contain water such as concrete. This necessitates special design features which may increase the cost of sodium cooled reactors.

In contrast molten salts used in MSR cores do not burn. In addition the tend to freeze as some as their temperature is dropped by air contact. Thus MSR salt leaks can be expected to self seal. Since the reactor core salt is under only a one atmosphere pressure the frozen salt leak seal can be expected to hold. During the Oak Ridge Molten Salt Reactor Experiment researchers experienced reactor salt leaks on laboratory floors. These were cleaned up without difficulty.

In addition, research on fluid flow inside sodium cooled fast reactors has indicated the existence of flow problems called voids. A void can potentially cause a loss of operator control of a sodium cooled reactor, and lead to reactor run aways with potentially catastrophic consequences. Avoiding the void problem may lead to penalties such as limiting reactor performance and breeding capacity.

A simple Uranium cycle Denatured Molten Salt Reactor (DMSR) would not include such a potential for reactor reactor run away. Single fluid MSRs are extremely stable, and will shut down automatically if they overheat, due to fluid fuel expansion. For this reason there is no reason for control rods, or reactor monitoring by operators. ORNL researchers preparing for the 1960's Molten Salt Reactor Experiment determined that MSR operators would have nothing to do, and so would be board. They chose to design the MSRE without a control room, and ran the reactor without an operator present.

More complex MSRs such as 2 fluid LFTRs would have more complex control issues, but it seems possible through careful design that they can be made as safe as the DMSR.

Reactor safety problems are created by things that are put in reactor cores, as well as things that are created in reactor cores. Solid core reactors are stuck with dangerous fission products, and other materials like plutonium which are created in the reactor core. In the event of a catastrophic accident such materials are seen as a significant menace. Radioactive gases are of continuous concern. Most of the escaped fission products following the Three Mile Island accident were radio active gasses, and voluble fission products. It is possible to bubble radioactive gases out of the carrier salt of a molten salt reactor at low expenses, and the recovery of voluble fission products would not be too expensive. In addition the recovery of other fission products, called nobel metals would not be technically difficult or expensive. Thus many of the most dangerous fission products can be removed from a Molten Salt Reactor core as the reactor operates. By removing radioactive fission products either periodically or as they are produced, the worst case MSR can be rendered significantly less dangerous,

In addition actinides such as plutonium-239 can be simply left in the reactor core until they burn up. In might be desirable to periodically clean the salts of DMSRs or LFTRs, but dangerous materials called actinides can be automatically returned to the reactor core with out ever being accessible to people. This would prevent the diversion of nuclear materials by terrorists, or state based would be nuclear proliferators. The DMSR was designed to be proliferation resistant, and it has many features that would lead a would be nuclear proliferator to chose other routs to produce nuclear weapons.

Molten Salt Reactors, such as the DMSR offer very teal safety advantages over Light and Heavy water reactors as well as sodium cooled fast reactors. These MSR safety features can significantly lower reactor safety related costs, while increasing public confidence in the safety of nuclear generated electricity.

Keys to Lowering Reactor Costs: Economies of Scale or Serial Production?

I consider my "Keys" series to be relevant to the current debate on the cost of nuclear power.

David Walters passed on to me a 2004 study, by the University of Chicago," The Economic Future of Nuclear Power." This study looked at both nuclear construction and capital costs, and challenged some frequent assumptions and common beliefs. We should be aware that Rod Adams had already done this. Let us begin with the notion of economies of scale. As Rod Adams explained 12 years ago: "Pick up almost any book about nuclear energy and you will find that the prevailing wisdom is that nuclear plants must be very large in order to be competitive. This notion is widely accepted, but, if its roots are understood, it can be effectively challenged."

In the small worked of nuclear blogger, Rod Adams is known as a mighty smart man. Adams argues that the notions about economies of scale in the nuclear power industry was a legacy of the experience reactor manufacturers had had with fossil fuel powered generating facilities. "Experience had taught" Westinghouse, General Electric and their competitors, "that larger power stations could produce cheaper electricity and that electricity from central power stations could be effectively distributed to a large number of customers whose varying needs allowed the capital investment in the power station to be most effectively shared between all customers."

Adams continued:

"Their experience was even codified by textbook authors with a rule of thumb that said that the cost of a piece of production machinery would vary by the throughput raised to the 0.6 power. (According to this thumb rule, a pump that could pump 10 times as much fluid as another pump of similar design and function should cost only four times as much as the smaller pump.)"

But in 1996 Adams challenged the idea that economies of scale worked with nuclear power. He asserted,

"it is safe to say that there has been no predictable relationship between the size of a nuclear power plant and its cost."

It appeared that large nuclear plant size tended to increase construction time, which in turn increased capitol expenses. Hence, some studies found diseconomies of scale. that outweighed the increased economies related to parts costs.

The University of Chicago's 2004 literature review came to the same conclusion that Adams had. The Chicago study concludes, "It seems reasonable to conclude that few if any scale economies existed in nuclear plant construction in the 1970s and 1980s to confound the identification of learning effects."

Adams advocated small rather than large nuclear power plants. "If a market demand exists for 300 MW of electricity, distributed over a wide geographic area, traditional nuclear plant designers would say that the market is not yet ready for nuclear power, thus they would decide to learn nothing while waiting for the market to expand."

Adams was clearly ahead of his time.

Small size, leads for the demand of a larger number of units in order to meet electrical demand. Thus if the standard reactor size produces 100 MWs of electrical power, 10 such units would be required to produce the same amount of electricity as 1000 MW unit. The demand for ten units would lead almost inevitably to serial production. Adams notes, "Though the "economy of scale" did not work for the first nuclear age, there is some evidence that a different economic rule did apply. That rule is what is often referred to as the experience curve. According to several detailed studies, it appears that when similar plants were built by the same organization, the follow-on plants cost less to build. According to a RAND Corporation study, "a doubling in the number of reactors [built by an architect-engineer] results in a 5 percent reduction in both construction time and capital cost."

This in tern lead Adams to point to another factor, that the learning curve, facilitated by serial production, lowers cost through time. It should be noted that the University of Chicago study did not take this line of thinking as far as Adams did, but then Adams thinking about reactor design was far in advance of the thinking found in the august halls of the University of Chicago.

Adams added,

"When picking the proper size of a particular product, the experience curve should lead one to understand that high volume products will eventually cost less per unit output than low volume products and that large products inherently will have a lower volume than significantly smaller products."

Adams did not say in 1996, "Mass produce 'em in a factory, but I will wager if I asked him if that was what he was thinking, Adams would have answered, "yes."

TVA reactor price estimates show reactor economics stiill favorable

TVA senior vice president of nuclear generation development and construction, Ashok Bhatnagar, has estimated that each of the new AP-1000 reactors at Bellefonte would cost between $2.5 billion to $3 billion to design and build. He reported that the application for the reactors “is very thorough and was prepared and submitted on schedule”.

This is good news, because some reports suggested that costs of new nuclear plants might run as high as high as $8 billion. TVA has previously estimated that the cost of the Bellefonte reactors would run between 2.5 to 3.5 billion dollars. Thus TVA has apparently lowered its top estimate by half a billion dollars per reactor. Bellefonteis the sight of a previous TVA reactor building effort. TVA, however has surrendered its licences to build the two 1970's era reactors it originally started to build at Bellefonte. It was not clear how much of the partially completed Bellefonte facility TVA intended to reuse, bet recently released drawing depict new reactor domes and turbine buildings, along with the existing cooling towers. The old reactor domes and turbine structure are shown in the background.

Thus it would appear that the TVA price reflects the cost of new AP-1000 reactors and major set up costs except for cooling towers. Thus it would appear that $3.o billion constitutes the top price for new AP-1000. It might be anticipated that there will be some inflation in the price of parts and materials over the next few years. This winters saw coal fired power plants in China running short of coal due to extreme snow conditions. China is also experiencing increasing coal production shortfalls, necessitating coal importation. It is likely then that china will greatly expand its reactor construction program in the near future. This will, in all probablity set off a round of rapid price increases for reactor parts, as suppliers struggle to keep up with demand. The AP-1000, as well as the GE Economic Simplified Boiling Water Reactor (ESBWR) are at something of an advantage, because of their diminished parts requirement, but neither can expect to entirely escape the inflationary pressures. But it appears that Westinghouse, and quite likely GE have achieved their aim of lowering reactor costs substantially.

Assuming that the the TVA reactors come in at the upward end of their estimated price range, the cost would be around $2.50 per KW of generating capacity. Even assuming a capacity factor of 75% for the reactors and 30% for wind generators, the capitol cost of wind generated electricity would be 50% higher, per actual unit of output. Thus wind has a vary large green premium over nuclear power generated by AP-1000s. Now it might well be that the cost of nuclear installations will rise substantially due to Chinese demand, and the general inflation in the price of steel, concrete and copper. However that inflation will probably affect the price of renewable power sources, and because they require significantly more materials than reactors do, the cost of building new renewable power sources might be subject to even greater inflation that the cost of new nuclear plants. Thus the "green premium" for the cost of wind generated electricity over nuclear generated power is likely to continue for some time to come.