The D A Ryan MSR/LFTR critique: Not ready for Prime Time

A blogging engineer named D A Ryan has recently written a critique of Molten Salt Reactor/LFTR/thorium nuclear technology that is decidedly a mixed bag. Most of the comments land off the mark, some seem to wonder away from reality. Many comments in the Energy from Thorium Comment Forum can be taken as critiques of MSR/LFTR technology. Any serious attempt to criticize MSR technology should review the technical discussions on EfT, before making an assessment of molten salt technology. This is quite a chore, but familiarity with the subject is a requirement of serious criticism. While Ryan is familiar with EfT, he has not gone to the trouble of checking out his criticisms with the EfT discussion forum. Ryan then is not a serious critic of nuclear power, but that is not his point. Ryan's conclusion is actually his starting point,

clearly, as regards the current discussion, we cannot run the world on nuclear energy; indeed we’d struggle to meet a tiny portion of global energy needs, for any prolonged period (and I mean a lot less that we currently manage!) with nuclear power, neither generation IV reactors, nor Thorium, nor even Fusion power will help much on this point. Even the most optimistic nuclear energy program we can realistically conceive of still has a substantial energy gap that something else will have to fill. And given our limited fossil fuel supplies (long term at least) that inevitably means alot more renewable energy, which has to take priority over nuclear.

Does Ryan reach this conclusion by sound reasoning, or dies he misrepresent facts, and engage in fallacious arguments? We need go no further than this comment to realize how dubious Ryan's enterprise is,

Another issue is that graphite core. I detailed previously with regard to the HTGR (part 6.4.3) it’s a fire hazard, i.e. Graphite is basically ultra high grade coal! Thus we would need to put the MSR within a containment dome of sorts. Again, as with the HTGR, this dome need not be built to the same exacting standards of a LWR dome as we are merely trying to contain a graphite fire, not an out of control reactor. We would need an effective on plant fire control team and some form of fire detection and suppression system, within the containment dome and all the necessary gear that this entails. I refer you the relevant section of the HTGR anaylsis, but needless to say such an arrangement would involve certain costs.

But is there a fire danger from Graphite? My regular readers might recall thata few months ago I looked at some questions related to the topic of graphite flammability and looked at the question, "Did the Graphite in the Windscale Reactor Burn?" My finding was,

When The UK Nuclear Safety Advisory Committee (NuSAC) meet in 2009 to examine evidence from the Windscale reactor, it found,

• Inspections have shown that there was NOT a graphite fire: damage to graphite, caused by severely overheated fuel assemblies, was localised.

In a third post, titled "Did Chernobyl Graphite Burn," I reviewed sections of a document prepaired for the Nuclear Regulatory Commission by Brookhaven National Laboratory, NUREG/CR-4981 "A Safety Assessment of the Use of Graphite in Nuclear Reactors Licensed by the U.S. NRC." NUREG/CR-4981 was a document intended to answer the question for the NRC. The Brookhaven researchers determined,

Experimental studies on graphite burning have shown that for all the geometries tested which Involved the conditions of small radiation and conduction heat losses, it was not possible to develop self-sustained rapid oxidation for graphite temperatures below about 650 C when the air temperatures were below the graphite temperature. At both high and low flow rates, the graphite was cooled by heat losses to the gas stream even under conditions where other heat loss mechanisms such as radiation and conduction were negligible.

At temperatures above about 650°C, in realistic geometries where radiation is a major heat loss mechanism, graphite will burn only in a limited range of flow rates of air and only when the air temperatures are high. At low flow rates, inadequate ingress of air restricts burning. At high flow rates, the rate of cooling by the flowing gas can exceed the rate of heat produced by oxidation.

Studies have shown that burning will not occur when there is no mechanism to raise the graphite temperature to about 650°C [Schweitzer, 1962a-f]. If the temperature is raised above 650°C, burning will not occur unless a flow pattern is maintained that provides enough air to sustain combustion but not enough to cause cooling. Since the experiments were designed to minimize all heat losses other than those associated with the air flow, 650°C can be considered a lower bound for burning. . . . . in order to have self-sustained rapid graphite oxidation in any of these reactors certain necessary conditions of geometry, temperature, oxygen supply, reaction product removal and favorable heat balance must exist.

The Soviets claimed and American nuclear safety experts like H.J.C Kouts accepted the notion that graphite could burn like charcoal.

The emission of radionuclide continued for about nine days, aided by burning of the graphite. It is estimated that upwards of ten percent of the graphite in the core burned, in a manner similar to the rapid oxidation of charcoal.

We know that Kouts view cannot be correct, nuclear graphite does not burn like charcoal, and the assertion that only 10% of the Chernobyl core graphite burned does not suggest graphite was the major source of the Chernobyl fire. There were, of course other materials in the Chernobyl reactor core that burned hot enough to oxidize nuclear graphite.

Both the NRC and a separate study commissioned by the United States Department of Energy determined that graphite reactor could be operated safely.

The NRC's answer to the original question which I asked at the beginning of this series is ";yes, graphite does burn" but only under a very limited set of conditions. Given this information it is quite possible to design a reactor in which those conditions will never occur.

Ryan references the wikipedia for his claim that "Graphite is basically ultra high grade coal!" What the Wikipedia actually says is,

Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is difficult to ignite.

Nuclear graphite is even more difficult to ignite than natural graphite. The wikipedia article on graphite also states,

during a fire, the graphite expands and chars to resist fire penetration and spread . . . .

What can I say? Here we have clear evidence of extremely shallow research or something worse. Ryan claims that

That big graphite core is a serious worry. As one nuclear physics put it to me “graphite is basically just high grade coal”. Obviously enough, building a nuclear reactor core out of coal doesn’t sound like a sensible idea! Its worth remembering that part of what made Chernobyl the disaster that it was, and why Fukushima is likely to have a much smaller level of fallout (despite 4 reactors involved, one fuelled with MOX against a single reactor at Chernobyl fuelled with only lightly enriched uranium) is because the graphite moderated core at Chernobyl caught fire. It was this fire and the smoke it generated that allowed the radioactive material from the core to spread over such a large area.

So clearly any FMEA process would zero in on this as a major issue that needs tackling. We need to take care in our design to make sure that any potential fire can be safely contained. Obviously this means that any ideas we have about building HTGR’s without containment domes, as some supporters of these reactors suggest we can (and indeed the UK’s AGR’s and Magnox reactors were also built without containment domes), wouldn’t be a good idea. I should note that the containment dome over a HTGR wouldn’t need to be build to the same exacting standards as one over a LWR as our goal is to contain a fire, not a melting down reactor core. This is important as it’s largely been the delays and difficulties in pouring concrete for these cores that is responsible for the messy cost overruns on the various new LWR reactor projects that are ongoing.

Our HTGR’s containment dome would need to be fitted out with some form of automatic fire detection and suppression system, specifically one that can cope with a high temperature graphite fire. As the Windscale power plant fire showed proper planning and equipment would be essential. At Windscale the initially attempt to put out the fire using CO2 failed, as the high temperatures of the fire simply stripped the oxygen from the CO2. The operators finally gambled and poured in water, knowing that this risked setting off an explosion, which fortunately didn’t happen. So clearly we’d need to be better prepared, an inert gas (Nitrogen, Argon or Xenon) or Halon gas should do the trick, if we have enough of it on site. I would note that a number of Halon’s have some potentially nasty environmental issues, such as being known carcinogens and mucking up the ozone layer, so inevitably storing a large quantity of them on site (never mind using them!) would have some environmental implications. Also, we don’t want to be relying, as at Chernobyl, on the local fire crew showing up and doing a Matrosov. Having a dedicated on-site fire crew covering the plant at all times (or nearby covering several plants in a geographical area), as is standard practice for airports, would be sensible. This fire crew, would be specifically trained in dealing with a high temperature graphite fire and be properly equipped to tackle such an event (i.e have working radiation suits! Unlike the situation at Chernobyl). These measures would close off this safety loop hole, but it will come with a cost.

But as we have seen Nuclear graphite is extremely difficult to ignite, and only burns when subject to heat of over 650 C, and then only if supplied with oxygen, and is not in contact with materials that are below 650 C.

Lets list some of Ryan's errors in this account:

1. He failed to note that the difference between the easy ignition of coal, and the ignition difficulties of graphite.

2. He ignores the mention in the wikipedia of graphite fire qualities.

3. His claim that a graphite fire was the primary cause of the Chernobyl radioisotope release is inconsistent with the evidence that 90% of the Chernobyl graphite did not burn, and the research that demonstrates that graphite does not burn in the absence of other heat sources and very hot air.

4. His claim that the Windscale accident included a major graphite fire is based on nothing more than old speculation that is now known to be untrue.

5. The word Chernobyl is used 6 times, Yet the basic premise of the Chernobyl discussion, "the graphite moderated core at Chernobyl caught fire" has been shown to be false. The relatively small amount of core graphite burning that toke place, had to be ignited by an external source and had to be continuously fed by a stream of very hot air.

6. The suggestion that HRGRs pose a fire danger is not supported by evidence.

7. The claim that HTGRs need containment domes is not on the invalid HTGR fire danger argument, thus is not supported by valid reasoning.

8. The argument regarding the supposed problems and costs related to containment dome concrete, is supported by an invalid chain of reasoning, and therefore is invalid itself.

In his account of the alleged graphite fire problems of MSRs, Ryan simply points to his invalid arguments related to the alleged HTGR graphite fire problem and then claims that MSRs will need specially trained fire fighting teams, special equipment, and a containment dome. All of this is hot air, because Ryan has not established reasonable grounds for believing that a MSR graphite fire problem exists.

Ryan criticizes both EfT and Nuclear Green,

Another misconception is that LFTR’s can be air-cooled (here and here) rather than being dependant on the water cooling process we utilise in most other power stations.

The Here and Here refer to one of my posts and a post by Kirk Sorensen.

How does Ryan justify this?

He claims,

Firstly, fire safety, air is an oxidising substance. Fires start all the time at power stations (fossil fuel fired and nuclear ones), especially in the turbine halls and the last thing we want in an emergency is a load of big cooling fans blasting in air and literally fanning the flames! In this scenario we’d face the dilemma between stopping the fans and cutting of the source of cooling (forcing us to SCRAM the reactor to prevent a LOCA scenario) or risk the fire spreading out of control, possibly to the point where it compromises the reactor’s safety. This was of course very similar to the dilemma faced during the Windscale fire, which was air cooled (although in this case directly, rather than indirectly as we currently discussing). And on the subject of Windscale, you will recall what I said earlier about fires and that Graphite core, so we’d be opening a very serious potential safety loophole.

But in nuclear plants, the turbine room is always separated from the reactor by a fire wall. The reference to the Windscle fire is simply confused. In the Windscale reactor air passed directly through the reactor core. There is no proposal to allow cooling air into the reactor core. Thus the Windscale analogy collapses and with it Ryan's first fire argument.

Ryan's second objection has to do with cooling fans

Cooling fans also aren’t terribly reliable, which is why the MSRE was down for several months due to a cooling fan failure. Air based cooling is also very weather dependant, indeed I note that the fans at the MSRE seems to have failed in the summer, when they would have likely been struggling to cope with higher daytime temperatures.

If cooling fans are unreliable, we can use a stack effect to accomplish passive air cooling. The reference to the MSRE cooling fan failure refers to a single incident early in the multiyear MSR test. Once the problems with the cooling fan were identified and corrected, the fan ran for something like 20,000 hours without a problem. The observations about summer related problems is bogus.

Finally we have a third argument

Thirdly, it’s the matter of thermal efficiency. Air based cooling is not very efficient, largely because air has such a low heat capacity compared to water (1.15 against 4.2 J/kg K). A typical COP (Co-efficient of Performance) for fans would be of the order of 2 – 3.7, while you can get 5 – 7.5 with water based cooling. Assuming a COP of 3 (it would be more like 2.5 at the temperatures in question, but bear with me!) and assuming a 1,000 MWth LFTR with a thermal efficiency of 50% (to keep my numbers easy!) = 500 MWe. Our cooling fans, in order to dispose of that 500 MW’s of excess heat, would be consuming 166.67 MW of electricity, dropping our effective plant efficiency down to 33%, barely Rankine cycle levels! This is why we use water in most power stations for cooling.

This argument is preposterous. The B&W mPower reactor is designed to be either air or water cooled. The air cooled mPower is rated at 125 MWe, while the water cooled mPower is reportedly rated at 136 MW, but officially described as a 125 MW reactor.. Thus the active air cooling system at worst consumes 11 MWs more electricity than the water cooling system does. We could probably expect even better performance is we use a stack effect based cooling system.

Ryan adds a further argument:

Also this air based cooling argument strikes me as a bit of a red herring, LFTR fans essentially inventing reasons why their “precious” is better than anything else. With the exception of a few geothermal power stations in arid areas (or hydroelectric plants!), I’m unaware of any major power project that was derailed for lack of cooling water. Either you can use cooling towers (forced draught or natural convection types) and minimise water losses to an acceptable level or simply move the plant next to a ready water source and transmit the power to where it is needed. Many desert countries operate large thermal power stations from around the coasts and several such as Iran, UAE and Libya are even planning to build nuclear stations too. So I fail to see how “air based” cooling offers any real benefits.

In fact water based cooling is usually considered by engineers to offer more thermal efficiency but the fact that Ryan is unaware does not mean consideration is not being given. In fact, as I have indicated, plans for an air cooled mPower reactor are moving forward, and plans for large air cooled solar thermal power plants are being considered in the Southwestern United States.

In addition this passage suggests an attack on Kirk Sorensen and myself for our enthusiasm about Molten Salt nuclear technology. The use of the word “precious” is highly inappropriate, and the use of the quotation marks would untruthfully attribute the word to us. Neither Kirk nor I have used the term “precious” to refer to the LFTR or MSR technology.

Furthermore, Ryan makes other attacks on LFTR/MSR supporters. Ryan describe us

the LFTR fanatics need to come off the Kool-Aid. I’ve gone to great lengths to debunk many of their crazy ideas because such cargo cult science as they are promoting does a great disservice to science, and gets in the way of more realistic and practical proposals. They also serve to confuse the public, and I mean even Wired News appears to have been taken in by this con, which makes the whole job of real scientists pursing real projects, all that harder. As I’ve shown many of the supposed advantages of the LFTR are simply figments of certain bloggers overactive imaginations. The fact that many of the LFTR supporters are Libertarians, individuals not entirely known for their grasp of basic physics, economics or social norms doesn’t help matters

This amounts to little more than a string of attacks on the character of LFTR supporters. The mention of Libertarians is especially silly. LFTR supporters come from the extreme right the extreme left and everywhere in between. The chinese communists who recently decided to invest in LFTR R&D are certainly not Libertarians. Nor am I. We regard MSR technology as promising, and even very promising, but that does not make us cargo cult scientists. The foundational ideas for the LFTR came from Eugene Wigner and Alvin Weinberg, who both were major figures in history of reactor science. LFTR supporters continue to look critically at alternative MSR technologies. The discussion pages of EfT are filled with debate on numerous MSR technology related topics.

In addition to my critique, the blogger uvdiv offers us a

Summary of some of the biggest howlers

* Claims MSRs have "Isotope Separation Plants" which separate 233U and 232U (the trace contaminant)
* Warns of hazardous fission products, such as thorium isotope "T-232" [sic], which supposedly is a disadvantage of thorium-fuelled reactors because of its 14 billion year half-life
* Warns that electrolyzing nuclear fuel salts is energy-intensive
* Warns that heat inputs in fluoride reprocessing are energy-intensive
* Asserts that thorium MSRs are constrained to a lower temperature limit of 1,110 °C, the melting point of pure ThF4. Concludes MSRs must be built entirely from ceramics
* "Obviously, once we exhaust the world’s U-235 stockpiles, LFTR’s and any other Thorium fuelled reactors will cease to function."
* Argues against using molten fuel salt as a working fluid in a gas turbine

"Uvdiv suggest that Ryan holds a misconception that

He has the misconception that 233U/232U isotopic enrichment is necessary for MSR operation. Spends many paragraphs speculating on this imaginary thing, finally concluding it will consume up to 25% of an MSR's electric output:

Uvdid find absurdities in Ryans accounts of fission products. Ryan quite literally describes Th-232 (Ryan calls it T-232) a fission product. Then uvdiv notes a strange error in Ryan's text,

The dendrite problem above demonstrates that the LFTR/LFUR has a relatively narrow thermal window. Its filtering plant will not work if the temperature of the fluid drops much below a certain threshold and the danger of fuel solidification raises the risk of the reactor being damaged. With UF4 the solidification temperature is 1,036 °C and its vapourisation temperature is 1,417 °C. [...] With TF4 our “window” is 1110 – 1,680 °C, but again we can potentially move this by lowering the pressure (or raising it if we want to go the other way…not that we do!). A low vapour pressure also creates a few potential problems in terms of keeping the reactor sealed (air is more likely to leak in if the pressure inside is less than atmospheric…possibly starting a fire!) and maintaining a good flow rate from our pumps.

Uvdiv then comments,

I don't know what confusion of his provoked this nonsense. Maybe he hasn't done his basic research, that all MSR proposals involve solvating actinide fluorides in other fluoride salts -- mixtures of LiF, NaF, BeF2, ZrF4, and/or others -- with the mixture having far lower melting points than actinide fluorides. Or maybe he's under the illusion that individual components of a chemical solution precipitate out at their pure melting points. At any rate, his chain of reasoning starts from this major error and leads to others:

Uvdiv then lists another chain of errors,

With the LFTR however, I doubt you could operate one made out of any Nickel alloy, contrary to everything said on the internet. Bare in mind I’m thinking in terms of a good lengthy service life with a sensible factor of safety, not a flimsy test reactor in a lab (with a 100 mile exclusion zone!).

[...]

Thus the pressure vessel of any LFTR would likely have to formed out of Ceramics (very expensive and difficult to form, especially given how critical getting an air tight seal is given the graphite core) and key internal components out of Refractory metals, as would be the case for certain high temperature parts of any ISP (in both the LFTR and LFUR cases) given talk of operating temperatures in the range of 1600 °C.

[...]

So my instinct from a materials science point of view would be to drop the LFTR idea altogether and focus instead on a LFUR. While this isn’t able to use the Thorium cycle, the point was raised earlier about how the Thorium cycle isn’t all its cracked up to be. Its going to be a lot easier to build a LFUR than a LFTR, cheaper (relatively speaking) and likely safer too. Of course it does come at the disadvantage of a slightly awkward acronym! but overall that would be my focus of attention.

We see once more Ryan's tendency to compound errors.

Uvdiv points to one Ryan error that did make me laugh out loud,

Another misconception is that a LFTR or LFUR can operate on an open cycle with a gas turbine. While true, it could be run this way, there are a host of practical reasons not to do it. Not least of them the fact that our turbine would have to be designed to withstand having a mixture of molten salt and fluorided fuel passed through it at very high temperatures. This would be tricky to say the least, likely requiring the use of those super expensive refractory metals, and while using such materials to make the odd turbine blade is one thing, an entire turbine casing is an entirely different matter. It would likely cost much more than the reactor itself!

Ryan confuses open cycle hear powered gas turbines, with fluoride salt turbines which indeed would be a difficult matter.

At this point I think we have enough. Further discussion and debate can be found here, and here.

I originally intended to write Good, Bad and Ugly critique of Ryan's essay on MSR/LFTR technology, but even the good is so tainted with the bad and the ugly that I find this impossible to do.