Friday, August 12, 2011

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

Several weeks ago, I posted a a critical review of DA Ryan's discussion of Molten Salt Reactor technology. Ryan is a British engineer, but his assessment did not appear to be at all well informed. Ryan began with questionable assumptions, failed to note well regarded information sources that simply disagreed with his controversial views, then proceeded to reason from unsupported assumptions to dogmatic conclusions about nuclear energy.

I generally judge how well a writer is doing by picking out an issue I am familiar with and looking at how well he treats that issue. In my review of Ryan, I looked at his assertion that there was graphite fires risk in Molten Salt Reactors. Ryan saw the fire risk ans a major hazard and claimed, “graphite is basically just high grade coal.” This is nonsense. Not only is graphite not vert flamible, but graphite powder based fire extinguishers are used to fight fires in metals like lithium. In addition, Post-Chernobyl studies attempting to assess graphite fire dangers as nuclear safety issues, have concluded that fires in graphite moderated reactors were much less likely than previously believed. Ryan insists that the fire in the Windscape unit 1 reactor, was a graphite fire. However recent remote visual inspections of the Windscale reactor demonstrate that very little fire related damage to its graphite structures occurred. This is wholly inconsistent with Ryan's contention, but in the face of this strong evidence, he refuses to acknowledge the weakness of the Windscale graphite fire contention, or the unlikelihood of a graphite fire in a Molten Salt Reactor. This behavior might be referred to as dogmatically clinging to a mistaken assumption after the assumption has been demonstrated to be false.

Bill Hannahan also posted several critical comments on Ryan's MSR critique. Bill has graciously offered to pass on his comments on Nuclear Green, and although delayed by my recent surgery, here they are.

The D A Ryan MSR/LFTR critique: Not ready for Prime Time, Part II
By Bill Hannahan

Charles Barton published an essay about a nuclear energy review that contained a chapter highly critical of Molten Salt Reactor technology. I began submitting review comments on each section of that chapter. After several comments were posted my comments were blocked. Charles has graciously offered to publish all the comments.

REVIEW COMMENTS ON 8.2 The MSRE experiment

“Notably, it never generated a single watt of electricity. As I’ve mentioned previously the turbo generator systems for high temperature reactors is technically challenging, especially for the LFTR as the molten salt presents a number of design challenges….

That said, the goal of the MSR experiment was to prove the reactor concept, not develop turbo machinery kit, which would have been a serious (and costly) distraction.”

The Author effectively counters his own point. When GE builds a new jet engine they do not build a new plane to test it on. They test it on a stand. Then they test it on an OLD plane with other well proven engines. After the new design has met its performance requirements it is mated with the new airframe for which it was designed. We know how to convert high temperature heat into electric power.

Checking the author’s link to part 3 to review the technical challenges for LFTR we find this;

“Several of these proposed reactors have operating temperatures in excess of +800 °C. Some, such as the LFTR would need critical parts to go even higher as much as +1,600 °C…

So before we even begin our evaluation, we have to conclude that a big stumbling block to several of the proposed reactor designs is this issue of materials choice.”

One of the great advantages of the MSR is the ability to go to high temperature without pressurization, thereby allowing higher thermal efficiency and reducing component size. The author is trying to make a silk purse look like a sow’s ear.

The most important quality in an engineer is the ability to compromise wisely. Engineers are trying to create the optimum balance over many issues, construction cost, life expectancy, efficiency, safety, maintainability, operating and maintenance cost etc. The engineer who focuses on one parameter at the expense of all others will design a failure.

The author makes it sound as if these issues only apply to the MSR, but all engineering is like that, the Chevy volt, Apple I pad, Boeing 787 etc. are all compromises.

Imagine doing the engineering for a solar thermal plant with molten salt storage. Some collectors may be a mile away from the storage facility. They go from blazing hot temperatures at high noon to freezing temperatures on some nights. The salt temperature is constantly changing throughout the cycle, flow rates are constantly being adjusted as temperatures change, to maintain the desired output. Heat exchangers, piping and storage vessels have to be extra large to envelope worst case conditions.

The constant steady flow of clean high temperature intermediate loop salt into the steam generator of an MSR makes the design of those components a breeze by comparison.

It is likely that the parametric studies will show that the first generation MSR’s should be simple uranium burning reactors made of familiar materials, operating at the low end of the MSR potential temperature range.

We must pay for the R&D to do the studies and build a few plants to get the engineering data. That is how we make progress. That is how we develop systems that can make energy cheaper than fossil fuel and end the age of fossil fuel.

“Stories of said pipe work glowing red (see below) are worrying, as it indicates they were operating well within the thermal creep zone... Consequently, its unlikely one could utilise the same design spec today for a commercial plant.”

Yes, the design engineers will have to do some engineering to ensure that all materials are operating well within their nominal performance envelope. Nothing unusual about that.

“Also, the MSRE never included the more tricky Chemical Processing Plant. One was designed by ORNL but never installed.”

Right. This is why I think the first generation MSR will be the simple uranium burner that does not need on line processing. We do not need breeders immediately.

http://www.youtube.com/watch?v=8F0tUDJ35So


http://www.thoriumenergyalliance.com/downloads/TEAC3%20presentations/TEAC3_LeBlanc_David.pdf

The general tone seems to be that the MSR is not mature fully developed technology; therefore we should not pursue it. If humans had taken that view throughout history we would still be living in caves.

Review of 8.3 Thorium Cycle questions and problems

“we’ll still need supplies of Uranium to get Thorium reactors going again whenever we have to turn it off (which will happen at least once a year or so during its annual maintenance shutdown)…

Obviously, once we exhaust the world’s U-235 stockpiles, LFTR’s and any other Thorium fuelled reactors will cease to function.”

For the LFTR you would only need uranium 235 to startup and breed the uranium 233 sufficient to continue operation. No additional uranium is needed for each shutsown/startup cycle.

There are 3.5 billion tons of uranium in seawater. Perhaps half of that is available at less than 5 times today’s price. That’s still cheap for conventional reactors that require 58 pounds of uranium to generate an 80 year lifetime supply of electricity for one American. It is very cheap for uranium MSR's that requires only 12 pounds of uranium to generate a lifetime supply of electricity for one American, and it is an insignificant cost in a breeder reactor that uses 6 ounces of uranium and/or thorium per lifetime supply of electricity.

“Thorium-232 is a problem with its half life of 14 Billion years (and while the T-232 isn’t a major worry its only mildly radioactive, all the time during this 14 Billion years it will be decaying and producing stuff that is!).”

Thorium-232 (natural thorium) is now scattered throughout the earths crust, including under your house and mine. So removing it, and converting it to fission products that loose the vast majority of their activity in a few hundred years, while extracting enormous quantities of emission free energy, and placing those fission products in a carefully selected location deep under ground or under the seabed, is a good idea.

Nuclear power means earth will be LESS radioactive for most of its remaining years than it would have been without humans.


Comments on 8.4 The Chemical Seperation Plant and waste output

“One other misconception on the internet is the view that a LFTR reactor will produce almost no nuclear waste”

It depends on your definition of almost. To generate an 80 year lifetime supply of electricity for one person in the U.S. with coal we burn 1,140,000 pounds of coal, producing 2,440,000 pounds of CO2 and thousands of pounds of toxic waste, much of it released into the atmosphere.

To generate a lifetime supply of electricity with today’s reactors we mine about 58 pounds of uranium of which about 10 pounds gets into the reactor and produces 6 ounces of fission products. With breeder reactors we mine 6 ounces of uranium or thorium to do the same thing.

The complete natural decay of one uranium atom to one stable atom of lead produces about 7 times more radiation than the complete decay of the fission products from one uranium atom. Uranium and thorium are nature’s radioactive waste, distributed throughout the earths crust without special containment vessels. Nature’s radioactive waste is not buried in carefully selected sites deep underground, it can often be found in soil on the surface.

The extraction of uranium from sea water has been demonstrated at an estimated cost of $160/kg.

http://nextbigfuture.com/2007/11/two-proposals-for-mining-ocean-for-720.html

Coal, our cheapest fossil fuel, costs 3.2 cents / kWh.

http://www.eia.gov/cneaf/electricity/epa/epat8p2.html

We generate about 1,500 watts per person in the U.S., so an 80 year lifetime supply of electricity is about 1,000,000 kWh's. Lifetime fuel cost with coal is $34,000, $424/year.

A LFTR will consume 6 ounces of fuel to make this much electricity. To be conservative lets assume that the uranium required to start the reactor is 10% of the lifetime reactor fuel consumption (it’s probably more like 1%, even less considering that at end of life the uranium 233 can be transferred into a new reactor).

Some fission products have positive value.

http://www.youtube.com/watch?v=rv-mFSoZOkE


By destroying 6 ounces of uranium we make earth LESS radioactive for most of its remaining years than it would have been without humans, we prevent the formation of six ounces of lead that would be toxic forever, we produce some valuable material, we produce a lifetime supply of electricity, and we prevent the harmful effects of generating that energy by some other means.

In my opinion any technology that destroys more waste than it produces meets this requirement; “will produce almost no nuclear waste”

“I’ve seen various dusty line drawings of the 1970’s ORNL proposal, you can see them yourself here and here, but that’s it. I would firstly note that materials science and chemical processing technology has moved on hugely in the last 40 years, so I doubt it would be sensible to build an CPP as shown in these plans. A new one would have to be redesigned from scratch.”

I agree with everything except “from scratch.” It makes no sense to ignore the knowledge and experience gained in the past. We should build on that.

“Either way building our entire energy strategy on a as of yet unproven concept would be dangerous. The same equally goes for Thorium.”

I agree, it is foolish to spend billions building huge numbers of windmills and solar farms that cannot produce reliable dispatchable kWh's. That is why I recommend an all out R&D program to develop all possible replacements for fossil fuel.

http://www.theoildrum.com/node/7275#comment-755200


Comments on 8.5 Graphite core and Fire Risk

“Graphite is basically ultra high grade coal!” …

The Windscale reactor is basically a stovepipe charcoal starter with forced air ventilation, scaled up to the size of a power plant. If the designers had actually used coal as a moderator it would have fired up like a blast furnace. It would have destroyed the vent filters, vaporized much of the fuel and likely collapsed the building.

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

http://www.hse.gov.uk/aboutus/meetings/iacs/nusac/131005/p18.pdf

Graphite clearly does not burn like coal. The claim that, “Graphite is basically ultra high grade coal!”, is either based on lack of knowledge or it is deliberate disinformation.

The author acknowledges that in a MSR the graphite will normally be submerged in molten salt, not air. The dump tank will be filled with an inert gas. When the core is dumped, a vent line from the top of the dump tank to the top of the reactor vessel will transfer the inert gas into the reactor vessel. The reactor room will likely be inerted as well.

For air to get to the graphite the salt must be dumped and at least two barriers must be breached, and there will be no fans to generate a high flow rate.

If the graphite did somehow burn, recall that the vast majority of fission products would be safely tucked away down below in the dump tanks, or previously removed to safe storage. Only a thin patina of fission products on the graphite would be subject to fire, not enough to support a big release.

The claim that a graphite fire in a MSR could result in a large release of fission products is a groundless fabrication with no supporting evidence and no potential mechanism.

A 50 year follow up of Windscale workers showed;

“Despite the higher doses received by the fire cohort workers the SMRs by decade for all malignant cancer are consistently lower than those of the non-fire cohort workers.”

http://iopscience.iop.org/0952-4746/30/3/001/pdf/0952-4746_30_3_001.pdf


Comments on 8.6 Why air cooling a LFTR would be a very bad idea

“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.”

Actually the high temperature of MSR’s makes them ideally suited for dry cooling in arid climates.

“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!”

I think the author has since acknowledged that the fans would be cooling the condensers located outside the turbine hall, not in the turbine hall or containment building. The turbine hall is separate from the reactor containment and its safety related equipment.

“In this scenario we’d face the dilemma between stopping the fans and cutting of the source of cooling”

The steam plant and its condenser are not safety related systems, the reactor does not rely on the steam plant for safe cooling. Decay heat will be removed by natural convection of air or water. There are no flammable materials in or around the dump tanks.

“The Uranium we’re mining was safe underground and seperate from the biosphere.”

According to the EPA, thousands die from radon exposure every year in the U.S. alone. Nuclear power is far safer than natural uranium left in the ground.

““basically high grade coal” was a quip”

Publishing a quip that you know is misleading and prejudicial is unethical.

The danger of a positive void coefficient of reactivity was well known before the Chernobyl reactors were built. The design could never have been approved for construction in the west, nor could any power reactor design without a containment building, as Chernobyl was. Operators bypassed the protection systems and violated the operating limits to perform a dangerous experiment and spiked the power to 100 times design limits resulting in a steam explosion that blew the reactor apart.

The risk of hydrogen production from the zirconium water reaction was well known, as are the mitigating mechanisms; ventilation to keep concentration below the flammability limit or ignition to burn the hydrogen as it is produced to avoid an explosion. Unfortunately the Japanese failed to deal adequately with the hydrogen production.

The only nuclear accidents to release large quantities of fission products are those where a direct path to the atmosphere is provided by design or by explosion. Even then it is interesting that out of hundreds of fission products, only a few of the most volatile constitute most of the risk.

MSR's have continuous online refueling. There is only enough reactivity for normal operation. I do not know of any way to make an MSR explode. Do you?

Cesium is by far the most problematic fission product in an accident. It melts at 28C, the boiling point is 671 C. When a cesium atom is produced in a MSR it immediately hooks up with a fluorine atom to make cesium fluoride, melting point 682C, boiling point 1251 C, so it has much lower volatility resulting in greatly reduced emissions under accident conditions. Jet fuel boils at about 200 C, and the temperature of burning jet fuel is 260-315C in open air, 980 C in an ideal burner.

http://en.wikipedia.org/wiki/Jet_fuel

You could cool a MSR by spraying it with burning jet fuel.

““the fuel will be safely tucked away in dumb tanks” IF the fuel dump process goes okay! This is the danger here, you’re relying on the successful functioning of your fuel dump process”

If the fuel is not dumped the graphite is submerged in salt, no oxygen contact, no fire. You might say, ‘what if it is half submerged?’ In that case the fission products are mostly below the liquid line. If the graphite above the liquid line burns, very little fission product will be volatilized, and it will plate out as soon as it contacts a cooler surface.

This is a fundamental difference between solid and liquid fueled reactors. Volatile fission products will be removed continuously and non volatile products will largely stay on site during an accident. The author cannot have it both ways; he provides no evidence or mechanism to support the idea that a graphite fire in a MSR can happen, and even if it does burn, no mechanism that would result in a large release of radioactivity. The graphite fire hazard claim with MSR's is a groundless fabrication.

“Defence in depth would require that other measures be taken also, although this could be as simple as just putting it all in a reinforced concrete building designed to withstand a high temperature fire.”

I have no doubt that all future power reactors, including MSR's, will have a robust containment. But the MSR containment can be much smaller, using far less material, because hi temperature heat exchangers are very small and steam generators can be small and located outside containment. A pipe rupture inside containment will not release a huge volume of gas or steam, so no need for a large expensive high pressure containment vessel.

“you still need some water on site”

There will be water on site, but you do not need it to keep MSR fuel safe. Engines and motors are air cooled. Light bulbs with white hot filaments are air cooled. In fact, the hotter an object runs, the easier it is to air cool, another big advantage of MSR's.

“So all in all I’d argue uranium mining causes as many (if not more) problems than it solves.”

If we replaced all coal plants with nuclear plants, eliminating mountain top removal, huge releases of mercury, cadmium, soot, CO2 etc that would save perhaps 1,000,000 lives per year and prevent millions more non fatal adverse health effects. How will uranium mining match those effects, especially with advanced designs that reduce mining to 6 ounces per lifetime?

FOLLOWUP on sea water uranium comment by bluerock.

“Extracting uranium from the sea is not a practical possibility.”

If Bardi is right why can’t he answer questions? Why can’t he find the error in contrary analysis? What is your answer to these questions?

http://europe.theoildrum.com/node/4558#comment-412498
http://europe.theoildrum.com/node/4558#comment-412127
http://europe.theoildrum.com/node/4558#comment-413193
http://europe.theoildrum.com/node/4558#comment-414051
http://europe.theoildrum.com/node/4558#comment-415226

“Maybe, like me, he can’t be bothered to read, research and respond to every challenge that appears on the interwebs.”

It is interesting that he found time to address the easy and favorable comments but not the hard questions based on facts and logic.

“Here’s one way to shut us all up: prove that it is technically and *economically* viable to extract uranium from seawater at quantities that could supply a global nuclear industry.”

Had you carefully reviewed your own reference you would know that I addressed that point.
“Why are there no sea water uranium extraction plants?
Historically the price has been under $60 / pound with a few big spikes.
Would you bet your life savings on uranium staying above $200 / lb? I don’t think so, and neither do professional investors, however if sea water technology keeps improving the cost may drop enough to make it happen sooner than most people think.
Sea water uranium is very important because it puts a cap of $200/pound on the maximum sustainable cost of uranium for thousands of years.
Sea water uranium does not have to supply all of our uranium in order to cap the uranium price at $200/pound. It only has to replace the percentage of land based uranium sources that cost more than $200/pound, and that percentage is zero for the foreseeable future.”

http://europe.theoildrum.com/node/4558#comment-413193

Comments on 8.7 Why power cycling a LFTR would be an even worse idea!

“The truth is that the LFTR is as constrained in it power output capabilities as other reactors, possibly more constrained in fact.”

It is interesting that you know the performance specifications of power plants that have not even been designed yet.

“Power cycling a LFTR would necessitate such cycles, worsening our already narrow materials choice and requiring a much more heavily constructed reactor.”

So you have already designed the plant, chosen the materials, selected the salt formula, determined the operating temperature. Sounds like you designed a poor reactor.

“It is also worth noting that existing nuclear stations are capable of some level of power cycling anyway just not much!”

The most popular gen. III reactor is the AP-1000. Its design includes the lessons learned from decades of experience running gen. II reactors. Look at its capability.

“The AP1000 is designed to withstand the following operational occurrences without the generation of a reactor trip or actuation of the safety related passive engineered safety systems. The logic and setpoints for the AP1000 Nuclear Steam Supply System (NSSS) control systems are developed in order to meet the following operational transients without reaching any of the protection system setpoints.

· ± 5%/minute ramp load change within 15% and 100% power
· ± 10% step load change within 15% and 100% power
· 100% generator load rejection
· 100-50-100% power level daily load follow over 90% of the fuel cycle life
· Grid frequency changes equivalent to 10% peak-to-peak power changes at 2%/minute rate
· 20% power step increase or decrease within 10 minutes
· Loss of a single feedwater pump

Off-site power has no safety-related function due to the passive safety features incorporated in the AP1000 design. Therefore, redundant off-site power supplies are not required

Containing Core Damage. The AP1000 design provides the operators with the ability to drain the IRWST water into the reactor cavity in the event that the core has uncovered and is melting. This prevents reactor vessel failure and subsequent relocation of molten core debris into the containment. Retention of the debris in the vessel significantly reduces the uncertainty in the assessment of containment failure and radioactive release to the environment due to ex-vessel severe accident phenomena.”

http://www.ne.doe.gov/pdfFiles/AP1000_Plant_Description.pdf


“The turbine generator is intended not only for base load operation, but also for load follow capability. Mechanical design of the turbine root and rotor steeple attachments uses optimized contour to significantly reduce operational stresses.”

https://www.ukap1000application.com/PDFDocs/Safety/UKP-GW-GL-740%20Rev%200.pdf


As implied above, load following thermal/mechanical stress cycles are largely limited to the steam turbine. If MSR designers want to keep reactor temperature constant, they can coordinate feedwater flow to the steam generators with reactor power to maintain constant reactor average temperature over the full range of operation.

As power is reduced the reactor hot leg temperature will cool slightly and the cold leg temperature will warm slightly, keeping the average constant. If the engineers want to eliminate even that small temperature swing they can modulate salt flow rate with power to keep the inlet and outlet temperatures constant over the full range of operation.

Six ounces of thorium can produce an 80 year lifetime supply of electricity in a LFTR. It requires no enrichment or fabrication into fuel rods. Assuming the fuel is free will induce a negligible error in the overall economic analysis.

These plants can be run a few percent over demand with fine control managed by dumping excess power into a resistor bank. This would allow near instant slew rates without subjecting the plant to rapid power jockeying. The grid itself could be used as the resistor bank by modulating power factor. With fuel cost essentially zero, they could run the plants continuously at 100% and avoid any thermal cycling of the steam turbine/generator, using the excess power to make hydrogen or carbon based fuel from atmospheric CO2.

http://www.lanl.gov/news/newsbulletin/pdf/Green_Freedom_Overview.pdf

As electric vehicles become more numerous, nighttime charging and smart grid technology will level out the day/night swings.

The addition of intermittent, unreliable, undispatchable wind and solar farms has made load balancing much more difficult.

“- the combination of wind facilities +balancing facilities is significantly less economical than using the balancing facility at rated output in base-loaded mode.”

http://theenergycollective.com/willem-post/57905/wind-power-and-co2-emissions

High variability induced by wind and solar farms may cancel all claimed emissions reductions.

http://www.bizjournals.com/denver/stories/2010/04/19/daily11.html

Intermittent, unreliable, undispatchable energy sources must be backed up by reliable dispatchable plants. The true value of intermittent, unreliable, undispatchable kWh's is the cost of fuel saved, 0.5 cents/kWh nuclear, 3.2 cents/kWh coal and 5.2 cents/kWh gas. The simplest non breeder uranium MSR would have a fuel cost of 0.1 cents/kWh, essentially zero for breeders.

The real reason nuclear plants do not load follow is that they have the lowest fuel cost. Intermittent, unreliable, undispatchable wind and solar kWh's would have no value on a nuclear powered grid.

“Several meltdowns of liquid metal cooled reactors have resulted from such clogging incidents.”

A sodium cooled experimental reactor with solid metal fuel and a serious design defect has little relevance to future MSR's.

Comments on 8.8 Thermal windows and material choices

This entire section boils down to “Some R&D is required.” No one denies that. There is no reason to believe that any of the issues mentioned are show stoppers.

Comments on 8.9 The Brayton cycle and MSR reactors

The Wright Brothers did not build an SR-71. Henry Ford did not start with the GT-40. Like all technologies, the MSR will start simple and build on that experience.

“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.”

There would be an intermediate heat exchanger, no fission products outside containment.

“oh! but we almost forgot about that chemical processing plant and its net energy inputs, say we deduct 5-10% of reactor power output to account for running that,”

6 ounces of thorium can produce about 1,000,000 kWh's. So processing 6 ounces of fission products requires 100,000 kWh's? Not a chance.

Comments on 8.10 Piping, FMEA and leak prevention

“the major risk to any MSR reactor is ….either a fire effecting its graphite core (which for a LF reactors running at low vapour pressure is a greater risk than with any other graphite cored reactor) or more likely a burst pipe.”

The fire risk was covered in a previous section.

“the major danger with a LF plant is that somewhere in the lengthy network of pipes that it and its CPP consist of, something breaks.”

The author carefully avoids describing the exact sequence of events that results in a large scale release of fission products to the atmosphere that he alludes to.

There is a strong incentive to minimize fuel volume. Therefore the intermediate heat exchangers will be close to the reactor vessel to keep pipe length short.

Small leaks will solidify on the floor. Large leaks will flow to the drain tanks. There is no large inventory of volatile fission products. There is no mechanism for a powerful explosion. The reactor room will be inerted.

During normal operations volatile fission products will bubble out of the hot salt as they are formed and be converted to a form that is non volatile and easy to store away from the reactor. Fission produces that do not come out of the molten salt are in forms that are stable at very high temperature. So there will be no inventory of volatile fission products available for release in an accident, as can happen when solid fuel melts under accident conditions.

So what is the detailed scenario resulting in a large scale release of fission products to the countryside? What is the chemical composition of the fission products? What are the melting and boiling temperatures of those compounds? What mechanism drives them out of the plant into the atmosphere?

By what path do they escape?

“Take for example the pipe at the base of the reactor that allows us to dump the core to the emergency dump tanks… suppose for example that it bursts during a dump scenario? Obviously we need a containment vessel around the pipe to catch any leaks.”

The answer is in the drawing of the FUJI MSR in your report. The spill would flow down the floor drain into the emergency drain tank.

“Also simply relying on gravity would be inadequate in certain scenarios, a pump on a separate stem (or a tank of inert high pressure gas connected up to the pressure vessel to “encourage” the fuel to drain away), would be necessary.”

Gravity has not failed in 14 billion years. Describe in detail an accident sequence of events where the proposed additional equipment would prevent a large offsite release of fission products that could not be prevented without that extra equipment.

“But what if the trigger for the accident is a clogging of fuel channels (as discussed earlier) by solidified fuel?”

The solidified fuel would heat up and re-melt.

“If we dump in that scenario we might cause the dump pipe to clog also, likely leading to a criticality incident or its failure and a breach.”

Maintaining criticality under normal operation with the minimum concentration of fissile material is the challenge. The poor geometry and lack of moderation in a spill avoids criticality problems.

“So we would need a thermal regulation system around the pipe to ensure it can be heated or cooled as necessary. Also I don’t like the idea behind this “freeze plug”. I realise the passive safety benefits it brings, but it’s just going to be too slow to act in a real emergency and there’s too much that can go wrong with it. If I were an engineer at such a plant I’d want a big shiny red “dump core now!” panic button on my control panel.”

I agree. I have never felt good about the fan cooled freeze plug.

If I were responsible for this part of the plant I would ask a dozen bright engineers to independently come up with a plan for handling this safety function, then pass them around and generate lists of pros and cons for each.

My suggestion would be to use a thermal rupture disk, or a flapper valve held shut by a thermal fuse or electromagnet. In each case there would be the option for quick manual operation. There would be an orifice to allow a continuous metered flow of salt into the drain tank. That flow would maintain the temperature of the drain line and verify its functional availability. The salt stream would be continuously pumped back into the primary loop. It could also be the source of fuel for continuous chemical processing.

There would also be another dump path with a conventional control valve; it would be the primary valve, the thermal device would be the backup, along with the floor drain.

In the extremely unlikely situation where everything fails the stockholders are going to take a hit, but there will be no major release of fission products to the countryside.

“see how in the process of getting one short section of pipe back to within a reasonable safety margin the result has been for it to balloon into a massively complex system in the space of 5 minutes.”

Welcome to the real world of engineering. All large scale power plants are complicated. A Boeing 787 is more complicated then a Cessna 150. MSR's can be much smaller and less complicated than coal plants with emissions controls of the same output.

“the benefits of a Molten-Salt fuel system are outweighted by the lengthy inspection process of all that pipe work.”

The compact design of the MSR allowed by high temperature and lack of active safety systems and complicated emission control systems makes the piping far less complex and easier to inspect than a conventional coal or nuclear plant.

The failure of that piping would be less dangerous than the failure of fuel system piping at a natural gas plant.

“any MSR reactor would inevitably have to have large stockpiles of salt stored on site or nearby,”

Why? Small amounts of material are coming out of the system; why/how would we put in large amounts of additional material?

“Fluorine gas is extremely toxic (several times more deadly than chlorine”

Toxicity Data, Fluorine
LC50 inhal (rat)
185 ppm (300 mg/m3; 1 h)

Toxicity Data, Chlorine
LC50 inhal (rat)
293 ppm (879 mg/m3; 1 h)

http://www.nap.edu/openbook.php?record_id=4911&page=320

By volume fluorine is less than twice as toxic as chlorine. The U.S. consumes ten billion kg of chlorine each year; enough to kill every man woman and child in the U.S. every 45 minutes. Essentially all of that is manufactured and consumed under conditions less secure than those inside a reactor containment building.

Fluorine will not be stored or transported in elemental form in large quantities. The chemical processing equipment in LFTR's will be very small by industrial standards, and they will be among the most secure and well regulated in the world.

“ Another misconception of the LFTR fans is that LFTR’s will not require the same large exclusion zones as other reactors. A.”

Other reactors do not have large exclusion zones, nor will LFTR's. Check Google Earth.

“A LFTR is essentially just a glorified chemical plant”

A large LFTR will produce a few pounds of fission products per day. The image of a large industrial chemical plant is false. Many common industrial facilities use far larger quantities of hazardous materials under far less secure conditions.

I expect the chemical processing will be done in sealed tamper resistant modules with standardized size and simple connections so that as processing technology improves, the older plants can have access to the latest technology.


8.11 MSR’s, A proliferate problem?

There are two relatively easy, fast, cheap paths to nuclear explosives;

1... Extraction of U235 from natural or reactor grade uranium. (enrichment technology).
2... Plutonium production using a simple unpressurized water cooled graphite reactor with natural uranium fuel.

There is at least one difficult, time consuming, and expensive path to nuclear explosives; using a commercial nuclear power plant.

If a group or nation wants to build nuclear explosives, the optimum level of proliferation resistance is that which is just barely easy enough to convince them to take the most difficult, time consuming, and expensive path to nuclear explosives.

All proposed future reactor designs are far beyond this standard, so it makes no sense to add complexity and cost to a plant design in response to the proliferation issue. That just makes it harder to build new energy sources that are much cheaper than burning fossil fuel, and there in lies a real risk.

The solution to the proliferation issue is education.

8.13 LFTR, the Kool-Aid Fuelled Reactor?

A collection of ad hominem attacks and insults, nothing substantial.

10 comments:

Andrew Jaremko said...

Thanks for this post Charles. I'm glad to see you're back, and I hope you'll continue with the excellent work.

DW said...

Best damn polemic I've ever seen. Sliced and diced. N I C E.

donb said...

Some of the technical errors stated by Mr. Ryan are real knee-slappers.

In the responses, there is one minor technical error:

These plants can be run a few percent over demand with fine control managed by dumping excess power into a resistor bank. This would allow near instant slew rates without subjecting the plant to rapid power jockeying. The grid itself could be used as the resistor bank by modulating power factor.

Assuming constant real power delivery by the generator to the grid, modulating power factor, or more correctly, modulating power factor correction done by the generator, does not (to first order) cause the generator to change its mechanical load on the turbine.

I believe that a more typical way of doing fast fine control is to bypass steam (or hot gas) around the turbine, dumping the excess energy as heat in the condensor (or cold heat exchanger).

Anonymous said...

Donb, what you said, “modulating power factor, or more correctly, modulating power factor correction done by the generator, does not (to first order) cause the generator to change its mechanical load on the turbine.” is true, but it does not contradict what I said.

Adjusting power factor at the generator can improve conditions for the generator by reducing waste heat production in the generator, but that does not change power factor on the grid beyond the power plant, so it does not use the grid as an adjustable resistor bank. It would be using the generator as an adjustable resistor which I do not recommend.

What I am suggesting is to ad or subtract reactive power at the far end of the major transmission lines so that the real power delivered at the end of the line can follow small fast load changes, while the real power leaving the plant remains constant or slowly varying, with the difference being released as heat from the transmission lines. It is a minor point in response to the authors implication that load following is a big problem.

In reality I think MSR's will have no problem load following by conventional means such as you describe.

Bill Hannahan

donb said...

Bill Hannahan wrote:
Adjusting power factor at the generator can improve conditions for the generator by reducing waste heat production in the generator, but that does not change power factor on the grid beyond the power plant, so it does not use the grid as an adjustable resistor bank.

Adjusting power factor at the generator DOES change power factor on the grid. The adjustment causes the generator to present a capacitance to the grid, thus providing power factor correction. As an extreme, I am aware of at least one case where a generating plant is used for peaking during during the summer, and the rest of the year the generator is disconnected from the turbine and run as a 'synchronous capacitor' on the grid to support voltage in the area. At anything less than full load, a generator can provide a combination real and reactive power to the grid as needed.

I can see your point using reactive power to dissipate excess power, but this control is less effective at smaller real load. At large real load it also become less effective as the grid operator tries to best compensate reactive power in order to deliver the needed real power.

daryan12 said...

...And my response here!

http://daryanenergyblog.wordpress.com/ca/#comment-220

Charles Barton said...

daryan12 rest assured your response will receive an answer in due corse.

Anonymous said...

Donb, consider a simple example of a single power plant driving a pure resistive load through a short power line. Neglecting the small reactance of the power line, the power factor will be 1.0 regardless of what you do inside the power plant boundary.

Now imagine we change the load to pure capacitive or inductive. The average power delivered to the load will be zero, the power factor will be 0.0 and the only energy released will be the heating of the power line conductors, regardless of what you do inside the power plant boundary.

In the example you give, the topping plant is not being used as a power plant, it is being used to provide capacitive reactance to optimize power factor on transmission lines delivering power from some distant power plant, similar to what I described before.

You cannot correct transmission line power factor at the source of the power. Transmission line power factor depends on the total impedance at the other end of the power line, combined with the impedance of the line itself.

The important thing is that for the first few decades MSR's will be run continuously at 100% because their fuel cost will be lower than any fossil plant and even lower than the fuel cost for most other nuclear plant designs.

BillHannahan

Fordi said...

“But what if the trigger for the accident is a clogging of fuel channels (as discussed earlier) by solidified fuel?”

To clarify Bill's response:
Fuel salt that has low enough fissile inventory to cool into a solid is no danger to anyone, anyway. Fuel salt that has somehow been cooled to its freezing point would still be undergoing fission; without continued cooling, it will re-melt and flow into the drain tank.

An exception to this is fuel salt in a narrow enough channel to be in a noncritcial configuration, such as like the freeze plug. However, it will be backed up-stream with fissile-loaded salt, which will, again, if not cooled, melt the clog.

This is not a strong concern, except to say that pinch points of low criticality should be avoided in core exit paths.

Anonymous said...

Donb, I think I understand your point now. On a grid with multiple generators operators can alter the relative phase angle between different plants by adjusting the excitation voltage of the generators to produce inductive or capacitive var’s

Sorry for the misunderstanding.

Bill Hannahan

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