achalhp

You're correct. The vessel & primary heat exchanger of a MSR which are in contact with liquid-fuel is equivalent to fuel assemblies of many solid-fuel reactors. In solid-fuel reactors the clad which is designed to contain fuel doesn't last long. Similarly, in MSRs the materials in contact with fuel doesn't last long.

So, we need to dispose the vessel and primary heat exchangers similar to Zr-clad million dollar fuel assemblies.(PWR/BWR reload costs $60-100 million per 12-18 months.) Material wise Zr clad is way more expensive than stainless 3XX & graphite combined. Even if Ni-alloy is used in disposable MSRs Ni-alloy+graphite will be slightly cheaper. (Base metal costs: Zr metal: ~$22,700/ton Ni metal: ~$13,100/ton)

I agree. But, in a molten-salt reactor, the vessel and heat exchangers are equivalent to fuel assemblies. Dispose the vessel and heat exchangers similar to Zr-clad million dollar fuel assemblies.(PWR/BWR reload costs $60-100 million per 12-18 months.)

Material wise Zr clad is way more expensive than stainless 3XX & graphite combined. Even if Ni-alloy is used in disposable MSRs Ni-alloy+graphite will be slightly cheaper. (Base metal costs: Zr metal: ~$22,700/ton Ni metal: ~$13,100/ton)

Many actinides have volatile fluorides. Fluoride volatility is a proven process used to enrich uranium for LWRs. Fuel salt can be disposed after recovering U & Pu. Vacuum distillation is physical separation, which can also be used to further recover expensive base salt FLi7Be. No vacuum distillation is necessary if inexpensive salt is used.

Good points.

Primary loop of a MSR is equivalent to a cladding of a solid fuel assembly. You get a REACTOR at the same cost/MWe of solid fuel assembly. Ni alloys are cheaper than Zr alloy. So, early MSR designers will not opt for maintenance of the primary loop.

Here's link to Weinberg's PIUS-LWR https://www.annualreviews.org/doi/pdf/10.1146/annurev.eg.10....

Planets rotate so backup power is needed during nights. Spacecraft has to avoid obstracles and has to move, so backup is needed. During interstallar journey there is time delay in communication, so it may take hours to adjust the power beam when spacecraft moves a little bit. Fusion is like solar energy just near to us and MSR will be eventually replaced by fusion reactors.

MSR and many other fluid-fuel reactors run hot and it makes radiators small: https://www.flickr.com/photos/oakridgelab/31537153147/

Stefan–Boltzmann law: Radiation heat transfer is proportional to 4th power of temperature.

You included my sentence: "Efficiency really matters when we have >1000 GW of installed nuclear capacity." I wanted to address that: efficiency matters.

Inefficient technologies will hit some constraints if not others.

We may run out of time: A pressure vessel production cycle is over one year[1]. By the time we reach >1000GW someone may make fusion practical or China's competent nuclear industry may start selling MSRs to everyone.

We may run out of highly skilled people required to build and operate these complex machines. The safety is highly dependent on operations and management throughout the life cycle of complex machines. From manufacturing to operations there is tiny margins for error. (Not a physical constraint.)

LWR technology is associated with military ships and submarines, no one shares it. Few countries control the technology and there are only a few places in the world to make pressure vessels. (Not a physical constraint.)

We may run out of waste disposal sites. A geological repository needs special rock formations away from earthquake zones.

The article is written by a nuclear industry professional who tells that routine things done by the nuclear industry today when applied to MSR is a "disadvantage". They open the lid of an LWR every 18 months and replace/shuffle highly radioactive fuel assemblies and say that it is a disadvantage for them to replace graphite. That is totally unfair.

[1] VVER pressure vessel production cycle needs 3 years. https://www.youtube.com/watch?v=91yVhrSZ5jQ

NuScale pressure vessel R&D: https://www.energy.gov/sites/prod/files/2016/10/f34/02%20-%2...

TL;DR Even small pressure vessels (used by nuscale) have lead times of about a year. A megafactory can build like 1 or 2 vessel per month. At 1.5GW/year/factory, we need like 22 factories to keep up with the production schedule if we need to reach 1000 GW of small-LWR capacity within, say 2050.

(Molten salt reactor is a fluid fuel reactor. Fluid: liquid, gas and plasma.)

Molten salt reactor is a stepping stone for fusion reactors. We need to master liquid and gaseous reactors before going plasma. Our civilization should aim for larger goals. We need some form of nuclear power to terraform other planets and spread earth's precious life and conciousness everywhere.

Highest temperature fission reactors are the gas core (vapor core) and ion core reactors. They are fluid-fuel reactors, but not demonstrated. Currently solid-fuel reactors hold the record for highest temperatures.

Fusion reactor runs hotter and again fuel is in fluid state.(Fluid: Liquid, gas & plasma.). But only runs for 10-100 minutes. Demonstrated fission reactors run for thousands of hours continuously.

>Tritium production: If lithium is used in the salt, tritium will be produced,

Not a disadvantage for all MSRs. Both lithium and beryllium can be avoided. FLiBe is required for efficient MSRs and MSBR.

>Mobile fission products

It is the only disadvantage common to all molten-salt reactors and all fluid-fuel reactors. Pumps and pipes have to handle a hot radioactive liquid.

> Material Degradation

Common to all nuclear reactors, solar, coal boiler tubes, etc. Components used in reactor core do not last long. MSRs dispose nickel tubes and LWRs dispose zirconium tubes and uranium.

>Proliferation...The problem with MSRs, then, is that the fuel is already completely cut open and melted. >it will be difficult for the IAEA to distinguish plate-out losses from actual proliferative losses.

The fuel salt loop can be sealed tamper-proof. The entire fuel salt loop is analogous to a fuel assembly. Weigh the entire fuel salt loop. Vapor pressure of actinide-halide salt is very low at operating temperatures. Actinides don't move out of this loop.

>Complex chemical plant

This is not a disadvantage for all MSRs. Only breeders need chemical plant. Not fair to compare a solid-fuel burner to liquid-fuel breeder.

Let us compare liquid fuel breeder vs. solid-fuel breeder: Reprocessing solid-fuel involves more complex chemical plant with physical mechanisms to declad and convert solid-fuel to a processable liquid. Fabricate processed liquid to solid-fuel and put it back in the reactor. Solid fuel breeders have additional physical and chemical processes/steps.

The successor of LWR/HWR should be a fluid-fuel reactor.

Once we setup a pebble/advanced fuel making factory, closing it will takes decades (because people may lose jobs) and the new solid-fuel factory will again pause nuclear innovation for another 100 years. The only way to continuously improve nuclear reactors is to go fluid-fuel. No engineered fuel, so no job loses. Reactor innovation is independent of fuel factory. Nuclear fuel becomes a commodity instead of engineered speciality. Example: MSRE ran U235 and U233 without any modification.

Secondly, solid fuel reactors throw away fuel along with heat exchange surfaces (clad). Fuel also undergoes crystal structure degradation along with other solid structures. Maybe there is enough fuel in the seawater, but there may not be enough places suitable for geological repositories.

Solid-fuel reactors always need excess reactivity reserve. Always needs control rods, and if someone (or a bad actor) pulls all the control rods, reactor gets supercritical. Needs highly skilled people and needs security.

For emergency shutdown of solid-fuel reactor, poison is added to coolant, not fuel. In an emergency, poison is added to the liquid-fuel, permanently destroying the fuel. Emergency can be anything, from a natural disaster to terrorist attack. Fluid-fuel reactors offer unbeatable safety features against anything.

Firstly heat from inefficient low temperature solid-fuel reactors can't be used directly for many applications. So consider electricity. Cars/planes/kitchen-stoves cant use uranium or nuclear heat!!

All 4.5 billion tons can't be extratcted. More we extract, concentration decreases and harder it gets. I keep asking this question: If seawater extraction of metals is practical, why aren't we extracting other costly metals now? https://twitter.com/AchalHP/status/1011661441412337665

From the article: >Problems with Molten Salt Reactors... >...but similar problems may show up in long-lived power reactors.

Author assumes that MSR components should last as long as vessels and secondary heat exchangers of solid-fuel reactors. The author should understand that vessel and primary heat exchanger of a fluid-fuel reactor is anologus to fuel rods. Solid fuel reactors just dispose primary heat exchangers or fuel rods every few years. Example: Zircolloy tubes worth a MSR vessel + heat exchanger is just disposed along with partially fissioned degraded solid fuel every 4.5 years in a LWR. Zircolloy (Hafnium separated nuclear grade zirconium + additives) is more expensive than commercially available nickel based alloys.

Graphite is a solid with a crystal structure. Crystal structure degradation under radiation is permanent and there is nothing anyone can do to reverse it. Solar panels degrade similarly. Nuclear industry handles solid-fuel rods which are far more radioactive than MSR graphite and complains that it can't handle MSR graphite. Just shows that either industry is incompetent or it is not interested in efficient fluid-fuel reactors. Does nuclear industry aims >1000 GW of nuclear capacity? Does nuclear industry care to solve global energy related issues? Efficiency really matters when we have >1000 GW of installed nuclear capacity. If all energy is obtained from nuclear, (12000-16000 GW) even seawater uranium get used up in 40-60 years with inefficient solid-fuel reactors.

From the article: >if something goes wrong in a MSR and the temperature starts going up, a freeze plug can melt,

A MSR does not need any sort of valve to drain the fuel. ORNL-MSBR was designed to drain the core when pumps stopped working. The real advantage of freeze valve is that is uses no moving parts and maintanence free/friendly.

ORNL-4528: "The fuel salt pump and its sump, or pump tank, are below the reactor vessel, so that failure of the pump to develop the required head causes the salt to drain from the reactor vessel through the pump tank to the fuel salt drain tank."

RE: Ah, the good old days!

<0.5 rem per quarter (or 5 mSV) is in compliance with today's dose limit. ORNL was a competent American national lab with high standards even back in the 1960s. Another hollow argument from today's incompetent nuclear industry.

"Exposure of personnel to radiation has been held well below permissible limits: the maximum exposure of any individual in any quarter has been <0.5 rem." http://moltensalt.org/references/static/downloads/pdf/NAT_MS...

"The maximum annual dose allowed for radiation workers is 20 mSv/yr" https://www.world-nuclear.org/information-library/safety-and...

MSRE had a charcoal-bed off-gas system which safely stored all the noble gases. It was cooled and shielded with water, similar to today's PWRs. PWRs also have water chemistry control and resin-bed filters for primary loop which is highly radioactive and shielded. Construction of the off-gas system is described in pages 58-60 in ORNL-3708: Molten-Salt Reactor Program: Semiannual Progress Report for the Period Ending July 31, 1964 https://energyfromthorium.com/pdf/ORNL-3708.pdf

RE: Furthermore, they were in the 1960s, before the NRC existed and before we worried about ALARA.

"Exposure of personnel to radiation has been held well below permissible limits: the maximum exposure of any individual in any quarter has been <0.5 rem." This is within the ALARA standards.

http://moltensalt.org/references/static/downloads/pdf/NAT_MS...

RE: no real fluid-to-fluid heat exchanger.

MSRE had salt-to-salt and salt-to-air heat exchangers made from hastelloy-N. https://www.flickr.com/photos/oakridgelab/31537153147/

RE: or power conversion cycle, which is where lots of maintenance troubles arise from.

That's the part which is not highly radioactive. Fluid fuel reactors have simplest fuelling mechanism of any reactors. The fuelling of a fluid-fuel reactor is even simpler than fuel injectors of diesel engine. Where the need for "maintanence" arise in this simple machine??

Only moving parts are the pump impellers and the control rods. ORNL had some difficulty designing the bearing, seals etc. for the salt pump. But, even that is solved today with concentrating-solar salt pumps.

RE: A line I heard recently regarding MSR maintenance is: "You'll need robots to do the maintenance of your maintenance robots." Another memorable gem is "If you can make robots that can do that, you should just sell the robots"

Maintenance of MSRE was done by humans without much downtime or exposure[1]. Ease of maintenance is a function of design. Just design it carefully.

[1] https://energyfromthorium.com/pdf/NAT_MSREexperience.pdf

Both metallic fuel and salt fuel are not suitable for geological repository. Salt fuel may be stored in salt mines, but unproven. More R&D is needed for geological disposal; but, the point in having metallic fuel or salt fuel is the ease of separating fission products and reusing fuel, not geological storage.

Iodine: Not 50%. It is a probability range. "Thus, of the order of one-fourth to one-third of the iodine has not been adequately accounted for."

RE: "but recognize that it is also a proliferation disadvantage"

MSR without reprocessing: MSR can be as hardened as anyone wants. Because of liquid fuel-form, MSR can be sealed tamper-proof. Fuel goes in and nothing comes out during operation.

Safeguard scenario in case of maintenance: By design the fuel will move to drain tank when shutdown for maintenance. IAEA can have the keys for the drain tank. Fuel can't be pumped back without the presence of IAEA inspector. If someone tampers this, license will be cancelled and the country will have no electricity.

MSBR with reprocessing: How easy separation of fission products from denatured liquid-fuel can be a proliferation disadvantage? It is actually a advantage because fuel always stays inside a tamper-proof system. ORNL attached a "add-on" apparatus for fluoride volatility, and fuel always stayed inside MSRE building. This is actually an advantage.

As material science improves, MSRs last longer and longer without need for maintenance. Safeguards will also become less frequent and less expensive.

I strongly agree that MSR needs a chance. MSR graduated with excellent results with MSRE. MSRE has answered most of the questions and raised very few new questions. MSR should be given a suitable employment like process heat or medical isotope production as soon as possible. We can scale it up for electricity later on.

RE "This kind of reactor needs enrichment once (to start up) and then can just be fed natural, DU, or SNF and it will run on a stream of it happily "forever" (until the vessel life is reached, at which point you transfer the core to a new machine and keep on shuffling)" As fission product concentration increases, even fast reactors have to remove fuel and reprocess it. What works for boron also works for fission products. I don't think any reactor (fast or thermal) can close fuel cycle without the help of reprocessing. May be fast reactors need less frequent reprocessing, that's it.

(LWR-SNF cannot go fast critical. May be fission products is not removed, but reprocessing is needed to concentrate Pu in LWR-SNF.) Even if LWR-SNF has to be used as-is, it has to be toasted in blanket region of fast reactor before it is used as fuel. Some designs like TWR claim no reprocessing needed between toast step and burn step. I agree with that. But, for complete fission of SNF, fission-product removal is needed at some stage when fission product concentration exceeds a particular level in the fuel rod. No exception for travelling wave burnup.

For a critical reactor core some minimum length of fuel rod is always required to be in use. If fission product starts accumulating from bottom of the fuel-rod towards top, somewhere at the midway core can't go critical because a minimum length of rod is needed for criticality.

4% of 1GW-LWR fuel runs for 4.5 years. 100% of this fuel has potential for 112.5 years. A solid-fuel rod can't maintain integrity for 100 years. The crystal structure damage can't be reversed by any amount of maintenance. This is the same phenomenon how solar panels get degraded in sunlight. A fuel rod has crystal structure damage by radiation as well as by fission products.

Fluid-fuel can be used indefinite time and it is easy to reprocess liquid fuel by any method. There is no crystal structure to get damaged. ORNL was working on physical separation of fission products like vacuum distillation when the project was cancelled. Chemical separation and isotopic separation may raise proliferation concerns and they may not be environmentally friendly.

There is a chemical separation of fuel from fission products called fluoride volatility, which is used in industrial scale for enrichment of fuel. But, it works only for fluoride salts. ORNL has demonstrated this process when they switched from U235 to U233. They irreversibly damaged the drain tanks and hastelloy plumbing by doing this. MSRE would have lasted longer if they had not done this fluorination experiment.

RE "Fluid fuel will have 50% of the periodic table in thermal gradients, plating out in heat exchangers and other cold surfaces."

Just throw away the hot leg plumbing and heat exchangers every 2.8 years initially (MSRE salt loop was circulated for 2.8 years) and increase this incrementally. Fact: In solid fuel reactors fuel itself acts as a primary heat exchanger. In 4.5 years LWRs throw away a heat exchanger worth of Zr tubes/cladding. Earlier LWRs threw away solid-fuel every 3 years. Why point fingers at MSR folks when solid-fuel reactors throw away stuff? Note the difference between Inconel 625 (similar to hastelloy-N) and Zr. https://www.tricormetals.com/cost-comparison.html

Yeah, I missed it the first time. You commented when I started editing it. I took (N,TOT) this time. Fission product cross sections is still higher. https://imgur.com/a/pjoNv1p

CANDU: DUPIC fuel cycle is not demonstrated. Canadians don't run PWRs. India, China and South Korea run PWR and CANDU, not much advanced R&D in India. Chinese CANDU in Qinshan may be testing this. US is most advanced in nuclear R&D. Why not build a CANDU in the US and demonstrate this?

I was talking about pressuriser and DNB. If there is no pressuriser (PWR) and constant adjustment of recirculation flow (BWR), clad may get damaged and fuel may melt because of DNB or denucleate boiling. Not inherently safe, engineered systems are needed. (In BWR fuel itself is engineered top-to-bottom with different enrichment levels and different burnable poison concentrations.)

Control rod adjustments are needed till a xenon equilibrium is attained. Also flux flattening circus, boron dilution circus etc. Operators are needed to babysit a LWR or CANDU. This is not like diesel generator or PV panel. Passive shutdown does not mean passive operation like a diesel.

I don't think first generation of MSRs can be like diesel generators. Operators are needed. But, there is potential for nuclear reactors to be like diesel generators with fluid-fuel reactors.

(Edit: Reply to "Today, most CANDU's use ~2% enriched feed, I believe." No. ALL heavy water reactors run with natural uranium in most tubes, depleted uranium or thorium in few pressure tubes for flux flattening circus. No enriched uranium in any tubes.)

Fission products have larger cross section than enriched Boron-10. It is all about concentration; that is the number of B-10 atoms per number of atoms of fuel. Here is the cross sections plot I took yesterday: https://imgur.com/a/uWb0SAa

Robert Steinhaus' Question for fast reactor folks: "While the theoretical case for fast reactors being used to burn nuclear waste down to fission products with short half lives has been made for decades, there has in all that time not been a single demonstration of a fast reactor actually experimentally burning any significant quantity (kilograms) of separated Minor Actinides and Transuranics down to fission products to a batch completeness exceeding 90%. The proposal of using fast reactors to treat nuclear waste has been vigorously put forward for decades. Why do fast reactor proponents not demonstrate with one existing fast reactor the burn up of some kilograms of separated long half life Minor Actinide waste to prove the technical feasibility of fast reactors for the application of waste burning and waste treatment?"

Yes, more neutrons are released for Pu239 fast fission. In CANDU, U238 fast fission is more because 99% of fuel is U238. If we increase Pu concentration Pu fast fission happens as well. U238 fast fission is ~3% of CANDU's power. This is because all neutrons are born fast. A FFR (MSR) can adjust heterogeneity as required, because heat transfer takes place outside the core. A MSR can have thicker fuel regions and higher lattice pitch than a CANDU and exploit fast fission further.

CANDU can use straight-up SNF. Check this or search it: http://www.iaea.org/inis/collection/NCLCollectionStore/_Publ...

"These things aren't like the F-22 or whatever, requiring active systems to stay in the air." That is exactly how pressuriser in a PWR works. A control system loop with Temp & pressure sensors with heater and water injection. Almost all reactors are directly synced with grid, reactors will participate in tiny load adjustments and there is also cooling water temperature variations in a day.

MSRs can be isolated from the power conversion using a thermal salt reserve. That is called inherent safety. Water temperature variations or frequency control wont hit the reactor.

Even if MSR is connected to grid directly, there is no DNB control, the boiling point margin is high. If Xenon is removed with >90% efficiency, -ve reactivity can take care of leftover xenon as well, no control rod circus for MSR till a xenon equilibrium is attained.

What applies for fission products should also apply for control rods in fast spectrum. If control rods do not absorb fast neutrons, how a fast reactor is controlled?

The cross section of fuel in fast spectrum also decreases. Fast reactors have larger fissile holdup. For every atom of fission fragment there are more fuel atoms in fast reactor than in thermal reactor. Fast reactors can run longer because fission products are dilute in the fuel. But, reprocessing is needed even for fast reactors to close the fuel cycle.

The advantages like U238 or Pu239 fission or fast fission factor can be also obtained in heterogeneous thermal spectrum reactors. (Example: A CANDU is heterogeneous reactor. It can burn more plutonium and it can use LWR SNF-fuel without reprocessing.) For a fluid-fuel reactor the fuel acts only as fuel and heat exchange takes place outside reactor core. Fuel region in a fluid-fuel reactor can be as thick as it is needed. So, reactor can be designed for maximum multiplication factor. (Solid fuel rods can't be very thick, because they are also heat exchangers.)

Slide 6 in this presentation. http://www.thoriumenergyworld.com/uploads/6/9/8/7/69878937/s...

Edit: This is a reply for: "I prodded him gently on it: "Oh, you mean the fast neutrons don't get readily absorbed in fission products, not the slow ones, right?" He doubled down. Some poor schmuck is funding this guy."