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PostPosted: Apr 25, 2014 3:31 pm 
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Cyril R wrote:
Lars wrote:
Cyril R wrote:
12 bar is a lot when it comes to the thermal and radiation creep regime this reactor vessel is in.

You may wish to go for a bit more conservative design, lower temp and lower pressure, to manage materials/thicknesses and accidents. Molten chloride reactors are themselves highly unconservative.

OR you could have a pool type reactor and keep the pool at a similar pressure but cooler.


12 bar is a lot of hydrostatic head. If buffer salt is used of 2 g/cc then it is 60 meters of buffer salt!


Or you could pressurize the pool. The key point being the pool is lower temp than the core and one could put insulation between the pool salt and the pool vessel so that there should be no concern about creep etc.


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PostPosted: Apr 25, 2014 4:27 pm 
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There are downsides to pressurizing the pool. For one thing this thing is big, assuming its also the emergency heat sink. Say you get 5 meters of buffer salt. This is 1 bar. Then you need a buffer salt vessel with cover gas of 11 bar.

Insulation works well, but it also takes out your long term heat sink.

Another downside of a pressurized pool is that it must be fully enclosed. No open pool. So we get into fully enclosed and nested engineering issues.

There are also various problems that occur with loss of cover gas pressure.

It may be better to insulate the vessel on the inside so it can operate as ASME section III nuclear pressure vessel. Failure of the insulation can be a dangerous scenario though.


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PostPosted: Apr 26, 2014 3:33 pm 
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Hi Cyrill...for engineers the challenge of a 4150mm diameter and 5760mm height vessel under 12 bar is very low compared to the other challenges of a MSR. The wall thickness of my concept is 50mm and the max. stress 39 MPA. The max. allowable stress for MO-TZC is 250 MPA (>100.000h) at 700°C. I strongly assume that if engineers will take over a fluoride MSR concept they will put the primary circuit under some pressure.

Main challenges for MSR are the HX with its thin structures and the fuel treatment/processing


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PostPosted: Apr 27, 2014 1:39 am 
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HolgerNarrog wrote:
Hi Cyrill...for engineers the challenge of a 4150mm diameter and 5760mm height vessel under 12 bar is very low compared to the other challenges of a MSR. The wall thickness of my concept is 50mm and the max. stress 39 MPA. The max. allowable stress for MO-TZC is 250 MPA (>100.000h) at 700°C. I strongly assume that if engineers will take over a fluoride MSR concept they will put the primary circuit under some pressure.

Main challenges for MSR are the HX with its thin structures and the fuel treatment/processing


There's your problem, you're assuming a magic molybdenum alloy pressure vessel, even though such vessels are STRICTLY prohibited by ASME code... for good reasons. We don't make pressure vessels out of brittle materials.

Also your hoop stress calculation is wrong. This is (1.2MPa*4.15/2)/0.05. Its about 50 MPa. Which is more than twice the allowable for Hastelloy N/SS316 @ 700C. And you want more safety margin than that since this is such a critical component for a molten salt reactor and there are many, many uncertainties wrt pressure vessels at this temperature and pressure and high flux radiation from fast spectrum reactor... plus possible stress corrosion issues with chlorides and mutants (sulphur etc.) that are basically unknown at this point.

Furthermore, 100kh is only 11.4 years.

I would suggest minimum 150 mm vessel wall thickness for your application.


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PostPosted: Apr 27, 2014 2:55 pm 
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Hi Cyril,

the Barlow formula for a ball shape is

Stress = Pressure * radius/(2*wall thickness)

Stress = (1.2MPA + 0.18 MPA (static pressure at the bottom)) * 2.832m* /(2 *50mm).

My computer gave me a result of 39 MPA

*2.832 is the bigger radius hence it is more conservative


Chloride salts are not as stable as fluorides and hence need more corrosion resistant structure materials. The molybdenum alloys are one of very few material groups that combine high temperature strength and corrosion resistance against chloride salts. In consequence molybdenum alloys are the preferred structure material for a MCFR concept. I do not have the impression that todays knowledge about molybdenum alloys is really sufficient to give final answers about the potential use as material for pressure vessels. If there is a real development of such a reactor it is to make tests and if possible to persuade organizations and authorities to approve such a material.

Having a look on the MSFR (fluoride) the nickel based materials are at its limits for the reactor vessel and primary pipes but overchallenged with the HX. The group from Grenoble propose a material that seems to be Mo-Tzm. The use of molybdenum alloys could increase potential operation temperatures the resistance against overheating in case of an accident.


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PostPosted: Apr 27, 2014 4:04 pm 
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Ok, the shape isn't cylindrical, got it.

There are a lot of questions on molybdenum alloy in high flux environment. There are things like ductile-to-brittle transition temperature that goes up with flux. Then there's the higher carbon content of the moly alloy you have in mind (compared to TZM). This generally means poorer performance under irradiation especially for the higher DPA rates you'd see in this application. It also raises questions of carburization in the salt environment, especially in a reducing environment needed to make chlorides less corrosive. The higher amount of titanium and zirconium can also be problems since they want to form chlorides. Then there is the sulphur corrosion issue from Cl35 activation. Then there are questions on irradiation creep of these alloys. These are just a few of the questions. It doesn't help that the power density (and so the flux and transient issues) is so high. It doesn't help if the pressure and temperature are high. It doesn't help if you use natural chlorine.

You could easily spend 20 years trying to experiment on just the basic chemistry and materials compatibility issues I'm afraid. In fact, chlorides reactors have been considered for much longer than that, and all of it is highly theoretical...


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PostPosted: Apr 27, 2014 5:16 pm 
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We spent a lot of time looking at Mo alloys, and specifically TZM.
For practical purposes, ithey are not weldable.

If youa re going to use TZM, i suggest getting familiar with a rivet gun.


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PostPosted: Apr 28, 2014 1:32 am 
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djw1 wrote:
We spent a lot of time looking at Mo alloys, and specifically TZM.
For practical purposes, ithey are not weldable.

If youa re going to use TZM, i suggest getting familiar with a rivet gun.


Supposedly, TZC is more weldable and has better plasticity at room temperature, than TZM. Not what you'd call a ductile alloy, but it seems ok at room temperature. Real question is what happens in high temperature high flux chloride environment to the ductility. I suspect it will be lost, very quickly.

Riveting is out of the question. It has to be absolutely leak tight, even if you can do this with riveting there are too many points where a leak could develop. Also I doubt anyone knows how to rivet molybdenum alloys. It can be hard to find companies that will do riveting with iron and steel.


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PostPosted: Apr 28, 2014 6:56 am 
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HolgerNarrog wrote:
Are there any new reports from Grenoble or the Euratom about the MSFR project.... Salt reprocessing, engineering, design, cost estimates???


Hello Holger,

Nothing that I know of. In fact, it depends how old are your infos. EVOL having ended, most institutions are back to either national programs (if any) or other european projects. There is little engineering as such ongoing in Europe. Most people participating in EVOL (and previous projects) have a reactor physics background. In the labs of CNRS participating, there was of course the LPSC of Grenoble (reactor physics & thermal-hydraulics), but also IPNO in Orsay (radiochemistry, reprocessing), CEHMTI (high temp. & radiation materials + salts), MSSMat (Materials again) and LGC in Toulouse (chemistry, corrosion, reprocessing).

Overall, nobody is *truly* focused on MSRs and working full-time on it (besides maybe a few PhD students)... because in the research world (the overall nuclear community, not just MSR fans), it is still considered as a *very* long-term option with questionable feasibility. (see for example the update in the GIF roadmap of January 2014)

There was otherwise an issue of Annals of Nuclear Energy that was partly dedicated to MSRs/FHRs (Volume 64, articles 41 and beyond) and some papers here and there by Ph.D. students just finishing their thesis.


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PostPosted: Apr 28, 2014 6:58 am 
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jaro wrote:
Thanks !

I note the following comments in the Conclusions section:
Quote:
In the nominal MSFR conditions, a certain fraction (1%) of the core volume is occupied by small gas bubbles.
In these conditions, the fuel mixture is likely to present a relatively high compressibility and a very low speed of sound (compared to the pure fuel salt).
...In this direction, consistent transient analyses are desirable, at least to exclude any meaningful difference with respect to incompressible simulations.


Indeed. There are also some people that would not deem it wise to inject the bubbles directly in the core. We shall see...


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PostPosted: Apr 28, 2014 7:17 am 
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HolgerNarrog wrote:
Having a look on the MSFR (fluoride) the nickel based materials are at its limits for the reactor vessel and primary pipes but overchallenged with the HX. The group from Grenoble propose a material that seems to be Mo-Tzm.


Not as far as I know. The reference material for MSFR is still EM-721, a Ni-W-Cr alloy (instead of the Ni-Mo-Cr base of Hastelloy-N and derivatives), because of its possible better high temperature irradiation behavior (W transmutes less readily than Mo, and the precipitates of W are better than the precipitates of Mo for creep resistance).

EDIT: Oh, maybe somebody proposed TZM along with SiC for the reprocessing system. But that's a bit of a guess.


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PostPosted: Apr 28, 2014 7:42 am 
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Neutron flux and fluoride/chloride corrosion is a difficult combination. It should best be confined to the reactor core. That leaves two possibilities.
1. Transfer the heat from fast spectrum core by a lead based coolant.
2. Put it in a water tube boiler and operate it as a reduced modification reactor with water as moderator-coolant. Pressure is confined to inside the tubes.


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PostPosted: Apr 28, 2014 8:30 am 
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Boris H wrote:
W transmutes less readily than Mo


Are you sure? In thermal spectrum its the other way around. Fluoride fast reactor still has quite a few thermal neutrons.


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PostPosted: Apr 28, 2014 9:15 am 
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Cyril R wrote:
Boris H wrote:
W transmutes less readily than Mo


Are you sure? In thermal spectrum its the other way around. Fluoride fast reactor still has quite a few thermal neutrons.


You're right, a quick calculation gave me ca. 0.7 barns for W and 0.3 barns for Mo in that spectrum.

I remembered the statement wrong. It's about long-term activation rather than transmutation itself.


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PostPosted: Apr 28, 2014 9:51 am 
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Boris H wrote:
HolgerNarrog wrote:
Are there any new reports from Grenoble or the Euratom about the MSFR project.... Salt reprocessing, engineering, design, cost estimates???



Overall, nobody is *truly* focused on MSRs and working full-time on it (besides maybe a few PhD students)... because in the research world (the overall nuclear community, not just MSR fans), it is still considered as a *very* long-term option with questionable feasibility. (see for example the update in the GIF roadmap of January 2014)


Well, that may be true for the European effort, but China is leading the way with regard to the FHR/MSR. Let's hope others will follow suit. Do you think there is a lot of institutional resistance from the established parties in the nuclear community ? I can recall one chairperson of the French Atomic Energy Commissariat in a video, dismissing the idea of a MSR out of hand.


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