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PostPosted: Oct 03, 2013 6:39 pm 
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An hour ago I got back from attending my first-full fledged NE conference, GLOBAL 2013, in SLC. It included several sessions devoted entirely to the utilization of thorium in various sorts of fission reactors.

While I made a couple of presentations myself (re my schemes for solving the Hanford tank waste problem & LFTR waste vitrification), in my opinion its most exciting/interesting papers were two presented by Carlo Fiorina about the sorta-fast (fluoride salt-based but no graphite) two-salt MSBR he'd recently developed as his PHD thesis project. I've just tracked that thesis down on the internet - see below.

https://www.politesi.polimi.it/bitstrea ... iorina.pdf

This design seems to address/solve all of the problems I've seen with others - it's simple, flexible, wouldn't require much "reprocessing" (6 liters/day) or 233Pa isolation to achieve breakeven, & should be both cheap & easy to maintain.

Let's all carefully read through & discuss it

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PostPosted: Oct 03, 2013 7:28 pm 
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Darryl,

Just to be clear, while I'm sure Dr. (or soon to be Dr.) Fiorina has lots of interesting new calculations it is by no means a newly developed concept. This is the MSFR design worked on for many years, mainly by the Grenoble group but with others around Europe.

It certainly has its merits but there are numerous challenges involved in this approach. 3000 MWth in 18 m3 of salt and no graphite doesn't give one much thermal inertia and they are relying on structural metal in an extreme neutron flux. PuF3 solubility in this fast spectrum is also a concern and I believe is the reason they've as of late been discussing upwards of 850 C peak salt temperatures.

David LeBlanc


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PostPosted: Oct 03, 2013 7:48 pm 
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No relation to Carlie Fiorina of HP?

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


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PostPosted: Oct 07, 2013 4:02 am 
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It might be easier to get funds for the fast MSFR as a waste burner. Using 37Cl in place of fluorine may burn the the bulk of used fuel-the 238U as also the TRUs better. Power will be a highly desirable 'side benefit'.


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PostPosted: Oct 08, 2013 8:52 pm 
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jagdish wrote:
It might be easier to get funds for the fast MSFR as a waste burner. Using 37Cl in place of fluorine may burn the the bulk of used fuel-the 238U as also the TRUs better. Power will be a highly desirable 'side benefit'.

Jagdish,
There is a fantastically large amount of 238U in spent fuel - crudely speaking you would have to generate 30 times as much electricity to use up the 238U in spent fuel. This is a huge job and fantastically expensive. You will never, ever, ever get this volume of funds to burn up 238U. You could get this much from producing electricity - but I doubt the fast MSFR will be cheaper than a thermal LFTR. If not, you won't get funding to build these for electricity purposes either.

The fast MSR is probably the best way to burn TRUs and this is feasible. Talk about burning off spent fuel 238U is nothing but politics - it isn't feasible.


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PostPosted: Oct 08, 2013 11:09 pm 
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If you make a start with burning the spent fuel, the 238U changes status from waste to fuel reserve, just like the DU. You could burn it over centuries if you stop building or extending the life of LWR and creating more of LWR-SNF.
You could export the MSFR and fuel instead of LWRs which need fresh uranium to be mined. RU and DU can be mined from stocks for centuries.
If the US, the top holder of the SNF does not do it, the Chinese will. They just happen to be short of SNF just now but they could import it from Germany, Italy etc. The French and the British just sold services of reprocessing but others could sell the MSFR fuel too. The British are stocking the recovered plutonium from clients but the Chinese could offer to buy it from them and sell the fuel.


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PostPosted: Oct 09, 2013 8:44 am 
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darryl siemer wrote:
in my opinion its most exciting/interesting papers were two presented by Carlo Fiorina about the sorta-fast (fluoride salt-based but no graphite) two-salt MSBR he'd recently developed as his PHD thesis project. I've just tracked that thesis down on the internet - see below.

https://www.politesi.polimi.it/bitstrea ... iorina.pdf

This design seems to address/solve all of the problems I've seen with others - it's simple, flexible, wouldn't require much "reprocessing" (6 liters/day) or 233Pa isolation to achieve breakeven, & should be both cheap & easy to maintain.

Let's all carefully read through & discuss it
Thanks for the invitation to "carefully read through & discuss it" Darryl.

It’s an excellent paper – actually a series of papers labelled chapters.

Dr. Fiorina goes to great lengths to compare the molten salt reactor to traditional fast neutron reactors, emphasising similarities and differences.

The introduction section explains that “The primary circuit is connected to 2 other circuits for salt processing. The first one is a gas system envisioning He bubbling into the fuel salt to extract gaseous and non-soluble fission products. A 30 seconds extraction time is assumed for both kind of fission products.”

In Figure 1.1, “Schematic view of the MSFR primary circuit” we see a “Bubble injector” near bottom of reactor core.

Section 4.3.1, “Reactivity feedbacks in the MSFR” states that “the possibility is considered in the frame of the EVOL project (EVOL, 2012) to operate the gas bubbling for extraction of non-soluble fission products directly inside the core. However, the MSFR fuel expansion coefficient translates into a reactivity insertion of 100-200 pcm for a 1% density increase.
Attention should then be paid to set a limit on the gas fraction in the core, as a problem to the gas injection system may cause a sudden density (and reactivity) increase.”

However, in section 6.2.1, “Geometry and main assumptions,” there is no further mention of volatile fission product or helium bubbling.

Thinking that this surely is one fundamental difference between molten salt reactors and traditional fast neutron reactors, I thought that even if helium is not introduced, volatile fission products will tend to form small bubbles in the salt fluid, comprising a certain small compressible volume fraction.

So I asked Dr. Fiorina how the results of his transients simulations would be affected by the presence of volatile fission product and/or helium bubbling.
I thought that with a neutron generation time on the order of a microsecond, significant reactivity oscillations could result from acoustic (pressure) waves induced by an initiating transient.

Dr. Fiorina replied yesterday as follows:
Quote:
Personally I think it's not a good idea to operate the bubbling inside the core. The reactivity effect from a gas system trip can be a serious problem. In addition, as you say, the induced salt compressibility can initiate oscillations or anomalous behaviors and, in general, it makes transients more difficult to predict and control. Since I am against this idea, I did not bother to much including this effect in my models (which, I admit, also made my life a lot easier). I agree that the effect might be sizeable and interesting to study. Unfortunately I do not have calculations on it and I don't think anyone tried anything similar. It's probably an interesting field of research and I (we?) may try to put some efforts in it in the future. But it won't be easy for me to find the time necessary...

In case one operates the bubbling in the out-of-core part of the primary circuit, the presence of gas in the core should be negligible (probably not more than the vapor caused by subcooled nucleate boiling in PWR, or?). As far as I know, reactivity effects originated by gas bubbling outside of the core were not observed in the MSRE and were not expected to happen in the MSBR (although I admit I have not read ALL the reports from ORNL).

I am left puzzled by the comparison of the 3,000 MWth MSFR to the small MSRE (7.4 MWth) to assume that “presence of gas in the core should be negligible” if no helium bubbling is used in the core:
We are comparing a reactor with 400-times higher power (MSFR) to a reactor that is only a few times smaller in volume (MSRE).
The rate of production of gaseous and volatile fission products like Kr, Xe, I, Br, tritium, plus some volatile fluorides, would be drastically different in the two cases.

Nevertheless, it is heartening that Dr. Fiorina agrees that “It's probably an interesting field of research and I (we?) may try to put some efforts in it in the future.”


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PostPosted: Oct 09, 2013 3:00 pm 
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Quote:
We are comparing a reactor with 400-times higher power (MSFR) to a reactor that is only a few times smaller in volume (MSRE).
The rate of production of gaseous and volatile fission products like Kr, Xe, I, Br, tritium, plus some volatile fluorides, would be drastically different in the two cases.

Nevertheless, it is heartening that Dr. Fiorina agrees that “It's probably an interesting field of research and I (we?) may try to put some efforts in it in the future.”


I don't see "rate of production" to be an issue because even in this case, the actual generation rate of FP inert gas bubbles would be trivially small. Here's why:

1) at 200 mev/fission 3e9 watts worth of heat corresponds to fissioning about 9.4 e19 atoms/second
2) if, let's say, 30% of those fissions generate inert gasses, that's 0.3*9.4e19/6.02e23 (N Avogadro) = 4.7e-5 mole gas/sec
3) if the reactor core operates at atmospheric pressure & 700C, that'd be 4.7e-5*(700+273)/273*22400 (cc/mole STP)=3.7 cc/s

That 3.7 cc of gas/s would be generated within the approximately 9,000,000 cc of salt in the core at any one time - I just don't see how that much gas could affect how the reactor would behave.

The features that make it especially exciting to me include;

1) beak even fissile(233U) regeneration would require only a tiny fuel salt "reprocessing" system (about 6 liters/day capacity) - that's almost lab bench scale
2) it doesn't have graphite “waste” or maintenance issues
3) it’d be cheap to maintain (if properly designed): a two cm thick, right circular cylindrical, 9 cubic meter, Hastalloy N “reactor core tank" would weigh about 4 tonnes – if we had to replace it every other year, at today’s international prices for that particular alloy (see Alibaba), that adds up to no more than about $50,000 year
4) most of its design & chemistry is based upon work performed by ORNL back when experimentation/verification was both affordable & strongly encouraged (there are practically no process chemists left at US DOE’s nuclear engineering R & D facilities)
5) and finally, it’s flexible enough to satisfy just about anyone’s perceptions about what a 4th generation of nuclear reactors is supposed to accomplish.

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PostPosted: Oct 09, 2013 6:00 pm 
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darryl siemer wrote:
That 3.7 cc of gas/s would be generated within the approximately 9,000,000 cc of salt in the core at any one time - I just don't see how that much gas could affect how the reactor would behave.
Thanks Darryl.
That 3.7 cc/s comes to 320,000 cc in one day of operation.
Guess the question becomes, at what rate can the gas & volatiles production be removed, and down to what level ?
….and of course, what level is tolerable from the point of view of stable operation ?

I figure that’s where a proper multi-physics simulation would be useful, before building anything, right ?


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PostPosted: Oct 09, 2013 7:17 pm 
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320,000 cc/day represents just 3.5% of one core volume's (9 cubic meters) worth of fuel salt which is normally moving through a maze of pumps, pipes & heat exchangers at a rate of 4.5 cubic meters/second. There's absolutely no way that any in situ generated inert gasses wouldn't become disengaged in one way of the other.

Here's a bigger issue: If the pumps were to totally quit, the fuel salt's temperature would immediately (within a few seconds) reach a point which would cause it to be dumped into a "poisoned" and/or geometrically safe cooling pit. With a 3 GWth reactor, keeping that pit cool enough to prevent problems would not be trivial.

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PostPosted: Oct 09, 2013 10:11 pm 
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jaro wrote:
That 3.7 cc/s comes to 320,000 cc in one day of operation.
Guess the question becomes, at what rate can the gas & volatiles production be removed, and down to what level ?
….and of course, what level is tolerable from the point of view of stable operation ?

I figure that’s where a proper multi-physics simulation would be useful, before building anything, right ?


We could still operate the gas extraction cyclones even if we don't include the helium bubbles. My understanding is that a significant portion of the offgases come out even without any such processing. While the addition of helium helps I expect we will still get a half-life measured in minutes without the helium bubbles.


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PostPosted: Oct 10, 2013 1:19 am 
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An MSR would generally have enough thermal inertia so that every three hours or so, the liquid fuel could be vacuumed for extraction of volatile fission products. Helium circulation could be dispensed with. This will simplify the reactor. Higher the operating temperature, more effective will this be.
If we provide a salt pool for covering the demand variation, there is greater scope for disposal of volatiles.


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PostPosted: Nov 05, 2013 12:52 pm 
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A week ago I presented a talk (attached) about the EU's MSFR at ISU (Pocatello) which has apparently generated interest manifesting itself in the form of a series of emails back & forth between myself & a number of correspondents. Since the discussion is mostly "technical" & and therefore somewhat lengthy, it's filling up inboxes which suggests that it'd probably be better to move it to this forum. I'll post the gist of my contributions to that discussion here & encourage my correspondents to visit/contribute too.


Attachments:
best MSBR.ppt [1.81 MiB]
Downloaded 240 times

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PostPosted: Nov 05, 2013 1:06 pm 
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Here's the first of my "contributions"...it was in response to an observation/opinion that it's silly to try to promote something along the lines of what I described in my talk at ISU.


______is certainly right about the current attitudes of Western-oriented political and nuclear business leaders. This means that he's also right in saying (implying?) that pushing for the implementation of any genuinely efficient/clean/cheap "nuclear renaissance" in a Western-oriented country constitutes a fantasy. This & the fact that some of those countries have apparently decided to frack the methane out of their shale beds is why I consider my efforts to be a retirement hobby/mission & suspect that the stuff we're talking about here will actually be implemented by China (or possibly India), not a Western-oriented country.

He's wrong about the world being awash in fissile - the world is awash with raw spent LWR fuel assemblies which don't contain enough "good" fissile to justify the huge costs/trouble of recovering it - certainly not if the goal is to make MOX . In my opinion, it's a mistake to confound the implementation of any sort of genuinely sustainable nuclear renaissance with solving today's politically driven LWR spent fuel management conundrum - let those sleeping dogs continue to lie until those same political decision makers screw up enough courage to decide where they're going to be sent.

The fissile - mostly 235U - in the fuel consumed by an average sized PWR (1 GWe) every five years or so would start up a MSFR after which it would be self sustaining & its core salt would still be fairly "clean" (not much TRU buildup). Since the USA currently seems able to access/afford sufficient 235U enrichment capability to generate about 100 GWe's worth of LWR generated electricity, it follows that utilizing that capability to make MSFR start up fuel instead would permit us to build about 20 genuinely sustainable 1.5 GWe (30 GWe's worth) nuclear reactors every year indefinitely.

Any "scientist" unwilling to challenge nonsensical assumptions isn't a scientist.

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PostPosted: Nov 05, 2013 1:12 pm 
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Here's the second...it was in response to an observation that the latest/greatest version of the MSFR would be very similar to ORNL's original "reference" tank-within-a-tank 2 salt reactor:

The definitive description of ORNL's "reference" 8 ft diameter, two salt, "semifast" (all metal, no graphite,) reactor is Chpt 7 of the 1958 Addison Wesley "homogeneous reactor" textbook (http://www.energyfromthorium.com/pdf/FFR_chap17.pdf).

That chapter's first paragraph states that...
"...from nuclear considerations, is capable of operating at power levels up to
1900'M'Tw (thermal) without excessive power densities in the core"

Since the volume of an 8 ft sphere is 7.58 cubic meters, 1.9 GWt translates to 250 Watts/cc - very similar to the 333 Watts/cc fig. that the EU's researchers are assuming for their MSFR, not "much less".

Second, extrapolation from ORNL's 8 ft dia. spherical core to one big enough to accommodate the MSFR's 9 cubic meters of fuel salt (8.48 ft) doesn't seem to be a great stretch either.

The guys working on ORNL's reactors back in those days - the same generation (& quality) of nuclear engineers, scientists, & managers that had recently designed the Nautilus for Adm Rickover - seemed to be pretty confident that their "INOR 8" reactor tank would last 10-20 years so I'm also happy with EURATOM's conclusion that one of today's super alloys could last at least 2-3 years.

Assuming a density of 8 g/cc, it'd take about 3.35 tonnes of that super alloy to make a 2 cm thick , 8.48 ft diameter spherical core tank. If we assume that a real tank's flanges, asphericity , etc. would add another 50% , that adds up to about 5 tonnes of super alloy that the reactor's service contract personnel would have to replace every few years. When you look up the "real world" costs of such alloys (e.g., what Alibaba's suppliers currently quote for Hastelloy N) they seem to cluster around 5$/kg for "large lots". That translates to replacing $25,000 worth of metal every few years to maintain a reactor generating roughly $7,000,000 worth of electricity per day.

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