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PostPosted: Jul 05, 2013 11:29 am 
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Interesting similarities and contrasts here.

Both are 100MW(th) lead or lead/bismuth cooled reactors, with steam generators inside the reactor pool primary cooling circuit (the arrangement is very similar, despite apparent difference in the picture - due to the different views).

But SVBR-100 is a fast reactor, while LEADIR-PS100 is thermal, using prismatic TRISO/graphite fuel.

Also, LEADIR-PS100 uses air cooling for the reactor vault, whereas SVBR-100 sits in a pool of water.
The containment boundary above the reactor is also quite different in the two designs.

Besides that, some differences relative to MSRs are hilighted by Ralph Hart of Northern Nuclear Industries Inc.,
Quote:
Steam and/or water escaping from a steam generator tube rupture aggressively reacts with the molten salt coolant creating heat and pressure. Hence, there is an intermediate heat transfer circuit employed on MSR reactors that transfers heat between the molten salt coolant in the reactor cooling circuit and the steam generators. This does not eliminate the potential for a molten salt/water/steam reaction but rather moves the potential event to a location remote from the reactor so that it is not a direct reactor safety issue. The use of the 208 lead coolant allows the steam generator tube bundles to be placed in the primary reactor vessel, which avoids an intermediate cooling circuit. This results in substantial capital cost saving (secondary circuit heat exchangers, pumps, real estate) and in reduced maintenance costs, and in increased plant reliability/availability.


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PostPosted: Jul 07, 2013 12:08 am 
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Combine the best of both. Have a fast reactor with Nitride/Carbide pebbles. Lead cooling and steam generation in the reactor are fine.


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PostPosted: Aug 05, 2013 5:04 am 
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Good to see a conceptual design in this area. Graphite and silicon carbide are compatible with molten lead, so you'd wonder why this path hasn't been investigated before. Lead is much more attractive as a coolant than high pressure helium.

In some ways, lead is more attractive than molten salts. It's compatible with steam, has a lower melting point and higher thermal conductivity than fluoride salts, doesn't make tritium, and shields gamma rays well.

In terms of heat capacity, transparency and weight it loses out to fluoride salts.

Of course, graphite is not compatible with hot steam, so a steam generator tube leak could still pose problems if steam/water bubbles aretrained and recirculated through the core. Such bubbles must also not cause positive power coefficients, which is hard with fast spectrum but probably doable with thermal spectrum (it is the reverse of what happened at Chernobyl where water was lost out of the core, in stead of leaking into it). Nevertheless, I imagine that considerable safety analysis and testing will have to be done with high pressure steam injected into molten lead core prototypes.


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PostPosted: Aug 05, 2013 8:37 am 
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jaro wrote:
Quote:
Steam and/or water escaping from a steam generator tube rupture aggressively reacts with the molten salt coolant creating heat and pressure. Hence, there is an intermediate heat transfer circuit employed on MSR reactors that transfers heat between the molten salt coolant in the reactor cooling circuit and the steam generators. This does not eliminate the potential for a molten salt/water/steam reaction but rather moves the potential event to a location remote from the reactor so that it is not a direct reactor safety issue. The use of the 208 lead coolant allows the steam generator tube bundles to be placed in the primary reactor vessel, which avoids an intermediate cooling circuit. This results in substantial capital cost saving (secondary circuit heat exchangers, pumps, real estate) and in reduced maintenance costs, and in increased plant reliability/availability.
This doesn't make much sense to me. The reaction in a MSR is thermal, not chemical. So why would lead be any different? Introduce water and you get a violent steam explosion. Sounds like someone is stretching here, trying to make MSRs look bad.

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PostPosted: Aug 05, 2013 9:02 am 
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Incidentally, Hart's presentation is now available on video.
He explains a few things that were not evident from the slide presentation....

http://www.youtube.com/watch?v=VgKSfoX05sY


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PostPosted: Aug 05, 2013 9:11 am 
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KitemanSA wrote:
jaro wrote:
Quote:
Steam and/or water escaping from a steam generator tube rupture aggressively reacts with the molten salt coolant creating heat and pressure. Hence, there is an intermediate heat transfer circuit employed on MSR reactors that transfers heat between the molten salt coolant in the reactor cooling circuit and the steam generators. This does not eliminate the potential for a molten salt/water/steam reaction but rather moves the potential event to a location remote from the reactor so that it is not a direct reactor safety issue. The use of the 208 lead coolant allows the steam generator tube bundles to be placed in the primary reactor vessel, which avoids an intermediate cooling circuit. This results in substantial capital cost saving (secondary circuit heat exchangers, pumps, real estate) and in reduced maintenance costs, and in increased plant reliability/availability.
This doesn't make much sense to me. The reaction in a MSR is thermal, not chemical. So why would lead be any different? Introduce water and you get a violent steam explosion. Sounds like someone is stretching here, trying to make MSRs look bad.


There is some chemical reaction, where HF is produced, which is both corrosive and volatile. Also there is a reaction of water with actinides fluorides. The MSRE used a lot of ZrF4 as a buffer in case any water got in. It never did, so ORNL went for no ZrF4 in the MSBR designs. But if we have a lot of reactors we will have to deal with a water ingress scenario. The best way to deal with it is to have intermediate loops with passive water locks/quenchers installed so we can avoid the scenarios. Making water ingress non-plausible simplifies the safety analysis.


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PostPosted: Sep 17, 2013 12:06 pm 
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The latest LEADIR-PS100 concept description: It differs somewhat from the one presented by Hart at the TEA conference in Chicago earlier this year.

It's starting to look a bit like Berkeley's PB-AHTR, except that here there is no secondary loop - the SGs are right inside the reactor pool.

http://www.northernnuclear.ca/our-product.html


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PostPosted: Sep 18, 2013 11:42 am 
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SGs inside the vessel, and no secondary coolant, is an attractive simplification that lead coolant allows.

However, it does bring up a specific scenario, namely reactivity insertion and pressurization damage from SG leakage entraining water (steam) into the core. Engineered safety features such as rapid isolation of SGs must be provided, and the pressure wave must be accomodated. It also makes it more difficult to have a low pressure containment (it is possible but more complicated, for example you'd want pressure suppression containment probably).

Why do they use steel shielding balls? Pb-208 is a better gamma shield than steel. Pb-208 is not a good neutron shield (having a huge mean free path for neutrons) but steel is not good either in terms of neutron shielding.


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PostPosted: Sep 18, 2013 6:26 pm 
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Cyril R wrote:
However, it does bring up a specific scenario, namely reactivity insertion and pressurization damage from SG leakage entraining water (steam) into the core. Engineered safety features such as rapid isolation of SGs must be provided, and the pressure wave must be accomodated. It also makes it more difficult to have a low pressure containment (it is possible but more complicated, for example you'd want pressure suppression containment probably).
That doesn't look likely: The yellow stuff in the diagram is solid graphite - no direct path into the core.

Cyril R wrote:
Why do they use steel shielding balls? Pb-208 is a better gamma shield than steel. Pb-208 is not a good neutron shield (having a huge mean free path for neutrons) but steel is not good either in terms of neutron shielding.
I wondered about that too.
But then it occurred to me that the steel ball shielding is likely intended for maintenance/repair outages, when the level of liquid lead is dropped down to the top of the graphite block, or lower....


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PostPosted: Sep 19, 2013 2:35 am 
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The issue with steam ingress would be entrainment with the coolant, so some steam will go where the coolant goes, which is through the core. Not much, likely - lead is heavy and steam is light - but the steam is under high pressure so some entrainment in flow is expected.

Also steam reacts with graphite, producing noncondensable gasses that pressurize containment (including a pressure suppression type containment).


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PostPosted: Sep 24, 2013 11:57 pm 
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Keeping the reactor core free of volatile matter gives a degree of safety not available in modern LWR or PHWR. Even LMFBR with sodium carries fire risk. Cooling with salts or non-reactive metals is a great improvement available in both the reactors being discussed.
Other things being equal, I would prefer fast spectrum. It helps burn more of plentiful U-238 or thorium.


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PostPosted: Oct 28, 2013 8:07 am 
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I really like the passive cooling concept of the LEADIR. It's very similar to something I've been working on. I've considered lead too, as the solid buffer material, it has many advantages, but it just has too high a thermal conductivity. Thermal losses in normal operation will be very high, especially for a small reactor, even with all the lead buffer frozen. Coolant freeze prevention would be quite hard as well, since the buffer lead has the same freezing point as the coolant lead, and lead's high thermal conductivity means a big thermal loss rate even when all buffer lead is solid. Since the cooling occurs at the coldest lead coolant temperature region, lead slug becomes a serious design issue during certain long lasting transients (like SBO).


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PostPosted: Oct 28, 2013 8:18 am 
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I am not sure breeders are going to be worth it any more.
Seawater extraction of uranium is down to $660/kg and still falling.
If it drops much more its going to start eating away the economic basis of using anything but a once through cycle.


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PostPosted: Oct 28, 2013 8:45 am 
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E Ireland wrote:
I am not sure breeders are going to be worth it any more.
Seawater extraction of uranium is down to $660/kg and still falling.
If it drops much more its going to start eating away the economic basis of using anything but a once through cycle.


It seems that the LEADIR concept gets this - they call it "creep, crawl, walk run approach". Start with a small developable uranium burner, using proving TRISO fuel and proven graphite moderator, for a high end market (oilsands). Then progress towards bigger reactors possibly with thorium fuel cycle.

Lead as a coolant is somewhat out of tune with that philosophy, however. It's one of the least proven nuclear reactor coolants. It must be hard to find manufacturers for lead pumps, HXs, maintenance/inspection, instrumentation equipment...


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PostPosted: Oct 30, 2013 4:52 am 
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Breeders or fast reactors are worth it for spent fuel disposal alone.
Russians have been using lead cooling for long. Rest will just have to learn from them.


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