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PostPosted: Jul 31, 2015 7:06 am 
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You could easily fit a neutron shield liner to the vessel if the 718 turned out to embrittle worse than the normal vessel.
Since, unlike the current corrosion liner it doesn't actually have to be intimately in contact with the vessel, it just has to be in between the core and the wall of the vessel.


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PostPosted: Jul 31, 2015 8:49 am 
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I am OK with nickel alloys if it works.

Quote:
These EPR problems aren't surprising, what is surprising is that so many PWRs have been built with few issues here.


I have the feeling that this story has been seriously overblown by the medias. If the vessel is in accordance with the previous regulation (and it seems it is the case) and if we kept the old regulation there would have been no problem at all. But now the vessel is ”unsafe” because we change the regulation, even if it was possible to use the previous regulation when the vessel has been forged.


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PostPosted: Jul 31, 2015 5:46 pm 
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E Ireland wrote:
You could easily fit a neutron shield liner to the vessel if the 718 turned out to embrittle worse than the normal vessel.
Since, unlike the current corrosion liner it doesn't actually have to be intimately in contact with the vessel, it just has to be in between the core and the wall of the vessel.


I checked and double checked some numbers...

"lifetime" ESBWR vessel flux appears to be only about 10e18 n/cm2. This is very small. Using a conversion of 2x10e22 n/cm2 per DPA it amounts to 0.00005 DPA!

So it must be ballpark of 0.0001 dpa/century.

This is just nothing at all even for very sensitive high nickel alloys. Rad damage must not be a concern for any suitable alloy for BWRs.

I might have been a bit over optimistic on the wall thickness for 718 though. The ASME stress design factor for tensile may be more like 0.3 than 0.5. This increases the ESBWR 718 alloy wall thickness to some 85 mm and the bottom would need to be around 130 mm.

I also checked up on the GT-MHR vessel. 31 meters tall, 8.5 meters dia, 280 mm thick A508 steel!!! This vessel is a lot thicker, a bit taller and wider than the ESBWR vessel. But it only generates 280 MWe.


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PostPosted: Jul 31, 2015 9:12 pm 
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Just read this interesting work on cobalt-free maraging steel:

http://www.journalamme.org/papers_vol29_1/2914.pdf

Now that cobalt free version has a higher fracture toughness, very interesting. Using this steel for the ESBWR would cut vessel wall thickness to 70 mm only! But you still need a stainless liner at least on the water bearing lower parts.


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PostPosted: Aug 01, 2015 1:05 pm 
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hmm, looks like there's lots of different dose conversion factors floating about!

A lower one appears 10e21 n/cm2 = 1 dpa.

Using this and the ~30 ish 'lifetime' dose of 10e18 for the BWR vessel ID flux, it will take 100 'lifetime doses' to get to 1 dpa, which is probably an upper bound of what we can ask from the A508 class RPV steels.

This gives us at least one upper 'limit' of about 3000 years for the vessel. :shock: :shock:

It also suggests an upper limit for PWR (with 10-15x higher peak dose) of around 200-300 years.

It suggests that PWR RPV cracking issues are manufacturing issues not actual intrinsic materials limits...


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PostPosted: Aug 02, 2015 10:19 am 
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How are they planning on forging that GT-MHR vessel?
That sort of diameter implies a 2500MWe gross passive BWR might be plausible.

Which would be the ultimate in bearing down on O&M costs.


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PostPosted: Aug 02, 2015 1:20 pm 
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E Ireland wrote:
How are they planning on forging that GT-MHR vessel?
That sort of diameter implies a 2500MWe gross passive BWR might be plausible.

Which would be the ultimate in bearing down on O&M costs.


I'm sure you can just make shorter ring forgings, but it does compound the crazy production and quality control stuff. There may be only 1 facility that can build this sort of stuff, that is a bad risk to take and even if it works will constrain GT MHR capacity buildout enormously (compounded by the small power output per RPV). Other than than stupid vessel I really like the GT MHR design.

The 8.5 m is OD, the ESBWRs 7.1 m is ID, so it should be about 8 m ID for the GT MHR. Assuming the same power density you would get about 5700 MWth from an ESBWR vessel of that ID. Definately over 2000 MWe but not quite 2500 unless many more steam plant improvements are made...

Keep in mind that even with the same RPV OD, if you have 0.1 m thinner vessel due to maraging steel, In718 or PH SS class steel, then you get 7.3 m ID, that means you get another 250 MWt - 4750 MWth ESBWR. Another 89 MWe with the same RPV size and buildings.

Another interesting option is to have more water annulus there, to cut fast neutron flux down on the vessel, allowing radiation sensitive alloys to be used...

Lots of interesting options, if LWR designers weren't so ultra conservative.


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PostPosted: Aug 02, 2015 6:01 pm 
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Right now my position has apparently turned into:

1. LWRs are capable of providing vast amounts of electricity cheaply almost forever using a simple once through cycle.
2. Breeders seem rather pointless due to the size of the available uranium resource.
3. Most other exotic reactor concepts are pointless because our improved LWR efficiencies (from things like the APWR and so on) and long reactor lives have the ability to pump out electricity at similar prices per unit energy as natural gas and some grades of coal.
4. The reference DMSR core is the only MSR likely to be worth it due to lower fuel costs (thanks to less uranium per unit energy and no fabrication costs) but even that is going to struggle to compete. The recent paper on recycling reactor graphite does help though.

So essentially a fleet of LWRs and potentially later reference-core DMSRs, operating almost forever.


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PostPosted: Aug 07, 2015 4:47 am 
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If, for the reactor part, go for a fast MSR at low pressures, it will make it more compact with lower costs and energy input. The generation part is a second issue. Is anybody, other than the Chinese, interested?


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PostPosted: Aug 07, 2015 7:58 am 
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E Ireland wrote:
Right now my position has apparently turned into:

1. LWRs are capable of providing vast amounts of electricity cheaply almost forever using a simple once through cycle.
2. Breeders seem rather pointless due to the size of the available uranium resource.
3. Most other exotic reactor concepts are pointless because our improved LWR efficiencies (from things like the APWR and so on) and long reactor lives have the ability to pump out electricity at similar prices per unit energy as natural gas and some grades of coal.
4. The reference DMSR core is the only MSR likely to be worth it due to lower fuel costs (thanks to less uranium per unit energy and no fabrication costs) but even that is going to struggle to compete. The recent paper on recycling reactor graphite does help though.

So essentially a fleet of LWRs and potentially later reference-core DMSRs, operating almost forever.


I largely agree with this viewpoint. Uranium is surprisingly abundant, and all the naysayers, sky-is-falling resource "experts" and journalists now seem silly and uneducated.


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