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PostPosted: Aug 04, 2015 5:30 pm 
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So we could forge a similar ingot weight as now?
What is the limiting factor on the size of forging in this place?
The fewer welds the fewer inspections.


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PostPosted: Aug 05, 2015 7:50 am 
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E Ireland wrote:
So we could forge a similar ingot weight as now?
What is the limiting factor on the size of forging in this place?
The fewer welds the fewer inspections.


Forging weight and thickness is typically the most limiting. Making bigger rings isn't too tough, as bending a flat plate to a larger diameter is easier, all other things being equal...

Taller rings would be more difficult to bend than shorter rings, so there will be a limit on the height there. But you could go quite tall (that is start with wide plate) with hot rolling.


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PostPosted: Aug 05, 2015 8:35 am 
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Ok I did a more detailed thickness calculation.

The ESBWR has a nominal wall thickness of 182 mm inc. stainless cladding. Assuming cladding of 6 mm (anyone know exact thickness?) gives 0.176 meter.

The vessel inner radius is 3.55 meter, design pressure 8.62 MPaG, giving (3.55*8.62)/0.176 = 174 MPa stress. The A508 has rupture strength of 550 MPa @ the design temperature of 316C, so this design pressure produces 0.316 of the rupture stress. So this appears to be tensile limited (not yield-limited as I had assumed).

So its a simple apples to apples comparison. Keeping the same safety factor to tensile, and using the lowest rupture stress of the reference given above for the tough maraging steel,

http://www.osti.gov/scitech/servlets/purl/4807312

@ 315C, that'd be 139200 psi or, in units that make nonzero sense, 959 MPa.

So the thickness can be reduced (959/550) = 1.74x

The wall thickness can be reduced to about 104 mm (110 with stainless cladding. Cladding strength is often not credited in PV codes). The wall stress is 294 MPa (actually less because of the cladding).

ESBWR bottom vessel head thickness is 260 mm. This is cut to 150 mm.

The thickness is greater than with In718, but the alloy is cheaper and more importantly has much better toughness and easier fabrication than In718.

These thicknesses should be quite feasible for most of the larger facilities. A 4.3 meter tall ESBWR ring forging would be only ~80 tonnes. There are many forging facilities that can do this.


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PostPosted: Aug 05, 2015 10:45 am 
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Cyril,
Conventional casting seems to limit the strength and toughness of the alloys you are interested in using. Semi-solid metal casting (rheocasting) is also a consideration, although mostly done with Al and Mg alloys, it can be done with steel. Mostly small highly complex parts that are die cast to near net shape seem t be the market for semi-solid metal casting. You might have to do some testing to see what the strength and toughness of rheocast steel is. Would save the capital expense of a large forge and make near net shape reactor vessels. Additionally, the mixing needed in the process should allow for a homogeneous casting of whatever alloy you chose.

Mike


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PostPosted: Aug 05, 2015 12:11 pm 
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michaelw wrote:
Cyril,
Conventional casting seems to limit the strength and toughness of the alloys you are interested in using. Semi-solid metal casting (rheocasting) is also a consideration, although mostly done with Al and Mg alloys, it can be done with steel. Mostly small highly complex parts that are die cast to near net shape seem t be the market for semi-solid metal casting. You might have to do some testing to see what the strength and toughness of rheocast steel is. Would save the capital expense of a large forge and make near net shape reactor vessels. Additionally, the mixing needed in the process should allow for a homogeneous casting of whatever alloy you chose.

Mike


Thanks. I'm not familiar with these processes. They are powder metallurgy right? It might just be ignorance but I am still skeptical of castings having as high a toughness as forgings. These higher strength steels are limited by toughness so any process that reduces it is not going to fly. Also maraging steel has quite a high melting point so we'd be talking a lot higher temperatures than aluminium powder metallurgy.

I'd be fine with any casting process if it produces equal or better toughness as forging. Forging is a good process, just limited facilities that can do really heavy forging, so reducing forging weight by going for high strength steel that gets its strength from a heat treatment, being soft in the annealed state as it is forged, seems very attractive to me. If there's only enough capacity to make 10 ESBWRs per year then that's a drop in the bucket, though GE-H would no doubt be very happy and think it a major success story.


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PostPosted: Aug 05, 2015 12:33 pm 
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Cyril,
Not a powder metal process. More like a slushie/slurpie/icee at the convenience stores. Solid metal mixed with liquid metal. The solid/liquid mixture is maintained by constant mixing, like a slushie machine. The mixture will solidify if not mixed. Proper temperature control is critical. The mixture is injected in a die and cooled. The liner could be part of the die. Injection mold the reactor vessel and bond the liner at the same time.
The united technologies paper was interesting. Spray formed Inconel 718 was equivalent to wrought Inconel 718. Spray form a reactor pressure vessel? Computer control should allow fine control of the thickness. A female mold, a robot arm, and a vat of Inconel, let's make a reactor. :)


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PostPosted: Aug 05, 2015 5:28 pm 
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Hmm that's funny, a slush metal! I can see that this would work well with pure aluminium or magnesium, but it seems tricky with a mixture of Fe Ni Cr Mo, must be a lot of phase separation going on. I can't find any reference of this production method for Fe base at all...


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PostPosted: Aug 05, 2015 7:32 pm 
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Cyril,
The information I found was from one of the original group from MIT all the way back in 1975.

http://dspace.mit.edu/bitstream/handle/1721.1/16247/06643458-MIT.pdf?sequence=2

"Rheocasting in Low Alloy Steel"

By Richard Lister Bye, Jr.

It really does seem to be light alloys that are used currently, but I don't know if it is a function of difficulty with iron alloys or familiarity with convention forging and cast that work well enough, that has prevented further use of rheocasting with iron alloys.

Just thought I would pass along another possibility to consider. Looks like technology readiness level for iron alloys precludes use in reactor vessels.

mike


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PostPosted: Aug 05, 2015 9:02 pm 
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The references show rheocasting of 304 stainless steel and an alloy called x-40. The mechanical strength and toughness are not addressed. It would be interesting to see if you could get close to forging strength or if it is closer to classical casting. If it isn't close to a forging it would appear to be a lot of additional processing expense for little gain.

mike


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PostPosted: Aug 06, 2015 5:08 pm 
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Cyril,
Ever heard of Super bainite? 2500 mpa yield strength and 28Mpa sqroot(m) toughness is reported. Specialized alloy plus heat treatment creates nanostructured steel. (10 days at 200C) Does not appear weldable, but if it could be cast, heat treated and mechanically joined. Press releases are unclear if any size limitations are known(could you cast a reactor vessel?). University of Cambridge and Tata Steel are working on it.
http://mathewpeet.org/thesis/superbainite/superbainite.html
Also, it is unclear if the nanostructure would be preserved at 320C operating temperature of a BWR.
The bottom section could rise above the boiling point in the reactor to limit water sitting on the seals.
The sections of the reactor could use a mechanism similar to a Welin breech block to mate the sections together. Place a metallic seal between the sections, mate the upper section on the lower section and rotate to seal the sections together, no welding needed. Short sections of breech block in weldable material could be attached at the penetrations of the reactor vessel to allow welding the steam loop to the reactor.
The bolts would have to resist only the rotation of the reactor vessel pieces to keep the reactor together. The breech block mechanism would bear the force of the steam pressure.
The decommissioning of the reactor could be as simple as the installation, just unscrew the reactor and haul it off.

Mike


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PostPosted: Aug 07, 2015 3:59 am 
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For economy, i would prefer 500MW modules any day. I am sure the next generation would be a fast MSR breeder on uranium or thorium cycle.


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PostPosted: Aug 07, 2015 3:59 am 
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For economy, i would prefer 500MW modules any day. I am sure the next generation would be a fast MSR breeder on uranium or thorium cycle.


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PostPosted: Aug 07, 2015 7:53 am 
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michaelw wrote:
Cyril,
Ever heard of Super bainite? 2500 mpa yield strength and 28Mpa sqroot(m) toughness is reported. Specialized alloy plus heat treatment creates nanostructured steel. (10 days at 200C) Does not appear weldable, but if it could be cast, heat treated and mechanically joined. Press releases are unclear if any size limitations are known(could you cast a reactor vessel?). University of Cambridge and Tata Steel are working on it.
http://mathewpeet.org/thesis/superbainite/superbainite.html
Also, it is unclear if the nanostructure would be preserved at 320C operating temperature of a BWR.
The bottom section could rise above the boiling point in the reactor to limit water sitting on the seals.
The sections of the reactor could use a mechanism similar to a Welin breech block to mate the sections together. Place a metallic seal between the sections, mate the upper section on the lower section and rotate to seal the sections together, no welding needed. Short sections of breech block in weldable material could be attached at the penetrations of the reactor vessel to allow welding the steam loop to the reactor.
The bolts would have to resist only the rotation of the reactor vessel pieces to keep the reactor together. The breech block mechanism would bear the force of the steam pressure.
The decommissioning of the reactor could be as simple as the installation, just unscrew the reactor and haul it off.

Mike


Thanks. 28 MPa^0.5 is almost certainly too low for pressure vessel construction. Typical RPV steels such as A508 and A533 are over 200 MPa^0.5. Even the lower strength maraging steels have trouble getting to 100 MPa^0.5. Also we really need it to be weldable, even if casting produces good toughness we're talking an enormous vessel. It may not be transportable in one piece. Quality control in super large castings is also very difficult. In fact I think that is one of the things that limits forging size, the cast ingot that is the starting point for forging, must have good quality.


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PostPosted: Aug 07, 2015 9:38 am 
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Thanks for the info. I was unclear if the toughness quoted was adequate. Not even in the ballpark. Strong and tough likely requires forging. I'll keep looking.
Does the reactor pressure vessel have to be one unitized product or can it be built up like a Built up gun barrel? Built up design could use lighter forgings in concentric layers.
Years of data from naval guns.
Mike


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PostPosted: Aug 07, 2015 9:53 am 
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michaelw wrote:
Thanks for the info. I was unclear if the toughness quoted was adequate. Not even in the ballpark. Strong and tough likely requires forging. I'll keep looking.
Does the reactor pressure vessel have to be one unitized product or can it be built up like a Built up gun barrel? Built up design could use lighter forgings in concentric layers.
Years of data from naval guns.
Mike


How does that work, do you weld different shells together?

I've mused before on some ideas to just coil up a thin plate and weld shut the ends with axial welds. One might build a very thick vessel out of, say 12 mm plate. Roll it up like a roll of toilet paper! If the plate is thin enough a very long roll could be fabricated, so the entire RPV shell could be one piece. I think such a vessel would be safer too since a defect in the plate would only penetrate one layer, which cannot become a safety problem. The strength should be higher too. There's all sorts of design modifications possible here, such as spiral-rolling up the plate, which theoretically allows and endlessly tall roll. But I've never seen anyone do this and wonder why.


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