3 ms·

Why would forging be a requirement? Hasn't material science reached a point where we can built alloys that can be just cast into the right shape? Can't the prob

by nnq 8y ago

Why would forging be a requirement? Hasn't material science reached a point where we can built alloys that can be just cast into the right shape? Can't the problem of them being slightly weaker be solved by just making them thicker (not a problem for nuclear I'd guess bc you don't build that many pieces and you don't need to move them much), or by just having stuff like turbines replaced more often? I know that mixing "nuclear" + "cheaper manufacturing" sounds scary, but maybe it's a better idea... why would you need "best of the best" materials for pieces that (1) stay in one place (they're not airplanes!) and (2) can be replaced/serviced/inspected on fixed schedules following fixed procedures on fixed budgets etc. Modern forges were perfected by the germans in the war because they wanted to build airplane parts (!!) and they wanter to build them fast... I'd imagine nuclear power technology has none of this requirements and can be re-designed to work with commodity low-quality parts and have the movable pieces easily replace-able... (I'd imagine that if people would get over the "uuh, nuclear, scarry, scarry" mindset nuclear technology could become a dirt cheap commodity and be build with a mixture of ceramics + cheap alloys just fine...)

tcpekin 8y ago
That's a pretty good question, so I looked things up a little. Casting, especially on pieces this big, is difficult. It has problems with chemical segregation due to temperature gradients in the material, as well as porosity from the differential shrinkage due to the same temperature gradients [1,2]. From [2] "Consolidation of porosity formed in the ingot during solidification and homogenization is the major aim of the initial stage of forging. After that, the material is forged to form the shape of the desired products." The porosity and chemical segregation if I remember correctly, is very bad in nuclear applications, where bubbling and embrittlement would only be accelerated in non-homogenous materials. They are usually 1 piece to minimize welds, and this is just a feeling, but I think replacing the pressure vessel is pretty much currently the same as buying a new reactor [4]. These are very radioactive 1000 ton pieces of solid metal that you need to move and dispose of. Interesting question though, and I'd want to look into it more later. [1] https://inis.iaea.org/collection/NCLCollectionStore/_Public/18/010/18010016.pdf https://inis.iaea.org/collection/NCLCollectionStore/_Public/... (pdf, p. 11) [2] https://www.sciencedirect.com/science/article/pii/B9781845699673500027?via%3Dihub https://www.sciencedirect.com/science/article/pii/B978184569... (can send a pdf if interested) [3] https://www.reddit.com/r/pics/comments/3mzltj/a_nuclear_reactor_being_forged/ https://www.reddit.com/r/pics/comments/3mzltj/a_nuclear_reac... [4] https://www.neimagazine.com/opinion/opinionreplace-the-rpv/ https://www.neimagazine.com/opinion/opinionreplace-the-rpv/
- 0xFFFE 8y ago
  You are absolutely right, casting large objects with homogeneous composition and mechanical properties is very difficult practically. Slightly off topic, but the turbine blades used in the aircraft/marine/power engines are grown from single crystal for similar reasons. https://en.wikipedia.org/wiki/Single_crystal https://en.wikipedia.org/wiki/Single_crystal

by nnq 8y ago

tcpekin 8y ago

That's a pretty good question, so I looked things up a little. Casting, especially on pieces this big, is difficult. It has problems with chemical segregation due to temperature gradients in the material, as well as porosity from the differential shrinkage due to the same temperature gradients [1,2]. From [2] "Consolidation of porosity formed in the ingot during solidification and homogenization is the major aim of the initial stage of forging. After that, the material is forged to form the shape of the desired products." The porosity and chemical segregation if I remember correctly, is very bad in nuclear applications, where bubbling and embrittlement would only be accelerated in non-homogenous materials. They are usually 1 piece to minimize welds, and this is just a feeling, but I think replacing the pressure vessel is pretty much currently the same as buying a new reactor [4]. These are very radioactive 1000 ton pieces of solid metal that you need to move and dispose of. Interesting question though, and I'd want to look into it more later. [1] https://inis.iaea.org/collection/NCLCollectionStore/_Public/18/010/18010016.pdf https://inis.iaea.org/collection/NCLCollectionStore/_Public/... (pdf, p. 11) [2] https://www.sciencedirect.com/science/article/pii/B9781845699673500027?via%3Dihub https://www.sciencedirect.com/science/article/pii/B978184569... (can send a pdf if interested) [3] https://www.reddit.com/r/pics/comments/3mzltj/a_nuclear_reactor_being_forged/ https://www.reddit.com/r/pics/comments/3mzltj/a_nuclear_reac... [4] https://www.neimagazine.com/opinion/opinionreplace-the-rpv/ https://www.neimagazine.com/opinion/opinionreplace-the-rpv/

0xFFFE 8y ago
You are absolutely right, casting large objects with homogeneous composition and mechanical properties is very difficult practically. Slightly off topic, but the turbine blades used in the aircraft/marine/power engines are grown from single crystal for similar reasons. https://en.wikipedia.org/wiki/Single_crystal https://en.wikipedia.org/wiki/Single_crystal