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Japan Earthquake: nuclear plants Fukushima part 2
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[QUOTE="Sotan, post: 6823854, member: 497173"] Hello Astronuc. Let me add a few things to what you said above - mainly just to keep the topic going and because I had some time to browse more. - About the lack of cooling water in the system, indeed there seem to be plenty of such mentions in the "Accident progression at Unit 3" which you can reach by visiting the DebrisWiki site linked by SteveElbows in his post of Nov 10 above - or [URL='https://fdada--plus-info.translate.goog/wiki/index.php?title=3%E5%8F%B7%E6%A9%9F%E3%81%AE%E4%BA%8B%E6%95%85%E9%80%B2%E5%B1%95&_x_tr_sl=ja&_x_tr_tl=en&_x_tr_hl=ja&_x_tr_pto=wapp+Reference:+https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants-fukushima-part-2.711577/page-50']via this link[/URL] which gives it in google translation. "Water injection by HPCI stopped...boiled lower plenum water rapidly supplied steam to the core... depletion of liquid water in the lower plenum... which caused a rise in the temperature of the debris in the lower plenum... the RPV boundary was damaged and the debris flowed toward the pedestal... evaporating the cooling water that had been in the pedestal." (I highlighted just the phrases referring to the cooling water.) - The above "Accident progression at Unit 3" text does not seem to clarify much my poor translation about "metals" melting. So I went back to Page 37 of that PDF to try and improve my translation. There was just one more mention that I overlooked: "Oxidized debris: from all the fuel debris (this refers mainly to) uranium, zirconium and stainless steel components in an oxidized state". As for my translation I cannot improve it much after all, but if I were to, it would be: "[I]- As the fuel debris accumulated at the bottom of the RPV, a new rise in temperature greatly affected the course of the accident; the [B](parts of)[/B] fuel debris containing a lot of metal [B]components[/B] melted first, at 1000-1300°C, but then, the [B](parts of)[/B] fuel debris containing [B]a higher proportion[/B] of oxide compounds reached a high viscosity state (the literal translation would be “[B]solid-liquid mixture[/B]”), at 2000-2300°C, which damaged the RPV bottom on a rather large area and, over a few hours, fell on the pedestal floor.[/I]" I think what puzzles you a bit is the lower range of temperatures mentioned (1000-1300°C). I tried to find more information about what type of compounds they suspect melted in that range. Among the documents shown in NRA meeting mentioned in my previous post there is [URL='https://www.nra.go.jp/data/000408671.pdf']this PDF[/URL] which deals with findings of the PCV inspection of Unit 1. Second slide of this PDF (with a big number 37 at the bottom) mentions the amounts of various materials present in the PCV. Amount of fuel debris 279 tons of which 76 tons of fuel component (UO[SUB]2[/SUB]...), 73 tons of fuel structural materials (Zr, SUS - I guess SUS refers to stainless steel), 130 tons of concrete. The volume of fuel debris is ~16m[SUP]3[/SUP]. Then melting points are mentioned: ~2800°C for UO2, ~1850°C for Zr, 1400-1450°C for stainless steel and - only this one seems to be missing from your post - Pb, lead from shielding components, with a melting point of ~330°C. They don't say how much lead might have been in there so maybe not "that" much. Not sure if it matters much with regard to the more damaging processes that took place at higher temperatures. - Next slide (number 3 or 38, whichever you like) mentions "melting of metallic components from inside the RPV - melting point somewhere around 1200-1300°C." - Moving on to another subject, in the [URL='https://www.nra.go.jp/disclosure/committee/yuushikisya/jiko_bunseki01/140000076.html']list of documents from that NRA meeting[/URL] the documents which contain in their name 4-1, 4-2 and 4-3 talk about the observed significant deformation of the shield plugs. 4-1 reports that older finding that the shield plugs of Unit 1, 2, 3, 5 show a certain degree of deformation. Most recently Unit 6 was investigated and the results are shown in diagrams. The shield of Unit 6, some of its central parts especially, are deformed, as if they got lowered in some areas by about 20mm (page numbered 138-139). Page 140 shows diagrams of the shield plugs of Unit 2 and 5, with a similar phenomenon. Page 141 shows the shield plug in Shimane NPP and Tsuruga Unit 1, which are considered to show no signifivant deformation. Last page in the slide summarizes: Fukushima units 1, 2, 3, 5 show deformation of the shield plus; Fukushima Unit 6, Shimane 1 and Tsuruga 1 shield plugs show no deformation. Perhaps for Fukushima 1 and 3 the deformation can be linked to the hydrogen explosions but for Fukushima 2 and 5 it's unlikely that the deformation was caused by some external force. Possible causes may be: deformation already existing or occurred at construction/installation time; or gradually occurred in time. It may have played a role in creating a route or contributing to the escape of radioactive materials during the accident. This is further explored in documents 4-2 and 4-3. - Finally - unrelated: [URL='https://www4.tepco.co.jp/library/movie/detail-j.html?catid=107299&video_uuid=og07od6u']a video from the May 2022 inspection of Unit 1 PCV[/URL] which I only saw now for the first time, maybe someone is interested to see it. The exposed rebars, again... (By the way somewhere in the 4h video of the NRA meeting and in one of the documents they mention that there appears to be a sufficiently large route for then to some day guide one of those underwater robots [I]into the pedestal[/I].) [/QUOTE]
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