When thediesel generators weregone, the reactor operators switched to emergencybattery power. The batteries were designedas one of the backups to the backups, to providepower forcooling thecore for 8 hours. And they did.

Within the 8 hours,another power source had to be found andconnected to thepower plant. Thepower gridwas down due to the earthquake. Thediesel generators were destroyed by thetsunami. So mobilediesel generators were trucked in.

This is where things started togo seriously wrong.The externalpower generators could not beconnected to thepower plant (the plugs did notfit). So after the batteries ranout, the residualheat could not be carriedaway anymore.

At thispoint theplant operatorsbegin to follow emergency procedures that are in place for a “loss ofcooling event”. It isagain a step along the “Depth of Defense” lines. Thepower to thecooling systems should never have failed completely, but it did, so they “retreat” to thenext line of defense.All of this, however shocking it seems to us, is part of the day-to-day trainingyou go throughas an operator, right through to managing acore meltdown.

Itwas at this stage that people started to talk about core meltdown. Becauseat the end of the day, ifcooling cannot be restored, thecore will eventually melt (after hours ordays), and the last line of defense, thecore catcher and third containment, would come into play.

But thegoalat this stagewas to manage thecore while itwas heating up, and ensure that the first containment (the Zircaloytubes that contains the nuclearfuel),as wellas the second containment (our pressure cooker) remain intact and operational foras longas possible, to give the engineerstime tofix thecooling systems.

Becausecooling thecore is such abig deal, the reactorhas anumber ofcooling systems, each in multiple versions (the reactor watercleanup system, the decayheat removal, the reactorcore isolatingcooling, the standby liquidcooling system, and the emergencycore cooling system). Whichone failed when or did not fail is not clearat thispoint intime.

So imagine our pressure cookeron the stove,heat on low, buton. The operators use whatevercooling system capacity they have toget rid ofas muchheat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of thefuel rods below 2200°C),as wellas the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressurehas to be released fromtime totime. Because the ability to do that in an emergency is so important, the reactorhas 11 pressure release valves. The operators now started ventingsteam fromtime totime to control the pressure. The temperatureat this stagewas about 550°C.

This is when the reports about “radiation leakage” starting coming in. Ibelieve I explained abovewhy venting thesteam is theoretically the sameas releasing radiation into the environment, butwhy itwas and is not dangerous. The radioactive nitrogenas wellas the noblegases do not pose a threat tohuman health.

At some stage during this venting,the explosion occurred.The explosion took placeoutside of the third containment (our “last line of defense”), and the reactor building. Remember that the reactor buildinghas no function in keeping the radioactivity contained. It is not entirely clear yet what has happened, but this isthe likely scenario: The operators decided to vent thesteam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in thesteam more time to subside). The problem is that at the high temperatures that thecore hadreachedat this stage, water molecules can “disassociate” into oxygen and hydrogen – an explosive mixture. And it did explode,outside the third containment, damaging the reactor building around. Itwas that sort ofexplosion, but inside the pressure vessel (because itwas badly designed and not managed properly by the operators) that lead tothe explosion of Chernobyl. Thiswas never a riskat Fukushima. The problem of hydrogen-oxygen formation isone of thebiggies whenyou design apower plant (ifyou are not Soviet, that is), so the reactor is build and operated in a way it cannot happen inside the containment. It happenedoutside, whichwas not intended but a possible scenario and OK, because it did not pose a risk for the containment.

So the pressurewas under control,as steam was vented. Now, ifyou keep boilingyour pot, the problem is that the waterlevel will keepfalling andfalling. Thecore is covered by several meters of water in order toallow for sometime to pass (hours,days) before itgets exposed.Once the rods start to be exposedat thetop,the exposed parts willreach the critical temperature of 2200 °C after about 45 minutes. This is when the first containment, the Zircaloytube, would fail.

And this started to happen. Thecooling could not be restored before therewas some (very limited, but still)damage to the casing of some of thefuel. The nuclear material itselfwas still intact, but the surrounding Zircaloy shell had started melting. What happened now is that some of the byproducts of the uranium decay – radioactive Cesium and Iodine – started to mix with thesteam. Thebig problem, uranium,was still under control, because the uranium oxide rods weregood until 3000 °C. It is confirmed that a very small amount of Cesium and Iodinewas measured in thesteam that was released into theatmosphere.

It seems thiswas the “go signal” for amajor plan B. The small amounts of Cesium that were measured told the operators that the first containmenton one of the rods somewherewas about to give. The Plan A had been to restoreone of the regularcooling systems to thecore.Why that failed is unclear.One plausible explanation is that thetsunami also tookaway / pollutedall theclean water needed for the regularcooling systems.

The water used in thecooling system is very clean, demineralized (like distilled) water.The reason to use pure water is the above mentioned activation by the neutrons from the Uranium: Pure waterdoes notget activated much, sostays practically radioactive-free. Dirt orsalt in the water willabsorb the neutrons quicker, becomingmore radioactive. Thishas no effect whatsoeveron thecore – itdoes not care what it iscooled by. But it makeslife more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water.

But Plan A had failed –cooling systems down or additionalclean water unavailable – soPlan B came into effect. This is what it looks like happened:

In order to prevent acore meltdown, the operators started to use sea water tocool thecore. Iam not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us.

Thepoint is that the nuclearfuel has now beencooled down. Because thechain reaction has been stopped a longtime ago, there isonly very little residualheat being produced now. The largeamount ofcooling water that has been used is sufficient totake up that heat. Because it is a lot of water, thecore does not produce sufficientheat anymore to produce any significant pressure. Also, boricacid has been added to the seawater. Boricacid is “liquid control rod”. Whatever decay is stillgoingon, the Boron will capture the neutrons and further speed up thecooling down of thecore.

Theplant came close to acore meltdown. Here is theworst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the watersteam to avoid pressure buildup. The third containment would then have been completely sealed toallow thecore meltdown to happen without releasing radioactive material. After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor,and all radioactive particles to settleon asurface inside the containment. Thecooling system would have been restored eventually, and the moltencore cooled to a manageable temperature. The containment would have beencleaned upon the inside. Then a messy job of removing the moltencore from the containment would have begun, packing the (now solidagain)fuel bit bybit into transportation containers to be shipped toprocessing plants. Dependingon thedamage, the block of theplant would then either be repaired or dismantled.

Now, wheredoes that leave us?

・Theplant is safe now and willstay safe.

・Japan is lookingat an INESLevel 4 Accident: Nuclearaccident with local consequences. That is bad for the company that owns theplant, but not for anyone else.

・Some radiation was released when the pressure vesselwas vented.All radioactive isotopes from the activatedsteam havegone (decayed). A very small amount of Cesiumwas released,as wellas Iodine. Ifyou were sittingon top of theplants’ chimney when they were venting,you should probably give up smoking to return toyour formerlife expectancy. The Cesium and Iodine isotopes were carriedout to the sea and will never be seenagain.

・Therewas some limiteddamage to the first containment. That means that someamounts of radioactive Cesium and Iodine will also be released into thecooling water, but no Uranium or other nasty stuff (the Uranium oxidedoes not “dissolve” in the water). There are facilities for treating thecooling water inside the third containment. The radioactive Cesium and Iodine will be removed there and eventually storedas radioactivewaste in terminal storage.

・The seawater usedas cooling water will be activated to some degree. Because the control rods are fully inserted, the Uraniumchain reaction is not happening. That means the “main” nuclear reaction is not happening, thus not contributing to the activation. The intermediate radioactive materials (Cesium and Iodine) are also almostgoneat this stage, because the Uranium decaywas stopped a longtime ago. This further reduces the activation. Thebottom line is that there will be somelow level of activation of the seawater, which will also be removed by the treatment facilities.

・The seawater will then be replacedover time with the “normal”cooling water

・The reactorcore will then be dismantled and transported to aprocessing facility, just like during a regularfuel change.

・Fuel rods and the entireplant will be checked for potentialdamage. This willtake about 4-5 years.

・The safety systemson all Japaneseplants will be upgraded to withstand a 9.0 earthquake andtsunami (or worse)

・Ibelieve the most significant problem will be a prolongedpower shortage. About half ofJapan’s nuclear reactors will probably have to be inspected, reducing the nation’spower generating capacity by 15%. This will probably be covered by runninggas power plants that are usuallyonly used forpeak loads to cover some of thebase loadas well. That will increaseyour electricity bill,as wellas lead to potentialpower shortages duringpeak demand, inJapan.

Ifyou want tostay informed, please forget the usual mediaoutlets and consult the following websites:

http://www.world-nuclear-news.org/RS_Battle_to_stabilise_earthquake_reactors_1203111.html

http://bravenewclimate.com/2011/03/12/japan-nuclear-earthquake/

http://ansnuclearcafe.org/2011/03/11/media-updates-on-nuclear-power-stations-in-japan/

Permalink |記事への反応(1) | 03:06

ツイートシェア

Movatterモバイル変換

「the plug」を含む日記

2025-05-15

■PS VitaのEnsoインストールで詰んだ人へ（2025年版 HENloによるCFW導入メモ）

＜なぜ情報が散乱しているか＞

＜どんな情報を採用すべきか＞

CFW導入まで

記事の補足

Enso導入 ※本題※

① Ensoインストール

② Enso実行 ※全てVITA 操作

3-a,問題がない場合

3-b,問題がある場合　※自分はこっちでした。Quick 3.65の副作用かも※

＜Enso導入の確認 方法＞

雑談：VITAのセーブ データは未だ檻の中

失敗の備忘録1：VitaDeploy版のEnsoで苦戦していた時に取った行動メモ

失敗の備忘録2：vita starting taiHENframework の対処法

（追記）より網羅的な補足

感想

2011-03-14

■【福島 原子力発電所】CNN のコメント欄 MITの科学者の見解2【東日本 巨大地震】