Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Gary7]

Regarding the "roof", the Tepco press release for today says:

As precaution against rain for the exposed top section of the turbine building for Reactor #3, construction of a temporary roof was begun at 8:30am (July 18th).

(original Japanese) ７月18 日午前８時30 分、３号機タービン建屋屋上開口部の雨水対策として仮屋根の取り付け作業を開始しました。

Also mentions a worker who was injured in a fall from an electric pole/pylon today, and was transported to hospital via helicopter.

http://www.tepco.co.jp/nu/f1-np/press_f1/2011/htmldata/bi1632-j.pdf

 

[tsutsuji]

http://www.spiegel.de/wissenschaft/technik/0,1518,774825,00.html" Dunno what is correct.

I think both are correct :

The functions of the ECCS accumulators are to supply water to the
reactor vessel during the blowdown phase of a loss of coolant accident
(LOCA), to provide inventory to help accomplish the refill phase that
follows thereafter, and to provide Reactor Coolant System (RCS) makeup
for a small break LOCA.
(...)
The accumulators are pressure vessels partially filled with borated water
and pressurized with nitrogen gas.
http://pbadupws.nrc.gov/docs/ML0916/ML091671716.pdf

See also the diagram released by Kepko showing the accumulator that broke down at Ohi NPP : http://www.kepco.co.jp/pressre/2011/__icsFiles/afieldfile/2011/07/16/0716_1j_01.pdf (ぼう酸水=borated water ; 窒素=nitrogen ; 弁=valve ; 蓄圧タンク= accumulator ; 水位計=water level gauge ;　圧力計=pressure gauge)

Here is Kepko's 16 July press release :

About the manual shutdown of Ohi NPP unit 1 (decline of pressure at accumulator C)

Ohi NPP unit 1 (pressurized water reactor, nominal output 1,175,000 kW, nominal thermal power 3,423,000 kW) was undergoing a test run as part of inspection No.24 when the "high/low pressure, accumulator※ C" alarm was issued, at 10:46 PM, 15 July 2011.

When we checked the pressure gauge, instead of the normal 4.60 MPa, the pressure was 3.65 MPa, which is below the safety limit of 4.04 MPa. For this reason, we started bringing nitrogen using the nitrogen supply line at 11:20 PM and at 11:45 PM the pressure had risen back to 4.09 MPa, satisfying the 4.04 safety standard.

The supply of nitrogen was completed at 12:38 AM, today, and a visual inspection of the accumulator and nearby valves was undertaken, but no abnormality was observed. The pressure was stabilized at 4.08 MPa.

As we prioritize safety, in order to inspect the causes of the pressure decline and to implement countermeasures, we decided to start decreasing the output at around 1 PM today, and at around 9 PM we shut down the reactor.

This event is not causing radiological consequence to the environment.

※ Accumulator : Accumulators are tanks storing borated water. Each of the 4 primary cooling systems is installed with one. During a loss of coolant or other accident, when the pressure in a primary cooling system drops lower than the pressure of the nitrogen-pressurized accumulator, borated water flows into that primary cooling system.About the manual shutdown of Ohi NPP unit 1 :
http://www.kepco.co.jp/pressre/2011/__icsFiles/afieldfile/2011/07/16/0716_1j_01.pdf (pdf 28.6 KB)

Source : http://www.kepco.co.jp/pressre/2011/0716-1j.html (my translation)

About Fukushima Daiichi NPP :

http://www.yomiuri.co.jp/science/news/20110718-OYT1T00495.htm there is more than one hole in the roof of unit 3 turbine building. The largest is 14 x 11 m wide. The repair is made with 3 steel sheets of 5 x 16 m each. While this repair is done today, the other holes will be repaired tomorrow. What is feared is that if too much rain water pours through the holes, the water accumulated in the turbine building might overflow and leak into the sea.

http://www.asahi.com/special/10005/TKY201107170417.html this is an assessment of the "step 1" of the roadmap. The following are marked with the "〇" (completed) symbol :

〇 closed loop reactor cooling
〇 starting the water treatment facility
〇 nitrogen injection
〇 SFP cooling (implemented in advance at units 2 & 3)

Then we have the "△" (under execution) symbol

△ reinforcement of unit 4 against earthquakes
△ hyperthermia prevention
△ assessment of the radiological status of the environment
△ removing debris

Then the "×" (execution impossible)

× repair the containment vessels (the locations of the damages are not even known)

It is expected that the government will announce tomorrow that they will start to study the lifting of some of the evacuation-prepared areas, based on the prerequisite that the nitrogen injection prevents hydrogen explosions and that new radiological emissions are curbed at a low level.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110718/0805_suiryou.html On 17 July afternoon, Tepco changed the pump that injects water into both unit 1 and unit 2 reactors. Its maximum flow rate is 20 m³/hour. On the morning of 17 July, the flow rate injected into unit 1 declined to about 3 m³/hour instead of the expected 3.8 m³/hour, ringing an alarm. The flow rate had to be ajusted again to 3.8 m³/hour. While nothing similar happened on the unit 2 line, it is the third time this sort of trouble happens at unit 1. For that reason it is believed that there is dirt in the piping to unit 1.

 

[Joe Neubarth]

Iodine 131 Four months after Reactor Three Blew? One hundred and twenty some days after Reactor Three Building blew, and they are still finding I-131 ?

This is very frightening. As previously stated, Iodine-131 being very radioactive has a rapid half life. Every week or so half of it is gone. After 80 days it should be almost impossible to detect. Yet, here we are FOUR months after the BIG Detonation of Reactor Three and we are still seeing large amounts of Iodine 131 in water samples.

Am I wrong or should this not be happening?

Tokyo gov’t finds iodine-131 levels up to quadruple cesium levels in water reclamation centers.
July 18th, 2011 at 07:35 AM


Measurements of radioactivity in sewage treatment, etc., Sewer Authority (Tokyo), July 15, 2011:
http://translate.google.com/translate?act=url&hl=en&ie=UTF8&prev=_t&rurl=translate.google.com&sl=ja&tl=en&u=http://www.gesui.metro.tokyo.jp/oshi/infn0533.htm

 

[robinson]

It may mean the amount of Iodine that was released was far higher than was reported.

 

[Atomfritz]

Tokyo gov’t finds iodine-131 levels up to quadruple cesium levels in water reclamation centers.
July 18th, 2011 at 07:35 AM


Measurements of radioactivity in sewage treatment, etc., Sewer Authority (Tokyo), July 15, 2011:
http://translate.google.com/translate?act=url&hl=en&ie=UTF8&prev=_t&rurl=translate.google.com&sl=ja&tl=en&u=http://www.gesui.metro.tokyo.jp/oshi/infn0533.htm

Maybe just a "spelling mistake" - the long-term iodine measurements after emissions usually regard I-129 (halftime 15 mill yrs).

See also the diagram released by Kepko showing the accumulator that broke down at Ohi NPP : http://www.kepco.co.jp/pressre/2011/__icsFiles/afieldfile/2011/07/16/0716_1j_01.pdf (ぼう酸水=borated water ; 窒素=nitrogen ; 弁=valve ; 蓄圧タンク= accumulator ; 水位計=water level gauge ;　圧力計=pressure gauge)

Thanks!
This makes me feel understand the differences of Xinhua and Spiegel report, both seem correct to me even if the first impression looks quite different.

Regarding the "roof", the Tepco press release for today says:

As precaution against rain for the exposed top section of the turbine building for Reactor #3, construction of a temporary roof was begun at 8:30am (July 18th).

The article Tsutsuji quoted says that only the biggest hole in T/B roof is 11x14 meters and there are others. On the satellite photos these holes seem soo small!
And that they appear to have set up some kind of harbor near units 5+6, this seems very sensible. They are really doing much much work, without any kamikaze like in Russia.

I well understand that they want to get the holes closed before the tsunami comes. Could else be like waterfall sinks.
And, the rain decontaminating the roofs so probably will just conveniently flow into the ocean. Nice!

 

[joewein]

Maybe just a "spelling mistake" - the long-term iodine measurements after emissions usually regard I-129 (halftime 15 mill yrs).

I have never seen I-129 mentioned in Tokyo water-related data.

The numbers for levels in drinking water published by the city only listed I-131, Cs-134 and Cs-137:
http://monitoring.tokyo-eiken.go.jp/monitoring/w-past_data.html

Same for most seawater figures released.

With its long half life it probably doesn't contribute a lot of becquerels relative to its weight, so I don't think a mixup with it would explain those becquerel figures.


Given that I-131 levels in early April where an order of a magnitude higher than cesium levels, they should have reached parity around early May. By July 4-5 when the water sludge was measured, another 8 half lives of I-131 should have passed, so I-131 should be two orders of a magnitude below cesium.


If in this particular source they were at similar levels, one would assume chemical reasons for that, i.e. cesium didn't precipitate with the mud as much iodine did. Cesium salts should be highly soluble (similar to potassium salts) and it would never occur in elementary form outside the lab. Iodine does have insoluble salts (such as silver iodide) and in elementary form is not particularly water soluble.

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20110719/t10014286881000.html With the purpose of recovering the 50 m³/hour flow rate from the decline to 37 m³/hour, the water treatment facility had been shut down on the morning of 15 July to make repairs such as bleeding air and changing hoses for ones with lesser resistance, and a 39 m³/hour flow rate had been achieved. However on the morning of 18 July the flow rate had dropped to 37 m³/hour again. Tepco admits that it ignores the cause of the problem.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110719/0625_kangae.html The expectation that the government would define more precisely today what is meant by the "cold shutdown" that should lead to a lifting of the 20 km range no-entry zone has been deceived. The definition provided by the government today remains vague, saying the RPV bottom temperature must be around 100°C and human exposure to radiation must be largely curbed. This is far from a concrete definition of radioactive substances and radiation dose limits.

http://mainichi.jp/select/weathernews/news/20110719ddm003040126000c.html The exposure of two workers who repaired the big hole on unit 3 turbine building roof yesterday passed 10 mSv, with a maximum of 12 mSv. Today the plan is to repair one 5 m x 2 m oval-shaped hole and a number of skylights blown up by the explosion, and to install sandbags preventing water to flow into a gutter whose down pipe is damaged.

 

[joewein]

We have discussed the video in which Arnie Gundersen spotted what looked like a single "handle" for a fuel assembly in the debris-filled unit 3 pool.

I just noticed a picture of the same pool from probably the refueling last year on this page. Look for the picture labeled "Reactor 3 refueling - mox in top left corner".

http://www.houseoffoust.com/fukushima/tepco_pics/R3_mox_upperleft.jpg

If the black items are fuel assemblies then many are quite spread out over the pool, instead of in largely complete rows as in unit 4.

 

[Joe Neubarth]

I would think that spreading them out would be a prudent thing to do. I expect that the holding racks are very secure, but a more uniform distribution of weight would just make sense.

 

[Joe Neubarth]

It may mean the amount of Iodine that was released was far higher than was reported.

I think many of us suspect that, simply because of the manner of revealing information that TEPCO established very early on.

 

[tsutsuji]

http://mainichi.jp/select/today/news/20110720k0000m010100000c.html This is a report from tonight's Tepco-government joint press conference. Tepco estimated the radiation emitted from 20 June 2011 to 28 June 2011 : 1,000,000,000 Bq/hour. This is 2,000,000 times less than the estimate for 15 March 2011. It amounts to a maximum yearly exposure of 1.7 mSv on the premises of the plant. A NISA official, Mr Hiroshi Yamagata said the goal for "step 2" (january 2012) is to achieve curbing the radiological emission inside the plant below the legal limit of 1 mSv per year.

http://www.tepco.co.jp/en/press/corp-com/release/11071905-e.html Tepco publishes the progress status of the "roadmap". Items marked with red ink on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110719e5.pdf are announcements of new tasks added on the roadmap. For comparison, here is the progress status that was published on 17 June : http://www.tepco.co.jp/en/press/corp-com/release/11061702-e.html

http://www.nikkei.com/news/headline...1949EE3EBE290808DE3EBE2E5E0E2E3E3E2E2E2E2E2E2 Before building the cover structure at units 3 and 4, the removal of debris has priority. (Judging from what is written in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110719e5.pdf what is meant here seems to be the debris located on the top floors of reactor buildings 3 and 4)

http://www.jiji.com/jc/zc?k=201107/2011071600400 (from the 16 July Tepco press conference) The present water treatment system has 4 km long pipes and a lot of troubles. When the end of the treatment of accumulated water in turbine buildings will become clear, they will switch to another system with short pipes. Moreover, they will increase the injection rate and bring reactor water temperature well below 100°C. Tepco is proceeding with the basic design of the ground water shielding wall.

 

[Joe Neubarth]

I have never seen I-129 mentioned in Tokyo water-related data.

The numbers for levels in drinking water published by the city only listed I-131, Cs-134 and Cs-137:
http://monitoring.tokyo-eiken.go.jp/monitoring/w-past_data.html

Same for most seawater figures released.

With its long half life it probably doesn't contribute a lot of becquerels relative to its weight, so I don't think a mixup with it would explain those becquerel figures.


Given that I-131 levels in early April where an order of a magnitude higher than cesium levels, they should have reached parity around early May. By July 4-5 when the water sludge was measured, another 8 half lives of I-131 should have passed, so I-131 should be two orders of a magnitude below cesium.


If in this particular source they were at similar levels, one would assume chemical reasons for that, i.e. cesium didn't precipitate with the mud as much iodine did. Cesium salts should be highly soluble (similar to potassium salts) and it would never occur in elementary form outside the lab. Iodine does have insoluble salts (such as silver iodide) and in elementary form is not particularly water soluble.

I thought that they were identifying the radioactive emitters by the energy level of the radiation detected therefrom.

 

[tanyaeasley]

We have discussed the video in which Arnie Gundersen spotted what looked like a single "handle" for a fuel assembly in the debris-filled unit 3 pool.

I just noticed a picture of the same pool from probably the refueling last year on this page. Look for the picture labeled "Reactor 3 refueling - mox in top left corner".

http://www.houseoffoust.com/fukushima/tepco_pics/R3_mox_upperleft.jpg

If the black items are fuel assemblies then many are quite spread out over the pool, instead of in largely complete rows as in unit 4.

According to my husband, who is in the nuclear industry and carried out a WANO inspection of a different Japanese nuke plant in December, the silvery square topped slots are the ones holding spent fuel assemblies. (Seen in upper left and upper right of photo.)

 

[NUCENG]

A question just popped into my mind.

Where could the oxygen for the hydrogen/oxygen reaction in unit two have come from?

If the overpressure/overtemperature of the containment caused a failure in the soppression chamber (torus) the oxygen was in the torus room. (This is my best guess).

If containment failure was at penetrations or PCV flange leakage the oxygen was in the air outside the containment. If the fuel pool was a source of hydrogen then the oxygen was in the air in the building. Once a breach occurred and the containment was depressurized oxygen would be able to enter the containment. But that would probably have meant a second deflagration/detonation. The relatively smaller damage to the reactor building of unit two may mean the hydrogen burn did not propogate back into containment. (Total speculation, but possible).

 

[NUCENG]

Iodine 131 Four months after Reactor Three Blew? One hundred and twenty some days after Reactor Three Building blew, and they are still finding I-131 ?

This is very frightening. As previously stated, Iodine-131 being very radioactive has a rapid half life. Every week or so half of it is gone. After 80 days it should be almost impossible to detect. Yet, here we are FOUR months after the BIG Detonation of Reactor Three and we are still seeing large amounts of Iodine 131 in water samples.

Am I wrong or should this not be happening?

Tokyo gov’t finds iodine-131 levels up to quadruple cesium levels in water reclamation centers.
July 18th, 2011 at 07:35 AM


Measurements of radioactivity in sewage treatment, etc., Sewer Authority (Tokyo), July 15, 2011:
http://translate.google.com/translate?act=url&hl=en&ie=UTF8&prev=_t&rurl=translate.google.com&sl=ja&tl=en&u=http://www.gesui.metro.tokyo.jp/oshi/infn0533.htm

It appears that you are seeing the results of a separation process that is skewing the results. The Iodine is soluble and is in the "sludge dewatering" which is the water remaining after the sludge is removed. Most of the Cs is in the sludge which has been separated. Since it isn't clear how much sludge is in how much water, I'm not sure how to interpret the relative magnitudes of the isotopes. If we had volumetric or mass concentrations of sludge and water it would make a calculation possible.

They say the dose rate readings were measured at 1 meter, but is it one meter from what?

 

[NUCENG]

According to my husband, who is in the nuclear industry and carried out a WANO inspection of a different Japanese nuke plant in December, the silvery square topped slots are the ones holding spent fuel assemblies. (Seen in upper left and upper right of photo.)

I believe you are seeing new non MOX-fuel in the upper right and new MOX fuel in the upper left. Spent fuel is darkened by thin layers of oxide and that explains the difference of the fuel distributed in the racks. Discharged fuel after five or six years isn't as bright and shiny as new.

Replacement batch sizes are generally a quarter to a third of the bundles and thae number of new MOX and non-MOX assemblies is a good chunk of the expected reload batch size.

32 MOX
64 Non MOX
96 total bundles

Unit 3 has 548 bundles in a full core.

 

[benzyme]

I read a quote from one of the farmers with contaminated hay, who said that because of the distance (150 km) and wind direction after the hydrogen explosions, he didn't think there was any risk. I was just wondering what some of you would reply to him? Would most of that contamination have been from unit 1 explosion (I think wind blew n/nw) or just steady accumulation over a few weeks/months?

 

[joewein]

I thought that they were identifying the radioactive emitters by the energy level of the radiation detected therefrom.

Yes, they are. They are not likely to confuse I-131 with I-129 from that. It almost certainly really is I-131, but for reasons discussed above the cesium got separated somewhere along the sludge and water processing path in the sewage treatment plant.

The ratio detected is unlikely to be a directly linked to nuclear decay of the respective isotopes. Somebody cherry-picked the data pointing out that in Minamitama Water Reclamation Center the I-131 was 4 times the Cs-134 level (66 vs 15 Bq/kg). At two sites I-131 was below detection level while cesium was > 100 Bq/kg. The ratios are all over the place, but "iodine at 4 times cesium levels in July" gets more attention than vice versa.

 

[joewein]

I read a quote from one of the farmers with contaminated hay, who said that because of the distance (150 km) and wind direction after the hydrogen explosions, he didn't think there was any risk. I was just wondering what some of you would reply to him? Would most of that contamination have been from unit 1 explosion (I think wind blew n/nw) or just steady accumulation over a few weeks/months?

There were two major plumes over land, from what I recall from documentaries I've seen.

The first one was traveling South over Ibaraki down to Chiba, then sweeping over the Kanto plain, touching as far south-west as Kanagawa and Shizuoka, and west into Tochigi and eastern parts of Gunma. This was the first spike registered in Tokyo. I think that was after the unit 1 venting and explosion. That's why tea in Shizuoka and Kangawa has been reaching levels beyond legal limits for food and why drinking water levels for babies and infants were briefly exceeded in Tokyo. This plume reached areas about 300 km from the plant.

The second plume headed mostly Northwest towards Fukushima City and dumping most of its contents within about 50 km, between Iitate and the plant itself, but somewhat lower concentrations reached areas to the West like Koriyama and Fukushima city further North West. The second plume coincided with the suppression chamber explosion in unit 2 and the hydrogen blast in unit 3. The most severely contaminated areas were hit by this one.

Almost certainly the bulk of the radioactive release happened during the first two weeks, especially during the containment venting operations and hydrogen explosions and before seawater injections brought temperatures down again.

The fallout pattern depends far less on proximity than on rain and snow fall on the particular day, as the precipitation extracts the radioactive load and deposits it on the ground. This was already the experience after the Chernobyl disaster: Contamination did not decrease linearly with distance, but you were truly unfortunate to see rain during those days. There is a lot of dairy farming in the picturesque alpine region of Allgäu, to the South West of Munich, Germany (1300 km from Chernobyl), but the government had to dispose of the milk there, because they ended up with a lot more I-131 than areas closer to the East that didn't have rain in late April 1986.

 

[joewein]

どうもありがとう for posting, as always!

http://mainichi.jp/select/today/news/20110720k0000m010100000c.html This is a report from tonight's Tepco-government joint press conference. Tepco estimated the radiation emitted from 20 June 2011 to 28 June 2011 : 1,000,000,000 Bq/hour. This is 2,000,000 times less than the estimate for 15 March 2011. It amounts to a maximum yearly exposure of 1.7 mSv on the premises of the plant. A NISA official, Mr Hiroshi Yamagata said the goal for "step 2" (january 2012) is to achieve curbing the radiological emission inside the plant below the legal limit of 1 mSv per year.

This way of converting the ongoing hourly release into an annual dose doesn't make any sense to me. It's like saying, if you borrow x amount of money every month, you will pay y amount of interest every year, as if it didn't matter how much you were already in debt or how many years you continued this.

Release or no release, there are already radioactive substances on the ground that produces background radiation, year after year. Maybe the rain will gradually wash out some of it and Cs-134 will decay with a half life of 2 years, but it won't go away quickly like the I-131.

A goal of 1 mSv/y (presumably on top of natural sources, not including them) seems very ambitious even outside the wrecked reactor building, let alone inside them.

EDIT: TEPCO http://www.tepco.co.jp/en/nu/fukushima-np/f1/index-e.html" at about 10 points mostly along the periphery of the plant. The official radiation readings published today (7/20) range from about 10 microsievert per hour at MP1 to 350 microsievert per hour south of the main building, near where the webcam stands. That's an annualized dose of 87 mSv to 3 Sv per year.

[URL]http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1_lgraph-e.gif[/URL]

Sure, you can get that down to 1 mSv per year, by not staying at the plant for more than a couple of hours a year...

EDIT 2: With this helpful http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1-sv-20110627-e.pdf" you can avoid hotspots of several 100 mSv/h around the reactor blocks, staying in zones with "only" 0.2-10 mSv/h.

http://www.nikkei.com/news/headline...1949EE3EBE290808DE3EBE2E5E0E2E3E3E2E2E2E2E2E2 Before building the cover structure at units 3 and 4, the removal of debris has priority. (Judging from what is written in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110719e5.pdf what is meant here seems to be the debris located on the top floors of reactor buildings 3 and 4)

I think this will have to include partly demolishing reinforced concrete portions of both unit 3 and 4 that are in danger of collapsing, which would destroy the polyester tent. Given the significant radiation levels at least in the unit 3 pool, I think its 5F/CRF area will need remote operated machinery for cleanup. Unit 3 should be the most challenging of the units for cover construction.

 

[tsutsuji]

A goal of 1 mSv/y (presumably on top of natural sources, not including them) seems very ambitious even outside the wrecked reactor building, let alone inside them.

Sorry, I made a mistake. The measured 1.7 mSv and the 1 mSv goal mentioned in the Mainichi article apply to the site boundary, not to inside the site.

Excluding the effect of already released radioactive materials, evaluation of exposure doses at the site boundary using the current release rate (approximately one billion Bq/hour) showed that the maximum exposure dose is 1.7 mSv/year.
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110719e6.pdf

http://mainichi.jp/select/opinion/closeup/news/20110720ddm003040043000c.html The present US-French-Japan water treatment system is a desperate effort with a durability of one year. Although repairing the containment vessel is indispensable, Tepco removed it from the schedule, because preventing accumulated water from overflowing has priority. The water treatment system is the plant's "safety net". Tepco added the study of the full-fledged water treatment system in "step 2" of the roadmap. At present this full fledged system is a clean slate. The person in charge at Tepco said it must be based on simple design with short pipes. Large sections of the 4 km pipes at the present water treatment system don't pass the country's earthquake safety standards. Pr. Koji Okamoto of Tokyo university said it is possible to achieve cold shut-down ahead of schedule, if the closed loop cooling system proceeds smoothly. The next system should be based on learning the lessons from the present system and combining Japanese technology with few troubles.

http://mainichi.jp/select/jiken/news/20110720ddm010040105000c.html The removal of fuel from pools will not start sooner than 3 years from now. The removal of fuel from reactors, not before 10 years from now. At Three Mile Island it took 10 years to remove the fuel from only one reactor. In comparison, Fukushima Daiichi has 3 accidented reactors, collapsed reactor buildings, serious reactor damage and radiological pollution. There are 1496 fuel assemblies in reactors and 3108 in pools, among which 2724 are spent fuel. Because there are few damages to the fuel assemblies in the pools, moving them to the common fuel pool is being considered. In normal time fuel is reprocessed at Rokkasho, Aomori prefecture, but the damaged fuel cannot be removed with usual equipment. Remote-controlled equipments to cut and transport melted fuel are necessary. Minister Goshi Hosono said the final disposal site must be located outside Fukushima prefecture. The Nuclear Safety Commission is forming an expert committee to study those questions. As it is difficult to do this with Japanese technology alone, cooperation from abroad is indispensable.

http://sankei.jp.msn.com/affairs/news/110720/dst11072013030016-n1.htm At 5 AM, 20 July, unit 1 RPV bottom temperature passed below 100°C, with 98.9 °C. However the accuracy of the temperature measurement is questioned.

http://headlines.yahoo.co.jp/videonews/jnn?a=20110719-00000058-jnn-soci A new video acquired by JNN, showing the tanks storing the low-contaminated water from units 5 and 6, and a site being prepared to store the highly radioactive debris. The storing must go on as long as ground water seeps into units 5 and 6.

 

[joewein]

Sorry, I made a mistake. The measured 1.7 mSv and the 1 mSv goal mentioned in the Mainichi article apply to the site boundary, not to inside the site.

Thanks for the correction, tsutsuji.

Again, checking the TEPCO map of the monitoring posts against Google Maps, it seems MP1-MP8 are all at most 150 m from the site boundary. For scale on http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1_lmap-e.gif", it's about 1200 m from the north side of the breakwaters to the south side, or about 3600 m from the northern tip of the plant site to the southern tip.

About 100 / 120 microsieverts / hour at MP-7 / MP-8 some 150 m inside the fence is 1700 / 2000 times the level we have in Tokyo right now (0.058 microsieverts / hour). That's 870-1000 mSv per year. I find it hard to believe it should be 1.7 mSv just the other side of the fence. The wind that contaminated MP-7 and MP-8 would not have cared too much about that fence...

 

[tsutsuji]

Sorry I should have said "estimated" not "measured". Please note that they say "Excluding the effect of already released radioactive materials". I think it means that things are not going to worsen by more than 1.7 mSv over a year. But the present radiation level at the MP-x measurement points is already very high and bad, as you said.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110720/index.html The utilization rate of the water treatment facility for the past week is 50%. The 70% target is not achieved. As a consequence of the typhoon, the water level in the basement of unit 1 reactor building rose by 13 cm between July 19th and July 20th.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110720e14.pdf the water treatment facility treated 4,510 m³ from July 13 to July 19, against 6,130 m³ during the preceding week ( http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110713e10.pdf ) (and a design capacity of 50 m³/hour *24*7 = 8,400 m³/week). Utilization rate : 4,510/8,400 = 53.7% (against 6,130/8,400 = 73.0%).

 

[Atomfritz]

[URL]http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1_lgraph-e.gif

[/URL]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110720/index.html[...]. As a consequence of the typhoon, the water level in the basement of unit 1 reactor building rose by 13 cm between July 19th and July 20th.

This is highly interesting.
The typhoon did really great decontamination work, reducing the background radiation by some percent.

According to the diagram above from joewein's post I think there have been at least four big swells each pushing down the background radiation a bit further.
Some curies will probably have ended up in the ocean.

 

[LabratSR]

A great piece about the work done at Oak Ridge National Labs on severe accident mitigation and station blackout.

http://sustainableenergytoday.blogspot.com/2011/07/post-47-tv-asahi-interview-on-bwr.html

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20110721/t10014352981000.html The rainfall from the beginning of the rain on 19 July to 21 july 11 AM measured in Namie town was 115 mm. The water level in unit 1 reactor building basement rose by 44 cm from 20 July to 21 July. The water treatment facility was mistakenly shut down at 08:40 this morning. There was a plan to shut down the facility as part of an electric power supply maintenance/construction work, but it was planned in the afternoon. The mistake was made during the preparation of that work.

http://www.asahi.com/national/jiji/JJT201107210053.html The 08:38 AM automatic shut down is the consequence of not having studied the consequences of the electric power line work. The original plan was a manual shut down at 03:00 PM. Tepco was aware that the power supply of the water level gauge at the tank between the decontamination facility and the desalination facility was turned off. What it was not aware of, was that this would trigger the automatic shut down of the whole facility. This mistaken shutdown will result into a 3 percentage points drop of the weekly utilization rate.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110721_01-j.pdf mentions the 08:38 AM shut down being a consequence of the doubling of the Yonomori power line.

http://www.nikkei.com/news/category...E3E2E2E18DE0E3E2E5E0E2E3E39F9FE2E2E2E2;at=ALL A sense of uncertainty is emerging out of the water treatment facility's poor utilization rate while Tepco's goal to treat 200,000 tons by the end of this year remains unchanged.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110721/0415_198.html The number of whereabouts unknown Fukushima Daiichi workers whose health cannot be checked rose to 198.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110721/index.html the special committee in charge of middle and long term questions is formed by Japan Atomic Energy Commission (not Japan Nuclear Safety Commision as I wrote above: sorry for the mistake). The 20 member committee comprises the 5 members of Japan Atomic Energy Commission and nuclear energy experts or Tepco advisers. They will use Three Mile Island as a reference. They are expected to reach their conclusions by the end of "step 2" in January 2012.

based on [a] false report, the central government established the Japan Atomic Energy Commission in 1956.
http://www.asahi.com/english/TKY201107180285.html

http://www.aec.go.jp/jicst/NC/about/kettei/kettei110721.pdf Japan Atomic Energy Commission Decision of 21 July 2011 : lists the 20 member names and 3 study objectives : (1) modalities of middle to long term efforts (2) effective technology development problems (3) international cooperation

 

[joewein]

http://www.nikkei.com/news/category...E3E2E2E18DE0E3E2E5E0E2E3E39F9FE2E2E2E2;at=ALL A sense of uncertainty is emerging out of the water treatment facility's poor utilization rate while Tepco's goal to treat 200,000 tons by the end of this year remains unchanged.

At least they're no longer putting all their eggs in one basket, as the http://www.tepco.co.jp/en/nu/fukushi...10714_06-e.pdf" is supposed to start operating from August. It has two processing trains that will provide an alternative to the Areva / Kurion system, with a similar target capacity. Let's hope it works better.

Maybe the bet is that either Areva / Kurion or Toshiba-IHI-Shaw would eventually work as designed, or that if both only manage to achieve half of what they were sold as, the combined throughput will still save the original goal.

It's been a while since I last heard anything about how many days were left before TEPCO would run out of storage for contaminated water...


Meanwhile the story about fall-out in rice straw used as cattle feed for beef cattle is getting worse:

The Miyagi prefectural government said Tuesday that three companies in the northeastern Japan prefecture have shipped a total of about 77 tons of rice straw containing radioactive cesium above the legal limit to five prefectures.
(...)
According to tests conducted by all five prefectures except Aomori, the straw showed radioactive cesium readings of between 8.0 to 25.8 times the legal limit of 300 becquerels per kilogram after adjustment for damp.

(http://jen.jiji.com/jc/eng?g=eco&k=2011071900919")

A man in Osaki, Miyagi Prefecture, who sold straw contaminated with high levels of radioactive cesium told the Mainichi on July 18 that he had never imagined that his straw was contaminated because the city is about 150 kilometers away from the crippled Fukushima No. 1 Nuclear Power Plant.

(http://mdn.mainichi.jp/mdnnews/news/20110719p2a00m0na011000c.html" )

It looks like the radioactive plume got as far as the northern part of Miyiagi prefecture. It makes you wonder what else besides straw bales was contaminated on those farms and how much cesium will be found in the soil across Miyagi prefecture (which lies to the North of Fukushima).

Smaller shops here have raised their prices for rice from about 1500 yen to 2000 yen per 5 kg bag because they've been experiencing difficulties getting supplies. More and more consumers are stocking up on 2010 rice, as it's yet to be seen what cesium levels will be found in 2011 rice 8 weeks from now, when it will be harvest time. We've heard very little about soil or other testing in rice growing areas so far, which is not reassuring.

 

[tsutsuji]

http://www.asahi.com/national/update/0722/TKY201107220127.html A partial blackout started at 07:10 this morning after a breaker tripped in a switchboard. The water treatment facility, some of the reactor surveillance equipments, spent fuel pool cooling systems and other systems stopped suddenly. The water injection into reactor cores, based on another power source, is going on. The circuit breaker might have broken down.

http://www.sanin-chuo.co.jp/newspack/modules/news/article.php?storyid=1114536015 This morning's blackout concerned the power supply to units 3 and 4, which is also supplying the water treatment system. Unit 3 spent fuel pool, the common fuel pool, and reactor surveillance equipments stopped. The power supply was recovered at 04:00 PM this afternoon. No sudden rise of temperature was observed at any pool.

http://www.yomiuri.co.jp/science/news/20110722-OYT1T00795.htm Equipments were sequentially switched to backup power source(s), resulting into full recovery at around 03:30 PM. The blackout did not affect the plant safety.

http://sankei.jp.msn.com/region/news/110722/fks11072211580002-n1.htm As part of the work to double the power line to units 5 and 6, units 3 and 4 had been switched to the power supply for units 1 and 2. The breaker that tripped is located on the power line supplying units 3 and 4 from units 1 and 2. The blackout cause is either the power consumption from units 3 and 4 was too much, or the breaker failed. The expected temperature rise in SFP 3 was 0.3 °C/hour.

The flow of information from Fukushima Daiichi is likely to decline from next week :

press conferences by the joint government-TEPCO disaster task force, which from April 25 had in general been held every day, will from next week only be held once on Mondays and once on Thursdays.
http://mdn.mainichi.jp/mdnnews/news/20110721p2a00m0na007000c.html

 

[gmax137]

I would like to know if the plant service water pumps survived the earthquake & tsunami. Sorry, I don't know how they are called in these plants - I'm talking about the pumps that provide seawater to cool the essential heat loads (diesels, RHR, etc.). So much emphasis now on SBO, but if the service water pumps didn't survive then loss of AC power was only part of the problem.

 

[MJRacer]

I would like to know if the plant service water pumps survived the earthquake & tsunami. Sorry, I don't know how they are called in these plants - I'm talking about the pumps that provide seawater to cool the essential heat loads (diesels, RHR, etc.). So much emphasis now on SBO, but if the service water pumps didn't survive then loss of AC power was only part of the problem.

See http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

Page 37, second picture from left at bottom of the page.

 

[joewein]

See http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

Page 37, second picture from left at bottom of the page.

In http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf" on page 50 I found a mention of air-cooled diesels at units 2 and 4. Previously I had only ever heard about one air-cooled diesel surviving in unit 6, saving both units 5 and 6 by powering their RHR system.

Until now I had wondered if units 1-4 could have survived if they had also had some air-cooled diesels, but the answer seems to be "no": They had them and they didn't make it.

If the emergency diesels in units 1-4 failed because of loss of sea water for cooling, one would expect the air-cooled units to have been unaffected. So the diesel in unit 2 could have operated the RHR for units 1 and 2 and the one in unit 4 could have run the RHR for 3 and 4.

Elsewhere I've seen it mentioned that their fuel tanks were swept away. Then of course when the basements were flooded, where all diesels were located, that would take out even the air-cooled ones.

Last but not least we have the electric switchboards there flooded by sea water.

From all of this it sounds like the were five hits by either the quake or the tsunami, the combination of which doomed the reactors:

1. quake: simultaneous destruction of all grid connections
2. tsunami: flooding of electric sea water pumps for diesels and RHR => loss of ultimate heat sink for water-cooled diesels, cores and spent fuel pools
3. tsunami: loss of fuel supply to emergency diesels
4. tsunami: loss of all diesels themselves due to turbine hall basement sea water flooding
5. tsunami: loss of electrical system due to turbine hall basement sea water flooding

The water-cooled diesels couldn't run without sea water, but even the air-cooled diesels needed fuel and somewhere to feed the power that wasn't shorted by salt water flooding.

Even after the first three problems the station could conceivably still have survived if emergency generators had been brought in quickly enough, but the flooding of the electrical systems meant that when they did eventually manage to find cables long enough to connect tuck-mounted mobile generators they shorted.

Perhaps those flooded switchboards were the worst single point of failure.

The loss of sea water for RHR and even for the diesels on its own would not have been fatal, as demonstrated by units 5 and 6. As we read on page 50 of that http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf", units 5 and 6 also lost their RHR sea water supply, yet they were saved by the combination of one air-cooled diesel that still had fuel and by temporary pumps and hoses set up by the fire brigades and emergency workers.

Those temporary pumps and hoses were recently in the news, when a pump failed and it took several hours to replace it.

It sounds like both units 5 and 6 and Fukushima Daini were located high enough that the turbine halls and reactor buildings doors weren't reached by the flood and in Daini the sea water pumps were better protected by being enclosed in a small concrete building.

 

[MJRacer]

In http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf" on page 50 I found a mention of air-cooled diesels at units 2 and 4. Previously I had only ever heard about one air-cooled diesel surviving in unit 6, saving both units 5 and 6 by powering their RHR system.

Until now I had wondered if units 1-4 could have survived if they had also had some air-cooled diesels, but the answer seems to be "no": They had them and they didn't make it.

If the emergency diesels in units 1-4 failed because of loss of sea water for cooling, one would expect the air-cooled units to have been unaffected. So the diesel in unit 2 could have operated the RHR for units 1 and 2 and the one in unit 4 could have run the RHR for 3 and 4.

Elsewhere I've seen it mentioned that their fuel tanks were swept away. Then of course when the basements were flooded, where all diesels were located, that would take out even the air-cooled ones.

Last but not least we have the electric switchboards there flooded by sea water.

From all of this it sounds like the were five hits by either the quake or the tsunami, the combination of which doomed the reactors:

1. quake: simultaneous destruction of all grid connections
2. tsunami: flooding of electric sea water pumps for diesels and RHR => loss of ultimate heat sink for water-cooled diesels, cores and spent fuel pools
3. tsunami: loss of fuel supply to emergency diesels
4. tsunami: loss of all diesels themselves due to turbine hall basement sea water flooding
5. tsunami: loss of electrical system due to turbine hall basement sea water flooding

The water-cooled diesels couldn't run without sea water, but even the air-cooled diesels needed fuel and somewhere to feed the power that wasn't shorted by salt water flooding.

Even after the first three problems the station could conceivably still have survived if emergency generators had been brought in quickly enough, but the flooding of the electrical systems meant that when they did eventually manage to find cables long enough to connect tuck-mounted mobile generators they shorted.

Perhaps those flooded switchboards were the worst single point of failure.

The loss of sea water for RHR and even for the diesels on its own would not have been fatal, as demonstrated by units 5 and 6. As we read on page 50 of that http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf", units 5 and 6 also lost their RHR sea water supply, yet they were saved by the combination of one air-cooled diesel that still had fuel and by temporary pumps and hoses set up by the fire brigades and emergency workers.

Those temporary pumps and hoses were recently in the news, when a pump failed and it took several hours to replace it.

It sounds like both units 5 and 6 and Fukushima Daini were located high enough that the turbine halls and reactor buildings doors weren't reached by the flood and in Daini the sea water pumps were better protected by being enclosed in a small concrete building.

I think http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e22.pdf" is a better illustration than page 66 of the May 24, 2011 TEPCO presentation of the damages on the station power facilities in Fukushima Daiichi Nuclear Power Station.

Also: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e18.pdf".

Page 46 of the TEPCO presentation shows that Fukushima Dai-ni (F#2) was built at O.P.+12m (O.P. IIRC is Onohama Peil or about mean sea level), whereas Fukushima Dai-ichi (F#1) was built at O.P.+10m for Units 1 to 4 and at O.P.+13m for Units 5 & 6 (which helped save the one diesel as the flood was only about 30cm there).

Just 2-3 meters made a lot of difference. However, the seaside pumps at Dai-ni also had a building around them that protected them better from the tsunami (2nd Picture from left at bottom of page 46).

And, yes the switchboards flooded with sea-water made the temporary station blackout (SBO), for all practical purposes, as good as permanent (the high voltage switchboard (M/C) operated at 6,900v and the "low" voltage switchboard (P/C) operated at 480v).

More detail can be seen in the following diagrams. First is a http://2.bp.blogspot.com/-UtgJZNeAdlU/Ta3z9i97ryI/AAAAAAAAEfs/HehSEK2k60I/s1600/R1-R4.PNG" with schematic drawings of the estimated sea water piping circuits.

At the top, the sea-side pumps are identified as "Pompe intake acqua mare" in blue. At the bottom right is a legend identifying the pipes carrying cooling seawater as "condotte intake acqua di mare" in dark green. Above it is a legend showing the switchboards for unit 3 in lighter green. The legend (in blue) says "sala quadri electtrici R3 interrata a OP+300," which I translate as electrical switchboard hall for Unit 3 buried at OP+300 (in this case millimeters). Ground level at this point was OP+10,000mm. At the bottom left there is a legend beginning with "Sovrapposizione ..." which I translate as superposition of the buried plan view of Reactor 3 in relation to the turbine building at various heights (OP-2060mm (the torus was below sea-level?), OP+1900mm (the diesel generators) and OP+300mm (the switchboards)). So the switchboards were apparently 1.6 meters or more than 5 ft below the generators.

Unit 3 can be seen in more detail http://3.bp.blogspot.com/-JaxFid8Qo...Ako/t5TVRl5sb-4/s1600/R3++completa+small.jpg".

The generators are at the top above the turbines (look for the word "diesel") and the switchboards are at the bottom in light green bracketed in blue with a note that says that Unit 2 probably did not have them or did not have them at that location. It is unclear if these switchboards were common to both units.

In hindsight, the seaside pumps may have been hardened at Dai-ichi like they were at Dai-ni by protecting them with a building, but there was no cure for the switchboards other than relocating them completely once the reactors were built. Obviously, the diesel generators could have been relocated as well.

 

[tsutsuji]

Fukushima Daiichi nuclear power plant:

http://www.jiji.com/jc/c?g=soc_30&k=2011072300145 Yesterday's blackout is the result of a simple breaker adjustment mistake. The breaking limit had been set too low when it was installed in May. Tepco will futher investigate whether the instruction manual was not clear enough. Tepco is changing the hoses at the exit of the Areva system as part of an experiment to check whether the cause of the declining flow rate is sludge sticking to the hose's inner surface, thus reducing the inner diameter.

http://www3.nhk.or.jp/news/html/20110723/t10014404491000.html The breaking current had been mistakenly set at one third of the normal value.

Hamaoka nuclear power plant unit 5 (this is a shut down unit with already a number of serious problems : see https://www.physicsforums.com/showthread.php?p=3313860&highlight=hamaoka#post3313860 and following posts) :

http://mainichi.jp/area/shizuoka/news/20110713ddlk22040177000c.html (Shizuoka local page of Mainichi dated 13 July 2011) 40 m³ of water devoid of radioactive substances leaked. On 12 July at 10:20 AM a flood alarm was issued in the basement of the reactor building. Traces of a water leak were observed by an employee on the second floor. The water may have run through the interval between the floor and the wall and reached the basement. Some equipments were flooded and broke down. The washing of equipments to remove salt accumulated as a result of last May's condenser sea water leak, was being performed. The diameter 25 cm PVC hose bringing water from the desalinated water tank seems to have failed. Chubu Electric is investigating the cause.

http://mainichi.jp/area/shizuoka/news/20110721ddlk22040036000c.html (Shizuoka local page of Mainichi dated 21 July 2011) On 20 July Chubu Electric said the worker bent the hose with an 85 cm radius while the hose specification requires a minimum radius of 3 metres. The leaked water flowed from the upper second floor to the underground second floor. It accumulated for a while in a liquid waste system tank, but the quantity being too much, it flowed backwards in the piping. 1.9 m³ of water containing radioactive substances overflowed from basement first and second floor's drainage ditches. It is believed that radioactive substances were adhering to the piping. The total amount of radiation is 2,280,000 Bq. None of it has leaked to the outside. Chubu Electric is working at wiping this contaminated water out. Chubu Electric said it was already aware of the radioactive water leak on 12 July. It explained that because the national reporting standard of 3,700,000 Bq had not been reached, it was publicly disclosed together with the disclosure of the damage cause.

http://www.chuden.co.jp/energy/hamaoka/hama_info/hinf_unten/__icsFiles/afieldfile/2011/07/15/230715saikangentai.pdf 15 July press release on the condenser trouble.
http://www.chuden.co.jp/energy/hamaoka/hama_info/hinf_tenken/__icsFiles/afieldfile/2011/06/17/230617shuhukusuiki.pdf 17 June press release on the condenser trouble.
http://www.chuden.co.jp/energy/hama...fieldfile/2011/07/04/230520shuhukusuiki5u.pdf 20 May press release on the condenser trouble.

Hamaoka nuclear power plant (all units):

http://www.asahi.com/national/update/0721/NGY201107200047.html Chubu Electric is going to raise the height of the 1.5 km long sand dune as a measure enhancing tsunami safety. The sand dune being a natural formation, its height is uneven. The lowest parts will be raised by 2 m. Chubu is also planning to build a seawall between the dune and the plant.

Chubu Electric Power Co. said Friday it will build seawalls as high as 18 meters at its Hamaoka nuclear plant
http://search.japantimes.co.jp/cgi-bin/nn20110723a1.html

http://www.chuden.co.jp/english/corporate/ecor_releases/erel_pressreleases/__icsFiles/afieldfile/2011/07/22/0722E_1.pdf 33 page long English language press release "Countermeasures for Tsunami in Hamaoka NPS"

Genkai nuclear power plant (Kyushu, Western Japan):

The discovery of errors in data incorporated in a report on the No. 3 reactor at the Genkai Nuclear Power Plant in Saga Prefecture illustrates problems with its operator's checking system and the government regulator's ability to examine safety data. (...) Two years passed before the errors were found.
http://mdn.mainichi.jp/mdnnews/news/20110723p2a00m0na015000c.html

 

[gmax137]

...

...

Thanks you guys! One thing to note, I think the seawater lines noted above are the main circulating water to & from the condensers; this is different from the safety-related sea water cooling of the RHR and other vital heat loads.

I'm still not sure whether the safety-related cooling survived the tsunami (but the photos of the intake area don't look good). My only point here is that typically the plant would shutdown but stay hot, with decay heat removal via RCIC (this is achieved by steam-driven pump providing water to be boiled off in the reactor). After some time they would then cooldown and get on RHR. If the safety-related cooling pumps were destroyed by the tsunami, then the RHR isn't going to work, and once the water supply to RCIC is used up, then heat removal won't be possible. Alternate water sources are typically not seismic, so there may have been loss of heat removal capability even if the diesels & switchgear were operable.

 

[tsutsuji]

If the safety-related cooling pumps were destroyed by the tsunami, then the RHR isn't going to work, and once the water supply to RCIC is used up, then heat removal won't be possible.

So if the water supplying tank is big enough, you can rely on the RCIC over an extended time :

According to the link provided by LabratSR at https://www.physicsforums.com/showpost.php?p=3413453&postcount=10680

Assured cooling water supply: a secure, large condensate storage tank capable of supplying water to the HPCI/RCIC system for extended periods (this was not an issue in our SBO analyses). Alternatively, dedicated diesel-powered portable pumps can be staged to provide this function from other water sources.
http://sustainableenergytoday.blogspot.com/2011/07/post-47-tv-asahi-interview-on-bwr.html

At Fukushima unit 5 and unit 6

On March 19, a temporary seawater pump was installed to activate the RHR system

pages IV-99 and IV-102 http://www.iaea.org/newscenter/focus/fukushima/japan-report/chapter-4.pdf

See also the diagram "installation of backup RHRS pump" page 78 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf.

At Fukushima units 1-2-3-4 after they ran out of fresh water, they pumped water directly from the sea

for example for unit 2

At 19:54 on March 14, the seawater injection into the reactor using fire engines was started.

page IV-58 http://www.iaea.org/newscenter/focus/fukushima/japan-report/chapter-4.pdf

It seems that finding a pump and (sea)water would not really be a problem if everything else would work fine.

At unit 2 the problem was not running out of water. The problem was the RCIC stopping for some not well identified reason :

From that point until 13:25 on March 14, the reactor water level began to drop, at which point the RCIC was judged to have shut down.

page IV-58 http://www.iaea.org/newscenter/focus/fukushima/japan-report/chapter-4.pdf

the fuel was uncovered for five hours from 13:25 on March 14 (75 hours after the Earthquake began) and [...] the core damage started two hours later.

p IV-59 and IV-60 http://www.iaea.org/newscenter/focus/fukushima/japan-report/chapter-4.pdf