Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[NUCENG]

A first glance at that table would sure make one think so.

Even that 3.9 ppm seems high to me, so i'd feel more comfortable with saying its pool got far less than the others.

3.9ppm is what, about 7600 to 1 dilution of seawater? Almost plausible it was from fire trucks overspray. I just don't remember anymore.

Alternatively they may be doing some cleanup in Unit 1 or the cover they installed is keeping that pool cleaner.

 

[westfield]

Thanks. So... there was salt water injected in SFP 2-4, but not in SFP 1?

I don't know if they managed to get any salt water into it or even if they needed to but -

Unit 1's SFP was quite sheltered by the U1 RB's surprisingly together roof cladding.
Early on there was little opportunity to get any sort of water into it's SFP with the choppers or snorkel for that reason.

Additionally I seem to recall it wasn't nearly as urgent to top up Unit 1's SFP because the decay heat from Unit 1's spent fuel is considerably lower than any of the other pools and there is less spent fuel in there being a smaller design.

Shoot me down if required, it's been a year since then.

 

[zapperzero]

Shoot me down if required, it's been a year since then.

No, you are quite correct.

 

[zapperzero]

I thought Unit 4 reactor was defueled for the shroud replacement project. All fuel was in the SFP. Has that changed?

Nope, although there is much confusion over this subject, in other places which shall remain unnamed.

This is somewhat unrelated but... how hot is the RPV's interior? If some water leaked out of it, could it be the cause of the high doses found above the building, all by itself?

 

[SteveElbows]

I don't know if they managed to get any salt water into it or even if they needed to but -

Unit 1's SFP was quite sheltered by the U1 RB's surprisingly together roof cladding.
Early on there was little opportunity to get any sort of water into it's SFP with the choppers or snorkel for that reason.

Additionally I seem to recall it wasn't nearly as urgent to top up Unit 1's SFP because the decay heat from Unit 1's spent fuel is considerably lower than any of the other pools and there is less spent fuel in there being a smaller design.

Shoot me down if required, it's been a year since then.

Yeah they didn't need to touch that pool for quite a while. Eventually though they did spray it, through the damaged roof no less. I was quite surprised when I saw a video of it. But by then its quite likely they had a fresh-water supply, I will double-check these records when I get spare time.

 

[NUCENG]

Nope, although there is much confusion over this subject, in other places which shall remain unnamed.

This is somewhat unrelated but... how hot is the RPV's interior? If some water leaked out of it, could it be the cause of the high doses found above the building, all by itself?

I assume you are talking about unit 4 as the other three units were fully assembled and inside a closed drywell.

If in fact the fuel was all in the SFP, it is possible for people to be inside the vessel to repair or inspect vessel internals. I have seen workers lowered into the vessel for work on feedwater spargers. They did use a lead lined work basket. but doses were within allowable limits. It is also possible they may have performed a chemical decontamination at Fukushima Unit 4 to further reduce the rad levels inside the RPV prior to beginning shroud replacement,

 

[zapperzero]

I assume you are talking about unit 4 as the other three units were fully assembled and inside a closed drywell.

Yes.

If in fact the fuel was all in the SFP, it is possible for people to be inside the vessel to repair or inspect vessel internals. I have seen workers lowered into the vessel for work on feedwater spargers. They did use a lead lined work basket. but doses were within allowable limits. It is also possible they may have performed a chemical decontamination at Fukushima Unit 4 to further reduce the rad levels inside the RPV prior to beginning shroud replacement,

Right. Thanks.

 

[westfield]

I thought Unit 4 reactor was defueled for the shroud replacement project. All fuel was in the SFP. Has that changed?

I think r-j was referring to the contamination in U3's SFP water, not U4's. Both units were referred to in the post r-j was replying to.

 

[westfield]

Unit 4 Spent Fuel Pool:

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203080066 "Fukushima No. 4 reactor saved by upgrade mishap"

According to the article, there was no separator gate in place between the Spent Fuel Pool and the Reactor Well, allowing for 1000 additional tons of water to flow to the SFP. Was that fact already known?

I appreciate you (and others) corrected that in a later post, just to clarify this for the more casual readers :

The Unit 4 SFP gate. It is there, closed, in place, but it leaks, definitely into the SFP from the reactor void witch is defuelled, open and full of water due to the maintenance that was taking place at the time. I'm not sure if Tepco confirmed that they know the gate is leaking back into the reactor void. Have they?

The "new news" is that it was only because of a delayed Unit 4 shroud replacement schedule that saw the reactor void and DS pit still full of water - It was scheduled to be emptied on the 7th of March. If it was on schedule it would have been potentially a much more disasterous disaster.


(Grabbed from May 2011 U4 SFP underwater video and the June 2011 U4 refuelling floor video, the lower half of the gate can be seen in the centre of underwater image and the top of it in the other image.)

Not really news as such, just a could have, would have story. There are dozens of them related to March 11.

 

[tsutsuji]

As there was a renewed talk about unit 3 SFP, I thought it would be convenient to translate the following :

Tepco's internal investigation report (interim report, 2 December 2011)

Attachment 8-8 (4): unit 3 SFP investigation

http://www.tepco.co.jp/cc/press/betu11_j/images/111202f.pdf page 238/314 - 248/314

1. SFP situation
On 11 March, Fukushima Daiichi NPP's unit 3 SFP was storing 514 assemblies of spent fuel and 52 assemblies of new fuel. The decay heat was evaluated to be 0.54 MW on 11 March and 0.46 MW on 11 June. The fuel assemblies stored in unit 3 SFP are shown in table 1.

Struck by the tsunami generated by the Tohoku region off Pacific ocean coast earthquake of 14:46 on 11 March, all the AC power sources were lost, and the cooling function and the water supplementing function of the SFP were lost. An explosion thought to be caused by hydrogen gas occurred at 11:01 on 14 March, and because of the damage to all the outer walls on the reactor building operating floor and above, large quantities of debris fell into the SFP. It was confirmed that large quantities of steam were released from the operating floor which had become exposed due to the building damages.

At 09:48 on 17 March, sea water was sprayed by helicopter onto the reactor building top part. It was confirmed that steam was rising after spraying. At 19:05 on 17 March, spraying toward SFP by spraying trucks began. From then until 25 March, spraying toward SFP by spraying trucks and retractable spraying tower trucks was performed. (with some exceptions, most was with sea water).

On 23 and 24 March, water injection (sea water) by the existing pool cooling and filtering system was performed, but the injection pressure measured at the pump was high, and as it was presumed that the line was blocked somewhere, or something similar, it was judged that most of the water was not injected.

On 27 March, the first spraying via concrete pump truck was performed. After performance, an increase of the steam quantities from the reactor building top part was observed. From then until 22 April, 815 tons of water were spayed by concrete pump truck.

On 29 March, the water source of the concrete pump trucks was switched to fresh water. On 12 April, as a result of changing for a concrete pump truck equipped with a camera, it became possible to inject water while checking the rise of the water level with the camera pictures, and for the first time it became possible to confirm that the full water level was reached. As the full water level was reached when half the predicted quantity of water had been used, it was confirmed that the predictions of evaporated quantities made until then had been conservative, and that more water had been injected than the needed quantities. Among the quantities that were injected until then, it is thought that the surplus overflowed. After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed.

On 22 April, using the existing pool cooling and filtering system, a water injection test was performed with the strainer removed. Confirming that the pool water level rose by 9 cm by injecting around 10 tons of water in 20 minutes, it was judged that injection is possible. On 26 April, the full scale water injection using the existing pool cooling and filtering system piping was performed and from then until 29 June, 824.5 tons were injected via the existing pool cooling and filtering system piping.

On 8 May, an SFP sampling and video was performed.

On 9 May, hydrazine injection for corrosion control was started, using the existing pool cooling and filtering system. As it had been confirmed from the sampling results that the pool water was alkaline as a result of the dissolution of alkaline metals (such as Ca) from the fallen debris, on 26 and 27 June, borated water was injected via the existing pool cooling and filtering system in order to balance the alkalinity. As a result, the water quality improved passing from a strong alkalinity of pH 11.2 (8 May measurement) to a low alkalinity of pH 9.0 (7 July measurement).

On 30 June, pool cooling by the alternative cooling system (figure 1 [ http://www.tepco.co.jp/cc/press/betu11_j/images/111202f.pdf page 240/314]) began. When cooling started, the temperature was 62°C (alternative cooling system entrance temperature) and around 7 July the stable state was reached with a temperature around 30°C.

On 7 July, a sampling of SFP water was performed taking water overflowed into the skimmer surge tank through the FPC sampling line. The records of water injection into unit 3 SFP are available in table 2.

Table 1: number of fuel assemblies that were stored in the SFP

８X８ ４２
STEP２ １４８
STEP３-A ３２４
spent total ５１４
new fuel (STEP３-A) ５２
fuel total ５６６

Table 2: water injection records
total injected water quantity (as of 12 August) : about 6167.5 tons

figures with "／" are "month/day"
figures with "：" are "hour:minute"
The figures after "water" are tons of water

３／１７
９：４８～１０：０１
Self defence force helicopter; sea water ３０

３／１７
１９：０５～１９：１３
riot police high pressure water spraying truck; sea water ４４

３／１７ １９：３５～,１９：４５～,
１９：５３～,
２０：００～,２０：０７～２０：０９
self defence force high pressure water spraying car fresh water ３０

３／１８
１４：００approximately～１４：３８
self defence force high pressure water spraying car fresh water ４０

３／１８
１４：４２～１４：４５
US army high pressure water spraying car fresh water ２

３／１９
０：３０～１：１０
Tokyo fire department retractable water spraying tower truck etc. sea water ６０

３／１９
１４：１０～３／２０ ３：４０
Tokyo fire department retractable water spraying tower truck etc. sea water ２４３０

３／２０ ２１：３６approximately～３／２１
３：５８
Tokyo fire department retractable water spraying tower truck etc. sea water １１３７

３／２２
１５：１０～１５：５９
Tokyo fire department retractable water spraying tower truck etc.
(Tokyo - Osaka fire departments)
sea water １５０

３／２３
１１：０３～１３：２０
ＦＰＣ sea water ３５

３／２４
５：３５～１６：０５ approximately
ＦＰＣ sea water １２０

３／２５
１３：２８～１６：００
Tokyo fire department retractable water spraying tower truck etc.
(Kawasaki fire department)
sea water ４５０

３／２７
１２：３４～１４：３６
Tepco concrete pump truck (52 m range)
sea water１００

３／２９
１４：１７～１８：１８
Tepco concrete pump truck (52 m range)
fresh water １００

３／３１
１６：３０～１９：３３
Tepco concrete pump truck (52 m range)
fresh water １０５

４／２ ９：５２～１２：５４
Tepco concrete pump truck (52 m range)
fresh water ７５

４／４ １７：０３～１９：１９
Tepco concrete pump truck (52 m range)
fresh water ７０

４／７ ６：５３～８：５３
Tepco concrete pump truck (52 m range)
fresh water ７０

４／８ １７：０６～２０：００
Tepco concrete pump truck (52 m range)
fresh water ７５

４／１０
１７：１５～１９：１５
Tepco concrete pump truck (52 m range)
fresh water ８０

４／１２
１６：２６～１７：１６
Tepco concrete pump truck (62 m range)
fresh water ３５

４／１４
１５：５６～１６：３２
Tepco concrete pump truck (62 m range)
fresh water ２５

４／１８
１４：１７～１５：０２
Tepco concrete pump truck (62 m range)
fresh water ３０

４／２２
１４：１９～１５：４０
Tepco concrete pump truck (62 m range)
fresh water ５０

４／２６
１２：００～１２：０２
Tepco concrete pump truck (62 m range)
fresh water （checking water surface）

４／２６
１２：２５～１４：０２
ＦＰＣ fresh water ４７.５

５／８ １１：３８（water level measurement）
１２：１０～１４：１０（water injection）
１４：１０～１４：５０（water level measurement and sampling)
ＦＰＣ fresh water ６０ （water level measurement and sampling) 

５／９
１２：１４～１５：００（injection） (water level measurement before and after injection)
ＦＰＣ fresh water 80 (water level measurement)

５／１６
１５：００～１８：３２
ＦＰＣ fresh water １０６

５／２４
１０：１５～１３：３５
ＦＰＣ fresh water １００

５／２８
１３：２８～１５：０８
ＦＰＣ fresh water ５０
６／１ １４：３４～１５：５４ ＦＰＣ fresh water ４０
６／５ １３：０８～１５：１４ ＦＰＣ fresh water ６０
６／９ １３：４２～１５：３１ ＦＰＣ fresh water ５５

６／１３
１０：０９～１１：４８
ＦＰＣ fresh water ４２

６／１７
１０：１９～１１：５７
ＦＰＣ fresh water ４９

６／２６
９：５６～１１：２３
ＦＰＣ
fresh water（including boric acid) ４５

６／２７
１５：００～１７：１８
ＦＰＣ
fresh water（including boric acid) ６０

６／２９
１４：４５～１５：５３
ＦＰＣ fresh water ３０

６／３０ ９：４５～１０：４３(check of replenishment and leaks)
１８：３３～(operation is confirmed)
１９：４７(start of alternative cooling system)
ＳＦＰclosed loop cooling system fresh water

2. Points confirmed by investigation

(1) Unit 3 SFP pool water
On 8 May 2011 at unit 3, a sample of pool water was taken using a concrete pump truck, and on 7 July 2011 and 19 August 2011 SFP water that overflowed to the skimmer surge tank was taken via the sampling line of the fuel pool cooling and filtering system. The samples of pool water were analysed to determine the radioactive substances (the dates of analysis are 9 May, 7 July, and 19 August). The results of the analysis are shown in table 3.

Table 3: Unit 3 SFP analysis results (Bq/cm³)

nuclide period     8 May     7 July   19 August 2 March(a) turbine building (b)
Cs-134 2 years  140,000   94,000  74,000         ND         1,500,000
Cs-136 13 days     1,600     ND        ND            ND             44,000
Cs-137 30 years 150,000 110,000  87,000         ND         1,600,000
I-131     8 days   11,000     ND        ND            ND            660,000

ND= below detection threshold
(a) 2 March 2011 (for reference)
(b) unit 3 turbine building basement accumulated water, 22 April 2011 (for reference)

The evaluation made upon the analysis results is provided below:

* Unit 3 was shut down for regular inspection on 19 June 2010. Among the fuel that was removed, the fuel with the shortest cooling period had been cooled for more than 10 months, so that it is difficult to think that the short lived nuclides that are Cs-136 and I-131 are a consequence of the fuel stored in the SFP, and there is a high probability that they are originating from the reactor. The fact that the proportions of each nuclide are about the same as in the analysis results of unit 3's turbine building basement accumulated water, is also showing that there is a high probability that it is a radioactivity originating from the reactor.
* As regards the routes used by the radioactivity originating from the reactor, it is thought that there is a high probability that the radioactive substances originating from the reactor dissolved into the SFP water via the condensation of the steam in the building, via dust, via deposits on the debris, etc.
* In the analysis results of the pool water sampled on 8 May and on 7 July, although the relative proportion of the Cs-134 and Cs-137 isotopes is about the same, their concentration declined by about 30%. However, as the number of samplings is small, and as the sampling methods are different, it is not clear if this difference of concentration is significant.

(2) Evaluation of unit 3 SFP water level
Figure 2 is representing the results of the evaluation of unit 3's SFP water level together with real measured values. The evaluation results are based on an hypothesis of a decline of about 2 m by 14 March caused by the earthquake sloshing and the explosion consequences, but as a concentrated water spraying was performed on 17 March and henceforth, the water level was recovered, and later it was regulated close to the full level via periodic water injection (water injection was impossible from the end of April to the beginning of May due to a pump truck breakdown). It must be noted that it is thought that water spraying by spraying trucks, water injection by concrete pump trucks, and water injection via the fuel pool cooling and filtering system are subject to different proportions of water actually reaching the pool, so that a yield rate is attributed to each of these means.

[I insert here attachment 8-8 (1) table 4 (3) of http://www.tepco.co.jp/cc/press/betu11_j/images/111202f.pdf page 221/314 Tsutsuji]

Attachment 8-8 (1) Table 4 (3): Records of unit 3 SFP injection

"／" figures are "month/day" followed by injected water in tons
The rates (from 0 to 1) are the yield rates estimated for each injection means

３／１７ ３０ helicopter ０.１
３／１７ ４４ spraying car ０.１
３／１７ ３０ spraying car ０.１
３／１８ ４０ spraying car ０.１
３／１８ ２ spraying car ０.１
３／１９ ６０ spraying car ０.１
３／１９ ２４３０ spraying car ０.１
３／２０ １１３７ spraying car ０.１
３／２２ １５０ spraying car ０.１
３／２３ ３５ ＦＰＣ ０
３／２４ １２０ ＦＰＣ ０
３／２５ ４５０ spraying car ０.１
３／２７ １００ concrete pump truck ０.９５
３／２９ １００ concrete pump truck ０.９５
３／３１ １０５ concrete pump truck ０.９５
４／２ ７５ concrete pump truck ０.９５
４／４ ７０ concrete pump truck ０.９５
４／７ ７０ concrete pump truck ０.９５
４／８ ７５ concrete pump truck ０.９５
４／１０ ８０ concrete pump truck ０.９５
４／１２ ３５ concrete pump truck ０.９５
４／１４ ２５ concrete pump truck ０.９５
４／１８ ３０ concrete pump truck ０.９５
４／２２ ５０ concrete pump truck ０.９５
４／２６ ４７.５ ＦＰＣ １
５／８ ６０ ＦＰＣ １
５／９ ８０ ＦＰＣ １
５／１６ １０６ ＦＰＣ １

Water level measurement was performed from mid April, using the pictures from a surveillance camera set up on the pump truck, and the measured values and the evaluated values coincide by and large. It is thought that the water level was regulated at a level close to the full level as a result of the repeating water level declines due to evaporation and water level recoveries due to water injections.

However, the quantity of water injected when the reaching of the full level was confirmed on 12 April (about 35 tons) was smaller than the quantity that had been predicted by taking into account the compensation of losses such as leaks (about 80 tons (real results of 10 April)). Also, as the evaporated quantity - estimated from the real results obtained after confirming that the full level was reached - is between 10 and 20 tons per day, the quantity of water evaporated until it was confirmed that the full level was reached, must be between 320 and 640 tons. Even under the hypothesis that the water injection into the pool had never reached the full level, the pool water quantity is 1400 tons, and as the pool depth is about 3 times the fuel effective length, we calculate that the water level remained higher than half [the pool depth]. Also, even if we make the hypothesis that apart from evaporation, the water level declined by sloshing or when the building exploded, there was a 2 meter or more margin against fuel uncovering. Therefore it is thought that unit 3's SFP water level was maintained and that there was no fuel uncovering.

The records of water temperature measurements consist of only one measurement of around 60°C. As it is a sampling result of the pool's surface layer, it is thought that it is lower than the pool water's average temperature. The water temperature during evaporation, based on the real results of unit 2's pool, which produces a similar amount of decay heat, is estimated to be 70°C.

At unit 3, after the building explosion, in comparison with other units, larger quantities of white steam were confirmed to be rising from the top of the reactor building. As the quantity of steam produced by the decay heat of the pool fuel is not bigger than that of other units, it is estimated that the cause of this steam is not the steam from the pool, but a steam generation from the water which did not hit the mark when spraying toward unit 3's pool and which, via some route, flowed into the primary containment vessel's head side.

As a result of putting the alternative cooling system into service at 19:47 on 30 June, the cooling of the SFP was enhanced, reaching a water temperature of around 30°C (30.8°C at 11:00 on 7 July (heat exchanger entrance temperature)).

Figure 2: unit 3 SFP evaluation results

dark blue square : water level measurement
red line : water level evaluation
light blue triangle : water temperature measurement
brown line : water temperature evaluation

(3) Underwater situation
On 8 May at the same time as the pool water sampling, a video camera photography was performed. Figure 3 shows the photograph that was taken, but as debris have fallen, we could not confirm the status of the fuel, etc. that had been stored in the pool.

Figure 3 : SFP underwater situation(4) Pool water level and pool temperature measurement method
At unit 3, water temperature measurement was performed during water sampling. The measurement method consists of using a concrete pump truck as shown on figure 4, of lowering, from the top of the building, a cable where thermocouples are installed, and confirming the temperature variation due to the arrival of water. As this is the temperature of the surface layer of pool water, there is a high probability that the deeper water has a higher temperature.

Figure 4: Pool water level and pool temperature measurement method using a concrete pump truck
全体監視ｶﾒﾗ(3個) cameras observing the whole scene (3 cameras)
水位監視ｶﾒﾗ camera observing the water level
天井ｸﾚｰﾝ overhead crane
燃料取扱機 fuel handling machine
注水 water injection
熱電対 thermocouple
サンプリング容器 sampling vessel
滑車 pulley
ﾌﾞｰﾑ先端取付け機材 tip of boom equipment
中継機材、ﾓﾆﾀを配置 installation of transmission equipment and monitor
機材車 car for equipments

 

[westfield]

As there was a renewed talk about unit 3 SFP, I thought it would be convenient to translate the following :

Plenty of discussion points in that document.


I'm sure there are many others like myself who are not able to post so much but follow with great interest this thread virtually every day. I take my turn to thankyou for your continuing and huge contribution to this thread, very much appreciated, thank you tsutsuji.

 

[Astronuc]

World Nuclear News (13 March, 2012) - Pond investigation towards Fukushima fuel removal
http://www.world-nuclear-news.org/RS_Pond_investigation_for_Fukushima_fuel_removal_1303121.html

The fuel pond of Fukushima Daiichi 4 will be inspected by an underwater robot this month as an early step in the program of work to remove the used nuclear fuel from the building.

Unit 4 had been out of service at the time of last year's natural disasters; its reactor vessel open and emptied for inspection with all its fuel assemblies and control rods transferred into the adjacent storage pond. The pond contains 1331 fuel assemblies, but the higher heat load from the 548 more recently used fuel assemblies made the pond more of a concern than those at the other three damaged reactors. For the same reason the pond now represents a high priority for Tokyo Electric Power Company (Tepco) engineers that are working to ultimately decommission the site.

. . . .

The bottom of the pool is about 11.3 m below the surface of the water. The top of the racks is about 4.7 m, and the fuel height is about 4.2 m, but sits on a bottom nozzle, so the active fuel probably about 0.2 m or so below the top of the racks.

 

[jim hardy]

Tsutsuji - just awesome..

Thank you.

 

[Yamanote]

Thanks a lot to all contributors for sharing information and thoughts!

Much obliged...

 

[duccio]

At unit 3, after the building explosion, in comparison with other units, larger quantities of white steam were confirmed to be rising from the top of the reactor building. As the quantity of steam produced by the decay heat of the pool fuel is not bigger than that of other units, it is estimated that the cause of this steam is not the steam from the pool, but a steam generation from the water which did not hit the mark when spraying toward unit 3's pool and which, via some route, flowed into the primary containment vessel's head side.

And a special thank goes to... tsutsuji! :) Along with the SDF measuring high radiation dose on top of reactor, it makes me wonder if reactor 3 concrete plug is still in place

(BTW, why in the hell would they want to move spent fuel from a cooled SFP to the RPV? The only reason I can think of is the weight)

 

[zapperzero]

(BTW, why in the hell would they want to move spent fuel from a cooled SFP to the RPV? The only reason I can think of is the weight)

I suppose you are referring to Unit 4 SFP. The plan there is to move control rods which are stored in the cask pit out of the cask pit and into the RPV. I presume this is done simply to make room in the cask pit for casks, in which fuel bundles will be put.

 

[jim hardy]

I suppose you are referring to Unit 4 SFP.

Might be a core shroud in there too. If so they need room.

 

[zapperzero]

Might be a core shroud in there too. If so they need room.

I think I remember seeing something big and cylindrical in the videos. Curse my memory, I've no time to check.

 

[Rive]

Might be a core shroud in there too. If so they need room.

I see no point in putting the shroud to the SFP. The SFP is connected to the reactor well with only a small channel, so you can't move the shroud through it. Only the equipment pool has an opening wide enough to the well.

And the new shroud is not irradiated so why put it underwater? It'll be fit to the reactor with the RPV dried.

 

[elektrownik]

Interesting, unit 1 temp:

 

[jim hardy]

I see no point in putting the shroud to the SFP. The SFP is connected to the reactor well with only a small channel, so you can't move the shroud through it. Only the equipment pool has an opening wide enough to the well.

And the new shroud is not irradiated so why put it underwater? It'll be fit to the reactor with the RPV dried.

U4 was underoing a shroud replacement. The new shroud is very tall so must be set in the pit in the area where half upper internals usually go, so it'll clear roof beams. So the steam dryer is set atop the separators and a green "doghouse" built around it to shield the workers.

Pictures of the plant showed that "doghouse" but the shroud i think wasn't set yet.

If i can find link to that shroud report will post it. Google TEPCO SHROUD REPLACEMENT it's a fascinating report on how they did it.

 

[jim hardy]

This should get to one report.

If it doesn't work, google on "Radiation Control in the Core Shroud Replacement Project of"

http://www.google.com/url?sa=t&rct=...-4i2Dg&usg=AFQjCNGSRNuj0xavsUQ9UqkD8z3cAkQ46w

see paragraph just below fig 7.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120314/index.html On 14 March, a total of 6 Tepco workers went down to the basements and inspected the vicinity of the entrances of unit 2 and unit 3's suppression chambers. Opening unit 2's suppression chamber entrance door they found a maximum radiation of 160 milisievert/hour. At unit 3 the door was deformed so they could not open it. The maximum radiation before the door was 75 milisievert/hour. It was confirmed that the 9 meter high suppression chambers in both units are partly submerged by 6 meter deep contaminated water. The inspection time was 20 minutes and the highest worker exposure was 2.87 milisievert. Junichi Matsumoto said "as the radiation is extremely high (...) in the future it will be necessary to use robots".

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120313_03-e.pdf "Field Survey on the semi-basement floor of the reactor building of Unit 2 and 3 at Fukushima Daiichi Nuclear Power Station"

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120314_01-e.pdf "Preliminary survey in Torus Room of Units 2 and 3,Fukushima Daiichi NPS"

 

[SteveElbows]

This should get to one report.

If it doesn't work, google on "Radiation Control in the Core Shroud Replacement Project of"

http://www.google.com/url?sa=t&rct=...-4i2Dg&usg=AFQjCNGSRNuj0xavsUQ9UqkD8z3cAkQ46w

see paragraph just below fig 7.

Yeah I see that, and I do not see this stuff as matching what has been discussed here on this topic recently by some people.

Because surely its the old shroud that ends up in the d/s pit, not the new one. The paragraph in question has this line:

To secure the area for cutting core internals at the D/S storage pool, the dryer and separator are stacked in two stages, allowing a 2.0 m portion of the dryer to be exposed to the air.

They mention cutting, well that would be cutting of the old stuff, the old shroud, not the new one. Or its equipment used to do the cutting. I do not know if the new shroud goes via the d/s pit at any point, I haven't seen any evidence that it does.

And in any case this has nothing to do with the spent fuel pool so I am not sure why that possibility was even raised. Surely the round thing in the unit 4 spent fuel pool video is the cask transfer thing.

I appreciate the link anyway because core shroud replacement work is interesting, but I really don't understand where the suggestion that shroud would be in the fuel pool comes from at all.

 

[SteveElbows]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120314/index.html On 14 March, a total of 6 Tepco workers went down to the basements and inspected the vicinity of the entrances of unit 2 and unit 3's suppression chambers. Opening unit 2's suppression chamber entrance door they found a maximum radiation of 160 milisievert/hour. At unit 3 the door was deformed so they could not open it. The maximum radiation before the door was 75 milisievert/hour. It was confirmed that the 9 meter high suppression chambers in both units are partly submerged by 6 meter deep contaminated water. The inspection time was 20 minutes and the highest worker exposure was 2.87 milisievert. Junichi Matsumoto said "as the radiation is extremely high (...) in the future it will be necessary to use robots".

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120313_03-e.pdf "Field Survey on the semi-basement floor of the reactor building of Unit 2 and 3 at Fukushima Daiichi Nuclear Power Station"

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120314_01-e.pdf "Preliminary survey in Torus Room of Units 2 and 3,Fukushima Daiichi NPS"

Thanks very much for the info. I was hoping the photos would be more interesting than they actually seem to be, and they have been published at a pretty low resolution.

 

[NUCENG]

Core Shroud Replacement sequence:

http://www.toshiba.co.jp/nuclearenergy/english/maintenance/replace/shroud03.htm

 

[jim hardy]

but I really don't understand where the suggestion that shroud would be in the fuel pool comes from at all.

From a shadowy memory of something last year. There was discussion of the doghouse over steam dryer and shroud replacement, and clearance to roof, but details have faded.

I may well be wrong. Withdrawn.

I'm guilty of referring to that whole wet area - refueling canal, laydown area and fuel pool as all just "the pool". Will be more precise hereafter.

 

[SteveElbows]

Thanks NUCENG, remember looking at that one when reactor 4 was under heavy scrutiny here, in fact that's probably the main document that influenced by understanding of core shroud work. I will be interested to see how the reactor well looks in the videos they will take in the near future.

Elsewhere I have noted that some people were anticipating seeing reactor 2 suppression chamber looking in real bad shape, probably having imagined a very dramatic explosion in the area or other very noticeable damage. Released photos of torus don't give us much to go on when it comes to the less visually dramatic damage that may in theory have occurred to the suppression chamber.

Anyway what I wanted to bring up at this point was the idea that the torus room itself could in theory be the scene of a number of different forms of dramatic activity at moments in the crisis at one or more reactors. So the suppression chamber itself is not the only thing to look for. For example under a scenario where a certain kind of drywell melt-through occurs, some core material can blowdown into the torus room. This scenario is included in MELCOR nuclear accident modelling systems so its not too far-fetched I wouldn't have thought, although I am not suggesting it has actually happened in this case.

 

[SteveElbows]

From a shadowy memory of something last year. There was discussion of the doghouse over steam dryer and shroud replacement, and clearance to roof, but details have faded.

I may well be wrong. Withdrawn.

I'm guilty of referring to that whole wet area - refueling canal, laydown area and fuel pool as all just "the pool". Will be more precise hereafter.

Ah yes I do have some memory of that, back when people were paying special attention to a small part of the east side of reactor 4 building on pre-accident photos.

Anyway no worries, to be honest it probably helps the conversation somewhat if people post things that are open to question, it gives us something to talk about and the chance to refresh some past details. I am sorry if I ever sound somewhat abrupt in my posts, sometimes I do get frustrated by stuff that turns out to be a red-herring, and there has been no shortage of what when it comes to Fukushima. Quite understandable given that the real story is not expressed only through the dramatic and the visual stuff that we can see without own eyes, and the lack of high-quality data exploring every nook & cranny of the site, a situation compounded by the rather sparse narrative that officialdom has provided. Even so I get frustrated because I keep spotting areas that are of interest to me but which do not sustain much conversation, so when people spend three pages talking about a cloud on the webcam I become sad.

 

[zapperzero]

At unit 3 the door was deformed so they could not open it. The maximum radiation before the door was 75 milisievert/hour.

Does that door look to be bulging outwards to any of you guys?

 

[r-j]

Has this been posted already?

http://youtu.be/_jlONo6kj10

Video of the waves hitting the power plant.

 

[elektrownik]

Does that door look to be bulging outwards to any of you guys?

Yes, maybe from explosion.

Has this been posted already?

http://youtu.be/_jlONo6kj10

Video of the waves hitting the power plant.

Interesting, wasnt posted before.

 

[zapperzero]

Interesting, wasnt posted before.

This is going to make SteveElbows even sadder (sorry, Steve!), but I think I see puffs of steam in that video, near the end.

 

[elektrownik]

This is going to make SteveElbows even sadder (sorry, Steve!), but I think I see puffs of steam in that video, near the end.

Yes, steam is visible.

 

[duccio]

Does that door look to be bulging outwards to any of you guys?

Yes, maybe from explosion.

Didn't tepco find evidence that the explosion happened on the upper floors? It looks like a thick metal door definitely bended outward. Maybe from heat?

(btw, the video of the ride. Unit 2 http://tepco.webcdn.stream.ne.jp/www11/tepco/download/120315_01j.zip and unit 3 http://tepco.webcdn.stream.ne.jp/www11/tepco/download/120315_02j.zip )