Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[SteveElbows]

OK I can say more about the water pumping assumptions used in the analysis we are discussing. I am just looking at reactor 2 for now.

This is their document that describes some stuff about the decay heat numbers they fed into their analysis:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_07-e.pdf

Note that on page 2 it says that they are basing the decay heat on the fuel loading history of the reactors, which is a good start. It then tells us that the time period that water injection & heat removal stopped for reactor 2 was judged to start when the RCIC failed, and end when SRV2open occurred.

Then we see a useful graph on page 3 which shows this in graphic form. By looking at the time scale on this graph and comparing it with the above statement and various information about the timing of events in other analysis documents & government reports to the IAEA, I get the following picture of their assumption:

RCIC was judged to have stopped working at 13:25 on the 14th, and this matches the graph.

The graph looks to end the period at some point between 7pm and 8pm. This fits with official narrative about events that says that reactor pressure was low enough for pumping by 19:03, but problem with fire engine running out out fuel puts the water injection start time at either 19:54 or 19:57. This also matches the government estimate that no water was injected for 6 hours and 29 minutes.

However there are problems with the assumption that this time period was the complete period that heat removal was unavailable:

I believe water level measurement started to drop after 12:00 on the 14th, so its possible that time period under consideration should start sooner than 13:25

TEPCO said that end period is when 2SRVopen, but according to other narratives this didn't happen till 21:20 (unless I or they made a mistake)

And the cabinet report that went into new detail about the disaster and was not afraid to point out mistakes made, mentions a further set of time periods when the measured reactor pressure level was considered too high for reliable water injection:

20:54 to 21:18
00:16 to 01:11

Also I cannot be quite sure due to small graphs, but it is possible that TEPCO's own Case-2 reactor 2 analysis decided to be conservative and not claim any significant quantity of water was injected into reactor 2 vessel until after 06:00 on the 15th. (I need to look at this one more if I can as its much later than other estimates of when water injection was possible)

Anyway I hope this gives some detail as to why I am concerned that Tepco's November analysis of core may not have been suitably cautious when considering the time period that removal of decay heat was unavailable.

And let alone getting the times right for start and end of 'no decay heat removal available' period, there is the question of how much heat was actually being removed by the water once pumping really got going. If their analysis was really as crude as that graph suggests, then surely its not good, how can you only take the decay heat for the time that no pumping was done and ignore all the heat that came after this period ended, as if the pumping was good enough to deal with all the heat from this later period?

Please let me know if you spot any mistakes I have made with this line of thought. Sorry I am not linking to every source in this post but I already made it too long and the details I refer to are from the usual set of documents I talk about (mostly the chapter 4 of report & attachments from government to IAEA and the investigation committee interim report, also chapter 4 I think).

 

[tsutsuji]

14 March 2012 international symposium

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/r120227_12-j.pdf International symposium on decommissioning of Fukushima Daiichi to be held on 14 March 2012 in Tokyo.

Tepco's documents for the symposium are now available at http://www.tepco.co.jp/nu/fukushima-np/roadmap/conference-j.html

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/e120314_01-j.pdf Onsite situation, and needs of technical know-how. Page 6, there is an image of the kind of improved inspection tool with a long arm and a mirror at the tip, inspecting the pedestal floor.

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/e120314_02-j.pdf Research plan regarding improvement of simulation code for understanding the status of fuel debris in the reactor

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/e120314_03-j.pdf Technical developments for the process and disposal of radioactive waste at Fukushima Daiichi NPP. Schedule on page 10.

The whole symposium documents (not only Tepco's) are available on the ministry website :

http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/20120315_01.html

http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20120315_02_005.pdf (Toshiba/Hitachi/Mitsubishi) on page 2 (3/10) there is a schedule. By this schedule, the research and development necessary to inspect inside PCV would be ready in 2016. The diagram on page 3 (4/10) shows the pedestal wall, sump pits, "slit", and another "pedestal opening" W: 0.7 m × H: 2.0 m. Page 9/10 shows a robot with a long arm deemed suitable to inspect inside pedestal.

28 March 2012 government-Tokyo Electric mid and long term response committee, steering committee (4th meeting)

The 4th monthly government-Tepco mid-long term meeting was held on 28 March 2012. The documents are available at:
http://www.meti.go.jp/earthquake/nuclear/decommissioning.html
http://www.tepco.co.jp/nu/fukushima-np/roadmap/conference-j.html

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02a.pdf agenda
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02b.pdf participants
Document 1 http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02c.pdf abstract of the proceedings of 3rd steering committee meeting
Document 2 http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02d.pdf plant status
Document 3 Study and execution of each special plan

3-1 Cooling by closed loop water injection
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02e.pdf schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02f.pdf Results of investigations toward installation of alternative thermometers at unit 2
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02g.pdf Unit 2 second investigation into PCV

3-2 Treatment of accumulated water
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02h.pdf schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02i.pdf multinuclide facility

3-3 Countermeasures to reduce environmental radiations
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02j.pdf schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02k.pdf management of debris, cut down trees, generated by the response to the accident
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02l.pdf about temporary storage in tents of the waste in drums in the solid waste storehouse
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02m.pdf Scattered debris survey plan
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02n.pdf Outline of suitability test for decontamination inside plant premises
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02o.pdf Measures to improve monitoring posts' environment
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02p.pdf Results of evaluation of additional releases from reactor building's primary containment vessels
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02q.pdf Evaluation of yearly radiation exposure at plant premises boundary

3-4 Improvement of working conditions
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02r.pdf schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02s.pdf proposal for a medical/health management system for fiscal 2012

3-5 Countermeasures for spent fuels pools
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02t.pdf schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02u.pdf Debris removal work, reactor building top part, unit 3
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02v.pdf Debris removal work, reactor building top part, unit 4
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02w.pdf Underwater inspection into spent fuel pool for the purpose of debris removal, unit 3 [this is planned for mid-April 2012]
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02x.pdf Results of survey of debris distribution in spent fuel pool, unit 4

3-6 Preparations for fuel debris removal
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02y.pdf Schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02z.pdf Results of tests performed inside a large size water tank for the purpose of stopping leaks between buildings
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02aa.pdf Survey in torus room

3-7 treatment and disposal of radioactive waste
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02bb.pdf schedule
http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02cc.pdf Installation of miscellaneous solid waste incinerator equipment

Document 4 http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02dd.pdf roadmap progress
Document 5 http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02ee.pdf establishment of plan to improve reliability at Fukushima Daiichi NPP

28 March 2012 government-Tokyo Electric mid and long term response committee, technical development progress headquarters (4th meeting)

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_01a.pdf Agenda

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_01b.pdf Abstract of the proceedings of 3rd meeting

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_01c.pdf Progress status of technical development projects concerning, for example, the development of machinery and equipments to prepare fuel debris removal, toward measures for the decommissioning of Fukushima Daiichi NPP, etc.

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_01d.pdf Results of the international symposium on research and development plans toward measures for the decommissioning of Tokyo Electric Fukushima Daiichi NPP units 1 ~ 4 etc.

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_01e.pdf Basic ideas for research, focussing on institutions that are necessary to achieve the mid-long term roadmap toward the decommissioning of Tokyo Electric Fukushima Daiichi NPP units 1 ~ 4 etc.

28 March press conference
http://www.ustream.tv/recorded/21418184 At 14:02 Junichi Matsumoto says the second inspections for installation of alternative thermometers at unit 2 is scheduled for 28 March and 29 March. Some of them were completed today, but the results have not been announced yet. He will announce the results when they are ready. The yellow word balloon on http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02f.pdf page 9 mentions taking dimensions, measuring pipes and valves' temperatures, and taking photographs, to prepare pipe cutting and freezing.

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02f.pdf page 7 is about the revision of priorities for installation of alternative thermometers. The high radiation routes are cancelled. What is left is Jet Pump system B X-40C/D in area B with priority 1, SLC differential pressure sensor X-51 in area C with priority 2, and TIP in area D as priority (1) with a note. The note says: "there is a possibility that the TIP guide tubes are surviving in the outer surroundings of the core (see page 8). →If undamaged TIP guide tubes are left, they can be promoted to priority 1." The figure in the left part of page 8 shows a yellow area where surviving TIP tubes are believed to exist.

 

[tsutsuji]

On unit 4 top level they have to repair and secure the FHM machinery: rails, crane and so.

The FHM was removed somewhere between 20 February and 20 March, according to the text and photographs at http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02v.pdf

They plan to remove the roof steel frame rows R1 to R4 by 22 April.

 

[r-j]

http://hisz.rsoe.hu/alertmap/site/?pageid=event_summary&edis_id=NC-20120328-34685-JPN

Does this mean anything?

 

[mheslep]

Decay heat question. It's estimated here that the decay heat from Daiichi-1 was down under 5MW after a couple months. Given an *undamaged* reactor and building, but still without power, what is the maximum heat level that can be rejected to ambient through passive means without uncovering the fuel? I suppose a similar, perhaps easier to answer question applies to spent fuel pools. Does "cold shut down" also imply no active cooling required?

 

[triumph61]

The FHM was removed somewhere between 20 February and 20 March, according to the text and photographs at http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02v.pdf

They plan to remove the roof steel frame rows R1 to R4 by 22 April.

https://www.physicsforums.com/showpost.php?p=3802908&postcount=12514

 

[Bandit127]

http://hisz.rsoe.hu/alertmap/site/?pageid=event_summary&edis_id=NC-20120328-34685-JPN

Does this mean anything?

Click the "details" tab - it is the result of the low water level found in the Unit 2 investigation.

 

[MadderDoc]

I am trying to get at terms with the emission systems for these plants, and sit back with some questions:

Would it be correct to say that the large pipes which connect the reactor buildings 1+2, and reactor buildings 3+4 to the two stacks respectively, are meant for the normal mode ventilation of the reactor buildings -- while the venting of the primary containment, i.e the D/W and S/C vent operations involved during the accident progression, were meant to be routed to the stacks through other and smaller pipes?

Now, I get the impression of three sets of feed pipes to the exhaust stack. Firstly, there are the large tubes already mentioned, secondly, there are those smaller pipes we've been talking about in relation to high radiation at the 1+2 stack, and in connection with the hypothesis of hydrogen transfer from unit 3 to unit 4 (I've got the impression that these pipes represent what has been termed 'hardened vents')

Then thirdly, looking at the foot of the exhaust stacks, there appears to be on both of them yet another pair of pipes, of medium caliber, emerging from underground, and entering the foot of the stack from the north and south direction, So, I wonder what purpose those pipes serve?

Finally, directly attached to the NW corner of the reactor buildings are (were) separate stacks, delivering their exhaust just a few meter above the buildings. What would those exhausts be for?

 

[zapperzero]

Finally, directly attached to the NW corner of the reactor buildings are (were) separate stacks, delivering their exhaust just a few meter above the buildings. What would those exhausts be for?

I would bet on those being the exhausts for the diesels. Don't quote me on this one though.

 

[tsutsuji]

https://www.physicsforums.com/showpost.php?p=3802908&postcount=12514

You were right. If I had carefully read your post and the ensuing talk I would have known. Sorry. I was influenced by Tepco's captions at http://photo.tepco.co.jp/en/date/2012/201203-e/120306-01e.html where they speak about "trolley of overhead traveling crane" and "girder of overhead traveling crane" without mentioning the FHM, so I thought it was still there.

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02aa.pdf In this document they tell what they plan to do next in unit 2's torus room.

[page 1]

Background: Because it is thought that the reactor's coolant water flows via the torus or the torus room, it is necessary to grasp the torus room's (and the torus') status, going toward the goal of repairing the PCV.

Purpose of torus room entry: At present, research and development is under way for equipments to inspect and repair the PCV and reactor building's leakage points, but ahead of the completion of this research and development we want to do the following:
* grasp the working environment inside the torus room
* as far as is presently possible, grasp the reactor coolant water leakage route (damaged parts/regions) inside the torus room, whose details are presently unclear, and the accumulated water inflow parts/regions .

[page 2]
Onsite survey ①

• Check reactor building triangle corner middle basement
- People could directly access the torus room entrance from the triangle corner
- check of accumulated water water level, etc.
- check of radiation, dust, temperature, humidity, lighting, etc.
- robot accessibility ; check of cable route
- check of torus room entrance door opening/closing status and radiation on the door surface
[see also the figures at the bottom of page 2]

[page 3]
Same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120314_01-e.pdf page 1

[page 4]
Same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120314_01-e.pdf page 2

[page 5]
Same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120314_01-e.pdf page 3

[page 6]

About future inspections

Onsite survey ② (proposal)

• check inside torus room from the reactor building first floor penetrations
(purpose) check environment inside torus room from outside of torus room

- After removing the rubber boot, insert an imagescope, a thermometer etc. into the torus room via the opening in the vertical penetration, and check the torus room's radiation, temperature, hydrogen concentration, lighting status, etc. (risk: if there is stuffing material in the vertical penetration, it might be impossible to perform this)

[see also the figures at the bottom of page 6 :]
２号機R/B北側エリア unit 2 R/B north side area
1階床貫通孔イメージスコープ first floor penetration hole imagescope
S/Cアクセスハッチ S/C access hatch
ラバーブーツ（撤去要） rubber boot (must be removed)
貫通孔（125A） penetration hole (125A)
配管（50A) pipe (50A)

[page 7]

About future inspections

Onsite survey ③ (proposal)

• check inside torus room with a robot, etc. as possible without long delay
(purpose) ahead of development of PCV inspection and repair equipments, as far as possible, check leakage points and torus room environment, etc.
- grasp the main leakage route from PCV to torus room (check damaged parts and leakage rate by visual observation of S/C manhole, sand cushion drain line, vent pipe)
- grasp (visual observation) the parts/regions [responsible for] accumulated water inflow into torus room
- grasp environment inside torus room
• check accumulated water water level etc.
• check radiations, dust, temperature, humidity, lighting status, etc.

[page 8]
Survey schedule

 

[zapperzero]

Survey schedule

Is it me, or is the pace of work picking up significantly?

 

[tsutsuji]

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02w.pdf Underwater preliminary survey into spent fuel pool for the purpose of debris removal, unit 3

[page 2]

1. purpose

* For fuel removal from unit 3 spent fuel pool to become a reality, it is necessary to remove debris from the reactor building top part and from inside the spent fuel pool.
* Then, for the purpose of building resources to build up the debris removal plan, an underwater preliminary survey is performed.
* The first survey is planned in mid-April. After that, surveys will be intermittently performed in response to the debris removal situation.

[page 3]
2. outline of the survey (planned to be performed in mid-April)

* using a crawler crane, a fixed type underwater camera is remote controlled from the control room in the seismic isolated building, and photographs of the spent fuel pool top part and of inside the pool are taken
* we plan a 3 day long work (preparation: one day; real work: one day; clean up: one day)

 

[NUCENG]

I did consider this, but the gap shown there is quite wide. And the big problem is that if you look on another version of this diagram you will see that the same kind of opening is shown on the other side, but I do not think there are two access points into the pedestal area.

(for example page 4 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120228_04-e.pdf )

There is a pedastal and possibly a bio shield wall aroung the RPV. The outer "wall" may be the bio shield. The pedastal has small opening to permit access to the CRDMs and cabling under the vessel but is supporting the tremendous weight of the vessel, its internals, and the coolant. The bio shield only supports itself so its openings may be larger.

 

[SteveElbows]

Thanks, that makes complete sense and does indeed sound like a candidate for what is seen on that outline diagram of reactor level 1.

And thanks so much again to tsutsuji for the most excellent translations & information. I look forward to learning more about reactor 3 fuel pool and reactor 2 suppression chamber & torus room when they do these missions.

 

[tsutsuji]

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02z.pdf Results of tests performed inside a large size water tank for the purpose of stopping leaks between buildings

[page 1]
1. Introduction
【present situation】
It is estimated that contaminated water leaking from PCV is leaking into the neighbouring building via the penetrations (interstice between pipe and sleeve) in the reactor building wall.

【purpose of watertighting】
By blocking the reactor building penetrations, the scope of the dispersion of contaminated water from PCV is reduced.

[page 2]
2. Image of the situation after water stopping material injection

[page 3]
3. Test in large size water tank < outline >

【Purpose of the test】
By injecting plastic grout, we check if water can be stopped in double pipes where water leakage is simulated

Plasticity... the quality of being deformed like clay when a force is applied, without coming back to the original shape when the force is removed. (The main flowability material and the plasticity material undergo separate pressurized feeding, then they mix at the same time as they fill up, and they solidify).
(to be continued)

 

[tsutsuji]

[page 4]
4. Test result ① < double pipe leakage point cut-off performance >

[page 5]
4. Test result ② < heaping up capacity of water stopping material >

(to be continued)

 

[tsutsuji]

[page 6]
4. Test result ③ < adherence of water stopping material's contact surface >

[page 7]
5. Results of large size water tank tests < summary >

【test results】

①double pipe leakage point cut-off performance
Simulating the largest diameter of the penetrations used at the real plant, we confirmed that water cut-off is possible with plastic grout, in a test under the condition where water is flowing.

②heaping up capacity of water stopping material
We used grout with such a composition that heaping up capacity can be expected, but inside the tank a relatively gentle slope (about 20° of angle) was obtained. → One cannot expect much heaping up capacity.

③adherence of contact surface
As the contact surface had no void interstices, the adherence was good.

【problems】

* Study of a practical construction method with the prerequisite that heaping up capacity cannot be expected

* Assessment of the influence of obstacles or interfering objects in the surroundings of the penetration mouths

* Study of practical construction method, taking hardenability (depends on temperature) of plastic grout into account.

* Determination of leakage points (check if there is leakage from the penetration)

【Future response】
We plan to study practical construction methods, to perform soundness assessments, and to develop equipments within the research and development (national project) that is presently under execution.

[page 8]
6. Future schedule (past achievements - plans)

[page 9]
< Reference > characteristics of water stopping material (plastic grout)

(the end)

 

[tsutsuji]

Having completed this translation, I have a question: what is the point of filling the penetrations between reactor building and turbine building with grout, as they tell us in that document ?

Would it not be enough to use a pump, and pump the water until the water level is lower than the lowest penetration (0.3 m above floor as in the large water tank test) ?

 

[clancy688]

Having completed this translation, I have a question: what is the point of filling the penetrations between reactor building and turbine building with grout, as they tell us in that document ?

Um, I just asked myself "What's the point anyway?". As far as I understand, they're simply pouring water on the cores. But there's no closed circuit, so they're NOT pumping the water out. Or am I wrong and there IS some kind of return?
Because if there's not and they are stuffing the lower leaks, the water will simply rise up to the next leak. And then flow out again.

-----------------

On a different note: So they are pouring water on top of the damaged/molten fuel. Several tons an hour, since over a year. And all that water's flowing out into the basement, new water enters the containment, flows out, and so on. For over a year. Doesn't that necessarily mean that every single soluble radioactive particle which isn't still protected by a crust of molten fuel is gone, being distributed in the basement?

 

[SteveElbows]

Having completed this translation, I have a question: what is the point of filling the penetrations between reactor building and turbine building with grout, as they tell us in that document ?

Would it not be enough to use a pump, and pump the water until the water level is lower than the lowest penetration (0.3 m above floor as in the large water tank test) ?

They might not have the spare contaminated water storage & processing capacity to want to drain the basement of reactor building that low at the moment.

I think its also possible that they do not want the water level in the torus room to fall below a certain level, in case the water is acting as shielding and cooling, in which case draining it would be a bad idea. Or perhaps they think it might affect the water level in the drywell somehow.

I don't even know how desperate they are to drain the turbine buildings, but as they have done this study I guess it is on the agenda.

They might also have other ideas for how to use this technology, e.g. to one day fill the torus room/plug suppression chamber leaks, if they are not afraid that anything that requires cooling or shielding is in the torus room.

 

[cockpitvisit]

Would it not be enough to use a pump, and pump the water until the water level is lower than the lowest penetration (0.3 m above floor as in the large water tank test) ?

Wouldn't the water then start flowing in the opposite direction through the penetration? The water level in all adjacent buildings would have to be lowered too. This could be very difficult due to the constant influx of groundwater in the turbine building basement.

 

[biggerten]

Having completed this translation, I have a question: what is the point of filling the penetrations between reactor building and turbine building with grout, as they tell us in that document ?

Would it not be enough to use a pump, and pump the water until the water level is lower than the lowest penetration (0.3 m above floor as in the large water tank test) ?

Because they are going to fill the place with water, and they have to stop the leaks to do so. This is all part of the plan to eventually fill the torus, PCV, pedestal and RPV with water for shielding during fuel debris (corium) removal - in about 10 or 15 years.

See pages 51, 52 and 53 of the following - http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/111221_02.pdf

Step 3 on page 51.

And continued thanks for your remarkable contributions, tsutsuji. Please accept my heartfelt, warmest, and sincere appreciation.

 

[westfield]

I am trying to get at terms with the emission systems for these plants, and sit back with some questions:

Would it be correct to say that the large pipes which connect the reactor buildings 1+2, and reactor buildings 3+4 to the two stacks respectively, are meant for the normal mode ventilation of the reactor buildings -- while the venting of the primary containment, i.e the D/W and S/C vent operations involved during the accident progression, were meant to be routed to the stacks through other and smaller pipes?

Now, I get the impression of three sets of feed pipes to the exhaust stack. Firstly, there are the large tubes already mentioned, secondly, there are those smaller pipes we've been talking about in relation to high radiation at the 1+2 stack, and in connection with the hypothesis of hydrogen transfer from unit 3 to unit 4 (I've got the impression that these pipes represent what has been termed 'hardened vents')

Then thirdly, looking at the foot of the exhaust stacks, there appears to be on both of them yet another pair of pipes, of medium caliber, emerging from underground, and entering the foot of the stack from the north and south direction, So, I wonder what purpose those pipes serve?

Finally, directly attached to the NW corner of the reactor buildings are (were) separate stacks, delivering their exhaust just a few meter above the buildings. What would those exhausts be for?

I'm going off engineering drawings from US plants and reviews of lots of documents regarding these designs - someone in the industry can clarify this if required -

In regards to similar USA BWR plants (Oyster Creek \ Duane) - The buildings have "normal" HVAC systems, then the SGTS, then the hardened vent systems (There are other ventilation systems as well but they are minor\ are more plant specific). SGTS is not related to normal building ventilation or the "hardened" vent system. SGTS is a standby system only for purging containment for startup\shutdown or (minor) emergency use.

We know for sure the hardened vent system is a totally separate system all the way to the stack. Early on (but post construction of this type of reactor unbelievably) it was found the SGTS would be inadequate and fail inside the RB during a high pressure venting scenario, filling it with steam and gases. So the hardened vent system was a retrofit to address this issue.

For others, some good insights on those systems and the accident in general in these two docs:

Role of BWR secondary containments in severe accident mitigation

Joseph Shephard - CalTech - The Crisis at Fukushima NPP (Sept 2011, some of it might be out of date but it's still worth a readRe - pipes diving underground at base of stacks - without TEPCO drawings who knows. There are sump pumps in the base of the stacks so there would be some outlets for those to send to waste treatment although those ones look a bit large for that purpose. This is a drawing for the stack at Oyster Creek which indicates there are lots of connections to their plant stack.

( Who knows, there may be separate lines to the stack for the "wet" & "dry" hardened vent lines although I've only seen drawings that contradict that.)

Re - exhausts on NW corners of Units 2,3,4 & 5 ("boxed in" on NW corner of U5 RB),
Unit 1 & 6 don't have it there but they but have a similar stack on the northside of their TB's. "Normal" building vent stacks (non SGTS) or are they steam exhausts?
Maybe someone can clarify which. US plant drawings show separate (from the large stack) "normal" building stacks with their own filter train.
@ ZZero - The EDG's exhausts are right over on the eastern sides of the TB's on units 1-5 as the EDG's are in the TB's of units 1-5 (Apart from the retrofitted two air cooled EDG's for units 2 & 4 over in the common spent fuel building which were added in the '90's. For a few million more they could have put those two air cooled EDG's and their switchgear on the hill...so much for SAM) , on unit 6 only you can see the EDG exhausts up the north side of the RB , the EDG's are in a building attached to the side RB 6 (however in another drawing they appear in the bridge building between RB 6 & it's TB but that's more the US style I believe) . Then to finish this for others benefit, U6 is unique at fukuichi in that it has three EDG's, one of the DG's is dedicated to powering HPCS, there is the separate air cooled EDG north of Unit 6 which likely saved units 5 & 6 (from exploding at least))

 

[Tepconium-311]

Having completed this translation, I have a question: what is the point of filling the penetrations between reactor building and turbine building with grout, as they tell us in that document ?

Would it not be enough to use a pump, and pump the water until the water level is lower than the lowest penetration (0.3 m above floor as in the large water tank test) ?

Other plausible reasons could be:
Technically Tepco tries isolating both basements.
Making two separate not-interconnected non-interacting water circuits makes sense.
Effects easily obtained:
Contaminants from R/B won't reach T/B anymore.
Possibility to prioritize on leaks in R/B.
Less groundwater contamination.
R/B protection from T/B salt water inflow.

P.S.: Thank you Mr. Tsutsuji-san! Excellent informative posts!

 

[thebluestligh]

Interesting scenes from TEPCO's video related to ocean monitoring of sea life in 20 km

http://photo.tepco.co.jp/en/date/2012/201203-e/120330-01e.html

 

[Yamanote]

Interesting scenes from TEPCO's video related to ocean monitoring of sea life in 20 km

http://photo.tepco.co.jp/en/date/2012/201203-e/120330-01e.html

If you mean that plant, it's neither Daiichi nor Daini.

 

[MadderDoc]

Um, I just asked myself "What's the point anyway?". As far as I understand, they're simply pouring water on the cores. But there's no closed circuit, so they're NOT pumping the water out. Or am I wrong and there IS some kind of return?
Because if there's not and they are stuffing the lower leaks, the water will simply rise up to the next leak. And then flow out again.

I was asking myself similar questions. It makes sense only, if another outlet for the water fed in is provided. The water balance of the plant is not something I've followed closely, but I do remember reading repeatedly, that some of the water taken out from the current outlets are returned to the reactors. Early in the water clean-up operation, I got the impression that the water taken out from the T/B basements were divided: partly to be sent back to the reactors, partly to be processed by Sarry and stuff, as and if capacity was provided. Currently, my impression is that some of the processed water is being returned to the reactors.

-----------------

On a different note: So they are pouring water on top of the damaged/molten fuel. Several tons an hour, since over a year. And all that water's flowing out into the basement, new water enters the containment, flows out, and so on. For over a year. Doesn't that necessarily mean that every single soluble radioactive particle which isn't still protected by a crust of molten fuel is gone, being distributed in the basement?

It would seem that much of it has been distributed. However I think such a material would be subject to significant erosion, which would give way for continued dissolution.
Yikes :-), now you've got me wondering how the contamination of the water in the R/B basements compares to that of the T/B basements and further downhill.

 

[Tepconium-311]

Currently, my impression is that some of the processed water is being returned to the reactors.

Seems correct.
Every TEPCO Daiichi plant status report contains this passage:

Others
- At around 10:00 am on June 13, 2011, we started the operation of the circulating seawater purification facility installed at the screen area of Unit 2 and 3.
- At 8:00 pm on June 17, 2011, we started operation of Water Treatment Facility against the accumulated water. At 6:00 pm on July 2, we started the circulating injection cooling to inject the water, which was treated by the accumulated water treatment system, to the reactors through the buffer tank.

Simply check latest Tepco News to verify.
However this doesn't exclude other water or additives (boron) potentially being added to cooling water.

Yikes :-), now you've got me wondering how the contamination of the water in the R/B basements compares to that of the T/B basements and further downhill.

Let's praise TEPCO for wise decision to isolate both basements from each other.
(see Tsutsuji's posts on previous page).

 

[tsutsuji]

Or perhaps they think it might affect the water level in the drywell somehow.

I think there are two cases.

A) The leakage point is located lower than the present torus room water level

The leakage rate would depend on the difference of height between the drywell water level and the torus room water level. In this case, lowering the torus room water level would be a bad idea, because the leakage flow rate would increase, and this would affect the water level in the drywell (if the injection rate into RPV is kept constant).

B) The leakage point is located higher than the present torus room water level

The leakage rate would depend on the difference of height between the drywell water level and the leakage point. In this case, lowering the torus room water level would not affect the leakage rate nor the drywell water level.

So I think it would be good to install a water level gauge in the drywell, and perform the torus room drainage with an eye on the water level gauge. If the drywell water level starts decreasing, you know that you are in the wrong case and you must stop what you are doing. At least you learned something : you learned that you are in case A).

You may want to consider the present 60 cm above PCV bottom as a minimum that must be kept. To create a margin, you could increase the RPV injection rate until the drywell water level rises to 70 cm above PCV bottom.

If this water was not badly contaminated, you may have wanted to try to do the opposite: to raise the torus room water level, and see if it affects the drywell water level.

 

[MadderDoc]

<..>
We know for sure the hardened vent system is a totally separate system all the way to the stack. Early on (but post construction of this type of reactor unbelievably) it was found the SGTS would be inadequate and fail inside the RB during a high pressure venting scenario, filling it with steam and gases. So the hardened vent system was a retrofit to address this issue. <..>

Thanks a lot for your input.

I am not sure the hardened vent is a totally separate system at these plants. From what Tepco has said, such retrofits were indeed made to the plants. Also it would seem implied by what Tepco has said, that these vent lines were used for the PCV ventings. However, Tepco has speculated that the Unit 1 PCV vent might have back-flowed into the Unit 1 R/B through its SGTS piping, causing the explosion. And Tepco has more than speculated that Unit3 PCV vent back-flowed into the Unit4 SGTS system. Either of these theories by Tepco implies that the PCV vent lines and the SGTS lines are not separate all the way to the stack, and it would be implied that the SGTS lines were either not protected by back-flow valves (seems to be the case of Unit 1) or the back-flow valve had failed open when power was lost (units 2-4). (All the SGTS systems were presumably operating per automation from shortly after the earthquake, and until power was lost.)

 

[tsutsuji]

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02m.pdf Scattered debris survey plan (28 March 2012 mid-long term steering committee meeting)

[page 2]

Purpose

To perform a survey, checking whether debris spread by the hydrogen explosions are staying in the electric power plant premises.

Survey method

Explore regions of the premises starting at the center where units 1~4 are located, and going toward monitoring posts MP1~MP8. (As the first 500 m closest from center have already been explored and the debris there have been collected, they are excluded)

[page 3]

Definition of the debris that are the object of the survey

* Shape: solids (building rubble) like small stones or bigger that can be checked by visual observation
* Radioactivity, radiation dose: high radioactivity, high radiation dose objects that depart from background (BG)

Scattered debris determination standard

* When a debris is discovered, it is measured with a surveymeter (Geiger tube, ionization chamber). BG is also measured.
* If the measured value is higher than BG, the object is judged to be a scattered debris.

System

* Leader : 1 person, survey: 4 groups of 3 people (total 13 people)

Draft schedule

* 26 March 2012 ~30 March 2012 (2 April ~ 6 April is reserved in case of rain)

planned exposure

* Below 1 mSv/person.day

[page 4]

Fukushima Daiichi premises general layout map

Recording method
In case building debris scattered material is discovered, the discovery location is marked on a map. [Computing] the distance from units 2 and 3 reactor buildings with the premises layout map CAD system, the maximum scattering distance is measured and a map of the scattering area is generated.

[see also the map on page 4:]
red=plant boundary
yellow=scattered object survey directions
red dots=500 m range where scattering was confirmed

 

[tsutsuji]

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02x.pdf Results of survey of debris distribution in spent fuel pool, unit 4 (28 March 2012 mid-long term steering committee meeting)

[page 2/8]
1. Survey of debris distribution in unit 4 spent fuel pool
same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120312_01-e.pdf page 1

[page 3/8]
2. Outline of survey of debris distribution in unit 4 spent fuel pool
same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120312_01-e.pdf page 2

[page 4/8]
3. Result of survey of debris distribution in unit 4 spent fuel pool (19 ~ 21 March)

[page 5/8]
4. Outline of survey of debris at the bottom of unit 4's reactor
same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120312_01-e.pdf page 2 except "(if
necessary, we will use ROV)" which was deleted.

[page 6/8]
5. Result of the survey of debris at the bottom of unit 4's reactor
The diagram is the same as the one on http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120312_01-e.pdf page 4

[page 7/8]
6. New transparency check inside unit 4 spent fuel pool (20 March)

1. Checking method
At almost the same location as the last time (9 February), using the same camera, the same wire and marks, the visibility distance is measured.

2. result
Visibility was comparable with that of February 9. Therefore, we conclude that there
has been no change in the degree of transparency.

[The diagram does not require a translation as it is almost the same as the one on http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120210_03-e.pdf except that the man is now standing on the float, the fuel handling machine is not shown, and the spent fuel is not shown.]

[page 8/8]
7. Result of the transparency check inside unit 4 spent fuel pool (20 March)
same as http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120322_02-e.pdf

 

[tsutsuji]

http://www.meti.go.jp/earthquake/nuclear/pdf/120328_02d.pdf plant status (28 March 2012 mid-long term steering committee meeting) [only partial translation]

[page 1/6]
[A table displaying the plant parameters on 26 February and 27 March]

As unit 1, unit 2 and unit 3's PCV temperatures and RPV temperatures are around 25°C ~ 55°C (as of 27 March), there is no significant variation of RPV and PCV parameters such as the released radiation doses, and we judge that the cold shut down status is comprehensively maintained.

In order to maintain the measuring instruments' soundness in the future, while the surveillance with measuring instruments is continuing, a study toward diversification and implementation of alternative temperature surveillance means is under way.

[page 2/6]

[page 6/6]

 

[tsutsuji]

http://weather.goo.ne.jp/earthquake/12040123040.html There was a magnitude 5.9 earthquake off the Fukushima coast on 1 April 2012 at 23:04 JST. JMA seismic intensity scale　"5 minus" was recorded at Tomioka and Naraha, Fukushima prefecture. There is no tsunami risk.

http://www3.nhk.or.jp/news/html/20120401/k10014131781000.html The NISA said that no problem was reported from Fukushima Daiichi or Daini (in consequence of this earthquake). Monitoring post radiations are stable.

 

[hellbet]

Interesting scenes from TEPCO's video related to ocean monitoring of sea life in 20 km

Background plant looks like Hirono Power Plant (Fuel + Coal Plant) which is 10 Km South of Daini and 20 Km South of Daiichi; the 2 largest units on the middle are 1000 MWe and others are 600 MWe.

http://toolserver.org/~geohack/geoh...n&params=37_14_18_N_141_01_04_E_type:landmark

Dark smoke looks quite normal so Doom is off ;)

 

[MadderDoc]

The implementation of the common pipe to the stack from the SGTS and the hardened vent system includes a diving section just before the vent pipe enters the stack. It can be seen as a foo or a feature to have what is essentially a a water trap incorporated in such a system. On one hand it might provide additional scrubbing during a hardened vent procedure -- otoh it might also provide increased back-pressure, and increase the risk of diverting the flow of the vented gases back into the buildings through the SGTS system.

 

[tsutsuji]

http://www.tepco.co.jp/cc/press/betu12_j/images/120402j0101.pdf Report to NISA on units 1 ~ 3 thermometer reliability. (the NISA requested Tepco to write a report once a month) : some of the thermometers not previously evaluated were found to be usable, and some were found to be broken. Some thermometers that were not connected to a digital recorder have been connnected to a digital recorder.

According to the plot on page 126, unit 2's 69 TE-16-114L#2 RPV BELLOWS SEAL AREA, newly connected to a digital recorder (on 8 March 2012) reached 100°C on 19 March 2012. (but it is not marked as "broken"). TE-16-114L#1 is having a similar rising trend, reaching 83°C on 19 March 2012. I will be curious to see if those two are marked "broken" in next month's report.

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20120403/k10014177241000.html Because strong winds of 18 metres [per second] are expected, outdoor work with cranes is suspended at Fukushima Daiichi on 3 April afternoon. Crane arms have been made shorter. Sheets covering debris have been reinforced with weights and ropes.

 

[biggerten]

http://www3.nhk.or.jp/news/html/20120403/k10014177241000.html Because strong winds of 18 metres [per second] are expected, outdoor work with cranes is suspended at Fukushima Daiichi on 3 April afternoon. Crane arms have been made shorter. Sheets covering debris have been reinforced with weights and ropes.

About 40mph, for those of us counting on our fingers and toes.

 

[tsutsuji]

http://sankei.jp.msn.com/region/news/120403/fks12040320560003-n1.htm Unit 1's cover is designed to withstand winds up to 25 m/s. According to Tepco, in the case of winds stronger than the limit for unit 1's cover, the cover could be totally displaced by the wind and hit the building, but it was designed so that the load would be distributed and the building would not collapse or be damaged.

 

[clancy688]

Isn't that only Beaufort 10?

What's with the occasional typhoon? According to wikipedia, a typhoon's a storm with wind speeds of at least 118 km/h+ - which's 33.8 m/s. Everything below is a "severe tropical storm" or less. So even the weakest typhoon would already overstrain the construction by 35%.

Isn't Japan a country which's being hit by typhoons fairly often? Wasn't there a typhoon hitting Fukushima last year? So how big are the chances for the construction of being exposed to wind speeds it wasn't designed for?

 

[zapperzero]

So how big are the chances for the construction of being exposed to wind speeds it wasn't designed for?

I can't seem to find open-source analysis. Here's an extended abstract of some research paper:
http://ams.confex.com/ams/pdfpapers/137995.pdf

 

[MadderDoc]

Everywhere I read says the complete inventory of noble gases was released from the reactors in the early phase of the accident.

But if so, why does Kr-85 still linger in unit 2?
Recent measurements at inlet of Unit 2 PCV Gas Control System:
28 March 2012 : 73 Bq/cm³
03 April 2012: 97 Bq/cm³

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120404_01-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120329_01-e.pdf

Could it be an effect of continuing fuel damage?

 

[zapperzero]

Could it be an effect of continuing fuel damage?

Well, some small proportion of the fuel fissions spontaneously, no? Same story as with the earlier detection of Iodine and Xenon.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120405/1450_12ton.html At 1:50 AM on 5 April it was found that water was leaking from a pipe connected to the tanks where the water is stored after removing cesium. The leak stopped at 02:20 AM after closing a valve. It is thought that much of the 12 tons of water that leaked and include high concentrated strontium, have flowed to the sea. Tepco is investigating why the pipe junction failed and the quantity that flowed to the sea.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120405_03-j.pdf diagram, pictures about this leak

 

[Yamanote]

Is there any detailed listing of all the radionuclides and their concentrations in the water from the reactor buildings available? I haven't seen one yet.

 

[MadderDoc]

A comparison of survey photos of the top of fuel racks in the spent fuel pool of unit 4, with the IAEA's map of assembly decay heat activities in the pool strongly suggests that the precipitation that has formed on top of the tie plates has been shaped by the magnitude of the decay heat of each individual assembly. On top of low activity assemblies, a uniform layer appears to have developed, with only few perforations over the water tubes. On higher activity assemblies a similar layer appears to have formed, but it tends to have been cracked up and/or blown away. Here illustrated with the comparison for rack no. 22:

A similar photo mount for rack no 09, and the original IAEA activity map of the racks are attached (as shown in this map, the racks are numbered from 00 upwards, proceeding from the lower left to the upper right).

 

[Cire]

A comparison of survey photos of the top of fuel racks in the spent fuel pool of unit 4, with the IAEA's map of assembly decay heat activities in the pool strongly suggests that the precipitation that has formed on top of the tie plates has been shaped by the magnitude of the decay heat of each individual assembly. On top of low activity assemblies, a uniform layer appears to have developed, with only few perforations over the water tubes. On higher activity assemblies a similar layer appears to have formed, but it tends to have been cracked up and/or blown away. Here illustrated with the comparison for rack no. 22:

A similar photo mount for rack no 09, and the original IAEA activity map of the racks are attached (as shown in this map, the racks are numbered from 00 upwards, proceeding from the lower left to the upper right).

This make sense. Hotter assemblies have induced thermals that carry away the lighter silt that has settled on them.

 

[MadderDoc]

This make sense. Hotter assemblies have induced thermals that carry away the lighter silt that has settled on them.

Yeah. While on the colder assemblies those thermals were weaker, so a layer of silt could well settle on them. Under the hypothesis that what we see is the sole result of preferential sedimentation on colder parts , we would predict the rack frames and the number tags on the racks to be all covered by silt, wouldn't we?

 

[tsutsuji]

A comparison of survey photos of the top of fuel racks in the spent fuel pool of unit 4, with the IAEA's map of assembly decay heat activities in the pool

Hello,

Would you be so kind as to provide links to the source documents where you found the photos and the "IAEA map of assembly" ?