Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Sotan]

A short presentation of another PDF document from the October 1st update of the Mid and Long Term Roadmap on Tepco’s sit, referring mainly to the spent fuel pools
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d151001_07-j.pdf
(in Japanese)

Progress in removal of large debris from the spent fuel pool of Unit 3

Page 5: diagram of the main steps carried out until now and future schedule. Main issues at the moment: placing of further protective panels over the spent fuel racks and removal of the “cover/lid of the CUW F/D hatch”. Intensive work is under way, with a lot of (most of?) the debris to be removed until the end of November.
- Google informs me that this CUW F/D hatch must be related to the “Reactor Water Clean Up System (CUW)”
(http://www.hitachi-hgne-uk-abwr.co.uk/downloads/UKABWR-GA91-9901-0032-00001-Rev2_P-Ver.pdf)

Page 6: Drawing as of Sep 21 showing the placement of protective panels over the fuel racks and the position of the CUW F/D hatch lid.

Page 7 presents the schedule again.

Pag 8 refers to the incident of Sep 3 during preparation work for the removal of the CUW hatch lid. A pressure hydraulic hose of the steel cutting machine got stuck around the handle of a protective panel, which led to the twisting/loosening of a hose connector and to an oil leak. The oil spread over the surface of the SFP but was controlled using the installed oil barrier/fence.

Pages 9 - 11 show the analysis of the incident, causes and corrective measures for the future. The two types of protective panels have different geometries, the height of the “handle” part is different, they didn’t pay enough attention to the risk of some hydraulic hose touching or becoming entangled to certain parts of the panels already placed in the pool. They will consider these things more carefully, and moreover they will strengthen the inspection of the tools used for cutting/handling the debris.

Page 12: Procedure for removing the CUW F/D hatch lid (1/2)
1 – sweep away small concrete debris from the top of the hatch lid
2 – remove pieces of concrete debris from around the hatch lid
3 – slowly lower the special device built for the purpose of lifting the hatch lid
4 – “encapsulate” the lid in the special device and fix it using 4 hydraulic cylinders, and then lift it up.
The last photo shows the concrete debris mentioned in steps 1 and 2 and the metallic handles envisaged to be used for lifting the lid.

Page 13: Procedure for removing the CUW F/D hatch lid (2/2)
5 – bring the lid to a horizontal position and place it temporarily on a rack protective panel
6 – attach some supplementary anti-drop wires to the lid, then lift it out of water and remove it from the SFP.

Page 14: Mockup trial
- Mockup was built at real size and weight and used to verify the procedure. The hydraulic cylinders can be seen in one of the photos.

Pag 15: Explanations about the CUW hatch
There seem to be 2 of them, South of the SFP (red squares in the first drawing).
The lid to be lifted in this operation is the one marked with the curvy red line.
The lid measures approx. 1 x 1 x 2m and weighs about 2.6 tons.

Page 16: Explanations of the specially designed device to be used for lifting the hatch lid
- It has two lifting "eyes", A for the initial lifting and B for bringing the hanging lid to a horizontal position

Page 17-21: areas of operating floors of Unit 1 and 3 to be sprayed with dust-fixing resine, once a months, over 1.5 liters per square meter. Schedule of this operation and so on.

Page 22: removal of the roof of Unit 1 Reactor Building.

Page 23: work done recently on the operating floor of Unit 3 (decontamination, debris removal etc)

Page 24: number and location of the spent nuclear fuel stored in the Fukushima Daiichi plant.

(end)

 

[Hiddencamper]

Holy dang those reactor water cleanup shield plugs are sideways!

 

[Sotan]

What does that mean, Hiddencamper?
What happened there (if you can speculate) and what are the implications.

 

[Hiddencamper]

What does that mean, Hiddencamper?
What happened there (if you can speculate) and what are the implications.

I'm just trying to figure out how those shield plugs got lifted. Those are very heavy. Was the hydrogen explosion that violent?

I don't know if the reactor water cleanup system isolated or not following the initial LOOP. It probably did, but if they didn't then those filter rooms and the heat exchangers would be in direct communication with the now broken bottom head of the vessel and the recirc loops.

 

[Sotan]

Well, Unit 3 did have the most violent explosion of all - at least it seemed so...
Old video, just to illustrate:

 

[cockpitvisit]

Is TEPCO still pumping water into any of the reactors? We are now 4.5 years away from the accident, so the residual heat should be very low now (IIRC, spent fuel can be put into dry casks after 5 years).

 

[Hiddencamper]

I'm assuming they still are.

At this point the water is for direct radiation shielding and for contamination control more than heat removal.

 

[Bandit127]

In addition, the reconfigured cores will:
Not necessarily follow the "normal rules" for the decay of decay heat so be somewhat unpredictable, certainly outside regulations for active/passive cooling timescales that would apply to neatly ordered and stored fuel rods.
Not be in a reliably measurable depth of water.

I suspect that pumping of water will need to continue until they can characterise the cores and positively work out that it is safe to stop.

 

[eXorikos]

Is TEPCO still pumping water into any of the reactors? We are now 4.5 years away from the accident, so the residual heat should be very low now (IIRC, spent fuel can be put into dry casks after 5 years).

They can be placed in dry storage after 3 years. This depends on the cask type and filling.

 

[etudiant]

Seen that the cores have turned into blobs somewhere beneath the reactors, the current heat production of the fuel may be very different from normal.

 

[nikkkom]

And also, bureaucrats would prefer to not change things, than change things and get the blame for any resulting change. In bureaucrat's logic, if entire building rusts through because of water, the blame goes to whoever started water injection program, not to people who could have stopped it years later, but did not.

 

[Rive]

Seen that the cores have turned into blobs somewhere beneath the reactors, the current heat production of the fuel may be very different from normal.

Due the already removed amount of Cs and such water-soluble stuff, the overall heat production is surely lower than 'normal'.
However, the surface of the stuff might be much lower than necessary to remove that heat on free air, at acceptable temperature.

 

[etudiant]

The bulk of the water inflow into the site currently is groundwater, afaik. Sadly that suggests that rust is inevitable, even if injections are ended.
It may be that TEPCO hopes to transform the situation once the ice dam is fully in place. That might then allow the site to be drained and dried if necessary.

 

[Sotan]

From the most recent "handout" about the plant situation, periodically published by Tepco (this one is from Oct 16; in Japanese)
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151016_10-j.pdf

Unit 1, water pumped in: 2.5 m3/h by (main?) water lines; 1.9 m3/h by core spray system. PCV lower region temperature: 25.6 degrees Celsius
Unit 2: 1.9 m3/h and 2.4 m3/h, respectively; 31.5 degrees Celsius
Unit 3: 2.0 m3/h and 2.4 m3/h respectively; 29.9 degrees Celsius.

 

[Sotan]

Also another report is out regarding the visual inspection after the removal of the CUW F/D shield plug from of Unit 3 SFP - mentioned in earlier posts (2 page PDF file, in Japanese)
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151016_08-j.pdf

The 2.6 ton concrete shield plug was removed on Oct 15.
A video camera was lowered then in the water to check the 4 fuel bundles that were under the displaced shield plug.
2 of these fuel bundles were found to have slightly bent handles. Check the photos on page 2 - red circles=bent handles, white circles=normally shaped handles.
The amount of rubble is again impressing, as is its missing from the region where the concrete shield plug had been sitting.

 

[etudiant]

It is surprising that TEPCO is still pumping in so much water, more than 4 m3/hr in all three cases. TEPCO engineers could get a pretty reasonable fix on the residual heat generated by the fuel by suspending/reducing injections and then looking at the rate at which the temperature rises in the lower PCV .
Presumably this has been done, even though the results have not been made public.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151020_07-j.pdf
(in Japanese)

An investigation was carried out yesterday into the PCV of Unit 3.

Page 2: A pan-tilt camera, a CCD camera, a radiation meter and a thermometer were inserted into the PCV through the X-53 penetration, then down along the PCV wall.

Page 3: Results from the pan-tilt camera and radiation meter
- No visible damage was observed on structural elements inside the PCV (such as RHR piping, PCV internal lighting elements, electric cabling, D/W spray sparger).
- Radiation measurements in air indicated about 1 Sv/h right near the PCV wall and about 0.75 Sv/h at 550 mm away from the exit of X-53 penetration, inside the PCV.

Page 4: Results from the pan-tilt camera and radiation meter. Photos.
- Left: D/W spray sparger
- Middle: RHR piping and PCV wall
- Right: PCV internal lighting

Page 5: Results from the pan-tilt camera and radiation meter. Photos.
Up-left: A view downwards toward the "inspection platform". The water surface can be seen.
Up-right: RHR piping
Below: Shielding support on the inspection platform

Page 6: Results from the CCD camera and thermometer
- The space between the 1st floor grating and the PCV wall is narrow and obstacles are present. Therefore the investigation went only down to 1st floor grating.
- The investigated portions of the PCV wall did not display visible damage.
- The two photos on the upper row show images of the PCV wall (regions depicted as "a" and "b" in the left-side diagram)
- The photo below shows the region "b" and the narrow space between the 1st floor grating and the PCV wall.

Page 7: Results from the CCD camera and thermometer
- Preliminary results on the water level in the PCV: water surface was confirmed to be somewhere around the upper level of the inspection platform - thus roughly matching previous assumptions (OP ~ 12,000)
- Temperature in air was 26-27 degrees Celsius; temperature in water was 33-35 degrees Celsius.
- The temperature was measured in 7 places (along the red line in the diagram), from the exit of X-53 penetration down to the 1st floor grating.
- It wasn't possible to insert the camera lower beyond the 1st floor grating.

Page 8: Conclusions (everything here was already mentioned above).

Page 9: Schedule from now on.
On October 21 a device will be inserted for taking water samples.
More pan-tilt camera investigation and water samples will be taken on Oct 22 and also possibly on 23 and 26.

Edit: There is also a 2min32s, 88 Mb film which I can't see on this computer, you can find it here:
http://photo.tepco.co.jp/date/2015/201510-j/20151020-01j.html

 

[Hiddencamper]

It is surprising that TEPCO is still pumping in so much water, more than 4 m3/hr in all three cases. TEPCO engineers could get a pretty reasonable fix on the residual heat generated by the fuel by suspending/reducing injections and then looking at the rate at which the temperature rises in the lower PCV .
Presumably this has been done, even though the results have not been made public.

That's only about 17 gallons per minute. Pretty low, well below what I would expect for water cleanup operations.

 

[etudiant]

Very true, but afaik it is essentially the same rate as has been in effect for the last several years. I'm surprised that there has not been more change since 2011.

 

[Sotan]

I remember reading, long time ago, on other sites how some people believed that the explosion that took place at Unit 3 was not a hydrogen explosion, but rather some sort of "nuclear blast", "atomic explosion" and I think I saw some other terms used as well. Many other people tried to debunk that theory, with more or less success, as it happens in such cases.

I don't think that theory has many adepts left, but I was thinking that these findings from the lower PCV of Unite 3 are good proof that such a thing did not happen. The destruction seen in the building - the walls and roof blown away, the FHM, the dislocation of the large concrete shield plugs from the SFP, on one side, and things like lighting fixtures remaining rather intact in the PCV on the other side, indicate to me that the explosion happened in the building, and the interior of the PCV was actually protected from the explosion. I suppose if the PCV is designed to keep stuff in when things go wrong, it works as we; when the things go "bang" outside of it.

Like everybody else, I can't wait until we get more solid information regarding the state of the fuel in the 3 reactors.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151022_04-j.pdf
(in Japanese)

Continuation of the investigation in the PCV of Unit 3

Page 1: This is a quick report on the activities carried out on Oct 22.
They were aiming to take water samples and to evaluate the corrosion inside of the PCV (based on pH, conductivity, salt content). Also to check the access routes (vicinity of X-6 penetration; 1st floor grating; CRD rails) for the investigation of the pedestal area.

Page 2: Using the pan-tilt camera of the water sampling device they checked some immersed structures from the inside of the PCV (electric cables, supporting structures, X-6 penetration, CRD rails) and, as far as they could see, no damage was observed. Some "sediments" ("Deposits") were confirmed on the CRD rails and on the 1st floor grating (see photo 3).

Page 3: Conclusions
- Two samples of water (800 ml each) were taken, one from right near the surface (about 10 cm below surface) and one from a little deeper (about 70 cm under the surface).
- No damage on structures
- Deposits on the CRD-rails and grating
- No obstacles that might cause trouble on the installation of measurement instruments in the PCV.

Page 4: Schedule
Mock-up work will be done throughout November
In late December some measuring instruments are scheduled to be installed in the PVC.

Film (92.4 Mb) available here:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=e1x74582&catid=69619

 

[Hiddencamper]

Another thing to consider:

The drywell was inserted with nitrogen during operation specifically to prevent an explosion wholly inside the containment.

Temperature and pressure went up in containment with no drywell cooling. This would prevent air Inleakage, as drywell pressure would be greater than outside air.

When the hot debris ejection occurred, any remaining steam inventory would have further raised pressure.

My guess is a penetration finally failed or the drywell head burped as a result of the debris ejection. Alternatively, water injection attempts may have introduced oxygen as air was purged through feed lines. Either way, not enough info yet.

 

[Most Curious]

Another thing to consider:

The drywell was inserted with nitrogen during operation specifically to prevent an explosion wholly inside the containment.

Temperature and pressure went up in containment with no drywell cooling. This would prevent air Inleakage, as drywell pressure would be greater than outside air.

When the hot debris ejection occurred, any remaining steam inventory would have further raised pressure.

My guess is a penetration finally failed or the drywell head burped as a result of the debris ejection. Alternatively, water injection attempts may have introduced oxygen as air was purged through feed lines. Either way, not enough info yet.

I missed something along the way. WHAT "hot debris ejection"?? Are you referring to the melt through of the fuel through the bottom of the reactor vessel or something else??

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151026_04-j.pdf
Tepco report (in Japanese) regarding the inspection of the big "exhaust tower" of Units 1-2.

(They found cracks and shape deformations here and there, but they conclude that it still has sufficient resistance in case of earthquake.)
But what I want to point out here are the new results of radiation measurements.
Page numbered 16 shows values of radiation measured in September 2015 - compared to results obtained in August 2011, in the areas where the "SGTS pipes" connect to the exhaust tower. (Standby Gas Treatment System "through which steam was vented to relieve reactor pressure during the accident in March 2011" - quoting from a source found through Google, http://www.world-nuclear-news.org/RS_Second_high_radiation_reading_308112.html)

From over the scale values (>10,000 mSv/h) in 2011 - down to 2,000 mSv/h today. But, still, so high...

 

[Hiddencamper]

I missed something along the way. WHAT "hot debris ejection"?? Are you referring to the melt through of the fuel through the bottom of the reactor vessel or something else??

In the BWR owners group severe accident guidelines, A debris ejection is the specific moment when the vessel melts through. It is industry lingo. A Hot debris ejection is when the melt through happens while the vessel is pressurized and results In a pressure boundary rupture.

BWR EOPs direct blowing down the reactor to depressurize it after you lose adequate core cooling for many reasons, one of which is to prevent a hot debris ejection which can damage the containment. Typically by the point you get to a debris ejection occurring, the containment is already at or over its heat capacity limit, meaning a hot debris ejection will result in exceeding containment's analyzed conditions.

Units 1 and 2 were not depressurized prior to the debris ejection. Unit 3 did have its ADS (automatic depressurization system) have an invalid actuation (logic circuits worked right, plant conditions weren't right, suppression pool pressure was so high that it pressure up the ECCS injection headers and tricked the ADS logic into thinking the ECCS pumps were running) and was at a reduced but not depressurized state when the core rupture occurred. I don't know the details but I suspect not enough relief valves opened to allow the core to fully depressurize. Typically for dual function SRV BWRs, you need at least 5 ADS SRVs to get pressure down with 10 minute post scram decay heat.

For reference: the ADS logic
Low level 3 plus low low low level 1 water level signals, a high drywell pressure signal, a 105 second time delay, and a check that at least one ECCS pump has sufficient discharge pressure. The logic is 2 out of 2 twice (two channels, two divisions, either division can actuate the ADS). Some plants removed the high drywell signal or put a bypass timer on it to ensure adequate core cooling for small break LOCAs or loss of feedwater events with no operator action. The level 3 signal and 105 second timer are only installed on one channel per division. The operator can inhibit the 105 second timer from starting, can reset the 105 second timer (annoying as hell having to hit the reset every 105 seconds), or can manually actuate the logic even if none of the permissive are made up.

 

[Most Curious]

Thank you Hiddencamper for the explanation! I suspected it had to do with the melt through but having not been exposed to the BWR owners group did not know the correct definition of the term. The additional info was very welcome as well.

 

[jim hardy]

I remember reading, long time ago, on other sites how some people believed that the explosion that took place at Unit 3 was not a hydrogen explosion, but rather some sort of "nuclear blast", "atomic explosion" and I think I saw some other terms used as well. Many other people tried to debunk that theory, with more or less success, as it happens in such cases.

i'm guilty of thinking that , and of suggesting it.
From the sheer size of the explosion, coupled with reports of high radiation readings accompanying it, i thought it must have been a small excursion with steam explosion. This, one of the few early views of 3, had me convinced there was a hole in the operating deck over the reactor.

Later pictures that are more clear show the plug in place with a crane laying on it.
The preponderance of evidence says the energy for explosion was hydrogen (chemical not nuclear).

Still, i'd like to see the top of the reactor vessel particularly around the head closure bolts. Its being in place should remove even unreasonable doubt.

..........................

Unrelated question to you BWR guys - do you use much hydrazine for O2 scavenging?

 

[Hiddencamper]

i'm guilty of thinking that , and of suggesting it.
From the sheer size of the explosion, coupled with reports of high radiation readings accompanying it, i thought it must have been a small excursion with steam explosion. This, one of the few early views of 3, had me convinced there was a hole in the operating deck over the reactor.

View attachment 90975

Later pictures that are more clear show the plug in place with a crane laying on it.
The preponderance of evidence says the energy for explosion was hydrogen (chemical not nuclear).

Still, i'd like to see the top of the reactor vessel particularly around the head closure bolts. Its being in place should remove even unreasonable doubt.

..........................

Unrelated question to you BWR guys - do you use much hydrazine for O2 scavenging?

Jim I recommend taking a look at Ian Goddard's video and webpage about this for unit 3. http://iangoddard.com/fukushima01.html

Couldn't find the video link directly but he has one on this. (Here is the video )

The BWR mark I containment has a known issue where high pressure excursions can cause the drywell head seals to give way and the head to momentarily lift to create a release path. This was known in the 70s and I believe is part of what lead the US to require a vent system for the drywell.

Ian's evidence points to a drywell steam release triggered by the hot debris ejection.

Furthermore, millstone and Brunswick have both had some type of drywell head lift/leakage during containment type A pressure testing (can google this).

And as much as I hate the site, Goddard pointed me to this: http://www.fukuleaks.org/web/?p=10740
As far as I know BWRs use nitrogen and do a purge of containment. No hydrazine. Push nitrogen in one side, allow oxygen to escape the other, and once oxygen concentration is low enough use nitrogen to maintain drywell pressure to prevent further Inleakage. Let me check though, it's been a while since I've been in a Mark I.

 

[Rive]

The preponderance of evidence says the energy for explosion was hydrogen (chemical not nuclear).

Still, i'd like to see the top of the reactor vessel particularly around the head closure bolts. Its being in place should remove even unreasonable doubt.

I'd say some kind of release paths will be found there, but hose were reasons of the H2 buildup in the building, not the explosion itself.
There were some simulations as I recall, which could account for both the power and direction of the blast only by suggesting H2 buildup in the whole building (even below the top floor).
For me this would suggest a steam/H2 release over a (relative) long period, not only around a specific event.

 

[Sotan]

Anticipating Hiddencamper's surely more detailed answer about the hydrazine:
The handouts released every couple of days by Tepco do mention briefly: "Adding hydrazine to the SFP and reactor well of each unit, appropriately/as needed."
Other documents periodically add the expression "to help prevent corrosion".

-------------
Also I would like to mention that the site of METI presents the English translation of the main document of the release of October 1, namely "Progress Status and Future Challenges of the Mid-and-Long-Term Roadmap toward the Decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station Units 1-4 (Outline)(PDF:5,775KB)".

Link is here:
http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20151001_e.pdf