Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[joewein]

The documents on Tepco's site:
http://www.tepco.co.jp/en/news/110311/
Refer to the the site of the high radiation as:
"Bottom of Main Exhaust Stuck of Unit 1/2 Connection of emergency gas treatment piping arrangement"
And the location of the high radiation inside the No.1 turbine building as:
"Near the entrance of the train room for the emergency gas treatment system."
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110803_01-e.pdf

Does someone have a piping diagram?
It's clear to me how the pipe relates to the reactor #1 building (it skirts around the outside south & east walls), but I am still trying to work out how it relates to the reactor plumbing. Does it come from the wet well? From somewhere in the primary circulation, such as the condenser?

Since the venting system is designed to protect the containment, it must release gas from the dry well and perhaps also the top of the torus. From there it would go to the filter "train", then outside the building along the fat pipe to the stack.

According to a NYT article the hardened venting system doesn't use filters, the regular venting system does.

And what is a "train room"?

They were also using "train" in the sense of several connected filtering systems (like wagons on a train) when talking about the Areva water treatment system. I think the train room holds several filters trough which gas would sequentially pass before being released into the stack.

 

[joewein]

It seems impossible that the solution to a leaking reactor is to vent it directly into the atmosphere. Seriously?

Torus.

Yes, the torus provides some filtering, but only until until it starts boiling, which it eventually will without a working RHR.

Basically, the reactors were not designed to cope with a station blackout and consequently outage of the RHR that went on for more than a couple of hours (unit 1) or a few days (other units).

 

[MadderDoc]

<..>
Does someone have a piping diagram?<..>

(http://www.ansn-elibrary.org/images/c/ca/Boiling_Water_Reactor_Power_Plant.pdf" )

 

[zapperzero]

Units 1 and 2 injection rates are unstable again:
Various troubles at the water treatment facility:

It's amateur hour in there, still. TEPCO should have been relieved of command long ago, they have zero experience with crisis management and it shows. Trouble is, no-one else seems willing to accept the responsibility.

I worry about the "injection rate reductions". It can only mean corrosion and gunk. Keep adding pressure and sooner or later something's going to give. At least, there's no shortage of alternative feed lines to the RPVs for now, thank goodness.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110806/0630_shiunten.html The 700 l leak rang an alarm, after which the facility was stopped for more than 2 hours.

Sorry, my translation above was mistaken. The alarm ringing 2 hour event is the event that started at 2:12 am on August 5. It is a distinct event from the 700 l leak found at 7 PM on August 4. The NHK article was merely listing these two events in a series of events that happened on 4 August and 5 August. Here is the Tepco press release with the sequence of events again :

At 5:32 am on August 4, we stopped Water Treatment Facility to improve the flow rate. After the work, we activated the facility at 3:30 pm and restarted operation of the water treatment system at 4:13 pm. When we adjusted the flow rate of the system at 6:55 pm, a pump of the decontamination instruments was stopped and the whole water treatment system was shut down. We confirmed soundness of the pump and reactivated the system at 8:30 pm, and operation of the water treatment system was restarted at 8:50 pm.

-At 2:12 am on August 5, a process alarm was activated and the water treatment system was shut down. At 4:03 am, the system was reactivated and the operation was restated at 4:21 am.

-Around 7 pm on 8:04, we discovered water leakage from a flange of transfer hose of filtered water which is used to clean up salt in a vessel of the cesium adsorption instruments in the site bunker building.

http://www.tepco.co.jp/en/press/corp-com/release/11080501-e.html

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110806/0630_shiunten.html At 7 AM on 7 August, a pump stopped at the Kurion system, but could not be restarted. At 8 AM on 7 August, a pump mixing chemicals at the Areva system stopped and the backup pump could not be started. As a result, the whole water treatment facility is down.

http://www.jiji.com/jc/c?g=soc_30&k=2011080700068 The Areva system is equipped with 4 chemical pumps. The co-precipitation process is performed twice: once in the upstream system and then once again in the downstream system. Each system has one normal time pump and one backup pump. On 4 August 7 PM, the normal time pump of the downstream system stopped and the backup pump could not be started. It was restarted at 8:30 PM without understanding the cause of the trouble. On 7 August, it is a similar trouble which is happening at the upstream system. While the facility is stopped, Tepco is also investigating the Kurion system pump trouble.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110807_01-j.pdf (not translated into English yet) [7 August 15:31] The water treatment facility was started in order to adjust the chemical pump(s). [7 August 16:11] The evaporation system is started at the desalination facility.

08/4 12:09 During a power connection test to enhance instrument power, a diesel generator (5B) automatically started due to an error signal related to the water level of reactors and we manually stopped it. There was no impact to electric power system.
page 2 http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110806_01-e.pdf

 

[nikkkom]

It seems impossible that the solution to a leaking reactor is to vent it directly into the atmosphere. Seriously?

That's why venting is not done *directly* into the atmosphere, vented gases go through various filters. However, looks like accident safety would benefit a lot from more beefy ones...

 

[htf]

That's why venting is not done *directly* into the atmosphere, vented gases go through various filters.

Now I am totally confused. My conclusion from the long lasting discussion in this thread is, that filtered venting is wishful thinking during severe accidents because the filtering system is undersized and therefore a hardened venting system has been installed, which by-passes the filters. So this means that the filtering system is more or less useless because it can't be used when needed most.

 

[AtomicWombat]

(http://www.ansn-elibrary.org/images/c/ca/Boiling_Water_Reactor_Power_Plant.pdf" )

Thanks MadderDoc. Thanks for the linked document.

Although it's unclear - the document is not well written - the Emergency Gas Treatment System appears to be part of the Stand-by gas treatment system (SGTS).
"Stand-by gas treatment system (SGTS)
The system is composed of exhaust fans, charcoal filters for iodine removal, particle filters of high performance and dehumidifiers. It can start up automatically in case of any such emergency as loss of coolant, etc. and maintain the indoor atmosphere of the reactor building at a negative pressure to check and restrain any emission of radioactivity into the environment."

This seems mostly to relate to the reactor building and probably corresponds to the large duct going to the stack.

I wonder if the smaller pipe - the source of the high reading - is part of a retrofitted "hardened vent". Note this is a high pressure pipe, unlike the ducting.
http://www.gereports.com/venting-systems-in-mark-i-reactors/
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

..., it is recognized that all
affected plants have in place emergency procedures directing the operator to
vent under certain circumstances (primarily to avoid exceeding the primary
containment pressure limit) from the wetwell airspace. Thus, incorporation of
a designated capability consistent with the objectives of the emergency
procedure guidelines is seen as a logical and prudent plant improvement.
Continued reliance on pre-existing capability (non-pressure-bearing vent path)
which may jeopardize access to vital plant areas or other equipment is an
unnecessary complication that threatens accident management strategies.
Second, implementation of reliable venting capability and procedures can
reduce the likelihood of core melt from accident sequences involving loss of
long-term decay heat removal by about a factor of 10. Reliable venting
capability is also beneficial, depending on plant design and capabilities, in
reducing the likelihood of core melt from other accident initiators, for
example, station blackout and anticipated transients without scram. As a
mitigation measure, a reliable wetwell vent provides assurance of pressure
relief through a path with significant scrubbing of fission products and can
result in lower releases even for containment failure modes not associated
with pressurization (i.e., liner meltthrough). Finally,...

The pipe involved does appear to be retrofitted rather than part of the original construction. It weaves its way around other structures in a very untidy, un-Japanese way.

I still don't know the design details - such as whether the venting is automatic on pressure transient & what form of filtering applies.

 

[AtomicWombat]

Hardened vents and filtering. Earlier posts.
https://www.physicsforums.com/showpost.php?p=3308489&postcount=7685
https://www.physicsforums.com/showpost.php?p=3433898&postcount=10763

It does appear hardened vents were implemented in Japan and if the NYT article can be believed, they were unfiltered.

It would appear that - at least for reactor 1 - the hardened vent was opened by the operators at some stage. Given the vast amounts of water added to the reactor, it may well be a direct route for highly contaminated (hot) water from the wet well to the base of the 1/2 stack. The heat would accelerate corrosion, which has been so severe at the join of the pipe and the stack that it has started to leak.

 

[etudiant]

Thanks MadderDoc. Thanks for the linked document.

Although it's unclear - the document is not well written - the Emergency Gas Treatment System appears to be part of the Stand-by gas treatment system (SGTS).
"Stand-by gas treatment system (SGTS)
The system is composed of exhaust fans, charcoal filters for iodine removal, particle filters of high performance and dehumidifiers. It can start up automatically in case of any such emergency as loss of coolant, etc. and maintain the indoor atmosphere of the reactor building at a negative pressure to check and restrain any emission of radioactivity into the environment."

This seems mostly to relate to the reactor building and probably corresponds to the large duct going to the stack.

I wonder if the smaller pipe - the source of the high reading - is part of a retrofitted "hardened vent". Note this is a high pressure pipe, unlike the ducting.
http://www.gereports.com/venting-systems-in-mark-i-reactors/
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html




The pipe involved does appear to be retrofitted rather than part of the original construction. It weaves its way around other structures in a very untidy, un-Japanese way.

I still don't know the design details - such as whether the venting is automatic on pressure transient & what form of filtering applies.

The diagram suggests that the system relies on power to function, at least for the routine operations.
The wet well venting however seems to be direct, with no filtering other than the scrubbing the emissions receive from passing through the suppression pool. If this is correct, the design does not reassure.

 

[MadderDoc]

<..>
I wonder if the smaller pipe - the source of the high reading - is part of a retrofitted "hardened vent". Note this is a high pressure pipe, unlike the ducting.
<..>

A retrofit of "hardened vents" would seem to be what we are told was done during 1999-2001 at the Daiichi plant on page 140 of the "[URL of Japanese Government
to the IAEA[/url]:

"TEPCO built new vent pipes extending from the S/C and D/W to the stacks from 1999 to
2001 as PCV vent facilities during severe accidents as shown in Figs. IV-2-13 and
IV-2-14. These facilities were installed to bypass the standby gas treatment system
(hereinafter referred to as SGTS) so that they can vent the PCV when the pressure is high.
The facilities are also provided with a rupture disk in order to prevent malfunction."

The MO valve, and the small and large AO D/W and S/C valves of that system, also shown in the figures referred to in the text, would seem to be the valves the opening of which the operators according to the Tepco timelines repeatedly had to struggle to achieve during their attempts to vent the containments. The problems seem to have been mainly, that the AO valves were dependent on DC for solenoids in order to stay open, and on air pressure for their actuation, while DC and air pressure due to the accident had become dwindling ressources.

 

[AtomicWombat]

A retrofit of "hardened vents" would seem to be what we are told was done during 1999-2001 at the Daiichi plant on page 140 of the "[URL of Japanese Government
to the IAEA[/url]:

"TEPCO built new vent pipes extending from the S/C and D/W to the stacks from 1999 to
2001 as PCV vent facilities during severe accidents as shown in Figs. IV-2-13 and
IV-2-14. These facilities were installed to bypass the standby gas treatment system
(hereinafter referred to as SGTS) so that they can vent the PCV when the pressure is high.
The facilities are also provided with a rupture disk in order to prevent malfunction."

The MO valve, and the small and large AO D/W and S/C valves of that system, also shown in the figures referred to in the text, would seem to be the valves the opening of which the operators according to the Tepco timelines repeatedly had to struggle to achieve during their attempts to vent the containments. The problems seemed to be mainly, that the AO valves were dependent on DC for solenoids in order to stay open, and on air pressure for their actuation, while DC and air pressure due to the accident had become dwindling ressources.

Are the AO valves fail-open or fail-shut?

In figure Figure IV-2-13 Overview of PCV Venting Facility (Unit 1) on page 154 of your linked document there is only one MO (manually operated) valve in the path to the stack and one rupture disk - presumably set near the wet-well maximum operating pressure.

At 9-11 minutes into this video David Lochbaum says that the operators manually openned the hardened vent valve.


http://vimeo.com/26231562"

 

[SpunkyMonkey]

Perhaps the red-brown stains and http://www.tepco.co.jp/en/news/110311/images/110802_1.jpg":

And there are signs that the reddish-brown gunk was splattered around the base of the stack

Perhaps there's a filter within the stack and was clogged up with cesium-vapor residue and a recent 'belch' from the containment blew out the filter contents. In fact, just after the last 6.5 earthquake there was a small drop in Unit 1 http://www.houseoffoust.com/edano/1pre.bmp" . Then within a day or two this new highest-dose location was discovered. Perhaps that marks the 'belch' that relieved some pressure, dropped the temperature and blew out a congested filter.

 

[robinson]

It makes me wonder how many other reactors are built like that. Maybe Fukushima is a wake up call to actually do something to prevent this sort of thing again.

 

[NUCENG]

Are the AO valves fail-open or fail-shut?

In figure Figure IV-2-13 Overview of PCV Venting Facility (Unit 1) on page 154 of your linked document there is only one MO (manually operated) valve in the path to the stack and one rupture disk - presumably set near the wet-well maximum operating pressure.

At 9-11 minutes into this video David Lochbaum says that the operators manually openned the hardened vent valve.


http://vimeo.com/26231562"

Normal usage
MO = motor operated
AO = Air Operated (pneumatic)
V = manual operated

 

[MadderDoc]

Are the AO valves fail-open or fail-shut?

The AO valves would be fail-shut.

In figure Figure IV-2-13 Overview of PCV Venting Facility (Unit 1) on page 154 of your linked document there is only one MO (manually operated) valve in the path to the stack and one rupture disk - presumably set near the wet-well maximum operating pressure.

Yes, that all seems consistent with the testimony/evidence of the reports.

At 9-11 minutes into this video David Lochbaum says that the operators manually openned the hardened vent valve.
http://vimeo.com/26231562"

I get from the testimony, that the operators on preparation of the vent procedure found that the MO-valve (Motor Operated) was designed such that it was possible to operate it manually, whereas the AO valves (Air Operated) could be operated only remotely using air pressure, not manually. In order to make a functioning vent line, they needed to open the MO valve, while keeping open either or both of the two AO valves. Once this configuration had been lined up, and as long as it could be kept lined up, actual venting would be triggered at the set value of the rupture disc.

 

[AtomicWombat]

I get from the testimony, that the operators on preparation of the vent procedure found that the MO-valve (Motor Operated) was designed such that it was possible to operate it manually, whereas the AO valves (Air Operated) could be operated only remotely using air pressure, not manually. In order to make a functioning vent line, they needed to open the MO valve, while keeping open either or both of the two AO valves. Once this configuration had been lined up, and as long as it could be kept lined up, actual venting would be triggered at the set value of the rupture disc.

Thanks MD, I've lost track of events. Do you have a link for the testimony?

Is it known if the "hardened vent" is still open?

 

[joewein]

Perhaps the red-brown stains and http://www.tepco.co.jp/en/news/110311/images/110802_1.jpg":

And there are signs that the reddish-brown gunk was splattered around the base of the stack

Perhaps there's a filter within the stack and was clogged up with cesium-vapor residue and a recent 'belch' from the containment blew out the filter contents. In fact, just after the last 6.5 earthquake there was a small drop in Unit 1 http://www.houseoffoust.com/edano/1pre.bmp" . Then within a day or two this new highest-dose location was discovered. Perhaps that marks the 'belch' that relieved some pressure, dropped the temperature and blew out a congested filter.

I'm sorry, that stuff still looks like rust to me. The horizontal pipe running right below the brown pipe elbow looks clean closest to the most stained portion of the elbow. That does not look like a high pressure cesium leak to me.

If you look at a http://www.tepco.co.jp/en/news/110311/images/110805_1.jpg", it looks like it was wrapped with some kind of tape, perhaps to protect it against corrosion. The brown stuff seems to have leaked out from underneath the tape. Perhaps the tape trapped moisture, allowing rust to fester underneath. The vertical brown lines are consistent with rust getting washed down by rain.

Below where the elbow connects to the stack is where the brown colour is the deepest. There should have been a lot of condensation at the bottom of the stack, with air from inside two buildings containing pools getting vented through here, especially when it's cold outside. Who knows how far the corrosion went there... The deepest stain may have been where runoff from the outside of the rounded pipe collected.

Is it known if the "hardened vent" is still open?

If the air-operated valve is fail-shut then it would only have staid open if compressed air had been fed to it for 4 1/2 months. So I wouldn't have thought so, unless something malfunctioned.

 

[AtomicWombat]

Perhaps the red-brown stains and http://www.tepco.co.jp/en/news/110311/images/110802_1.jpg":

And there are signs that the reddish-brown gunk was splattered around the base of the stack

Perhaps there's a filter within the stack and was clogged up with cesium-vapor residue and a recent 'belch' from the containment blew out the filter contents. In fact, just after the last 6.5 earthquake there was a small drop in Unit 1 http://www.houseoffoust.com/edano/1pre.bmp" . Then within a day or two this new highest-dose location was discovered. Perhaps that marks the 'belch' that relieved some pressure, dropped the temperature and blew out a congested filter.

It really needs a chemical, elemental & isotopic analysis to resolve the issue. As TEPCO is in charge...

 

[Dmytry]

(http://www.ansn-elibrary.org/images/c/ca/Boiling_Water_Reactor_Power_Plant.pdf" )

afaik this system may have rather low throughput and could not be used in the event of serious emergency. But that may depend to particular reactor.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110807/index.html The Areva system chemical pump was restarted after 3 and a half hours. Tepco says the pump tripped because a high viscosity increased the load, but is still clueless about why the backup pump did not start. Concerning the pump that stopped at the Kurion system, the recovery is nowhere in sight. The NISA has requested Tepco to write a report on the causes of the water treatment facility troubles.

http://mainichi.jp/select/jiken/news/20110808ddm003040141000c.html Tepco decided to reduce the chemical pump's flow rate, while increasing the frequency of chemical injections. Without evaporation systems, the desalinating facility produces 1.5 times more high concentration salty water than freshwater. The two evaporation systems that were launched yesterday can bring this rate down to 30%.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110808_01-e.pdf "Diagram of Desalination System"

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110808_02-e.pdf "Leakage detected between cable duct for starting transformer and control building Unit 3, Fukushima Daiichi Nuclear Power Station"

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110808_03-e.pdf (page 2) From 10:03 to 10:43 AM on 8 August, unit 5 reactor cooling was stopped to enable the switching of power supply for RHRS pump (C).

 

[MadderDoc]

afaik this system may have rather low throughput and could not be used in the event of serious emergency. But that may depend to particular reactor.

Yes, in all likelihood the venting systems used by the operators were not the Emergency Gas Treatment Systems, but rather the retrofitted hardened vents we have been talking about. Here's the unit 1/2/3 diagrams of the hardened vent lines cropped from the report of the Japanese governement to the IAEA (see attachments for better rendering):

 

[tonio]

Concerning the source of the high radiation readings, maybe the following information from http://www.world-nuclear-news.org/RS_Second_high_radiation_reading_308112.html is of interest:Second high radiation reading
03 August 2011
Another radiation hotspot has been found at the Fukushima Daiichi site - again in part of the emergency venting and filtration system.

Yesterday an extremely high reading of 10,000 millisieverts per hour was announced as having been found in pipework leading to an exhaust stack. Today that was followed by a reading of over 5000 millisieverts per hour inside one of the buildings.

Both of the readings were taken from parts of the Standby Gas Treatment System (SGTS), through which steam was vented to relieve reactor pressure during the accident in March. In that sense, it is highly likely that Tokyo Electric Power Company will make several more findings of radiation hotspots as it conducts stabilisation work inside the power plant buildings.

The first hotspot was detected in a part of the SGTS pipework immediately before the exhaust stack shared by units 1 and 2. The latest one is on the second floor of unit 1's turbine building, near the entrance to a room related to the SGTS.

Each reactor building has an SGTS which maintains slightly lower air pressure during normal operation to reduce the possiblity that potential contamination could exit the plant building through any tiny holes. It has air intakes and components on several floors. Should contamination be present in the buildings for any reason, the SGTS is there to filter the air before release through the stack. It also provides the filtered route for venting from the reactor system, as used during the accident.

The radiation levels indicated by these off-the-scale readings mean that no worker can approach to within a few metres of the areas to take detailed manual measurements. Instead, levels were estimated using gamma cameras mounted on robots.

 

[joewein]

The SGTS in unit 1 has two units capable of filtering 1800 m3/h each, capturing > 97% of iodine. In unit 2 and 3 there are also two units, capable of filtering 2700 m3/h each, capturing > 99.9% of iodine (source: http://fukushima.grs.de/sites/default/files/NISA-IAEA-Fukushima_2011-06-08.pdf -- page IV-15).

It's a good system except you can't use it when you really need it, because it needs power for its electric blowers and dehumidifiers and can't cope with high temperatures or pressures or very rapid releases.

The weight of 1800 m3 of steam at 100 deg C and 1 bar is just about a single ton of water. You can see how this was not designed to clean up vent gases from a boiling suppression chamber holding thousands of tons of water.

 

[zapperzero]

http://channel6newsonline.com/2011/08/report-japans-fukushima-reactor-possibly-melted-twice/

 

[etudiant]

The SGTS in unit 1 has two units capable of filtering 1800 m3/h each, capturing > 97% of iodine. In unit 2 and 3 there are also two units, capable of filtering 2700 m3/h each, capturing > 99.9% of iodine (source: http://fukushima.grs.de/sites/default/files/NISA-IAEA-Fukushima_2011-06-08.pdf -- page IV-15).

It's a good system except you can't use it when you really need it, because it needs power for its electric blowers and dehumidifiers and can't cope with high temperatures or pressures or very rapid releases.

The weight of 1800 m3 of steam at 100 deg C and 1 bar is just about a single ton of water. You can see how this was not designed to clean up vent gases from a boiling suppression chamber holding thousands of tons of water.

So if this insight is put together with the earlier recognition by the NRC that a 24 hr SBO meant a meltdown,
the basis for the US governments recommendation for a 50 mile evacuation zone becomes quite clear.
It also does suggest very strongly that nuclear facilities should have belt, suspenders and a girdle, just in case.
Certainly the current designs do not appear to fail at all gracefully if the emergency venting is just flushed through the stack. That just maximizes the problem. What is the rationale for such a design?

 

[joewein]

Certainly the current designs do not appear to fail at all gracefully if the emergency venting is just flushed through the stack. That just maximizes the problem. What is the rationale for such a design?

I think the rationale is the mistaken assumption that extended station blackouts do not happen in the first place. It's a "beyond design base" condition.

However, venting from the wet well air space as in unit 1 does still seem the lesser evil compared to an uncontrolled containment failure from over-pressure as may have happened in unit 2, which is assumed to have released a lot more contamination than unit 1 (think Iitate-mura). At least the vented gas has been scrubbed to some extent by first bubbling it through the pool water in the torus. With a cracked containment all bets are off what gets released.


The hardened vent path was mostly designed with hydrogen releases in mind. The Areva report by Dr. Braun estimate H2 production from the Zirconium-steam reaction in unit 1 as 300-600 kg and 300-1000 kg in units 2 and 3.

At 100 deg C the density of H2 is about 0.065 g/L, or 15 m3 per kg. Therefore to release the non-condensable hydrogen from the air space of the torus would have involved a release of 4500-9000 m3 in unit 1 and 4500-15000 m3 in the other units, not counting the steam also accumulated there or allowing for temperatures beyond 100 deg C.

 

[SpunkyMonkey]

I'm sorry, that stuff still looks like rust to me. The horizontal pipe running right below the brown pipe elbow looks clean closest to the most stained portion of the elbow. That does not look like a high pressure cesium leak to me.

Perhaps, but to me it looks like a water-carried distribution of the similar-colored dark stuff splattered around and heaped at the base of the same pipe. And because that heap of red-brown gunk is extremely radioactive and associated with a ventilation/filtration system, it may well be (largely) cesium-vapor residue, which is also dark red-brown.

If you look at a http://www.tepco.co.jp/en/news/110311/images/110805_1.jpg", it looks like it was wrapped with some kind of tape, perhaps to protect it against corrosion. The brown stuff seems to have leaked out from underneath the tape. Perhaps the tape trapped moisture, allowing rust to fester underneath. The vertical brown lines are consistent with rust getting washed down by rain.

What we can say for sure is that the stain lines are consistent with some red-brown substance washed down with rain. But that does not entail that it's rust.

Yes I see the tape, it's obvious, but what kind of tape allows rust to fester as you suggest? I don't see why the tape increases the likelihood of the staining being rust. Maybe it's to stop corrosion as you suggest, or then maybe to reduce the escape of cesium-vapor residue in the event of a filtration-system rupture. It might be there for a number of reasons. I doubt we can infer much from the tape being there.

 

[swl]

When it rains hard, as it has recently in the Fukushima area, what happens to all the water that falls down the ventilation stack? After rinsing down the inner walls of the stack, it then hits the bottom, and what? Does anyone know if there is an automatic drain mechanism? Knowing that heavy rain is common here, I'm certain that something has been done to address this issue, but I don't remember reading about it. I'm curious where rain water and condensate goes after reaching the bottom of the stack.

 

[AtomicWombat]

Certainly the current designs do not appear to fail at all gracefully if the emergency venting is just flushed through the stack. That just maximizes the problem. What is the rationale for such a design?

I think the rationale is the mistaken assumption that extended station blackouts do not happen in the first place. It's a "beyond design base" condition.

However, venting from the wet well air space as in unit 1 does still seem the lesser evil compared to an uncontrolled containment failure from over-pressure as may have happened in unit 2, which is assumed to have released a lot more contamination than unit 1 (think Iitate-mura). At least the vented gas has been scrubbed to some extent by first bubbling it through the pool water in the torus. With a cracked containment all bets are off what gets released.

I agree with joewein.

As I take it, the rationale behind the hardened wet well vents is as a last ditch attempt to prevent a hydrogen explosion or primary containment over-pressurisation, on the basis that either event would release more radioactivity (due to catastrophic failure of the containment) than direct venting of the torus to the environment.

See:
http://www.gereports.com/venting-systems-in-mark-i-reactors/
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

Ironically all 3 operating units experienced hydrogen explosions and the hardened vents did nothing to prevent these. It appears that in at least one case (unit 1) the hardened vent was operated as well, created the worst of both worlds.

 

[AtomicWombat]

When it rains hard, as it has recently in the Fukushima area, what happens to all the water that falls down the ventilation stack? After rinsing down the inner walls of the stack, it then hits the bottom, and what? Does anyone know if there is an automatic drain mechanism? Knowing that heavy rain is common here, I'm certain that something has been done to address this issue, but I don't remember reading about it. I'm curious where rain water and condensate goes after reaching the bottom of the stack.

I have a nasty suspicion that the rain water simply is passed to the normal storm water system and then to the ocean and/or ground water. The rationale being that on the "design basis" only filtered gases are exhausted through the stack. Remember that the hardened vent was a retrofit.

 

[westfield]

snip >


. At least the vented gas has been scrubbed to some extent by first bubbling it through the pool water in the torus.

<snip.

This document appears to indicate the operators aligned the venting from both drywell AND S\C. No scrubbing from the drywell venting.

The document also indicates very high dose rates in the buildings and onsite well before the venting even took place. To my laybrain that seems odd - was there containment failure before they even got to vent?

source : http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110618e15.pdf"


On the SGTS\HVS contamination - why the high dose rates in the Unit 1 Turbine building early on? And why does SGTS even go into the turbine building? Why does the SGTS appear to be HEAVILY contaminated, it shouldn't have even been possible for it to be working after loss of power. So SGTS just opens itself up on loss of power? WTF. The more I read about the design of these systems the less I want to know, kind of.

 

[SpunkyMonkey]

Let me suggest these possible flow patterns that seem to be both logico-physically intuitive and empirically observed:

By stalagmatic accumulation I refer to the process slow water-carrier driven http://en.wikipedia.org/wiki/Stalagmite" .

Moreover, the same rust-colored stain (that I propose is http://iangoddard.com/journal/fukushima/cesiumCOLOR.jpg" .

 

[joewein]

This document appears to indicate the operators aligned the venting from both drywell AND S\C. No scrubbing from the drywell venting.

If the RPV steam from the pressure release valves is always released into the wetwell, the air space there should be much more contaminated than the nitrogen in the drywell. The drywell would get more severely contaminated later on, once the RPV melts through or the seals around it start leaking, but initially all the good stuff ends up in the torus.

There may be some exchange of pressure via the downcomer tubes between the two if there is a large pressure differential (will water get pushed up the tubes if pressure gets too high in the torus, opening a path for contaminated gas to leak from the torus into the drywell?), but my understanding is that until the RPV gets damaged by excessive temperatures the wetwell would be the more contaminated of the two spaces.

The document also indicates very high dose rates in the buildings and onsite well before the venting even took place. To my laybrain that seems odd - was there containment failure before they even got to vent?

source : http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110618e15.pdf"

It says they prohibited entry to R/B 1 at 21:51 on 2011-03-11 because of radiation (about seven hours after the quake). Tepco estimates that fuel was exposed five hours after the quake because the water level had fallen too far. So by the time they prohibited entrance, the meltdown had been in progress for about two hours. I don't know what the containment pressure was like by then, but 4 hours later, at 02:00 JST it was 0.6 MPa and at 05:30 it was at 0.82 MPa. The containment may already have been near or at design pressure (0.42 MPa = 4.2 bar) when the radiation went up.

For radiation levels inside the building to go up without venting there must have been some leaks. But in a way it is not surprising that the unit 1 containment was leaking in 2011 (when it was 40 years old and stressed to the max by a melting core) when it had already leaked unacceptably in 1992 during routine inspections when tested at 3 bar:

Faked pressure test

Yet in the most serious case of all, Tepco officials are alleged to have faked a pressure test designed to test the integrity of the containment building. The test involves pumping nitrogen gas into the building to increase the pressure to about three times atmospheric pressure, then taking pressure readings to measure the leak rate.

Regulations state that the leak rate must be less than 0.45% per day. However, at Fukushima I-1 in 1992, the company conducted its own tests before the government inspectors turned up, and discovered that the building might not pass the test. One source quoted in the Daily Yomiuri said that leak rates fluctuated from 0.3% to 2.5% per day.

Documents found at Hitachi by Tepco’s own investigative team describe a method to fake the test by secretly pumping in extra air from the main steam isolation valve. At the time, Hitachi had a contract to check Tepco equipment. It is alleged that Tepco officials followed this procedure when the government inspectors were checking the leak rate.

http://www.klimaatkeuze.nl/wise/monitor/574/5441

2.5% of several thousand cubic meters of nitrogen at 3 bar is several hundred cubic meters that would have leaked per day.

On the SGTS\HVS contamination - why the high dose rates in the Unit 1 Turbine building early on? And why does SGTS even go into the turbine building?

Probably because most of the pipes coming out or going into the containment go next door to the turbine building. It's like the belly button of the reactor. The turbine hall is also more spacious.

 

[joewein]

When it rains hard, as it has recently in the Fukushima area, what happens to all the water that falls down the ventilation stack? After rinsing down the inner walls of the stack, it then hits the bottom, and what? Does anyone know if there is an automatic drain mechanism? Knowing that heavy rain is common here, I'm certain that something has been done to address this issue, but I don't remember reading about it. I'm curious where rain water and condensate goes after reaching the bottom of the stack.

I have a nasty suspicion that the rain water simply is passed to the normal storm water system and then to the ocean and/or ground water. The rationale being that on the "design basis" only filtered gases are exhausted through the stack. Remember that the hardened vent was a retrofit.

That is a very interesting question. Note that the guy who measured the radiation with a 3 meter long pole (and took a 40 mSv hit) http://www.tepco.co.jp/en/news/110311/images/110802_1.jpg" inside the structural frame of the stack pipe.