Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[MadderDoc]

The vertical brown-stained pipe is probably connected to one of the two smaller pipes that run along the fat pipe from the Y-section leading to units 1 and 2. There's one at each side of the fat pipe.

The brown-stained section of the pipe is the last final bit of pipe before entry into the stack, this last bit is shared by the exhausts from unit 1 and 2 EGTS (Emergency Gas Treatment Systems).

Right above the stained part you see the forking out of one pipe up and towards south, that pipe is connected via a 90 deg bend to the smaller pipe along the fat pipe, coming from unit 2. The other fork proceeds vertically for a bit, then makes an upwards bend towards the north, and then a 90 deg bend to become aligned and connected with the smaller pipe coming from unit 1. I think you can make out the arrangement from the attached photo that is shot from the south-west.

Ian Goddard speculates on his site that the brownish colour is not rust but cesium. However, for that the pipe would have to be leaky, for you to see cesium condensate on the outside, not just the inside.

Cesium compounds are generally colorless, so taking the color brown as an indicator color for the presence of cesium appears like madness. Quite on the contrary. if a cesium mineral is found to be brownish a geologist will reasonably suspect the color is due to the presence of impurities, e.g. Fe³⁺ impurities aka 'rust'.

 

[Dmytry]

The stain is indicative of some sort of leak, which evaporated, depositing the dissolved material. You can guess it would include radioactive isotopes. Also the pipe bends inside meaning some dust could have deposited there. The piping would be very radioactive even if only a small fraction of the vented material had deposited.

 

[AtomicWombat]

Exactly where does the pipe come from. It's hard to follow in the Cryptome pictures. It is not the large emergency relief duct from the airspace in the reactor building. It appears to be an emergency steam relief pipe from the reactor circulation, perhaps from the condensers.

It may have flooded as a result of too much water added to the RPV. It is possible that the bottom of the stack is filled with water. I notice the most severe corrosion is at the join between the pipe and the stack. There is thick brown layer of rust on the shield below it.

 

[joewein]

Exactly where does the pipe come from. It's hard to follow in the Cryptome pictures. It is not the large emergency relief duct from the airspace in the reactor building. It appears to be an emergency steam relief pipe from the reactor circulation, perhaps from the condensers.

It comes from a filter room on the second floor, where also extremely high values were measured.

Attached are cropped images from a Cryptome set.

 

[robinson]

So after something goes very wrong you vent the reactor directly into the atmosphere? What the .. ?

 

[jim hardy]

So after something goes very wrong you vent the reactor directly into the atmosphere? What the .. ?

better a controlled vent through filters than waiting for it to vent itself.
Think of the engine coolant reservoir in your automobile - keeps ethylene glycol off the pavement, within its design limits.

recall the operators were VERY hesitant to use it - the top brass had to directly order it.

old jim

 

[robinson]

Why not vent it into a giant reservoir of water? So the steam condenses, and it doesn't go wafting down wind?

 

[Caniche]

I have to say I don't understand how you can have a hydrogen explosion blowing apart the confinement building, and not the reactor vessel.

I also don't understand how you can let any pressure build up in the confinement building at the risk of rupture if it is slowly. One should prefer steam releases (even contaminated) in order to ensure the integrity of the confinement building if ever the reactor vessel breaks, no ? Now we are not very far from a full release of the core in the environment.

First point is easy ,the reactor vessels and secondary confinement are distinct and separate.

If hydrogen collects in the secondary containment and is ignited ,then the seat of the detonation is identifiable ,but the product is less predictable.

We have been exposed to full release of the core from the day these reactors went pop, but if you pour lots of water on the nuclear pile you can limit the geographical spread(however ,local concentration does increase)

 

[Cryptome]

Exactly where does the pipe come from. It's hard to follow in the Cryptome pictures. It is not the large emergency relief duct from the airspace in the reactor building. It appears to be an emergency steam relief pipe from the reactor circulation, perhaps from the condensers.

Here are two high-res photos of the location dated August 4, 2011, captions by TEPCO:

Stack drain pipe of exhaust stack of Units 1 and 2, Fukushima Daiichi Nuclear Power Station(from east side) (pictured on August 4,2011)

http://www.tepco.co.jp/en/news/110311/images/110805_1.jpg

Stack drain pipe of exhaust stack of Units 1 and 2, Fukushima Daiichi Nuclear Power Station(from west side) (pictured on August 4,2011)

http://www.tepco.co.jp/en/news/110311/images/110805_2.jpg

These are from TEPCO's news site updated every day or so:

http://www.tepco.co.jp/en/news/110311/

 

[etudiant]

So after something goes very wrong you vent the reactor directly into the atmosphere? What the .. ?

The stack, unless filtered, then ensures maximal dispersion of the vented materials.
That does seem a serious oversight, as a bad accident is thereby made worse.
Are there not any requirements for filtering the hardened stack emissions in case of accident?

 

[Caniche]

The stack, unless filtered, then ensures maximal dispersion of the vented materials.
That does seem a serious oversight, as a bad accident is thereby made worse.
Are there not any requirements for filtering the hardened stack emissions in case of accident?

In the UK it is termed "Cockcrofts folly" , it did however probably save much of NW England from a lethal dose in 1957. Discuss

 

[robinson]

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

 

[Joe Neubarth]

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

Torus.

 

[AtomicWombat]

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? I.e. Where does this "emergency gas treatment piping arrangement" fit into the safety systems for a BWR?
http://en.wikipedia.org/wiki/Boiling_water_reactor_safety_systems

And what is a "train room"?

 

[Bandit127]

The documents on Tepco's site:
http://www.tepco.co.jp/en/news/110311/
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

Where does this "emergency gas treatment piping arrangement" fit into the safety systems for a BWR?

My assumption was that the "emergency gas treatment system" was the nitrogen gas feed system. If so, it is new and a result of the accident.

 

[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