Japan Earthquake: nuclear plants Fukushima part 2

[nikkkom]

etudiant got it exactly right.

 

[etudiant]

Just as an aside on the topic of filtering, I would have thought that the nuclear industry would have been the first to ardently embrace the necessity of filters.
The 1957 Windscale incident in the UK was only a disaster rather than a catastrophe because the belatedly installed stack filter effectively limited the emissions from the burning reactor. It is noteworthy that it was not agreed within the industry that the filters were needed, but a senior scientist had the political clout to compel their installation after the plant was already under construction.
A tall stack as a pollution solution is bad policy if there is enough pollution around to keep the emission plume lethal even at 20-50 km. Scrubber and filter options have to be integral to the vent design and for an industry whose survival is at risk, this seems an unwise retrofit to refuse imho.

 

[LabratSR]

This filter is a passive device. In Fukushima, to survive tsunami it would need to only be secured to the ground strongly enough to not float away.

It seems that they should be planning for ALL scenarios, not just for what happened at Fukushima.

 

[mheslep]

Nuclear plants are more strictly regulated because accidents can be much worse than on a natural gas plant, ...

Are they really worse?

 

[etudiant]

It seems that they should be planning for ALL scenarios, not just for what happened at Fukushima.

No argument there, agree entirely.
But the idea of an unfiltered vent stack does give me pause.
I have spent time near Sudbury, Ontario, once the home of a world class nickel mine. The roasting plant for the ore has a 1250 foot stack, to keep the SO2 emissions dilute enough.
The effect is for 30 miles around, the rock is mostly bare, devoid of life courtesy of acid rain.
I don't think an unfiltered stack possibly emitting long life radionuclides in quantity is good engineering practice.

 

[Most Curious]

Would filtered venting made a lot of difference at Fukushima ? When the hydrogen explosions occurred the nasty stuff bypassed the venting system anyway.

 

[etudiant]

Would filtered venting made a lot of difference at Fukushima ? When the hydrogen explosions occurred the nasty stuff bypassed the venting system anyway.

The venting system was not brought into play effectively, afaik, partly because the valves were inoperable without power. There were burst disks, but how well they performed is uncertain, some apparently did not.
The system was unable to relieve pressure because there was no safe vent option that was available. Partly because the vent that was built in was not designed to deal with emissions from a melting reactor, venting was not ever an attractive option for the operators.


If anyone has an English language timeline of the operator choices and options during the period between the quake and the explosions, it would be a real service to post it as a sticky.
The Melcor codes show that the reactors melt down within a half hour of losing cooling, so the ability to depressurize and inject water was understood to be crucial, yet it did not happen.

 

[westfield]

As someone who works in a design department for a nuclear power plant, this type of modification is drastically more complex than it looks on the surface.

For one, you are extending containment to a location outside of the plant. You also have to add new penetrations to the containment which have a design to fail the containment in a controlled fashion. <SNIP>

Of course there is some engineering to be done but don't the existing "Hardened Vent" lines on these plants already do exactly what you say would need to be done.

Are you saying these additional filter proposals are not going to be retrofitted to these existing 'Hardened Vent" lines or are you saying most plants of this type do not have existing "Hardened Vent" retrofits?

 

[Hiddencamper]

Of course there is some engineering to be done but don't the existing "Hardened Vent" lines on these plants already do exactly what you say would need to be done.

Are you saying these additional filter proposals are not going to be retrofitted to these existing 'Hardened Vent" lines or are you saying most plants of this type do not have existing "Hardened Vent" retrofits?

I can only directly speak for what the US is doing as I've been following this pretty closely. In the US, all BWR Mark I plants have some form of hardened vent, although it is not really standardized and many of these vents don't meet all the new requirements. Mark II containment plants do not have a hardened vent. Mark IIIs are exempt as they are similar to a PWR containment and also contain many venting paths (probably too many).

The current US regulations do not require hardened vents to have filters, unless the utility is crediting filters to meet specific decontamination goals during a core damaging event. For example, Columbia generating station, due to the unique design of their Mark II containment, they are highly susceptible to wetwell bypass during an unmitigated core melt, and drywell vent filters may be required for them.

Hardened vents simply refer to a vent line which is capable of opening under post accident conditions and releasing to an elevated release point. Filters may or may not be a part of this. Currently passive filters are not required in US plants. The US industry is attempting to get permission to credit their FLEX strategies for wet scrubbing. The industry argues that FLEX equipment and strategies can achieve >1000 decontamination factor (remove > 99.9%), under more scenarios than a permanently installed filter, and would have a higher conditional success probability as the portable equipment would not be at the site at the time of the accident, meaning it is free from the common mode failure which caused the ECCS to fail in the first place. FLEX equipment also manages the core-damaging event, while a filter can only deal with releases caused by such an event. Those opposed believe that the complex strategies for wet scrubbing during a severe accident are challenging and would take resources away from managing the core damaging event. In any case, managing the core damaging event directly reduces the amount of radioactive material being released in the first place, which everyone agrees on.

 

[Hiddencamper]

The venting system was not brought into play effectively, afaik, partly because the valves were inoperable without power. There were burst disks, but how well they performed is uncertain, some apparently did not.
The system was unable to relieve pressure because there was no safe vent option that was available. Partly because the vent that was built in was not designed to deal with emissions from a melting reactor, venting was not ever an attractive option for the operators.


If anyone has an English language timeline of the operator choices and options during the period between the quake and the explosions, it would be a real service to post it as a sticky.
The Melcor codes show that the reactors melt down within a half hour of losing cooling, so the ability to depressurize and inject water was understood to be crucial, yet it did not happen.

http://www.cas.go.jp/jp/seisaku/icanps//eng/03Attachment2.pdf

There are some timelines on here. They don't talk about operator choices though. I have seen what you are looking for, but I'm having trouble finding it.

What I do know is that containment venting was challenging. On at least one unit, the rupture disc did not break. It appears the cause was the overpressure of the containment created enough leakage that pressure would not exceed the rupture disc capacity.

Also, just so we are clear, based on your comment about Melcor codes and the like. I think the timeline is a bit longer than that, as they were already 1 hour post scram (lower decay heat, and no shrink effect). If a plant was scramming on a loss of feedwater, I agree 30 minutes and you are at TAF (top of active fuel), this is primarily due to the shrink effect that occurs on a reactor scram, which causes water level to drop 30+ inches. I've had to deal with loss of feed scenarios a lot in the plant simulator, you go from +35 inches to -45 inches in the first two minutes on a loss of feed (top of fuel in my plant is around -160").

But, when you consider they were just under an hour after the scram, and water levels should have been restored to nominal ranges, there is substantially more time (up to 2 hours) prior to reaching TAF. Lower decay heat combined with greater actual inventory (no swell effect) give more time. Additionally if pressure is reduced even a couple hundred pounds, that adds another 15-20 minutes.

In either case, I get the impression you might be mixing up reactor depressurization with containment venting. It is crucial to activate the ADS (automatic depressurization system) to blowdown the reactor pressure vessel shortly after the TAF is uncovered. First off, the swell effect from ADS will cool the fuel for another 20 minutes without feed, second off this allows you to reduce RPV pressure below the shutoff head for portable pumps. This is the single best way to ensure adequate core cooling when you lose all your ECCS. But containment venting is not required for this strategy. Containment venting would only be required if you failed to inject with the portable pump for several hours. Containment venting is not required in the first few hours post accident as the suppression pool would handle the decay heat loads from the reactor for quite a while.

Alternatively, if the reactor was considered to be a lost cause, containment venting would be used to help support flooding the containment to the BAF (bottom of active fuel), and allowing conductive cooling through the metal skirt of the reactor to the water inventory.

 

[nikkkom]

It seems that they should be planning for ALL scenarios, not just for what happened at Fukushima.

you know, by now I'll settle for nuclear industry planning *at least* for the scenarios which already happened at TMI/Chernobyl/Fuku.

Because *it does not do even that* - a number of things in Fukushima, such as lack of radiometers with adequate range and lack of autonomous emergency lighting, should not be happening because Chernobyl should have taught these lessons already.

 

[rmattila]

http://pbadupws.nrc.gov/docs/ML1214/ML12143A336.pdf

Some specifics of the Swedish and Swiss filtered vents as seen by the NRC.

http://pbadupws.nrc.gov/docs/ML1217/ML12178A670.pdf

Report from the fact-finding trip.

 

[rmattila]

Would filtered venting made a lot of difference at Fukushima ? When the hydrogen explosions occurred the nasty stuff bypassed the venting system anyway.

The filtered venting system is designed to conduct the hydrogen from the containment to the stack in a controlled manner. At least in the Finnish and Swedish system this happens completely passively by means of a rupture disk, unlike the Japanese/American hardened vents, which require active opening of the valves in the venting line.

 

[rmattila]

Those opposed believe that the complex strategies for wet scrubbing during a severe accident are challenging and would take resources away from managing the core damaging event. In any case, managing the core damaging event directly reduces the amount of radioactive material being released in the first place, which everyone agrees on.

This argument is very difficult for me to follow, as the very idea behind the design in the 80's was to eliminate the need for unreliable decision-making in the case of a severe accident by enabling a completely passive initiation of venting. If your vent lines don't have filters, you probably want to keep the valves in the lines closed, and must count on the personnel to be able to open them at the right time.

 

[LabratSR]

This is about blocking the pipes and vents below the plant, not the famed ice wall.


TEPCO to start water-freezing work at Fukushima plant in Dec.


http://the-japan-news.com/news/article/0000785092



Link to an earlier Enformable article about it

http://enformable.com/2013/10/tepco-plans-new-freeze-mission-underground-tunnels-fukushima-daiichi/

 

[LabratSR]

I should point out that the NRC document I posted back on page 5 talks about these filtered vents in Enclosure 4, starting around page 12

http://www.nrc.gov/reading-rm/doc-collections/commission/secys/2012/2012-0157scy.pdf


And here again is the EPRI report often referenced in the NRC paper

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001026539

 

[gmax137]

This argument is very difficult for me to follow, as the very idea behind the design in the 80's was to eliminate the need for unreliable decision-making in the case of a severe accident by enabling a completely passive initiation of venting. If your vent lines don't have filters, you probably want to keep the valves in the lines closed, and must count on the personnel to be able to open them at the right time.

I agree that installing filters is the right approach, and the NEI efforts against the filters are misguided. But I still don't agree with characterizing this as a cheap or easy modification. And the filters aren't a silver bullet that solves all of the issues. Just my 2-cents.

 

[LabratSR]

TEPCO Release - Key Safety Measures at Fukushima Daiichi NPS

http://www.tepco.co.jp/en/press/corp-com/release/betu13_e/images/131108e0101.pdf

 

[etudiant]

I agree that installing filters is the right approach, and the NEI efforts against the filters are misguided. But I still don't agree with characterizing this as a cheap or easy modification. And the filters aren't a silver bullet that solves all of the issues. Just my 2-cents.

Again, no argument that filters are no silver bullet and are not just a slap on fix.
Nevertheless, they do seem a sensible addition to the 'defense in depth' concept, without substantial downsides. Even the cost is moderate, especially considering the potential damage avoided. Frankly, they seem to me to be an obviously needed element for any hardened venting.

Separately, thank you again, hiddencamper, for the clarification on the difference between depressurization and containment venting. It helps clarify why it took three days for the Fukushima reactors to get to explode, which actually is even more depressing, that no cooling could be reestablished for so long.
Is there any good reason, other than cost and regulatory uncertainty, why filters should not be added to the hardened vents?

 

[LabratSR]

Performance-Based Strategy for Filtering Is Best Choice NEI Tells NRC

http://www.nei.org/News-Media/News/News-Archives/Performance-Based-Strategy-for-Filtering-Is-Best-C

 

[gmax137]

... Is there any good reason, other than cost and regulatory uncertainty, why filters should not be added to the hardened vents?

I think [strike]Exelon[/strike] NEI is standing on the principle that the regulator should establish requirements in measurable terms (such as, offsite dose or dose rate limits) and the licensee should do the engineering to design the features that result in those requirements being met. This is the essence of what "performance-based" means in nuke-speak. This principle has always been a source of tension within the regulating body (AEC or NRC), going back into the early 1960s. Also, the utility engineers still remember the costs associated with a number of the NRC-mandated post-TMI modifications that turned out to be pointless engineering and operational quagmires (e.g., H2 monitors in the large dry PWR containments, post-accident sampling systems, etc.). Whether the filters are a good place to take this stand is debatable in my mind, because (like you said) they seem to be such an obvious application of defense-in-depth (another long-standing principle which is sometimes forgotten).

 

[etudiant]

I think [strike]Exelon[/strike] NEI is standing on the principle that the regulator should establish requirements in measurable terms (such as, offsite dose or dose rate limits) and the licensee should do the engineering to design the features that result in those requirements being met. This is the essence of what "performance-based" means in nuke-speak. This principle has always been a source of tension within the regulating body (AEC or NRC), going back into the early 1960s. Also, the utility engineers still remember the costs associated with a number of the NRC-mandated post-TMI modifications that turned out to be pointless engineering and operational quagmires (e.g., H2 monitors in the large dry PWR containments, post-accident sampling systems, etc.). Whether the filters are a good place to take this stand is debatable in my mind, because (like you said) they seem to be such an obvious application of defense-in-depth (another long-standing principle which is sometimes forgotten).

Since we are talking here about 'beyond design basis' accidents, is the NEI stance sensible?
If the Ramapo fault causes a serious failure at Indian Point and NYC gets the vented plume, it might impair nuclear industry shareholder value more substantially than any filter retrofit.

 

[a.ua.]

There are leaks in the containment of the reactor 1.

http://ru.fotoalbum.eu/images1/200905/95064/273731/00000057.JPG

It was about 0.9 to about 1.8Sv / h in the navigation route.

http://photo.tepco.co.jp/date/2013/201311-j/130313-04j.html

 

[zapperzero]

There are leaks in the containment of the reactor 1.

Hm. Can you get more specific? Where in the containment? Looking at the PDF it appears there's a penetration at the elbow of the steam downcomer, as it exits the PCV. But maybe I'm misreading the schematic?

 

[a.ua.]

It depends on what is considered the boundary containment.
In fact, this handset is in a sand layer between the steel and concrete primary containment.?
Look at the photo.

 

[LabratSR]

According to this article, they will be using the boat mounted camera a second day.

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201311140046

 

[a.ua.]

there is already an "photo.tepco.co.jp/en/date/2013/201311-e/130313-04e.html"
and the second day of the Japanese

 

[westfield]

There are leaks in the containment of the reactor 1.

Isn't that jumping to a conclusion?

Yes, Tepco say there is water coming out of one of the sandbed drain\s but the source of the water is unknown isn't it?

It could be a leak in the containment steel liner but it could be water finding its way down there on the outside of the liner between the liner and the concrete or it could be from some other source. There is a reason why the sand bed has drains in the first place.

It's interesting though.

 

[Hiddencamper]

Since we are talking here about 'beyond design basis' accidents, is the NEI stance sensible?
If the Ramapo fault causes a serious failure at Indian Point and NYC gets the vented plume, it might impair nuclear industry shareholder value more substantially than any filter retrofit.

Since it's beyond design basis it really depends on the philosophy. If you are beyond design basis, it means something unpredictable or extremely unlikely disabled all the safety systems which were in place. So on one hand its challenging to say another filter will survive the same accident to help, but if the filter does survive it will no doubt be a help for extreme damaging events.
NEI's position (and it was actually EPRI that studied this, NEI took the stance after the EPRI report), is that the portable equipment from FLEX can meet filtration goals after an extreme event. But really...at this point its more of, do we feel that a containment ventilation filter is necessary to minimize release to the public, or can we minimize those releases using existing methods without challenging the ability to cope with an extreme event.

Personally I think it depends on the plant design. Take my current plant for example, (Mark III containment, very different from Mark I/II in a LOT of ways) has so many cross connects that we can realign systems to vent to water tanks already on site, meaning we can do wet scrubbing without needing an additional filter and get those >1000 decontamination factors. We also have had training and portable equipment in place since 9/11 to flood the basement of our fuel storage building and vent through there. Also note that our Mark III design has 5 existing filter trains (which can be repowered by a portable generator) and 3 separate containment venting systems (regulations changed so much during the Mark III construction that all Mark IIIs ended up with multiple vents for containment. This is also a reason why Mark IIIs are currently exempt from venting requirements). So in my plant's case, I think an external filter doesn't add much value, we already have equipment staged, know what to do, and can implement solutions with limited actions (no need to do massive repiping).

For Mark I/II plants, its kind of a different story. Limited vent paths, few if any system cross connects, no good floodable volume. Maybe depending on the specific design filters are a sensible solution. I don't know...

 

[zapperzero]

The talk about re-aligning systems is over-optimistic for sure. Power might be out, places where valves are might be inaccessible for a reason or another. You need water and pumps and time, one or more of which might be lacking.

Generally speaking, you are telling us that active measures are as good as passive ones, which is simply not true.
With a pre-emplaced filter at the end of a hardened vent line, all the operators have to do, to vent safely, is exactly nothing - as compared to running around the plant in the dark, in unknown radiation field, to open valves and start-up pumps under time pressure, while lugging around gensets.

There's the matter of expertise too. To realign cooling systems and whatnot, you need to know the plant. To hook up a fire engine, you need to know exactly nothing, just find the right connector (big red pipe, conspicuously marked, by the side of the access road). All the operators could be dead (or evacuated, as was almost the case with Fukushima), and you'd still successfully flood the containment while the passive vent+filter keeps emissions down.

 

[Hiddencamper]

The talk about re-aligning systems is over-optimistic for sure. Power might be out, places where valves are might be inaccessible for a reason or another. You need water and pumps and time, one or more of which might be lacking.

Generally speaking, you are telling us that active measures are as good as passive ones, which is simply not true.
With a pre-emplaced filter at the end of a hardened vent line, all the operators have to do, to vent safely, is exactly nothing - as compared to running around the plant in the dark, in unknown radiation field, to open valves and start-up pumps under time pressure, while lugging around gensets.

There's the matter of expertise too. To realign cooling systems and whatnot, you need to know the plant. To hook up a fire engine, you need to know exactly nothing, just find the right connector (big red pipe, conspicuously marked, by the side of the access road). All the operators could be dead (or evacuated, as was almost the case with Fukushima), and you'd still successfully flood the containment while the passive vent+filter keeps emissions down.

If you think during a severe accident that there's going to be some easy way to do ANYTHING you're going to have a bad time.

All nuclear plants have containment isolation systems that automatically close the valves on the pipes passing through containment. Almost all of these systems consist of valves just inside and just outside of containment, meaning if the isolation occurred (like at Fukushima), that you cannot use most of these lines without going inside containment, which really isn't an option during a severe accident. You would need a deep knowledge of the plant, or existing pre-staged procedures and equipment (like the ones the US has had since 9/11) to know which lines likely did not isolate, or know which lines only have isolation valves outside of containment. Example, the third LPCI (Low pressure coolant injection) system at my plant only has an outboard containment isolation valve, (the inboard valve is a check valves), and this is readily accessible and could be a good place to hook a fire truck up to.

The point I'm trying to make, is in all causes you will need to take manual actions. That is the definition of how a severe accident works. If you didn't need manual actions, then you wouldn't be in the severe accident in the first place. There is nothing passive that's going to help you. "Passive" filter? Only if you can get the first outboard valve open (and approval to have a pipe penetrating containment without double isolation). Or are we saying that these valves are going to be pre-aligned to start venting automatically (which means during DBAs like a LB-LOCA where my ECCS is working, I'm going to allow unacceptable and unnecessary radioactive releases because my passive filter is going to take care of it?, when my safety systems on site could readily handle it)

You can all pontificate all you want about how you think it should work, but you need to understand the design of these plants, along with the regulatory design requirements, to understand where the challenges are in just saying that some passive thing can be installed that will magically solve all your problems post accident. No matter what, it will take significant efforts by those at the plant to cope with a beyond design basis accident, with or without a filter.

 

[SteveElbows]

Isn't that jumping to a conclusion?

Yes, Tepco say there is water coming out of one of the sandbed drain\s but the source of the water is unknown isn't it?

It could be a leak in the containment steel liner but it could be water finding its way down there on the outside of the liner between the liner and the concrete or it could be from some other source. There is a reason why the sand bed has drains in the first place.

It's interesting though.

It is true that speculative errors could be made. However when reading the pdf and watching the video, I am under the impression that the clearly visible gushing water is not coming from the detached sandbed drain pipe, it is coming from the S/C side of the vent pipe, and flowing down the side of the S/C torus. They clearly mention in the PDF not just leakage from the drain pipe, but from the vent pipe in this location, and this is also shown in the photos taken from the video.

Going further into the realms of speculation, I am very interested in this discovery. There are obviously multiple reasons why a vent pipe failure could have occurred in this area, and I should not leap to inclusions. But I will keep in mind that some core melt studies do have the area around the vent pipe as being a strong potential pathway for corium flow. And although I do not believe we have a definitive answer as to the location of the pedestrian pedestal opening for reactor one, the south east direction is a strong contender, and that happens to be the location of the vent pipe where this leak has been found. None of this is enough to form strong conclusions, but given that reactor 1 had in theory the strongest melt potential for several reasons, and that the radiation levels in its torus room are far more interesting than those of the other reactors, I am both fascinated and unsurprised by what the boat has found.

 

[SteveElbows]

The second day of reactor 1 torus room boat investigation is available in English. Some damage to other sandbed pipes was detected, but no other vent pipe damage other than the one at location 4 was detected as far as I can tell.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_131114_05-e.pdf

Regarding reactor 4 pool fuel removal, various certificates have now been obtained and one of the transportation casks is now inside the reactor 4 building.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_131113_12-e.pdf

 

[a.ua.]

Such high doses that there are measured
(and in the torus is 2.2 Sv) can only nuclear fuel.

It's a pity, they did not use the gamma camera, then it would all be seen.

many high-quality photos from the mission boat

http://www.fukuleaks.org/web/?p=11733

 

[etudiant]

If you think during a severe accident that there's going to be some easy way to do ANYTHING you're going to have a bad time.

No matter what, it will take significant efforts by those at the plant to cope with a beyond design basis accident, with or without a filter.

Agree entirely, severe accidents are like wars, even the simplest thing becomes very difficult.
The concern is that the regulators are missing the good in their effort to achieve perfection.

That said, it is just incomprehensible to me that a nuclear vent stack should be unfiltered. It may never be needed, hopefully, but it sure is much more useable with a filter than without.
Venting relatively safely should be another option for the operator, not a desperation necessity.