Japan Earthquake: nuclear plants Fukushima part 2

[Most Curious]

At the edge of the current subject:

What were the alternatives to the sea water pumps if all were destroyed or rendered inop? Were any still functional after the "wave?

 

[Hiddencamper]

At the edge of the current subject:

What were the alternatives to the sea water pumps if all were destroyed or rendered inop? Were any still functional after the "wave?

Well...if JUST the seawater pumps were inoperable, Fukushima Daiichi still had air cooled diesel generators. The scenario could have played out like Fukushima Daini or Daiichi units 5/6, which had no UHS for the first couple days. Seawater pumps provide "ultimate heat sink", and without them you are inherently limited on how you can remove heat from the plant.

If you had electrical power but no UHS, one method to make a BWR safe is to feed and bleed the suppression pool and reactor. You would need to use portable pumps or other systems to get water out, and you would have to pump cold water in, until you could establish a UHS. This is challenging though.

Edit: Just to add. A BWR has 2 safety related methods to remove decay heat. The first is to boil water to steam, vent the steam to the suppression pool which acts as a temporary heat sink. Then you cool the suppression pool using your residual heat removal system heat exchangers. Suppression pool water or Condensate Storage System water is then injected to the reactor to make up for the steam vent. This is the method that most plants use when they are > 100 PSI and hot. To cool down, you release more steam than you are generating to the pool.

<100 PSI, you can line the reactor up directly to the residual heat removal system heat exchangers. The heat exchangers are cooled by the ultimate heat sink water system. In this mode, you do not need to inject any water, because you won't need to release any steam.

You can extend how long you can go w/out UHS by injecting outside/cold water directly to the pool and/or reactor, but you'll eventually need UHS to cool down. Most BWRs do not have a method to remove decay heat directly to atmosphere, with the exception of the Isolation Condenser plants (Fukushima unit 1, Oyster creek, dresden, and a few others).

 

[Most Curious]

If I understand correctly then, the plant can be safely cooled for up to 2 days without seawater for UHS.

Is the required UHS cooling requirement then within the capabilities of, say fire trucks, or must larger pumps be rigged?

 

[nikkkom]

> Quote by nikkkom
> BTW, did anyone of you hear of any NPP anywhere in the world
> (other than Japan) which builds or significantly improves its
> flood protection barriers post Fukushima?

Well, we went and reviewed our entire flood analysis. Then we walked down all the flood protection barriers. Found a few that were degraded, but as far as our analysis goes, my plant is not susceptible to external flooding (inland and built above our lake a considerable amount). So we aren't really doing anything different.

I know one plant built a pedestal 15-20 feet above plant elevation, and on it there is a full set of safe shutdown equipment. Two emergency generators, 2 pumps which can be hooked up for UHS/Aux feed.

It really depends on the plant.

My angle is that it's suspicious that no other country upgrades its dams as much as Japan does now.

I find it unlikely that all other countries have excellent flood protection for their NPPs. A picture of sandbagged Fort Calhoun NPP isn't helping to prop up such a notion.

The only other theory why no dam/seawall building is happening is that other countries aren't shocked by Fukushima enough to admit and fix their problems.

How is that filtered vent saga going in US? Still nothing? It's been three years now.

 

[turi]

My angle is that it's suspicious that no other country upgrades its dams as much as Japan does now.

I find it unlikely that all other countries have excellent flood protection for their NPPs. A picture of sandbagged Fort Calhoun NPP isn't helping to prop up such a notion.

The only other theory why no dam/seawall building is happening is that other countries aren't shocked by Fukushima enough to admit and fix their problems.[...]

I don't know much about other countries, but in Switzerland several enhancements have been done, are ongoing or planned after Fukushima. Right now the dam of a hydroelectric power plant upstream of a reactor scheduled for decommissioning in 2019 is being reenforced (a dam break could cause a tsunami like flood). Several external emergency control rooms have been built or enhanced, more mobile generators and water pumps were deployed and better monitoring of spent fuel pools has been installed.

 

[Hiddencamper]

My angle is that it's suspicious that no other country upgrades its dams as much as Japan does now.

I find it unlikely that all other countries have excellent flood protection for their NPPs. A picture of sandbagged Fort Calhoun NPP isn't helping to prop up such a notion.

The only other theory why no dam/seawall building is happening is that other countries aren't shocked by Fukushima enough to admit and fix their problems.

How is that filtered vent saga going in US? Still nothing? It's been three years now.

I met with several people from Ft. Calhoun last August. Apparently the water level was still several feet below their design basis flood. The water in the parking lot, at its crest, was only around 1-1.5 feet. From what the people at the plant said (and this wasn't a public meeting, this was me meeting with engineers from the plant at an industry event), there was still substantial margin on their safety systems with respect to the flood.

With regard to filtered vents, the NRC is making an order for reliable vents. Filters are going to be pursued through the formal rulemaking process. Apparently there was insufficient cost benefit to use the adequate protection measures required, however enough qualitative factors that it should be considered for full rulemaking. This will continue to develop for a few years.

 

[nikkkom]

I met with several people from Ft. Calhoun last August. Apparently the water level was still several feet below their design basis flood.

I saw pics with "Aquadam" keeping river's waters off merely feets away from reactor building's walls with my own eyes.

http://www.cartoradiations.fr/image...le_Nucleaire_Alerte_Inondation_24_06_2011.jpg

That's not acceptable, plain and simple. How do you manage to not understand that?

 

[Hiddencamper]

I saw pics with "Aquadam" keeping river's waters off merely feets away from reactor building's walls with my own eyes.

http://www.cartoradiations.fr/image...le_Nucleaire_Alerte_Inondation_24_06_2011.jpg

That's not acceptable, plain and simple. How do you manage to not understand that?

The only components at risk at fort Calhoun were non safety components. Commonly referred to as balance of plant. A loss of BOP equipment, while it can raise unit risk, does not result in core damage or radioactive release.

The vital equipment at fort Calhoun was more than adequately protected at all times, from what I've read, from people I've spoken to. I know it doesn't "look" good, but it's important to remember that there is extensive design basis and safety analysis on nuclear plants and there are many things that don't "look good" that these plants are designed for. The flood was still in their plant's design basis flood.

 

[nikkkom]

The only components at risk at fort Calhoun were non safety components. Commonly referred to as balance of plant. A loss of BOP equipment, while it can raise unit risk, does not result in core damage or radioactive release.

The vital equipment at fort Calhoun was more than adequately protected at all times, from what I've read, from people I've spoken to. I know it doesn't "look" good, but it's important to remember that there is extensive design basis and safety analysis on nuclear plants and there are many things that don't "look good" that these plants are designed for. The flood was still in their plant's design basis flood.

I can't take your word for it. Japanese were saying exactly the same things before Fukushima - that everything is fine - whereas it was not. My trust in nuclear industry's PR is about 0% as of now.

What would shore up my confidence is seeing Fort Calhoun building a dam around itself, roughly along the perimeter currently fenced with a wire fence.

That's less than one mile of a dam. In case you don't know how to do that, take a hint from Germans and Czechs who erected tens of kilometers of dams along Danube in mere *days*, over unprepared terrain:

http://www.scmp.com/sites/default/files/styles/980w/public/2013/06/03/a8cabd10d18c87601fce95bdce7e5f41.jpg

 

[nikkkom]

http://icons.wxug.com/hurricane/2013/danube_floodwall.jpg

http://i2.cdn.turner.com/cnn/dam/assets/130605145455-02-europe-flood-0605-horizontal-gallery.jpg

 

[Sotan]

New report from Tepco (only Japanese for now, unfortunately):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140320_04-j.pdf

Most content is about general safety improvements, cleaning the site and measures taken to reduce the level of radiation in Fukushima Daiichi plant.

The last 4 pages refer to shielding with Pb plates 3-12 mm thick, in various areas around the SFP of Reactor 4, in order to reduce radiation exposure during the fuel extraction operations.

 

[a.ua.]

Interesting stuff about the study Fukushima Unit 2; 5th Floor.
http://www.meti.go.jp/earthquake/nuclear/pdf/20140327_02/140327_02_020.pdf
little English http://www.fukuleaks.org/web/?p=12766
there lost robot came pretty absurdly http://enformable.com/2014/03/human-errors-strand-dead-robot-fukushima-daiichi-reactor-building/

 

[Sotan]

From here:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140424_05-j.pdf

They are starting work to remove the main body of the FHM from the spent fuel pool of Reactor 3.
Because there might still be oil in that structure, to avoid it entering the SFP cooling circuits, they will stop cooling the SFP from Monday 7:00 to Saturday 16:00 every week until mid June or so.

 

[jadair1]

From here:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140424_05-j.pdf

They are starting work to remove the main body of the FHM from the spent fuel pool of Reactor 3.
Because there might still be oil in that structure, to avoid it entering the SFP cooling circuits, they will stop cooling the SFP from Monday 7:00 to Saturday 16:00 every week until mid June or so.

What is a FHM?

A fuel handling module perhaps?

And stopping cooling for 6 days a week seems fairly risky to me when they don't even know the state of the fuel rods in the pool IIRC.

Then again I don't know when the last batch of "hot rods" was loaded into the pool and how radioactive they may still be.

And please don't get all condescending and tell me to go to Wikipedia or some such thing, I come here for the expert information that is available.

 

[Rive]

What is a FHM?

And stopping cooling for 6 days a week seems fairly risky to me when they don't even know the state of the fuel rods in the pool IIRC.

Fuel Handling Machine. The big green bridge-like machinery which moves the fuel rods between- and in the core and the pool. In U3 it was fallen in the pool.

The actual state of the fuel rods are not really relevant regarding the stop of the cooling. It's the amount and activity (thermal power) of the rods what matters. I cannot check of course but if the procedure has the required permissions and such then (I hope) somebody had made the homework and the temperature of the pool should remain within limits during the stop.

I wonder how they plan to decontaminate/check that machinery. I think there is some possibility that that some fuel fragments (from a damaged fuel assembly) remains on the wreck as they remove it from the pool.

 

[zapperzero]

They won't decon it, it's just another piece of junk. It goes straight to radwaste storage (presumably after they determine exactly how radioactive it is, so they can drop it on the appropriate pile of junk).

 

[Rive]

They won't decon it, it's just another piece of junk. It goes straight to radwaste storage (presumably after they determine exactly how radioactive it is, so they can drop it on the appropriate pile of junk).

I hope you are wrong. A pile of general radioactive junk vs. some fuel fragments out of the pools/units (first time! ) - IMHO it's a completely different matter.
I think they should be able to exclude even the possibility of this WCS.

 

[zapperzero]

I hope you are wrong. A pile of general radioactive junk vs. some fuel fragments out of the pools/units (first time! ) - IMHO it's a completely different matter.
I think they should be able to exclude even the possibility of this WCS.

A good hosing down should take care of that. Btw, you're falling into the same mindset which has been making recovery operations drag on since day 1. It is not a power plant anymore. It is a pile of radioactive junk. The faster it is all broken down into smaller pieces of radioactive junk, containerized, carted off, and buried, the better for all involved.

 

[Rive]

Btw, you're falling into the same mindset which has been making recovery operations drag on since day 1. It is not a power plant anymore. It is a pile of radioactive junk. The faster it is all broken down into smaller pieces of radioactive junk, containerized, carted off, and buried, the better for all involved.

You are right with the general rubble. The faster it is cleaned up is the better.

However, it's completely different with used fuel involved. Right now, the radiation level gives enough time for the workers to control the situation at close range - it makes things (relative) fast, (relative) safe.

If some fuel gets out of the pool, then the radiation levels there jumps at least one or two magnitude immediately. Some areas of the site would go 'Chernobyled'.

I think to remove that machine is a really critical operation. I hope they are thoroughly prepared for it. I hope it'll go without problems.

We will see.

 

[Hiddencamper]

With regards to shutting off SFP cooling.

A full pool with flooded up gates this long out (3+ years) is going to have heatup times of much more than 1 week. By heatup, I mean the amount of time to increase the temperature to 200 degrees F.

For freshly offloaded fuel, and a fully flooded pool, a month after offloading fuel you have a couple days until boiling. 2 years out you have several days.

Once boiling starts, it will take over several weeks to boil down. Remember, the enthalpy required to vaporize a unit of water is several times greater than the amount of enthalpy required to raise water from normal temp to boiling point. Per my steam table, about 920 ish BTU/lbm to vaporize water, while heating it up will be around 100 BTU/lbm. Now obviously I'm not accounting for evaporation or the like, but the point remains, you have a long period that you can have a loss of cooling without even boiling, let alone boil down. On top of it, if your heat exchangers cannot be restored, any fire truck or small addition water source can make up the pool.

Anyways, even if boildown does happen, that's a radiation concern, but at this point, there is not enough heat density to cause auto-ignition.

 

[jadair1]

Thank you HC that was the information I was looking for.

Nothing to be concerned about then because even in the unlikely event of rods becoming exposed the operation could be halted and water could be added.

ZZ I believe that Tepco knows it is a pile of radioactive junk but the safest place to store much of it is in the concrete structures that still exist. Think of the reactor buildings one to three as high level radioactive storage sites. Not good ones mind you but that is what they are.

If they can empty all the spent fuel pools, or what's left of them, then they can seal off what is left.

I don't believe they will be able to get at the corium's or what's left of them for decades, TMI had a partial meltdown and it took 11 years to defuel according to Wikipedia.

I don't believe TEPCO knows where all 3 of the corium's even are at this point and if they do they aren't talking.

 

[Hiddencamper]

From a computer/mathematical model, we have a very good idea of where the fuel mostly likely can and cannot be. The models run are not perfect, and there are uncertainties, but we know that units 2 and 3 couldn't have melted through the containment liner. It's very likely that unit 1 didn't melt through the containment liner either.

From an actual physical perspective, where exactly it is, you can't just go into containment. The dose rates and contamination levels are beyond acceptable for something like that. Additionally the fuel is not going to look like what you expect it to look like. We all need to remember that fuel < 5 years old, when it has little or no shielding, can deliver lethal doses in minutes.

TEPCO is looking into techniques to provide a definitive location of the core material. http://www.japantimes.co.jp/news/20...ic-rays-peer-into-reactor-cores/#.U1rNOFVdWSo

This is one method they plan on using, which seems pretty cool, and has been tested. The issue is the cosmic rays and other stuff they are looking for have very low interaction rates, and as a result it will take months to collect a sufficient 'image' to 'develop' the picture.

I for one am glad TEPCO is not saying they "know" where the fuel is with certainty. There is a degree of confidence involved, but it's much better to prove it. This isn't like Chernobyl where you had all this piping and other stuff below the reactor where the fuel could potentially slump. The BWR containment system pretty much puts bounds on how far it could have migrated, as the further the fuel tries to migrate, the more concrete and other materials will mix in with it, which will effectively reduce the heat density and limit the maximum possible transit.

 

[nikkkom]

If some fuel gets out of the pool, then the radiation levels there jumps at least one or two magnitude immediately. Some areas of the site would go 'Chernobyled'.

I think to remove that machine is a really critical operation.

I would imagine there will be several radiometers around the pool while the machine is being pulled up. If they go up significantly, the crane would be stopped.

 

[jadair1]

I would imagine there will be several radiometers around the pool while the machine is being pulled up. If they go up significantly, the crane would be stopped.

You have far more confidence in the competence of TEPCO than I do.

 

[jadair1]

From a computer/mathematical model, we have a very good idea of where the fuel mostly likely can and cannot be. The models run are not perfect, and there are uncertainties, but we know that units 2 and 3 couldn't have melted through the containment liner. It's very likely that unit 1 didn't melt through the containment liner either.

From an actual physical perspective, where exactly it is, you can't just go into containment. The dose rates and contamination levels are beyond acceptable for something like that. Additionally the fuel is not going to look like what you expect it to look like. We all need to remember that fuel < 5 years old, when it has little or no shielding, can deliver lethal doses in minutes.

TEPCO is looking into techniques to provide a definitive location of the core material. http://www.japantimes.co.jp/news/20...ic-rays-peer-into-reactor-cores/#.U1rNOFVdWSo

This is one method they plan on using, which seems pretty cool, and has been tested. The issue is the cosmic rays and other stuff they are looking for have very low interaction rates, and as a result it will take months to collect a sufficient 'image' to 'develop' the picture.

I for one am glad TEPCO is not saying they "know" where the fuel is with certainty. There is a degree of confidence involved, but it's much better to prove it. This isn't like Chernobyl where you had all this piping and other stuff below the reactor where the fuel could potentially slump. The BWR containment system pretty much puts bounds on how far it could have migrated, as the further the fuel tries to migrate, the more concrete and other materials will mix in with it, which will effectively reduce the heat density and limit the maximum possible transit.

Did they not attempt this over a year ago? I seem to remember something about this from Los Alamos National Laboratory.

Found the link, http://www.lanl.gov/newsroom/news-r...ushimas-nuclear-scar.php#.UH7TRWP9jq0.twitter

Never did hear the results of this and if they even did try it, but from my limited understanding and faulty memory they would use some sort of triangulation method to locate the corium's or determine that Elvis had indeed left the building.

If Elvis had left they would not be able to locate him with this method they would just know he was not there.

 

[nikkkom]

You have far more confidence in the competence of TEPCO than I do.

Yes, I think TEPCO employees are not eager to get fatal dose from a piece of an unshielded spent fuel rod accidentally brought up.

 

[jim hardy]

Yes, I think TEPCO employees are not eager to get fatal dose from a piece of an unshielded spent fuel rod accidentally brought up.

yes, when the exposure meters begin to show any unexpected increase - it's all stop...

 

[Hiddencamper]

yes, when the exposure meters begin to show any unexpected increase - it's all stop...

While I'm not familiar with Fukushima's current setup. I know of plants that have their refuel equipment interlocked with radiation and criticality monitors. If those go off, the withdrawal function on the crane locks out to prevent you from pulling a bundle out.

 

[etudiant]

Imho TEPCO has actually performed pretty well in managing the aftermath of this disaster.
The wreckage is being cooled, the cooling water is getting decontaminated from all but the tritium and the SFP of reactor 4 is almost half emptied. The site is leaking less contamination, primarily because the short lived products are pretty much gone, but also because the site is somewhat better sealed. The crisis is clearly over, but clearing the wreckage will be a decades long process still.
While the company has been very secretive, something that has not helped its credibility, it is obviously a ward of the state at present and hence unable to release anything without government approval. It is therefore reassuring that the actual clean up work is proceeding reasonably on schedule, with work beginning on clearing the reactor 3 SFP. It is doubtful that any other country's nuclear industry would have done better, given that all aspects of the work are unprecedented, so everything had to be designed from scratch. In many respects, this effort is Japans equivalent to the Apollo project and Japan's industry deserves credit and admiration for the quality of their work in mitigating this disaster.

 

[jadair1]

Imho TEPCO has actually performed pretty well in managing the aftermath of this disaster.
The wreckage is being cooled, the cooling water is getting decontaminated from all but the tritium and the SFP of reactor 4 is almost half emptied. The site is leaking less contamination, primarily because the short lived products are pretty much gone, but also because the site is somewhat better sealed. The crisis is clearly over, but clearing the wreckage will be a decades long process still.
While the company has been very secretive, something that has not helped its credibility, it is obviously a ward of the state at present and hence unable to release anything without government approval. It is therefore reassuring that the actual clean up work is proceeding reasonably on schedule, with work beginning on clearing the reactor 3 SFP. It is doubtful that any other country's nuclear industry would have done better, given that all aspects of the work are unprecedented, so everything had to be designed from scratch. In many respects, this effort is Japans equivalent to the Apollo project and Japan's industry deserves credit and admiration for the quality of their work in mitigating this disaster.

TEPCO in my opinion has done a horrendous job in managing this disaster.

What of the reports of continual Strontium 90 releases to the Pacific?

Also reports of Iodine 131 still being detected in significant quantities, with a half life of approximately 8 days this would seem to me to indicate that criticality is still ongoing. Sorry I cannot find any credible links to this.

And what of the reports of the Yakuza conscripting homeless people with no knowledge of nuclear to work on this mess.

TEPCO's track record here has been horrendous in my opinion.

 

[jim hardy]

The anti-nuclear propagandists certainly take advantage of "people with no knowledge of nuclear" . Pull-eze stop with the 'ongoing criticality' tabloid crapola.

Also reports of Iodine 131 still being detected in significant quantities, with a half life of approximately 8 days this would seem to me to indicate that criticality is still ongoing. Sorry I cannot find any credible links to this.

no, I don't reckon you will find any either.

The hubris of Fukushima and Chernobyl

Dan Drollette Jr

Dan Drollette, Jr. is a science writer/editor and foreign correspondent who has filed stories from every continent except Antarctica. His stories have appeared in Scientific American,...

A new, 300-page UN report says that the Fukushima nuclear disaster is unlikely to cause radiation-related cancers on anything comparable to the scale of what followed the Chernobyl meltdown. At an April 3 scientific conference in Vienna this year, the United Nations Scientific Committee on the Effects of Atomic Radiation said that the amount of radioactive substances such as iodine 131 released after the 2011 accident were much lower than after Chernobyl. Consequently, the radiation exposures—and subsequent cancers—were minimal, especially when compared to the thousands of cancer cases that occurred in the decades after Chernobyl.

http://thebulletin.org/hubris-fukushima-and-chernobyl7038
links there lead to the UN reports.

The mistakes were made before the accident .
Given the size of the resulting mess they've done quite well.
A lesser people would have just buried it.

 

[Rive]

TEPCO in my opinion has done a horrendous job in managing this disaster

By my opinion: they made a good job with some mistakes.
But those mistakes are not the 'mistakes' often mentioned by the media or the gundersenists.

What of the reports of continual Strontium 90 releases to the Pacific?

Once that water gets out of the bucket and reaches the soil, you can't really stop it.
The initial release happened around 2011.04. They had no chance to prevent it or to clean it up. The amount leaked out to the soil that time will all reach the ocean eventually.

 

[Borek]

To all: please remember to read and follow the forum rules.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140428_06-j.pdf
(in Japanese)
This PDF document presents the planned investigation of floors 2 and 3 of reactors 1-3, using two robots, one equipped with a radiation measuring devices and one with a gamma camera (also both bearing normal cameras and lighting). One is radio controlled, one has a 300m long cable. The investigation is probably ongoing right now in Reactor Building 1, then will move to Reactor 2 in late May, and then to Reactor Building 3 in mid June. The results are expected to be useful for the decontamination/shielding/decommissioning activity.- And this is the daily report from TEPCO issued on April 28 (again, in Japanese).
http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140428_07-j.pdf
It’s not the most recent one, but I wanted to ask what do you think of this piece of information listed on the first page, right under the first table:

“Reactor 1
H26/4/26 9:31: A change in the amount of cooling water supplied to the Reactor was observed. Therefore, the amount of water supplied through the main line (is this the word?) has been increased from 2.2 m3/h to 2.5 m3/h. (The amount of water supplied through the core spraying system is maintained at 2.0 m3/h).

Reactor 2
H26/4/26 9:26: A change in the amount of cooling water supplied to the Reactor was observed. Therefore, the amount of water supplied through the main line (is this the word?) has been increased from 1.8 m3/h to 2.0 m3/h. (The amount of water supplied through the core spraying system is maintained at 2.5 m3/h).”

The wording seems a little wrong (“a change was observed, therefore we modified/increased the amount of water supplied”). But besides that, do you find this significant in any way? Why do they need to pump more cooling water?

- I’d also like to ask something about the amount of contaminated water accumulated in the basement of turbine buildings for units 1 and 2. The numbers reported daily keep rising, the volume approaches 11,000 m3 by now, and I don’t understand, isn’t there a need to do something to decrease it? As in, don’t they aim to process more water from these basements than gets added daily from the cooling of the reactors, to reverse the trend? Or is this postponed for later when storing space becomes available (presumably after releasing some treated, deemed-safe water into the ocean)? In that case – does anyone have an idea about how much water can actually be stored in those basements?

(Sorry if the questions are a bit naïve, I don’t really know much about these things.)

 

[Rive]

But besides that, do you find this significant in any way? Why do they need to pump more cooling water?

Not a significant change. My bet is on the weather - as it gets warmer, more cooling might be needed to keep the 'cold shutdown' temperature - , but I don't have any real information.
Was there any change in RPV temperature data recently?

- I’d also like to ask something about the amount of contaminated water accumulated in the basement of turbine buildings for units 1 and 2. The numbers reported daily keep rising, the volume approaches 11,000 m3 by now, and I don’t understand, isn’t there a need to do something to decrease it? As in, don’t they aim to process more water from these basements than gets added daily from the cooling of the reactors, to reverse the trend? Or is this postponed for later when storing space becomes available (presumably after releasing some treated, deemed-safe water into the ocean)? In that case – does anyone have an idea about how much water can actually be stored in those basements?

Generally, they have to keep level of the water there lower than the groundwater level, to prevent it leaking out. Apart from that, the lower the level inside the more water leaking in, which is also inconvenient. So on long term they have to keep a water level which is close to the groundwater level, but a bit lower than that.

The management of the water level is also a question of available treatment and storage capacity. It's a complex problem.

As they started with the groundwater bypass, I would expect the groundwater level sink -> the water level in the basements should decrease, not increase. But I did not checked the water levels for some time. I will try to look them up.