Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Hiddencamper]

This might have been the reason before Fukushima.

But what are the reasons why filtered vents are not mandated in US even _after_ Fukushima experimentally demonstrated that meltdowns are a realistic possibility?
Well, they definitely could have properly engaged IC on Unit 1, if accident manuals has clear directives to do so in station blackout. Thus, Unit 1 could have been saved.

And if manuals would have sections directing them to do so, they could have vented RPVs of Units 2 and 3 down to atmospheric pressure _before_ fuel started to melt. This would have released small amounts of radioactivity, yes, but then they could start injecting water with much less powerful pumps, since there would be no pressure difference to fight against. Units 2 and 3 could have been saved, too.

In reality, and as the video above clearly explains, with no manuals, they tried to reach two opposing goals at once: keep RPVs pressurized, and pump water into them. It was not possible to achieve both at once.

We need to clear up this misconception about what happened at unit 1.First off, the operators performed all required actions in accordance with the BWR Owners Group Emergency Procedure Guidlines (EPGs).

You have to simultaneously stabilize level and pressure, then commence a controlled cooldown. You are not allowed under the conditions they were into exceed the cooldown rate of 100 degF per hour. That means manually cycling the IC motor operated 003 valve to turn the IC on and off to stabilize pressure. This is as written in the EPGs, and is how the operators are trained. There are very limited cases where EPGs allow you to exceed the 100 degF per hour cooldown rate. (Post Fukushima we have a lot more, but I’ll write about that later).

Anyways, when the IC is running, there’s really no need to inject water to the reactor, because it was isolated at the time. That’s the purpose of the IC, to allow an isolated reactor to cool down without steaming or feedwater supply. The only leakage would be if a reactor coolant pump seal started to leak, and as they cooled down, the leakage would decrease greatly. The leakage is based on time at high pressure without seal cooling, so by following the EPGs you would avoid gross seal failure or leakage. All signs and data point to the operators doing that during the time between the earthquake and tsunami. They followed their procedures and training correctly.

Anyways, it didn’t matter if the IC was on service or not. The best data we have tells us the containment inboard IC isolation valves went partially or fully closed during the flooding and electrical failures that occurred. The operators even tried to manually open the 003 valve and had no success.

So we need to get away from incorrect statements deriding the operators for following the EPGs as written. (I’m on the emergency procedure committee).

Post Fukushima, we have a lot of changes, and one of them is if you are in a situation with no high capacity reflood capability (similar to Fukushima), you do have permission to exceed 100 degF per hour in order to prevent the core from being uncovered while trying to maintain level with low capacity reflood pumps. I should note that during the first hour at Fukushima daiichi unit 1, this would not have changed the operator response. During the first hour, the plant had all safety systems available and there was no need or requirement to violate the cooldown limit. You can’t just violate the EPGs without a need to do so.

Also hardened vents ARE mandated in the US for Mark I and II plants and are being installed in upcoming refuel outages. They are mandated by adequate protection requirements, however when 10CFR50.155 is issued within the next 6 months they will be required by regulations as well. This regulation is about mitigating severe /beyond design based accidents. The BWROG emergency procedure committee also just issued revision 4 of the EPG/SAGs which complies with hardened vent and all remaining post Fukushima requirements. Rev 3 was the initial/immediate changes required for safety after Fukushima, and rev 4 is based on all the data and learnings we’ve had in the last 5 years since then. Rev 4 also includes more comprehensive scram failure response actions, better actions and strategies for when core flooding is required, procedures for emergencies with a shutdown or refueling reactor, and a lot of cleanup of legacy items in the EPGs including calculation and model updates.Talking about units 2/3, if they had depressurized those units earlier they would have lost their injection systems (RCIC/HPCI). Even today that’s not the right action initially. When RCIC and HPCI failed, the operators did attempt to perform an emergency blowdown. Unit 2 they were unsuccessful. Unit 3 they couldn’t get relief valves to open manually, but later on the ADS system automatically did blowdown the reactor, but water wasnt being pumped in adequately for many reasons (bad lineups mostly). But there’s a lot of learnings here and there are technical reasons why you have to be very careful in these station blackout situations with depressurizing the core, because it consumes a massive amount of inventory during the depressurization and causes you to lose your steam driven injection systems.

If you have any questions please let me know.

 

[nikkkom]

We need to clear up this misconception about what happened at unit 1.

First off, the operators performed all required actions in accordance with the BWR Owners Group Emergency Procedure Guidlines (EPGs).

You have to simultaneously stabilize level and pressure, then commence a controlled cooldown. You are not allowed under the conditions they were into exceed the cooldown rate of 100 degF per hour. That means manually cycling the IC motor operated 003 valve to turn the IC on and off to stabilize pressure. This is as written in the EPGs, and is how the operators are trained. There are very limited cases where EPGs allow you to exceed the 100 degF per hour cooldown rate. (Post Fukushima we have a lot more, but I’ll write about that later).

Anyways, when the IC is running, there’s really no need to inject water to the reactor, because it was isolated at the time. That’s the purpose of the IC, to allow an isolated reactor to cool down without steaming or feedwater supply. The only leakage would be if a reactor coolant pump seal started to leak, and as they cooled down, the leakage would decrease greatly. The leakage is based on time at high pressure without seal cooling, so by following the EPGs you would avoid gross seal failure or leakage. All signs and data point to the operators doing that during the time between the earthquake and tsunami. They followed their procedures and training correctly.

Anyways, it didn’t matter if the IC was on service or not. The best data we have tells us the containment inboard IC isolation valves went partially or fully closed during the flooding and electrical failures that occurred. The operators even tried to manually open the 003 valve and had no success.

So we need to get away from incorrect statements deriding the operators for following the EPGs as written. (I’m on the emergency procedure committee).

I'm not deriding the operators. I'm "deriding" whoever wrote the manuals, and whoever went as far as to postulate that total loss of power is so improbable that there is no need to analyze and prepare for that scenario. The situation with closed inboard IC isolation valves is the result. "We cannot end up in that situation". Oops, they did. Now what??

Operators were left in a position where they had to invent emergency procedures on the fly, and worse, in some cases they plainly had no necessary equipment to handle their situation.

 

[nikkkom]

Talking about units 2/3, if they had depressurized those units earlier they would have lost their injection systems (RCIC/HPCI).

I don't fully understand how that setup is supposed to work long-term. If you don't remove heat from the reactor and PCV, it will heat up. Churning water around PCV (pumping colder water from suppression pool into RPV, and discharging steam through turbines which power those pumps, back to pool) does not actually remove the heat from the entire thing. What you do initially achieve is you prevent RPV from overheating, but eventually you'll start overheating/overpressuring other parts of the system.

 

[Rive]

I don't fully understand how that setup is supposed to work long-term.

It needs to work only long enough for giving time for the staff to start up (restart) the ultimate heat sink of the plant.

I'm "deriding" whoever wrote the manuals, and whoever went as far as to postulate that total loss of power is so improbable that there is no need to analyze and prepare for that scenario. The situation with closed inboard IC isolation valves is the result.

There was once (twice?) a document linked here about such analysis. That document clearly described the situation what happened with U1 of Fukushima. The predictions were also pretty close to the results as I recall. To put it simply: that type of plant is not able to handle a 'left alone' type SBO for long, therefore the only real way to 'handle' such event is to prevent it happening. That is exactly what failed there, and the reasons for that starts with the failed predictions regarding tsunami heights. The manuals has not much to do with this. Nobody can write a manual for a bicycle about traveling to the Moon. Bicycles are not about traveling to the Moon.

 

[nikkkom]

It needs to work only long enough for giving time for the staff to start up (restart) the ultimate heat sink of the plant.

In which case I prefer that "outdated" IC concept which Unit 1 had. That one did not require anything drastic to work. A few fire trucks per day refilling IC tanks under zero pressure differential would work. (And, of course, with valves which are not placed outside of the personnel's reach).

 

[Rive]

In which case I prefer that "outdated" IC concept which Unit 1 had.

I too like the ESBWR design. But different times, different preferences.

Ps.: just read the whole page where that linked post is. Everything brought up here are already there... This is not the first time we are discussing this.

 

[Hiddencamper]

First up, your comment that the EPGs were short sighted is not informed. I know the men (Ken Ross from KLR, Bill Williamson from TVA, and others) who created the BWR symptomatic EPGs. The EPGs were separated into the EOPs for all events up until core damage, and SAGs (Severe accident guidelines), for events after core damage. At no point was an attempt made to specify a type of event and the procedures were written as generic symptom based procedures with specific contingencies. There was no effort to explicitly define any event because they didn’t want the put the operators into a situation where something that was beyond their planning led the operators to be stuck in a procedure or situation that leads to core damage or worse due to something that nobody even though of yet. The EOPs are generic in nature and while they aren’t perfect, they cover everything by focusing purely on key safety function response. They never said “we aren’t going to look at beyond design basis events” or “we won’t look at beyond design basis events”, they simply said “for this critical safety function, what are all the tools that can stabilize it and restore it, and what are the critical thresholds before more drastic actions are needed”. You have to get your mindset away from an event based response. Events don’t exist in the EPGs.

The need to make stuff up on the fly was because of two reasons: First is Japan did not require their plants to implement the SAG portion of the EPGs for core melting events, and second is that the SAGs were mostly based on assumptions of how the plant would behave in a severe accident situation. The SAGs have been heavily reworked since Fukushima and now more appropriately utilize methods to minimize unnecessary injection and maintain decay heat removal methods.

With regards to unit 1, as I said the IC was lost and was unrecoverable due to actions by automatic systems that inappropriately responded to the loss of power. Not due to operator actions, as closing the 003 valve is not unrecoverable as you can manually open that valve if needed. One thing I will say, is that Dresden station in the US designed an alternative power supply and hookups to forcibly open the drywell inboards for the IC which Fukushima daiichi did not have, and could have prevented this. This plant modification was custom at Dresden though.

With units 2/3, if you would have depressurized unit 2 immediately, you would have lost injection, instead of being able to inject for 70 hours. Plus you would have burned up a massive amount of inventory. Depressurizing with the automatic depressurization system consumes roughly 100 inches of inventory with no injection. That’s over 20,000 gallons of water lost, and for my plant that’s 2/3rds of our inventory above top of active fuel. You need to have an alternative injection source lined up BEFORE you depressurize.

Just a word about the difference between the IC and RCIC, IC requires external water to extend the coping time and in general contains less than 1 hour of water in the shell. RCIC has days of coping time. The IC cannot make up for leaks and when your reactor recirculation pump seals do start to fail, inventory drops. The seals are estimated to leak 36 gpm during this event, which RCIC can make up for, but IC cannot, and at 36 gpm you are looking at a time to drain the reactor somewhere between 12-16 hours. This is a big part of why RCIC was installed instead of IC. Along with the fact that RCIC was intended to be used with the RHR heat exchangers in steam condensing mode to allow for a controlled cooldown versus the all or nothing approach ic has.

Esbwr doesn’t have recirc pumps, but does have passive gravity feed tanks and suppression pool equalization valves which can keep the core covered long term, which is why the IC is appropriate for that type of unit. IC is an ok system if in bwr gen 2/3 designs, but it really doesn’t shine until the ESBWR design.

 

[etudiant]

Presumably the central objective should be to always keep the core covered and prevent a meltdown.
Given the functional survival of the installation falls into the secondary, nice to have, category, then any water will serve to replenish the inventory in those circumstances and if the reactor is depressurized, it can be freely added..
Obviously the Japanese site managers has not been prepared for this kind of choice, I remember the debate about them using sea water for coolant, not sure if it was on a still pressurized reactor.

 

[mheslep]

We need to clear up this misconception about what happened at unit 1...

Does "isolated reactor" refer to a loss of station grid power, or a loss of all power including emergency site power? The isolation condenser (IC) apparently requires pump power (or is it also gravity fed)? If the latter, then in the case of the Fukushima accident, it seems the IC is no help after the wave arrives.

 

[Hiddencamper]

It needs to work only long enough for giving time for the staff to start up (restart) the ultimate heat sink of the plant.There was once (twice?) a document linked here about such analysis. That document clearly described the situation what happened with U1 of Fukushima. The predictions were also pretty close to the results as I recall. To put it simply: that type of plant is not able to handle a 'left alone' type SBO for long, therefore the only real way to 'handle' such event is to prevent it happening. That is exactly what failed there, and the reasons for that starts with the failed predictions regarding tsunami heights. The manuals has not much to do with this. Nobody can write a manual for a bicycle about traveling to the Moon. Bicycles are not about traveling to the Moon.

A station blackout is only a 4-6 hour event. And it’s a specific event based mitigation guideline, not an emergency operating procedure. Your EOPs are always used, even in a station blackout. However if you were in an SBO you would use those procedures in tandem with the EOPs. The EOPs don’t care what event you are in. P

Does "isolated reactor" refer to a loss of station grid power, or a loss of all power including emergency site power? The isolation condenser (IC) apparently requires pump power (or is it also gravity fed)? If the latter, then in the case of the Fukushima accident, it seems the IC is no help after the wave arrives.

Isolated means your containment and main steam isolation system actuated, closing the main steam lines, preventing the turbine driven feedwater pumps from operating, and loss of all non essential systems to the containment. Loss of reactor recirculation pumps, drywell cooling, instrument pressurized air, etc.

Your reactor can end up isolated either due to a loss of power, loss of main condenser, a LOCA signal (whether spurious or actual, or if just in response to a momentary loss of feedwater).

When you are isolated, you lose your normal pressure control methods (condenser). Safety or relief valves will actuate, causing huge swings in level and pressure which are difficult to control. Operators will utilize alternate means to remove decay heat and add inventory if required (like running IC, injecting with RCIC, or placing RCIC/HPCI into recirculation mode for supplemental pressure control), and if necessary, will use extended manual relief valve actuations to help stabilize level and pressure.

IC and RCIC are mitigating systems for isolation events. Under a design basis LOOP, these systems are supposed to be able to support a cooldown to less than the shutdown cooling permissive without the need for actuating the ECCS. For the IC, it has to operate in tandem with a makeup pump of some sort (or a diesel driven fire protection pump). IC also needs control rod drive pumps to supply injection of up to 200 gpm to support the cooldown and any leakage. As for RCIC it was designed to operate in a closed loop with the RHR heat exchangers in steam condensing mode, but that mode is disabled due to the potential to damage the heat exchangers. Instead you dump steam to the suppression pool with relief valves, cool the pool with RHR, and inject the pool back to the reactor with RCIC.

Isolation events are challenging to stabilize for BWR plants and require manual operator action. Unlike a pwr where the steam generator PORVs have variable lift capability to control pressure and temperature, BWR relief valves are all or nothing shots, add heat to the containment, cause huge reactor water level swings due to shrink/swell, and your flow controller on RCIC needs manual action to dial in flow once level is recovering. At my plant, every ops candidate for a license has to be able to stabilize level and pressure on their own during an isolation transient to pass license class.

 

[Hiddencamper]

Presumably the central objective should be to always keep the core covered and prevent a meltdown.
Given the functional survival of the installation falls into the secondary, nice to have, category, then any water will serve to replenish the inventory in those circumstances and if the reactor is depressurized, it can be freely added..
Obviously the Japanese site managers has not been prepared for this kind of choice, I remember the debate about them using sea water for coolant, not sure if it was on a still pressurized reactor.

The objective is to protect the health and safety of the public first, and prevent core damage second. The priorities have flip flopped on how exactly you do that though. For example, there was a point in time where you took actions to preserve the containment even if it meant losing core cooling. The idea is if the containment fails, you will cabotage your eccs pumps and now have a loss of both core and containment cooling and integrity. Well today, the EPGs prioritize the core over the containment in virtually all conditions, as preventing core damage also prevents dangerous rad levels in the plant which can hinder response. So that’s a post Fukushima change.

The decision for seawater use is weird. The base EOPs allow you to use seawater injection systems as part of alternate level control contingency C1 if you determine that you will be unable to maintain level above the minimum steam cooling reactor water level. That said, typically lining up for seawater takes a lot of effort and your tech support center usually has command and control by the time that happens. So the decision goes to them.

The major risk with seawater, is it will clog the bottom debris filters for the fuel and challenge core cooling. You need to raise level above the steam dryer skirt to allow for reverse circulation over the top of the core, bypassing the debris filters. If you are in a situation where you can’t raise level that high, you risk causing damage earlier and having molten salt now. So it’s not a simple “go put seawater in”, not to mention the increased potential to degrade and damage reactor internals and dry tubes, which leads to bottom head unisolable leakage.

 

[etudiant]

The objective is to protect the health and safety of the public first, and prevent core damage second. The priorities have flip flopped on how exactly you do that though. For example, there was a point in time where you took actions to preserve the containment even if it meant losing core cooling. The idea is if the containment fails, you will cabotage your eccs pumps and now have a loss of both core and containment cooling and integrity. Well today, the EPGs prioritize the core over the containment in virtually all conditions, as preventing core damage also prevents dangerous rad levels in the plant which can hinder response. So that’s a post Fukushima change.

The decision for seawater use is weird. The base EOPs allow you to use seawater injection systems as part of alternate level control contingency C1 if you determine that you will be unable to maintain level above the minimum steam cooling reactor water level. That said, typically lining up for seawater takes a lot of effort and your tech support center usually has command and control by the time that happens. So the decision goes to them.

The major risk with seawater, is it will clog the bottom debris filters for the fuel and challenge core cooling. You need to raise level above the steam dryer skirt to allow for reverse circulation over the top of the core, bypassing the debris filters. If you are in a situation where you can’t raise level that high, you risk causing damage earlier and having molten salt now. So it’s not a simple “go put seawater in”, not to mention the increased potential to degrade and damage reactor internals and dry tubes, which leads to bottom head unisolable leakage.

Thank you for a very enlightening response. It is interesting that EOP priorities have been reset as a result of the Fukushima experience.
I'd not seen any public reference or discussion as to these changes. Yet one might think that the nuclear power industry should take the lead in publicizing them.

Imho, they are clear proof that the industry is adapting and learns from experience, contrary to the media generated image of a sclerotic bureaucracy focused on examining minutiae while unable to address major challenges.

Separately, thank you also for the discussion on sea water use. I'd also found that stunning, thinking the cooling channels would be salt clogged in a heartbeat.
Do we know how well or how badly it worked? I've never seen any follow up report which addresses that.
Was it perhaps because the meltdown happened before the salt water injections began?

 

[Hiddencamper]

The owners group emergency procedure committee started on post Fukushima findings right away, and about 3 years later all plants had to issue changes.

Thank you for a very enlightening response. It is interesting that EOP priorities have been reset as a result of the Fukushima experience.
I'd not seen any public reference or discussion as to these changes. Yet one might think that the nuclear power industry should take the lead in publicizing them.

Imho, they are clear proof that the industry is adapting and learns from experience, contrary to the media generated image of a sclerotic bureaucracy focused on examining minutiae while unable to address major challenges.

Separately, thank you also for the discussion on sea water use. I'd also found that stunning, thinking the cooling channels would be salt clogged in a heartbeat.
Do we know how well or how badly it worked? I've never seen any follow up report which addresses that.
Was it perhaps because the meltdown happened before the salt water injections began?

Well, all units have some level of core melt, so all we know is seawater injection at that point prevented a liner melt through.

One of the biggest EOP changes (in my opinion), is the new Minimum PreDepressurization Reactor Water Level. The basic idea is this: under normal conditions, if you don’t have high pressure injection you wait until adequate core cooling is lost (about core 1/3rd uncovered), then you perform an emergency depressurization. The ED provides adequate core steam cooling, however at the end of the blowdown you lose steam cooling and your core spray system has to be injecting to quench the fuel back to cold conditions to support the reflood.

If you have no core spray and no high capacity injection, (if your only injection is low capacity, like a fire pump or FLEX pump), this is a horrible strategy, because what we learned during Fukushima, is low capacity pumps cannot quench the fuel faster than the hydrogen reaction can generate heat, so the water you inject actually causes the core to melt down faster by producing more hydrogen.

Anyways, under a situation with no high capacity reflood, we give permission to violate the 100 degF per hour cooldown limit to get to those low capacity / low pressure injection pumps before level drops below the top of the fuel. Additionally the MPDRWL curve is now on the flow charts and establishes the lowest safe water level for a given pressure to ensure if you had to perform an emergency blowdown that level stays above the top of the core and it never goes into superheat, meaning you don’t have to quench it before your injection actually improves your inventory situation. This whole thing is generic so it applies to Fukushima situations, or any situation where you find yourself here.

Just babbling now. But yes, we have been working on it. Revision 4 of the emergency planning guidelines was issued on June 1st starting a compliance clock for all bwrs to implement it.

 

[Astronuc]

Great information/discussion Hc.

With regards to unit 1, as I said the IC was lost and was unrecoverable due to actions by automatic systems that inappropriately responded to the loss of power. Not due to operator actions, as closing the 003 valve is not unrecoverable as you can manually open that valve if needed. One thing I will say, is that Dresden station in the US designed an alternative power supply and hookups to forcibly open the drywell inboards for the IC which Fukushima daiichi did not have, and could have prevented this. This plant modification was custom at Dresden though.

Does QC have something similar to that employed at Dresden? As I recall, the BWR/2s and BWR/3s are ECCS limited/challenged, and their LOCA analyses produce the highest PCTs in the fleet.

 

[Hiddencamper]

Great information/discussion Hc.
Does QC have something similar to that employed at Dresden? As I recall, the BWR/2s and BWR/3s are ECCS limited/challenged, and their LOCA analyses produce the highest PCTs in the fleet.

Pct is for LOCA response. The IC/RCIC systems are not for LOCA response although they help with smaller LOCAs.

I do know that quad cities does have a separate safe shutdown pump (400 gpm) in addition to their RCIC and HPCI systems. I believe it’s motor driven but not positive. So it provides an important backup to maintain minimum injection required to keep the core covered during isolation events.

 

[Hiddencamper]

deleted by mod

SBO was outside of the original design basis and nrc regulations were put in place to require adequate coping. Considering that a LOOP is a once in a decade to once in the lifetime of the plant event, then to have all diesels fail and have no onsite power, that’s very low risk so the nrc allowed for realistic assumptions like return to service time for the closest black start unit, station blackout generators, and the requirement that every nuclear unit have a dedicated black start plant that can restore limited offsite power in that time frame. (4-8 hours)

At the time it made sense. Today, the FLEX program covers plants indefinitely, using portable and offsite equipment to cope beyond the SBO period.

 

[etudiant]

The revised Emergency Planning Guidelines seem to be quite a substantive piece of work, yet they have not been mentioned, much less discussed, in any public forum that I know of. Is this a deliberate low profile policy?
The current administration seems less hostile to nuclear energy. Both it and the public would probably welcome tangible demonstrations of industry improvement measures.

 

[Hiddencamper]

The revised Emergency Planning Guidelines seem to be quite a substantive piece of work, yet they have not been mentioned, much less discussed, in any public forum that I know of. Is this a deliberate low profile policy?
The current administration seems less hostile to nuclear energy. Both it and the public would probably welcome tangible demonstrations of industry improvement measures.

It’s not really deliberate. It’s just something we maintain. One of the dozens of programs that protect nuclear safety that aren’t even thought about day to day. It’s not really a low profile policy. I mean, what’s the announcement? Business as usual in nuclear plant : )

 

[Astronuc]

Pct is for LOCA response.

I only mentioned PCT and LOCA with respect to the older BWR designs that are ECCS limited. Fukushima Daiichi unit 1 was a BWR/3 and Units 2, 3 and 4 were BWR/4s.

I suspect there was some damage to the penetrations underneath, so possibly one or more units actually had a SBLOCA in addition to the LOOP and loss of ECCS.

 

[Sotan]

"Tepco mulling decommissioning Fukushima Daini nuclear plant: chief"
https://mainichi.jp/english/articles/20180614/p2g/00m/0dm/055000c

 

[Hiddencamper]

I only mentioned PCT and LOCA with respect to the older BWR designs that are ECCS limited. Fukushima Daiichi unit 1 was a BWR/3 and Units 2, 3 and 4 were BWR/4s.

I suspect there was some damage to the penetrations underneath, so possibly one or more units actually had a SBLOCA in addition to the LOOP and loss of ECCS.

The initial NAIIC report didn’t not see evidence of an SBLOCA between the earthquake and tsunami and this was later confirmed in follow up studies. We do know we saw 36-38 gpm of Reactor recirculation pump seal leakage that developed over several hours (expected design leakage is less than 50 gpm which is not typically considered a SB LOCA as it is within the capacity of the CRD injection pumps). To my knowledge and the owners group knowledge is there was no LOCA at any unit.

I think PCT is limiting for small to moderate LOCAs where there is a loss of high pressure injection combined with a required ADS activation on low level. In this case, because quad (and many BWR 3 plants) have only 3-4 ADS valves, there is less steam cooling to the core during the blowdown phase before reflood commences, causing elevated PCTs. Compared to newer plants which utilize 5-7 SRVs and have steam cooling down to 150 psig or less, such that core spray is not only in service but has several minutes of runtime prior to losing adequate steam cooling flow. Those plants do have higher power densities as a result, but still have managed PCTs.

 

[russ_watters]

The revised Emergency Planning Guidelines seem to be quite a substantive piece of work, yet they have not been mentioned, much less discussed, in any public forum that I know of. Is this a deliberate low profile policy?

Such a thing can be considered "low profile" in that it is a down-in-the-weeds piece of work that isn't meant or useful for public consumption.

The current administration seems less hostile to nuclear energy. Both it and the public would probably welcome tangible demonstrations of industry improvement measures.

I'm not sure what you are looking for. The NRC did indeed take action (and force nuclear companies to take action) to identify and correct vulnerability to Fukushima-like events, and produced public-consumption reports on the subject. Here's an example:
https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/japan-events.html

Also, per @Hiddencamper's response; it is difficult to "demonstrate improvement" in something with a near-flawless record. Any policy/procedure/design changes would have only theoretical impacts; say, reducing an accident odds from 1:1000 to 1:10000 (made-up numbers). Such risk factors are difficult to digest.

 

[etudiant]

Maybe our approaches differ, but after an horrific accident which damaged nuclear power globally, I'd not be hiding any gains that I made or lessons that I learned.

Hiddencamper speaks of substantive changes in the emergency procedures.
I'd consider that to be a very newsworthy development, not something to be slipstreamed in below the radar. At a minimum, a public release puts all the players on notice as to what is considered 'best practice'. The insurers will want to know why these were not followed if things go sour.
Note that implementing this is insurance for the operators and the industry, it shows that all was done that could reasonably be expected, which is a legally defensible position.

 

[russ_watters]

Maybe our approaches differ, but after an horrific accident which damaged nuclear power globally, I'd not be hiding any gains that I made or lessons that I learned.

Nobody is hiding anything. I don't know how you got that from my post.

Hiddencamper speaks of substantive changes in the emergency procedures.
I'd consider that to be a very newsworthy development, not something to be slipstreamed in below the radar.

The US government does not control the media.

At a a minimum, a public release puts all the players on notice as to what is considered 'best practice'.

It doesn't feel like you read the link I posted. The NRC does not just provide "notice", they demand (and receive) compliance.

 

[etudiant]

In other industries, it is common to issue press releases and even to hold news conferences when agreement is reached on a new industry standard.
Hiddencamper indicated that considerable effort had been spent to codify new emergency procedures, some of which involve drastic changes from prior practice.
This is worthy of news coverage, imho.
I do not expect the US government to control the media, but I do expect the industry to speak up when there are major changes to process that may have major public impact. That is clearly not happening. It is a missed opportunity, both here as well as abroad, to show the world that the nuclear industry is serious about improving. Just asserting such a commitment without ongoing supporting evidence is what got the industry to where it is today, staving off terminal decline.

 

[russ_watters]

In other industries, it is common to issue press releases and even to hold news conferences when agreement is reached on a new industry standard...

I do not expect the US government to control the media, but I do expect the industry to speak up when there are major changes to process that may have major public impact.

I do not expect the US government to control the media, but I do expect the industry to speak up when there are major changes to process that may have major public impact. That is clearly not happening.

This is just plain wrong. Here's the link to the NRC's press releases:
https://www.nrc.gov/reading-rm/doc-collections/news/

There's hundreds of them.

Just asserting such a commitment without ongoing supporting evidence...

This is is just plain wrong too -- again, I linked the NRC's webpage with a report of what they are doing. It's not fantasy. It's things that are actually happening.

You have this vision in your head of something that isn't real. You really need to stop treating it like it is and start paying attention to what is actually real.

 

[etudiant]

Thank you, russ_waters, for your perspectives.
My concern is that the NRC press releases you so helpfully linked to do not even hint that there has been a substantial revision of emergency procedures.
It is all site specific small stuff, nothing addressing the larger picture.
Hiddencamper reports that there was a big effort of senior people to pull the new emergency procedures together, but there is not a trace of this development, not even an acknowledgment, in the NRC press releases.
That makes no sense to me and my comments reflect the frustration that generates.

 

[Astronuc]

Thank you, russ_waters, for your perspectives.
My concern is that the NRC press releases you so helpfully linked to do not even hint that there has been a substantial revision of emergency procedures.
It is all site specific small stuff, nothing addressing the larger picture.
Hiddencamper reports that there was a big effort of senior people to pull the new emergency procedures together, but there is not a trace of this development, not even an acknowledgment, in the NRC press releases.
That makes no sense to me and my comments reflect the frustration that generates.

One can search the NRC website on topics such as Fukushima and find pages such as https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/japan-events.html, which describe the actions the NRC took following the accident.

With regard to revising the EPGs, NEI has such an article (18 November 2013)
http://www.neimagazine.com/features/featurerevising-bwr-emergency-procedures/

The NRC has a publication on the revised EPGs, but I'm having trouble with the link.

 

[russ_watters]

My concern is that the NRC press releases you so helpfully linked to do not even hint that there has been a substantial revision of emergency procedures.

I don't even know how to address this. It's like I'm holding up a giant sign saying "YOU ARE HERE" and you are responding with "Where am I?"

I guess all I can say is you will never see that which you don't look at.

[edit: ehh, that's not true, I do have something to say:]

I'm not naive - in fact, I'm cynical. I do believe that most people form opinons based on what their chosen news source tells them to think and if their news source doesn't report on it, they don't even know about it much less have a serviceable opinion on it. But the fact of the matter is that the media doesn't care about boring things like safety protocols because safety protocols just aren't sexy. They don't sell newspapers/ad space. So when a plane almost crashes, it gets a full week of wall-to-wall news coverage, but 6 months from now when the reports come out about why and how to fix it, you won't see them unless you are paying attention or actively looking.

So if you want to have informed opinions, you will need to put some effort into it. And here's how I do it: I remember incidents and issues that pique my interest and I periodically check-up on them to see if the official reports have come out, and then I read the official reports, press releases, etc.

If we want to be informed we have to take responsibility for ourselves and make ourselves informed.

That's just the general principle though. In this case, you are denying the existence of information that you have been shown.

 

[gmax137]

https://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard.html
This looks like a good place to start.

 

[etudiant]

Thank you, gmax137, for the excellent link. It provides much more focused data than the NRC news releases.
Indeed, there was no mention of the EPG Revision 4 in the NRC news releases that russ_waters so helpfully linked to.
I'd not know it ever was formulated if hiddencamper had not discussed it and pointed out that it materially changes the priorities..

I'm an interested citizen, not an industry specialist, so I rely on the industry spokespeople to supply material information.
Their selection criteria may want improving.

 

[jim hardy]

I wonder if "Nuclear News" magazine would make a gift subscription to an interested engineering student ? Surely they'd make one available to his engineering department...
http://www.ans.org/pubs/magazines/nn/
If you're an ANS member it's probably free. Most professional societies have a student rate...

there are others, but that's the one most circulated at my plant.

http://www.world-nuclear-news.org/
http://www.neimagazine.com/
http://www.nuclearplantjournal.com/old jim

 

[Astronuc]

Thank you, gmax137, for the excellent link. It provides much more focused data than the NRC news releases.
Indeed, there was no mention of the EPG Revision 4 in the NRC news releases that russ_waters so helpfully linked to.
I'd not know it ever was formulated if hiddencamper had not discussed it and pointed out that it materially changes the priorities..

I'm an interested citizen, not an industry specialist, so I rely on the industry spokespeople to supply material information.
Their selection criteria may want improving.

jim hardy gave some good examples of the trade press. ANS Nuclear News requires a subscription, although one might be able to find some comment on the ANS website (www.ans.org) and they have something called ANS Nuclear Café (https://ansnuclearcafe.org/) on which one might find some discussion of current topics.

The NRC does not take out adds in newspapers or journal regarding rule-making. They do publicize meetings and requests for public comment. Otherwise, one has to search their website with keywords.

In 2010, NRC released - https://www.nrc.gov/docs/ML1025/ML102560007.pdf (a report from 1982) - Guidelines for the Preparation of Emergency Operating Procedures

In the wake of the Fukushima disaster, the Guidelines were revisited.

The Nuclear Energy Institute (NEI) issued a report, NEI 14-01 [Revision 1], Emergency Response Procedures and Guidelines for Beyond Design Basis Events and Severe Accidents, February 2016. It's basically a summary of the industry's response to the NRC requirements for utilities to review their emergency procedures and responses. NEI 14-01 [Revision 0] - https://www.nrc.gov/docs/ML1424/ML14247A092.pdf - if interested.

On the regulatory side, there is the Code of Federal Regulations (CFR).
§ 50.34 Contents of applications; technical information.
https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0034.html

See (f) Additional TMI-related requirements, and find (ii) Establish a program, to begin during construction and follow into operation, for integrating and expanding current efforts to improve plant procedures. The scope of the program shall include emergency procedures, reliability analyses, human factors engineering, crisis management, operator training, and coordination with INPO and other industry efforts. (Applicable to construction permit applicants only) (I.C.9)

§ 50.34a Design objectives for equipment to control releases of radioactive material in effluents—nuclear power reactors.
https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0034a.html

10 CFR 50.54(q), requirements for following and maintaining in effect emergency plans
§ 50.54 Conditions of licenses.
https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0054.html

Appendix E to Part 50—Emergency Planning and Preparedness for Production and Utilization Facilities
https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-appe.html

See more on CFR here - https://www.archives.gov/federal-register/cfr

EPGs and related discussion is a whole topic for a separate thread.

 

[nikkkom]

https://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard.html
This looks like a good place to start.

For BWR containments Mark I and II:
Hardened vent from wetwell is mandated.
Hardened vent from drywell is optional.
Filtering on the vents: not required.

 

[Hiddencamper]

The nrc is not supposed to be promoting the industry. That’s why it was formed and separated from the atomic energy commission.

The industry heavily tried to advertise the SAFER/FLEX program throug the nuclear energy institute. Sadly they weren’t very effective as their YouTube videos barely break 100 hits most of the time.

Revision 3 of the EPGs was issued in tandem with SAFER/FLEX for immediate response actions. Revision 4 is the major roll up that was issued June 1st this year (a few weeks ago). So there hasn’t even been much time to do anything about it.

 

[gmax137]

WANO reports on post-Fukushima improvements
http://www.world-nuclear-news.org/RS-WANO-reports-on-post-Fukushima-improvements-27061803.html

 

[Sotan]

https://www3.nhk.or.jp/nhkworld/en/news/20180726_42/
"TEPCO to retrieve suspected fuel debris"

 

[nikkkom]

Is there research on the plant response to Cs/Sr contamination from Fukushima?

Japanese being culturally inclined to be obsessed with details, I bet their scientists are examining every plant species growing in that region. Something good may come out of this: we may find plants which are extremely good at pulling Caesium from the soil. I also wonder whether removal of Cs can be improved by adding various salts to the soil.

 

[Astronuc]

Is there research on the plant response to Cs/Sr contamination from Fukushima?

Japanese being culturally inclined to be obsessed with details, I bet their scientists are examining every plant species growing in that region. Something good may come out of this: we may find plants which are extremely good at pulling Caesium from the soil. I also wonder whether removal of Cs can be improved by adding various salts to the soil.

There are numerous open articles from Nature and PNAS on studies related to Fukushima contamination and particularly Cs.

https://www.nature.com/articles/s41598-017-08261-x
Temporal changes in the radiocesium distribution in forests over the five years after the Fukushima Daiichi Nuclear Power Plant accident

One can search Nature using "Fukushima, cesium" and find numerous articles.

https://www.tandfonline.com/doi/abs/10.1080/00380768.2014.954269
Distribution of radioactive cesium in soil and its uptake by herbaceous plants in temperate pastures with different management after the Fukushima Dai-Ichi Nuclear Power Station accident

https://www.tandfonline.com/doi/pdf/10.1080/00380768.2014.1003191
Effect of the Fukushima Daiichi nuclear power plant accident on radiocesium distribution in tea fields in Saitama Prefecture: Intercultivar differences

http://www.pnas.org/content/114/42/11092
Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan

 

[Kochia]

The major risk with seawater, is it will clog the bottom debris filters for the fuel and challenge core cooling. You need to raise level above the steam dryer skirt to allow for reverse circulation over the top of the core, bypassing the debris filters. If you are in a situation where you can’t raise level that high, you risk causing damage earlier and having molten salt now. So it’s not a simple “go put seawater in”, not to mention the increased potential to degrade and damage reactor internals and dry tubes, which leads to bottom head unisolable leakage.

Thank you very much on the comment on seawater injection! For the case of Fukushima Unit 3, would it make any difference to initiate seawater injection right after HPCI was manually shutdown (due to concerns for HPCI turbine damage)? Or was it actually too late because it could lead to even more serious situation that cause earlier core damage and molten salt?

 

[Hiddencamper]

Thank you very much on the comment on seawater injection! For the case of Fukushima Unit 3, would it make any difference to initiate seawater injection right after HPCI was manually shutdown (due to concerns for HPCI turbine damage)? Or was it actually too late because it could lead to even more serious situation that cause earlier core damage and molten salt?

We talked about this I’m the last emergency procedure committee meeting. At unit 3 they were trying to open safety relief valves to keep the reactor depressurized when HPCI finally stalled out and failed so they could inject seawater. They were trying! The srvs were not opening because battery voltage was too low. Later on, the HPCI auxiliary oil pump and booster pump tripped off, and after that happened, battery voltage rose up high enough to open the srvs, but the operators weren’t aware of that. After the core was uncovered, the automatic depressurization system opened srvs to blowdown the reactor, but the operators weren’t prepared to transition to low pressure feed for that as they weren’t expecting the blowdown.

In terms of the right thing to do today, and what we are doing with contingency 1 (alternate level control) in the emergency procedures, is we want the plants to prepare alternate / low pressure injection, even if it means sea water. Then you maintain pressure low, but not so low that rcic/HPCI can’t operate properly. When you you can no longer maintain level, you blowdown the reactor before level drops below the minimum pre depressurization reactor water level, which ensures the core is never uncovered so you don’t have to deal with quenching superheated fuel. Next You flood back up over the steam separator/dryer skirt for natural circulation and to ensure your raw water can get to the fuel if the lower inlet debris strainers block up.

The debris that goes into the vessel including the salt is a challenge only if you are on it for extended periods of time (corrodes the hell out of the fuel and core internals), or if you can’t get level high enough to bypass the debris strainers which may block cooling and natural circulation.

At the end of the day, you keep the core covered at all times, even if it means poor water quality. And you try to get clean water back ASAP. You’ll probably never restart the unit if you dump seawater in while it’s hot, but if you are in the situation where all you have is seawater, not putting it in will result in core damage and never restarting the unit. So the preference is to try and keep the core cooled or at least contained even if it’s seawater.

 

[Kochia]

So two important points: 1. maintain pressure level low enough for alternate water injection without disrupting RCIC/HPCI; 2. if depressurization had to be initiated, it should be ensured that core is not left uncovered. Again thanks very much for elaboration!

 

[Sotan]

Hi all, I trust everybody is doing well. A Happy New Year to you all!

It's been quite a while since I posted in here. I did continue to follow the Fukushima news, I wouldn't say with less interest, but it did seem like the amount of news on the subject has been decreasing. I didn't find anything that felt worth posting.

Now I found this in the 12/27/18 dated "Long- and mid-term roadmap update":
http://www.tepco.co.jp/decommission/information/committee/roadmap_progress/pdf/2018/d181227_08-j.pdf
(sorry, only Japanese for now)

Looks like a new investigation into the PCV of Unit 2 is being planned for end of February 2019. This time they want to actually "pinch" the sediment located in the previous investigations.

A few points from the PDF file linked:

Page numbered 1: Short recap regarding the results of previous investigation(s). Last time, a probe was lowered through the gaps in the grating (where grating panels are gone) and, while no great damage was observed on pre-existing metallic structures, a large amount of sand-like and gravel-like "sediment" was found piled up on the floor of the pedestal. At the surface of this sediment they found the tie-plate of a fuel bundle and other fallen objects.

Pages 2-4: The newly planned investigation aims to determine some of the properties of this sediment (hardness, brittleness) as they are important in view of the future extraction operations. They will use basically the same path and method as last time - modifying only the suspended unit, which will be brought in contact with the sediment in order to assess its properties. Of course images, film, and measurements will also be taken. The unit will be equipped with a set of "mechanical fingers" which will actually probe and "feel" the sediment. As before, an airtight boundary will be set so that no gas escapes from inside the PCV.

Page 5: The new investigation unit will be equipped with a thermometer and radiation meter, will be able to rotate to look around, will have lighting to facilitate viewing and, at the bottom, will feature two "fingers" which can be opened and closed while in contact with the sediment.

Page 6 shows the area intended to be studied (the blue-line pentagon). It's a very small alrea, 400x350mm or so.

Page 7 gives the schedule. The actual investigation is to start around mid-February.

 

[Sotan]

On the road so just a quick link:
https://www.japantimes.co.jp/news/2...ation-probe-melted-reactor-fuel/#.XGR_xGmxVdY

 

[Azby]

Thanks, Sotan. Here is TEPCO's report, with photos and diagrams. Odd there's no photo of the probe itself.

https://www7.tepco.co.jp/wp-content/uploads/handouts_190213_01_e-1.pdf

 

[Sotan]

Thank you Azby.

Short film with images from the control room during the inspection:
https://www4.tepco.co.jp/library/movie/detail-j.html?catid=107299&video_uuid=i8v6r4co

And a 6 minutes film with the probe pinching the deposits:
https://www4.tepco.co.jp/library/movie/detail-j.html?catid=107299&video_uuid=yq53a9f4

 

[Azby]

Here's a nice Toshiba PR video showing the Unit 2 device being tested prior to deployment. It shows the design and operation clearly. There's also a good illustration.

https://www.toshiba-energy.com/en/info/info2019_0128.htm

 

[turi]

A new video by Tepco; the year in review:
https://www4.tepco.co.jp/en/news/library/archive-e.html?video_uuid=xh57k85s&catid=61795

 

[LabratSR]

Removal of fuel at Fukushima's melted nuclear reactor begins

https://www.latimes.com/world/la-fg...VK8kD3SN09fTf6ghjb-YnC0YSHRAGBptWEGgZrHrQIOmY

 

[Astronuc]

Removal of fuel at Fukushima's melted nuclear reactor begins

Emphasis on the spent and fresh (Unused) fuel from the pool, not the damaged core.

"Tokyo Electric Power Co. said workers started removing the first of 566 used and unused fuel units stored in the pool at Unit 3. The fuel units in the pool located high up in reactor buildings are intact despite the disaster, but the pools are not enclosed, . . . "