Fukushima Have they located the melted fuel at Fukushima?

[Hiddencamper]

The IC has code class 1 isolation valves that are inside AND outside of the containment. The inside containment ones cannot be accessed for manual operation just like the SRVs which are inside containment cannot be accessed. So yes, there is ASME code class 2 piping for the IC which lies OUTSIDE of containment, but there are code class 1 isolation valves still that are directly inside and outside of the containment boundary.

ASME code class 1 piping and valves go out to the 2nd isolation valve. In the case of SRVs, there is only 1 valve because they are only inside containment. If I wanted some kind of SRV which could vent outside of containment, I would need at least 2 valves, to allow for single failure (fail open) and to ensure that radioactive releases don't occur. This doesn't fix the problem, in fact, it makes it harder to relief reactor pressure.

With regards of sitting at ~1atm, the issue is that you have to manually open and close your SRVs to do this, and you will deplete your SRV accumulator air supply. IF the Instrument Air isolation valves can be reopened and portable air supplies are available and you have available DC power to actuate the solenoids, THEN holding at 1 atm is ok, but as I've said, its not optimal for all situations.

Holding at 1ATM for the 4-8 hour station blackout scenario is ok, but when you don't have enough knowledge to know what situation you are in, the best thing is to keep the reactor hot, as you don't waste DC power OR SRV accumulator air.

I meant that in this hypothetical scenario steam vent from RPV should be opened and *remain open*.

Then your pressure in the reactor will drop to roughly 0, and your RCIC will fail, causing a loss of all injection. Just to be clear, we are talking about the scenario where your AC power is completely failed and you need to rely on your onsite DC or steam driven systems for some period of time. You can't assume that you are going to have a portable pump lined up for hours as part of the accident scenario. (This is the fukushima response requirement. It doesn't matter what a common sense approach says, you have to follow the rules of the scenario).

 

[nikkkom]

The IC has code class 1 isolation valves that are inside AND outside of the containment. The inside containment ones cannot be accessed for manual operation just like the SRVs which are inside containment cannot be accessed.

Correct me if I'm wrong, but adding valves inside PCV was Japanese "improvement", in original design IC steam lines did not have those valves. Japanese paid dearly for this when power failed, PCV was inaccessible, and they failed to open them. Unit 1 went BOOM first.

With regards of sitting at ~1atm, the issue is that you have to manually open and close your SRVs to do this, and you will deplete your SRV accumulator air supply.

Because relief valve design is bad. They should not need anything to remain open.

Then your pressure in the reactor will drop to roughly 0, and your RCIC will fail, causing a loss of all injection. Just to be clear, we are talking about the scenario where your AC power is completely failed and you need to rely on your onsite DC or steam driven systems for some period of time.

I am saying that relying on such things isn't good enough. Fukushima proved it. They were running their RCIC and kept RPVs pressurised. Did it save them? No. What it did achieve is it made fire trucks incapable of injecting fresh water against high pressure in RPV and PCV. Excellent...

You can't assume that you are going to have a portable pump lined up for hours as part of the accident scenario.

..."therefore let's make sure that portable pump, even if available, will be of no use"? That's a strange position, no?

 

[Hiddencamper]

Correct me if I'm wrong, but adding valves inside PCV was Japanese "improvement", in original design IC steam lines did not have those valves. Japanese paid dearly for this when power failed, PCV was inaccessible, and they failed to open them. Unit 1 went BOOM first.

Containment isolation valves are NOT a Japanese "improvement". They are a required design feature to meet ASME codes for nuclear power plants and associated standards, along with meeting general design criteria requirements. Containment isolation valves are designed to prevent radioactive release, as you have to assume all valves and piping beyond the second containment isolation valve fail in the worst possible manner, and that at least one containment isolation valve fails to shut properly.

The IC was offline at the time of the event because the IC cools the reactor down too rapidly (cooldown rate is > 100 deg F /hr). So the operators manually cycled the system on and off. The tsunami hit while the system was still cycled off or nearly off.

Unit 1 went "boom" first because it had no makeup or decay heat removal. The HPCI isolation valves were also closed (because HPCI was not inservice) (and the HPCI injection valve was probably closed too), otherwise the HPCI system could have been used for injection as well. With no AC or DC power none of these isolation valves could operate.

Because relief valve design is bad. They should not need anything to remain open.

Again we are getting into nuclear plant design requirements. The RPV should be essentially leak teak for all conditions except emergency situations where pressure relief is required. For this reason, the relief valves should FAIL SHUT. The relief valve design is consistent with requirements to minimize radiological consequences and mitigate core damage. Relief valves sticking open are considered a design basis accident condition as it rapidly cools down the core, allows reactor coolant to escape, heats up your suppression pool, and allows radioactive material to escape. If I open a relief valve and force it to stay open, that increases the potential for accident scenarios and increases the probability of radiological release. It also challenges my ECCS, as ECCS is now required to function to maintain reactor water level. Open relief valves increase suppression pool temperature, containment activity, and put cyclic wear and thermal fatigue on the SRV tailpipes. Leaving SRVs open for too long heats the tailpipes up and can lead to earlier failure of the sparger mechanism or downcomers. There are a number of other SRV related issues which are rather complex and ultimately being able to open and close SRVs at will and having SRVs which "fail closed" is the solution.

I am saying that relying on such things isn't good enough. Fukushima proved it. They were running their RCIC and kept RPVs pressurised. Did it save them? No. What it did achieve is it made fire trucks incapable of injecting fresh water against high pressure in RPV and PCV. Excellent...

Please read the various reports from both Japan, http://www.cas.go.jp/jp/seisaku/icanps/eng/final-report.html, and the US industry (INPO Level 1 IER 11-05 http://www.nei.org/resourcesandstat...t-the-fukushima-daiichi-nuclear-power-station).

I know very specifically that at units 2 and 3 they depleted their SRV air accumulator supply while they were holding pressure low for portable injection pumps to try and inject. Unit 3 also manually shut down their HPCI thinking they were about to transition to a portable pump. As a result, pressure went back up, and they lost the ability to inject with portable pumps again. Your idea of trying to immediately blowdown to 1 atm and stay there would have caused them to deplete their SRV air accumulators EARLIER in the event. Depressurizing rapidly is ONLY useful in situations where you can do an EARLY portable injection, but you can't assume that you will have the ability to do that early, and when you aren't able to get that portable injection going and you deplete your SRV accumulators and can no longer control pressure, that greatly increases the probability of core damage which is not acceptable.

There's a lot of complexities with any nuclear power plant and how it functions, combined with the regulations, required codes and standards, operational requirements, etc. You seem to be applying what you think is a "common sense approach", but unfortunately those things do not work in nuclear power.

..."therefore let's make sure that portable pump, even if available, will be of no use"? That's a strange position, no?

By definition during a Fukushima event, you have a loss of that pump if it is pre-installed, and if it is not pre-installed, you still have to "cope" for a certain period of time prior to having any portable equipment available.

Tell me, for an event that destroyed things which were not designed to be destroyed, how are you going to prevent damage to this pre-staged or pre-installed portable pump? You can't have it in the plant, you need it in an elevated, seismic category 1, controlled weather proof enclosure, and it needs to be seismically secured. If its not, you have to assume it failed. And if it is, you need time to identify the extent of the event, then time to get teams to move the equipment to the plant (while operators are working on not losing the plant), time to hook it up, then time to establish the conditions necessary for it to function. You cannot assume something will just work and be available and you could simply hook it up willy nilly, as that violates the initial conditions of the Fukushima scenario.

The Fukushima scenario has a set of complex initial conditions that we have to assume. There are requirements for how long we have to wait before we are "allowed" to assume that the operators can identify the condition and begin hooking up FLEX equipment (from a design space). If we do not follow those initial conditions or requirements then we are not in compliance with the new orders from INPO/NRC.



One last thing, if you want to talk about what you think new plants should be, we can do that. But if we are talking about existing plants, there's really not much room to argue. Existing plants are designed the way they are and have specific design requirements and challenges. They are not going to change into these new passive gravity cooled plants with all of these whizbang features which are designed to automatically blowdown and stay cooled for 72+ hours. And existing gen 2 plants are not KISS in any part of the facility. Even our light switches are complicated (I have a story behind this that involved 2 guys getting suspended for flipping a light switch). Anyways I hope I helped answer some of your questions.

 

[a.ua.]

Good day Hiddencamper

What do you think, could the gas bubble will appear at the input of IC for 2 hours, until it was turned off?
This was the first version of IC failures.

At the cut-off valve inside the standing PCV AC motors.
Small chance that he will remain an alternating current, but not DC.
Or there are inverters?

 

[nikkkom]

The RPV should be essentially leak teak for all conditions except emergency situations where pressure relief is required. For this reason, the relief valves should FAIL SHUT.

That is okay. What I don't get is where the requirements to make valves fail shut *and be inaccessible* inside PCV come from; and why, after opening the valves, *merely keeping them open* requires power and/or air.

The relief valve design is consistent with requirements to minimize radiological consequences and mitigate core damage.

Many people in Japan noticed recently that it didn't work so well. Looks like it's a good time to rethink how these things are done.

The Fukushima scenario has a set of complex initial conditions that we have to assume.

Why? They are not complex at all: "all offsite power is lost. All on-site power, including DGs and batteries are lost". Operators should have this situation described in their emergency manuals. They should perform realistic drills which simulate this condition, and their response. There should be necessary preparations for it (such as filters on vent lines).

None of this was done, and judging by your responses, it is not fully addressed *even now*.

I'll tell you more. I want operators to go *further*. They need to know what to do if not only the above happened, but what to do if they discover that they have no portable water sources and can't cool down the reactor and prevent its meltdown. I don't want to hear them going "oh my gosh, run for your lives!"; I want them to turn the page of their manuals and go to a chapter which tells them what they should do. Should they vent? Through which vent, which valves to open? How to avoid hydrogen explosion? Is there national fast response team which can bring help from unaffected region? etc...

One last thing, if you want to talk about what you think new plants should be, we can do that. But if we are talking about existing plants, there's really not much room to argue. Existing plants are designed the way they are and have specific design requirements and challenges.

Are you saying that next tsunami inundating a BWR/4 plant should be *expected* to make it melt down? That we should _not_ think how to avoid that?

 

[Hiddencamper]

Good day Hiddencamper

What do you think, could the gas bubble will appear at the input of IC for 2 hours, until it was turned off?
This was the first version of IC failures.

At the cut-off valve inside the standing PCV AC motors.
Small chance that he will remain an alternating current, but not DC.
Or there are inverters?

I'm not familiar enough with the IC to give a good answer about a gas bubble. I do know after a scram, a lot of gasses can come out of solution.

With regards to the cut off valve/AC motors. Again I'm not positive with the IC, but the majority of isolation valves use low voltage AC or DC for control power, and AC for the actual valve motor. Some systems, like RCIC, use an inverter for AC power off the battery system to activate when all AC power is lost. The IC may be similar. I'll try to get schematics from an IC plant tomorrow to check.

 

[Hiddencamper]

That is okay. What I don't get is where the requirements to make valves fail shut *and be inaccessible* inside PCV come from; and why, after opening the valves, *merely keeping them open* requires power and/or air.



Many people in Japan noticed recently that it didn't work so well. Looks like it's a good time to rethink how these things are done.



Why? They are not complex at all: "all offsite power is lost. All on-site power, including DGs and batteries are lost". Operators should have this situation described in their emergency manuals. They should perform realistic drills which simulate this condition, and their response. There should be necessary preparations for it (such as filters on vent lines).

None of this was done, and judging by your responses, it is not fully addressed *even now*.

I'll tell you more. I want operators to go *further*. They need to know what to do if not only the above happened, but what to do if they discover that they have no portable water sources and can't cool down the reactor and prevent its meltdown. I don't want to hear them going "oh my gosh, run for your lives!"; I want them to turn the page of their manuals and go to a chapter which tells them what they should do. Should they vent? Through which vent, which valves to open? How to avoid hydrogen explosion? Is there national fast response team which can bring help from unaffected region? etc...



Are you saying that next tsunami inundating a BWR/4 plant should be *expected* to make it melt down? That we should _not_ think how to avoid that?

Fail shut is to prevent reactor coolant discharge and radiological release. It's a safety function and is required. As I've said, a stuck open SRV is considered an accident. You want them to go back closed, as if one sticks open it will rapidly decrease coolant inventory in the core.

Operators in the US have been training on total loss of major systems including AC power since 9/11, and if you read the reports from the national diet of Japan, they state that if they had incorporated b.5.b rules from the US (our 9/11 response) they would have been in much better shape.

 

[jim hardy]

.............

None of this was done, and judging by your responses, it is not fully addressed *even now*.

I'll tell you more. I want operators to go *further*. They need to know what to do if not only the above happened, but what to do if they discover that they have no portable water sources and can't cool down the reactor and prevent its meltdown. I don't want to hear them going "oh my gosh, run for your lives!"; I want them to turn the page of their manuals and go to a chapter which tells them what they should do. Should they vent? Through which vent, which valves to open? How to avoid hydrogen explosion? Is there national fast response team which can bring help from unaffected region? etc...



Are you saying that next tsunami inundating a BWR/4 plant should be *expected* to make it melt down? That we should _not_ think how to avoid that?

It is probably mostly still in the 'thinking' stage.
It took a couple years for TMI related changes to be formulated.


I'm retired now so largely out of touch with the plant guys. I rely on internet for what's going on.
Here's an interesting country-by-country snapshot of what's being done, dated this month.

The purpose of this paper is to investigate the
activities relating to the safety reviews by
international organizations and by individual
countries within the limit of available information
such as their published national reports and data on
their websites, and to clarify safety related issues that
are common across the world and should be solved in
the future.
OHSUGA Yasuhiko
Nuclear Safety and Simulation, Vol. 3, Number 1, March 2012

http://www.ijnsweb.com/?type=subscriber&action=download&file=final&ext=pdf&id=106

 

[Astronuc]

That is okay. What I don't get is where the requirements to make valves fail shut *and be inaccessible* inside PCV come from; and why, after opening the valves, *merely keeping them open* requires power and/or air.

Many people in Japan noticed recently that it didn't work so well. Looks like it's a good time to rethink how these things are done.

Why? They are not complex at all: "all offsite power is lost. All on-site power, including DGs and batteries are lost". Operators should have this situation described in their emergency manuals. They should perform realistic drills which simulate this condition, and their response. There should be necessary preparations for it (such as filters on vent lines).

None of this was done, and judging by your responses, it is not fully addressed *even now*.

I'll tell you more. I want operators to go *further*. They need to know what to do if not only the above happened, but what to do if they discover that they have no portable water sources and can't cool down the reactor and prevent its meltdown. I don't want to hear them going "oh my gosh, run for your lives!"; I want them to turn the page of their manuals and go to a chapter which tells them what they should do. Should they vent? Through which vent, which valves to open? How to avoid hydrogen explosion? Is there national fast response team which can bring help from unaffected region? etc...

Are you saying that next tsunami inundating a BWR/4 plant should be *expected* to make it melt down? That we should _not_ think how to avoid that?

A lot of this is based on the benefit of hindsight. The situation in Japan was different than the US, e.g., " if they had incorporated b.5.b rules from the US (our 9/11 response) they would have been in much better shape."

In Japan, while they did forsee a tsunami, they underestimated the magnitude. Most of the coast was unprotected. It was not only the nuclear plants, but also the chemical plants and other industries.

Following Fukushima, regulatory authorities and utilities world-wide re-assessed their safety and emergency programs. I'd expect deficiencies were found and addressed. Most BWR/4s are not subject to tsunami.

Should the plants have been better protected? Probably. Should they have expected such a tsunami, based on historical record? Probably, especially since there were earlier reports about such a hazard, and there was a substantial earthquake in Alaska in 1964.

"Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, . . . "
http://en.wikipedia.org/wiki/1964_Alaska_earthquake

Had the sites in Japan been designed for a 10+ m tsunami, then we'd have had a different story perhaps. I would imagine that the EDG oil tanks would have been better protected, or at least not located at shore line. Also, the EDGs should have been located in an area not subject to flooding. And so on.

In three days with be the second anniversary of the event.

 

[nikkkom]

A lot of this is based on the benefit of hindsight.

And?

If nuclear industry failed to foresee and prepare for the probabilistically likely events, it should AT LEAST fix those deficiencies which now DEFINITELY known to exist (the "hindsight").

In Japan, while they did forsee a tsunami, they underestimated the magnitude.

Which says to me that NPPs *elsewhere* can be in the same situation: underestimating flooding hazards. (Calhoun? Blayais? Rings any bells?)

Following Fukushima, regulatory authorities and utilities world-wide re-assessed their safety and emergency programs. I'd expect deficiencies were found and addressed.

I was thinking exactly the same thing wrt Chernobyl.
I'm not so sure about that now. Because...

Most BWR/4s are not subject to tsunami.

...people tend to think like this.

"We physically can't have Fukushima scenario, let's write a report that 'we studied out accident preparedness and we are fine'".

Somehow, I'm not buying it. I would rather read "we bought two more fire trucks and two mobile diesel generators and situated them in two different locations close to plant, and we drill our operators in using them every time we have a refueling outage. Because, although we aren't susceptible to tsunamis, we aren't arrogant a-holes and we think we might be failing to anticipate a possible disaster scenario, Oh, and BTW, we installed four more 100-ton tanks with fresh water on the NPP premises, and stockpiled flexible hoses. Just in case."

 

[Astronuc]

And?

If nuclear industry failed to foresee and prepare for the probabilistically likely events, it should AT LEAST fix those deficiencies which now DEFINITELY known to exist (the "hindsight").

And at the time of the Fukushima event, US utilities had emergency meetings to assess their own sites and their emergency preparedness programs - even before the NRC made any statement. US BWRs had already installed safety features not present in the Japanese reactors. Combined natural events were reviewed and reassessed. SAMGs were reviewed.

Which says to me that NPPs *elsewhere* can be in the same situation: underestimating flooding hazards. (Calhoun? Blayais? Rings any bells?)

Calhoun came through that flooding fairly well. It was in a refueling outage, and is still down.
http://www.nrc.gov/info-finder/reactor/fcs/special-oversight.html

I was thinking exactly the same thing wrt Chernobyl.
I'm not so sure about that now. Because...

...people tend to think like this.

LWR operators simply assume Chernobyl will not happen to them, because they don't operate like that, and LWRs don't have graphite moderation. LWRs in flood prone areas are required to assess the flooding potential and have prevention and mitigation plans.

"We physically can't have Fukushima scenario, let's write a report that 'we studied out accident preparedness and we are fine'".

Somehow, I'm not buying it. I would rather read "we bought two more fire trucks and two mobile diesel generators and situated them in two different locations close to plant, and we drill our operators in using them every time we have a refueling outage. Because, although we aren't susceptible to tsunamis, we aren't arrogant a-holes and we think we might be failing to anticipate a possible disaster scenario, Oh, and BTW, we installed four more 100-ton tanks with fresh water on the NPP premises, and stockpiled flexible hoses. Just in case."

Folks have planned to prevent that.

 

[Hiddencamper]

And?

If nuclear industry failed to foresee and prepare for the probabilistically likely events, it should AT LEAST fix those deficiencies which now DEFINITELY known to exist (the "hindsight").
Which says to me that NPPs *elsewhere* can be in the same situation: underestimating flooding hazards. (Calhoun? Blayais? Rings any bells?)
I was thinking exactly the same thing wrt Chernobyl.
I'm not so sure about that now. Because...
...people tend to think like this.

"We physically can't have Fukushima scenario, let's write a report that 'we studied out accident preparedness and we are fine'".

Somehow, I'm not buying it. I would rather read "we bought two more fire trucks and two mobile diesel generators and situated them in two different locations close to plant, and we drill our operators in using them every time we have a refueling outage. Because, although we aren't susceptible to tsunamis, we aren't arrogant a-holes and we think we might be failing to anticipate a possible disaster scenario, Oh, and BTW, we installed four more 100-ton tanks with fresh water on the NPP premises, and stockpiled flexible hoses. Just in case."

The industry is reassessing their seismic and flooding hazards and seeing if they are deficient as part of post fukushima response. So we ARE actively doing something about it.With Fort Calhoun, the flood was actually below the maximum expected flood for the site still. The problems at Fort Calhoun stemmed from the fact that 2 years before the flood, their flood preparations were deficient. The NRC made them fix it. And as far as I can see, the US regulatory system did a good job of identifying a deficiency and ensuring it was corrected such that the flood was non-eventful. Fort Calhoun's problem now really stems from years of deficiencies, and to understand how they got there, you need to have spoken to people who have gone there to help "Clean up". I think Fort Calhoun basically being told that the NRC does not want OPPD to operate the plant anymore was the right thing.

The whole "we did a report and we are fine" thing is NOT what the US has done. In the US, we purchased millions of dollars of new equipment, built 2 regional response centers that can deploy a full set of portable equipment to any site in the country in less than 24 hours (and all the equipment is regularly tested and kept in like new condition), have reviewed and upgraded our emergency procedures to utilize this equipment, and are developing portable equipment hookups and plans. This is all part of the FLEX initiative, and is also an NRC order, to be able to maintain core cooling and critical safety functions indefinitely, in three phases. The first phase is using only on-site permanent equipment that is available after a Fukushima-like event, the second phase starts 24 hours later, and involves portable equipment on site and off site. The third phase is after 72 hours when "offsite help" is allowed to come in. It's assumed that it takes 72 hours for resupplies of fuel, water, personnel, and other non-portable equipment for critical safety functions to arrive. This is what the US nuclear industry has done. NOBODY has simply said "We looked at it and its ok".

With regards to fire trucks, extra fuel, portable pumps, water, the US already did that after 9/11. But 9/11 only required enough equipment for 1 plant, not both. Many plants are installing more generators and equipment. We are going to be pouring concrete at my plant and building a new section where we can put a new generator, and us engineers are figuring out the power requirements to make sure we are capable of restoring critical safety functions in the event all of our normal generators and equipment fail. Post Fukushima, we've added more portable equipment to that because now we are assuming ALL units on site fail simultaneously. Operators, maintenance personnel, and emergency responders (myself included) are regularly trained on our extensive damage procedures and severe accident guidelines.

This is what the US has been doing, and will continue to be doing over the next several years.

 

[nikkkom]

The whole "we did a report and we are fine" thing is NOT what the US has done. In the US, we purchased millions of dollars of new equipment, built 2 regional response centers that can deploy a full set of portable equipment to any site in the country in less than 24 hours (and all the equipment is regularly tested and kept in like new condition), have reviewed and upgraded our emergency procedures to utilize this equipment, and are developing portable equipment hookups and plans. This is all part of the FLEX initiative, and is also an NRC order, to be able to maintain core cooling and critical safety functions indefinitely, in three phases. The first phase is using only on-site permanent equipment that is available after a Fukushima-like event, the second phase starts 24 hours later, and involves portable equipment on site and off site. The third phase is after 72 hours when "offsite help" is allowed to come in. It's assumed that it takes 72 hours for resupplies of fuel, water, personnel, and other non-portable equipment for critical safety functions to arrive. This is what the US nuclear industry has done. NOBODY has simply said "We looked at it and its ok".

With regards to fire trucks, extra fuel, portable pumps, water, the US already did that after 9/11. But 9/11 only required enough equipment for 1 plant, not both. Many plants are installing more generators and equipment. We are going to be pouring concrete at my plant and building a new section where we can put a new generator, and us engineers are figuring out the power requirements to make sure we are capable of restoring critical safety functions in the event all of our normal generators and equipment fail. Post Fukushima, we've added more portable equipment to that because now we are assuming ALL units on site fail simultaneously. Operators, maintenance personnel, and emergency responders (myself included) are regularly trained on our extensive damage procedures and severe accident guidelines.

Sounds good.