Japan Earthquake: nuclear plants


by gmax137
Tags: earthquake, japan, nuclear
MadderDoc
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Apr29-12, 12:27 AM
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Quote Quote by SteveElbows View Post
A couple of possibly silly questions about detected level of hydrogen in reactor 2.

Firstly how come they don't seem to have increased the rate of nitrogen injection into the reactor beyond 5.0N m3/h for reactor 2? Im under the impression that they originally reduced it when they were getting things ready to do the endoscope investigation, and I think they turned the injection to PCV back up since then, but why they haven't done this with the reactor too?
Perhaps they have other things they want done in Unit 2 or they want to make observation a while yet under the present degree of intervention -- in any case the job of the nitrogen injection is not to keep the hydrogen concentration low as possible, only to keep it at a safe level.

Edit: Just an afterthought, would one be able to say that "release of radioactive materials from the PCV is under control" while one would need to flush the PCV with huge amounts of N2 in order to keep other PCV parameters under control?

Secondly the measured level of hydrogen seems to have ten increasing lately, and the 5am report for today seems to indicate its reached 0.42 vol %. What could explain this, and how high should the level reach before I express concern?
In itself I can't see the current H2 level as a concern, it is more the fact that it has been rising significantly recently, and with no obvious explanation why. Explosive limit for hydrogen is about 4 %, but that is assuming there is oxygen, I don't know if the reactor atmosphere has any significant content of oxygen, I should hope not.

Current data shows a further increase over yesterdays value (0.44-->0.48 %) http://www.tepco.co.jp/nu/fukushima-..._summary-j.pdf )
jim hardy
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Apr29-12, 12:53 AM
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how much steam pressure need to be to be in this 'free state' for a steam flow channel to actually result from an actuation (0.686 MPag) , and at which lower pressure the valve body from the open position will reseat by its own weight (0.345 MPag).
Thanks !!

is 0.686 mpa just 100 psi
and 0.345 mpa just 50 psi ?

sounds like just enough to lift the internal parts.


thanks again. Perusing part IV now.
MadderDoc
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Apr29-12, 01:41 AM
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Quote Quote by jim hardy View Post
Thanks !!

is 0.686 mpa just 100 psi
and 0.345 mpa just 50 psi ?

sounds like just enough to lift the internal parts.


thanks again. Perusing part IV now.
I hope you will return. I'd like to know, in Fukushima after the depressuring with such a valve -- on the assumption they kept the valve energized with power and compressed air throughout after that time, would that mean they upheld a pressure relief system that would make the RPV pressure cycle between 100, and 50 psi? And would that be psi gauge, or relative to the backpressure of the exhaust? (I imagine most parameters for such a system would be given for a situation where steam inlet pressure is very high and exhaust about at ambient, such as to moot the distinction, but that was not necessarily the situation in Fukushima)

Otoh, should in the midst of the explosions power or compressed air have failed them, wouldn't the valve have returned to normal mode, to open again only on re-actuation, or by the RPV pressures reaching high pressure set point, about 7-8 MPa, or 1000 psi?
zapperzero
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Apr29-12, 03:00 AM
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Quote Quote by MadderDoc View Post
Edit: Just an afterthought, would one be able to say that "release of radioactive materials from the PCV is under control" while one would need to flush the PCV with huge amounts of N2 in order to keep other PCV parameters under control?
Sure, why not. "Under control" does not mean "stopped".

In itself I can't see the current H2 level as a concern, it is more the fact that it has been rising significantly recently, and with no obvious explanation why. Explosive limit for hydrogen is about 4 %, but that is assuming there is oxygen, I don't know if the reactor atmosphere has any significant content of oxygen, I should hope not.
Of course there is oxygen. The limit is 4% in air, by the way. Inside the reactor there is not "normal" air, but rather air with a lot of added nitrogen (i.e. with a much smaller than normal proportion of oxygen).

Anyway, the H2 level should by all rights be rising, as they have decreased the rate of nitrogen injection.
zapperzero
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Apr29-12, 03:06 AM
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Quote Quote by mheslep View Post
And? How far does the decay heat have to drop to eliminate the need for active cooling?
IOW, used bundles are moved to dry cask storage after how long?
MadderDoc
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Apr29-12, 04:15 AM
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Quote Quote by zapperzero View Post
<..>the H2 level should by all rights be rising, as they have decreased the rate of nitrogen injection.
But they have kept the reduced rate of nitrogen injection constant now for several weeks with H2 concentration steady at about 0.2 %. It is only during the last few days the H2 level has increased now to about 0.5 %.
SteveElbows
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Apr29-12, 07:13 AM
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Quote Quote by SteveElbows View Post
Firstly how come they don't seem to have increased the rate of nitrogen injection into the reactor beyond 5.0N m3/h for reactor 2? Im under the impression that they originally reduced it when they were getting things ready to do the endoscope investigation, and I think they turned the injection to PCV back up since then, but why they haven't done this with the reactor too?
Oops I just noticed that I got this the wrong way round, they had put the RPV nitrogen injection back to previous levels but its the PCV they left at only 5.0N m3/h
r-j
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Apr29-12, 08:16 AM
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Quote Quote by mheslep View Post
And? How far does the decay heat have to drop to eliminate the need for active cooling? Or more to the point, what is the Watts/deg C heat flux path to ambient?
In the US it is after 5 years in a cooling/storage pond. http://en.wikipedia.org/wiki/Dry_cas...#United_States
jim hardy
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Apr29-12, 11:10 AM
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on the assumption they kept the valve energized with power and compressed air throughout after that time, would that mean they upheld a pressure relief system that would make the RPV pressure cycle between 100, and 50 psi?
indeed that's what is described by that attachment.
I am accustomed to valves where the stem lifts the disc directly, but this one may instead lift the spring which would allow the disc to behave as described.

And would that be psi gauge, or relative to the backpressure of the exhaust?
Yes, gage, that bellows keeps discharge pressure away from top of disc. So force up on disc is steam pressure X wetted area and force down is its weight plus pressure inside bellows (atmospheric - that's why bonnet is open type) plus spring force.

I'd like to find the Crosby manual for that specific valve. The link i gave is a bit generic.

should in the midst of the explosions power or compressed air have failed them, wouldn't the valve have returned to normal mode, to open again only on re-actuation, or by the RPV pressures reaching high pressure set point, about 7-8 MPa, or 1000 psi?
Yes, The piston would collapse back down to bottom of cylinder and allow spring to push stem down against disc.

That's how i see it.

old jim
MadderDoc
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Apr29-12, 11:42 AM
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Quote Quote by mheslep View Post
Decay heat question. It's estimated here that the decay heat from Daiichi-1 was down under 5MW after a couple months. Given an *undamaged* reactor and building, but still without power, what is the maximum heat level that can be rejected to ambient through passive means without uncovering the fuel? <..>
The reactor would need to be held at a relatively low temperature such as to avoid SRV's opening, and even lower than that, since we also don't want to degrade any part of the PCV. Just to pick a figure, lets say we think we can handle 127oC or 400 K. A black-body of this temperature will radiate 5.67E-8*4004 watt/m2. That's about 1.5 kW/m2. The surface area of the RPV is in the neighbourhood of 500 m2, so that would be 0.7 MW, as the maximum we would like to have in the RPV *if there were no containment around it*. But seeing there is, we would like to have less, and probably much less than 0.7 MW. I know this is not quite the figure you are asking for, but at least it puts a cap to it.
jim hardy
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Apr29-12, 11:43 AM
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hmm two thoughts while i was eating breakfast.

1. That statement "..valve body is then in a free state.." is written by a technical writer for the report , i'd sure like to find it in the valve documentation. My skepticism is because i am accustomed to a direct plug-stem connection in the smaller safety valves in my experience. So i am allowing the possibility that's an error of translation by a bright fellow who's picked up a manual for pilot operated valve instead of that safety valve. If that's so, then lifting the valve handle would open the valve irrespectine of pressures. Hence my remark about finding the Crosby manual for that valve.
But for now i have to accept what's written.

2. I told you gage pressure. But - is not that valve located inside PCV ? So gage pressure in there is relative not to atmosphere but to PCV pressure.

The sketch you posted shows something called "Eductor" which i haven't figured out yet. I think its purpose is to reduce pressure above disc but outside bellows which helps give that snap-open characteristic you want in a safety valve.

I would like to more completely understand that valve's internals.
As an instrument guy i worked on regulating valves. Safety valves were in mechanical discipline and my small knowledge of them comes from talking with the mechanics who maintained them.
Ahh our regrets in life are mostly about the things we didnt learn. I could have learned more about code safeties.

old jim
MadderDoc
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Apr29-12, 12:02 PM
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Thanks, that was a great help. Now I think I've got some thinking to do as regards the implications. Up till now I had the SRVs in Fukushima as something that was flipped to stay open, come what may. I can't remember reading about anything done with the SRVs after the time the reactors got depressurised.
jim hardy
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Apr29-12, 12:48 PM
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Found some more Crosby literature.

The "Balancing Piston" is a backup in case the bellows ruptures.
A person accustomed to control valves might well interpret it as a pilot
and make the mistake i mentioned.

This link takes me to Crosby catalog 310 for their JOS and JBS series valves used on PWR's. Still trying to find exactly what's a 6R10.
http://www.google.com/url?sa=t&rct=j...eKGFteuMsdFGYg
page 59 describes the balancing piston.

And from a generic study of nuclear safety valves, page 11
http://www.osti.gov/bridge/purl.cove...able/41402.pdf
The disc is the movable sealing element and seating
surface on which the following two forces act: (1) the
downward spring force transmitted by the spindle and
disc holder and (2) the upward force from the process
fluid pressure acting on the bottom surface of the disc.
The disc holder and spindle are held together by a
spindle retainer, and the disc is secured inside the disc
holder by a disc retainer, with both retainers generally
being snap rings.
and page 12:
Another component frequently found in PRVs is the
manual lift lever shown in Fig. 3.4. In nuclear
facilities this lever is wired down and not used by
operators in any procedures, but only by maintenance
personnel. The movement of the lever rotates the
lever shaft and lifting fork (or “dog”) that acts against
a release nut or load plate, thus lifting the spindle and
opening the valve.
page 4 has a photo of BWR safety. The piston that operates the handle is prominent.

Doc, i am ready to believe that "floating state" comment is an innocent error by technical writer.
That stem is i believe directly coupled to the disc, ie raising handle opens valve irrespective of pressure.

So by opening the valve they conneccted RPV to torus . I beieve. So long as their air and batteries held out.

old jim

EDIT sorry to flip on you
but one must go with best info available. I wasn't ready to accuse tech writer nased on my own limited experience. Apologies for the flip-flop.
mheslep
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Apr29-12, 01:49 PM
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Quote Quote by MadderDoc View Post
The reactor would need to be held at a relatively low temperature such as to avoid SRV's opening, and even lower than that, since we also don't want to degrade any part of the PCV. Just to pick a figure, lets say we think we can handle 127oC or 400 K. A black-body of this temperature will radiate 5.67E-8*4004 watt/m2. That's about 1.5 kW/m2. The surface area of the RPV is in the neighbourhood of 500 m2, so that would be 0.7 MW, as the maximum we would like to have in the RPV *if there were no containment around it*. But seeing there is, we would like to have less, and probably much less than 0.7 MW. I know this is not quite the figure you are asking for, but at least it puts a cap to it.
Thanks. This is the approach I'm looking for. Some questions:

Is the temperature of the PCV the critical figure for a walk away state, rather than the temperature of the fuel assembly? I assumed that on the low side no pressure was allowable in walk-away thus 100C was the limit internal to the PCV. Or, if a low steady-state pressure could be sustained indefinitely then something short of a temperature that trips the SRVs? I have no idea.

With regard to heat transfer, convective free air would dominate at about ~10W/m^2/K depending the humidity. If ~100K above ambient is allowable as you suggest, then ~1KW/m^2 is the convective heat transfer, so that a 500m^2 RPV allows .5 MW of decay power. For Daichi 2&3 I gather .5 MW is still many months away.
mheslep
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Apr29-12, 01:59 PM
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Quote Quote by zapperzero View Post
IOW, used bundles are moved to dry cask storage after how long?
Quote Quote by r-j View Post
In the US it is after 5 years in a cooling/storage pond. http://en.wikipedia.org/wiki/Dry_cas...#United_States
The cask storage stage is the time required to allow deer and rabbits to nuzzle the outdoor casks without cooking them, or to prevent rain/snow from cracking an otherwise super heated cask. The PV (without active cooling) inside containment might sustain a somewhat more elevated power level might for a time without in a radiation release.
MadderDoc
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Apr29-12, 05:13 PM
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Quote Quote by mheslep View Post

Is the temperature of the PCV the critical figure for a walk away state, rather than the temperature of the fuel assembly? I assumed that on the low side no pressure was allowable in walk-away thus 100C was the limit internal to the PCV. Or, if a low steady-state pressure could be sustained indefinitely then something short of a temperature that trips the SRVs? I have no idea.
Thanks for the link.

Yes, I think the PCV temperature would be the critical figure. Something just short of a temperature that trips the SRVs would fry the PCV within hours, it only works under normal operation because the PCV is being cooled. With no power no cooling at hand it would be imperative to have the RPV and fuel at a temperature far below what they themselves can withstand. I'd agree that 100C could be the pain threshold for the PCV, rather than the figure I suggested, we also wouldn't like the PCV to loose steam.
MadderDoc
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Apr29-12, 05:50 PM
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Quote Quote by jim hardy View Post
Doc, i am ready to believe that "floating state" comment is an innocent error by technical writer.
That stem is i believe directly coupled to the disc, ie raising handle opens valve irrespective of pressure.

So by opening the valve they conneccted RPV to torus . I beieve. So long as their air and batteries held out.

old jim

EDIT sorry to flip on you
but one must go with best info available. I wasn't ready to accuse tech writer nased on my own limited experience. Apologies for the flip-flop.
I really don't mind, jim, and I much appreciate your efforts to get it right, not just answered, also as long as I am getting wiser all the time, and I think I am.. :-)

Still most of the stuff about the technical workings of the valve is a bit over my capacity, but I do understand, that it is one crucial point whether that thing called the stem is directly connected to that thing called the disc. Assuming, as you, and everything else I have been able to dig up indicates, they are directly connected. So actuation of the valve would seem to imply that the valve would simply be forced open.

Otoh, the investigation committee who wrote it, and Tepco who I assume read it, have let pass in the interim report the considerations quoted below, which imply contrarily, that the SRV is not unconditionally forced open on actuation, so how to square the conflicting evidence? Could the situation be that the stem/disc action facilitates the opening of the valve, but that a certain steam pressure still would be needed to produce the flow channel?

"In general, the SRVs can be manually opened by remote control, if the RPV pressure is over 0.686MPa in gage. According to the plant parameters released by TEPCO, the Unit 3 RPV pressure at around 2:44 on March 13 was 0.580MPa in gage. Therefore the possibility that RPV pressure was below the required value at the time of the first opening operation at around 2:45 cannot be ruled out. On the contrary, taking into account a shift team operator’s logbook saying that the RPV pressure was 0.8 MPa at around 2:45 on the same day, it can be concluded that the lower pressure was not the real cause of the “fail to open.” To return to TEPCO’s plant parameters, the RPV pressure at Unit 3 around 3:00 on the same day elevated up to 0.770MPa in gage. If so, it is highly possible ...[snip]"

Edit: Jim, I just experienced a potential serendipity, please can I have you take a look page number 68 of the report and ff
http://pbadupws.nrc.gov/docs/ML1111/ML111170549.pdf
What is described there is technically way, way over my head, but just scanning the figures with my eyes
I get much too similar signals from this text as I get from the interim report to ignore.
Perhaps we are looking at Target Rock SRV's not Crosbys.
jim hardy
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Apr29-12, 10:11 PM
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Thaks m'doc for the encoraging words.

that it is one crucial point whether that thing called the stem is directly connected to that thing called the disc. Assuming, as you, and everything else I have been able to dig up indicates, they are directly connected. So actuation of the valve would seem to imply that the valve would simply be forced open.

Otoh, the investigation committee who wrote it, and Tepco who I assume read it, have let pass in the interim report the considerations quoted below, which imply contrarily, that the SRV is not unconditionally forced open on actuation, so how to square the conflicting evidence?
I've found Dresser makes such valves and i found their catalog. It has nice color drawings that definitely show snap-rings . Will post link if i can find it again.

I have a personal dislike for pilot operated valves in this application. So i didnt look into Target Rock.

Crosby's drawings that i've found are lower resolution and dont seem to show a snap ring. In fact some of the drawings look like they'd agree with the TEPCO statement of floating disc.

After making that post i went outside to work on an old engine and thought about this.
I am biased by prior experience so tended to disbelieve the lack of firm stem-to-disc connection. That's my prejudice i realize now.
Given that safety valves evolved from a simple hole covered by a disc with weights stacked on top of it, there's no need for a solid connection to stem.
Indeed there's that historical pecedent.

So i answered before i should have. Realized that upon reflection.
However - the reason i gave answer i did is this:
Assume some reasonable diameter for the disc, say four inches. That gives it area of 4∏ square inches.
When pressure below disc X area of disc equals weight of parts to be lifted by steam , those parts will indeed be lifted by steam. (Assuming spring is held away by operating handle.)
Now 4∏ square inches X 100 psi is 1257 pounds. That's just too much for a disc and retainer to weigh. We're talking about something the size of harmonic damper on a big car engine.
At 2 inches it's still 314 pounds which pushes the credibility limit for me.


I found this line in the 179549 link you gave:
The reactor vessel pressure muat
be at least 50 psi (0.345 MPa) above the wetwell pressure in order for
the main stage- to upen.
That quote is describing the Target-Rock as you suggested and it sure sounds a lot like what the TEPCO technical writer wrote.


Target-rocks in my plant were maintenance headaches. And a pilot valve caused TMI. So i am biased against pilot valves for 'important to safety' service. I assumed the mechanical designers would stick to the simpler dierct acting design like Crosby.



another serendipity moment for you

Some operating BWRs are equipped with three-stage Target Rock valves, which have exhibited a greater tendency to stick open in the past than have other types of valves. Many BWR utilities, however, have replaced the original three-stage valves with the newer two-stage Target Rock valves (Figure 3.7-8). Some operating BWRs are equipped with Dresser electromatic relief valves. BWR-5 and BWR-6 plants are equipped with Crosby and Dikkers dual function SRVs (Figure 3.7-9).
Looks like the designers came around .

That's from NUREG/CR-6042 Rev. 2 section 3.7.2.5 , page 7 of 213
http://www.google.com/url?sa=t&rct=j...M8y8zg5f6ovsUw

Fig 3.7-9 on page 33 is a better drawing of the Crosby type valve. Zoomiing in to 300% i still can't tell how it's put together. It's frustrating - when i worked at plant we could go to warehouse and look at the on-hand spare parts.

But i'm coming to my senses now.
We dont know which valve they have.
So i withdraw my accusation against their tech writer, he may well have been describing a different valve than i was looking at. Apology to you, unknown writer.

And i back off my claim in last post. Go ahead with your thinking per TEPCO writer.

M'doc I admire you guys' doggedness and attention to detail. You're doing it right..


Imagine what Microsoft could have been if they had an industrial strength mindset.


old jim


PS - somebody has put pilot valves in main steam safety service. no comment.


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