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Offline Starkist

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BWR questions
« on: Jun 14, 2011, 08:49 »
Need a license to speak.
« Last Edit: Jun 25, 2011, 09:29 by Starkist »

Offline Higgs

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Re: BWR questions
« Reply #1 on: Jun 14, 2011, 10:04 »
This will help answer some of your questions.

http://tinyurl.com/6gvtq3f

Money answers others.
« Last Edit: Jun 14, 2011, 10:08 by TheHiggs »
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Offline Higgs

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Re: BWR questions
« Reply #2 on: Jun 14, 2011, 11:43 »
I am not sure of your concern for the jet pumps. IIRC, each manifold is semi-circular which goes 5 jet pump risers spaced equally apart. And you realize the PIDs don't reflect 100% reality, right?

And you can't figure out why a vessel has different thicknesses in different regions? Don't think so much pressure, think neutron bombardment...., and money. Why pay for a uniformly thick vessel when you don't need it? Trim a little fat, as it were.

And head corrosion can be a concern if not properly maintained. I am not sure what you have there, but we had hydrogen water chemistry control at PB.

« Last Edit: Jun 15, 2011, 12:06 by TheHiggs »
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Offline Higgs

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Re: BWR questions
« Reply #3 on: Jun 15, 2011, 12:14 »
I modified my answer because I changed my mind about feeding you answers.  8)


This is what I remember of a recirc manifold. (I won't confirm/deny that I still have all of my BWR notes. :P)

« Last Edit: Jun 15, 2011, 12:15 by TheHiggs »
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Offline Higgs

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Re: BWR questions
« Reply #4 on: Jun 15, 2011, 12:22 »
You are over thinking it.
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Offline Higgs

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Re: BWR questions
« Reply #5 on: Jun 15, 2011, 12:34 »
Well, it is a simple system that you want to over complicate. It is two 28 inch recirc loops going into 2 semi circular 22 inch distribution manifolds, each feeding 5 jet pump risers. Each riser feeding two jet pumps. Whatever pressure differences you think are there, are negligible at best. Is flow equal through each jet pump? No, of course not..., but many things play into that, maybe some of what you think. Flow differences are tech spec. That is all I know about that part of the system. That is all I was taught in my license class. Sorry. Maybe Broadzilla can shed some more light.
« Last Edit: Jun 15, 2011, 12:37 by TheHiggs »
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Offline Higgs

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Re: BWR questions
« Reply #6 on: Jun 15, 2011, 12:44 »
You won't see them all on the boards, unless they are better than pb. We only had 4, 2 per loops. The nlos took the rest in the field. Although, you can probably bring it up on the plant computer if theu dont have board indicators for all of them.
« Last Edit: Jun 15, 2011, 12:45 by TheHiggs »
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Nuclear Renaissance

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Re: BWR questions
« Reply #7 on: Jun 15, 2011, 09:28 »
Flow is not the same through all the jet pumps in a manifold - you will see the extremes will have a little lower flow. Ask your RO to see the numbers for his daily jet pump operability test. You will see that engineering provides a plotted range for what each jet pump can be expected to be for a given loop flow.

The valve you were asking about is a manifold-to-manifold crosstie, originally designed to be open during single recirc pump operation. I can't think of any BWR that uses it, though, since the system oscillations were quite severe when it was field tested.

Offline Higgs

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Re: BWR questions
« Reply #8 on: Jun 15, 2011, 10:28 »
So my thoughts were correct :)

We just care about average flow between the 2 loops being the same right?

First I've heard of the crosstie, I'll have to ask about it.




Yeah, that is what I said.

Above/below a certain total core flow, your loops have to be within a certain deviation. At PB, below a certain total core flow, you could have a bigger loop deviation..., above a certain total core flow, you had a tighter band.

That is diffferent than what he was talking about, the daily jet pump ST, because like I said, many things determine what the flow is through the jet pump, their position in the manifold being a small part of that (last time I was at PB, the outer jet pumps weren't always the lowest flow). So, engineering will give you data that you compare your readings to to ensure they are operating properly. So they have to be within whatever band is provided. If not, you enter the jet pump inoperable AOP.

Also, in case you weren't aware, a jet pump is basically a nozzle.
« Last Edit: Jun 15, 2011, 10:33 by TheHiggs »
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Offline Higgs

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Re: BWR questions
« Reply #9 on: Jun 15, 2011, 10:42 »
What is level 3?

And what is slow?

We had variable speed recirc pumps that would "run back" on certain conditions, such as a condensate pump trip, or reactor scram.
"How feeble is the mindset to accept defenselessness. How unnatural. How cheap. How cowardly. How pathetic.” - Ted Nugent

Nuclear Renaissance

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Re: BWR questions
« Reply #10 on: Jun 15, 2011, 12:08 »
Recirc pumps go to "slow" at the low level scram to protect the pumps/loops from cavitation effects of an increasingly lowering level.

Of course you are a BWR/6, so your recirc runbacks are primarily achieved by 2 pumps speeds and a variety of recirc loop flow control valve positions. Most of the rest of the BWRs use variable speed pumps with no control valves in the loop.

Nuclear Renaissance

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Re: BWR questions
« Reply #11 on: Jun 15, 2011, 12:15 »
By the way Starkist, you will have to preface most of your BWR/6 questions with exactly what you are talking about and not the lingo. Most BWR folks aren't familiar with things like the Level 8 scram, and Levels 3, 2, 1 are actually the opposite of what most understand them to be. HPCS, aux building, Div III DG, etc are also going to be different.

Offline Higgs

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Re: BWR questions
« Reply #12 on: Jun 15, 2011, 12:17 »
low level scram. we have 2 speed pumps. why is it an automatic function with a scram signal I guess is what im asking

Ah, I see now what these Levels are for your unit.

Here;

http://www.houseoffoust.com/fukushima/GEMANUAL.pdf

I am really shocked that you can't get this information from your training department. Or... some licensed guy that has notes on the intranet.
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Offline Higgs

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Re: BWR questions
« Reply #13 on: Jun 15, 2011, 12:20 »
That .pdf explains all of your level trips, and gives a mini-basis for them.
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Fermi2

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Re: BWR questions
« Reply #14 on: Jun 15, 2011, 03:31 »
GE control rod design has holes in the blades. Why?

edit: instructors dont know, google is bringing up nothing. been looking through STM's and stuff too.

Flow for cooling.

Also cladding is not required in the upper head because steam tends to be non corrosive.

Offline cypher89

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Re: BWR questions
« Reply #15 on: Jun 15, 2011, 07:37 »
Recirc loop flows can change even under steady state conditions based on the piping layout in the risers and how random the flow pattern becomes.  At out plant this can cause up to half a percent power change known as bistable flow.  Not all bwr's have it but many do.  Check the ISO drawing to see actual piping layouts for the recirc loops.

Fermi2

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Re: BWR questions
« Reply #16 on: Jun 15, 2011, 08:37 »
Recirc loop flows can change even under steady state conditions based on the piping layout in the risers and how random the flow pattern becomes.  At out plant this can cause up to half a percent power change known as bistable flow.  Not all bwr's have it but many do.  Check the ISO drawing to see actual piping layouts for the recirc loops.


Not entirely correct.

Offline Bigchris

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Re: BWR questions
« Reply #17 on: Jun 15, 2011, 09:27 »
Hello Starkist,


2) The vessel is head is, relatively speaking, much thinner then the rest of the vessel. Again. Why? I understand the vessel head has less pressure then the bottom of the assembly, but its almost 40% thinner.

I would like to take a shot at question #2.

My experience is not in Nuclear Power Plants; however there may be some principles from ASME Boiler and Pressure Vessel Code  (BPVC) Section I Power Boilers that may explain why the upper head is thinner than the shell and bottom head. (See PG 27 Cylindrical Components Under Internal Pressure, PG 29 Dished Heads and PG 33 Compensation Required for Openings in Shells and Formed Heads etc.)

Is it possible that the top head is thinner than the sides of the vessel because the minimum required thickness is less, due to the differences in the formulae used to calculate thickness in heads and cylindrical vessels subject to internal pressure?

The reason the bottom head is thicker than the top head (if that is what you have said), may be due to the hydrostatic head and the weight of the vessel internals and due to the compensation in thickness required because of  the number of openings in the bottom of the vessel for control rod drives etc. That is my guess.

The required thickness of the head is probably determined by using the calculations shown in the code (ASME Section III?). Different parts of a pressure vessel require different calculations. I would expect that ASME BPVC Section III would explain the calculations needed for nuclear construction and Section II to list the allowable stresses for the listed materials.

The required thickness for a material depends on the shape of the object, among other things. A sphere for example would be subject to about half the stress at a given internal pressure than a cylindrical object of the same material and thickness at the same pressure and temperature. The BWR head, although it may not be exactly semi- hemispherical, may benefit from this.  We can see this if we consider the following.

The stress of a “thin” (according to code) sphere, can be calculated by the formula S=PR/2t. Now imagine the sphere cut in half and then welded to the end of a cylindrical vessel. This is something like what we have when bolt or weld a head to a cylindrical vessel. “The stresses in the longitudinal direction on a cylindrical vessel carrying internal pressure can readily be seen to be the same as those in a spherical vessel. These stresses are often considered as those tending to blow the heads off cylindrical vessels.” 

The stresses in the circumferential direction of the cylinder can be pictured by imagining a cylindrical vessel cut in half lengthwise. The circumferential stresses would act along theses (imagined) seams. This stress is calculated by the formula S=PR/t.

Comparing S=PR/2t with S=PR/t we can see that the stresses on the longitudinal seam are twice that of the circumferential seam. 

This is why dished heads can be thinner than the sides of a cylindrical vessel. The stress along the longitudinal seam is twice that of the circumferential seam and the dished head. This explanation seems to correspond with your observation that the head is almost 40 % thinner, which I would suggest, may be related to the half as much stress shown above.
 
Not to confuse the matter, but consider this, circumferential stresses will tend to open a longitudinal seem while longitudinal stresses will tend open a circumferential seam, if I am not mistaken.

I think you are correct that the upper head has less pressure than the bottom. This might be due to the weight of steam and water mixture or hydrostatic head. To see more on static head and other loads in Power Boilers, go to BPVC Section I PG 22.1.

If you are saying that the bottom head is much thicker than the top, I guess this is due to an increase in material thickness in order to compensate for the number of holes cut into the bottom head in order to allow control rod assemblies to enter the head, possibly some increases in thickness due to the weight of the internal components and possibly some consideration of the hydrostatic head.

In general, at least for Power Boilers, if there are enough openings of sufficient size cut into the vessel material (and close enough to each other), then in some circumstances the thickness of the remaining material must be increased to compensate for the reduction in strength that the openings would cause in the material. This is because the area around the opening is subject to the forces that would have been applied to the material that was removed to make the opening. The area above, below and to either side of the hole, that is relatively close to the hole which may be considered to carry the extra stress, is referred to as the ‘limits of compensation’. This area can be built up around each opening with a pad or the whole head can be made thicker to compensate for the openings. Sometimes, some parts of the materials connected to the hole may also be considered as compensation.

Sometimes if you calculate the amount of metal removed in making the openings and then increase the thickness of the material around the openings, by an amount that would equal the amount of material removed, then that is sufficient compensation. In other words, the amount of material removed from the area of the openings is the same as the amount of material added to the area around the openings. At least that is the general principle and it can work if the openings are close together, otherwise some of the added thickness would be outside of the ‘limits of compensation”.

This might explain why the top head is thinner than the sides of the vessel and the bottom head. Of course I would like to know the ‘real reason”  :)the top head is thinner than the rest of the reactor vessel, if anybody cares to reply.

1. http://www.asme.org/kb/standards
2. The ASME Code Simplified Power Boilers Carroll
3. The ASME Code Simplified Power Boilers Carroll http://books.google.com/books?id=peRSAAAAMAAJ&q=%22longitudinal+seam+are+seen%22
4.  Ibid Carroll

Thank you.
Bigchris

Offline Bigchris

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Re: BWR questions
« Reply #18 on: Jun 15, 2011, 09:36 »
Sorry about the misuse of the quote function above. :(
Thank you.
Bigchris

Fermi2

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Re: BWR questions
« Reply #19 on: Jun 15, 2011, 09:42 »
The bottom is thicker than the top due to the CRD, Nuclear Instrument, and RWCU Taps.

Offline jams723

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Re: BWR questions
« Reply #20 on: Jun 15, 2011, 10:15 »
The bottom is thicker than the top due to the CRD, Nuclear Instrument, and RWCU Taps.

'sup
 Mike, I need a good bwr6 primer... Got anything for me?

Offline HydroDave63

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Re: BWR questions
« Reply #21 on: Jun 16, 2011, 01:05 »
I can email you STM's if you wish. 

They aren't copyrighted or proprietary, right?

Offline RDTroja

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Re: BWR questions
« Reply #22 on: Jun 16, 2011, 06:32 »
Fair use act. read it up please sir.

I once had a copyright holder's attorney explain to me that the Fair Use Act when applied to educational purposes was a courtroom defense and he offered me the chance to put it to use.

I declined the invitation.
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Fermi2

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Re: BWR questions
« Reply #23 on: Jun 16, 2011, 02:22 »
Fair use act. read it up please sir.




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Fermi2

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Re: BWR questions
« Reply #24 on: Jun 16, 2011, 02:23 »
'sup
 Mike, I need a good bwr6 primer... Got anything for me?

I have a bunch of BWR 4 stuff. Six isn't much different and I can help you with the differences.

 


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