San Onofre steam generator tubes leaking - why?

  • Thread starter Thread starter jensjakob
  • Start date Start date
  • Tags Tags
    Generator Steam
Click For Summary

Discussion Overview

The discussion revolves around the leaking and corrosion issues of steam generator tubes at the San Onofre Nuclear Generating Station. Participants explore potential causes, including manufacturing defects, water chemistry, and metallurgy, while referencing historical context and previous incidents in the industry.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants suggest that the leaking tubes may be a result of a manufacturing defect, particularly since the replacement steam generators were installed recently.
  • Others emphasize the importance of water chemistry on the secondary side, noting that even minor impurities can lead to significant issues.
  • Concerns are raised about the metallurgy of the tubes, with references to past experiences where materials like copper contributed to corrosion.
  • A participant questions the source of the metal used for the tubes in the replacement steam generators, highlighting the need for scrutiny on material procurement.
  • There are mentions of a crack found in the divider plate of the Unit 3 steam generator, with discussions on whether this could relate to current leakage issues.
  • Some participants express uncertainty about the implications of welding dissimilar metals and the potential for cracking, suggesting a need for clarity on fabrication practices.
  • Historical context is provided, with references to similar problems faced in the 1970s and the lessons learned from those experiences.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the leaks, with multiple competing views and uncertainties remaining regarding the manufacturing quality, material properties, and operational conditions.

Contextual Notes

Participants note that the discussion is ongoing and that investigations are still being conducted to determine the exact causes of the leaks and any potential correlations with previous issues in the steam generators.

  • #31
jim hardy said:
i'm sure curious why the new tubes fail .

Vibration can be excited from either inside or outside a tube.
Flow inside those tubes barely changes with power.
If the tubes are contacting each other, then that's some relatively large amplitude vibration, which means the tubes are not sufficiently stiff, or there is some pretty substatial excitation mechanism.

Flow might have increased because of the reduced pressure drop, and perhaps flow was increased slightly, on the primary and/or secondary side in order to increase power output. Increased flow in the primary circuit always an issue when replacing steam generators.

I'm puzzled about what kind of analysis was performed concerning the design. In this day and age, we have pretty advanced CFD capability. I'm left wondering - what did they miss, or not consider, in the design and the analysis.

Seems to me a microphone on the steam generator could hear tubes clattering.
I'd instrument a steam generator and listen. If they clatter at zero power then excitation is from primary flow not secondary.

Most plants have loose parts monitors that are basically microphones at natural collection points like reactor vessel bottom and steam generator inlet side tubesheet. Move one up to vicinity of the tube wear region.
Acoustic emissions (noise) analysis would be appropriate, but I'm not sure it if is done on SGs.
 
Engineering news on Phys.org
  • #32
If the tubes are contacting each other, then that's some relatively large amplitude vibration, which means the tubes are not sufficiently stiff, or there is some pretty substatial excitation mechanism.

iirc the tube diameter was decreased and bending moment is in proportion to moment of inertia of cross section, i think 3rd or 4th power of diameter ?
http://en.wikipedia.org/wiki/List_of_area_moments_of_inertia
(Pardon me I'm no mechanical engineer) so reducing diameter will reduce stiffness ? Surely they calculated that. The tubes get additional stiffness due to internal-external Δp and i don't know how to calculate that. That Δp is not constant as main steam pressure changes from ~ 1000 psi to ~ 800 with power.
As you said surely they couldn't have missed that.

It gets curioser and curioser.
They'll figure it out. They have my genuine sympathy .

Acoustic emissions (noise) analysis would be appropriate, but I'm not sure it if is done on SGs.

we had loose parts sensors at entry point of feedwater line to steam generator. You could hear internals of check valve tinkling at low flow. That'd be the closest point i know of. Sound telegraphs pretty well through steel , so one might hear something at primary tube sheet.



old jim
 
  • #33
Installing such acoustic monitors might have been possible as part of the RSG startup, but I don't think they will be heating the unit up / running the RCPs just so they can listen in and try to identify the problem. Too late for that. They will have to figure it out with inspections, whatever operating data is available now, and some fancy analysis.
 
  • #35
Astronuc, How do you feel this affects MHI's reputation in the USA industry after this?
 
  • #36
Thermalne said:
Astronuc, How do you feel this affects MHI's reputation in the USA industry after this?
I think it's a blow to their credibility - at least the division responsible. If I were a utility, I'd be very cautious concerning their products.

One thing I review in component design and manufacturing is 'anything new'. It's a question I ask each and every time (or a variant, "what's different"), particularly as part of a design review or technical surveillance.

There were manufacturing changes, and apparently design changes, as well as a faulty CFD analysis. That's why design reviews and oversight (by competent engineers who know at what and where to look) are so critical.
 
  • #37
One thing I review in component design and manufacturing is 'anything new'.

There exixts a mechanism in design review process called "Item Equivalency Evaluation" that is intended to allow replacing parts with equivalent parts.
It exists to allow for obsolescence, eg procuring newer transistors or electric motors or pumps to replace old models that have been discontinued by manufacturers, or to allow use of manufacturers' improved parts.
It requires that competent people study the equipment and make an honest assessment that the proposed new part will in fact perform its function at least as well as the original part did.
I understand that this IEE process was used for San Onofre's steam generator replacement.

The extent of alterations was described in a January article for Nuclear Engineering International magazine; it was written by a top-level Edison engineer and a collaborator from Mitsubishi. In that piece, published before the tubing crisis became public, they also described how the project was configured to meet federal guidelines without triggering a prolonged regulatory review.

Ultimately, the engineers couldn’t guarantee that their redesign would function flawlessly without putting them to work at San Onofre.

“Even though all design and fabrication challenges were addressed during manufacturing, it was not known if the as-designed and fabricated replacement steam generators would eventually perform as specified,” the authors wrote.
http://www.utsandiego.com/news/2012/may/26/did-san-onofre-fix-cause-the-problem/?print&page=all


To accomplish a design change via IEE pushes the intent a bit , so must be done with extreme caution and attention to detail if at all.


Looks like the mechanics and hydro-dynamics up around the top of u-tubes weren't studied quite well enough. Somebody should have hollered for help if he was in over his head.


It's a black eye for all involved
but before the floggings begin, one should find out how much of that analysis was assigned by the contract to each party.

For as Astro pointed out, responsibility rests with "Responsible Design Organization".

old jim
 
  • #39
Lengthy review possible at damaged Cal nuke plant
http://news.yahoo.com/lengthy-review-possible-damaged-cal-nuke-plant-235404211.html
The Nuclear Regulatory Commission is considering if the complex proposal submitted by operator Southern California Edison last week to repair and start the damaged Unit 2 reactor will require an amendment to San Onofre's operating license, Regional Administrator Elmo Collins told reporters.

Such reviews can involve a thicket of public hearings, appeals and commission actions on safety and design issues that can take as long as two years to complete.

In a March letter, federal regulators outlined a series of benchmarks Edison must reach to restart the plant, including determining the cause of vibration and friction that damaged scores of steam generator tubes, how it would be fixed and then monitored during operation.

Those requirements, however, did not involve amending the plant's operating license.

. . . .

It's "an open question" if a license amendment is needed, Collins said during a news conference. "It's a possibility. I'm not saying yes or no."

. . . .
The utility is hoping to operate Unit 2 at reduced power.
 
  • #40
Four months later: Uncertainty clouds future of Calif nuke plant
http://news.yahoo.com/uncertainty-clouds-future-calif-nuke-plant-222737326.html

LOS ANGELES (AP) — The mounting bill tied to the shuttered San Onofre nuclear power plant in California jumped to more than $400 million through December, as the company that runs it contends with costly repairs and a host of questions about its future, regulatory filings and officials said Tuesday.
. . . .
The figures come as SCE pushes the Nuclear Regulatory Commission for permission to restart one of the twin reactors, Unit 2, and run it at 70 percent power for five months in hopes of ending vibration and friction blamed for tube damage.
. . . .
 
  • #42
SONGS Closing

Pulling the plug:

http://www.cbsnews.com/8301-201_162-57588196/calif-utility-to-retire-troubled-san-onofre-nuclear-power-plant/
 
  • #43
NUCENG said:
Pulling the plug:

http://www.cbsnews.com/8301-201_162-57588196/calif-utility-to-retire-troubled-san-onofre-nuclear-power-plant/
Ouch! So much for the Renaissance.

Crystal River is also down and out, and Kewaunee was just permantely shutdown. So the number of operating reactors has dropped to 100, down from 104.
 
  • #44
Astronuc said:
Ouch! So much for the Renaissance.

Crystal River is also down and out, and Kewaunee was just permantely shutdown. So the number of operating reactors has dropped to 100, down from 104.

And Fort Calhoun hasn't got a restart from the CAL (confirmatory Action Letter) yet as far as I know.
 
  • #45
  • #46
Thermalne said:
Astronuc, How do you feel this affects MHI's reputation in the USA industry after this?

I know of a plant who is discussing not even doing steam generator replacement after looking at CR3 and SONGS. They would just shut down after their SGs reach the ASME code limits. They are seeing that the potential risk might not be worth the reward. (this is partially influenced by natgas prices as well). It's kind of a blow in reputation of anyone making SGs.
 
  • #47
Ouch! So much for the Renaissance.

It sure hurt the industry's image.

This article
https://s3.amazonaws.com/s3.documentcloud.org/documents/347889/col-nrc-tech-paper.pdf

describes an administrative process used by the utility to avoid some reviews of changes to the design.

At SONGS, the major premise of the steam
generator replacement project was that it
would be implemented under the 10CFR50.59
rule, that is, without prior approval by the US
Nuclear Regulatory Commission (USNRC). To
achieve this goal, the RSGs were to be
designed as ‘in-kind’ replacement for the
OSGs in terms of form, fit and function.

That is a very useful shortcut for little things like replacing obsolete transistors or when a vendor changes his paint color.
But there's a fine line somewhere between parts replacement and redesign.

A little further down same article:
The term ’AVB structure’ describes tube
supports in the tube bundle U-bend region.
The AVB structure had to be designed such
that the potential for tube wear due to flow
induced vibration was minimized.
To achieve this objective, six sets of Vshaped
AVBs made from Type 405 ferritic
stainless steel, providing up to 12 support
points per tube bend, were installed in the U
bend region to provide support in the region
where the tubes are most susceptible to
degradation due to wear from flow-induced
vibration. The single major challenge here
was control of the AVB thickness and
flatness, and tube-to-AVB gap size. This
challenge was addressed by customizing the
fabrication and assembly processes and
implementing strict quality control in various
stages of AVB fabrication and AVB structure
assembly.

Scuttlebutt is that the high void fraction in that region gave less fluid damping than assumed so the tubes rattled more than expected.

Whether additional NRC review would have caught the design mistakes beforehand I don't know.
But they sure found them after the fact, around page 56 here:
http://www.nrc.gov/info-finder/reactor/songs/ML12188A748.pdf
The team developed an independent model of the new steam generators using the ATHOS thermal hydraulic code3
Mitsubishi provided a comparison of their ATHOS model to their FIT-III model results. The Mitsubishi ATHOS model fluid velocities were approximately 3 times higher than the FIT-III model velocities with the 1.5 multiplier applied. Other independent code calculations, including an analysis by Westinghouse using their in-house modified version of ATHOS and an analysis by AREVA using their French code CAFCA4 showed similar thermal-hydraulic results (up to 4 times higher velocities than FIT-III) as those computed in the Mitsubishi ATHOS results and the NRC independent ATHOS calculations. Based on these comparisons, it was concluded that the FIT-III code and model results used for design were non-conservative even with the multiplier applied. . The calculations were intended to assess operating cycle differences between Units 2 and 3 steam generators and review thermal hydraulic phenomena within the steam generators in order to investigate key parameters and causal factors for the excessive tube wear rates. The NRC ATHOS calculations determined that the differences in primary inlet temperature and steam flow between the units were negligible. NRC ATHOS results indicated high void fractions and high u-bend gap velocities existed in the bundle as compared to Mitsubishi FIT-III analyses used for design.

It's always obvious to close the barn door after the horse has got out.

but IMHO the old bureaucratic dodge of "just blame the vendor" isn't honest.
SCE needed to provide Mitsubishi any help they needed, even if they had to pay CE for some trade secrets and Westinghouse for some consulting.

That's my opinion.

Thanks guys for all the links and info

old jim
 
Last edited:
  • #48
jim hardy said:
It sure hurt the industry's image.

This article
https://s3.amazonaws.com/s3.documentcloud.org/documents/347889/col-nrc-tech-paper.pdf

describes an administrative process used by the utility to avoid some reviews of changes to the design.



That is a very useful shortcut for little things like replacing obsolete transistors or when a vendor changes his paint color.
But there's a fine line somewhere between parts replacement and redesign.

A little further down same article:


Scuttlebutt is that the high void fraction in that region gave less fluid damping than assumed so the tubes rattled more than expected.

Whether additional NRC review would have caught the design mistakes beforehand I don't know.
But they sure found them after the fact, around page 56 here:
http://www.nrc.gov/info-finder/reactor/songs/ML12188A748.pdf


It's always obvious to close the barn door after the horse has got out.

but IMHO the old bureaucratic dodge of "just blame the vendor" isn't honest.
SCE needed to provide Mitsubishi any help they needed, even if they had to pay CE for some trade secrets and Westinghouse for some consulting.

That's my opinion.

Thanks guys for all the links and info

old jim



This could have been done under 50.59...EVALUATION.

The SONGS 50.59 is available on the NRC website, and they claim that the RSGs are not adverse and can be changed under just a screening. They claim the only things that are adverse are the tech spec changes, but that the RSGs were not adverse to the design function of an SSC. Being familiar with the 'new' 50.59 rule, I have no idea why they would have thought this was ok...but o well.
 
  • #49
SONGS is certainly not the first unit to install RSGs under 50.59. Not saying I agree that that path is appropriate. In fact the first time I read a 50.59 screening for RSGs I was very surprised. But licensing types tend to emulate lawyers and thus place stock in precedents. Again, not saying I agree with that approach, either.

All that aside, I seriously doubt that the NRC would have "caught" anything had SCE done the change under a license amendment. The NRC is not a SG designer much less a manufacturer. there's a slim chance that they might have asked a question that would have led MHI to uncover the problem, but who knows?

In the end, I think beating SCE up over the 50.59 is a red herring. Old Jim is right, SCE should have had some input from Westinghouse née CE. The guys in Chattanooga know a few tricks.
 
  • #50
jim hardy said:
It sure hurt the industry's image.

This article
https://s3.amazonaws.com/s3.documentcloud.org/documents/347889/col-nrc-tech-paper.pdf

describes an administrative process used by the utility to avoid some reviews of changes to the design.
That is a very useful shortcut for little things like replacing obsolete transistors or when a vendor changes his paint color.
But there's a fine line somewhere between parts replacement and redesign.

A little further down same article:Scuttlebutt is that the high void fraction in that region gave less fluid damping than assumed so the tubes rattled more than expected.

Whether additional NRC review would have caught the design mistakes beforehand I don't know.
But they sure found them after the fact, around page 56 here:
http://www.nrc.gov/info-finder/reactor/songs/ML12188A748.pdfIt's always obvious to close the barn door after the horse has got out.

but IMHO the old bureaucratic dodge of "just blame the vendor" isn't honest.
SCE needed to provide Mitsubishi any help they needed, even if they had to pay CE for some trade secrets and Westinghouse for some consulting.

That's my opinion.

Thanks guys for all the links and info

old jim

Combustion Engineering's IP are owned by Westinghouse since ABB merged Westinghouse Nuclear Services and CE together.
 
  • #51
Thermalne said:
Combustion Engineering's IP are owned by Westinghouse

true enough

...since ABB merged Westinghouse Nuclear Services and CE together.

Not quite. ABB never had any part of Westinghouse.

In 1990, ABB bought Combustion Engineering (both the nuclear and fossil power businesses).

In 2000, ABB sold their nuclear businesses to Westinghouse Electric. Shortly after that, they sold their fossil equipment business (including the CE fossil interest) to Alstom.

WEC is the nuclear part of the "old" Westinghouse, which had been sold to BNFL when CBS broke the old Westinghouse into fragments around 1996. So if anything, BNFL is the one that "merged" CE nuclear into WEC (but even that is stretching things).

In 2006, BNFL sold Westinghouse Electric (including the previously absorbed CE nuclear) to Toshiba.

Interestingly, in the past Westinghouse and MHI had a good relationship (MHI built the PWRs in Japan originally following the W design under license). When BNFL sold Westinghouse, MHI was in the bidding, but Toshiba won out.

Anyway, Toshiba now owns the Westinghouse nuclear business, including the CE technology. Due to the Toshiba / MHI competitive dynamic it was never likely that they would cooperate on the SONGS RSG design.
 
  • #52
Astronuc said:
Ouch! So much for the Renaissance.

Crystal River is also down and out, and Kewaunee was just permantely shutdown. So the number of operating reactors has dropped to 100, down from 104.


There's a trickle of new construction here in US:

http://www.nytimes.com/2013/06/12/b...oject.html?pagewanted=1&_r=1&ref=matthewlwald

Until recently, a new reactor construction project had not been started in the United States for 30 years, and now Vogtle and a similar project in South Carolina, V.C. Summer 2 and 3, are supposed to provide the answer to nuclear power’s great questions: What does a new reactor cost? With the price of natural gas near historical lows, can it even be worthwhile?

As the current generation of reactors moves toward retirement, the two projects may be the industry’s last best hope.

“Everybody’s watching the construction of that plant,” said Barry Moline, executive director of the Florida Municipal Electric Association, speaking of Vogtle. Several association members are considering investing in a nearly identical plant proposed by Florida Power and Light in Miami. Mr. Moline said of Vogtle’s builders, led by Georgia Power, “If they can do it, that will be the model.”

And if they can’t, it could be years before anybody thinks of trying again. The new designs are supposed to be a tenth as likely to have an accident and to be easier to operate, but if they cannot be built roughly on time and on budget, then nuclear power will have trouble in the era of plentiful natural gas and emerging technologies like wind.

Nuclear power could become a bypassed technology — like moon landings, Polaroid photos and cassette tapes.

Bypassed technology indeed.
I worked on the Westinghouse analog control systems. I feel sort of like a Brontosaurus veterinarian .
Well, it was interesting while it lasted.

And that carbon tax could start it all over again.

old jim
 
  • #53
jim hardy said:
but IMHO the old bureaucratic dodge of "just blame the vendor" isn't honest.
SCE needed to provide Mitsubishi any help they needed, even if they had to pay CE for some trade secrets and Westinghouse for some consulting.

How would that happen? Mitsubishi would have to know they were incompetent and ask SCE for help? But did Mitsubishi know their analysis was inadequate before the fact (should they have known, could they have known?)
 
  • #54
atyy said:
How would that happen? Mitsubishi would have to know they were incompetent and ask SCE for help? But did Mitsubishi know their analysis was inadequate before the fact (should they have known, could they have known?)

I am sure that had Mitsubishi known they would have refused to build the generators.

Here is my reasoning for not excusing the utility.

Any design change is the sort of thing a prudent engineer triple checks. On something this important you quadruple check and then get somebody else to check your work.

Here's what they DID know:

SCE's engineers know that Mitsubishi long ago licensed from Westinghouse to build reactor components. So Mitsubishi is unquestionably qualified to build a replacement for a Westinghouse steam generator.

SCE's engineers also know that being a CE plant, San Onofre's steam generators differ in design by whatever CE and Westinghouse did to avoid one another's patents.

SCE's engineers also know that they made a design change to smaller diameter tubes.
Skinny tubes are more limber than fat ones.

SCE's engineers also know that due to different "Recirculation Ratio" of the Westinghouse and CE designs, the fluid properties in the u-bend region differ. Mitsubishi is accustomed to building for the Westinghouse properties.
 (If I recall correctly the respective recirc ratios are 10 and 4.)

In my opinion those two italicized facts should have been a red flag to SCE's engineers that they must pay very special attention to that region.

Apparently they had an inkling:
from that NEI article:
AVB support structure
The term ’AVB structure’ describes tube
supports in the tube bundle U-bend region.
The AVB structure had to be designed such
that the potential for tube wear due to flow
induced vibration was minimized.
To achieve this objective, six sets of Vshaped
AVBs made from Type 405 ferritic
stainless steel, providing up to 12 support
points per tube bend, were installed in the U
bend region to provide support in the region
where the tubes are most susceptible to
degradation due to wear from flow-induced
vibration. The single major challenge here
was control of the AVB thickness and
flatness, and tube-to-AVB gap size. This
challenge was addressed by customizing the
fabrication and assembly processes and
implementing strict quality control in various
stages of AVB fabrication and AVB structure
assembly.

Skinnying-down the tubes made a fundamental change to the mechanical properties of the tubes, one that affects their dynamics.

Had that NEI article mentioned " Because of the mechanical changes to the tubes and the potential effect dynamic behavior, an independent review was performed by third party"
I would have more sympathy for the utility.

But from what I've seen, they accepted Mitsubishi's analysis.

And that u-bend area is right where they had their trouble.
From Nuceng's link http://www.nrc.gov/info-finder/reactor/songs/ML12188A748.pdf
If operating velocities reach this critical value, vibration amplitudes can increase rapidly and fluid-elastic instability forces can lead to rapid pulsation and damaging of tubes. The U-bend region is most susceptible because (1) the local fluid has a higher void fraction, with high velocities; (2) the fluid flow is in a direction normal to the tube, and (3) the anti-vibration bars are limited in their dampening capability along the plane of the tubes. Traditional design of anti-vibration bar systems have not considered in-plane fluid forces since it was accepted that the rigidity and dampening strength of the tube in this direction was adequate to preclude it. This event at SONGS is the first US operating fleet experience of in-plane fluid-elastic instability, sufficient to cause tube-to-tube contact and wear in the U-bend region. ). The parameter of local velocity divided by critical velocity is referred to as stability ratio. The accuracy of calculating fluid-elastic instability is limited based on inputs that are best determined by design-specific mockup test data. Mitsubishi did not perform design-specific mockup tests, but used generally accepted test data, and other data based on Mitsubishi test rigs that were not specific to the SONGS replacement steam generator design.
The team noted that Design Specification SO23-617-1 did not address specific criteria for stability ratio and does not mention fluid-elastic instability. The team did find that the Mitsubishi calculated design values for stability ratios did not exceed 0.5. It is important to note, that each steam generator manufacturer has different design values for maximum stability ratios; therefore there is no standard value. The smaller that the design stability ratio is (has to be less than 1), the more margin to fluid-elastic instability.

Bold suggests the SCE procurement spec didn't even address fluid stability.

When you push a vendor too hard you take the risk he'll make a mistake.
An astute manager knows it's necessary to be a helpful partner, even if you have to give up appearing such a tough customer.So how could they know?
They couldn't.
IMHO there was good reason to suspect - So they needed to make absolutely sure.
It became a matter of judgment and somebody goofed.
old jim
 
Last edited:
  • #55
atyy said:
How would that happen? ...

I agree that this would have been very difficult for practical reasons if nothing else (see my post above). But recognizing that the CE steam generators are quite different (twice the size) of the typical MHI SGs, it might have been wise of SCE to put some kind of compensatory effort in place (like a third-party review) once they decided to go with a designer other than the OEM. Who knows - maybe that happened and we haven't heard about it. The bid evaluations that led to SCE selecting the MHI offer might be interesting.

edit: cross posted with Old Jim's post above. I think we're on the same wavelength
 
  • Like
Likes   Reactions: 1 person
  • #56
Not to pile on, but in this instance everyone lost by trying to avoid outside scrutiny and review.
So the industry as a whole suffers another avoidable black eye and 1100 people lose their jobs.
If the regulators had not been bypassed in the first place, they would surely have been sufficiently invested in the plant to let it run at a safe 70%, even assuming that they would not have caught the design defect.
 
  • #57
jim hardy said:
When you push a vendor too hard you take the risk he'll make a mistake.
An astute manager knows it's necessary to be a helpful partner, even if you have to give up appearing such a tough customer.

Do you think they pushed the vendor too hard, or was it just not being careful enough (well, I guess pushing the vendor too hard is also not being careful enough)? Like gmax137 and etudiant maybe leave it open it's more of the latter?

So do the laws really put all the blame on the vendor, when as you argue, it should also fall on the utility? If so, are there modifications to the law that can prevent this - I assume it's not in the state's interest to suddenly run out of power?
 
  • #58
Do you think they pushed the vendor too hard, ...

Well, without actually being there there's no knowing what was the dynamic between the two outfits.

The Mitsubishi non-proprietary 'root cause' report at
http://libcloud.s3.amazonaws.com/93/92/5/2795/MHI_Root_Cause.pdf
has a couple interesting paragraphs in it:
The Certified Design Specification S023-617-01, Rev. 3 stated that SCE intended to use the provisions of 10 C.F.R. §50.59 as the justification for the RSG design, which imposed physical and other constraints on the characteristics of the RSG design in order to assure compliance with that regulation.
I don't know what were the constraints.

Mitsubishi built steam generators for Ft Calhoun , pdf page 9 of 64

The replacement steam generators for OPPD's Fort Calhoun Nuclear Generating
Station are the only other steam generators designed by MHI operating in the United
States. The OPPD RSGs replaced Combustion Engineering OSGs and are of a similar
design and construction as the SONGS RSGs with certain differences, including:
" Identical tube diameter (3/4") and wall thickness (0.043")
" Identical tube pitch (1.0" equilateral triangle)
" Identical pitch-to-diameter ratio (P/D = 1.33)
" OPPD has greater average tube to AVB gap
* OPPD RSGs are smaller than SONGS RSGs
* Fewer AVBs than SONGS
" Fewer tubes than SONGS
" Smaller U-bend radius than SONGS
" Lower maximum steam quality (void fraction) than SONGS

The Fort Calhoun RSGs have operated more than three fuel cycles with no evidence of
U-bend tube degradation (no tube-to-AVB wear, no tube-to-tube wear, and no
retainer bar-to-tube wear).Other steam generators designed by MHI (operating
outside of the United States)are of a different design and have a variety of tube sizes,
tube pitches and operating conditions. These steam generators have years of
operation without significant tube wear.

So, when they stuck to original CE physical design they were okay.

But they tinkered with the design:
Page 48 of 64 :
Identification of the changes from previous SG designs led to the recognition that the RSG design deserved close scrutiny. MHI considered the changes in the SONGS design from previous steam generator designs and compared the basic design parameters of the SONGs RSGs (e.g., heat transfer area, circulation ratio, steam pressure, etc.) with other steam generator designs. Further, as part of the development of the SONGS RSG design, MHI conducted a detailed comparison between its proposed AVB support for the tubes in the U-bend region and that of a comparison plant of similar design. A special AVB team was formed and included
industry experts to conduct an extensive design review process in 2005 / 2006 to optimize the U-bend design and address the technical issues. The team concluded that the SONGS design was significantly more conservative than previous designs in addressing U-bend tube vibration and wear. Also MHI and SCE recognized that the SONGS RSG steam quality (void fraction) was high and MHI performed feasibility studies of different methods to decrease it. Several design adjustments were made to reduce the steam quality (void fraction) but the effects were small. Design measures to reduce the steam quality (void fraction) by a greater amount were considered, but these changes had unacceptable consequences and MHI and SCE agreed not to implement them. It was concluded that the final design was optimal based on the overall RSG design requirements and constraints. These included physical and other constraints on the RSG design in order to assure compliance with the provisions of 10 C.F.R. §50.59. (emphasis mine - jh)

So do I think there was a push to avoid that 50.59 trigger ?

It's reading between the lines, but yes I do.
Phrases "close scrutiny"
and "optimal based on the overall RSG design requirements and constraints"
tell me somebody was worried but they yielded to schedule and contract pressures.

old jim
 
  • #59
Interesting presentation on the failures here:

https://ric.nrc-gateway.gov/docs/abstracts/palmisanot-hv-w13.pdf
 
Last edited by a moderator:
  • #60
oops -
I think I have to withdraw my claim that SCE changed tube diameter.
In process of double checking myself I can not find where I picked up that idea.
They changed the material and number of tubes and heat transfer area,

but I cannot find a statement that they changed diameter. Don't know where I got the impression.

sorry for posting that mis-statement.

old jim