ML082330501
| ML082330501 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee  |
| Issue date: | 01/26/2005 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | NRC/SECY/RAS |
| SECY RAS | |
| References | |
| 06-849-03-LR, 50-271-LR, Entergy-Intervenor-NEC-JH_39, NRC-194, RAS M-207 | |
| Download: ML082330501 (22) | |
Text
'PAS - ý-O NEC-JH_39 Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Thermal Hydraulic Phenomena Subcommittee Docket Number: (not applicable)
Location: Rockville, Maryland Date: Wednesday, January 26, 2005 Work Order No.: NRC-194 Pages 1-364 NEAL R. GROSS AND CO., INC.
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197 1 Okay. I also review the section on leak 2 before break. And the operating conditions under the 3 uprated conditions will not alter the conclusions of 4 the previous leak before break analysis for Waterford 5 3. It's still valid.
6 Are there any additional questions?
7 I'll turn it over to John Tsao.
8 MR. TSAO: I'm John Tsao from the 9 Materials and Chemical Engineer Branch. I reviewed 10 five sections; coding system, flow accelerated 11 corrosion programs, steam generator tube inspections, 12 steam generator blowdown systems and chemical and 13 volume control systems.
14 I will be talking about only two systems 15 here; flow accelerated programs and steam generator 16 tube inspections because they are more significant in 17 terms of power uprate.
18 For the flow accelerated corrosion 19 programs, this morning there was some issue as to how 20 much you increase. I have this backup slide.
21 The FAC program measure the wear rates in 22 terms of mils per year. And these are the changes 23 that would be due to power uprate conditions.
24 Also, I want to show you another slide 25 that gives the effectiveness of the FAC program. This NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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198 1 is provided by the licensee. And as licensee said, it 2 is more in the -- they used CHECWORKS. It's a 3 computer program that considers hydrodynamics, heat 4 balance, temperature in particular.
5 As you can see the predictive method is 6 conservative considered to actual measurement.
7 DR. FORD: I'm sorry. Could you explain 8 that?
9 MR. TSAO: Okay.
10 DR. FORD: It looks as though it's equally 11 scattered around the one to one line. So why are you 12 saying it's conservative?
13 MR. TSAO: Well, for example, you can see 14 -- let's see.
15 You can see just for example, this point 16 here the measurement is about 300 mils. The predict 17 value, let's say, from here tohere is about 240 mils.
18 So what it says *is that the methodology will predict 19 that the tube wall thinner than measured, therefore it 20 also indicated that the licensee may need to do some 21 monitoring or replacement of that pipe.
22 DR. FORD: But equally there are points on 23 the other side which are not, what you call it --
24 MR. TSAO: Well, that's true. Yes, that's 25 correct. But as you know this is only a prediction.
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199 1 Predictions, hopefully -- well, from the data point 2 you can see they are scattered toward the conservative 3 side. And also the FAC program according to EPRI is 4 that it's a process. In other words, the licensees 5 would go out, make an inspection, UT or ultrasonic 6 measurements or the pipe thickness and then they will 7 come back and they input that data into the computer 8 code so that to make sure there is a certain accuracy 9 in their predictions.
10 Also predict that the -- in the prediction 11 method they include some safety factors.
12 DR. FORD: It seems to me as though 13 there's a huge amount of scatter around that one-to-14 one line. And so the question immediately arises as 15 to what is the impact of that in terms of could you 16 get a through wall erosion event taking place when you 17 had predicted it would not have done so?
18 MR. TSAO: It could.
19 DR. FORD: Did you go through that sort of 20 "what if" argument? I mean if you look at that data 21 base, you don't really have too much confidence in 22 CHECWORKS.
23 MR. TSAO: Well, I wouldn't say they would 24 be relying on CHECWORKS per se. The licensees, not 25 only Waterford but other licensees, you know they NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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200 1 include other factors. For example, other industry 2 experience. You know if some plants have some problem 3 with FAC water lines, then they will consider --
4 DR. FORD: I recognize that.
5 MR. TSAO: Right.
6 DR. FORD: But this particular EPU is 7 putting a lot of basis on CHECWORKS to manage this 8 problem. And if this a general observation as to how 9 good CHECWORKS is, my confidence is a little bit 10 shattered.
11 MR. TSAO: I should point out that 12 Waterford is not unique. I did the review for license 13 renewal, and I also asked questions. And this is type 14 of plot that, you know, other licensee has shown me.
15 DR. FORD: Yes, I know.
16 MR. TSAO: In other words, I don't think 17 that licensee is depending solely on what prediction 18 is. They also, you know, include other experiences and 19 inspections. Not only the inspections for the fact, 20 but there are other SME code inspections they have to 21 perform.
22 DR. FORD: I'll ask again. Did you go 23 through the "what if" scenario?
24 MR. TSAO: I have Kris Parcziewski from my 25 branch to elaborate on this.
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201 1 DR. FORD: With that amount of uncertainty 2 in your modeling capability and therefore your 3 management capability, do you not feel uncomfortable?
4 MR. TSAO: No.
5 DR. FORD: No?
6 MR. PARCZIEWSKI: Kris Parcziewski from 7 the Chemical Engineering Branch.
8 To answer your question, those points are 9 predicted. CHECWORKS predicts but in addition there 10 is a correction factor for each individual line which 11 is here at the top right hand side, line correction 12 factor which indicates that it is corrected for each 13 individual line all the points predicted in the line 14 are corrected by this line correction factor. And the 15 line is defined as a portion of the system which has 16 the same chemistry but not necessarily the same 17 temperature. If I answer your question.
18 So all those points are already corrected.
19 Ideally, if they were ideal, they would lie in the 45 20 degree line, the middle line. However, obviously, 21 there is some scatter.
22 DR. FORD: I understand the physics --
23 MR. PARCZIEWSKI: Yes.
24 DR. FORD: -- of the erosion process.
25 It's highly dependent on ph. High dependent on NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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202 1 temperature. Highly dependent on corrosion potential 2 and all of those things are interacting. So that if 3 you're a little bit off on your definition of one of 4 those parameters, then you're going to get a big 5 change. So I can understand why there is a scatter 6 there because you're not able to define your system 7 adequately enough, and therefore that's the physical 8 origin of your LCF. But I still feel uncomfortable 9 about that huge scatter and how you use it in 10 management from their point of view and in terms of 11 regulation from your point of view.
12 MR. TSAO: Okay. For regulation, 13 basically there's no regulation on FAC program.
14 DR. FORD: That'.s what worries me.
15 MR. TSAO: The FAC program is instituted 16 because of the bulletin. Back in the '80s it was 17 result of Bulletin 87-01 where Surry had a --
18 DR. FORD: Yes, sure.
19 MR. TSAO: -- a rupture. And Generic-20 Letter 89-08 that required the licensees to institute 21 some type of program, FAC program. And then the 22 industry, you know, with EPRI guidance come up with 23 this program. And so --
24 DR. FORD: I understand all that. I'm 25 just looking at what the history has been since then.
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203 1 And, you know, a few months ago we had fatalities in 2 Japan because of this phenomenon, which was not 3 managed well. And you know if this is supposed to be 4 the state-of-the-art of prediction of management and 5 therefore regulation, I just don't feel comfortable.
6 MR. TSAO: Okay. Speaking of the 7 Japanese, again from my understanding is that Japanese 8 did not inspect, you know, the last 20, 30 years.
9 DR. FORD: Correct.
10 MR. TSAO: Where here under FAC program 11 the licensees will. have to inspect at least they say 12 50 to 100 inspection points for their large bore 13 piping and small bore piping they probably sometime 14 inspect 100 percent. And so there's a constant 15 inspections going on to make sure that the --
16 DR. FORD: I understand that.
17 MR. TSAO: Right.
18 DR. FORD: All I'm pointing out is 19 everyone bows to CHECWORKS and says yes, yes that's 20 the best thing that's around. And I'm just 21 questioning it. Is it adequate?
22 MR. HOWE: This is Allen Howe.
23 And I'd just like to add in at this point 24 that we understand the question and we will be happy 25 to get back with you with a response on that.
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236 1 We're now going to complete the NRR 2 presentation.
3 MR. KALYANAM: I have one question.
4 Before Rich Lobel goes, we have two experts, one of 5 the FAC CHECWORKS program, the other one on the steam 6 generator tubes. So we had some questions before the 7 break, and I'm sure they'll be able to provide their 8 response to that. Is that okay.
9 DR. FORD: Well, I've been bagging on the 10 head about this FAC business. I understand it 11 perfectly. The other members might enjoy having a 12 presentation on that.
13 MR. KALYANAM: Okay. Either way is fine.
14 CHAIRMAN WALLIS: If it's something we're 15 going to enjoy, I think we should do it.
16 MR. ROSEN: As many times as possible.
17 MR. SIEBER: That's one time.
18 MR. KALYANAM: I have Ken Karwoski from 19 EMCB 20 MR. KARWOSKI: I guess I understand this 21 morning there were questions from the steam generator 22 two integrity standpoints some questions about whether 23 or not the power uprate, what effect it would have on 24 wear and cracking along the length of the tubes as a 25 result of the increased flow through the steam NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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237 1 generator. And then there may have also been a 2 question about the adequacy of the 75 gallon per day 3 leakage link.
4 In terms of the effect of the power uprate 5 on the increased flow through the steam generator, 6 there is a potential effect on the amount of wear that 7 can happen at the various support locations, whether 8 it be at the vertical straps, the diagonal bars or at 9 the egg crate supports. There could be an effect on 10 the wear.
11 In addition, Waterford has exhibited 12 stress corrosion cracking at a number of locations 13 along their steam generator tubes. Both of those 14 mechanisms could be effected by the power uprate.
15 However, the change in the conditions in terms of the 16 flow, the temperatures and the pressures across the 17 steam generator tubes are relatively small and well 18 within the bounds of what exists at other plants. And 19 it's been our experience at the other plants which 20 have uprated power that these small changes have 21 negligible increases in corrosion rates, negligible 22 increases on wear rates. And by "negligible," I mean 23 that it's well managed from one inspection to the 24 next; that when they go in and do an inspection after 25 a power uprate or after an interval, that they still NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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238 1 have tube integrity. That the tubes have adequate 2 regulatory margin --
3 CHAIRMAN WALLIS: This is where? On the 4 inside of the tubes you're talking about?
5 MR. KARWOSKI: On the outside.
6 CHAIRMAN WALLIS: Are the tubes rattling 7 and wearing.
8 MR. KARWOSKI: Rattling and wearing. And 9 that happens at almost every --
10 CHAIRMAN WALLIS: These fluid interactions 11 are a little hard.to predict, aren't they?
12 MR. KARWOSKI: Actually, they're quite 13 reliable. I mean there are some instances where some 14 tubes, and this is usually in the life of a steam 15 generator, where some tubes will wear quicker than 16 others because of the placement of the anti-vibration 17 bars or the diagonal straps in the case of Waterford.
18 So some tubes may wear more than others, 19 but in general these phenomenon are very predictable.
20 Plants leave wear scars in service, and in general 21 they're very predictable. The wear rates tend to be 22 very low and they're left in service for many cycles 23 before they exceed the tech sped.
24 MR. ROSEN: Do they tend to decrease in 25 rate because they kind of wear off whatever the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE.,- N.W.
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239 1 contact point and that's it?
2 MR. KARWOSKI: That has been the 3 experience, and I can't comment on the combustion 4 engineering data, but I know that that's definitely 5 been the experience at Westinghouse design steam 6 generators. But the wear rates decrease with time 7 because of the contact issue point.
8 MR. ROSEN: Now the question is brought up 9 how. about the effect of vibration, vibrational 10 stresses on the kinetics of stress corrosion cracking?
- 11. MR. KARWOSKI: once again, you know, it is 12 possible that that would increase the rate of 13 cracking, may even change the initiation of cracks.
14 But it's been our experience that any change that does 15 occur: (1) it's not readily measurable, and; (2) that 16 it can be managed within the normal frequency of in 17 service inspections. And certainly if there is a 18 change, we will detect that as we review the annual 19 reports that the plant sends in regarding their 20 inspections. And we would expect them to take 21 corrective action, and that would be something we 22 would followed up. But in general we have not 23 observed that. And in the case of Waterford, it's been 24 their practice that when they find a crack, they plug 25 that crack on detection. It's not like some of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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24.0 1 other plants which leave cracks in service and try to 2 manage cracks that --
3 MR. ROSEN: My questions on those two 4 issues.
5 MR. SIEBER: The displacements are 6 extremely small and the number of cycles is extremely 7 large. So if there is going to be failure, it would 8 show up fairly early, I would expect.
9 MR. KARWOSKI: That would be for like the 10 cycle type of fatigue failure.
11 MR. SIEBER: Right.
12 MR. KARWOSKI: In this case it's more just 13 the wearing of the tube, which it can be low cycle--
14 MR. SIEBER: But that's not fatigue 15 failure.
16 MR. KARWOSKI: No, that is not fatigue.
17 Yes, that's correct.
18 MR. SIEBER: Right. It's just wearing i9 out.
20 MR. KARWOSKI: That's just wear.
21 DR. FORD: Jack, there's a problem 22 discussed earlier on. It's not trangranular fatigue, 23 cracking you see.
24 MR. SIEBER: Right.
25 DR. FORD: And therefore it's not covered NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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241 1 by the ASME 3 code or anything like that. Similarly 2 it's just stress code in cracking that's been 3 accelerated.
4 MR. SIEBER: But wear phenomenon is 5 covered by the ASME code.
6 DR. FORD: Yes.
7 MR. KARWOSKI: Through the plugging limits 8 and what not and through the plant technical 9 specifications.
10 DR. FORD: Right.
11 CHECWORKS?
12 MR. KARWOSKI: I think Louise Lund was 13 going to talk about CHECWORKS.
14 *DR. FORD: Maybe if I could just state 15 what my problem was, Louise, and that would make it 16 more efficient for you to answer it.
17 MS. LUND: Should I introduce myself first 18 for the record?
19 DR. FORD: Yes.
20 MS. LUND: I'm Louise Lund. I'm. the 21 Section Chief for the Steam Generator and Integrity 22 and Chemical Engineering Section, NRR. And, anyway, 23 I was asked to come over and discuss the FAC program.
24 DR. FORD: My concern was that the way 25 that they're using CHECWORKS right now, it is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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242 1 primarily a prioritization tool as to where you're 2 going to look in the carbon steel piping. From the 3 measures that were shown this morning, it's apparent 4 that CHECWORKS is not good on one-to-one correlation.
5 Therefore, it's quite possible that you may use 6 CHECWORKS to say that I should not look at that pipe 7 because of the particular operating conditions of that 8 pipe, but I should look at this pipe. But in fact that 9 pipe there might well be eroding at quite a large 10 rate, but you wouldn't look at it for one, two, three 11 cycles. In that time you could go through wall. So 12 that was essentially my worry that you're using a 13 model which is not precise to make prioritization 14 decisions.
15 MS. LUND: Right. And I just want to say 16 off the top, you know we have a very active interest 17 in the FAC programs. Specifically we've had generic 18 letters or generic correspondence that has asked 19 industry to put together these type of programs which 20 manage FACs and also have these predictive 21 methodologies. However, it's not a case of just using 22 the predictive methodologies blindly and looking at 23 information on one line or another; there's a number 24 of things that inform the decision as far as what's 25 inspected and how it's inspected. Because it is a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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243 1 tool, but it's not a blind tool in that particular 2 way. And, in fact, this gentleman I believe is from 3 Waterford and he was mentioning, we had a kind of 4 offline discussion about it and that's why I asked him 5 to come up here and help discuss this, and 6 specifically for Waterford.
7 I also wanted to say that for these FAC 8 programs, I think that we have an interest in looking 9 at them through power uprate and license renewal in 10 that we ask that the licensee provide information on 11 their most susceptible lines with their measures 12 versus their predicted and whether it gave them 13 information such that they could replace the lines, 14 you know, in a timely manner. Because that's really 15 what we want to know is, is it giving you the 16 information at the time that you need it in order to 17 make the decisions you need to make good decisions 18 about running your plant.
19 So that's the kind of questions we ask. We 20 do not do a re-review of their CHECWORKS data. We do 21 not take all their raw data and subsequently do an 22 audit of it. Okay. So I just wanted to kind of 23 clarify what it is that we do, you know, in our review 24 process. Usually through a request for additional 25 information we usually will ask them for the most NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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244 1 susceptible lines.
2 MR. ROSEN: We call that a performance-3 based regime?
4 MS. LUND: Right. Right. And when we put 5 out that generic letter where we asked the licensees 6 to put together a FAC program and also have these 7 predictive methodologies, we did inspections of those 8 programs at that time. Okay. In fact, to make sure 9 that these programs were in place and in fact doing 10 what we thought that they were doing. Okay.
11 Now, I now in license renewal, true 12 license renewal we've been asked to come and give a 13 presentation to the ACRS on FAC and FAC programs. And 14 we've actually been in contact with CHECWORKS user 15 script to ask them to come in and help present this 16 information such that you can look industry-wide at 17 how well these FAC programs are working, specifically 18 with the CHECWORKS program and give you a lot of sense 19 -- instead of looking at just one graph, kind of get 20 a sense for generically how this is working and where 21 it may be challenged in certain ways or another, 22 because they think that they have a very good story to 23 tell.
24 Now maybe if you could introduce yourself, 25 and then also explain how programmatically it's a much NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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245 1 lighter look at how you choose the lines and --
2 because there's a surrogate aspect to it where, you 3 know, if you see something you look at other things 4 that are like that. There are a lot of things that go 5 into the program that don't rely on just this 6 measurement.
7 So, anyway --
8 MR. ALEKSICK: Good afternoon. My name is 9 Rob Aleksick. I'm with CSI Technologies representing 10 Entergy today.
11 Real quick about my background. I've had 12 the opportunity to be involved with flow accelerated 13 corrosion since 1989 and in particular have modeled or 14 otherwise addressed approximately 20 EPU efforts in 15 the last two years.
16 Dr. Ford made a very good point earlier 17 when he said that the graph that we looked at did not 18 display a very good correlation between the measured 19 results and the predicted results out of CHECWORKS.
20 Programmatically -- well, let me back up a second.
21 That is certainly true in the example that we looked 22 at. That is not always the case.
23 CHECWORKS models are on a per line or per 24 run basis. The run --
25 CHAIRMAN WALLIS: Could we go back to that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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246 1 graph that we saw? The graph was a plot of thickness 2 versus predicted thickness.
3 MR. ALEKSICK: That's correct.
4 CHAIRMAN WALLIS: Because if you looked at 5 amount removed versus predicted amount removed, it 6 seems to me the comparison will be even worse.
7 MR. ALEKSICK: That's correct. In fact --
8 CHAIRMAN WALLIS: That's what you're 9 really trying to predict is how much is removed.
10 MR. ALEKSICK: Yes, that is true. And my 11 point is that in some subsets of the model, the one 12 that we looked at here which was high pressure 13 extraction steam, the correlation between measured and 14 predicted is not so good. And in some subsets of the 15 model, the correlation is much better.
16 CHAIRMAN WALLIS: It looks to me that in 17 some cases it's predicting no removal whereas in fact 18 there's a lot of removal. So the error is percentage 19 wise enormous?
20 MR. ALEKSICK: Yes, 'exactly. Exactly.
21 Some runs results are imprecise and some more precise.
22 And we look at both accuracy and precision.
23 Programmatically we account for that, that reality, by 24 treating those runs that have what we call well 25 calibrated results, i.e., precise and accurate results NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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247 1 coming out of the model that are substantiated by 2 observations, we treat those piping segments 3 differently programmatically than we do areas where 4 the model is less good. If the model results do not 5 correlate well with reality, different actions are 6 taken primarily increased inspection coverage to 7 increase our level of confidence that those systems 8 can continue to operate safely.
9 In addition to the CHECWORKS results many 10 other factors are considered to assure that the piping 11 retains its integrity, chief among these are industry 12 experience as exchanged through the EPRI sponsored 13 CHUG group. Plant experience local to Waterford in 14 this case. And the FAC program owner maintains an 15 awareness of the operational status of the plant so 16 that, for example, modifications or operational 17 changes that occur are taken into account in the 18 inspection of the secondary site FAC susceptible 19 piping.
20 DR. FORD: And my final question on this 21 particular subject was given the uncertainties in the 22 model, changed by this performance based aspect that 23 you just talked about, is there any way that you can 24 come up with a quantification of the risk associated 25 with a failure of a specific pipe?
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248 I MR. ALEKSICK: There's currently no 2 accepted methodology to quantify that risk, no.
3 However, it is accounted for primarily on a judgment 4 basis through industry experience and information 5 exchange through the EPRI CHUG group.
6 DR. FORD: Okay.
7 MR. MITCHELL: Yes, this is Tim Mitchell.
8 Just to give you a feel for how we're 9 addressing for this upcoming refueling outage, we have 10 increased our scope for a couple of reasons. One to 11 get additional data and we always do more than just 12 exactly what CHECWORKS supports. So you're always out 13 validating and getting more data to be able to help 14 predict where do you need to be looking. But in 15 addition, we're taking some additional points to make 16 sure we have good baseline data for the next cycle to 17 ensure that those points give us a good indication 18 going forward after the EPU.
19 The analysis for flow accelerated 20 corrosion shows very minimal changes as a result of 21 power uprate. But we are taking seriously our 22 inspection program and expanding it for this upcoming 23 outage to ensure that we know what's happening not 24 just what we're predicting.
25 MR. ROSEN: Let me roll that back now, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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249 1 Tim. Can you tell me like for the last three or four 2 outages have you done some actual replacement of 3 pipingbased on predictions of PAC from the CHECWORKS 4 code or have you never replaced anything? What are 5 you seeing at Waterford?
6 MR. MITCHELL: I can give you non-7 Waterford data better than I can give Waterford to 8 ponder.
9 MR. CHOWDHURY: My name is Prasanta 10 Chowdhury and I'm working with Entergy design for last 11 20 years.
12 I was involved with PAC also for several 13 years in the past.
14 It's not the CHECWORKS model that 15 determines what replacement is to be done. We base it 16 on actual measurement we take during the refuel 17 outage. So we also project based on actual measurement 18 that what will be our future projected thickness in 19 next refueling outage. So you can survive until next 20 cycle. And then we do some evaluation based on our 21 criteria that makes the stress criteria -- or based on 22 the code requirement. Like make all the equation.
23 Now code allows to go thinning in local 24 area but the FAC is a local thinning. So we do some 25 local thinning evaluation to make sure that it goes to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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