ML20134D495

Transcript of Public Meeting in Rockville,Md on 961016 Re Briefing on Containment Degradation.Pp 1-34.W/related Correspondence

ML20134D495
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Issue date:	10/16/1996
From:	NRC
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REF-10CFR9.7 NUDOCS 9610220381
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{{#Wiki_filter:_ _ _ _ _ _ _ _ _ _ _ _ ORLG \\ A_ UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION

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BRIEFING ON CONTAINMENT DEGRADATION - PUBLIC MEETING Location: Rockville, Maryland l l Date: Wednesday, October 16,1996 1 l Pages: 1 - 34 l i l l 9610220381 961016 .7 PDR ANN RILEY & ASSOCIATES, LTD. 1250 I St., N.W., Suite 300 's )(0f Washington, D.C.20005 (202) 842-0034 0\\

1 0 DISCLAIMER This is an unofficial transcript of a meeting of the United States Nuclear Regulatory Commission held on October 16, 1996 in the Commission's office at One White Flint North, Rockville, Maryland. The meeting was open to public attendance and observation. This transcript has not been reviewed, corrected or edited, and it may contain inaccuracies. The transcript is intended solely for general l ' informational' purposes. As provided by 10 CFR 9.103, it is not part of the formal or informal record of decision of the matters discussed. Expressions of opinion in this transcript do not necessarily reflect final determination or beliefs. No pleading or other paper may be filed with the Commission in any proceeding as the result of, or addressed to, any statement or argument contained herein, except as the Commission may authorize. 9

1 1 UNITED STATES OF AMERICA 2 NUCLEAR REGULATORY COMMISSION 3 4 BRIEFING ON CONTAINMENT DEGRADATION 5 6 PUBLIC MEETING 7 8 9 Nuclear Regulatory Commission 10 11555 Rockville Pike 11 Rockville, Maryland 12 13 Wednesday, October 16, 1996 14 15 The Commission met in open session, pursuant to 16 notice, at 9:10 a.m., the Honorable SHIRLEY A.

JACKSON, 17 Chairman of the Commission, presiding.

18 19 COMMISSIONERS PRESENT: 20 SHIRLEY A. JACKSON, Chairman of the Commission 21 KENNETH C. ROGERS, Member of the Commission 22 GRETA J. DICUS, Member of the Commission 23 NILS J. DIAZ, Member of the Commission 24 EDWARD McGAFFIGAN, JR., Member of the Commission 25 ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

2 1 STAFF AND PRESENTERS SEATED AT THE COMMISSION TABLE: 2 KAREN CYR, GENERAL COUNSEL 3 JAMES TAYLOR, EDO l 4 ASHOK THADANI, Associate Director for Inspection 5 and Technical Assessment, NRR 6 JOSEPH MURPHY, Special Assistant, RES i l 7 ANDREW MURPHY, Chief Structural and Geological Engineering Branch, RES 8 4 9 GOUTAM BAGCHI, Chief Civil Engineering & 10 Geosciences Branch, NRR \\ l 11 12 l 13 14 15 1 16 1 17 l 18 l 19 l 20 21 22 ' 23 24 25 ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

3 1 PROCEEDINGS 2 (9:10 a.m.] 3 CRAIRMAN JACKSON: Good morning, ladies and 4 gentlemen. The purpose of this meeting is for the NRC Staff 5 to brief the Commission on degradation of containment 6 structures. 7 The containment is a fission product boundary, and 8 it is a cornerstone of the defense in depth strategy applied 9 at all power reactors in this country. Containment 10 degradation, particularly if it involves a challenge to the 11 capability of a containment to perform its safety function 12 is of concern. 13 Additionally, our recent implementation of a 14 performance-based 10 CFR Appendix J rule further underscores 15 the importance of keeping abreast of this issue. 16 The Commission recognizes that a great deal of 17 effort has been expended over the last several years in 18 better understanding the material condition of containment 19 structures. 20 Following the identification of examples of 21 degraded containments and varying degrees of licensee 22 containment inspection programs, a new inspection rule 23 endorsing the applicable sections of the ACME Code, Section 24 11, was made effective in September of this year. 25 During today's briefing, the Staff will inform the ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

4 1 Commission of the nature of the degradation observed to date 2 and long-term staff efforts in this area. We are also 3 interested in how the new inspection rule addresses these 4 degradation mechanisms. 5 I understand that copies of the presentation are 6 available at the entrance to the room. Do any of my fellow 7 Commissioners have any additional comments? 8 [No response. ) 9 CHAIRMAN JACKSON: Mr. Taylor, please proceed. 10 MR. TAYLOR: Good morning. Chairman, you have 11 already outlined the important safety function of 12 containments. 13 I would note in starting that containments are 14 typically very robust structures designed to withstand the 15 loading of external events such as tornadoes and hurricanes 16 and earthquakes in addition to the internal pressures in 17 elevated temperatures associated with design basis accident. I 18 With me at the table to continue the briefing are 19 Ashok Thadani, Goutam Bagchi from the Office of NRR, and 20 from the Office of Research, Joe Murphy and Andy Murphy. 21 CHAIRMAN JACKSON: Are you brothers? 22 (Laughter.] 23 MR. TAYLOR: Chairman, they formally disclaim 24 that. 25 Ashok has some additional opening comments. ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

5 1 MR. THADANI: Good morning. 2 CHAIRMAN JACKSON: Good morning. 3 MR. THADANI: Thank you, Jim. 4 This morning, the briefing will be given by 5 members of NRR as well as members from the Office of 6 Research. 7 Goutam Bagchi, sitting to my right from NRR, and 8 Andy Murphy from Research will outline the containment 9 degradation mechanisms and problems that have been detected 10 in the operating reactors, discuss the kind of responses 11 that the NRC has undertaken as a result of these identified 12 problems, and in particular, will focus on the recently 13 issued inspection requirements and to go on and talk about 14 type of research activities that are underway now, 15 recognizing that we are seeing a variety of degradation 16 mechanisms in structural containment. 17 The key point is that the number of incidents of 18 degradation is increasing. That is an important point to 19 note. 20 Some of these problems have actually been 21 identified by the NRC. Many of them, of course, have been 22 identified by the licensees themselves. 23 Mr. Bagchi will describe the mechanisms involved, 24 as well as the degradation rates, and this is clearly a 25 time-dependent phenomenon, and that is another important ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

6 1 element to where we are going. 2 While the degree of degradation that has been 3 observed to date has not been significant, but it is 4 critical that early attention be given because, as I said, 5 it is a time-dependent phenomenon and there could be a 6 problem over the long term in terms of maintaining the types 7 of margins we believe that exist with robust containment. 8 You have indicated, Chairman Jackson, that 9 Appendix J does, in fact, call for inspections, particularly 10 when you do integrated leak rate testing prior to and 11 afterwards, but there is no specific guidance provided 12 either in Appendix J or elsewhere as to what does that 13 really mean, what do we mean by inspections, and that is-1 14 where the need for this rule became evident. There is a 15 need for specific guidance, and it is captured as part of 16 the ASME 1993 addendum codes. 17 So what we have proposed here -- in fact, not 18 proposed -- the final rule actually calls for adoption of 19 this 1992 addendum, 250.55(a) requirement of the 20 regulations. 21 Now, the other issue that is important is to make 22 sure that what we do is properly integrated in terms of our 23 activities. The maintenance rule scope includes structural 24 systems and components, in particular. That means the 25 containment structure is certainly part of the maintenance ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

7 1 rule requirements. It is within the scope of the 2 requirements. 3 The role of containment is going to be obviously 4 critical for reactors as they continue to operate. 5 Therefore, it becomes an important issue as part of the 6 license renewal activities, and whatever we do in terms of 7 our inspections or monitoring licensees' performance needs 8 to recognize that. There is no need to have separate 9 programs to deal with these issues. So what we are looking 10 at is one -- at least from our side -- one inspection 11 approach that would be good enough in terms of maintenance 12 rule considerations, would be good enough in terms of 13 license renewal considerations. That is an important 14 element that work is currently ongoing. 15 I will go to Mr. Bagchi to give you some of the 16 details of what we are seeing and the actions that we have 17 taken. 18 MR. BAGCHI: Thank you, Mr. Thadani. 19 Good morning, Chairman Jackson and Commissioners. 20 Containment structures, as was pointed out, are 21 designed to withstand the effects of conservative loads and 22 combinations of extreme loads while remaining essentially 23 within elastic limits. 24 For example, the design basis internal pressure 25 caused by loss of coolant accidents and the large seismic ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

8 1 loads are applied simultaneously. These structures are 2 built with high-quality materials and construction 3 techniques. However, as good as the structures are, they 4 are showing signs of degradation, but the integrity of 5 containment structures is being maintained through timely 6 repairs. l 7 Next slide, please. 8 This is the outline of our presentation. I am 9 going to cover the problems encountered so far, the safety 10 significance, NRC response, and the summary, and Dr. Murphy 11 will speak about the inspection rule and the research 12 programs. 13 Next one, please. 14 Prior tc the issuance of the containment 15 inspection rule, the Commission was informed about the need 16 for the rule to ensure that degraded condition are detected 17 in a timely manner using uniform and technically sound 18 methods, such as those incorporated in the ASME criteria, 19 but today's presentation is intended to provide the details 20 of degradation and the status of containment structures at 21 operating plants. 22 The next picture, please. 23 I would like to go over very quickly with some 24 sketches and pictures, so that I can set the context of our 25 t ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

_ ~. - 9 i 1 CHAIRMAN JACKSON: Could we have the next slide, 4 l 2 lease? I think there is a list of the problems detected. 3 It is the previous slide. 1 4 MR. BAGCHI: Let me go over this one. This is a 5 Mark I, BWR metal containment structure. It is light 6 bulb-shaped, and it is the bottom of the light bulb where t 7 vent lights come out and go into the torroidal shape wet 8 wells. Corrosion has been found in the sand cushion area 9 which transitions from the embedded concrete just below the 10 vent pipes. That is on the outside surface of the steel 11 shell. 12 MR. THADANI: If I may make a comment, those areas 13 are being pointed on the screen as Mr. Bagchi is describing 14 them. 15 MR. BAGCHI: Also, inside the wet well, near the 16 free surface of the water, that is where the water is in 17 contact with the steel shell. That is where corrosion has 18 been found. 19 They are coded primarily, except for one plant, 20 but they are regularly, generally inspected frequently, and 21 they are being monitored with respect to their condition, 22 measuring thicknesses by non-destructive techniques and so 23 forth. 24 The next picture, please. 25 Programs, of course, have been implemented to ANN RILEY & ASSOCIATES, LTD. Court Reporters I 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

10 1 maintain the integrity of the containment. There have been 2 some repairs, but in other cases, they are being monitored 3 through surveillance to make sure that the thickness 4 required is maintained. 5 This is a picture looking at the dry well shell 6 from the outside, putting a camera inside_the sand cushion 7 area. It is a very small opening, and it does show 8 extensive area of rusting. 9 Next one, please. 10 This picture shows the steel shell area which is 11 in contact with the sand cushion. The lower portion of the 12 picture, you see the sand cushion, and in the upper 13 right-hand corner, the interface goes right through the 14 middle of the picture. You can see the steel shell. 15 In some cases, corrosion has been extensive, but 16 as I pointed out earlier, rust has been scaled off and it 17 has been repainted. 18 Next picture, please. 19 I am trying to give you instances of what the 20 containment structures look like, what their specialties 21 are. This is a distressed, as they call it, post-tension 22 reinforced concrete containment structure. 23 The thing to point out is that this is such a 24 large volume. The entire inside surface of this prestressed 25 concrete containment structure is lined with steel liner. ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034 1

11 1 That provides the barrier against radionuclides coming 2 outside. Even on the top of the base mat, the liner goes 3 underneath a little bit of cover of concrete, and those 4 areas were being pointed out as we were looking at the 5 picture. 6 The next picture, please. 7 Now, this is instructive. People think that 8 structures are built forever, especially those made out of 9 concrete. One is built to last forever, but this one 10 clearly didn't. It is on the top of a dome somewhere on the 11 containment structure, and that is the extent of spalling of 12 concrete that was observed. 13 Now, this has, of course, been repaired and-14 resurfaced. 15 Next picture, please. 16 This picture shows grease coming out of the 17 outside surface of the containment structure. This is in a 18 prestressed concrete containment structure. Grease is used 19 to protect the tendons that go through the sheaths embedded 20 inside the concrete, and the grease itself is supposed to 21 prevent chemical contaminants that might attach and corrode 22 the free-stressing tendons. 23 Please note here that the streaks line up with the 24 locations of the tendon ducts. 25 CHAIRMAN JACKSON: Is it that this leaching of the ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

12 1 grease out -- is it evidence of corrosion or is it partly a 2 corrosive mechanism itself? 3 MR. BAGCHI: It is neither, and this is an 4 intriguing thing. The grease comes out of the concrete, and 5 therefore, the presence of grease, whether or not it changes 6 mechanical properties of the concrete itself so that it 7 might affect the compressive behavior of the sheer transfer 8 behavior -- it is something that is being studied, and Dr. 9 Murphy is going to talk about that in his research program. 10 We are not sure how this affects the safety of the 11 containment, but to some extent, the mechanical properties 12 of concrete could be affected. 13 Next picture, please. 14 This is an ice condenser containment. It has a 15 steel shell inside an outside concrete shield building. 16 Corrosion has been observed on the outside surface of the 17 steel shell near the bottom where the pointer is being 18 pointed, and then, also, on the inside near the upper floor, 1 19 that is where there is a piece of core that is going around 20 it, the containment shell, which attracted water and, 21 therefore, had local corrosion, but this has since been 22 repaired, and they are being monitored and so forth. 23 Next picture, please. 24 This is probably trying to go into a little more 25 detail than necessary, but it would show how free-stress ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

13 1 concrete containments look. 2 This is a cross-section between the wall and the 3 base mat, and if you notice right through the inside core of 4 the concrete, there is some hollow ducts that are going on 5 and the tendons go through those ducts and anchor on the 6 underside of the concrete so that the concrete is 7 compressed, and when the inside pressure pressurizes inside 8 the containment, the pressure would be released somewhat, j 9 but the concrete would still essentially remain in 10 compression. 11 In French practice, pre-stress concrete i + 12 containments are used without any liners, but here, we do 13 use liners. 14 Next picture, please. 4 15 This is a cross-section through the vertical wall 16 of a prestressed concrete containment, the upper one, and 17 again, please note the tendon duct going through the i 18 concrete, right through there. 19 Then, the lower portion is a cross-section through l 20 the buttress, and the buttress is an area of tensions that 21 go horizontally around the containment structure. These are 3 22 very large, 130-feet-diameter structures, and usually, they 23 use three of them. This is one buttress where the tendon 24 steel is anchored on the concrete. 25 Next slide, please. 1 ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

14 1 Well, this is another cross-section through a 2 reinforced concrete containment wall. In the picture, you 3 don't see the effective scale, but in the reinforced 4 concrete, the wall thickness is bigger. It is 4 feet 6 as 5 opposed to 3 feet 6 in a prestressed concrete containment 6 because concrete is being compressed, and it is used in a 7 different manner, but this is a typical cross-section. 8 Next slide, please. 9 I pointed out earlier incidents of local corrosion 10 of scale through the pictures in the Mark I containment. 11 That is the typical degradation. 12 Degradation of bellows. Now, bellows are typical 13 devices that are connected to penetrations, usually 14 processed piping and things like that. For example, the 15 vent pipe that you saw is connected through bellows to the 16 wet well portion. The purpose of the bellows is to allow 17 the containment to grow and breathe when the 18 accident-induced load is going to pressurize the containment 19 from inside. 20 Now, these bellows are an integrate part of the 21 containmant boundary, and during some integrated leak rate 22 testinr,, there have been instances of bellows leaking, and 23 they have eventually been replaced and then the integrity 24 has been restored, but nevertheless, those have been 25 observed. ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

v 15 1 .Also, in concrete area, cracking of anchors for 2 post-tensioning tendons, corrosion and relaxation of ) 3 tendons, tendon wires and wire anchor head failures have 4 been encountered. ] 5 Something to remember with respect to prestressed j 6 concrete containments is that the tendon itself is a 7 collection of a large number of wires, individual wires that j l 8 ended up in the head, and the head is anchored through an 9 anchoring plate, and then it deposits its compressive load 10 on the concrete through that plate, i 11 Those anchor heads or buttons, those are the ones 12 that have been found to be cracked, but because they are so 13 numerous, one or two crackings is not a problem. 14 Next slide, please. i 15 For steel, the degradation mechanism are generally 16 an accelerated corrosion in normal and corrosive 17 environments. Corrosive environments are encountered when l 18 the steel is in contact with perhaps spilled or borated 19 water or some other kind of water that contains 20 contaminants. 21 In cases of stainless steel bellows, they are 22 subjected to transgranular stress corrosion cracking, and 23 this is a very common degradation mechanism in stainless 24 steel. 25 Next slide, please. ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

16 1 Degradation of concrete is perhaps best understood 2 in case of environment specifics. There is some crack that l 3 develops and moisture gets in, and in the case of very cold 4 weather, when it freezes, it expands in volume, and the 5 crack is aggravated, and then the cycle goes on and the 6 degradation takes place. 7 The other mechanisms are creeping of the concrete 8 when subjected to large compressive force as it is in case 9 of a prestressed concrete containment. The deformation of 10 the concrete in resoonse to the load applied to it remains 11 proportional to some extent, but after a while, it begins to 12 creep, even without an increase in load. So that is the 13 phenomenon that causes loss of pre-stressing force. 14 Shrinkage cracks are very common on concrete. Any 15 time you build a structure out of concrete, your shrinks and 16 cracks develop, very minute cracks. These are not 17 structural. 18 Spalling of concrete and anchorage cracking, I 19 talked about those before. l 20 Next slide, please. 21 These are degradation rates. I wanted to put it 22 in perspective by saying the steel shells vary in thickness 23 from half an inch to 1-3/4 inch or, in other words, 500 to 24 1,750 mils, and the liner plate itself varies in thickness 25 from a quarter inch to half an inch or 250 to 500 mils. t l N ANN RILEY & ASSOCIATES, LTD. s Court Feporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

17 1 So the general degradation rate of 1 mil per year 2 does not really pose a safety concern. However, the 3 accelerated degradation rates that have been observed 4 require an effective inspection program to be put in place, 5 and the need for'the inspection rule and the fact that we do 6 have a rule in place has been spoken to before. 7 Next slide, please. 8 The load-bearing capacity of the containment can 9 be reduced as a result of degradation, but it is a 10 time-dependent phenomenon, a Mr. Thadani pointed out and Mr. 11 Taylor. In steel shells, localized corrosion and pitting do 12 not significantly affect the strength of the containment. 13 For instance, one could have a pin hole in the containment 14 and not necessarily reduce the capacity of the containment, 15 but we don't want any compromise of the pressure boundary of 16 the containment. That is why inspection and monitoring is j 17 necessary. 18 In case of concrete structure, spalling and 19 cracking of concrete has been observed, and the effect is to 20 generally expose the reirforcing bars which can then corrode 21 in a typical reinforced concrete containment, the 22 reinforcing bars, the main reinforcing bars, the No. 18's. 23 These are 2-1/4-inch, 2-1/2-inch-diameter bars. They are 24 huge, and to date, we have not had any instance of corrosion 25 of the reinforcements inside the containment, but it is the j ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

18 1 reinforcing bar that takes the load. The major loading is 2 inside pressure, and it is subjected to tension, and the 3 entire tension load is taken by the reenforcing bars. 4 Concrete does not take or carry any tensile load. 5 In post-tension containments, premature loss of pre-6 stressing force is an area of concern, but as we have wisely 7 incorporated the design feature that our containments are 8 mostly designed with non-grouted tendons. That means we can 9 later on go in and re-tension those steel wires and 10 reintroduce the force that might have been lost. l 11 COMMISSIONER ROGERS: Is that being done? 12 MR. BAGCHI: That has been done in one plant. The 13 entire tendons in the vertical direction were re-tensioned, 14 all of the tendons. N 15 COMMISSIONER ROGERS: Does everybody agree that 16 that is a good thing to do? 17 MR. BAGCHI: That is a good thing to da when th 18 loss has been predicted to be beyond a certain rate. We 19 used to have technical specification which required that the 20 stressing force be monitored and trended. 21 When the design was initially conducted, there was 22 an expectation that creep and shrinkage would bring down the 23 pre-stressing force below a certain point after 40 years, 24 and that is being monitored, and if the degradation rate 25 seems to be accelerated, then the best thing to do is to re-ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

19 1 tension them. 2 COMMISSIONER ROGERS: My understanding is that in 3 the Russian containments, where the tendons are helical 4 rather than just simply circular, that the studies that have 5 been done there seem to indicate that it's not a good idea 6 to re-tension. 7 MR. BAGCHI: The designs are different. The 8 helical design requires that the wires go in a tortuous way, 9 in a very narrow, restricted path. It is very difficult to 10 rethread the wires if substantial numbers get broken, but 11 here, we have mostly buttresses that I indicated, and the 12 ability to go and tension the wires is very simple. 13 COMMISSIONER ROGERS: It doesn't introduce any new 14 problems? 15 MR. BAGCHI: It does not introduce any new 16 problems. Even if large amounts of wires break, we can 17 introduce new tendons and re-tension them. It is important 18 to ensure that the pre-stressing force remains in place and 19 the design condition is maintained and the margins are 20 maintained. 21 Next slide, please. 22 These are the NRC responses. I won't go over the 23 details of every one of those, but I will touch upon the 24 important aspects, so that I save your time and everybody's 25 time. ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

~ ~= 20 1 The information notices, the first two were 2 related to Mark I dry well and wet well steel containments, 3 and the last one, the third one, is with respect to 4 corrosion and steel shell for ice condenser containments. I 5 introduced the picture and showed where these corrosions 6 occurred. 7 The Generic Letter that was prepared was to gather 8 information from licensees with respect to corrosion and 9 conditions that existed at their plant. This was for Mark I 10 containments. Once this information was received, the staff 11 evaluated the responses and determined that Mark I and Mark 12 II steel containments should be under some kind of an 13 inspection program, required inspection program, and that 14 led to the proposed Generic Letter. j 15 However, around this time, the work was continuing 16 on a rule for inspection of containment structures of all 17 types rather than just the Mark I and II. They were already 18 underway. 19 So the proposed inspection of Mark I and II steel 20 containments through the Generic Letter was canceled, and 21 the whole effort was subsumed in the now rule that endorsed 22 the semicode criteria for all containment types. 23 Next slide, please. 24 From 1991 to 1992, the Staff conducted audits of 25 six older plant sites to assess conditions of structures, l ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

_ ~___ _m 21 1 The results of these audits are discussed in NUREG 1522. It 2 is pointed out here in this NUREG that surveillance and 3 maintenance of str'uctures is essential to maintain their 4 functional performance. 5 This document was influential in the development 6 of structural maintenance guidelines prepared by the 7 industry. 8 NUREG 1540 provides a history of BWR steel 9 containment corrosion and endorses the need to adopt the 10 ASME Section 11 inspection criteria. 11 The new rule on containment inspection endorsing 12 IWE for steel shell and steel liners and IWL for reinforced 13 concrete containment structures became effective as of 14 September 9, 1996. l 15 Now Dr. Murphy is going to go over the rule itself 16 and the research program that is in place and will address 17 some of the complex issues. 18 DR. ANDREW MURPHY: Good morning. Thank you, 19 Goutam. 20 This morning, I will describe the content of the 21 two ASME subsections on containment inspection that were 22 recently incorporated by reference into 10 CFR Part 100. 23 The two subsections that I will be talking about 24 are Subsection IWE which covers metal containments and the 25 steel liners of concrete containments and Subsection IWL ANN RILEY & ASSOCIATaS, LTD. Court Reporters 1250 I Street, N.W., Duite 300 Washington, D.C. 20005 (202) 842-0034

22 1 which covers concrete containments, both reinforced concrete 2 and prestressed concrete containments and the 3 post-tensioning systems that are used for the prestressed 4 concrete containments. 5 This rule became effective, as Goutam noted, on 6 September 9, 1996. With an expedited implementation period, 7 the inspections are to be completed by all utilities by 8 September of 2001. Those inspections require 100-percent 9 inspection of all accessible metal areas. There is also a 10 requirement for inspection, an augment inspection of areas 11 of special interest. 12 Two examples of these would be areas with no 13 codings or areas that have suffered repeated loss of coding, 14 leading to substantial corrosion or pitting. 15 A second example would be areas subjected to 16 excessive wear or erosion that would cause, again, the loss 17 of the coding and corrosion degradation. 18 These augmented inspections are required until the 19 areas examined have remained substantially unchanged, no 20 further corrosion, for at least three inspection periods. 21 At that time, they would fall back into an unaugmented 22 inspection, a simple visual inspection. 23 There is also a requirement for a visual 24 inspection of seals, bolts, and gaskets that are integral to i 25 the containment system. l ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034 1

l 23 1 For IWL, the inspection of the concrete 2 containments and the post tensioning systems, they are 3 required to be inspected twice in 10 years. Again, it is 4 100-percent visual inspection of all accessible concrete 5 areas. There is also a requirement for an inspection of the 6 post-tensioning system. This includes tendon monitoring, 7 monitoring of the forces on the tendons, sampling and 8 removal of tendon wires for further laboratory testing, and 9 for the re-tensioning of tendons as they have become exposed 10 to creep. 11 We will go to the next viewgraph No. 12. 12 Here, we will talk for a few moments about three 13 research projects that we have ongoing at the moment. The 14 first at Oak Ridge National Laboratory and the second at 15 Sandia Laboratory are coupled, one being the first phase and 16 the other being a second phase, of a general degradation of 17 containment research effort. 18 The program at Oak Ridge is intended to identify 19 corrosion mechanisms to assess the available techniques, 20 both destructive and nondestructive, for evaluating the 1 21 corrosion or detecting the corrosion, for the establishment 22 of the effectiveness and/or the limitations associated with 23 techniques to prevent or mitigate damage. l 24 Looking at the viewgraph itself, the contractors l 25 involved in the analysis and evaluation of these ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

24 1 nondestructive and destructive techniques, at this time, 2 particular emphasis is being given to areas that are called 3 inaccessible. These would be areas of the containment 4 shells that are below concrete floors or, in the case of the 5 steel liners, behind the liner itself. 6 CHAIRMAN JACKSON: What kinds of techniques are 7 used to do that? 8 DR. ANDREW MURPHY: At this stage, they fall under 9 the general category of ultrasonics and associated 10 techniques. The sophistication isn't so much in the 11 technique or the transducers that are involved, but in my 12 opinion, in the analysis that is able to be done with that. 13 Another part of the program, another task that is 14 ongoing is a subcontract from Oak Ridge to Johns Hopkins 15 University to enlarge or expand upon a program and technique 16 that we had developed under our structural aging program, 17 which was a concrete aging program, again at Oak Ridge, to 18 assess the residual strength and service life of a 19 containment, given its past history and the current 20 condition of degradation. 21 Looking at the next program, the next phase in 22 this program, I will return to Sandia National Laboratory 23 and their efforts. They are working to provide for the NRC 24 reviewers as means to assess the current structural capacity 25 of a containment or the margins associated with that ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

~. __ - 25 1 capacity and to estimate the residual capacity of a degraded 2 containment. This would be as a service tool for the NRR. 3 We will drop down to the fourth bullet for a 4 moment. We participate in a program at CNSI. This is the 5 principal working group, three subgroups on concrete 6 structures. That is a newly formed subgroup, and it is 7 becoming very active. It has already scheduled a specialist 8 meeting on NDE techniques for inaccessible areas that will 9 be held in March of next year, and it's in the fairly 10 well-developed program stages, planning stages for a .1 specialist meeting in July, probably on the tendon issues 12 that we spoke about earlier. 13 We also have been making overtures and contacts 14 with the folks in Germany at GRS, NUPEC in Japan, INER in 15 Taiwan, and the KIND's folks in Korea to develop cooperative 16 exchange programs on containment degradation and the general 17 aging of the structures. 18 Dropping back to the third bullet, which is a 19 topic that we have already touched on a little bit, this is 20 the grease intrusion into the concrete on the prestressed 21 containments. 22 As Goutam noted and showed you in the photograph, 23 we are seeing grease, the protective grease in the tendons 24 leaking through to the concrete surface. Our concern is for 25 the degradation of the concrete. We have a program ongoing i ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C.20005 (202) 842-0034

26 1 at Oak Ridge where they are in the process of collecting 2 approximately 60 core samples from the Trojan containment. 3 These will be tested to failure using, I: 11 say, standard 4 structural techniques, materials testing techniques, to tell 5 us whether or not we have got a problem here and whether 6 there is an issue that needs to be addressed. 7 CHAIRMAN JACKSON: So it is too early to say 8 whether there is a direct linkage? 9 DR. ANDREW MURPHY: Yes, there is. We have done a 10 lot of, I'll say, background studies, industry in general, 11 that makes use of concrete structures, including the oil 12 industry where leakage and the presence of grease has been 13 found on concrete structures. A number of studies in that 14 area have been done, and at this moment, it would probably 15 be best to call those equivocal as to whether or not there 16 is a significance to our problems. 17 Like I say, I expect that we will have preliminary 18 results from this Oak Ridge study probably by the beginning 19 of next summer. 20 With those comments, I will turn it back to 21 Goutam. 22 COMMISSIONER DICUS: I would like to ask a 23 question on the time frame for these research projects. You 24 have mentioned the ene that you hope to have your results 25 next summer. ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 l Washington, D.C. 20005 l (202) 842-0034

27 4 1 The other ones are ongoing. Do they have finite 2 limitations on the time limits to complete them? 3 DR. ANDREW MURPHY: We expect to have the results 4 from the other two programs, the other two phases of the 5 program within two to three years. 6 COMMISSIONER DICUS: I have raised the question 7 because of the aging nature of our plants. These research ] 8 projects do not need to be too long term. They may outlive ] 9 the plant. 1 10 DR. ANDREW MURPHY: I understand the point, and 11 the projects are intended to provide results in a timely 12 fashion. 13 CHAIRMAN JACKSON: Let us put the question another 14 way. 15 DR. ANDREW MURPHY: Okay. 16 CHAIRMAN JACKSON: Given the general and 17 accelerated rates that you talked about, how long would it 18 take for there to be corrosion below some acceptable wall 19 thickness level or strength level? 20 MR. BAGCHI: We can discover one tomorrow. 21 CHAIRMAN JACKSON: I see. 22 MR. BAGCHI: That is not to say that we don't have 23 a process in place to take care of it. The repairs will 24 take care of it. I 25 CHAIRMAN JACKSON: So, if it does go below, it can ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034 l

28 + 1 be mitigated. That is what you are telling us? 2 MR. BAGCHI: That is correct. 3 CHAIRMAN JACKSON: Okay. 4 MR. BAGCHI: The last slide, please. 5 We have talked about the importance of the 6 containment structure, what kinds of degradations we will 7 observe, and all of the NRC responses. I would like to 8 really emphasize the point that we have an integrated 9 approach. 1C We are attacking this problem from several fronts. 11 One was the performance-based Appendix J rule which looks at 12 the containment leak rate and integrity from the tightness 13 standooint. Also, visual examinations are required as a 14 result of that rule. 15 We have containment inspection rules specifically 16 endorsing the ASME Section 11, the Subsections IWE and IWL. 17 This would provide a uniform and technically sound method of 18 performing these inspections. 19 We also have the maintenance rule, which is an 20 overall rule requiring not only the pressure boundary 21 portions of the containment structure, but also things like 22 foundation and other pertinence that might have impact on 23 the safety significance or safety performance of these 24 containment structures. 25 We also have a license renewal rule, license ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

l l ) 29 l 1 renewal activity that is in process to think about what 2 kinds of things the Commission needs to take care of in 3 terms of aging management. 4 But in summary, then, the integrity of containment 5 structures is being maintained, and their conditions are 6 generally good. Where degradations were observed, they have 7 been repaired to restore their integrity. Our monitoring 8 and surveillance programs have been implemented to ensure 9 that degraded conditions are detected in time. 10 With the implementation of the new rule, j 11 containments will be inspected routinely, and degradation 12 will be detected and appropriate corrective actions will be 13 taken. Thus, inspection and maintenance are essential to 14 ensuring the current licensing basis or margins that these 15 structures have been designed with, and research programs, 16 of course, are going to give us insights with respect to 17 what kind of overall margin we can get, what is the behavior 18 of degraded conditions given that certain local degraded 19 conditions could be simulated and assessed in analytical 20 models and tests, as necessary. 21 We are also exchanging information with 22 international entities, and these will address other 23 long-term issues. 24 CHAIRMAN JACKSON: Thank you. 25 Commissioner Rogers? ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

30 1 COMMISSIONER ROGERS: Have any of the lessons 2 learned from our experience here with existing reactors been 3 translated into any design feature requirements for the 4 advanced reactor? 5 MR. BAGCHI: Primarily, the access to inspection, 6 but this structural engineering aspect is old, if I may say 7 so, and they have bene utilizing the traditional methods, 8 use of good materials, good construction practice, and the 9 ability to inspect the containments. That is one area where 10 I have personally put emphasis on. 11 The engineering aspects of advanced reactor 12 application review is being conducted in my branch, and I am 13 quite familiar with that area, but that is an area where we 14 have put some emphasis. 15 COMMISSIONER ROGERS: Good. 16 MR. BAGCHI: And also, related to fracture 17 toughness of the material, that is required by the general 18 design criteria. That is nothing new. 19 CHAIRMAN JACKSON: Do ice condenser containments 20 present any particular inspection challenges? 21 MR. BAGCHI: They are smaller in size. They are 22 smaller pressure; for example, 15 pounds per square inch 23 accident pressure, design basis pressure, as opposed to 45 24 to 55, 67 PSI and prestressed dry concrete containments. 25 They do provide a challenge in the sense that the ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

31 1 accessibility is restricted. 2 When we went out to look at the corrosion at the 3 bottom of the shell, this was about 12 to 18 inches above ) 4 the base nat. So it was hard to inspect, but folks who had 5 the plan really did a very good job. 6 CHAIRMAN JACKSON: ' Commissioner? 7 COMMISSIONER DICUS: Yes. How well do you feel 8 that -- I just need to get a feel for this. How well do you 9 feel that you think we understand the effects of 10 degradation, particularly with concrete, and how well we are 11 really able to quantify the effects of what we are seeing? 12 MR. BAGCHI: With concrete, degradation for 13 containments, it is not a problem that I can see. 14 COMMISSIONER DICUS: What about with steel? 15 MR. BAGCHI: With steel containments, the emphasis 16 would have to be on local corrosion, and areas of extended 17 corrosion, areas where aggressive environmental conditions 18 exist, it is a concern that we have to keep our eyes open 19 and look for areas of degradation and do a thorough 20 inspection. 21 CHAIRMAN JACKSON: Commissioner McGaffigan? 22 COMMISSIONER McGAFFIGAN: Could I just ask on the 23 research programs, what is the total amount of money in FY 24 '97 going to these four projects? Do you know? 25 DR. ANDREW MURPHY: Let me start with the easy ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

32 1 one. The tendon, grease tendon work at Oak Ridge, we have 2 got about $120,000 set aside for fiscal '97. If there are 3 additional problems identified, we hope that the basic work 4 will be paid for with fiscal '96 money. The two programs, 5 one at Oak Ridge and Sandia, are funded at about the 250- to 6 $300,000-a-year level. 7 MR. BAGCHI: May I take that question back to 8 Commissioner Dicus? You are probably aware that we had, 9 again, through a research program, conduct.ed ultimate 10 strength test of the reinforced concrete containment scaled 11 one-sixth or scaled one-eighth -- 12 MR. TRADANI: One-eighth. 13 MR. BAGCHI: One-eighth scale. Fairly large, and i 14 it retained pressure three and a half times more than it was i 15 designed for. We have substantial margin in concrete 16 containments. j 17 MR. THADANI: Since this issue is up, I might note i 18 that is really important, and a lot of the studies that are 19 done to really understand risks from severe accidents, that 20 margin to be able to handle certain loads is quite important 21 in terms of the risk to public health and nafety, and that 22 is an important element that I think the containments here 23 provide. That may not be the case in some other places. 1 i 24 MR. TAYLOR: I think that structure is still j 25 standing out at Sandia. We haven't been abl.e to rent it to i l l ) l ANN RILEY & ASSOCIATES, LTD. Court Reporters ] 1250 I Street, N.W., Suite 300 j Washington, D.C. 20005 (202) 842-0034 l 3 1

l l ) 33 1 anybody. 2 COMMISSIONER ROGERS: It's got a crack in it. 1 3 MR. TAYLOR: Right. If you go out there, it's I 1 4 worth a short ride out to look at it. You can actually see l 5 it was, I believe, at some type of penetration into the l l 6 containment that the first damage occurred, and it was at 7 quite a high pressure. So it is an interesting model. 8 COMMISSIONER DICUS: The important issue here is 9 that we are able to identify in a timely fashion when we 10 have lost our margin of safety. 11 MR. THADANI: Thank you. 12 CHAIRMAN JACKSON: So, in fact, that anticipates a 13 comment. Is it fair to say that what you are trying to tell 14 us is that an appropriate focus has to be on detection l 15 because if there is detection, there can be mitigation? 16 MR. BAGCHI: Absolutely. 17 CHAIRMAN JACKSON: With respect to looking at 18 degradation mechanisms, we are particularly interested in 19 the effect of degradation on the strength to withstand the 20 pressures under accident conditions. Is that a fair 21 statement? 22 MR. BAGCHI: Yes. 23 CHAIRMAN JACKSON: Okay. Well, let me thank you. 24 I thank the Staff very much for a very informative briefing. 25 You have presented a great deal of information today on the ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

34 1 mechanisms, the significance, and the impact of containment 2 degradation and the research that is being done to assess 3 all of these issues. 4 I beliete the challenge now is how best we are 5 going to review and understand, if there is further 6 understanding needed, the licensee's containment inspection 7 programs. That is what we all seem to be saying or 8 understanding; that that is where the focus has to be. So 9 it is critical in that sense that our initial reviews of 10 licensee and inspection programs be timely and provide 11 fbedback to other licensees, as well as to our inspection 12 programs. 13 So, unless my fellow Commissioners have any 14 closing comments, we stand adjourned. Thank you. 15 (Whereupon, at 9:59 a.m., the briefing concluded.] 16 17 18 19 20 21 22 23 24 25 ANN RILEY & ASSOCIATES, LTD. Court Reporters 1250 I Street, N.W., Suite 300 Washington, D.C. 20005 (202) 842-0034

i CERTIFICATE This is to certify that the attached description of a meeting of the U.S. Nuclear Regulatory Commission entitled: TITLE OF MEETING: BRIEFING ON CONTAINMENT DEGRADATION - PUBLIC MEETING PLACE OF MEETING: Rockville, Maryland DATE OF MEETING: Wednesday, October 16, 1996 was held as herein appears, is a true and accurate record of the meeting, and that this is the original transcript thereof taken stenographically by me, thereafter reduced to typewriting by me or under the direction of the court reporting company Transcriber: O e nmtC.. LM (2b jr-o Reporter: Mark Mahoney

r uo, v I e 1 United States Nuclear Regulatory Commission J n .+ m ~. _ m, w m a. a. _,, _ _ _ DEGRADATION OF CONTAINMENT STRUCTURES COMMISSION BRIEFING P October 16,1996 i Presented By: Goutam Bagchi, Chief ECGB Division of Engineering, NRR Andrew Murphy, Chief SGEB I Division of Engineering Technology, RES

pmREGy + ~ t..U-7 ]7. '! E. ;,I . [C AM { ,j United States Nuclear Regulatory Commission g,.e / msmz=ru,z:an = renc.xum - - ., s t OUTLINE OF PRESENTATION O Problems Detected O Degradation Mechanisms O Degradation Rate O Significance i O NRC Response O Inspection Rule and Research Programs i i O Summary 1 l i t 2

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? a,,~ l PURPOSE i i i O Provide an Information Briefing on Containment Degradation Following the Approval of New Inspection Rule Endorsing ASME Code Criteria in Section XI t l I i k 3 i

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-8 - e- [ .) United States Nuclear Regulatory Commission g, f-m t.. ----~.,~~~. e. . &. ~ DEGRADATION MECHANISMS Steel O General Corrosion O Areas of Water Accumulation and High Humidity Q Chemical Attack O Borated Water Spills and Contaminants Leaching Out of Insulation Material O Trans Granular Stress Corrosion Cracking O Stainless Steel Bellows 5

t ,/p RECo,g . + - %. _ - _.m., _ _ _.- _.. [ ] United States Nuclear Regulatory Commission g / ~~~-w->.~~~.~.,-=- DEGRADATION MECHANISMS Concrete O Creep, Relaxation, and Shrinkage O Minute Cracks Develop that Eventually Lead to Degradation Loss of Prestressing Force O Environmental Conditions O Freeze-Thaw, Alkali-Carbonate Aggregate Reactions O Failed / Corroded Tendons O Other Causes O Splitting, Spalling, and Leaching of Concrete O Anchorage Cracking O Grease Intrusion from Tendon Ducts 6 u

em } O .. p. t. y; ,y yg g.gys g p,,,5,_p -q,y.;....e,g 43.. n. g. [1Tl[g] United States Nuclear Regulatory Commission g%dfY, f o s-,,- , -_ ~.,.,.~. m., DEGRADATION RATES i Steel Containment Shells and Liners O General Corrosion Rate O 1 mil (0.001 inch) Per Year O Accelerated Corrosion Rate O 9.5 to 10 mils Per Year in the Presence of Contaminants O 20 to 38 mils Per Year in the Presence of Aggressive Chemicals 7 i

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~ : E*v - - ., -. - N [ e) United States Nuclear Regulatory Commission n g / - - -,-~ ~ - m - ~ ~~ ~ NRC RESPONSES O Information Notices on Containment Corrosion O IN 86-99 " Degradation of Stee? Containments" & Supplement O IN 88-82 " Torus Shelis with Corrosion and Degraded Coatings in BWR Containments" & Supp. O IN 89-79 Degraded Coatings and Corrosion of Steel Containment Vessels" & Supp. O Generic Letters O GL 87-05 " Request for Additionalinformation - Assessment of Licensee Measures to Mitigate and /or Identify Potential Degradation of Mark i Drywells " O Proposed GL " Augmented Inservice Inspection Requirements for Mark I and Mark 11 Steel Containments, Refueling Cavities, and Associated Drainage Systems" November 20,1992 (57 FR 54860) 9 I

ga REGg g 9 . : *'-...L# M M W1WW OC* 'td*M_ :Nb'- ^. -'" - W. ^ i j United States Nuclear Regulatory Commission NRC RESPONSES l O Other NRC Documents l O NUREG-1522 " Assessment ofInservice Conditions of Safety-Related Nuclear Plant Structures" Dated June 1995 l t O NUREG-1540 "BWR Steel Containment Corrosion l Dated April 1996 t O Regulation Endorsing ASME Section XI Subsections IWE and IWL (August 8,1996 - 61 FR 41303) O Inservice inspection, Repair, and Replacement Per ASME Code Requirements - All Containment Structures 10 t

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i INSPECTION RULE Subsections IWE & IWL h O Subsection IWE - Metal Containments and the Liners of Concrete l Containments i O Inspection Frequency - 3 Times in 10 Years

• Visual of 100% of Metal Surfaces
• Augmented Inspections of Special Areas f
• Visual of Seals, Bolts, and Gaskets O Subsection IWL-Concrete Containments and Their Post-Tensioning Systems O Inspection Frequency - 2 Times in 10 Years
• Visual of 100% of Concrete Surfaces
• Post-Tensioning System Examination i

11

/ p FEG O o + m, ; ; y.w, A www.,.p.m + m. m m w.n.wm [ ) United States Nuclear Regulatory Commission I RESEARCH PROGRAMS 0 Oak Ridge National Laboratory -Inspection / Mitigation / Reliability o State-of-the-Art Destructive and Nondestructive ExaminaFon Techniques (With Emphasis on inaccessible Areas) O Root Cause Analysis and Mitigation Techniques 0 Time-Dependent Reliability; Residual Strength and Service Life Given Past History and Present Containment Conditions O Sandia National Laboratory - Containment Load-Bearing Capacity O Evaluate Effects of Corrosion on the Capability of Containment to Withstand Accident i Pressures O Oak Ridge National Laboratory - Grease intrusion into Concrete O Evaluate Effects of Grease on Concrete Strength O CSNI - PWG3 Subgroup on Concrete Structures (includes containments) o Specialists Meetings on NDE for inaccessible Areas and Tendon issues Q international Interest on NRC Research Programs 12

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SUMMARY

O Current State of Containments is Generally Good l 0 To Date, Units with Degradation Have Repaired, Instituted Mitigation i Measures, or Are Monitoring on a Frequent Basis i 3 0 With implementation of New Rule, Degradation is Expected To Be Discovered on a Timely Basis O Inspection and Maintenance Are Key to Maintaining Licensing Basis / Margins O Research Programs Addressing Long-Term issues 13 ? I}}