ML20214F424

Summary of 870422 Meeting W/Util in Bethesda,Md Re Steam Generator Insps.List of Attendees & Agenda Encl

ML20214F424
Person / Time
Site:	Yankee Rowe
Issue date:	05/13/1987
From:	Mckenna E Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8705260077
Download: ML20214F424 (35)

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ortig)g UNITED STATES 8 ) e ( ) " p,E' NUCLEAR REGULATORY COMMISSION l; * ,

WASHINGTON, D. C. 20555 MAY 131987 Docket No.50-029

, FACILITY: Yankee Nuclear Power Station LICENSEE: Yankee Atomic Electric Company (YAEC)

SUBJECT:

MEETING

SUMMARY

APRIL 22, 1987 - STEAM GEhERATOR INSPECTIONS

, On April 22, 1987, members of the NRC staff met with representatives of Yankee Atomic Electric Corrpany in Bethesda, MD, to discuss steam generator inspec-tions. A list of attendees is provided in Enclosure 1. Presentation material used by the licensee is provided in Enclosure 2.

There were two main purposes for the meeting: 1) to discuss the licensee's plans for steam generator inspections during the upcoming refueling outage, and

2) to discuss Technical Specification changes related to steam generator inspections as proposed in a January 27, 1987 submittal.

Steam Generator Inspections 1

The licensee described the plant history of steam generator inspections, and the key elements of the steam generator design. In particular, they noted that the steam generator tubes are made of stainless steel and that the wall thickness (.072 inches) is larger than that of other steam generators.

Approximately 4% of the total tubes have been plugged to date; the degradation experienced has been secondary side pitting. This has resulted in pin hole leaks which slowly progress.

Steam generator 1 was inspected in 1985; steam generators 3 and 4 were inspected in 1984. For steam generator 2, cold leg inspections were conducted in 1984; however, at that time YAEC encountered a deposition of magnetite on the hot leg side of the tubes extending about six feet up from the tube sheet. This material interfered with collection of eddy current data for this region both in 1984 and in 1985. The hot leg side of this generator is thus due for inspection in 1987. ,

i The reason for the preferential buildup of this material in this area is not fully understood. The licensee noted that loop 2 ran for two cycles (about three years) in the late 1970's with slightly reduced flow when the reactor  ;

coolant pump in that loop had to be repaired.- Since then, there has been no -l such trend in the flow. The staff suggested that the licensee might remove the loose magnetite from some of the tubes such that at the next inspection they could be rechecked to see whether the magnetite has returned.

The licensee presented plant data of parameters such as steam generator pressure, heat transfer coefficient, flow and tenperature over time for the four individual loops to support their conclusion that the operational performance of generator ? has not been affected by this magnetite layer.

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The problem that the loose magnetite poses .is in obtaining results from the eddy current inspections. The licensee noted that the material tended.to accumulate around the probe guides and would lead to binding if the probe was not regularly cleaned. Furthemore, the magnetite causes signal noise which prevents them from obtaining valid signals. To resolve this problem, the ,

licensee has been working with Dak Ridge Nationel Laboratory to develop a probe that would be able to provide acceptable results in the presence of the magnetite. YAEC is also obtainin'g probes from Chalk River that have a shield over the detection coils such that the noise is not a problem.

The licensee's objective for the 1987 inspection is to inspect steam generator 2 from the cold leg side with the probes used in previous inspections and to inspect the hot leg side with the new probes. l

' Should the probes be unsuccessful in providing data for the magnetite region of the hot legs,. YAEC'would propose to inspect another steam generator instead provide a basis for operation until next cycle when generator #2 would be inspected and continue development efforts on the probes.

The licensee stated that the inspection history shows that the number of j defects is decreasing with time, that the secondary water chemistry is excel-lent, that there degradation is slow and does not lead to catastrophic failure, j and therefore that would not be a safety concern if they could not inspect this area of the hot leg of steam generator #2. The licensee has considered cleaning of the tubenbut considers that the cleaning procys may be more damaging to

, the tubes than~the pitting process.

The staff expressed concern that the results for steam generator #2 may not be representative of the perfomance of the other three steam generators, and therefore that some inspection should be done in one of the other steam generators in addition to the hot leg of generator #2.

i 4

The licensee noted the operational perfomance of the generators and the degradation mechanism of the tubes (secondary side pitting) and thus argued

' that inspection of generator #2 (including the cold leg and the hot leg) would be representative of all 4 generators. The licensee noted that entry into another steam generator would result in significant occupational radiation exposure (about 25 person-rem per gener4 tor). No decision on this issue was reached at the meeting. >

Technical Specification Changes >

There were two major parts of the Technical Specification (TS) changes ,

4- proposed by the licensee: '

. 1)definitionof'tubeinspection

2) sample size _ criteria '

- l' The existing TS. defines a tube inspection es .s Mt leg entry past the top support and where practical completely arotno the U bend to the top support of ,

the cold 49. OThe licensee wished to change *:his definition to permit cold 7eg; entry ,since many of the defects they have found are on the cold leg side.

.i e ,The staff agreed that there is no technical reason to limit the inspection - i definition to hot leg entry as .fong as full length. inspection is perfomed.

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sample size selection and interpretation of the action requirements. ~The Technical Specifications in place start with a minimum sample size (3% of the total number of tubes). The first sample is intended to include these areas that have experienced degradation before. Depending on the results of inspection ~ of this sample, additional inspections are required depending on-the extent of degradation found.

The licensee had proposed that when they inspect most of a steam generator

()84%), that the_ action requirement they follow be those for the third sample i rather than for.the first sample.

The licensee noted that for a minimum first sample (195 tubes), two defects would require all other steam generators he inspected, whereas for plants with larger generators, a much larger number of defects would have to exist before such expanded inspections were required. However, if a large initial sample is chosen, and additional samples are required by the action requirements (such as if one defect is found) there would not be enough tubes remaining in ,

that generator and this could require entry into other steam generators that would not be required if a smaller sample was originally chosen.

The staffI s concern with the licensee's proposal is that with the large initial sample that includes areas of the steam generator that have not historically i had problems, the percentage criteria could result in a relaxation of the inspection requirements.

The staff suggested that the licensee might pre-select which tubes would constitute the first . sample (and second sample) before data was collected for-the. entire generator. This would alleviate any problem in which the first sample was' the entire sample, and the inspection results then required that additional samples be taken (which could be from the same generator).

However, no resolution was reached concerning the size of the first sample or on the proposed changes in action requirements at the meeting. .

Sunenary In summary, the s' team generator inspections at Yankee will begin in mid-May 1987. The staff will inform YAEC of'its conclusions regarding the

' acceptability of the proposed inspection program and the Technical Specifications in the near future.

Eileen McKenna, Project Manager Project Directorate I-3 Divison of Reactor Projects I-II

Enclosures:

As stated

.cc w/ enclosures: See next page y , wb'b

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Enclosure 'l NRC/YAEC MEETING STEAM GENERATORS April 22, 1987

' Name. Affiliation Eileen McKenna NRC/PD I-3 C. Y. Cheng -NRC/EMTB J. D. Haseltine Yankee Atomic Paul Bergeron Yankee Atomic Russell A.-Mellor Yankee Atomic Herb Conrad NRC/EMTB-

- A.-J. Lodewyk NRC/ Region I Tim Henderson Yankee Atomic George Papanic, Jr. Yankee Atemic C. D. Sellers NRC/EMTB Keith Wichman NRC/EMTB O

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YNPS' PROPOSED-CHANGE #204-t

STEAM'CENERATOR TUBE INTEGRITY TESTING:

. AGENDAL INTRODUCTION' General plantJdescription1 The Yankee: steam Benerators

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Chemistry ~in the Deerfield Valley INSERVICE INSPECTION OF STEAM GENERATORS AT YANKEE Steam generator inspection. history-Plugging history Dominant failure mechanism MAGNETITE INTERFERENCE Description of the~ magnetite deposit When and where it has appeared Effects or, inservice inspections Effects on heat transfer coefficient Potential for adverse corrosion effects Potential cleaning mechanisms, pros _and cons 1997 INSPECTIO!:- OF #2 STEAM GENERATOR ,

General objectives:

New' probes present future alternatives. ,

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INTRODUCTION A. Yankee is a 185 MWe, four loop Westinghouse PWR that began commercial operation in 1960. It was constructed with many inherent conservatisms which make it simple and safe to operate.

B. Cooling and makeup water is taken from an artificial lake on the Deerfield River, a fresh mountain river draining portions of southern Vermont. Tapping this highly pure water source has been a key to successfully minimizing ingress of impurities into the steam generators at Yankee.

C. The four vertical U-tube steam generators at Yankee are similar in design concept.to standard Westinghouse steam generators, but are also unique in several ways. Though physically small, their construction, power loading and operation are conservative.

Number of tubes............... 1620 per generator Tube height..................... 18 feet (nominal)

Tube outside diameter............ 0.75 inches Tube wall thickness.............. 0.072 inches Tube material.................. 304 Stainless Steel Primary side pressure......... 2000 psi Primary side temperature....... 542 F (average)

Note especially that the wall thickness is considerably heavier than standard and that the material is stainless steel and not-inconel. l

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TUBES PLUGGED BY INSPECTION PROGRAM

-YEAR SG TEST TUBES TUBES TESTED USED TESTED. PLUGGED 1960 1 HYDRO ALL 14 to 2 HYDRO ALL 1 <<<<<<

1976 3 HYDRO ALL 11 i 4 HYDRO. ALL 9 1970 4 EC 75 -5 1971~ l EC 101 7

. 1974 4 EC 87 '8 1975 1 EC 162 5-4 EC 158 8

(" baseline" EC began in 1977) 1977 - 2 EC 1580* 5 <<<<<<'

3 EC 1580* 10 1978 1 HYDRO ALL 2 1 EC 1580* 15 4 EC 1580* . 13 1981 2 EC 634 3 <<<<<<

(cold leg EC began'in 1982) i 1982 1 HYDRO ALL l' 1 EC 1570 8 1984 2 EC 1592 40 <<<<<<

3 EC 1550 62 4 EC 1536- 21 1985 1 EC 1492 1 2 EC ** ** <<<<<<

TOTAL 249

• approximate number

• • unsuccessful attempt I

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TUBES PLUGGED BY STEAM GENERATOR SG EC . HOT LEG COLD LEG TOTALS .

YEAR PLUGS PLUGS 1 1971 7 -

7 1975 5 -

5 1978 15 * -

15 1982 3 5* 8 1985 1 0 1

(+ hydro plugs) .17 TOTAL 53

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2 1977 5* --

5 1981 3 -

3 1984 -

40

• 40

(+ hydro plugs) 1 TOTAL 49 3 1977 10 * -

11 0 1984 3 59

• 62

(+ hydro plugd) 11 TOTAL 83 4 1970 5 -

5 1974 8 -

8

. 1975 8 -

8 1978 13 * -

13 1984 7 14

• 21

(+ hydro plugs) 9 TOTAL 64 GRAND-TOTAL 249.. -

• Baseline inspections-

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EFFECTS OF MAGNE. TITE ON EDDY CURRENT EXAM. OF SG TUBES THE MAGNETITE WE ARE CONCERNED WITH IS NOT THE TIGHTLY ADHERING PASSIVE FILM FOUND ON ALL INTERNAL SURFACES OF A REACTOR PRIMARY SYSTEM THE MAGNETITE OF CONCERN IS'THE LOOSELY BOUND LAYER OF MAGNETITE FOUND ON THE HOT LEG TUBE ID ON # STEAM GENERATOR THE LOOSE LAYER OF MAGNETITE CAUSES TWO PROBLEMS THE LOOSE MATERIAL IS REMOVED BY PROBE MOTION AND ACCUMULATES IN AND AROUND THE PROBE GUIDES AND BODY CAUSING THE-PROBE ~TO BIND IF IT IS NOT REGULARLY CLEANED - CLEANING IS HIGH EXPOSURE THE LOOSE MAGNETITE CAUSES NOISE ON THE TEST SYSTEM WHICH HAS CAUSED A NO TEST SITUATION WHEN ENCOUNTERED BY EXAMINERS THE EFFECTS OF THE LOOSE MAGNETITE DEPOSIT HAVE BEEN THAT A "NO ,

TEST" AREA HAS BEEN ESTABLISHED FOR THE NUMBER TWO, STEAM GENERATOR TUBES FROM THE TUBE SHEET TO APPROXIMATELY 6 FEET ABOVE THE-TUBESHEET ON THE HOT LEG SIDE.

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PLANT SAFETY' ANALYSIS-o POTENTIAL AREAS-lMPACTED o REVIEW 0F PLANT TREND-DATA o SAFETY ANALYSIS ASSUMPTIONS o SAFETY ANALYSIS SENSITIVITY o DISCUSSION OF LOCAL-EFFECTS o CONCLUSIONS O

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POTENTIAL AREAS IMPACTED o MAIN COOLANT SYSTEM (MCS) FLOW o PRIMARY-TO-SECONDARY HEAT TRANSFER i

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SAFETY ANALYSIS ASSUMPTIONS

'o' MCS FLOW AT TECH. SPEC. LIMIT 6

38.-3x10 Las/HR o COLD LEG TEMPERATURE AT TECH. SPEC.

LIMIT 520 F + 4 F UNCERTAINTY-o INITIAL STEAM PRESSURE BASED ON RANGE OF OPERATION AND-TREND DATA o SETS OVERALL HEAT TRANSFER

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'a NEW EC PROBES AND METHODS PROVIDE FUTURE ALTERNATIVES ISSUE: THE ABILITY TO PERFORM AN ACCEPTABLE EDDY CURRENT EXAM. IN THE PRESENCE OF A LOOSE LAYER OF MAGNETITE ON THE ID OF A STEAM .

GENERATOR TUBE THE PROBLEM: WHEN A STANDARD EDDY CURRENT PROBE IS' PULLED THRU THEN AREA CONTAINING LOOSE MAGNETITE A VERY STRONG NOISE-SIGNAL,SLIGHTLY OUT OF PHASE WITH THE LIFT OFF SIGNAL,IS ENCOUNTERED. THIS SIGNAL IS ABOVE THE LEVEL WHERE A STANDARD TEST CAN BE PERFORMED.

THERE ARE THREE POSSIBLE AND SOMEWHAT RELATED CAUSES FOR THIS NOISE THE MAGNETITE HAS THE EFFECT OF BLOCKING THE PENETRATION OF

THE EDDY CURRENTS BECAUSE OF ITS HIGHER PERMEABILITY. THIS IS A SITUATION SIMILAR TO THE INSPECTION OF FERRO MAGNETIC TUBING THE LOOSE LAYER OF MAGNETITE IN THE AREA BETWEEN THE DETECTION COILS AND THE TUBE WALL CREATES A LOWER RELUCTANCE PATH THAN THAT OF AIR AND AS SUCH AMPLIFIES THE LIFT OFF.

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i Cd5EiENT PROGRAMS *TO PROVIDE A SOLUTION TO THE PRODLEMS-i

• PULSED DC SATURATION METHOD: YANKEE CURRENT HAS A DEVELOPEMENT CONTRACT WITH ORNL TO DEVELOP A PULSED DC' SATURATION'ME'THOD TO s

EXAMINE THE YANKEE SG TUBES.

CHALK RIVER PROBE DESIGNS: DIFFERENTIAL PROBES DESICNED WITH A SHIELD OVER THE DETECTION COILS AND 'A MODIFIED CENTERING : DEVICE CHANGE IN EXAM PARAMETERS: USING' EMPIRICAL' TEST DATA. GENERATED

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r LIMITING' CONDITION FOR-OPERATION

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' ,4 3.4.10 Each steam: generator in a non-isolated cain coolant loop'shall be Qp AL .,

j, 9 OPERABLE.:

..' s M jb MODES.1,-2, 3 and 4. ?

APPLIC ABILITY :

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M. k'ith one or more steam generators in non-tsolated m

- th increasing T,yg abou t 2000T.

SURVEILLANCE REQUIREMENTS '

s y 4.4.10.f* Steam Generator Samole Selection and Insrection~ ~ Each- st i d '.' ,

I[ # generatarl shall ,be deter;:ined OFIRA3LE during shutdow. fied:in byTable select ng an g, ,

inspecting-at least the mini =um numbergof. steam. generators speci M d >

a.4-4.

4.4.10.2 Steam Generator Samsle Selection and' Inspection - The steamclassification ~ '

5. The ~

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generator tube minist: , sz=ple siae,' inspection resultcorr

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' finserviceinspectionofstea:ngeneratortubesshallbe 4.4.10.4. ,

be verified acceptable per the acceptance: criteria of Specification

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least 3'; of The tubes ' selected for each inservice -inspectionh shall' b sinclude selectedatfor.

the .cotal nu=ber- of tubes in all steam generators; it e tu e t:

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these inspections shall be selected on a random bas s excep k

a.

Vnere experience in similar plants withLsimilar water 50% chemistry of the

, indicates critical areas to be ' inspected, then d least i tubes inspected shall be from these critical areas.

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The first sample of tubes selected for each inservice inspection o

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b.

each steam generator shall include:

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1. All nonplugged tubes that previously had detectable vall penetrations ( 20%).-

2.

Tubes in those areas where expe.ience h a indicated potential J problems. i

. for Section 4.4.10.1 is

• The intent of the 18 month surveillance requirement r ling oasis. For this.

that this - surveillance would be performe , on a retue i nt of' j

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reason, as well as ALARA considerations,' the surveillance limit until requ thereme ]

4-

/- sections 4.4.10.1 may be deferred past:the 18 month

\ end of'the-1981 refueling outage, but nri later than July -31,1981.

Amendment No. 54, 68 3/4 4-3z

- YAtMEE-ROWE

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MAIN COOLANT SYSTEM SURVEILLANCE REOUIREMDiTS (Continued

3. A tube inspection (pursuant to Specification 4.4.10.4.a.8).

shall be perforced on' each selected tube. If any selected . ' ~

tube does not permit the passage of the eddy- current prebe for a tube inspection, this shall be recorded and an 4

- adjacent tube shall be selected and subjected to a tube ~

. inspection.

. c. The tubes selected as 'the second and third samples (if re:;uired by Table 4.4-5) during each inservice inspection may be subjected  ;

to a partial tube inspection provided:

1. The tubes selected for these samples -include the tubes -

from those areas of the tube sheet array where-tubes with - -

i imperfections were previously found.

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2. The inspections . include those portions'of the tubes where.

i imperfecticns were previcusly found, i

The results of each sample inspection shall be classified into one of. the ,

l 4 - follcwing three categories:

Catecory Inspertien Results C-1 Less than 5% of the total tubes inspected-are degraded' tubes and none'of the' inspected tubes are defective. .,

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C-2 One. or more tubes, but not more than it of the total. tubes -inspected

- are defective, or between 5% and 10% of the tobal' tubes inspected are degraded tubes.

C-3 More than 10% of the total' tubes '

inspected are degrade'd tubes or more.

than 1% of the inspected-tubes are

-defective.

I Note: In all inspections, previously degraded tubes r:ust exhibit significant (>10%) further wall penetrations to be included in the above percentage calculations. .

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YANKEE-ROWE 3/4 4 33- A.endment fio. 54 v t e .r y y- u .,,[,e - + = . - , , ,,w- , , , .w..+- w -

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(, MAIN COOLANT SYSTEM SURVEILLANCE REQUIREMD4TS (Continued) 4.4.10.4 Acceptance Criteria

a. As used in this Specification:

1. Imperfection means an exception to the dimensions, finish or contour of a tube from that required by fabri-cation drawings or specifications. Eddy-current testing indications below 20% of the nominal tube wall thickness, if detectable, may be considered as imperfections.

2. Degradation means a service-induced cracking, wastage, wear or general corrosion occurring on either inside or -

outside of a tube.

3. Degraded Tube means a tube containing imperfections t 201, of the nominal wall thickness caused by degradation.

4.  % Degradation means the percentage of -the tube wall thickness affected or removed by degradation.

( 5. Defect means an imperfect' ion of such severity that it exceeds the plugging limit. A tube containing a defect is defective. '

6. Plugging Limit means the imperfection-depth at or- beyond which the tube shall be removed from service because it may become unserviceable prior to the next inspection and is equal to (40)% of the nominal tube wall thickness.

7. Unserviceable describes the condition of a tube if it leaks or contains a defect large enough to affect its structural integrity in the event of a loss-of-coolant accident or a steam line or feedwater line break as-specified in 4.4.10.3.c , above.

8. Tube Inspection means an inspection of tKe steam generator l

tube from the point of entry (hot leg side). past the top j (fifth) support and, where practical, completely around l the U-bend to the top support of the cold leg. l

b. The steam generator shall be determined OPERABLE after com-pleting the corresponding actions (plug all tubes exceeding the plugging limit and all tubes containing through-wall cracks) {

required by Table 4.4-5.

l YANKEE.ROWE 3/4 4 -35 Amendment No. 54 .

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A l,; TABt.E 4.4-4 MINIMtM NUMBER OF STEAM GDIERATORS TO BE INSPECTED DURING INSERVICE INSPECTION ,

Preservice Inspection No No. of Steam Generators per Unit Four

$ First . Inservice - Inspec tion All-l M Second & Subsequent Inservice Inspections One Table Notation:-

1. The inservice inspection may be limited to one steam generator on a rotating schedule encompassing 3 H % of. the tubes (where N is the number of steam generators in the. plant if the results of the first or previous-inspections indicate that all steam generators

.are performing in a like manner. -. Note that under ~some circumstances,-the operating conditions in one or more steam generators may be found 'to be more severe than those M in other .s team generators. Under such circumstances the sanple sequence shall be modified ,

, G to inspect the most severe conditions.

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TABLE 4.4-5 STEAM GENERATOR TUBE INSPECTION

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lst SAllPLE INSPECTION 2ND SAMPLE INSPECTTT)N 3RD SMIPLE INSPECTION

~ Sample Size Resul t Action Required Result Action Required Result Action Required .'

A minimum of C-1 None N/A N/A ll/A N/A 5 Tubes per S.G.

C-2 Plug defective tubes C -1 None N/A N/A and inspect additional Plug defective tubes T,-l None 25 tubes in this S.G. C-2. and inspect additional C-2 Plug defei:tive tubes 45 tubes in this S.G. Perfonn action for C-3 result of fi'rst C-3 sample Perfonn action for C-3 C-3 result of first N/A N/A sample +

te k 'C-3 Inspect' ail tubes in All other #

this S .G.. plug de- S.G.s are None N/A N/A k= fective tubes and C-1

$ inspect 25 tubes in lame 5.G.s Perform action for N/A N/A each other S.G. C-2 but no C-2 resul t of second additional sample Prompt notification S.G. are to NRC pursuant C-3 to specification [ Additional Inspect all tubes in 6.9.4 i S .G . i s C-3 each S .G. and plug j defective tubes.

• Prompt notification N/A N/A to NRC pursuant i I to specification l l

6.9.4 N

S = 3 - % Where N is the number of steam generators in the unit, .and n is the number of steam generaters g inspected during an inspecyton, o-2 P

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'O PDI-3/MTG 'StP99ARY. DISTRIBUTION Distribution fi M JerSteilletM M h72 NRC PDR Local PDR-.

PDI-3 r/f PDI-3 s/f VNerses EMcKenna OGC-Bethesda EJordan JPartlow.

ACRS~(10)

-CYCheng-

' Herb Conrad

AJLodewyk CDSellers KWichman (cc: Licensee and Plant Service List)

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