L-03-103, Reactor Head Inspection 60-Day Report

Reactor Head Inspection 60-Day Report

ML031820173
Person / Time
Site:	Beaver Valley (DPR-066)
Issue date:	06/24/2003
From:	Pearce L FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EA-03-009, L-03-103
Download: ML031820173 (18)

Text

FENOC Beaver Valley Power Station "Oft%

~~~~~~~~~~~~~

168 P.O. Box 4 FrstEnergy Nuclear Operating Company Shippingport PAM 1077-0004 L William Pearce 724-682-5234 Site Vice President Fax: 724-643-8069 June 24, 2003 L-03-103 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001

Subject:

Beaver Valley Power Station, Unit No. 1 BV-1 Docket No. 50-334, License No. DPR-66 Reactor Head Inspection 60-Day Report

Reference:

1)

NRC Order (EA-03-009) Establishing Interim Inspection Requirements for Reactor Pressure Vessel Heads at Pressurized Water Reactors, dated February 11, 2003 During the recent BVPS Unit I IR15 Refueling Outage, inspections of the reactor pressure vessel (RPV) head and associated penetration nozzles were performed.

In accordance with NRC Order EA-03-009 (Reference 1)Section IV.E, the 60-day report, detailing the inspection results is being provided.

The BVPS Unit 1 iR15 report is enclosed with this letter.

There are no new regulatory commitments contained in this letter.

If there are any questions concerning this matter, please contact Mr. Larry R. Freeland, Manager, Regulatory Affairs/Performance Improvement at 724-682-5284.

Sincerely, William Pearce Enclosure c:

Mr. T. G. Colburn, NRR Senior Project Manager Mr. D. M. Kern, NRC Sr. Resident Inspector Mr. H. J. Miller, NRC Region I Administrator 410A1b

FirstEnergy Nuclear Operating Company (FENOC)

Evaluation Report for IR15 Visual and Under-head Inspection of Beaver Valley Unit 1 Reactor Vessel Head Penetrations (Ref: Order EA-03-009)

Evaluation Performed by Eric Loehlein Evaluation Reviewed by Dennis Weakland June 2003

Introduction Reactor Pressure Vessel (RPV) Head Inspections were performed at Beaver Valley Power Station (BVPS) Unit 1 during the IR15 Refueling Outage in accordance with NRC Order EA-03-009.

The Order establishes criteria by which licensees must perform periodic inspections of the reactor vessel head. FirstEnergy Nuclear Operating Company (FENOC) provided a response to the Order for BVPS via letter L-03-035 dated March 3, 2003. A Relaxation Request to the Order for BVPS Unit lwas filed on March 27, 2003 (letter L-03-053, and supplemented by letter L-03-057 dated April 2, 2003). To account for limitations in the current industry accepted inspection technology, it was requested that ultrasonic and eddy current inspection coverage of the Control Rod Drive Mechanism (CRDM) tubing extend to "the lowest elevation that can be practically inspected on each nozzle with the probe being used". Written approval from the NRC of this relaxation was received on April 18, 2003, stipulating that "examination coverage from the bottom of the J-groove weld shall be at least 1 inch". The approval was contingent upon further licensee action should the NRC find the crack growth formula in industry report MRP-55 unacceptable.

Purpose and Scope The purpose of the inspections performed was 1) to identify any evidence of leakage from the CRDM penetrations or Head Vent piping penetration onto the surface of the RPV head, and 2) to identify any relevant indications in the J-groove welds or RPV head penetration base material.

The susceptibility of the Beaver Valley Unit 1 RPV head to PWSCC-related degradation was calculated using the formula provided in Section 1V(A) of the Order. Using best estimate values for each parameter, the Unit 1 RPV head susceptibility was calculated to be 13.84 Effective Degradation Years (EDY) at the conclusion of Operating Cycle 15. This value places the Unit 1 RPV head at greater than 12 EDY, the "High Susceptibility" category as outlined in the Order.

The required inspection techniques for High Susceptibility plants to be completed each refueling outage are outlined in Sections 1V(C)(1)(a) and (b) of the Order, namely:

(a) Bare metal visual examination of 100% of the RPV head surface (including 3600 around each RPV head penetration nozzle), AND (b) Either:

(i) Ultrasonic testing of each RPV head penetration nozzle (i.e., nozzle base material) from two (2) inches above the J-groove weld to the bottom of the nozzle and an assessment to determine if leakage has occurred into the interference fit zone, OR (ii) Eddy current testing or dye penetrant testing of the wetted surface of each J-Groove weld and RPV head penetration nozzle base material to at least two (2) inches above the J-Groove weld.

Qualified contractor personnel using high-resolution remote visual inspection equipment performed visual inspection of the top of the RPV head. Qualified contractor personnel with BVPS Site Non-Destructive Examination (NDE) personnel providing concurrence performed VT-2 inspection of the RPV head penetrations and base metal. Qualified visual examination was completed on 3600 around each CRDM penetration and the Head Vent, as well as a complete assessment of the carbon steel base metal inside the ventilation shroud where the RPV head penetrations are located.

2

The nondestructive examinations performed were conducted in accordance with site-specific field service procedures. With the exception of the vent line examination procedures, all have been demonstrated through the Electric Power Research Institute / Materials Reliability Program (EPRI/MRP) protocol. In the absence of an EPRI/MRP protocol for the vent line applications, the examination procedures and techniques followed the basic requirement outlined in ASME B&PVC (edition 2000) Sec. XI, Appendix IV, Supplement 2 - "Qualification Requirements for Surface Examination of Piping and Vessels".

The technique used is further outlined in Westinghouse Technical Justification WDI-TJ-01 1-03.

Under-head inspections of the RPV head penetration base material and J-groove welds were performed by qualified Level Il/IHI NDE personnel. A NDE examiner from EPRI provided independent review of the data.

The preceding inspections satisfy Order EA-03-009 requirements for BVPS Unit 1. This included eddy current examinations performed on the wetted surface of all RPV head penetration J-groove welds, the penetration tube I)s (from at least 2 inches above the J-groove weld to at least 1 inch below the J-groove weld), and the penetration tube ODs (from the bottom of the weld to the lowest extent possible, to a minimum of at least 1 inch).

In addition, ultrasonic examination was performed on 27 of 65 penetrations from at least 2 inches above the weld to within 1 inch of the bottom of the nozzle. RPV head configuration issues prohibited ultrasonic inspection on most outer penetrations.

Inspection Results: Visual Inspection of the RPV Head Surface VT-2 visual inspection of 3600 around each of the 65 CRDM penetrations and the vent line showed no indication of penetration leakage characteristic of a through-wall leak. Figure 1 shows the typical condition found around each penetration during the penetration exam.

PEN 3: QURD f E i i d,** < ; i.

7 0 Figure 1: Typical 1R15 CRDM Penetration Condition 3

The carbon steel assessment performed on 100% of the RPV head carbon steel base metal inside the ventilation shroud found no new degraded conditions on the RPV head surface. Figure 2 shows the typical condition of the RPV head base metal.

Fiur 2

ypca II Crbn t-lCodii on Figure 2: Typical iRiS Carbon Steel Condition Minor corrosion of the RPV head base metal was observed around CRDM Penetrations 53 and

65. This condition was previously observed in the visual inspection performed during the IM02 Maintenance Outage in November 2002 and in the lR14 refueling outage in 2001 (Penetration

1. 65). The leakage that caused the degradation was determined to have originated at the adjacent canopy seal (Penetration #53) above the RPV head mirror insulation. Following a warm water rinse of the R$(head in IM02, the extent of the degradation was assessed. This documentation was reviewed with the NRC BVPS site resident inspector in November.

The conditions of Penetrations 53 and 65 observed during the 1RI5 refueling outage were compared with the previously documented conditions. No change in the condition of the RPV head base metal around Penetrations 53 and 65 was observed. Figures 3 through 6 show the conditions documented during iR15.

Evaluation of Results: Visual Inspection No evidence of RPV head penetration leakage was observed.

Additionally, the under-head examination performed during iR1S further confirmed that no through-wall flaw was present in any RPV head penetrations or J-groove welds.

The minor corrosion observed around Penetrations 53 and 65, previously evaluated during iM02 in November 2002 and reviewed with the NRC BVPS site resident inspector, was found to be approximately 1/8" in depth and 1/2" wide around the perimeter of the two CRDM penetrations.

This degradation was concluded to be minor in nature and well within the acceptable limits for 4

the BVPS Unit 1 RPV Head. As no change in conditions was observed during lR15, this assessment remains valid.

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Figures 3 and 4: Penetration 53 Figures 5 and 6: Penetration 65 Inspection Results: Under-head Inspection (BV Condition Report # 03-03756)

Eddy current wetted surface examination of all 65 CRDM penetration J-groove welds found no indications characteristic of cracking in any of the welds. Eddy current inspection was also performed on the vent line J-groove weld using a 12-channel probe-array. This exam also found no indication of degradation.

Eddy current wetted surface examination was performed on the OD surface of all 65 CRDM penetrations.

Reportable indications, with characteristics of Primary Water Stress Corrosion Cracking (PWSCC), were identified in the penetration tube scans of four CRDM locations.

Penetrations #50, 51, 52, and 53 contained indications initially classified as having crack-like characteristics; single axial indications (SAI), single circumferential indications (SCI) and/or multiple circumferential indications (MCI).

Following Time of Flight Diffraction (ToFD)

Ultrasonic analysis of the four penetrations from the ID surface, all indications were ultimately 5

classified as axial in orientation. Neither eddy current nor ultrasonic test results identified any crack extension into the J-groove weld.

There were no indications characteristic of cracking identified in any of the remaining 61 CRDM penetration OD surface eddy current exams.

Eddy current wetted surface examination was also performed on the ID surface of all 65 CRDM penetrations as well as the vent line. Results from the tube ID eddy current surface scans identified nine penetration tubes (#8, 9, 12, 36, 47, 49, 51, 52, 53) with indications characteristic of craze cracking. The craze cracking was not detectable with the ToFD ultrasonic probes, indicating the depths of the condition are less than 0.040", the ToFD probe detection limit. As such, they are not considered to have any impact on the integrity of the RPV head penetration tubes, per the flaw evaluation guidance provided in the letter from J. Strosnider, NRC, to A.

Marion, the Nuclear Energy Institute (NEI), dated November 21, 2001.

Eddy current ID surface examination of the remaining 56 CRDM penetrations, as well as, eddy current examination of the reactor vessel head vent line, found no reportable indications.

ToFD ultrasonic examination was performed on 27 CRDM penetrations (the four penetrations having OD indications identified through OD eddy current surface examination, as well as 23 other penetration tubes) and the reactor vessel head vent line. The TOFD ultrasonic examinations performed on Penetrations #50, 51, 52, and 53 were used to characterize the OD indications identified during the eddy current wetted surface exam. The indications were found to vary in depth between 0.060" and 0.300". The length of the indications varied between 0.25" and 1.6".

Ultrasonic examinations performed on the other 23 CRDM penetrations identified no reportable indications.

Evaluation of Results: Under-head Inspection The details of the relevant indications found on Penetrations #50, 51, 52, and 53 are provided in the attached figures and tables. Figure 7 shows the typical location of each flaw axially on the penetration.

Tables 1 through 4 describe the approximate length, depth, disposition, and circumferential location of each indication. Figures 8, 10, 12, and 14 show the tube profile and each indication extending up to the toe of the J-groove weld. Figures 9, 11, 13, and 15 show a top-view of each penetration and approximate location of the indications discovered.

Each of the four penetration tubes that exhibited OD cracking was manufactured from the same heat of Alloy 600. This heat, M3935, made by B&W Tubular Products Division, was procured to the requirements of ASME SB-167 as supplemented by Article 3,Section III of the ASME Boiler and Pressure Vessel Code. A comparison of the certified materials test report and the ASME requirements indicates the material meets all chemistry and mechanical property requirements.

Nevertheless, reactor vessel head penetrations of this heat of material have been reported as cracked in several other domestic plants. In each case, the environmental degradation mechanism has been identified as primnary water stress corrosion cracking (PWSCC).

The susceptibility to PWSCC is a function of the specific material characteristics (microstructure, carbide distribution, etc.), the effective stress, and the service temperature. For austenitic nickel-base alloys such as Alloy 600, PWSCC is a thermally activated process; the initiation rate can be described by Equation 1:

6

Rate = A ne-QGIRT Equation 1 where:

A is a term that daecribes the nincrostructural and other mnaterial conditions of the material; c

is the effective stress term (resulting from applied and residual stresses) n is the stress exponent; a value of4 is used for PWSCC Q

is the activation energy for the crack initiation process; a value of SO kcallmolc is commonly used for Alloy 600; this same value has been used in the EPRI MRP reports on Alloy 600 R

is the gas constant (1.987 cal/mole K)

T is the absolute tenpature in K, ad t

is the time to initiate cracking While the specific factors contributing to the apparently low resistance to PWSCC of heat M3935 have not been established, it is judged to most likely be the result of a marginal microstructure combined with high residual stresses. Of the four heats of Alloy 600 represented in the Beaver Valley Unit 1 head penetrations, heat M3935 has the highest reported yield strength. A summary of these values is presented in the following table:

Heat j

No. of j

Mteria Mfgr.

Yleld Strength, lsi IPenetratons M3935 4

B&W 48.4 C2649 S

55B&W 35.9i M2065 5

B&W 43.2 NX9420 I

Huntington Alloys 39.0 Note that all four of the penetrations made with heat M3935 were found to exhibit degradation.

Equation 1 indicates that the time-to-crack-initiation varies inversely with the fourth power of stress. The net effective stress includes contributions due to residual, operating, and/or thermal stresses. Other conditions remaining constant, higher yield strength material is likely to maintain higher residual stresses from fabrication and, hence, may be prone to cracking in a shorter period of time. In most cases, local (residual) stresses introduced by cold work and welding during fabrication are more important than service stresses since service stresses are generally well below the yield stress. Component fabrication processes such as welding, rolling, reaming, bending and cold work will introduce residual stresses in the material that may contribute to PWSCC.

A common practice with B&W penetrations was the use of rotary straightening following all primary fabrication of the pipes. This process is known to induce high residual stresses on the OD surface and would tend to further exacerbate the residual stresses introduced by welding and other manufacturing processes. This is judged to be a major reason why degradation of this heat of Alloy 600, and other B&W Alloy 600 heats, has occurred predominantly on the OD surface.

7

Remedial Actions Repairs were performed on Penetrations 50 through 53 using the Embedded Flaw Repair Technique, consisting of a three-pass Alloy-52 weld overlay of the J-groove weld and a two-pass overlay of the penetration tube OD for each of the four penetrations. Verbal NRC approval of BVPS Relief Request BV3-RV-04 for the use of this technique was received on April 18, 2003, followed by written approval from the NRC on May 14, 2003.

Post-repair dye penetrant examinations of all repaired regions were satisfactory.

Upon completion of the repairs Ultrasonic and Eddy Current examinations were performed to verify that that repair process did not introduce any new flaws or adversely change the size of characteristics of the previously reported flaws. Analysis of the post-repair TOFD ultrasonic examination results revealed no new indications. Furthermore, the TOFD sizing results indicate the through-wall dimensions and lengths of the reflectors did not change as a result of the repair process.

The conclusion can be made that the applied repair process had no detrimental effect on the tubes, did not result in any crack growth and did not result in the initiation of any additional cracking in the tubes.

Summary Visual and under-head Inspections of all RPV Head Penetrations were completed in accordance with NRC Order EA-03-009 and the relaxation to the Order approved by the NRC on April 18, 2003. Visual Inspection of the RPV head surface showed no evidence of a through-wall RPV head penetration leak or undocumented RPV head degradation. Under-head eddy current and/or ultrasonic inspection of RPV head penetrations revealed relevant indications on the OD of four CRDM penetrations. None of the indications were through-wall, nor did analysis show them to extend into the pressure boundary region of the tube or J-groove weld.

Repairs were effected on Penetrations #50, 51, 52 and 53 using the embedded flaw repair technique per BVPS Relief Request BV3-RV-04, which was approved by the NRC. A three layer Alloy-52 weld overlay was applied to each J-groove weld, and a two-pass weld overlay was applied to the OD of each of the affected penetrations. Post-repair dye penetrant examinations of all repaired regions were satisfactory.

Furthermore, post-repair eddy current and ultrasonic examination of each penetration confirmed no new flaws were created nor did the size and characteristics of the existing flaws change as a result of the repair process.

8

Figure 7: Tviucal Axial Flaw Location Penetrations #50, 51, 52, and 53 Carbon Steel Alloy 182 J-groove Weld Inconel Stainless Steel Clad Typical BV-I Axial Flaw Location 9

Penetration #50: Flaw Characterization Table 1: Penetration #50 Flaw Characterization Length Depth Circ.

(Inches)

(Inches)

Disposition Location 1

1.25" 0.30" Single Axial 970 2*

-0.8"

<0.125" Multiple Shallow Axial 900-1350 3*

1.55"-1.80" I <0.125" Multiple Shallow Axial 1 2300-3200

• Length dimension indicates range of affected area not the length of individual flaws.

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Appendix A Repair Parameters Penetration Tube: 56 S-degrees I

J~~~~ig i8-degrees Penetration Tube/J-weld Repair Diagram Figure 9: CRDM Penetration #50 Repair Parameters 11

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Penetration #52: Flaw Characterization Table 3: Penetration #52 Flaw Characterization Length Depth Circ.

(Inches)

(Inches)

Disposition Location 1

0.3" 0.25" Single Axial 750 2

0.3" 0.20" Single Axial 1300 3

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Penetration #53: Flaw Characterization Table 4: Penetration #53 Flaw Characterization Length Depth Circ.

(Inches)

(Inches)

Disposition Location 1

0.3" 0.25" Single Axial 420 2

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0.3" 0.25" Single Axial 2150 4

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AppendjxA Repair Parameters Penetration Tube:

Penetration Tub~e/JT-weld Repair Diagram Figure 15: CRDM Penetration #53 Repair Parameters 17