ML13080A074
| ML13080A074 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/15/2013 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML13080A074 (8) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 March 15, 2013 U.S. Nuclear Regulatory Commission 10 CFR 2.201 ATTN: Document Control Desk Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Facility Operating License Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 50-328
Subject:
Reply to a Notice of Violation 05000327, 328/2012005-05, Failure to Adequately Evaluate and Qualify Molded Case Circuit Breakers
Reference:
Letter from NRC to TVA, "Sequoyah Nuclear Plant - NRC Integrated Inspection Report 05000327/2012005, 05000328/2012005," dated February 13, 2013 The Enclosure to this letter provides Tennessee Valley Authority's response to the subject Notice of Violation of 10 CFR 50, Appendix B, Criterion Ill, "Design Control" identified in the Reference Letter.
There are no new regulatory commitments contained in this submittal.
If you have any questions, please contact Mike McBrearty at (423) 843-7170.
Resp c ully,
.W hesau Vic resident, Nuclear Licensing
Enclosure:
Reply to a Notice of Violation 05000327, 328/2012005 Failure to Adequately Evaluate and Qualify Molded Case Circuit Breakers cc: (Enclosure)
Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant
'~v 1
Printed on recycled paper
ENCLOSURE Reply to a Notice of Violation 05000327, 328/2012005 Failure to Adequately Evaluate and Qualify Molded Case Circuit Breakers Description of the Violation "During an NRC inspection conducted on October 1 - December 31, 2012, a violation of NRC requirements was identified. In accordance with the NRC Enforcement Policy, the violation is listed below:
10 CFR 50, Appendix B, Criterion III, "Design Control," states that measures shall be established for the review for suitability of application of materials, parts, and equipment that are essential to the safety related functions of the structures, systems, and components (SSCs). The design control measures shall provide for verifying or checking the adequacy of design, such as by the performance of design reviews, by the use of alternate or simplified calculational methods, or by the performance of a suitable testing program.
Where a test program is used to verify the adequacy of a specific design feature in lieu of other verifying or checking processes, it shall include suitable qualifications testing of a prototype unit under the most adverse design conditions.
Contrary to the above, measures used to review the suitability of application of materials, parts, and equipment essential to the safety related functions of molded case circuit breakers and measures to provide for the verification of checking the adequacy of design, such as calculational methods, performing a suitable test program, including qualification testing of a prototype unit under the most adverse design conditions, were not adequate in that:
- 1. Licensee Drawing 1, 2-45N706 (Series) contains a note that, "The circuit breaker restraint bars may be modified by adding extra scotch 13 or 23 tape, approximately 1/4 inch thick and 1 inch wide, to secure the newer styles of Heinemann breakers."
- The licensee failed to perform adequate review for suitability of application of parts and material used to modify dimensional critical characteristics in molded case circuit breaker application; further, the licensee failed to verify the adequacy of design for the modification and the effects on essential safety related functions of the circuit breakers.
- The inspectors observed that the licensee's application of the tape repair was inconsistent and not governed by suitable acceptance criteria. Several instances of tape only on the lower restraint bar, with a gap at the top restraint bar were observed, along with instances of tape modification to both top and bottom restraint bars.
- 2. The inspectors identified additional instances in the field where the licensee had failed to perform an adequate review for suitability of application of parts and material used to modify the dimensional critical characteristics in molded case circuit breaker application, and for which the adequacy of design had not been properly verified or checked:
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- The licensee had installed maintenance aids (foam weather-stripping and vertical support rods applied to the restraint bars) which were not on drawings, nor listed in the original seismic testing documents.
" The licensee had installed circuit breakers which were less conservatively seated across the rear restraint bars than those originally tested in that they only made contact from the vertical centerline to one side, which might allow the breaker to roll out in a seismic event.
- The inspectors observed several instances where molded case circuit breakers which had been aligned to protrude through the face-plate did not exhibit seating upon the weather-stripping as neighboring breakers were.
This violation is associated with a Green Significance Determination Process finding."
TVA Response to the February 13, 2013 Violation:
TVA admits that the violation occurred.
Reason for the Violation:
The violation occurred as a result of weak design documentation for the 120 Volt Alternating Current (VAC) Vital Instrument Power Boards (VIPBs). Contributing causes are a lack of documentation of critical thinking for the use of electrical tape to maintain seismic qualification of Heinemann breakers in the VIPBs, and the breaker depth was not identified as a critical dimension pertaining to the mounting of the Heinemann breakers in VIPBs.
Background Information:
The 120 VAC VIPBs were designed by Westinghouse Milwaukee Engineering Service Division and supplied to TVA. Use of Heinemann Type CF circuit breakers was specified as design data in the contract.
TVA supplied drawings to Westinghouse as part of the design specification for the 120 VAC VIPBs.
TVA approved Westinghouse supplied contract drawings showing the details of the 120 VAC VIPB design and seismic qualification test report in 1974 and 1975, respectively.
Changes made to the design of the cabinet were not incorporated into the "As Constructed" TVA drawing. Therefore, when the "As Designed" and "As Constructed" drawings and associated change paper were reviewed to generate the "Configuration Control Drawing,"
these changes were not captured; however, a note is included that references the contract.
The Problem Evaluation Report (PER), initiated at Sequoyah Nuclear Plant (SQN) as generic review to Watts Bar Nuclear Plant (WBN) NRC-identified violation concerning the Heinemann breakers did not identify the extent of the discrepancies between the TVA drawing and field configuration.
Within the design specification and as noted on drawings, TVA specifies that this equipment is designated as Class I equipment (IEEE Publication 308) and shall be subject to 10 CFR 50, Appendix B Quality Assurance requirements and seismic design requirements.
The contractor (Westinghouse) shall furnish equipment included in the contract, completely wired, painted, and ready for installation.
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Correspondence within the contract files suggests that structural modifications were made to stiffen the cabinet as a result of issues discovered during seismic testing with resonant frequency. The Heinemann breakers are shown to be mounted using angle iron bolted to the cabinet in the back of the breakers and the inside face of the front panel of the cabinet.
Heinemann breaker supplied mounting is not used. Westinghouse mounting of Heinemann breakers is as shown on the vendor drawing. The details shown on the vendor drawing are reflective of the changes made by Westinghouse and most consistent with the configuration installed in the plant.
The following analysis evaluates the identified discrepancies between drawings and field configuration.
Analysis of potential non-conforming conditions:
- 1. Orientation of the angle iron as found installed in the plant does not match configuration shown on vendor drawing.
The orientation of the two pieces of angle iron as shown on the vendor drawing is not consistent with the configuration as installed in the plant. The observed as-installed angle iron configuration is consistent between SQN and WBN Unit 1. Field installation of the angle iron turned 180 degrees from vendor drawing configuration was identified as a drawing discrepancy at WBN and resolved by a design change. Westinghouse evaluated the deviation in the mounting of angle irons and concluded that the as-installed angle irons are structurally equivalent to the original mountings shown on the vendor drawing and, therefore, the existing seismic qualification was not impacted by the deviation. This is documented in Westinghouse letter WAT-D08856. No evidence was identified at SQN that the orientation of the angle iron was modified by TVA. TVA concludes that the cabinets were supplied to TVA with the angle installed as it is installed in the plant.
- 2. Cabinets have an all-thread rod on each of the angles which connects the two angles. This is not shown on the drawing.
The vendor contract drawing framing isometric shows the angle iron bolted to the frame at both ends, but does not provide any details on these bolts. Drawing detail shows that angle iron shall be bolted in place, but again does not specify any details about these bolts.
Vendor drawings provide cabinet mounting detail and bolt size for mounting of the cabinet to channel welded to steel plate embedded in concrete floor. Specific information on the bolts between the angle iron and steel frame is not provided. Details of the mounting of the angle iron to the cabinet are not shown on this drawing. The vendor drawing shows the mounting of the breakers in the cabinet. The all-thread does not appear on vendor drawings and is not expected, based on a general lack of detailed information on bolting within the cabinet.
All-thread is not listed in the bill of material. The bill of material only lists electrical components. No mechanical hardware is listed.
Over spray of paint matching the inside of the cabinet has been observed on the all-thread and associated hardware. Contract files indicate that painting of the cabinet was to be performed by the vendor prior to delivery to TVA. This is evidence that the all-thread is original configuration as supplied by Westinghouse. All-thread appears to be used to maintain alignment of the angle against the breakers.
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- 3. Foam tape exists on angles, but is not on drawings or other design output.
Similar to the all-thread, detail on the foam tape would not be expected to appear on vendor drawing or bill of material due to the general lack of detail of non-electrical components internal to the seismically qualified cabinet. Foam tape is observed to be one continuous piece on the angle iron and improves the fit of the breakers against the angle. The use of foam tape is consistent between SQN and WBN. TVA concludes that the cabinets were supplied to TVA with foam tape as it is found in the plant.
- 4. In some locations, the bus bar stops short and does not connect to the last two breakers.
Breakers number 37 and 38 on the 1-111 and 1-IV boards are not directly connected to the bus bar, but instead wired through an isolation transformer. This configuration is unique to these four breakers in these two boards and does not exist in the other six boards. This is accurately reflected on TVA Connection Diagrams. As shown on the vendor drawings, this unique connection existed in the original design of the boards. Additionally, the vendor drawing contains information about the isolation transformer. Original design seismic test report states that power boards 1-111 and 2-111 were tested. Therefore, this configuration is seismically qualified by the original test.
- 5. Maintenance has filed the sides of the opening in the front panels to facilitate breaker installation. In some cases it appears that the panel has been filed so much that the breaker protrusion through the panel will no longer resist the potential rotation during a seismic event. This is allowed by a note on the drawing.
The mounting of the Heinemann breakers by Westinghouse design in the VIPBs is such that the raised face of the breaker fits in the window of the front panel. The corners of the windows on the front panel as supplied by Westinghouse were rounded. However, the corners of the raised face on the Heinemann breakers are square.
The corners of the raised face on original breakers were filed down. This conclusion is reached from visual inspection of an originally installed Heinemann breaker with filed corners and paint over spray. This issue was addressed in a 1987 corrective action document and light filing was recommended to improve fit of breaker in front panel. It is unclear whether this was meant or understood to be light filing of the panel or the breaker itself. There was a lack of guidance as to the limitations of the filing which is considered to be an inappropriate action. This lack of guidance contributed to the inconsistencies seen in the field.
The gaps noted in the field between breaker bezels and the edge of the front panel opening was found to vary as much as 0.125 inches. This was initially assumed to be a result of filing of the openings. Westinghouse drawings did not specify dimensions for the size of these openings. Seismic testing associated with immediate corrective actions, conducted on January 25, 2013, evaluated an excessive gap up to 0.250 inches between the breaker bezels and the edge of the front panel opening. A detailed description of the test is included in the "Corrective Steps That Have Been Taken And The Results Achieved," section of this letter. The test results prove these gaps do not invalidate seismic qualification of the breakers.
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In 2004, this fit up issue was raised again and an administrative change to the drawing was issued. This administrative change added a note saying, "To improve the fit of the circuit breaker in the cut out on the front panel, the field may, as required, "square up" the corners of the cut out and/or de-bur the edges of the cut out."
This fit up issue appears to have existed since original construction of the panel, which was delivered to TVA with breakers installed. Light filing on the corners of the breaker itself or the front panel of the cabinet is consistent with original equipment manufacturer, so long as the broad sides are not altered.
- 6. There is tape wrapped around the angles in some locations to make up the gap to the breaker. This is allowed by a note on the drawing, but there is no critical thinking behind the note. Also, the tape installed doesn't always conform to what's implied on the drawing note, which only states "The circuit breaker restraint bars may be modified by adding extra Scotch 13 or 23 tape, approximately %"thick and 1" wide, to secure the newer style Heinemann breakers." In some locations the tape spacers are only installed on the bottom retaining angles. This would indicate the potential for space at the top.
A change was made by the breaker vendor to the breaker that uniquely affects its mounting in this application at TVA. The design provided by Westinghouse does not use the provided mounting points that are intended by the breaker vendor for this style breaker. Original breakers had a cover plate installed over the auxiliary switch. Breaker design changed to eliminate the need for this cover plate. Although the depth of the molded case did not change, the overall dimension from front to back of the breaker was reduced by the thickness of the cover plate (0.250 inches). The need for a design change of breaker mounting was not identified until field implementation.
It appears that this was discovered upon implementation of a design change to replace Heinemann breakers in the 120 VAC VIPBs. Engineering issued a design change to allow the use of electrical tape to make up the 0.250 inch gap between the breakers and the angle introduced by changes made by Heinemann to the breaker with notes added to connection diagrams.
In accordance with TVA procedure for Seismic/Structural Qualification and Civil Design Standard for Maintaining Seismic/Structural Qualification - Replacement Items, seismic/structural qualification for replacement items may be by a combination of analysis, test, or seismic experience. It is not uncommon for engineering to exercise judgment with thorough technical justification for replacement items to be installed on equipment previously qualified by test if the change will clearly not affect the overall seismic qualification of the equipment or assembly. However, in this case, the use of electrical tape changes the mounting of a safety-related electrical device qualified by test. This change could challenge the validity of the test for seismic qualification of the device.
The design change lacks a technical justification for this change with respect to seismic qualification of the breaker. Although the description of the design change describes wrapping the tape around the angle, the note added to the drawing is not specific in how to use the tape in this application. This ambiguity led to inconsistencies on application in the field.
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A change was issued August 2012 to provide an alternate detail for use of Micarta board instead of tape to accommodate mounting of newer style breakers. Seismic qualification of the Micarta mounting detail is by test.
Corrective Steps That Have Been Taken And The Results Achieved:
" A detailed walk down of each 120 VAC VIPB was performed on January 3, 2013 and January 4, 2013 to verify issues, including the locations of tape, alignment issues, Micarta boards, etc. For each breaker location, the type of breaker and any issues were documented.
- A seismic test was performed on January 25, 2013 to qualify the current mounting conditions. The qualification testing was implemented by triaxial testing and was conducted at the QualTech NP facility in Cincinnati, Ohio, using Seismic Qualification Test Procedure for Heinemann Circuit Breakers with Attached Electrical Buss Bar.
The test included a breaker representing each of the issues which were identified, including several different configurations of electrical tape spacers. Two Operating Basis Earthquake (OBE) and three Safe Shutdown Earthquake (SSE) tests were performed. On the third SSE test, the foam tape was stripped off of the angle and replaced with two strips of duct tape to give a conservative representation of aged foam which is no longer resilient. The tests were successful with no breaker trips, contact chatter, loss of continuity or structural damage noted.
- The functional evaluation related to Heinemann breakers as documented in corrective action document has been revised to document the additional issues which were identified as well as the results of the latest seismic qualification testing.
The conclusion of the functional evaluation that the 120 VAC Heinemann breakers are non-conforming, but functional, did not change.
" The Maintenance procedure for Testing of Molded Case Circuit Breakers on 120 VAC Vital Instrument Power Boards was placed on administrative hold. This interim action will ensure the corrective action plans for Heinemann breakers is in place prior to any additional work on the VIPBs.
" The Maintenance procedure for Testing of Molded Case Circuit Breakers on 120 VAC Vital Instrument Power Board has been revised to reference the appropriate drawing for mounting detail to ensure breakers are installed properly (using Micarta board)
- Work Orders were initiated to remove existing tape on 120 VAC VIPBs and replace tape with Micarta.
Corrective Steps That Will Be Taken:
Based on the cause evaluation associated with this NOV, SQN will:
" Issue an Engineering Change Package (ECP) to adequately document the existing breaker mounting details for the 120 VAC VIPBs, or improve and adequately document breaker mounting details by May 9, 2013.
- Implement measures within Engineering to identify that for Heinemann CF2 series breakers, the overall depth of the breaker is a critical dimension and that this dimension will be maintained or evaluated, as necessary by April 16, 2013.
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- Verify Work Orders to remove tape from breakers are field work complete for Unit 1 before start-up from the Unit 1 Refueling Outage 19 (UIR19), currently scheduled to complete on November 13, 2013.
- Verify Work Orders to remove tape from breakers are field work complete for Unit 2 before start-up from the last day of the Unit 2 Refueling Outage 19 (U2R1 9),
currently scheduled to complete on June 11, 2014.
Date When Full Compliance Will Be Achieved:
Full compliance for SQN Unit 1 will be achieved on or before the last day of the fall 2013 U1R19 refueling outage.
Full compliance for SQN Unit 2 will be achieved on or before the last day of the spring 2014 U2R19 refueling outage.
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