ML102520435
| ML102520435 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 09/07/2010 |
| From: | Bajestani M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| IR-10-603 | |
| Download: ML102520435 (10) | |
See also: IR 05000391/2010603
Text
Valley Authority, Post Office Box 2000, Spring City, Tennessee
37381-2000
September
7, 2010 U. S. Nuclear Regulatory
Commission
ATTN: Document Control Desk Washington, D.C. 20555-0001
Watts Bar Nuclear Plant, Unit 2 NRC Docket No. 50-391 Subject: Reference:
Watts Bar Nuclear Plant (WBN) Unit 2 -Denial of Notice of Violation (NOV)05000391/2010603-08, Failure to Adequately
Evaluate and Qualify Molded Case Circuit Breakers 1. NRC letter to TVA, 'Watts Bar Nuclear Plant Unit 2 Construction
-NRC Integrated
Inspection
Report 05000391/2010603
and Notice of Violation," dated August 5, 2010 By letter dated August 5, 2010 (Reference
1), the U.S. Nuclear Regulatory
Commission (NRC) issued Inspection
Report Number 05000391/2010603
concerning
the April 6-30, 2010, inspection
conducted
at Tennessee
Valley Authority's (TVA) WBN Unit 2.The inspection
report identified
one Severity Level IV violation
involving
the suitability
of molded case circuit breakers.
The enclosure
to this letter provides TVA's response denying the NOV.There are no new commitments
associated
with this submittal.
If you have any questions, please contact William Crouch at (423) 365-2004.7I\r c-' C
U.S. Nuclear Regulatory
Commission
Page 2 September
7, 2010 I declare under penalty of perjury that the foregoing
is true and correct. Executed on the 7th day of September
2010.Respectfully, Masou ajest ni Watts r Unit 2 Vice President Enclosure:
1. WBN Unit 2 Reply to NOV 05000391/2010603-08
cc (w/enclosure):
Director, Office of Enforcement
U.S. Nuclear Regulatory
Commission
Washington, DC 20555-0001
U. S. Nuclear Regulatory
Commission
Region II Marquis One Tower 245 Peachtree
Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257
NRC Resident Inspector
Unit 2 Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee
37381
Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
Description
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
qualifications
testing of a prototype
unit under the most adverse design conditions, were not adequate in that: 1. On October 5, 2009, the applicant
installed
molded case circuit breakers into the 120VAC vital instrument
power boards; however, the test program used to seismically
qualify a prototype
circuit breaker failed to use a suitable mounting method that reflected
the most adverse mounting condition.
2. On September
3, 2009, the applicant
failed to perform an adequate review for suitability
of application
parts and material used to modify dimensional
critical characteristics
in molded case circuit breakers;
further, the applicant
failed to verify the adequacy of design for the modification
and the effects on essential safety related functions
of the circuit breakers.This is identified
as violation (VIO) 005000391/2010603-08, Failure to Adequately
Evaluate and Qualify Molded Case Circuit Breakers.TVA Response TVA denies the violation.
Basis for Denial of the Violation This issue involves the 120 VAC Vital Instrument
Power Board and its internally
mounted Heinemann
Model CF2-Z51 -1 molded case circuit breakers.
This assembly was seismically
tested in 1974 and supplied as a unit by Westinghouse.
Subsequent
to the testing in 1974, the breaker was procured as a replacement
from a third party, and the breaker (not the assembly)
was seismically
tested in 1992 as part of the commercial
grade dedication
process.E-1
Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
The notice of violation (NOV) cited two examples of failure to adequately
evaluate and qualify molded case circuit breakers currently
in use.Example 1 stated: "On October 5, 2009, the applicant
installed
molded case circuit breakers into the 120VAC vital instrument
power boards; however, the test program used to seismically
qualify a prototype
circuit breaker failed to use a suitable mounting method that reflected
the most adverse mounting condition." TVA disagrees
that the 1992 qualification
device test did not use a suitable mounting configuration.
The seismic qualification
of the replacement
circuit breakers is described
below.In 1974, Westinghouse
seismically
qualified
the 120 VAC Vital Instrument
Power Board (Westinghouse
Seismic Test Report CO-33419-MKE, TVA Contract No. 74C4-85216, RIMS No. B07890914035)
by testing a complete board assembly with Heinemann
Model CF2-Z51 -1 circuit breakers mounted in the board. The actual mounting of the breakers is shown on Westinghouse
Drawing CO-33419-MKE-M3
in Section C-C. The tested board assembly duplicated
the actual configuration.
The mounting of the breakers consisted
of a 36" front panel with two horizontal
angle iron supports in the rear. The breakers were held in place solely by the clamping pressure applied by the front cover pushing the twelve breakers against the rear angle supports.
There were no additional
screws to secure the breaker to the frame. This configuration
duplicated
the actual configuration
in the plant.o The 1974 Westinghouse
qualification
testing subjected
the assembly to the required seismic motion. The test demonstrated
the response of the assembly and the individual
breakers.
The test procedure included instrumentation
to collect acceleration
data at the locations of the individual
breakers.o The Westinghouse
qualification
testing determined
the natural frequencies
of the test specimen simulating
the boards at WBN.Sine beat tests were then performed
at the natural frequencies
of the panel as determined
by the resonance
search and at 1/2 octave intervals
over the range from 1 to 33 Hertz. The tests were a conservative
simulation
of the actual earthquake
motion at upper building elevations
at WBN. The ten-cycle
sine beat test accelerations
measured at the breaker locations
are conservative
in-cabinet inputs (seismic demand) for testing the breakers as devices.The highest measured acceleration
at the device locations
in the board test was 2.72g.E-2
Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
- IEEE-344-1975, Section 6.4 Device Testing, states, "Devices shall be tested simulating
operating
conditions
to either the levels dictated by expected service requirements
or to their ultimate capability.....
If a device is intended to be mounted on a panel, the panel should be included in the test mounting, or the response at the device mounting location should be monitored
in the assembly test (see Section 6.5), in which case the device may be mounted directly to the shake table if the in-service
excitation
can be simulated."" In 1992, TVA WBN purchased
Heinemann
Model CF2-Z51 -1 circuit breakers from Southern Testing Services as replacement
items for the original Model CF2-Z51-1
circuit breakers in the Westinghouse
120VAC Vital Instrument
Power Boards. The 1992 test was performed
by Southern Testing Services as part of the commercial
grade dedication
for the breakers, not the overall assembly.
The testing was performed, and the breaker configuration
was the same as was tested in 1974. Southern Testing Services chose to perform a test of the breaker (since that was the part they were supplying)
and did not intend the test to address the entire assembly.
The assembly qualification
from 1974 was deemed by TVA to remain valid. In the 1992 test, an individual
breaker was attached directly to the vibratory
source with bolting. A 3g input motion (which exceeded the 2.72g highest measured acceleration
[seismic demand] in the 1974 test) was applied. This 1992 test simulated
the in-service
excitation
as required by IEEE-344-1975
because the 3g input motion exceeded the highest measured acceleration
in the 1974 test. Therefore, the 1992 test confirmed
that the breaker was seismically
qualified.
- The mounting configuration
used in the 1992 test was appropriate
for device testing of replacement
breakers.
The retention
of breakers in the board assembly was by a clamping arrangement
provided by two rear retaining
angle iron members and the front cover panel. The calculated
natural frequencies
of the front cover panel in the three directions
were also in excess of 33 Hz and rigid. Therefore, the rigid clamping arrangement
of rear retaining
angles and front cover panel did not introduce
any additional
localized
flexibility
that would require replication
in device testing of replacement
breakers.
Since there is no additional
flexibility, the measured maximum in-cabinet
acceleration
of 2.72g was confirmed
to be the minimum seismic input for testing of replacement
breakers (the actual test used 3g). This also confirms that the appropriate
configuration
for testing of replacement
breakers is by rigid mounting to a test fixture. This rigid mounting is provided in the 1992 testing by bolting the breakers to a rigid test fixture.* Rigid attachment
of the breaker was done in the 1992 test by bolting the breaker to the test fixture using the rear tab slotted holes, which resulted in the entire weight of the breaker cantilevered
from the test fixture. Device testing in this manner maximizes
the input of test motion into the test specimen.Thus, TVA believes that the 1974 and 1992 tests meet the provisions
of IEEE-344-1975 and demonstrates
that the original board and the breakers remain seismically
E-3
Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
qualified.
The 1992 test used to qualify a replacement
breaker used a suitable mounting method for single breaker testing, i.e., a rigid mounting arrangement
that reflects the rigidity of the clamping arrangement
in the board assembly.
The seismic qualification
of the overall assembly is demonstrated
by the 1974 test.Example 2 stated: "On September
3, 2009, the applicant
failed to perform an adequate review for suitability
of application
parts and material used to modify dimensional
critical characteristics
in molded case circuit breakers;
further, the applicant
failed to verify the adequacy of design for the modification
and the effects on essential
safety related functions
of the circuit breakers." TVA disagrees
that that the impact of the modification
to the method of retaining
the auxiliary
contact switch was not accounted
for in the seismic qualification
of the circuit breakers and overall assembly.The original Heinemann
Circuit Breaker, CF2-Z51 -1, was altered by the manufacturer
by changing the auxiliary
contact switch retainer that attaches to the main body of the breaker. This change was a result of new tooling that removed the thick retaining
plate for the Auxiliary
Contact Assembly mounted on the rear of the breaker. It was replaced by a small molded retainer bracket which secures the auxiliary
contact switch in the same position without adding to the entire depth of the pole containing
it. This alleviated
the difference
in the depth of one pole that contained
the retainer plate versus the depth of the other pole on the two pole breaker. Thus, the back of the new breaker is flat.* In order to accommodate
the shorter depth of the case, a Micarta plate is secured to the back face of the breaker. The thickness
of the Micarta plate is chosen such that the total depth of the breaker and the Micarta plate is identical to the depth of the original breaker and thus the clamping configuration
of the frame remains unchanged.
The Micarta plate is placed over the entire back surface of the breaker, thus creating a larger contact surface between the breaker and the rear angle irons which makes it more stable when secured by the front cover.* The Micarta plate is rigidly secured to the breaker using four screws and thus becomes an integral part of the breaker. The change in weight due to deletion of the previously
used retainer plate and substitution
of the Micarta plate adds approximately
1.5 oz. to the weight of the breaker. The mounting of the breaker with the Micarta plate provides an equivalent
fit to that shown on Westinghouse
Drawing No. CO-3341 9-MKE-M3 in Section C-C and exposes the bus bar to minimum additional
loading.* The functionality
of the breaker has not changed and the basic components (molded case frame, operating
mechanism, contacts and arc extinguisher, trip E-4
Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
elements, Auxiliary
contact switch, and thermal connectors)
have not changed.Note that the auxiliary
contact switch does not provide a safety function.
The change in the method of retaining
the auxiliary
contact switch on the Heinemann
breaker and the addition of the Micarta plate spacer for installation
in the board does not impact the seismic qualification
of the reconfigured
breakers.
Therefore, even with the failure of the non-safety-related
auxiliary contact switch to function, the safety-related
function of the circuit breaker would not be affected.Some confusion
during the NRC's inspection
was created by information
contained
in the 1992 qualification
report. The 1992 qualification
report indicated
a Z dimension
of 3.75" and the manufacturer's
catalog now indicates
2.609" for the critical characteristic.
There is an explanation
for the difference.
- Vendor schematics
show the Z dimension
of 3.75" given in the 1992 qualification
report includes the depth of the main body of the breaker of 2.609" plus the dimension
from the rear body of the breaker to the end of the auxiliary contacts (0.510") plus the dimension
from the front body of the breaker to the end of the lever (0.656") (reference
Attachment
1 and 2 in this Enclosure).
The total dimension
is 3.775" at the maximum arc of the breaker arm and is less than 3.775" in the closed or open position.
The clamping depth of the breaker as installed
in the power board is 2.8509" (2.609" + 0.25"). The depth (2.609")of the main body of the breaker is the same for the original and the reconfigured
breaker. Therefore, the purpose of the 0.25" thick Micarta plate is to maintain the required clamping depth for the reconfigured
breaker." In calculation
WCG-ACQ-1004
the change in mounting depth of the breaker was recognized
and the change with the addition of the Micarta plate was evaluated.
NRC stated that the breaker was modified by attaching
a Micarta plate to the rear of the breaker using 4 nuts and bolts to fit them in the power boards, as described
in Example 1, without updating the qualification
package. However, the qualification
package includes calculation
WCG-ACQ-1
004, which addresses
the qualification
of the circuit breakers with the Micarta plate and concludes
that the component (i.e., circuit breaker) remains seismically
qualified
under like for like conditions
per the 1992 seismic qualification
device test. Since breaker clamping configuration
was improved by creating a larger contact surface between the breaker and the rear angle irons which makes it more stable when secured by the front cover and the change in breaker weight was minor, the seismic qualification
of the overall board was not affected.Calculation
WCG-ACQ-1004
analyzed the effects that were introduced
by the modification, demonstrated
an adequate review for suitability
of application, and analyzed the impact on other components.
Calculation
WCG-ACQ-1004
was prepared to qualify the new Heinemann breakers that will replace existing breakers located in the 120 VAC Vital E-5
Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
Instrument
Power Boards. The methodology
of the calculation
was to address maintaining
the seismic qualification
of host equipment
with the replacement
of existing components.
Specifically, calculation
WCG-ACQ-1004
addressed
the following:
o Qualification
of the breaker by identifying
the changes to the breaker as minor changes to the physical shape and the breaker was seismically
qualified
under like for like conditions.
o Attachment
of the breakers to the panel by stating that the breaker attaching
to the panel contains many similar parts with similar weights, all of which have qualified
connections.
The breaker will attach in the same fashion as the existing breakers and is thus qualified
under like for like conditions.
o Panel remains qualified
by recognizing
that the impact of the small change in weight has a negligible
impact on shifting the frequency response of the panel.o Qualification
of the anchorage
of the panel remains unchanged
due to the small change in design weight.The discussion
above demonstrates
that the design control process was followed to ensure that replacement
breakers, including
the reconfigured
breakers, as well as the board assembly, are seismically
qualified
to appropriate
design criteria.
Thus, the replacement
breakers are seismically
qualified
as like for like replacements
using the 1974 and 1992 tests as baseline qualification
tests. Calculation
WCG-ACQ-1004, as explained
above, provides the engineering
analysis that supports the conclusion
that the breakers are qualified.
Conclusion
Testing performed
to qualify both the 120VAC Vital Instrument
Power Boards as an assembly and the replacement
circuit breakers as individual
components
met the requirements
and was suitable for seismic qualification.
TVA evaluated
the modification
to the molded case circuit breakers for safety-related
120VAC power applications
and confirmed
that the reconfigured
circuit breakers are qualified
for application
in the 120VAC Vital Instrument
Power Boards. Accordingly, TVA denies the violation.
E-6
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Enclosure Watts Bar Nuclear Plant Unit 2 Reply to Notice of Violation (NOV)NOV 05000391/2010603-08
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