IR 05000313/1993013
| ML20045E767 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 06/21/1993 |
| From: | Westerman T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20045E763 | List: |
| References | |
| 50-313-93-13, 50-368-93-13, GL-89-10, NUDOCS 9307060023 | |
| Download: ML20045E767 (18) | |
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APPENDIX
.i U.S. NUCLEAR REGULATORY COMMISSION-
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REGION IV
Inspection Report:- 50-313/93-13; 50-368/93-13
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Operating Licenses: DPR-51; NPF-6
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Licensee:
Entergy Operations, Inc.
Route 3, Box 137G
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Russellville, Arkansas 72801 Facility Name: Arkansas Nuclear One, Units 1 and 2 (AN0).
Inspection At: ANO, Russellville, Arkansas Inspection Conducted: May 17-21 and June 18, 1993 Inspectors:
M. Runyan, Reactor Inspector, Engineering Section-Division of Reactor Safety R. Vickrey, Reactor-Inspector, Engineering Section,
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Division of Reactor Safety Accompanying Personnel:
M. Holbrook, Consultant, EG&G Idaho-INEL-
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Date T. Westerman, Chief, Engineering Section Division of Reactor Safety, Region IV-Inspection Summary Areas Inspected:
Special, announced inspection of the implementation of the licensee's program to meet commitments to Generic Letter 89-10, " Safety-Related Motor-0perated Valve Testing and Surveillance."
Results:
The licensee's motor-operated valve program was capable of
satisfactorily demonstrating the capability of motor-operated valves subject to Generic Letter 89-10 and generally fulfilled the licensee's commitments in this area (Section 1).
The licensee appeared slow in the establishment of final test acceptance
criteria and in the response to some emerging issues. The staffing:
assigned to the motor-operated valve project may be somewhat strained -
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due to work load (Section 1).
Three alternating current motor-operated valve motors were subject to-
degraded voltages less than the minimum-specified by the actuator _ vendor 9307060023 930629 PDR ADOCK 05000313
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to permit use of the standard motor capability calculation. There.
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appeared to be sufficient motor capability margin for the interim. 'The, licensee intends to implement modifications to correct this situation
(Section 1.1).
An example was identified where the observed packing load was greater.
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than the packing load assumed in the controlling thrust calculation.
The licensce stated that the procedure would be revised to ensure that-packing loads used in calculations are conservative (Section 1.2).
The licensee had not established a margin to account for' stem-
lubrication degradation.(Section 1.2).
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The uncertainty associated with the springpack tester.was missing from
the licensee's analysis of torque measurement error (Section 1.2).
The licensee was in the process of evaluating changes in the assumptions
for torque switch repeatability as delineated in Limitorque Maintenance Update 92-02 (Section 1.2).
The licensee had not developed justification for its use of linear
extrapolation to estimate thrust requirements (Section 1.2).
Many test results exceeded design assumptions made in the original
motor-operated valve sizing calculations. The licensee plans to validate or revise these-assumptions (Section 1.3).
The licensee agreed to extrapolate differential pressure test results
from the higher of points of C10 (flow cutoff) or C11 (seat contact).
Preliminary results from. implementing this policy for the completed.
t differential pressure tests revealed one potentially inoperable motor-
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operated valve; however, other considerations supported the short-term operability status of this valve (Section 1.3).
The licensee stated that a second-engineer review would be initiated for
diagnostic test data sheets and post-test evaluations of diagnostic data (Section 1.3).
The inspectors identified errors in the placement of VOTES diagnostic
software marks.
The licensee committed to review the remaining differential pressure traces for similar problems and to provide a second-engineer review of future. test traces (Section 1.3).
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Motor-0perated Valve CV-3812 initially appeared to be inoperable based
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on an extrapolation of thrust values from the closing differential pressure diagnostic trace. The licensee stated that the maximum expected differential pressure for this valve could be reduced to zero -
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because it has no closing safety function within the design basi _
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Based on this information, this motor-operated valve appeared to be operable (Section 1.3).
The licensee's implied assumption that the thrust at torque switch trip
would be the same at design-basis conditions as at test conditions will require additional justification (Section 1.3).
Two examples were identified where the placement of the open torque
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switch bypass was not conservative (Section 1.3).
A significant problem was identified in the licensee's post-test review
process as exhibited by two tests that were specified as differential pressure tests but, based on the diagnostic traces, were actually conducted under static or near-static conditions. An additional test exhibited an excessive amount of data scr.er, compromising the validity of the test results. The licensee committed to review the remaining differential pressure traces for similar problems (Section 1.3).
The licensee's request to extend its compliance date for implementing
the recommendations of Generic Letter 89-10 was found to be acceptable (Section 1.4).
The licensee was in the process of implementing a formal evaluation for
the potential effects of pressure locking and thermal binding (Section 1.5).
The licensee had not justified their intent to use static tests to
periodically verify motor-operated valve capability (Section 1.6).
The program to track and trend motor-operated valve performance and'
maintenance history was not fully implemented (Section 1.7).
Summary of Inspection Findinas:
Inspection Followup Item 313/9313-01; 368/9313-01 was opened
(Section 1.1).
Inspection Followup Item 313/9313-02; 368/9313-02 was opened
(Section 1.2).
Inspection Followup Item 313/9313-03; 368/9313-03 was opened
(Section 1.2).
Inspection Followup Item 313/9313-04; 368/9313-04 was opened
(Section 1.2).
Inspection Followup Item 313/9313-05; 368/9313-05 was opened
(Section 1.3).
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Inspection Followup Item 313/9313-06: 368/9313-06 was opened
(Section 1.3).
Inspection Followup Item 313/9313-07; 368/9313-07 was opened
(Section 1.3).
Inspection Followup Item 313/9313-08; 368/9313-08 was opened
(Section 1.3).
Inspection Followup Item 313/9313-09; 368/9310-09 was opened
(Section 1.3).
Inspection Followup Item 313/9313-10; 368/9313-10 was opened
(Section 1.3).
Inspection Followup Item 313/9313-11; 368/9313-11 was opened
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(Section 1.3).
Inspection followup Item 313/9313-12; 368/9313-12 was opened
(Section 1.5).
Attachments Attachment 1 - Persons Contacted and Exit Meeting
Attachment 2 - ANO Gate Valve Data
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-5-DEAILS 1 GENERIC LETTER (GL) 89-10 " SAFETY-RELATED MOTOR-0PERATED VALVE [MOV)
TESTING AND SURVEILLANCE" (2515/109)
On June 28, 1989, the NRC issued GL 89-10, which requested licensees and construction permit holders to establish a program to ensure that switch settings for safety-related M0Vs were selected, set, and. maintained properly.
Subsequently, four supplements to the GL have been issued and one issued for comment. NRC inspections of licensee actions implementing commitments to GL 89-10 and its supplements have been conducted based on guidance provided in Temporary Instruction (TI) 2515/109, " Inspection Requirements for GL 89-10, Safety-Related Motor-0perated Valve Testing and Surveillance." Instraction TI 2515/109 is divided into Part 1, " Program Review," and Part 2,
" Verification of Program Implementation." The TI 2515/109 Part 1 program review was conducted at Arkansas Nuclear One (ANO) May 4-8, 1992, and is documented in NRC Inspection Report 50-313/92-18; 50-368/92-18. The inspection documented by this report was the initial inspection at AN0 under Part 2 of TI 2515/109, and thus was focused on verification of program implementation. Nevertheless, programmatic issues were addressed during this inspection in response to followup of findings in the Part 1 inspection and in the context of issues that developed in the course of the inspection.
As an overall assessment, the inspectors concluded that the licensee's H0V program was capable of successfully demonstrating the capability of MOVs subject to GL 89-10.
For the most part, the program appeared to implement the licensee's commitments to the GL.
The inspectors observed that the licensee appeared to have been slow in the establishment of final diagnostic test acceptance criteria, and in the response to the emerging issue of pressure locking, and Limitorque 10 CFR Part 21 issue concerning torque switch repeatability.
Based on this apparent slow-response tendency and impressions gained in discussions with licensee-personnel, the inspectors observed that the staffing assigned to the MOV project may be somewhat strained due to work load. However, the program was not considered to be of poor quality. The safety consciousness of engineering personnel did not appear to be affected by the work load.
The principal focus of the inspection was to select and review in depth several MOVs from the GL 89-10 program. The selection was based on an information matrix provided by the licensee as requested by the inspector:,.
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The selection was biased toward MOVs that appeared to have less than avr. rage margin; otherwise, an attempt was made to select various sizes and differential pressure conditions.
For each MOV selected, the inspectors reviewed the design basis calculation of the maximum expected differential pressure (MEDP), the sizing and switch setting calculation, the diagnostic test data package, and the diagnostic
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-6-traces using V0TES 2.3 software. The following MOVs were selected for review:
CV-1234 Reactor Coolant System Makeup Block Valve
CV-1400 Loop B Low Pressure Safety Injection Block Valve
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CV-2667 Main Steam to Emergency Feedwater Turbine Isolation Valve
CV-2870 P-7A Test Recirculation Isolation Valve
CV-3812 Loop 1 Service Water Supply Valve to VCC-2A and 2B
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2CV-0789-1 Condensate Suction Isolation Valve for Emergency Feedwater Pump 2P-78
2CV-5103 High Pressure Safety Injection Header Orifice Bypass Valve The selected MOVs were gate valves and were configured as shown below:
Actuator Closure Control falyg Size (inches)
CV-1234 SMB-00 TORQUE 2.5 CV-1400 SMB-3 TORQUE
CV-2667 SMB-000 TORQUE
CV-2870 SMB-00 TORQUE
CV-3812 SB-1 TORQUE
2CV-0789-1 SMB-00 TORQUE
1.1 Desian-Basis Review 1 The inspectors reviewed the calculations determining the maximum expected differential pressure, design flow conditions, design temperature, and other design parameters for each of the MOVs selected for review.
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The inspectors reviewed the results of the licensee's calculations estimating the minimum (degraded) voltage that each M0V in the GL 89-10 program may experience at the time of operation. Three MOVs (CV-7403, CV-7404, and 2CV-5086-2) were subject to operation at voltages less than 70 percent of the nominal ac voltage (460 volts).
Limitorque has not endorsed the use of the standard motor capability calculation for ac voltages less than 70 percent.
The licensee stated that it intended to continue to use the standard equation
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for these MOV motors for the short-term, stating that none of the three motors
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appeared marginal.
For the long-term, the licensee stated that efforts would
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be made to implement modifications to restore the minimum voltage for these MOVs to greater than 70 percent. This issue was identified as an inspection followup item (313/9313-01; 368/9313-01).
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-7-1.2 MOV Sizino and Switch Settino The inspectors reviewed calculations determining the thrust and torque requirements and switch settings for each of the seven MOVs selected for review. The controlling procedure for these calculations was AND Standard MES-01, " Guideline for Preparing Motor-0perated Valve Setpoint -
Calculations."
The licensee's gate valve thrust equation incorporated valve disk friction coefficients (valve factors) ranging from 0.30 to 0.50.
MOV load sensitive behavior (also known as " rate of loading") was typically addressed by adding a 15 percent margin.
Stem friction coefficient assumptions ranged.from 0.15 to 0.20.
Thrust requirements were adjusted to account for diagnostic equipment inaccuracy and torque switch repeatability. Thrust' requirements were to be revised (if necessary) to reflect the results of dynamic test results, including extrapolation to design-basis conditions (if required).
During review of Calculation No. V-CV-1234-10, "MOV Torque Switch Setpoints,"
Revision 0, dated August 5,1992, for M0V CV-1234, the inspectors noted that the minimum required thrust calculation used an estimated value of.563 pounds force (1bf) to account for packing drag. This value was based on a provision in Standard MES-01, which estimated packing drag to be 500 lbf/in of stem diameter (M0V CV-1234 stem diameter: 1.125 inch).
However, the licensee had conducted a static test of MOV CV-1234 4 months prior to the approval of-this calculation that showed the packing drag to be 1518 lbf. The licensee agreed to revise Standard MES-01 to compare actual test results to standard assumptions used for packing drag. Where actual test results are more conservative, the measured value will be multiplied by 20 percent. to allow for future adjustments to the packing. This issue was-identified as an inspection followup item (313/9313-02; 368/9313-02).
The inspectors noted that the licensee had not established a margin to account for stem lubrication degradation. The licensee justified this based on the current lubrication interval of 18 months. However, the licensee did not have test data to support this position. Over a typical 18-month operating cycle, the grease applied to the valve stem may tend to harden or become impregnated with dust or other debris. The overall effect is to increase the stem factor (and stem friction coefficient) resulting in less thrust delivered to the stem for any given amount of applied torque. At this time, there is very little test data in the industry to quantify the effects of stem lubrication degradation.
Some licensees have made interim assumptions in the range of 5 to 10 percent to account for this phenomenon, though it is possible that for certain configurations and lubricants, the degradation may be negligible. The licensee stated that the trend analysis program now in place will evaluate for the effects of stem lubrication degradation and that appropriate margins will be established if they are shown to be necessary.
Stem lubrication degradation will be generically inspected at each site during closeout of GL 89-10 Phase 2 inspection.
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uncertainties associated with torque measurements.
This accounted for uncertainty associated with_ the spring pack displacement transducer, data acquisition system, and torque switch repeatability. However, the. licensee did not consider the uncertainty associated with the spring pack tester which is used to generate the curves for relating spring pack displacement tn
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actuator output torque. Licensee personnel agreed to include this consideration in their error analysis. This item has been identified as an inspection followup item (313/9313-03; 368/9313-03).
The licensee had received Limitorque Maintenance Update 92-02 that identified.
recommended changes to the torque switch repeatability values for MOVs with torque switches set at the No. I setting.
The licensee was in the process of
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assessing the impact of this change, but no revisions had been made. The licensee indicated that the M0V program will be revised to include the new-values at the first available opportunity. Onsite test data may be used to demonstrate that the repeatability condition of specific MOV actuators is either more or less precise than the Limitorque recommendations. This issue has been identified as an inspection. followup item (313/9313-04; 368/9313-04).
1.3 Desian-Basis Capability The inspectors reviewed the diagnostic test data packages and the VOTES 2.3
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diagnostic traces for each of the seven MOVs selected for review. On the basis of this review, the inspectors concluded that the licensee had satisfactorily demonstrated the immediate operability of these MOVs. In some
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cases the licensee will need to perform additional evaluation to consider the valves fully addressed under the GL.
h The dynamic tests reviewed were conducted under the following conditions:
CV-1234 95.6% of closing design-basis differential pressure CV-1400 40.5% of closing' design-basis differential _ pressure
2CV-0789 10.0% of closing design-basis differential pressure 2CV-5103 109.0% of closing design-basis differential pressure.
- CV-2667 84.0% of closing design-basis differential-pressure
CV-2870 108.2% of closing design-basis differential pressure
CV-3812 30.6% of closing design-basis differential pressure
The inspectors reviewed the selected dynamic test data using the industry standard equation, the valves' orifice diameter for the Velan gate. valves and-mean seat diameter for the Anchor Darling gate valves, and the dynamic test conditions. The results from three of the tests are provided.in Attachment 2.
A review of these MOVs indicated that valve factors in excess of 0.40 existed for these MOVs (see Attachment 2).
Stem friction coefficients were observed i
from 0.16 to 0.19 for the selected MOVs (see Attachment 2).
Load sensitive behavior ranged from 2.5 percent to approximately 19 percent.
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-9-Where testing could not be practically conducted at design-basis conditions, the licensee utilized a straight line extrapolation of the thrust to overcome
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differential pressure using the ratio of design-basis differential pressure to the test differential pressure. However, the licensee had not performed multi-point testing or developed other methods to justify the long-term acceptability of its extrapolation method. Therefore, the inspectors
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considered the licensee's extrapolations to design-basis conditions to be the first stage of a two-stage approach where the valves have been temporarily set up using the best available data, as discussed in GL 89-10.
The licensee would be expected to justify its method of extrapolation by the schedule commitment date for the completion of their GL 89-10 program.
Extrapolation to design-basis conditions will be generically inspected at each site during the closeout of GL 89-10 Phase 2 inspections.
The licensee's analyses of results from 51 differential pressure tests (the tests analyzed at the time of the inspection) indicated that the design assumptions made in the M0V sizing calculations were often not conservative.
For example, the observed stem friction coefficient was often greater than the assumed value of 0.2, the valve factor was often in excess of the assumed value of 0.5, and the load sensitive behavior (rate-of-loading) often exceeded-15 percent, the value generally assumed in the sizing calculations. As discussed in the GL, the licensee will be expected to utilize MOV diagnostic test results to either validate or revise any design assumptions made in the calculations used to size MOVs and establish proper switch settings.
This effort is especially important for MOVs that will not be tested under differential pressure conditions or that will be tested at only a small percentage of the MEDP. The licensee stated that an analysis of test results to validate design assumptions in its calculations would be completed before the original ANO GL 89-10 compliance deadline (June 1994). The validation of design assumptions based on the analysis of test results will be generically
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inspected at each site during the closecut of GL 89-10 Phase 2 inspections.
When differential pressure tests were conducted at less than the MEDP, the licensee extrapolated the measured closing thrust (corrected for running and.
stem rejection loads) to the MEDP using a direct linear relationship.
The point used in the extrapolation was the V0TES software point CIO, which is the.
mark for flow cutoff. The inspectors considered the use of point C10 for the purpose of extrapolating closing thrusts to be potentially nonconservative.
To ensure that-the valve can properly seat against the assumed differential pressure load, the point of highest stem thrust in the region between C10 and C11 (seat contact) should be chosen as the basis for the extrapolation. As long as CIO is marked at the point of highest thrust prior to seat contact, the practice of using the higher of C10 or C11 in the extrapolation would be conservative. The licensee agreed to adopt the policy of using the higher of C10 and C11 in its extrapolations of closing thrusts.
This would not exclude the use' of C10 in a case where the design basis only s eguires a cutoff of the major portion of the flow and can permit a large quant ity of bypass flow.
During the inspection, the licensee performed a quick analysis of the existing diagnostic test results using point C11 as the basis for extrapolation. Only one valve (2CV-5057-2) was determined to have less than the minimum required
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-10-margin to account'for torque switch repeatability and diagnostic system uncertainty. This MOV had a negative margin (-1.9 percent) before any corrections were made to the measured values. The total correction applicable to this MOV to account for torque switch repeatability and diagnostic system inaccuracy was approximately 11 percent. The licensee initiated a condition
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report (still unnumbered at the-time.provided to the inspectors) that concluded that the valve was still operable on the basis of a large inertial thrust available to seat the valve, as exhibited during the diagnostic test.
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The licensee stated that MOV 2CV-5057-2 would either be modified or h:ve its switches reset during the next available outage.
The inspectors reviewed the condition report and examined the diagnostic traces associated with this MW.
Considering that M0V 2CV-5057-2 was a globe valve with flow over the seat, that the diagnostic traces were marked conservatively for points C10 and Cll, and that the large inertial thrust was plainly evident, the inspectors concluded that the licensee's interim operability determination was justified.
The scheduled corrective actions for MOV 2CV-5057-2 and the implementation of the revised extrapolation method described above were identified as an inspection followup item (313/9313-05; 368/9313-05).
During review of the test packages for MOV CV-1400, the team noted that the average running force and the maximem thrust values were not consistently recorded on the analysis data sheets.
Further, the design-basis differential pressure was incorrectly transferred from the thrust calculation to the differential pressure data sheet. This caused an overly conservative extrapolation to be performed. The licensee agreed to revise the M0V program to require a second-engineer review of data sheets and post-test evaluations of diagnostic data. This issue was identified as an inspection followup item (313/9313-06; 368/9313-06).
An analysis of M0V CV-1400 determined that the stem friction coefficient under dynamic conditions was 0.4815. This was based on an observed' torque output of 1,600 foot-pounds (ft-lb). After further review by the licensee, it was determined that the springpack curve was invalid based on-the unavailability of any SMB-3 springpack that would generate the torque range identified by the
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curve for MOV CV-1400. Use of a generic spring pack curve indicated that 650 ft-lb of torque would be expected at the current dial setting of 1.0.
The licensee considered the torque data to be invalid and plans to. remove the springpack and develop a unique calibration curve to reanalyze the test data.
The dynamic test for MOV 2CV-0789 was conducted at 10 percent (16.psid) of the design-basis differential pressure (160 psid). The calculated open and-close valve factors (see Attachment'2) were in excess'of the 0.50 valve factor used in the thrust calculation; however, the licensee considers this data' to be-
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unreliable based on the low differential pressure present during the test.
The licensee will continue to pursue the best available data for this valve.
During a review of the V0TES diagnostic traces associated with the seven MOVs selected for review, the inspectors identified several instances where software marks were placed in an incorrect or nonconservative position. On the opening differential pressure traces of MOVs CV-2667, CV-1234, CV-2870,
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.g-11-and 2CV-5103-1, the mark for point 010, " force right after disc pullout," was not placed at the point of highest stem force in the. region after disc pullout. Since point 010 is used to compute the valve factor in the opening direction, placing the mark as observed on these traces was nonconservative.
On the closing differential pressure trace of MOV CV-2667, the marks for C10 and Cll, " flow cutoff" and " seat contact," respectively, were not properly positioned. Both marks had been placed in the region after seat contact where stem force was ramping at a high slope. These errors, though, were conservative since they overestimated the seating forces necessary to close the valve. As discussed later in this section, however, the inspectors determined that this test was not a true differential pressure test.
The mark for point CIO on the closing differential pressure trace of MOV CV-3812 was positioned directly on the peak of a' cyclic load pattern. Marking the point-in this manner was nonconservative, since it had the effect of lowering the estimated thrust to achieve flow cutoff. As a general rule, V0TES diagnostic marks should be placed at the midpoint amplitude of a cyclic load pattern, not
on either the upper or lower peak.
The licensee stated that there were no current plans to provide any additional formal training ~in the use of the
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VOTES 2.3 software, although some informal onsite refresher training is normally provided prior to each outage. The licensee committed to review all of the remaining differential pressure traces (those not reviewed by the NRC)
to identify any additional problems in the placement of the diagnostic marks.
Additionally, the licensee committed to provide a second-engineer review of diagnostic traces to ensure proper placement of software marks.
This was identified as an inspection followup item (313/9313-07; 368/)313-07).
The inspectors noted that the licensee determined the open valve factor based on the thrust required to overcome opening dynamic effects (V0TES mark 010).
However, the differential pressure at this point of the valve stroke is typically unknown and would be expected to be less than the recorded differential pressure that existed at the start of the opening stroke. The licensee's combined use of dynamic and force data that occurs at different points in the valve stroke could potentially result in a lower calculated valve factor than would actually exist at the 010 mark.
Licensee personnel agreed to consider this concern during future determinations of open valve factors.
The inspectors' review of the closing differential pressure diagnostic trace of MOV CV-3812 revealed information that appeared to challenge the operability of this MOV. As discussed above, the mark for point C10, flow cutoff, had.
been placed at the peak of a large cyclic load pattern. When the mark was placed more conservatively at the middle amplitude of the cyclic pattern, the resulting thrust at CIO, when extrapolated to the MEDP, exceeded by a large amount the measured thrust at the as-left torque switch setpoint.
This suggested the possibility that the MOV motor would stop prior to flow isolation during design-basis conditions.
If the extrapolation had used point Cll, seat contact, the same conclusion would have applied in that the valve motor could have stopped prior to the disc contacting the seat. The licensee concluded that the valve was operable on the basis of the fact that the MOV does not have to actuate in the closing direction to fulfill any
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-12-safety function within the design basis of the plant. Thus, the MEDP could be reduced from the previously calculated value of 124 psid to O psid.
MOV CV-3812 is one of the service water supply valves to the containment coolers.
It is normally open and receives a confirmatory open containment isolation signal. The licensee stated that this valve _does not.have any assigned leakage requirement and is not tested under a local leak rate test.
The licensee stated that the valve would close only due to inadvertent
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mispositioning, in which case, it could be reopened as exhibited by ample available margin in the opening direction. The licensee stated that the valve is used procedurally to isolate leakage in the downstream portions of the service water piping, but that such leakage in combination with a loss-of--
coolant accident (L.0CA) is beyond the design basis of the plant.
In conclusion, the licensee stated that the MEDP would be adjusted -in the design calculations for this MOV and that adequate justification would be provided in the revision. On the basis of the information provided, the inspectors concluded that MOV CV-3812 was operable. However, as discussed elsewhere in this section, the amount of data scatter due to the large cyclic load pattern rendered the closing differential pressure test results of questionable validity.
If for any reason the licensee were to retain a reduced (but still positive) MEDP assumption in the closing direction, a retest of this MOV may be necessary. This future disposition of MOV CV-3812 was identified as an inspection followup item (313/9313-08; 368/9313-08).
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The inspectors noted that the licensee assumed that the same amount of thrust observed at torque switch trip under any dynamic test condition will be
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available during a design-basis event. The inspectors were concerned that this may not be a conservative assumption for low differential pressure tests.
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t The licensee agreed to continue to look for best available information regarding how load sensitive behavior varies under different test conditions.
This item has been identified as an inspection followup item (313/9313-09; 368/9313-09).
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During "eview of the opening differential pressure traces for MOVs CV-2667 and CV-1234, the inspectors noted that the open torque switch bypass settings were potentially not conservative.
In each case, the bypasses had been set at a point in the opening stroke where significant flow effects were still present.
Optimally, the open torque switch bypass should be positioned in the region where only normal running loads are present. This concern was somewhat lessened by the fact that the open torque switch was set in each case at the same setting as the close torque switch, meaning that the probability of a spurious trip on the opening stroke was very low. Nevertheless, the licensee agreed that a'more conservative placement of the open torque switch bypass would be prudent and stated that increased attention would be placed in this area during future diagnostic testing. This issue was identified as an inspection followup item (313/9313-10; 368/9313-10).
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The inspectors identified a significant concern regarding the licensee's overall control of the diagnostic testing process.
This concern was based on two instances where it was apparent that a presumed differential pressure test
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-13-was, in fact, little more than a static test and one. instance where the test data was so severely scattered that the test should not have been considered'
valid. During review of the closing differential pressure traces for MOVs CV-2667 and 2CV-5103, the inspectors noted that the designated differential pressure traces were not significantly different from the
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corresponding static traces. The inspectors questioned the licensee concerning the test lineups and pressure instrumentation available during the tests.
In both cases, it was evident that a true differential pressure test-had not been achieved.
In the case of MOV CV-2667, downstream pressure was not measured and the licensee determined that backpressure had developed in the emergency feedwater turbine to an extent that the test differential pressure was much less than had been assumed (the original test had assumed that the downstream' pressure was at atmospheric pressure).
In the case of MOV 2CV-5103, the. test lineup permitted bypass flow around the M0V being tested through an orifice. The licensee had measured the pressure drop across the orifice as the MOV test differential pressure. The inspectors agreed that the MOV had experienced the full differential pressure across the orifice, but-that the flow rate was so small near the point of flow cutoff that-the test was little more than a static test.
In this case, the test itself may have -
correctly simulated the design-basis condition and, thus, may be valid for the valve.in question.
However, the test results should not be considered along with other differential test results as a means of validating generic design assumptions. The closing differential pressure diagnostic trace of MOV CV-3812 exhibited a large cyclic component in the _ region of flow cutoff.
Both the inspectors and the licensee agreed that the test results derived from this trace were of questionable validity. The inspectors were concerned that the
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licensee had not discovered these problems or observations in the course of the post-test review process.
It appeared that a critical element of -
reviewing test results for consistency and validity was missing in this
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process. The licensee comitted to review all of the other differential pressure traces to identify any other similar problems. - The licensee also comitted to initiate a second-engineer review of diagnostic traces. This issue was identified as an inspection followup item (313/9313-11; 368/9313-11).
1.4 Schedule Extension
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In a letter to the NRC dated March 19, 1993, the licensee requested an extension to the June 28, 1994, deadline for completing actions pursuant to GL 89-10. The requested extension was for one additional outage on each unit plus 120 days for completion of test data analysis. The extension would include refueling outage IR12 on Unit 1, scheduled for the spring of 1995, and refueling outage 2R11 on Unit 2, scheduled for the fall of 1995. The corresponding requested compliance dates would therefore.be approximately the sumer of 1995 for Unit 1 and the winter of 1996 for Unit 2.
The licensee had originally comitted to complete its testing program in response to GL 89-10 within the recommended schedule of June 28, 1994, or three refueling outages after December 28,1989 (whichever is later).
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-14-During this inspection, the inspectors reviewed a document entitled " Program Extension Justification," dated March 1993 and discussed with the licensee several issues related to the acceptability of the requested extension. The
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major points the licensee presented in support of-the extension were (1) the large number of valves in the GL 89-10 program (124 in Unit 1,160 in Unit 2),
(2) the large amount of retesting resulting from changing diagnostics from the H0 VATS to the V0TES system, (3) the implementation of hardware changes on more than 100 MOVs to reestablish design margin, (4) the delay in the development of valve performance models by the Electric Power Research Institute, (5) and the fact that more differential pressure testing will be needed than had been-originally expected because of the non-repeatability of test results from similar valves.
The licensee informed the inspectors that current projections indicated that all testing on Unit I valves would most likely be completed during refueling outage IRll, scheduled for the fall of 1993. The licensee also stated that prior to the original commitment date of June 28,1994, all M0Vs will have been tested under at least static conditions and that all design assumptions will have been validated by analysis of site test results. The licensee provided a listing of the Unit 2 MOVs for which the differential pressurc test would be conducted after the original commitment date. The inspectors concluded that the MOVs on this list were of low safety significance.
The licensee was actively tracking MOVs considered to be marginal, as discussed in Section 1.8 below. The identification of marginal valves included considerations that spanned the entire population of MOVs, indicating that most if not all of the valves that were actually marginal in the two units were on the list. Modifications were planned for the majority of these valve to reestablish a desirable thrust and torque margin.
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In consideration of these facts, the inspectors concluded that the licensee's request for a schedule extension to GL 89-10 was acceptable. The licensee actions have been discussed and concurred in by the Office of Nuclear Reactor Regulation. This report, therefore, represents the NRC acceptance of the schedule extension as requested by the licensee.
1.5 Pressure Lockina and Thermal Bindina The Office for Analysis and Evaluation of Operational Data has completed a study of pressure locking and thermal binding of gate valves. Office for Analysis and Evaluation of Operational Data concluded in its report that licensees have not taken sufficient action to provide assurance that pressure locking or thermal binding will not prevent a gate valve from-performing its safety function. The NRC regulations require that licensees design. safety-related systems to provide assurance that those systems can perform their safety functions.
In GL 89-10, the staff requested licensees to review the design bases of their safety-related MOVs.
The inspectors reviewed the licensee's evaluations of the potential for pressure locking and thermal binding of gate valves. The licensee had
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evaluated six gate valves in each unit for these effects and had concluded-that' the probability of pressure locking or thermal-binding was small. The
licensee had identified other valves as potential concerns, but these valves were apparently removed from the list because they were not required to open to mitigate an accident. The licensee did not have a formal methodology. for selecting the valves that were evaluated and the previous history of the valves was not detailed. Subsequently, the licensee issued a " Gate Valve Pressure Locking and Thermal Binding Review Plan" on May 14, 1993. The review plan consisted of three phases. Phase I of the study will evaluate the licensee's past actions in response to pressure locking and thermal binding issues.
Phase II will present a detailed thermal binding / bonnet overpressurization selection and evaluation process applicable to gate valves included in the scope of the GL 89-10 M0V Program.
Phase III will expand the Phase II selection and evaluation process to include all power-operated gate valves and eventually manual. gate valves. The licensee planned to complete Phase I in several months, Phase II by June 1994 or earlier, and Phase III by-June 1996 or earlier. The implementation of the pressure locking and thermal binding plan will be reviewed during a future inspection and has been identified as inspection followup item (313/9313-12; 368/9313-12).
1.6 Periodic Verification of MOV Capability The licensee planned to perform periodic verification of MOV capability every
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third refueling outage, as recommended in GL 89-10. The licensee intended to perform static tests for this verification, but has yet to develop justification to show that such tests would confirm MOV design basis capability. Such justification would be necessary because, to date, a reliable correlation between static and dynamic test results has not been demonstrated. The testing performed to demonstrate MOV design basis long-term capability will be generically inspected at each site during the closeout of GL 89-10 Phase 2 inspections.
1.7 MOV Failures. Corrective Actions. and Trendina The licensee had procedures in place that, if followed, would result in a trending program meeting the recommendations of the GL. The program was not fully implemented at the time of this inspection. The licensee's quarterly Equipment Failure Trend Report contained the rolling 18-month failure rate for MOVs. The licensee was in the process of inputting valve test data into a bar graph data base for trending purposes. The implementation of the trending program will be reviewed during a future inspection.
1.8 followuo of Weaknesses and Observations Enumerated in the M0V. Part 1 Reoort Response Item During the Part 1 inspection, many MOVs appeared to be marginally sized, possessing less-than-desirable thrust windows between minimum required and maximum allowable values. The licensee was requested to identify all MOVs
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Y O-16-which could be categorized as marginal and to reevaluate the capability of these MOVs using supportable assumptions and factors that a.ccount for all known sources of inaccuracy. The licensee's subsequent screening identified 36 MOVs in Unit I and 33 in Unit 2 that did not have at.least a 15 percent design margin available above minimum thrust requirements. The 69 MOVs were evaluated using operability criteria which allow the use of some factors which are less conservative than those used for standard design criteria-(to allow time for appropriate actions to be taken to return the M0V to standard design criteria status). The result of these evaluations was that the 69 MOVs were found to have sufficient capability to perform their safety function. The licensee subsequently identified modifications or other actions that would be necessary to permit the marginal M0Vs to meet the standard design criteria.
The implementation of these actions were scheduled to occur over the next two refueling outages for each unit. The licensee's implementation of their scheduled actions should resolve this concern.
A weakness had been identified during the previous MOV inspection.that a formal feedback method was not available to validate assumptions in the M0V design calculations.
The licensee subsequently developed Engineering
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Standard MES-04, " Guideline for Review of Motor-0perated Valve (MOV) Test
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Data," Revision 0, which formalizes a method to feed back testing information back into setpoint calculations. The inspectors concluded that' proper implementation of MES-04 would resolve the concern.
The licensee's actions has adequately addressed the concern.
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The licensee's assumptions on temperature for cable voltage drop and ampacity calculations did not agree with engineering standard EES-12.
The calculations used 75* C for ambient temperature, while the standards used 90' C.
The
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licensee subsequently revised calculation 92-E-0009-01 to reflect a cable temperature of 90' C.
The licensee actions have appropriately addressed the concern.
The licensee had changed the assumed value for stem friction coefficient from 0.20 to a less-conservative value of 0.15.
The licensee's position was based on engineering report 92R-0018-01, "AN0 MOV Program Position Paper, Stem Factor Variations," Revision 0, which justified use of 0.15 stem friction coefficient based on improved stem lubrication and results of other industry testing.
The licensee subsequently revised engineering report 92R-0018-01, Revision 1 to include additional justification supporting the use of valve i
stem friction coefficients used by design engineering in the M0V program. As a result of site and industry test results, the M0V program group changed its position and returned to the use of 0.20 as a conservative value of stem thread friction.
In certain cases, the licensee still utilized a 0.15 assumption but intended to implement modifications as necessary to pernit the use of the more conservative 0.20 value. The licensee's actions have appropriately addressed the concern.
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AIIACHMENT 1 1 PERSONS CONTACTED 1.1 Licensee Personnel
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- S. Boncheff, Nuclear Safety and Licensing Specialist
- H. Cooper, Licensing Specialist
- W. Eaton, Director, Design Engineering
- R. Edington, Plant Manager, Unit 2
- J. Fisicaro, Director, Licensing
- C. Fite, In-House Events Analysis
- C. Gaines, Supervisor, IEA
- R. Gillespie, Manager, Central
- R. Gordon, Supervisor, Central Maintenance Engineering
- J. Haley, Licensing Specialist
- G. Hines, Design Engineering
- G. Holt, Unit 2 Electrical Maintenance
- L. Humphrey, Director, Quality
- R. Lane, Manager, MCS
- T. Ott, Supervisor, Electrical and Instrumentation Control Design Engineering
- S. Pohl, Central Maintenance Engineer
- J. Powell, Superintendent,-Central
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- W. Rogers, Design Engineering
- E. Rogers, Central Maintenance Engineer
- H.- Ruder, Technical Specialist, IHEA
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- M. Sellman, General Manager
- R. Thweatt, Engineering Programs
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- J. Vandergrift, Plant Manager, Unit i 1.2 NRC Personnel
- L. Smith, Senior Resident Inspector-
- H. Murphy, Reactor Inspector
- T. Westerman, Chief, Engineering Section
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In addition to the personnel listed above, the inspectors contacted other personnel during the inspection.
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- Denotes personnel that attended the exit meeting.
- Denotes personnel that attended the followup exit meeting on June 18, 1993
(M. Runyan and T. Stetka, Region IV, participated by telephone).
2 EXIT MEETING An exit meeting was conducted on May 21 and a followup exit meeting on June 18, 1993. During these meetings, the inspectors reviewed the scope and findings of the report. The licensee did not identify as proprietary any information provided to or reviewed by the inspector.
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o ATTACHMENT 2 ANO GATE VALVE DATA i
Diagnostics: VOTES System with LVDT for Torque Measurements VALVE VALVE SIZE TEST DYNAMIC STEM LOAD NUMRFA
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CONDITIONS VALVE FItJCIlON SENSITIVE MANUFACTURER FACTOR *
COD 71C4NT BFJ1AVIOR CV-1234 2.5" 2804 psid (Close)
0.40 (Close)
0.16 (Dynamic)
10.7 %
Velan 2804 paid (Open)
0.03 (Open)
CV.1400 10" 230 psid (Close)
0.54 (Close)
Unknown-2.5 %
Velan 173 paid (Open)
0.11 (Open)
2CV-0789 8"
16 psid (Close)
0.98 (Close)"
0.19 (Dynamic)
19.1 %
Anchor Darling 16 paid (Open)
1.46 (Open)~
'The dynamic valve factors listed were calculated by the licensee using a mean seat diameter for the Anchor Darling valve and orifice diameter for the Velan valves.
~See report text for explaration.
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