ML20072G748
| ML20072G748 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/16/1994 |
| From: | Opeka J NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20072G752 | List: |
| References | |
| B14930, NUDOCS 9408250085 | |
| Download: ML20072G748 (9) | |
Text
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Docket No. 50-122 B14930 Re:
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U.S.
Nuclear Regulatory Commission Attention:
Document Control Desk Washington, DC 20555 Millstone Nuclear Power Station, Unit No. 3 Proposed Revision to Technical Specifications Residual Heat Removal Pumo Outaae Time Introduction Pursuant to 10CFR50.90, Northeast Nuclear Energy Company (NNECO) hereby proposes to amend Operating License NPF-49 by incorporating the proposed changes described in Attachments 1 and 2 into the Technical Specifications of Millstone Unit No.
3.
NNECO is proposing to revise Action Statement "a" of Limiting Condition for 1
Operation (LCO) 3.5.2 of the Millstone Unit No.
3 Technical Specifications by increasing the time'that a residual heat removal i
(RHR) pump may be out-of-service before a plant shutdown is required to be initiated.
Currently, LCO 3.5.2 requires that a plant shutdown be initiated after one emergency core cooling subsystem has been inoperab h for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
NNECO is. proposing to increase this time to 120 to
's in the event that an RHR pump is inoperable.
The intent of 1M t proposed change is to reduce the potential for an unnecessary plant shutdown, thus, eliminating a source of unnecessary challenges to the plant's safety systems.
Rockaround Nuclear industry experience has indicated that the mechanical seals on RHR pumps, similar to those on the Millstone Unit No. 3 RHR pumps, have a history of failing after approximately 5 to 7 years of operation.
Thus, NNECO has been examining whether it would be prudent to replace the Millstone Unit No. 3 RHR pumps with a pump design which makes seal replacement substantially easier.
While this conceptual modi f ication could potentially reduce the time required to replace tne mechanical seals, it was determined to be
~l cost prohibitive (the modification was estimated at $2,200,000)..
Therefore, other potential solutions to this condition were examined.
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Nuclear Regulatory Commission B14930/Page 2 August 16, 1994 The number of pump starts and pump run-time are the significant contributors to seal wear and overall lifetime.
The RHR pumps are started during the performance of surveillances.
These surveillances result in numerous starts per pump per quarter, and dozens of starts per fuel cycle per pump.
In addition, during each refueling outage, the pumps are run for approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> each.
There are no clear indications in the industry as to whether the seal is more likely to fail due to the number of pump starts or run-time.
With the present RHR pump design, the minimum time to replace an RHR pump mechanical seal on-line is close to the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limit of Action Statement "a" of LCO 3.5.2.
NNECO has a high degree of confidence that the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limit could be met, however little r
i margin exists for the pre-staging and engineering of the replacement mechanical seal.
Voluntary entry into an LCO to perform preventive maintenance is discussed in detail in Part 9900 of the NRC Inspection Manual.
It states: "A licensee may take equipment out of service to perform PM
[ preventive maintenance) during power operation of the facility (on-line PM) if it expects the reliability of the equipment to improve such that the overall risk to safe operation of the f acility should decrease." Additionally, the NRC Inspection Manual denotes that "if a licensee has a reasonable expectation that an on-line PM will improve safety by making equipment more reliable, then the licensee can implement that program even though it may increase the unavailability of equipment." NNECO has discussed the use of technical specification LCO action statements and the guidance contained in Part 9900 in internal correspondence.
While NNECO continues to actively pursue the activities necessary for optimizing the mechanical seal replacement activity, we have determined that repairing an inoperable RHR pump (including the l
replacement of a mechanical seal) while on-line is preferable from a plant safety standpoint than repairing an RHR pump while in cold shutdown.
In Mode 1 (power operation), there is no immediate need for the RHR pumps.
The RHR pumps are required in Modes 4 and 5 (hot and cold shutdown).
Even though the capability for low head safety injection for an accident is lost on one train while the repairs are in progress during Modes 1 through 4, we believe that repairing the RHR pump on-line is preferable from an overall plant safety standpoint.
Thus, NNECO is proposing to revise Action Statement "a" of LCO 3.5.2 by increasing the allowed outage time for an RHR pump from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />.
9 f:
U.S. Nuclear Regulatory Commission B14930/Page 3 August 16, 1994 Description of the Proposed Chance 1
NNECO is proposing to revise Action Statement "a" of LCO 3.5.2 of the Millstone Unit No. 3 Technical Specifications by increasing the I
time that an RHR pump may be out-of-service before a plant shutdown is required to be initiated.
Currently, LCO 3.5.2 requires that a plant shutdown be initiated after one emergency core cooling subsystem has been inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
NNECO is proposing to l
increase this time to 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> in the event that an RHR pump is l
Action Statement "a" of LCO 3.5.2 currently reads:
"With one ECCS subsystem inoperable, restore the inoperable subsystem to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />."
NNECO is proposing to rewrite Action Statement "a" of LCO 3.5.2 as follows:
l With one ECCS subsystem inoperable, restore the inoperable subsystem to OPERABLE status within the times shown on the l
following table or be in at least HOT STANDBY within the next l
6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Subsystem Time (Hours) l l
Centrifugal charging pump 72 Safety Injection pump 72 RHR heat exchanger 72 l
RHR pump 120 Containment recirculation heat exchanger 72 l
Containment recirculation pump 72 Flow path capable of taking suction from the RWST 72 on an SIS and capable of being manually realigned to transfer suction to the contain-ment sump for the recirculation phase The proposed table lists the allowed outage times for the various emergency core cooling subsystems.
The allowed outage time for most of the subsystems will continue to be 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The only subsystem allowed outage time that NNECO is proposing to change is the allowed outage time for an RHR pump.
NNECO is proposing to increase the allowed outage time from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />.
This proposed change is similar to a license amendment issued for the Vcgtle Electric Generating Plant, Units 1 and 2,
on May 31,
4 U.S. Nuclear Regulatory Commission B14930/Page 4 August 16, 1994 1994.m However, the Vogtle license amendment was only valid for a limited period of time.
Safety Assessment NNECO's proposed change to Action Statement "a" of LCO 3.5.2 of the Millstone Unit No. 3 Technical Specifications would permit one RHR pump to be inoperable for up to 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />, instead of the current technical specification limit of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The proposed change is desired to enable RHR pump repairs to be performed while the plant is at power.
Given the uncertainty ansociated with actual task completion time, the plant would be required to be shutdown if the repairs cannot be completed within the current 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> outage time.
The extended time that an RHR pump may be permitted to be inoperable results in an insignificant increase in core melt frequency (CMF) due to a
loss of coolant accident (LOCA).
Extending the outage time may enable the RHR pump repairs to be completed while at power.
This action would permit a plant shutdown to be avoided.
Based on our risk assessment, the option of performing the RHR pump repairs while the plant is at power is more favorable than performing the repair while the plant is shutdown.
The following discussion provides a summary of our risk analysis:
1.
RHR Train Unavailability Due to Maintenance The RHR pump seal replacement activity will significantly alter the "RHR pump out-of-service unavailability" probability from the current plant-specific value of 2.2E-03 to 3.2E-03 (based on a seal replacement performed at power once every five years).
- However, this increase is applicable irrespective of whether or not the proposed technical specification change is approved since periodic RHR seal replacement is inevitable.
2.
RHR System Unavailability Due To Increase In Maintenance Unnvailability Larae Break LOCAs i
The increase in RHR pump maintenance unavailability results in l
a negligible change in the yearly-averaged RHR system unavailability for large break LOCA mitigation (current value I
l (1)
L. L. Wheeler letter to C. K. McCoy, " Issuance of Amendments
- Vogtle Electric Generating Plant, Units 1 and 2 (TAC Nos.
M88481 and M88482), dated May 31, 1994.
U.S. Nuclear Regulatory Commission B14930/Page 5 August 16, 1994 of 1.75E-02).
With one RHR pump out of service (e.g.,
for seal replacement), the instantaneous RHR system unavailability for large break LOCA mitigation increases from 1.75E-02 to 2.1E-02.
To mitigate a large break LOCA, the RHR injection flow must be delivered through the three intact Reactor Coolant System (RCS) cold legs to prevent excessive flow resistance.
The RHR unavailability is dominated by a set of nine injection line check valves (three valves in series per cold leg).
The check valve dependency reduces the impact of having one RHR pump out of service for soci replacement.
Small and Medium Break LOCAs The increase in pump maintenance unavailability results in a change in the yearly-averaged RHR system unavailability for Small and Medium LOCA mitigation from 6.7E-04 to 6.9E-04.
With one RHR pump out of service, the instantaneous RHR system unavailability increases from 6.7E-04 to 4.3E-03.
These LOCAs require RHR injection flow to be delivered through any two (or all three) of the intact cold legs.
Thus, the check valve dependency and the overall unavailability are reduced, though the relative impact of having one RHR pump out of service is greater.
3.
CMF Increase Due to System Unavailability Increase The increased RHR unavailability will only affect the core melt frequency (CMF) contribution from LOCA injection phase failures.
The instantaneous CMF increase due to one RHR pump out of service at power is calculated to be 4E-08/yr (based on the RHR pump being unavailable for an entire year).
Since the increased pump unavailability is estimated to be only an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> per year (2x120 hours every 5 years), the yearly-averaged at power CMF increase attributed to the i
proposed change is of the order of 2E-10/ year
[(4E-08/ year)x(48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> / year)/(8760 hours0.101 days <br />2.433 hours <br />0.0145 weeks <br />0.00333 months <br /> / year)).
Even j
accounting for potential uncertainties, this is an insignificant increase by many orders of magnitude.
4.
On-Line Repair versus Shutdown Risk Comparison Given the need for an extended repair of the RHR pump, the j
risk (in terms of core melt probability) associated with performing the repair at power is SE-10 based on an exposure time of 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> and a core melt frequency of 4E-08/yr.
The risk incurred by shutting the plant down is on the order of SE-08.
This is determined by multiplying the probability that a controlled shutdown will result in a plant transient (0.064 per EPRI-TR-101894) times the conditional probability that a
I U.S.
Nuclear Regulatory Commission B14930/Page 6 August 16, 1994 transient will result in a core melt accident (9E-07 per the Millstone Unit No. 3 Probabilistic Safety Study).
This does not consider contributions from 1) a potential transient during the time spent at shutdown, or 2) a potential transient during the return to power operation.
Based on the above risk assessment, the option to perform the seal rep 1.acement at power is favorable compared to performing the repair at shutdown, and results in a negligible impact on core melt frequency.
Bionificant Hazards Consideration NNECO has reviewed the proposed changes in accordance with 10CFR50.92 and has concluded that the change does not involve a significant hazards consideration (SHC).
The basis for this conclusion is that the three criteria of 10CFR50.92(c) are not compromised.
The proposed change does not involve an SHC because the change would not:
1.
Involve a
significant increase in the probability or consequences of an accident previously evaluated.
There are no actual plant changes that will result from NNECO's proposal to revise Action Statement "a" of LCO 3.5.2 of the Millstone Unit No. 3 Technical Specifications.
The change would increase the time available to repair an RHR pump while the plant is at power.
The intent is to avoid unnecessary challenges to plant systems by reducing the number of forced shutdowns.
The change does not affect any initiating event.
Thus, the change does not affect the probability of occurrence of any previously evaluated accident.
Additionally, the safety analysis of the plant is not affected by the change.
Therefore, the radiological releases associated with the currmt analysis are not affected.
i 2.
Create the possibility of a new or different kind of accident from any accident previously evaluated.
This proposed change only affects the time that the Millstone Unit No. 3 Technical Specifications permit an RHR pump to be inoperable during Modes 1 through 4.
It will not change, in any way, the manner in which plant equipment functions.
Since the operation of the plant is not changed, there is no potential for a new, unanalyzed accident.
U.S. Nuclear Regulatory Commission B14930/Page 7 August 16, 1994 l
3.
Involve a significant reduction in the margin of safety.
The proposed change does not impact the physical protective boundaries, nor does it affect the performance of safety systems, or the assumptions utilized
'n the Millstone Unit No. 3 accident evaluations.
Thus, there is no adverse impact on the margin of safety.
The Commission has provided guidance concerning the application of the standards of 10CFR50.92 by providing certain examples (51 FR 7751, March 6, 1986) of amendments that are not considered likely to involve a SHC.
NNECO's proposal to revise Action Statement "a"
of LCO 3.5.2 of the Millstone Unit No.
3 by increasing the time that an RHR pump may be inoperable in Modes 1 through 4 from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> is not enveloped by any of the examples.
As discussed above, NNECO has concluded that the proposed change does not involve a
significant hazards consideration.
Environmental Considerations NNECO has reviewed the proposed license amendment against the criteria of 10CFR51.22 for environmental considerations.
The proposed change does not increase the types and amounts of effluents that may be released offsite, nor significantly increase individual or cumulative occupational radiation exposures.
Based on the foregoing, NNECO concludes that the proposed change meets the criteria delineated in 10CFR51. 22 (c) (9) for a categorical exclusion from the requirements for an environmental impact statement.
Nuclear Review Board The Millstone Unit No. 3 Nuclear Review Board has reviewed and concurred with the above determinations.
Notification of the State of Connecticut In accordance with 10CFR50. 91(b), we are providing the State of Connecticut with a copy of this amendment.
Schedule for NRC ADDroval and Issuance Because this proposed change is not required for continued safe plant operation, and the RHR pumps are currently operable, NNECO is not requesting the NRC to review and approve this p1'. posed change by a specific schedule.
However, this proposed change should be acted on at your earliest convenience.
This action will help to prevent any emergency need for this proposed change in the future.
i
i o
U.S. Nuclear Regulatory Commission B14930/Page 8 August 16, 1994 l
NNECO will implement the license amendment within-30 days of the date of issuance.
Should you have any questions regarding this submittal, please contact Mr. R. G. Joshi at (203) 440-2080.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY l s h_.
J. F(Opeka
(/
Executive Vice President
?
cc:
T. T. Martin, Region I Administrator V. L. Rooney, NRC Project Manager, Millstone Unit No. 3 P.
D.
Swetland, Senior Resident Inspector, Millstone Unit Nos.
1, 2,
and 3 Mr. Kevin T. A. McCarthy, Director Monitoring and Radiation Division Department of Environmental Protection 79 Elm Street P.O.
Box 5066 i
Hartford, CT 06102-5066 Subscribed and sworn to before me this
/d, dayofdisued 1994 ort /blb whW Date Co ission Expires:
dwgAx/ @ /9M
~
i
t Docket No. 50-421 B14930 Millstone Unit No. 3 Proposed Revision to Technical Specifications Residual Heat Removal Pump Outage Time Marked-Up Pages l
l August 1994 l
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