ML17157A464
| ML17157A464 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 12/05/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17157A463 | List: |
| References | |
| NUDOCS 9012130218 | |
| Download: ML17157A464 (9) | |
Text
~
~p,S 4fqy gGv
- 0) 1~
%)
n C
O
,<c ~
Op o~
/p ++*<<+
UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 70 TO FACILITY OPERATING LICENSE NO.
NPF-22 PENNSYLVANIA POWER 5 LIGHT COMPANY ALLEGHENY ELECTRIC COOPERATIVE INC.
DOCKET NO. 50-388 SUSQUEHANNA STEAM ELECTRIC STATION UNIT 2
1.0 INTRODUCTION
By letter dated October 30, 1990, Pennsylvania Power
& Light Company requested an amendment, on an emergency basis, to Facility Operating License No. NPF-22 for the Susquehanna Steam Electric Station, Unit 2.
The proposed amendment would grant relief from the requirements of action "a" of Technical Specification Section 3.6.3 related to a reactor water cleanup system isolation valve.
The licensee has identified that the "closing" torque switch on the Unit 2 RWCU HV-244F001 Inboard Containment Isolation Valve was incorrectly set at lk turns rather than the specified 1 3/4 turns.
As a result of this lower torque
- setting, the valve may not fully close when it experiences the maximum differential pressure of 1000 psid.
Under these conditions, the valve would be limited to a 97K closure position.
Contrary to the requirements of the Technical Specifications, further manual action would be required to fully close the valve.
As a result, the valve was declared inoperable and appropriate actions taken to allow continued operation for an interim period of time.
For pressure differentials of 890 psid or less, the valve will function normally and is expected to fully isolate the penetration.
Therefore, there are a limited number of potential break locations that would prevent the valve from complete closure.
The only design basis accident or operating scenario that the licensee has determined to be capable of generating these high pressure differentials is a large break in the RWCU suction line outboard of the valve in question.
In addition, there is a limiting break size below which the differential pressure would be below the 890 psid value.
Therefore, the valve would function normally for these smaller break sizes.
However, the licensee has not taken credit for these limited break sizes in assessing the impact of continued operation.
The licensee has requested the above stated temporary relief to allow continued operation until March, 1991 to permit it to correct the torque setting and fully restore the valve to an operable status during an outage of suitable duration.
90i2'f302ie 500033 90i206 PDR ADQCK 05 P
On October 24, 1990, the staff granted a Temporary Waiver of Compliance which was immediately effective.
This action was verbally authorized and confirmed by a followup letter on October 30, 1990.
2.0 EVALUATION To support the request for a one-time relief from the Technical Specification Section 3.6.3, the li'censee evaluated the consequences of an accident with only 97% closure of the valve, from two perspectives:
the probability of a line break which would result in this limited closure and the consequences of such an event-if it were to occur.
For the period of time between now and March 1991, the licensee has computed the probability of a line rupture in the suction area (6-inch carbon steel line in the penetration room) of the RWCU system coi~cident with a random failure of the outboard isolation valve to be 4.3 X 10 Although the staff does not agree with the assumptions used in this calculation, the staff agrees that the probability of this occurrence is expected to be low.
A leak detection system is also installed to detect leakage from the RWCU System.
The leak detection system provides for automatic isolation on high room temperature or high delta-T between ventilation inlet and exhaust.
The set points are low enough to allow timely detection of a 5 gpm leak.
In addition, high flow rate, high change in flow rate, or a low reactor water level will initiate an automatic isolation of the RWCU System.
Area radiation monitors provide alarms on increasing radiation in the RWCU rooms which will alert operators to the possibility of leaks developing in the RWCU System.
The licensee has also reviewed existing procedures to determine if the consequences of the limiting break can be minimized.
As a result of this review, the licensee has taken the the following actions:
1.
Made provisions for bypassing the isolation signal per revised emergency operating procedures and removed the open seal-in feature in order to reset the torque switch without moving the valve to the full open position.
This will allow remote-manual full closure of the valve after the differential pressure has been reduced below 890 psid.
2.
Developed procedures for remote-manual valve closure as described in
- 1. above.
3.
Provided operator training to make. operators aware of degraded conditions and the special procedures in place to assure manual valve closure.
Based on these added procedures,,the licensee has indicated that complete closure of the valve under the most limiting conditions can be accomplished within 19 minutes of the initiation of the event.
Using this time for
~
L
- closure, the licensee has performed a dose-consequence analysis which demonstrated that the main steam line rupture remains as the most limiting pipe rupture.
The licensee has indicated that the motor and actuator can accomodate the loads during the closure stroke when the torque switch is bypassed, but has not discussed the availability of thermal overload protection for the motor.
The capability of the motor actuator as well as the availability of the thermal overload will be addressed by the licensee in its response to Supplement 3 of Generic Letter (GL) 89-10.
To assure protection of the motor, actuator, and valve, the licensee has decided not to make temporary modifications to the electrical circuits and bypass the torque switch.
The staff agrees with the licensee's decision not to bypass the torque switch and thus protect the valve against possible damage.
The staff is concerned about the licensee's procedures for torque switch
- setting, which have resulted in two incorrect torque switch settings during the past three years.
The licensee should review and, if needed, improve its methods for torque switch settings, and avoid any future possibilities that torque switches may be incorrectly set.
Based on the above, the staff finds that the licensee can continue power operation with the degraded torque switch setting of the reactor water cleanup system inboard isolation valve.
The staff's conclusion is based on the consideration that the probability of a pipe rupture which would cause the valve to close slightly off the seat is very low, and the consequences of such an accident would be bounded by the radiological doses calculated for the design basis rupture of the main steam line, and the dose guidelines of 10 CFR Part 100 will be met, should a pipe rupture downstream of the outboard isolation valve of the reactor water cleanup system occur.
In order to continue power operation, the licensee requested the following footnote to be added to the Table 3.6.3-1.
"The RWCU HV-244 F001 Valve may be considered OPERABLE with its current minimum torque switch setting for the period beginning October 30, 1990 until an outage of sufficient duration to revise the setting occurs".
Although the staff has found that the licensee can continue power operation with the degraded torque switch setting of the valve HV-244 F001, the staff finds that the valve HV-244 FOOl must not be considered OPERABLE.
On November 9, 1990, the staff informed the licensee that the staff would find
,the Technical Specification change acceptable if it modified the footnote to read as follows:
"For the RWCU HV-244 F001 valve, the ACTION statement 3.6.3.a need not be followed for the period beginning October 30, 1990 until an outage of sufficient duration to revise the current torque switch setting occurs".
The licensee verbally agreed to the staff proposal to change the footnote.
Therefore, the revised footnote may be incorporated in the Technical Specifications.
3.0 EMERGENCY BASIS The licensee has provided the following basis for the existence of an emergency required by 10 CFR 50.91.
[Guidance is provided underJ 10 CFR 50.91 on what information the NRC requires in support of an application for an emergency change.
First, it requires the applicant to justify that an emergency exists, i.e. "... failure to act in a timely way would result in derating or shutdown of a nuclear power plant...".
Unit 2 is currently operating at full power.
Since the affected valve is inside containment, the torque switch cannot be reset without a unit shutdown and a containment entry.
Isolation of the affected RMCU penetration as required by Technical Specification 3.6.3 Action "a" would result in a unit shutdown due to exceeding Chemistry limits on reactor water conductivity (reference Technical Specifications 3.4.4) in approximately 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
- Secondly, 10 CFR 50.91 requires the licensee to "... explain why this emergency situation occurred and why it could not avoid this situation...".
The improper setting was discovered during a records search pursuant to a request from the BWR Owners'roup.
After some evaluation, discussion and clarification of guidance, the valve was declared inoperable and a temporary waiver of compliance was applied for.
Application in advance of this situation was impossible since the problem was discovered during full power operation.
Based on the time necessary to evaluate the problem and to prepare and review this proposal internally, we believe that this application has been submitted in a timely fashion.
The staff believes that the licensee made a timely application after determining on October 24, 1990 that the torque setting was incorrect.
The staff agrees with the above basis for an emergency provided by the licensee.
Therefore, the staff finds that the proposed Technical Specification changes should be processed on an emergency basis.
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Commission has provided standards for determining whether a significant hazards consideration exists (10 CFR 50.92(c)).
A proposed amendment to an operating license for a facility involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not:
(1) involve a significant increase in the probability or consequences of an accident previously evaluated; (2) create the possibility of a new or different kind of accident previously evaluated; or (3) involve a significant reduction in a margin of safety.
The staff has reviewed the licensee's request and concurs with the following basis and conclusions provided by the licensee in its October 30, 1990 submittal.
The proposed change does not:
I.
Involve a significant increase in the probability or consequences of an accident previously evaluated.
As delineated
- above, the only event of concern given the current condition of the F001 valve is a
RMCU. line break outside containment.
The probability analysis indicates that this is an unlikely event over the slightly more than four months that the proposed change could be in effect.
The radiological consequences were conservatively determined to be the same as the bounding FSAR analysis of a Main Steamline break outside containment, but the increase is insignificant given the implicit error in such calculations and since both numbers are such a small fraction of 10 CFR Part 100 limits.
II.
Create the possibility of a new or different kind of accident from any accident previously evaluated.
No hardware or procedural changes are proposed that would create a
new event requiring evaluation.
III. Involve a significant reduction in a margin of safety.
As delineated
- above, the event of concern has been shown to be unlikely, and its consequences, both, in terms of affect on safety-related equipment and radiologically, have been shown to be acceptable from a regulatory standpoint.
'herefor e, the margin of safety is not significantly reduced due to operation with the improper torque switch setting until the Unit 2 Fourth Refueling and Inspection Outage.
5.0 STATE CONSULTATION
The Commonwealth of Pennsylvania was contacted on November 5, 1990,and had no Comments on the Amendment.
6.0 ENVIRONMENTAL CONSIDERATION
S This amendment involves a change to a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has made a final no significant hazards
~
U
finding with respect to this amendment.
Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement nor environmental assessment need be prepared in connection with the issuance of this amendment.
7.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, that:
(1) the amendment does not (a) significantly increase the probability or consequences of an accident previously evaluated, (b) create the possibility of a new or different kind of accident from any previously evaluated or (c) significantly reduce a safety margin and, therefore, the amendment does not involve a significant hazards consideration; (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed
- manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security nor to the health and safety of the pub 1 ic.
Princi al Contributors:
J. Kudrick, T. Scarborough, and M. Thadani Dated:
December 5.
1990