ML20137A490
| ML20137A490 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/31/1985 |
| From: | Opeka J NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.E.4.2, TASK-TM A04542, A4542, TAC-44864, NUDOCS 8601140394 | |
| Download: ML20137A490 (15) | |
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(203) 66s-5000 December 31,1985 Docket No. 50-336 A04542 Director of Nuclear Reactor Regulation Attn:
Mr. Ashok C. Thadani, Director PWR Project Directorate //8 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
Millstone Nuclear Power Station, Unit No. '!
NUREG-0737 Item II.E.4.2.7 Containment Venting through Hydrogen Purge Valves in a December 11, 1984 letter,(I) the Staff advised Northeast Nuclear Energy Company (NNECO) that further analysis would be necessary to justify NNECO's position for not complying with item II.E.4.2.7 of NUREG-0737.
NNECO hereby revises our position concerning the capability for automatic isolation, on high radiation in the containment atmosphere, of the 6-inch containment isolation valves, at Millstone Unit No. 2. Information is provided in Attachment I which demonstrates compliance with the recommendations of item II.E.4.2.7 of NUREG-0737.
Additionally, in a September 2,1983 letter,(2) the Staff requested information concerning operability / qualification of the hydrogen purge valves.
NNECO provided information in response to that request on October 27,1983(3) and July 11,1984(4). Attachment to this letter supplements NNECO's responses to the Staff's September 2, 1983(2 request.
The Staff also requested, on April 25, 1984(5) that NNECO address the issue of surveillance frequency for the containment purge valve and hydrogen purge valve seal leakage. NNECO addresses this issue in Attachment 3 to this lett er.
(1)3. R. Miller letter to W. G. Counsil dated December 11,1984.
(2)3. R. Miller letter to W. G. Counsil, dated September 2,1983.
(3)W. G. Counsil letter to J. R. Miller, dated October 27,1983.
T (4)W. G. Counsil letter to J. R. Miller, dated. July 11,1984.
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(5)J. R. Miller letter to W. G. Counsil, dated April 25,1984.
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4 NNECO considers that the attached information addresses all outstanding NRC concerns regarding NUREG ltem II.E.4.2.7 at Millstone. Unit No. 2 and should provide the basis for a final SER on this action plan item. We trust you will find this information satisfactory.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY i
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Docket No. 50-336 Millstone Nuclear Power Station, Unit No. 2 Closure of Hydrogen Purge Valves on High Radiation Signal i
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December,1985
Issue in a letter dated February 9,
1983 (Reference 1) and in subsequent correspondence (References 3, 5, 7, and 10), the Staff has requested that NNECO:
" Modify the isolation logic for the 6-inch hydrogen purge valves to receive an isolation signal from radiation monitor (s) that sense primary containment atmosphere."
The request is based on the Staff's concern that, for loss-of-coolant accidents (LOCA) involving very small breaks, a high radiation signal would provide the only isolation signal to the purge and vent valves, thereby limiting the radiological consequences of such a postulated accident. The Staff maintains that a Containment isolation Actuation Signal (CIAS) based on a Safety injection Actuation Signal (SIAS) might not be generated rapidly enough to preclude the release of excessive radioactive material from containment.
Resolution As documented in Reference 4, in order for significant amounts of radioactive material to be released to containment, and subsequently to the environment, through the open hydrogen purge valves, one must assume significant core damage has occurred. The Millstone Unit No. 2 licensing basis small break LOCA analysis models such a scenario. This analysis conservatively predicts that the SIAS and CIAS occur within 60 seconds following the design basis small break LOCA.
A SIAS automatically initiates containment isolation, thereby closing any potential leakage path from containment. Furthermore, Millstone Unit No. 2 Operating Procedure 2532, " Loss of Primary Coolant," refers the control room operators to ESF actuation panel COlX, on which the position of the 6-inch purge valves is indicated and may be verified. It remains NNECO's position that the probability of obtaining fuel damage without first obtaining a CIAS is significantly small such that modifications of the type proposed are unwarranted.
Nevertheless, in order to be responsive to the Staff's concerns, NNECO will isolate the 6-inch hydrogen purge valves on a high radiation signal. The isolation signal for the 6-inch hydrogen purge valves (HV-3377,8378,8379, and 8380) will be derived from existing containment high range radiation monitors. Use of the existing radiation monitors (RE8240 and RE8241) will be expanded to provide an isolation signal to close the purge valves. The isolation signal will be generated upon reaching a setpoint of 10R/ hour. Below a dose rate of 10R/ hour, venting of the containment would be terminated via administrative controls. Specifically, since the venting release pathway is through the Millstone Unit No. I stack, the stack monitor will alarm once the Technical Specification limit is reached, and the operators will then take action to terminate the release within fif teen minutes, in accordance with existing plant procedures.
- The radiological consequences of such a scenario have been evaluated conservatively assuming a release of 15 minutes duration and a dose rate of 10R/ hour, corresponding to the isolation setpoint for the containment high range radiation monitors.
The results of the evaluation confirm that thyroid and whole body doses at the site boundary are well below the limits established in 10CFR100. NNECO concludes that isolatica of the 6-inch hydrogen purge valves upon receipt of an isolation signal from the containment high range radiation monitors coupled with existing procedural controls will provide additional assurance of the protection of public health and safety.
In order to allow adequate time for design, review and scheduling of activities, we propose to implement this design modification during the end-of-cycle 8 refueling outage (currently scheduled for January,1983). Based on this commitment, NNECO considers this issue to be resolved.
Docket No. 50-336 Millstone Nuclear Power Station, Unit No. 2 Operability / Qualification of Hydrogen Purge Valva December,1985
Issue in a letter dated September 2,1983 (Reference 3), the Staff requested that NNECO provide information concerning the operability of the 6-inch hydrogen purge valves in order to determine the long-term acceptability of these valves.
Resolution References 2, 4 and 8 provided the Staff with design information regarding the operability of the 6-inch hydrogen purge valves. Further, as documented in the Staff's Safety Evaluation Report (Reference 1) on purge and vent valve isolation dependability (i.e., NUREG-0737, Item II.E.4.2, Position 6), the Staff:
" review of NNECO's response dated May 20, 1981 and Section 6.6 and 6.7 on Containment Post Incident Hydrogen Control System and Enclosure Building Filtration System, respectively," of the Millstone Unit No. 2 FSAR
" indicates that the 6-inch hydrogen purge valves meet the intent of Position 6. The performance, reliability and size (less than 8 inches) of the 6-inch hydrogen purge lines are acceptable."
NNECO points out that meeting the intent of Position 6 of NUREG-0737, Item II.E.4.2, relies on the 6-inch purge lines satisfying the operability criteria set forth in Branch Technical Position CSB 6-4 and *he Staff " Interim Position for Purge and Vent Valve Operation Pending Resolution of Isolation Valve Operability." This position is further supported by the Staff in Reference 1, wherein it is documented that multi-plant Generic Issue B-24 is resolved for
. Millstone Unit No. 2, with the exception of specific concerns which NNECO addressed in Reference 2.
Nonetheless, for convenience, we have summarized information provided in our previous submittals below and in Table 1.
The hydrogen purge system consists of open-ended pipe headers which draw from the highest point in the dome of the containment. The piping is then routed from i
the dome to separate penetrations. Containment isolation valves are provided inside and outside the containment for both trains. Each train of the hydrogen purge system is provided with independent valving and instrumentation and powered from independent 125 VDC emergency power sources.
The 6-inch hydrogen purge valves at Millstone Unit No. 2 are solenoid actuated, air operated Fisher Control Company Butterfly Type 9212 valves with a Fisher 656-40 Diaphragm Actuator.
They are built to ASME Section III, Class 2 standards and receive redundant Containment Isolation Actuation Signals (CIAS).
A CIAS is generated on two diverse parameters, namely pressurizer pressure -
low and containment pressure - high. Upon receipt of a CIAS, they are required to close in not more than five (5) seconds. These valves are tested to verify isolation time at least once every 92 days, pursuant to Technical Specification 4.6.3.1.1.
The operators and valves are designed to close against a 60 psi differential pressure at 2890F.
Note that for the worst case large break LOCA, the maximum containment pressure during closure of the 6-inch purge valves is predicted to be approximately 25 psig. This value is well below the design limit of 60 psig for these valves. In addition, the predicted peak pressure occurs 238 seconds following initiation of this event and is below the containment
. design pressure of 54 psig. The containment vent valves will be closed well before the peak containment pressure is reached. The actuators, solenoids and attached piping are seismically qualified for a DBE. Additionally, the valves and limit switches are environmentally qualified as documented in our August 18, 1983 letter (Reference 11) to the NRC (reference SCEW Sheets ll A and 21A).
Additional design data are presented in Table 1.
Each hydrogen purge valve is provided with an auxiliary air accumulator to assure an air supply for operation. The cylinder air-operated valves,if open, are closed by the accumulator air assuming a failure of the normal instrument air i
system. Air is available in the accumulater for opening the purge valves, if required. Each accumulator is sized for four open or closed operations.
To summarize, NNECO concludes that adequate design information has been provided to the NRC to demonstrate the ability of the 6-inch hydrogen purge d
valves to function in the event of a postulated design basis accident.
We conclude that the operability requirements of Enclosure 1 of Reference 3,
" Operability Qualification of Purge and Vent Valves" have been met.
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TME 1
HYDROGEN PURGE VALVE QUALIFICATION DATA
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Valve Numbers:
2-EB-91 2-EB-92 2-EB-100 2-EB-99 Bechtel Valve Designations:
HV 8378 HV-8377 HV 8380 I!V-83 79 Valve Location Inside Containment Enclosure Building Valve Type / Size Butterfly /6-Inch Butterfly /6-Inch Valve Model Fisher 9212 Fisher 9212 Operator Type Air Cylinder Diaphragm Operator Model Fisher 481-1.5-30 Fisher 656-40 Design Code ASME Section III ASME Section III Class 2 Class 2 "N" Staaped Yes Yes Desi;n Conditions (PSIg))
Pressure 60 60 Temperature (F 289 239 Flow (SCFM) 250 250 Design Life (Years) 40 40 Flange Rating 150*
'50?
Onerating Conditions Normal:
Pressure (PSIg))
15 15 Temperature (F 200 200 Maximum:
Pressure (PSIg))
54 54 Temperature (F 289 2S9 Medium Hydrogen Hydrogen External Environment:
Temperature ( ?)
N/A 120 Relative Humidity N/A 100 Radiation Exposure (Accumulated) 10 Rads 10 Rads (except seating =aterial)
(C:ntinued on next page)
, o TELE.
1 N
l HYDROGEN PURGE VALVE QUALIFICATION DATA Operating Conditions (Cont'd)
Max / Min AP at Design Flow (PSI) 0.009/0.013 0.009/0.013 Closing Time Max (Seconds)
S 5
Normal Position Closed Closed Failure Position As Is Closed Handwheel No Yes Minimum Air Required (PSIG) 80 80 Normal Air Supplied (PSIG) 8.0-100 80-100 Valve Flange Orientation Horizontal 2S3-92 Horizonal 2S3-99 Vertical Valve Materials Body SA 516, Gr. 70 Seat Ethylene Propylene Disc SA 516, Gr. 70 Shaft ASTM A 564, Gr. 630 Pins ASTM A 564, Gr. 630 Accumulator Package Minimum Number of Operations 4
4 Double Acting Solenoid Valves ASCO 4-Way Dual Control Model 534445 Seismically Qualified Yes Yes Valve Ocerators Maximum Shutoff Pressure 60 PSI at 289 ?
Limit Switches:
Indicate Full Open Yes Yes Redundant Indication Fully Closed Yes Yes Seismic Recuirements Valves are capable of operation during and after the loading due ;o seismic forces.
Valves withstand an inertial load of 3.0 g in any direction in addition to normal operating loads.
The extended parts of the valves have a natural frequency of vibration greater than 20 CPS.
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Docket No. 50-336 Millstone Nuclear Power Station, Unit No. 2 Surveillance Frequency of Containment Purge Valve and Hydrogen Purge Valve Seal Leakage i
December,1985
r Issue In letters dated February 9,
1983 (Reference 1), September 2,
1983 (Reference 3), and April 25,1984 (Reference 5), the Staff requested that NNECO propose Technical Specifications for Millstone Unit No. 2 to periodically test the 6-inch containment purge and vent valves as well as the 42-inch valves.
Specifically, the Staff stated that appropriate Technical Specifications would be:
"The leakage integrity tests of the 6-inch isolation valves in the hydrogen purge lines shall be conducted at least once every three months (active systems). The leakage integrity tests of the 42-inch kolation valves in the containment purge lines shall be conducted at least once every six months (passive systems)."
Response
As stated in Enclosure 5 of the Staff's February 9,1983 letter (Reference 1) to NNECO, the long-term resolution of Generic Issue B-24, " Containment Purging During Normal Plant Operation," includes the implementation of item B.4 of BTP CSB 6-4. Item B.4 of BTP CSB 6-4 specifies that leakage rate testing provisions should be made for testing of purge and vent valves. Item B.4 does not specify a test frequency; however, 10CFR50, Appendix 3 specifies a maximum test interval of 24 months.
As a result of Staff concerns regarding unsatisfactory performance of resilient seals for some containment purge and vent valves, Generic issue B-20,
" Containment Leakage Due to Seal Deterioration," was implemented. Based on evaluations conducted for Generic Issue B-20, the Staff concluded that the leakage test frequency for containment purge and vent valves should reflect consideration of the occurrence of severe environmental conditions and valve use rather than the requirements of Appendix 3.
The test frequencies previously requested by the Staff reflect this recommendation.
Millstone Unit No. 2 Technical Specification 3/4 6.1.2 presently requires periodic testing of the 42-inch valve seals in accordance with 10CFR50, Appendix 3.
These valves are normally locked closed and electrically disconnected during operating modes I through 4, and, thereby, meet the Staff's definition of a passive purge / vent system. The Staff's concern regarding passive purge / vent systems, as stated in Reference 3, is expressly related to the potential adverse effect of seasonal weather conditions on integrity of valve seals. The Millstone Unit No. 2 containment is completely surrounded by the enclosure building (reference FSAR Section 5.3). This prevents degradation of valve seals due to seasonal weather extremes.
Based on the preceding discussion, NNECO believes that the existing leakage testing frequency for these valves is appropriate and that. no Technical Specification changes for Millstone Unit No. 2 are warranted.
Currently, the 6-inch purge valves are leakage tested in accordance with Technical Specification 3/4 6.1.2 and meet the requirements of 10CFR50, Appendix 3.
As with the 42-inch valves discussed above, extreme seasonal weather conditions have no impact on these valve seals. In References 2 and 4, we provided the Staff with our position concerning the need for more frequent surveillance of the 6-inch valves. NNECO has individually tested these valves at
. every refueling outage since plant ' operation began in December 1975. Test results to date evidence no failures due to degradation of ' resilient seals.
Millstone Unit No. 2 has experienced no degradation of containment purge valve resilient seals more rapid than that stated by the manufacturer.
- Further, maintenance and repair of the resilient seals for these valves are in accordance with manufacturer's recommendations and are reflected. in plant procedures.
Based on the above information, NNECO concludes that the existing testing frequency coupled with proceduralized. maintenance and repair practices are adequate to assure seal integrity. Therefore, changes to the e'xisting Technical Specifications for the 6-inch containment purge valves are not warranted.
In summary, NNECO considers the issue of surveillance frequency for the 6-inch and 42-inch purge valves to be resolved. No Technical Specification changes are required to assure adequate resilient seal testing and maintenance.
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Docket No. 50-336 Millstone Nuclear Power Station, Unit No. 2 Attachment References December,1985
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References:
(1)
R. A. Clark letter to W. G. Counsil, dated February 9,1983.
(2)
W. G. Counsil letter to R. A. Clark, dated March 28,1983.
(3)
- 3. R. Miller letter to W. G. Counsit, dated September 2, 1983.
(4)
W. G. Counsil letter to 3. R. Miller, dated October 27,1983.
(5)
- 3. R. Miller letter to W. G. Counsil, dated April 25,1984.
(6)
W. G. Counsit letter to 3. R. Miller, dated May 15,1984.
(7)
- 3. R. Miller letter to W. G. Counsil, dated June 11, 1984.
(8)
W. G. Counsil letter to 3. R. Miller, dated July 11,1984.
(9)
W. G. Counsil letter to 3. R. Miller, dated July 13,1984.
(10)
- 3. R. Miller letter to W. G. Counsil, dated December 11, 1984.
(11)
W. G. Counsil letter to D. G. Eisenhut, dated August 26, 1981.
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