ML19291C467
| ML19291C467 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/18/1980 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001240460 | |
| Download: ML19291C467 (8) | |
Text
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TOLEDO Docket No. 50-346 EDISON License No. NPF-3 R:cnAno P. CaousE Wce Preset Serial No. 577
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January 18, 1980 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention:
Mr. Robert W. Reid, Chief
' Operating Reactors Branch No. 4 Division of Operating Reactors
Dear Mr. Reid:
The attached is in response to your letter dated November 19, 1979 requesting additional information on the containment purge and vent systems used during normal operation at the Davis-Besse Unit No. 1.
These systems at Davis-Besse were not required to meet the requirements of the NRC Branch Technical Position (BTP) CSB 6-4 entitled " Containment Purging During Normal Plant Operation",
when Davis-Besse Unit No. I was licensed.
The attached response discusses how the Davis-Besse purge and vent systems meet the requirements of the BTP CSB 6-4.
Since the Davis-Besse Technical Specifications limit all purging and venting to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year, Paragraphs B.l.c and B.5.a of the subject Branch Technical Position were not addressed.
The containment hydrogen dilution system and containment hydrogen purge system as shown on Davis-Besse Nuclear Power Station Unit No. 1 FSAR Fig. 9-12A are not used during normal operation and are not addressed in this response.
Yours very truly, A c w __
Ch Attachment I
RPC:TEH 1794234'///
THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO. OHIO 4365 [d
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800124 0
Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980 ATTACl&fENT Response to Request for Additional Information on Containment Purge and Vent Systems 1794 235~
Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980 This attachment discusses how the Davis-Besse purge and vent systems satisfy the requirements of the Branch Technical Position CSB 6-4, entitled " Containment Purging and Venting During Normal Operations".
At our Davis-Besse Unit No. 1 Nuclear Power Station, we have only one containment purge system with four (4), 48" isolation valves. The access of containment to the outside atmosphere due to opening of any of the purge supply and/or exhaust isolation valve is limited to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year in modes 1, 2, 3 and 4.
Para. B.I.a The performance and reliability of the purge system isolation valves should be consistent with the operability assurance program outlined in MEB Branch Technical Position MEB-2, Pump and Valve Operability Assurance Program (Also see SRP Section 3.9.3).
The design basis for the valves and actuators should include the buildup of containment pressure for the LOCA break spectrum, and the purge line and vent line flows as a function of time up to and during valve closure.
Respegge Performance, reliability, and design basis for the purge system isolation valves are described in response to NRC Question 6.2.32 in the Davis-Besse Unit No. 1 FSAR.
The valve manufacturer is presently performing an analysis to demonstrate the ability of the valves to close, from the full open position, following a design basis LOCA. The results of this analysis are expected to be available in June of 1980.
In the interim, the valve manufacturer has determined that maximum valve open position be set it 65 degree-
.o that the valve will tend to close when subject a to the LOCA luced fluid dynamic forces.
According to ths. manufacturer's prelirainary c 31culations, the aerodynamic torque with the valves positioneu at 65 degrees open'is approximately half that of the full open condition. Thus the manufacturer's engineering judgment is that the resultant loads in critical valve components will also be reduced by the same magn,tude thus enhancing the capability of these valves to withstand LOCA[ h 4 2 } h generated forces.
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A mechanical stop will be installed on each valve to limit the valve opening to 65 degrees. This modification will be installed at Davis-Besse during the refueling outage presently scheduled to begin in late March or early April of 1980.
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Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980 Para. B.I.b The number of purge and vent lines that may be used should be limited to one purge line and one vent line.
Response
There is a single purge supply line and a single exhaust line as shown in Figure 9-12A of the FSAR.
Para. B.1.c The size of the purge and vent lines should not exceed about eight inches in diameter unless detailed justification for larger line sizes is provided.
Response
No response required per NRC letter of November 19, 1979.
Para. B.1.d The containment isolation provisions for the purge system lines should racet the standards appropriate to engineered safety features; i.e.,
quality, redundancy, testability and other appropriate criteria.
Response
The containment purge penetrations and isolation valves meet all the requirements for the containment isolation system as described in subsection 6.2.4 of the FSAR.
Para. B.I.e Instrumentation and control systems provided to ison.'e the purge system lines should be independent and actuated by diver ' parameters; e.g.,
containment pressure, safety injection actuation, and contain
- ment radiation level.
If energy is required to close the va'1ves, at least two diverse sources of energy shall be provided, either of which can affect the isolation function.
1794L 23f7 '-
Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980
Response
Upon detection of high containment pressure or low reactor coolant pressure indicative of a loss of coolant accident, the safety features actuation system will close the containment purge system valves. The trip setpoints and margin between normal operating limits and trip setpoints are given in Table 7-5 of the FSAR.
In all cases, the setpoints have been determined to reflect a safe margin to ensure that the setpoints are reached and that containment isolation occurs. Refer to FSAR Figures 7-4A and 7-4B for SFAS logic and signal diagrams. The purge isolation valves are air operated and fail in the closed position. They require no power to close.
Para. B.I.f Purge system isolation valve closure times, including instrumentation delays, should not exceed five seconds.
Respons-The val /es are designed to close (from the full open position) within 5 seconds of the receipt of the closure signal, against containment post-accident conditions. The valve manufacturer is presently performing a detailed analysis to verify this ability.
In the interim, the valve will be limited to 65 degrees maximum opening. The valve manufacturer has stated that at this position, LOCA-induced dynamic forces will tend to close the valve, thus the closure time will be less than the design value of 5 seconds. We meet the requirement of our FSAR, Table o-8 and Technical Specifica-tions Table 3.6-2 both of which call f a 10 sec of valve closing time, including instrumentation delayr In the ECCS minimum backpressure analysis discussed in response to Item B.5.c, the valves are not assumed to be fully closed until 11 seconds following the LOCA.
Para. B.I.g Provisions should be made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.
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1794 238 '
Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980
Response
The inboard containment isolation valve in the containment purge supply ductwork is located at Elevation 646'-6", and the inboard containment isolation valve in the containment purge exhaust ductwork is located at Elevation 617'.
Debris which could potentially become entrained in the escaping air and steam is not expected to affect the valves due to their remote locations.
Furthe rmore,
redundant outboard containment isolation valve in each path assures closure thereby achieving the desired isolation.
Para. B.2 The purge system should not be relied on for temperature and humidity control within the containment.
Response
The containment air coolers are provided to maintain temperature and humidity control within the containment.
The purge system is not relied on for this function.
Para. B.3 Provisions should be made to minimize the need for purging of the containment by providing containment atmosphere cleanup systems within the containment.
Response
The need for purging of the containment vessel atmosphere for personnel access during power operation is controlled by the concen-tration of noble gases and not by iodine concentration. Atmosphere cleanup systems within the centainment vessel would thus not affect the need for purging and are therefore not provided.
Provisions are made in our Technical Specifications, Section 3.6.1.7 to minimize the need for purging of the containment. This section requires that accumulated time of access to the outside atmosphere due to opening of any contain. cent purge supply and/or exhaust isolation valve be limited to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> for the preceding one year in modes 1, 2, 3 and 4.
I794 239
Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980 Para. B.4 Provisions should be made for testing the availability of the isolation function and the leakage rate of the isolation valves, individually, during reactor operation.
Response
Provision for periodic testing of the purge isolation valves is described in subsection 6.2.4.4 of the FSAR.
Para. B.5 The following analyses should be performed to justify the containment purge system design:
B.S.a An analysis of the radiological consequences of a loss-;f-coolant accident. The analysis should be done for a spectrum r,f break sizes, and the instrumentation and setpoints that will actuate the vent and purge valves closed should be identified. The source term used in the radiological calculations should be based on a calculation under the terms of Appendix K to determine the extent of fuel failure and the concomitant release of fission products, and the fission product activity in the primary coolant. A pre-existing iodine spike should be considered in determining primary coolant activity. The volume of containment in which fission products are mixed should be justified, and the fission products from the above sources should be assumed to be released through the open purge valves during the maximum interval required for valve closure. The raiiological consequences should be within 10 CFR 100 guideline values.
Response
No response required per NRC letter of November 19, 1979.
B.5.b An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related equipment; e.g.,
fans, filters and ductwork, located beyond the purge system ~ isolation valves against loss of function from the environment created by the escaping air and steam.
1794 24D'
Docket No. 50-346 License No. NPF-3 Serial No. 577 January 18, 1980
Response
An analysis is in progress to demonstrate that the environment created by escaping air and steam does not result in the loss of function of safety related structure and equipment. The results of this analysis will be submitted on or before March 15, 1980.
B.S.c An analysis of the reduction in the containment pressure resulting from the partial loss of containment atmosphere during the accident for ECCS backpressure determination.
Response
An analysis of the minimum containment backpressure (for the ECCS analysis) has been made assuming the 48 inch purge line valves are not fully closed until 11 seconds following a LOCA. The peak containment backpressure was calculated to be 22.96 psig at 18.90 seconds.
It is conservatively assumed that the valves begin to close at 6 seconds after the LOCA and are completely closed at 11 seconds. The result indicates that the calculated containment pressure is above the B&W assumed minimum pressure prior to initiation of ECCS, and remains above thereafter.
Therefore, the ECCS analysis is not affected by the open purge line valves.
B.S.d The allowable leak rates of the purge and vent isolation valves should be specified for the spectrum of design basis pressures and flows against which the valves must close.
Response
The containment purge system containment isolati.n valves are designed for a pressure of 59.4 psia and the valves have been shop tested to be bubble tight at pressure of 45 psig. This pressure is higher than the peak pressure against which purge valves must close.
In addition, the valves are tested for leakage in place as part of tue integratei leak rate test (ILRT) and local leak rate test (LLRT). The allovable leakage of the valves under LOCA con-ditions is determined it. combination with the other leakage paths as part of the ILRT with acceptance criteria. established.in technical Specification 3.6.1.2.
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