ML20116N414
| ML20116N414 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 11/16/1992 |
| From: | William Cahill, Woodlan D TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TXX-92535, NUDOCS 9211240006 | |
| Download: ML20116N414 (5) | |
Text
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M Log # TXX-92535
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File # 10010
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E 0.4 (clo)
-T E
Ref. # 10CFR50.34(b) illELECTRIC November 16, 1992 wmam 3. c.hm. ar.
Group Voce Pvesalem U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)
DOCKET NOS. 50-445 AND 50-446 ADVANCE FSAR SUBMITTAL DELE 110N OF INPUTS TO STEAM GENERATOR WATER HAMMER CIRCulT Gentlemen:
e The attachment to this letter provides an advance CPF e FSAR submittal to facilitate NRC Staff review of the subject area in support of licensing Unit 2.
The attachment is organized as follows:
1.
A description / justification of each change.
2.
A draft copy of the revised FSAR pages (changes are indicated in the margin by the word " DRAFT").
The attached material will be incorporated in CPSES FSAR Amendment 87 which is currently scheduled for December, 1992.
If you have any questions regarding this submittal, please contact Mr. Bob Dacko at (214) 812-8228.
Sincerely, William J. Cahill, Jr.
by:
O. R.Woodlan Docket Licensing Manager BSD Attachment c-Mr. J. L. Milhoan, Region IV Resident Inspectors, CPSES (2)
Mr. T. A. Bergman, NRR Mr. B. E.-Holian, NRR 9211240006 921116
,A ADOCK0500g5 gf DR SU N. Olive Street L.B. H I Dattas, Texas 73201 e-
r Attach ent to TXX-92535 Page 1 of 4 CPSES - FINAL SAFTEY ANALYSIS REPORT (FSAR)
DETAILED DESCRIPTION Page 1 Prefix Page (a1 amended)
Group Descriotion l
10.4 61 3
Corrects the FW temperature below which water hammer may be expected to occur. from 200 to 250 degrees.
Correction The Westinghouse tests described in this paragraph used 250 degrees which is consistent with the FW temperature setpoint described on FSAR page 10.4 67.
Change Request Number
- SA 92-800.
Commitment Register Number :
Related SER : 10.4.7 SSER :
SER/SSER Impact
- No 10.4-61 2
See Sheet No(s) :66 Deletes the SG low pressure and low 1. vel as inputs to the feedwater isolation valve water hammer interlock.
Revision The low S/G pressure and low S/G level inputs to the Feedwater Isolation Valve (FIV) interlock, along with low FW fiow and low FW temperature inputs, are part of the non-safety water hammer minimization system.
This system is designed to prevent bubble collapse water hammer in Westinghouse model 0 steam generators. The S/G pressure and S/G 1evel inputs are believed to be the cause of two recent spurious FIV closure incidents resulting in reactor trips.
These trips were documented in CPSES Licensee Event Reports (LER)92-014 and 92-019.
At TU alectric request. Westinghouse performed an analysis (SECL-92-336) in support of the removal of the suspect inputs to the water hammer-circuit.
Westinghouse concluded that the automatic feedwater isolation function on low S/G water level may be deleted from the water hammer minimization system concurrent with the deletion of the automatic-isolation function on low S/G pressure since:
- 1. The main feedwater system supplies feedwater to the steam generators only in Mode 1 and it is highly unlikely that the SG pressure could drop as low as 605 psi (low pressure set point) during Mode 1.
- 2. Analyses of three bounding low level scenerios concluded that the feedwater system is isolated by procedure, or, an automatic reactor trip on low SG 1evel coincident with low RCS temperature causes isolation of the feedwater system. before conditions occur which are conducive to-water hammer.
Change Request Number
- SA-92-800.
Commitment Register Number :
Related SER : 10.4.7 SSER :
SER/SSER Impact
- No I-
Attachment to TXX-92535 Page 2 of 4 CPSES/FSAR Tests have shown (Ref 19) that pressure transients, due to steam void ORAFT collapse, can occur in the steam generator and main feedwater piping if feedwater below 2500F is supplied through the main feedwater nozzle concurrent with low steam generator water level (at or below the level of the main feedwater nozzle in the preheater region) or low steam generator pressure. Although analysis of these test results has demonstrated (Ref 19) that the maximum pressure transients produce 10 stresses below the allowable limits, a feedwater bypass system has been incorporated to minimize the possibility of steam generator preheater and feed water piping pressure transients.
The feedwater bypass system consists of a connection between the auxiliary feedwater nozzle and the main feedwater line upstream of the feedwater isolation valve on each-steam generator.
This bypass line contains a feedwater preheater bypass valve. The feedwater bypass system also include a feedwater isolation bypass valve.
Q210.5 To minimize pressure transient potential, it is necessary to prevent the introduction of cold water to the steam generator through the main feedwater nozzle at any time when significant void may be.present.
Therefore, total feedwater flow is not aligned to the normal feedwater 87 nozzle during a startup until the feedwater line temperature i; above a set limit. Conversely, feedwater flow is diverted to the auxiliary feedwater nozzle from the main feedwater nozzle during a shutdown.
Q210.5 The feedwater split flow bypass line inside the containment, which 66 connects the main Teedwater line and the feedwater bypass line, is designed to minimize the thermal transients in the steam generator nozzles and to preclude the flow induced tube vibration in the pre-heater section of the steam generator (see reference 21) by maintaining a feedwater flow split during feedwater injection through the main feedwater line. The designed feedwater flov split is 90:10 between the main feedwater line and the split flow bypsss line, respectively, at 100 percent rated power output.
In addition, selected steam generator tubes in the preheater section have been 41 expanded at two support plate locations to minimize vibration Draft version 10.4-61
Attachment to TXX-92535 Page 3 of 4 CPSES/FSAR 59 In order to preclude water hamer in the steam and faedwater systems, the following interlocks and controls are provided.
These water j
hammer interlocks are non-safety grade controls.
However, where the non-safety grade water hammer interlocks interface directly with safety class equipment electrical isolation devices preclude any adverse impact on the safety class equipment caused by potential failure of the ncn-safety equipment.
59 1.
FEEDWATER ISOLATION VALVE (FIV)
Q210.5 t
59 In order to minimize the potential-for water hammer, interlocks are provided to prevent the FIVs from being opened (if they are l
closed) or, to close them if the FIVs are open, and route the feedwater through the auxiliary feedwater nozzle via the l
85 preheater bypass line. All of the listed interlocks must be l
present and the absence of a feedwater isolation signal to allow l
the FIVs to open.
i DRAFT i
l i
i i
I l
[
Draft version 10.4-66 l-
W Attachment to TXX-92535 Page 4 of 4 CPSES/FSAR a.
Feedwater Flow 59 Feedwater flow must be above a low-flow set-point, as 59 measured by a flow switch at the feedwater flow venturi meters.
FS-2189, -2190, -2191, and -2192 are provided for loops 1, 2, 3 and 4 respectively. The set-point for these 78 flow switches corresponds to approximately 12 to 15 percent of full feedwater flow.
Once the flow permissives have been cleared allowing the 79 FIV to open, the FIV can remain open irrespective of flow, providing the FW temperature remains high (above the set point as described in item (d) below).
Interlocks are provided for this condition.
10 b.
Feedwater Temperature 10 The feedwater temperature must be above approximately 59 2500F (as measured by resistance temperature detectors on the main feedwater lines).
In addition, the difference in 81 temperature between the RTDs installed outside containment, downstream of the FIVs and RTDs mounted at a piping low point on the feedwater lines inside containment, near the main feedwater nozzle must be within about 100F of each other. This arrangement of temperature sensors is used to preclude pocketing of cold water at the piping low point 10 during startups and, also, to avoid the possibility of a single RTD open circuit failure causing a false temperature permissive signal to open the FIVs.
Once the temperature permissives have been cleared allowing 10 the FIV to open, the FIV can remain open irrespective of temperature, providing the FW flow remains high (above the low flow set point as described in item (c) above).
Interlocks are provided for this condition.
Draft version 10.4-67
-.