ML19249A223
| ML19249A223 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 08/08/1979 |
| From: | Reed C COMMONWEALTH EDISON CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7908210368 | |
| Download: ML19249A223 (5) | |
Text
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@ Cm rm Nraw oya Commonwealth Edison cnicar m no.s Address Rec 9 to Post Off ce Box 767 Chicaco.11no.s 60690 August 8, 1979 Mr. A.
Schwencer, Chie f Operating Reactors - Branch 1 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Zion Station Units 1 and 2 Additional Information on Steam Generator Water Hammer Evaluations NRC Docket Nos. 50-295 and 50-304 Reference (a):
June 20, 1979 letter from Cordell Reed to A.
Schwencer
Dear Mr. Schwencer:
Per Reference (a), Commonwealth Edison Company indicated that it would evaluate the advisability of raising the setpoin. for steam generator water level actuation in order to reduce the likelihood of steam generator water hammers.
This evaluation has been completed with the con-clusion that no setpoint changed is warranted.
The basis for this conclusion follows.
Commonwealth Edison's experience at Zion Station indicates that none of the thirteen water hammer incidents experienced over nearly six years of plant operation would have been prevented with the auxiliary feedwater initiation setpoint above the top of the feedwater ring.
This is because the auxiliary feedwater flow rate is not sufficient to maintain the feedring filled with water after a reactor trip, primarily due to the rapid drainage that occurs through the existing discharge holes on the bottom of each sparger and to a lesser extent the drainage that occurs through the gap between the thermal sleeve and feedwater nozzle.
However, with the in-sta11ation of J-tubes these draintge holes are plugged, thus ensuring that auxiliary feedwnter flow will maintain the feedring filled with water.
Commonwealth Zdison's experience does indicate that most, if not all, the water hammer incidents at Zion Station would not have occurred if J-tures had been
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Commonwealth Edison NRC Docket Nos. 50-295/304 Mr.
A.
Schwencer: August 8, 1979 Altnough, to date, changes in the actuation setpoint would not have precluded any of the water hammer incidents at Zion Station, Commonwealth Edison's evaluation did indicate that raising the actuation setpoint after installation of J-tubes on all steam generators could possibly prevent future water hammer incidents in the following two situations:
1.
Hot standby or low power operation in which, with automatic auxiliary feedwater flow secured, operator inattention to steam generator level results in the level dropping below the top of the feedring; and 2.
Reactor trips from power ranges between 15 and 27% power may result in partial uncovery of the feedring, but the water level dces not fall sufficiently to automatically actuate feedwater flow.
At Zion Station, both of these situations are very low probability cases.
For instance, during low power operation an operator is normally assigned full time to monitor steam generator level con-trol, thus ensuring that the feedring remains full of water.
With regard to reactor trips from power ranges between 15 and 27% power, Zion Station is normally base loaded at full-rated power and encounters the subject range only for brief periods several times a year during reactor startups to full power.
In addition, Zion operating procedures require manual initiation of auxiliary feedwater flow after any reactor trip, thus ensuring that the feedring remains full of water.
For these reasons, commonwealth Edison has concluded that raising the actuation serpoint for automatic auxiliary feedwater flow after J-tube installation has been completed is not warranted.
In addition, Commonwealth Edison's evaluation also indicated that the above situations are applicable to all Model 51 Steam Generators and hence, any changes to actuation setpoints should be approached on a generic basis.
Per recent discussions with the NRC Staff, additional information concerning Zion Station water hammer history was requested.
The attached Tables 1 and 2 provide the water hammer history of Zion Units 1 2nd 2, respectively.
As Table 1 indicates, 840 543
Commonwetith Edison NRC Docket Nos. 50-295/304 Mr.
A.
Schwencer: August 8, 1979 Zion Unit 1 has had five water hammers in the last eight months, primarily on the 1C Steam Generator.
As a result, during the Fall 1979 retueling outage J-tubes will be installed on this steam generator.
J-tubes were installed on the 2C Steam Generator of Zion Unit 2 in March 1978.
The remaining steam generators will be modified as outlined in Reference (a) which also includes a discussion as to why an accelerated cchedule for J-tube installation is not necessary.
Note that since the installation of J-tubes on 2C Steam Generator, there have been no water hammers on Unit 2.
Please address any additional questions that you might have to this office.
Very truly yours, Cordell Reed Assistant Vice-President attachments 1 b' k BAO J
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t TABLE 1
T O'I U"I T 1 ' WP. T II' Um F T STORY A t' X. Fu.
LER No.
Rx Trip /3.I.
Plant F l o'.
S.G.
Date 150-295/1 (Time)
Condition (GPi L isficcted FW Ring namage Comments 6/20/76 76-S-1 1427/1427 20%
N.A.
1D Covered Hone Aux. FW Off 9/26/76 N.A.
N.A./1801 To CSD N.A.
1D Uncovered None Aux. FW Off 7/8/77 77-91 0033/0038 IISD 300 1C Uncovered None Admin. Change to 100-105 GPM, Max.
Aux. FW Per Pump 9/14/78 78-95 0817/0819 IISD Within 1D Uncovered None EOP-1 Limits I
12/5/78 78-130 N.A./0150 IISD N.A.
1C N.A.
None Cooling 1 LCV-FW520 12/5/78
[78-130 N.A./0428 IISD N.A.
1C N.A.
None U Condensate ca 3/2/79 79-12 0827/0827 N.A.
N.A.
1C Uncovered 1 MOV -
Have Tape of FW0017*
Water llammer 3/16/79 trG 9-19 0431/0524 IISD 150-D200 1A or 1C Uncovered 1 MOV -
IIave Tape of
--O 100 FWOOl7**
Water llammer 6/8/79 79-44 0629/0645 IISD 150->200 1D Uncovered None IIave Tape of Water Hammer U.A.
- Not Applicable
- Cracked printed circuit board 2
- Equipment found inoperable, not due to Water llammer
i e
TABLE 2 HON UNIT 2 WATER HAMMER IIISTORY Aux. FW LER No.
Rx Trip /S.I.
Plant Flow S.G.
Dat_o (50-304/)
(Time)
Condition (GPM)
Affected FW Ring Damage Comments 12/30/74 3/7/75 1357/1424 IISD N.A.
Suspected Uncovered None First Docu-letter to Water mented Water J.G.
Koppler IIammer IIamracr/S. I.
5/25/76 76-S-1 1053/1129 IISD 100 2C Uncovered None IIigh 4p on D&D Loops 6/20/76 76-S-3 0103/0205 IISD N.A.
2C Uncovered None 7/10/77 77-S-3 1121/1149 II3 D N.A.
2C Uncovered MOVs Occurred when
- FWOOl6, main FW by-17, 10** pass opened N.A.
- Not Applicable
- Equipment found inoperable, not due to Water 11ammer O?
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