ML20126E767
| ML20126E767 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 12/23/1992 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9212290309 | |
| Download: ML20126E767 (3) | |
Text
.
Bear a y Power Statton SNppmgport, PA 15077 4 04 (412) 393 5255 December 23, 1992 JOHND $lEBER Wce Pres 4ent, Nacicat Group U.
S.
Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555
Subject:
Beaver Valley Power Station, Unit No. 2 Docket No. 50-412, License No. NPF-73 Auxiliary Feedwater System Waterhammer By letter dated November 5,
1992, the NRC forwarded Inspection Report Nos.
50-334/92-20 and 50-412/92-20 and requested a review of "waterhammer" events occurring on the Beaver Valley Unit 2 (BV-2)
Auxiliary Feedwater System (FWE) and our plans to resolve this issue.
We have reviewed past "waterhammer" events on the FWE system and have determined that the root cause of these events can be attributed to back leakage and bonnet leakage on the FWE check valves, which will be addresed through valve upgrade.
Leakage on the FWE check valves has resulted in the following three conditions occurring in the FWE system:
1.
Main feedwater flow recirculation into the FWE system (Intra System Recirculation).
2.
Steam pocket formation ir FWE piping with subsequent steam pocket collapse (slugging noise).
3.
Steam pocket formation in FWE piping with a FWE pump start and unthrottled auxiliary feedwater flow resulting in a steam pocket collapse waterhammer.
The auxiliary teedwater piping system has been evaluated for the effects of the postulated waterhammer events.
The evaluation includes operating conditions for
- deadload, pressure, thermal and waterhammer transient londing.
In cases where the pipe stress levels under the postulated water hammer transients exceed normal and upset
- values, an assessment cif system operability was laade to faulted code allowables.
In all cases system operability was demonstrated.
In addition, actions have been taken to detect and mitigate intra system recirculation and steam pocket formation in the FWE system in order to reduce the probability of a
waterhammer event from occurring.
Our sho::t and long term corrective actions to resolve this issue are provided in Attachment 1.
r'
'(l 9.90088 9212290309 921223 PDR ADOCK 05000412 G
..- 4
-Auxiliary Feedwater System Waterhammer 1c Page 2 If there are any questions concerning this matter, please contact _.
Mr. Nelson Tonet at (412) 393-5210.
Sincerely, bW J.
D.
Sieber Attachment cc:
Mr. L.
W.
Rossbach, Sr. Resident Inspector Mr. T-T.
Martin, NRC Region I Administrator Mr. A.
W.
De Agazio, Project Manager Mr. M.
L.
Bowling (VEPCO) 1.-
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ATTACHMENT 1 Short and Lona Term Corrective Actions The following actions have been taken to detect and mitigate intra system recirculation and steam pocket formation in the FWE system.
The operator-checks the FWE system pipe temperatures once por shift to detect the onset of intra system recirculation.
If the pipe temperatures exceed 120*F, the FWE system is flushed per Operating Manual Procedure OM 2.24.4.Q
" Steam Binding in Auxiliary.Feedwater System".
This procedure provides a
means for flushing out the FWE system by throttling the FWE system flow to ' prevent-a waterhammer from occurring.
Temporary pressure gauges have been installed on all three auxiliary feedwater lines (A,
B C).
These gauges are located in the piping segment upstream of the main feedwater system isolation check valves, and provide a means to check
'l the FWE system for a potential steam pocket formation.
i The operators check the FWE system for noise / slugging and logs the pressure on the temporary gauges once per shift for indications of steam oocket formation in the FWE system.
If Indications of a steam pocket exists, then'the FWE system is flushed per OM 2.24.4.Q to preclude the existance of' steam pockets.
Appropriate Operating Manual procedures have been revised to monitor the FWE system flow recorders for spiking after power changes of greater than 10%.
Spiking on the FWE flow l
recorders has also been an indicator of steam pocket formation.
Operating Manual Procedure OM 2.24.4.J " Auxiliary Feedwater Pump Start" has_ been' revised to initiate inspection of FWE system for waterhammer damage following any automatic start of an auxiliary feedwater pump.
The FWE pump Operating Surveillance Tests have been' revised to ensure _ that the downstream-check valves are_ properly seated following pump testing.
Inspections of the 'FWE system piping inside and outside of
~ignificant.
containment will be' performed following any-s noise / slugging occurrence.
T he' following long term actions.will be implemented during the Unit '2 Fourth Refueling Outage.
FWE system check valves (FWE-42A, 42B, 43A, 43B, 44A and 4
44B) will be modified to minimize seat and bonnet leakage.
Temporary instrumentation will-be installed _on the FWE-l system to verify that the FWE check valve modifications have i
been effective and to quantify and assess any additional-transient' loadings.
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