ML20204H364
| ML20204H364 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 08/23/1984 |
| From: | NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20204H359 | List: |
| References | |
| TASK-AE, TASK-T421 AEOD-T421, NUDOCS 8411120268 | |
| Download: ML20204H364 (3) | |
Text
. , . .
AEOD TECHNICAL REVIEW REPORT
- UNIT: Peach Bottom 2 TR REPORT NO. AE0D/T421 DOCKET NO.: 50-277 DATE: August 23, 1984 LICENSEE: Philadelphia Electric Co. EVALUATOR / CONTACT: M. Chiramal NSSS/AE: GE/Bechtel
SUBJECT:
DESIGN DEFICIENCY IN STANDBY GAS TREATMENT SYSTEM (SBGTS)
EVENT DATE/LER No.: April 27, 1984/84-008 SUP9tARY Peach Bottom 2 LER 84-008 describes an event that occurred on April 27, 1984.
The plant SBGT system was manually started to de-inert the Unit 2 drywell, however, no flow was achieved when the A fr was started because both the inlet and outlet dampers failed to open. As a result of an investigation of the event, it was determined that the potentiel existed for a single failure to prevent the fulfillment of the safety function of the SBGTS. This was
. determined to be due to a design deficiency of the flow meter that monitors the flow through the fan. Based on the generic implication of such a design deficiency, we reviewed the design of the SBGTS of several operating BWRs.
The plants reviewed were: Brunswick 1 and 2, Quad Cities 1 and 2, Hatch 1 a.nd 2,= Cooper, Vermont Yankee and Pilgrim. Our review showed that none of these plants had the same design deficiency of the Peach Bottom plant. At the Peach Bottom station the licensee has proposed to correct the problem by replacing
.the' existing flow switch with a flow sensor using a duct pitot tube. We have forwarded a copy of the Peach Bottom 2 LER 84-008 to IE for consideration in the process of evaluating AEOD Engineering Evaluation Report (AE0D/E 410)
" Operational Experiences involving SBGT systems which illustrate potential common cause failure or degradation mechanisms." This report had recommended the issuance of an IE Information Notice on problems associated with SBGTS at operating BWRs.
Based on the above considerations, we believe that no further AE00 action is required regarding the SBGTS design deficiency at Peach Bottom 2.
- This document supports ongoing AE00 and NRC activities and does not represent the positions or requirements of the responsible NRC program offices.
kk$0h S
0 1 d
INTRODUCTION During the routine screening of LERs, Peach Bottom 2 LER 84-008 was identified as one that required follow up because.of its potential generic implication.
This LER described an event that occurred on April 27, 1984 involving the Standby Gas Treatment System. The SBGT system A fan was manually started to de-inert Unit 2 drywell. However, no flow was achieved because both the inlet and outlet dampers failed to open due to failure of solenoid value, SV-0009.
The Peach Bottom 2 and 3 SBGT system consists of filter assemblies A and B and three fans, A, B and C ducted in parallel. The A fan is aligned to Unit 2, with B fan as a standby, and the C fan is utilized for Unit 3 with the B fan as a stanuby. During investigation of the failure of the solenoid valve, the licensee determined that the potential existed for a single failure to have prevented the SBGTS from performing its safety function. This was due to the location of sensing taps of the differential pressure switch associated with the A fan which monitors the fan flow. The high and low sensing taps of the dp switch are connected between the inlet and outlet dampers of the A fan and with the dampers c1csed and the fan running the switch would have sensed a differential pressure and prevented the automatic starting of the standby B fan as required.
The SBGT system at several other operating BWRs also utilize the standby arrangement similar to the Peach Bottom station. Hence this type of failure could have generic implications. Because of this, we reviewed the updated FSARs of Brunswick 1 and 2, Quad Cities 1 and 2, Hatch 1 and 2, Cooper, Vermont Yankee and Pilgrim to see if this concern was valid.
The review of the Peach Bottom 2 event and the review of the design of SBGTS at the above plant are discussed below.
, DISCUSSION At the Peach Bottom station, the inlet and outlet dampers on the SBGT system l fans are actuated by pneumatic operators controlled by a pilot solenoid valve.
This solenoid valve is normally energized when the corresponding fan is started.
When en.rgized the solenoids pass a pneumatic signal to open the inlet and outlet dampers. In this instance when the A fan was started solenoid valve SV 0009 failed to operate and the dampers remained closed. The licensee has replaced the defective solenoid and the cause of failure of the SV is under further analysis. The rephced solenoid was satisfactorily tested and placed
, in service the day following the event. The licensee is planning to replace
! the standby start differential pressure switches on the A and C fans with a I flow sensor using a duct pitot tube. Implementation is scheduled for July 1984. An engineering evaluation is being performed by the licensee to determine optimt.m positioning of the sensors in the duct work to ensure proper flow sensing. In the interim a daily routine test of the operability of the SBGTS fans inlet and outlet dampers will be performed. Based on these corrective actions we consider that the problem is being adequately addressed at the Peach Bottom station.
2 1
e
' We reviewed the information provided in the updated FSARs of Quad Cities 1 and 2, Hatch 1 and 2, Brunswick 1 and 2, Cooper,' Vermont Yankee and Pilgrim regarding the design and operation of SBGT systems. Although most of these plants utilize a differential pressure sensing flow element and flow transmitter to
-monitor flow through the SBGT system, none of the plants reviewed has the specific arrangement utilized at the Peach Bottom plant. In all cases reviewed the dp is measured across a flow element that is located in the suction or discharge duct of the SBGTS fan and with the fan running and dampers closed these elements would not register spurious flow. Thus the problem seen at Peach Bottom is not evident at the other plants reviewed.
Recently AE00 issued an Engineering Evaluation Report AE0D/E 410 entitled
" Operational Experiences involving SBGT systems which illustrate potential common cause failure or degradation mechanisms" which studied SBGTS events similar to the one that occurred at Peach Bottom 2. This report recommended that IE consider the issuance of an Information Notice to alert licensees of
-operating BWRs of the problems associated with SBGT systems. We have forwarded a copy of Peach Bottom 2 LER 84-008 to IE for inclusion in the follow-up consideration of AE0D/E410. 4 FINDINGS AND CONCLUSION Based on the review of the Peach Bottom 2 event and the review of the design and operation of the SBGT system at Quad Cities 1 and 2, Brunswick 1 and 2, Hatch 1'and 2, Cooper, Vermont Yankee and Pilgrim stations, the following findings and conclusion were reached.
- 1) The physical arrangement of the flow element that monitors the SBGT system fan flow at Peach Bottom-2 had a potential design deficiency in that it could indicate spurious flow when the fan is operating with the inlet and outlet dampers closed. This would prevent the required automatic starting of the standby fan as designed.
- 2) At Peach Bottom 2 and 3, the licensee has taken or is planning to take adequate corrective actions to address the problem.
- 3) The specific design deficiency at Peach Bottom was not apparent in our review of the design and operation of the SBGT system at certain other operating BWRs.
Based on these findings we conclude that the problem identified at Peach Bottom has been adequately. corrected by licensee actions. We can also conclude that the problem does not appear to be generic based on the review of a limited number of plants. However we believe that the description of the event should be disseminated to licensees at other operating plants and hence have reqwsted IE to consider the Peach Bottom event in the follow up actions being taken by them in response to our previous Engineering Evaluation Report AE0D/E430. (This event has already been included in the INP0 NOTEPAD system to alert the operating plants.)
3