ML20206B547
| ML20206B547 | |
| Person / Time | |
|---|---|
| Issue date: | 03/27/1987 |
| From: | Thomasson N NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Rubin S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| Shared Package | |
| ML20206B554 | List: |
| References | |
| AEOD-E705, NUDOCS 8704090205 | |
| Download: ML20206B547 (2) | |
Text
P l-4 b March 27, 1987 AE0D/E705 MEMORANDUM FOR: Stuart D. Rubin, Chief Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data THRU: Patrick Baranowsky, Chief Reactor Systems Section 1 Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data FROM: Neill Thomasson, Senior Reactor Systems Engineer Reactor Systems Section 1 Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data
SUBJECT:
RWCU SYSTEM AUTOMATIC ISOLATION AND SAFETY CONSIDERATIONS Enclosed is an er.gineering evaluation report that addresses the causes for the frequent automatic isolation of the BWR reactor water cleanup (RWCU) system and the safety significance of the events. The scope of the study encompassed the events reported between January 1984 and October 1986 in Licensee Event Reports (LERs) and in some NRC Daily Reports, which were the only reports of certain recent RWCU system leakage events at some earlier vintage operating reactors.
This study was initiated following two such events at Dresden 2 and Millstone 1 in the summer of 1986.
Based on the results of the study, RWCU system events constitute approximately 15% of all LERs submitted by licensees operating plants with RIICU system leak detection system (LDS) initiated isolation capability. About 74% of all PWCU system isolation events during the period of the study were spurious. The valid isolation events, i.e., those associated with actual high system dif-ferential flow rates or high system fluid or area temperatures exceeding the monitor trip setpoints, were generally of no or little safety significant. The ;
two most serious events were a Dresden 2 filter-demineralizer valve leak that released 140,000 gallons of coolaat, which collected without harm in the reactor building basement torus room, and a high-energy coolant leak from a ruptured Nk k$" kjj27 PDR
9 e> Stuart D. Rubin F vent line on the regenerative heat exchanger at Millstone 1 that resulted in a discharge of 2,200 gallons of coolant. No evidence was found in the events covered by the study to suggest significant safety concerns associated with the operating experience.
The spurious isolations were largely associated with lack of temperature co.rpensation of differential flow sensors and the design of the differential flow rate LDS, such as the sensor and flow orifice location, orifice size, and the location of the differential flow rate meter on a "back panel" in the con-trol room.
About half of the spurious isolations were initiated by the LDS temperature sensors monitoring area and differential temperatures across room supply and exhaust ventilation ducts. The LDS temperature-based spurious isolations were principally due to the daily surveillance testing of these temperature sensor circuits and the design sensitivity of the Riley Panalarm temperature detectors to electronic noise pulses..
i Licensees have implemented or. proposed a number of design and procedural improvements that appear to have solved many of the problems contributing to spurious isolations of the RWCU system. These actions are characterized in the enclosed report. It is suggested that an industry organization, such as INPO, may find useful the information in the report in studies of ongoing maintenance programs and evaluations of new plant operating experience to help improve
- licensee operations. The study characterizes the design and operational changes which can be implemented to reduce spurious engineered safety feature actuation by the RWCU system. Further, it is suggested that the reporting of RWCU events be limited to those having actual or potential safety-related impacts and that NRR reevaluate the need for daily testing of the RWCU system LDS temperature monitors in view of the relatively low safety significance of the recently reported events.
/4 Neill Thomasson, Senior Reactor Systems Engineer Peactor Systems Section 1 i Reactor Operations Analysis Branch Office for Analysis and Evaluaton I of Operational Data
Enclosure:
As stated DISTRIBUTION:
PDR WLanning ROAB CF KBlack ROABSR(conc.) MWilliams ,
NThomasson FHebdon PBaranowsky CHeltemes SRubin AE0D SF Plam j OFC :RCA OD :SC: A :AE00: BC:ROAB : D:AEOD : : :
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NAME :NTi n :PBa sky : SRubin : DJ es : : :
i DATE :3/y1/87 :3/U1(87 :3/J7/87 / /87 : :-
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