Information Notice 1986-51, Excessive Pneumatic Leakage in the Automatic Depressurization System

Excessive Pneumatic Leakage in the Automatic Depressurization System

ML031220687
Person / Time
Issue date:	06/18/1986
Revision:	0
From:	Jordan E L NRC/IE
To:
References
IN-86-051
Download: ML031220687 (4)

, -4 a .".'118 ORIGtINASSINS No.: 6835IN 86-51UNUCLEAR ROFFICE OF INSWASHININITED STATES R CE IVEDtEGULATORY COMMISSION E ant D. WithersiPECTION AND ENFORCEMENT Vice resident. NuclearIGTON, D.C. 20555 JUN 241986Route To:lune 18, 1986EXCESSIVE PNEUMATIC LEAKGE iNHRE-AUTOMATIC DEPRESSURIZATION SYSTEMIE INFORMATION NOTICE NO. 86-51.

Addressees

All boiling water reactor (BWR) nuclear power facilities holding an operatinglicense (OL) or construction permit (CP).

Purpose

This notice is being provided to alert recipients to a potentially significantproblem pertaining to possible pneumatic supply leakage through pathways nearthe accumulators serving automatic depressurization system (ADS) safety reliefvalves. It is expected that recipients will review this notice for applicabil-ity to their facilities. However, suggestions contained in this notice do notconstitute NRC requirements; therefore, no specific action or written responseis required.Past Related Documents:IE Bulletin No. 80-01:January 11, 1980"Operability of ADS Valve Pneumatic Supply,"IE Bulletin No. 80-25: "Operating Problems with Target Rock Safety-ReliefValves at BWRs," December 19, 1980IE Information Notice 85-35: "Failure of Air Check Valves to Seat,"April 30, 1985IE Inspection Report 50-458/84-18: "Integrated Design Inspection of the RiverBend Station," Section 2.4, "Automatic Depressurization System Design,"August 16, 1984

Description of Circumstances

On March 19, 1986, after noting that the booster compressors were operatingmore than was normal, the licensee at Grand Gulf determined.that excessiveinstrument air flow was required to maintain the ADS's normal operating pres-sure of 183 psig. The licensee isolated the air supply and observed headerpressure to decrease from 183 to 155 psig in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Based on licenseemeasurements, the air system was leaking at a rate of 600-1200 standard cubicCopies to: Withers, Yundt, Lentsch, Orser, Steele, E. Burton, E. Jordan, A. Holm,LIS, C. A. Olmstead, S. Hoag, S. Sautter, TNP:GOV REL F:NRC CHRONO,TNP:GOV REL F:NRC IE Information Notice 86-51PGE OAR Action -M. H. Malmros (Due 9/5/86)., : .:! lo IN 86-51June 18, 1986 feet per hour (SCF/hr). This pressure decrease and the previously observedexcessive air makeup indicated that the ADS receiver and accumulator combinedleakage exceeded the long-term requirements for ADS safety relief valve actuationspecified in the final safety analysis report (FSAR). The FSAR assumes a leakrate of 1.0 SCF/hr for each valve on the system. Technical Specifications (TS)require that eight ADS valves be operable, but they do not specify leakagerequirements.The air supply to the ADS valves was reinstated and the instrument air pressureremained above the minimum operating pressure of 150 psig. However, if therehad been a failure of the non-safety portions of the instrument air system (thecompressors or the piping upstream of the receiver), the ADS system would havenot remained operable. Therefore, the licensee declared the ADS inoperable andshut down the reactor for repairs. Investigation of the cause of the high leakrate showed that the accumulator relief valves in the drywell were defective.It was determined that 16 of 17 were leaking and required rework and thesevalves were repaired. Normal operating pressure was reduced from 183 psig to165 psig. This increases the margin between the operating pressure and therelief set point (190 psig). The operating pressure is now below the pressure(171 psig) at which seat leak tightness is tested yet sufficiently above theminimum required pressure (110 psig) for meeting FSAR commitments.Discussion:Previous generic correspondence has identified problems in pneumatic-systemsthat could affect ADS operability. IE Bulletins 80-01 and 80-25 noted problemswith the control air system in maintaining operability of the ADS. In the caseof Bulletin 80-01, the ADS was not operable for all events because of combinedmisapplication of the accumulator inlet check valve, lack of accumulatortesting, and seismic considerations. For Bulletin 80-25, excessive pressure inthe pneumatic. supply system caused an ADS safety relief valve to stay open whenit should have closed. The reactor coolant system was then depressurized whilethe reactor was operating at power.The problem at Grand Gulf described above is analogous to the situation describedin Information Notice 85-35 and the referenced inspection report on the RiverBend plant. In that case, back leakage through the inlet check valve (ratherthan accumulator relief valves) resulted in reduced accumulator pressure. TheGrand Gulf ADS accumulators are designed asSection III, Class 3 components,according to the ASME Boiler and Pressure Vessel Code. Relief valves areattached to the accumulators for overpressure protection. Such relief valvesmay not be found at all plants, depending on the accumulator design. Thisevent indicates that such leaking relief valves and any other leaking mechanicaljoints provide pathways for air leakage that compromise the operability of theADS during accident conditions.Only portions of pneumatic systems in nuclear power plants are designed assafety systems. In general, the air compressors are not powered from emergencybuses; therefore, the supply of air is dependent on the availability of off-sitepower. Further, piping between the air compressors and the safety grade IN 86-51June 18, 1986 portions of the system is not designed to withstand major seismic events.Thus the components that require compressed air to perform their safety func-tion are heavily dependent on the leak-tightness of the seismic resistantportions of the pneumatic systems, including appurtenances such as reliefvalves and check valves. Although the TS do not require monitoring of the ADSpneumatic supply system makeup rate, lack of monitoring the makeup rate sub-jects the ADS to potentially undetected excessive leakage. This could resultin the ADS being unable to meet its design bass requirements upon loss of thenon-safety-related instrument air system.No written response to this information notice is required. If there are anyquestions regarding this matter, please contact the Regional Administrator ofthe appropriate NRC regional office or this office.a i Jsordan, DiTrecDivisio of Emergency Preparednessand Engineering ResponseOffice of Inspection and Enforcement

Technical Contact:

Vern Hodge, IE(301) 492-7275

Attachment:

List of Recently Issued IE Information Notices Attachment 1IN 86-51June 18, 1986LIST OF RECENTLY ISSUEDIE INFORMATION NOTICESInformation Date of -Notice No. Subject Issue Issued to86-5086-4986-4886-4786-4686-4586-4486-43Inadequate Testing To Detect 6/18/86FailureaOf Safety-RelatedPneumatfc Components OrSystemsAge/Environment Induced 6/16/86Electrical Cable FailuesInadequate Testing Of Boron 6/13/86Solution Concentration In TheStandby Liquid Control SystemFeedwater Transient With 6/9/86Partial Failure Of TheReactor Scram SystemImproper Cleaning And Decon- 6/12/86tamination Of RespiratoryProtection EquipmentPotential Falsification Of 6/10/86Test Reports On FlangesManufactured By Golden GateForge And Flange, Inc.Failure To Follow Procedures 6/10/86When Working In High RadiationAreasProblems With Silver Zeolite 6/10/86Sampling Of Airborne Radio-iodineAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll BWR facilitiesholding an OL or CPAll BWRs and PWRsfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CP andfuel fabricationfacilitiesAll power reactorfacilities holdingan OL or CP andresearch and testfacilitiesAll power reactorfacilities holdingan OL or CP andresearch and testreactorsAll power reactorfacilities holdingan OL or CPOL = Operating LicenseCP = Construction Permit