Information Notice 1986-51, Excessive Pneumatic Leakage in the Automatic Depressurization System
| ML031220687 | |
| Person / Time | |
|---|---|
| Issue date: | 06/18/1986 |
| From: | Jordan E NRC/IE |
| To: | |
| References | |
| IN-86-051 | |
| Download: ML031220687 (4) | |
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SSINS No.: 6835
118 ORIGtINA IN 86-51 UINITED STATES R CE IVED
NUCLEAR RtEGULATORY COMMISSION Eant D. Withers
OFFICE OF INSiPECTION AND ENFORCEMENT Vice resident. Nuclear
WASHINIGTON, D.C. 20555 JUN 241986 Route To:
lune 18, 1986 IE INFORMATION NOTICE NO. 86-51. EXCESSIVE PNEUMATIC LEAKGE iNHRE-
AUTOMATIC DEPRESSURIZATION SYSTEM
Addressees
All boiling water reactor (BWR) nuclear power facilities holding an operating
license (OL) or construction permit (CP).
Purpose
This notice is being provided to alert recipients to a potentially significant
problem pertaining to possible pneumatic supply leakage through pathways near
the accumulators serving automatic depressurization system (ADS) safety relief
valves. It is expected that recipients will review this notice for applicabil- ity to their facilities. However, suggestions contained in this notice do not
constitute NRC requirements; therefore, no specific action or written response
is required.
Past Related Documents:
IE Bulletin No. 80-01: "Operability of ADS Valve Pneumatic Supply,"
January 11, 1980
IE Bulletin No. 80-25: "Operating Problems with Target Rock Safety-Relief
Valves at BWRs," December 19, 1980
IE Information Notice 85-35: "Failure of Air Check Valves to Seat,"
April 30, 1985 IE Inspection Report 50-458/84-18: "Integrated Design Inspection of the River
Bend 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 operating
more than was normal, the licensee at Grand Gulf determined.that excessive
instrument air flow was required to maintain the ADS's normal operating pres- sure of 183 psig. The licensee isolated the air supply and observed header
pressure 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 licensee
measurements, the air system was leaking at a rate of 600-1200 standard cubic
Copies 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 86-51 PGE OAR Action - M. H. Malmros (Due 9/5/86)
., : . :! lo
IN 86-51 June 18, 1986 feet per hour (SCF/hr). This pressure decrease and the previously observed
excessive air makeup indicated that the ADS receiver and accumulator combined
leakage exceeded the long-term requirements for ADS safety relief valve actuation
specified in the final safety analysis report (FSAR). The FSAR assumes a leak
rate 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 leakage
requirements.
The air supply to the ADS valves was reinstated and the instrument air pressure
remained above the minimum operating pressure of 150 psig. However, if there
had been a failure of the non-safety portions of the instrument air system (the
compressors or the piping upstream of the receiver), the ADS system would have
not remained operable. Therefore, the licensee declared the ADS inoperable and
shut down the reactor for repairs. Investigation of the cause of the high leak
rate showed that the accumulator relief valves in the drywell were defective.
It was determined that 16 of 17 were leaking and required rework and these
valves were repaired. Normal operating pressure was reduced from 183 psig to
165 psig. This increases the margin between the operating pressure and the
relief set point (190 psig). The operating pressure is now below the pressure
(171 psig) at which seat leak tightness is tested yet sufficiently above the
minimum required pressure (110 psig) for meeting FSAR commitments.
Discussion:
Previous generic correspondence has identified problems in pneumatic-systems
that could affect ADS operability. IE Bulletins 80-01 and 80-25 noted problems
with the control air system in maintaining operability of the ADS. In the case
of Bulletin 80-01, the ADS was not operable for all events because of combined
misapplication of the accumulator inlet check valve, lack of accumulator
in
testing, and seismic considerations. For Bulletin 80-25, excessive pressure
the pneumatic. supply system caused an ADS safety relief valve to stay open when
it should have closed. The reactor coolant system was then depressurized while
the reactor was operating at power.
The problem at Grand Gulf described above is analogous to the situation described
in Information Notice 85-35 and the referenced inspection report on the River
Bend plant. In that case, back leakage through the inlet check valve (rather The
than accumulator relief valves) resulted in reduced accumulator pressure.
Grand Gulf ADS accumulators are designed asSection III, Class 3 components, according to the ASME Boiler and Pressure Vessel Code. Relief valves are valves
attached to the accumulators for overpressure protection. Such relief This
may not be found at all plants, depending on the accumulator design.
mechanical
event indicates that such leaking relief valves and any other leaking of the
joints provide pathways for air leakage that compromise the operability
ADS during accident conditions.
Only portions of pneumatic systems in nuclear power plants are designed as
emergency
safety systems. In general, the air compressors are not powered from of off-site
buses; therefore, the supply of air is dependent on the availability
power. Further, piping between the air compressors and the safety grade
IN 86-51 June 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 resistant
portions of the pneumatic systems, including appurtenances such as relief
valves and check valves. Although the TS do not require monitoring of the ADS
pneumatic supply system makeup rate, lack of monitoring the makeup rate sub- jects the ADS to potentially undetected excessive leakage. This could result
in the ADS being unable to meet its design bass requirements upon loss of the
non-safety-related instrument air system.
No written response to this information notice is required. If there are any
questions regarding this matter, please contact the Regional Administrator of
the appropriate NRC regional office or this office.
a i Jsordan, DiTrec
Divisio of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact:
Vern Hodge, IE
(301) 492-7275 Attachment: List of Recently Issued IE Information Notices
Attachment 1 IN 86-51 June 18, 1986 LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information Date of -
Notice No. Subject Issue Issued to
86-50 Inadequate Testing To Detect 6/18/86 All power reactor
FailureaOf Safety-Related facilities holding
Pneumatfc Components Or an OL or CP
Systems
86-49 Age/Environment Induced 6/16/86 All power reactor
Electrical Cable Failues facilities holding
86-48 Inadequate Testing OfBoron 6/13/86 All BWR facilities
Solution Concentration In The holding an OL or CP
Standby Liquid Control System
86-47 Feedwater Transient With 6/9/86 All BWRs and PWRs
Partial Failure Of The facilities holding
Reactor Scram System an OL or CP
86-46 Improper Cleaning And Decon- 6/12/86 All power reactor
tamination Of Respiratory facilities holding
Protection Equipment an OL or CP and
fuel fabrication
facilities
Potential Falsification Of 6/10/86 All power reactor
86-45 facilities holding
Test Reports On Flanges
Manufactured By Golden Gate an OL or CP and
Forge And Flange, Inc. research and test
facilities
Failure To Follow Procedures 6/10/86 All power reactor
86-44 facilities holding
When Working In High Radiation
research and test
reactors
Problems With Silver Zeolite 6/10/86 All power reactor
86-43 facilities holding
Sampling Of Airborne Radio- iodine an OL or CP
OL = Operating License
CP = Construction Permit