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' D. C. Cook 1, 2 (50-315,-50-316)
Cincinnati Gas and Electric Company Zimmer -(50-358)
.The Cleveland Electric Illuminating Company Perry 1, 2 (50-440,30-441)
. Commonwealth Edison Company g
Braidwood 1, 2-(50-456,-50-457) y,4 g
Byron 1, 2-(50-454,50-455)
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[ff Dresden 1, 2, 3 -(50-10, 50-237,'50-249)
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Zion 1, 2 (50-295,-50-304)
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Palisades-(50-255) t 7y g $ '
Midland 1, 2-(50-329, 50-330)
-Dairyland Power Corporation 1.AC3WR -(50-409)
'Ihe Detroit Edisea Company Fermi 2*(50-341)
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Illinois Power Company Clinton 1, 2 (50-461, 462)
- Iowa Electric Light and Power Company, Duane Arnold.(50-331)
' Northern Indiana Public Service Company Bailly-(50-367)
" Northern States Power Company Monticello-(50-263)
Prairie Island 1, 2 (50-282, 306)
- Public Service of Indiana Marble 11111 1, 2'(50-546, 50-547)
-Toledo Edison Company Davis-Besse 1-(50-346)
-Union Electric Company Callaway 1, 2 140-483,60-486)
'Misconsin Electric Power Company Point Beach 1, 2'(50-266, 50-301)
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. Illinois Department of Nuclect Safety I
Gary N. Wright, Manager, Nuclear Facility Safety f[f OO O
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SSINS No.: 6835 Accession No.:
8103300415-IN 81 '
UNITED STATES NUCLEAR REGULATORY COMMISSIQ'1 0FFICE OF INSPECTION AND ENFORCEMtNT WASHINGTON, D.C.
20555 September 3, 1981 IE INFORMATION NOTICE NO. 81-27:
FLAMMABLE GAS MIF. LURES IN THE WASTE GAS DECAY TANKS IN PWR PLANTS Description of CircumstanceC In July 1981, hydrogen ignition occurred in one gaseous waste decay t'ank at San Onofre Unit 1 while tne plant was in cald shutdown.
This resulted in a release of about 8.8 curies of noble gases and minor tank damage.
The cause of the hydrogen ignition was air contamination of the inert nitrogen system which is used to control the hydrogen-oxygen concentrations in the tank.
The source of air was identified as instrument air leaking through check valves at the cross connections between instrument air and nitrogen lines.
Under normal operating conditions, the pressure in the instrument air system is higher than that of the nitrogen system. These cross connections had been installed in response to TMI Action Plan requirement item II.E.1.2 of NUREG-0737.
The nitrogen system provided a backup gas supply to the air-operated steam supply valve for the steam-driven auxiliary feedwater pump.
This backup was installed to provide a " safety grade" auxiliary feedwater system that satisfies the single-failure criteria.
Other cross connections, which apparently did not leak air into the nitrogen system, had been previously installed in response to TMI Action Plan requirement II.G.1 of NUREG-0737 to provide a redundant gas supply to the air-operated pressurizer relief valves and the associated block valves.
Following the occurrence, the licensee sampled all potentially affected tanks and determined that most of the tanks had oxygen levels above 10 to 15 percent.
Generally, the gas in pressurized water reactor (PWR) waste gas systems is hydrogen rich and the oxygen concentration is controlled to prevent flammable gas mixtures.
Flammable concentration of gas mixtures can be prevented by limiting either the hydrogen or the oxygen concentration to less than 3 percent.
To eliminate the possibility of recurrence, the licensee has now completely separated those portions of the nitrogen system that are a backup supply to the air system from the balance of the nitrogen system that supplies cover gas.
Bottles of compressed nitrogen are now used to provide the backup to the air system.
We are aware of another instance of flammable mixtures in waste gas tanks.
In August 1980, Arkansas Power and Light Company (AP&L) discovered flammable concentrations of hydrogen and oxygen in the waste gas decay tanks at Arkansas Nuclear One, Unit 1.
The flammable gas mixtures were created after the primary coolant picked up oxygen from the air during refueling and maintenance.
No ignition or explosion was reported.
p IN 81-27
-September 3, 1981 Page 2 of 2 l
It appears that-licensees need to devote mcre attention to the potential effects
^ of. nitrogen-aie system cross connections when systems are modified to use nitrogen l',_
as a backup to air systems.
If cross connections exist, the potential for the formation of flammable gas mixtures shculd be evaluated.
A sampling program to assure that flammable gas mixtures do not exist in tanks sh'ald be considered.
No written response to this information notice is required.
If you need
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additional information with regard to this subject, please contact the Director of the appropriate NRC Regional Office.
Attachment:
Recent1;. issued IE Information Notices i
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Attachment i.
-IN 81-27~
September 3, 1981
- RECENTLY IS5t'ED IE INFORMATION NOTICES g
Information Date of j
- Notice No.
Subject Issue Issued to
___ 26:
Compilation of Health.
9/3/81 All power. reactor Physicr. Related Informition
. facilities with an Items OL or CP 81-25 Open Equalizing Valvr 8/21/81' All power reactor-E of Differential 9re',sure facilities with an Transmitter Cau:ss Reactor OL or CP Scram anc Loss of Redundant Safety Signals l
81-24 Auxiliary Feed Puinp 8/5/81 All power reactor l
Turbine Bearing Failures
' facilities with an OL or CP -
(
81-23 Fuel Assembly Damaged 8/4/81 All power reactor due to, Improper Positioning facilities with an of. Handling Equipment OL or,CP l
81-22 Section 235 and 236 7/31/81 All power research Amendments to the reactor, fuel Atomic Energy Act fabrication and of 1954 reprocessing, and
. spent fuel storage
. licensees and applicants i:
81-21 Potential-Loss of Direct 7/21/81 All power reactor l
Access to Ultimate Heat Sink facilities with an OL or CP-81-20 Test Failures of Electrical 7/13/81-All power reactor l
Penetration Assemblies facilities witii an L
OL or CP l 19 Lost Parts in Primary 7/6/81 All power reactor j
Coolant System' facilities with an OL or CP OL = Operating Licenses CP = Construction Permits
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SSIN No.: 6835 Accession No.:
8103300413 IN 81-28 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 September 3, 1981 IE INFORMATION NOTICE NO. 81-28:
FAILURE OF ROCKWELL-EDWARD MAIN STEAM ISOLATION VALVES Description of Circumstances:
There have been several recent mechanical failures of the "Rockwell-Edward Flite Flow Stop Valve," a "Y" pattern globe valve made by Rockwell International, used for main steam isolation valves (MSIV) at some BWR facilities.
Operating BWR facilities using this valve include Brunswick Un!t 1 and 2, Cooper, Duane Arnold, Fitzpatrick, Hatch Unit 2, and Vermont Yankee.
Of the seven total reported mechanical failures, five occurred at Brunswick Unit 2 and one each occurred at Brunswick Unit 1 ard Hatch Unit 2.
The valve components that have failed are shown in Figure 1. The piston assembly is attached to the main disk (2) by thread engagement and then restrained from unwinding by pin (4).
The stem disk (1) is also attached to the stem (6) by thread engagement tightened to 1050 ft-lb torque specifications with an anti-rotation restraint provided by pin (3).
The valve is closed primarily by spring forces.
The valve is installed so that reactor steam pressure works to seat the main disk.
The stem disk provides pressure equalize ion action to reduce over-seat load for opening the main disk against system pressure.
The failures that have occurred involved a mechanical separation of valve i
internals.
This separation was either at the stem-to-stem-disk threaded l
connecticn or at the main-disk-to piston threaded connection.
Either failure permits the main disk to be free of the stem.
The failure in either mode results from failure of the threaded conncction, which in some cases is caused by vibration ~ induced rotation of the disk a that it becomes disconnected from its threaded mate.
Such rotation is beiieved to be caused by or aided by l
the propensity of steam flow to produce vibration and to create turning forces on valve internal components when antirotation restraint is ina&quate due to a failed or missing pin.
Other contributing causes are believed to result from reassembly of the valve after disassembly at the site; such reassembly my have included inadequately torqued connections and failure to properly install the pins.
Also, an examination of spare parts at the Brunswick site showed that the thread dimensions cn the stems and stem disks did not meet drawing tolerances.
The individual failures are described below in chronological order.
1.
In January 1976, the Brunswick Unit 2 "D" steam line inboard valve main disk separated from the piston.
There was no evidence that pin (4) was installed.
a IN 81-28 September 3, 1981 Page 2 of 2 s
2.
On January 30, 1979, the Brunswick Unit 2 "A" steam line inboard valve stem disk separated from the stem.
A square pin was used in the round hole at point (3).
The corners of the pin experienced high stress, thereby causing cracking of the pin.
3.
On January 15, 1981, the Brunswick Unit 2 "C" steam line ottboard valve main disk scparated from the piston.
There was m, evidence that, pin (4) was ever inserted.
This was deduced from finding the nole not deformed and no sign of a plug weld.
4 On March 5, 1981, the Hatch Unit 2 "A" steam line inboard valve stem disk separated from the stem.
Pin (3) was not fully inserted.
5.
On March 30, 1981, the Brunswick Unit 1 "C" steam line outboard valve stem disk separned from the stem.
Pin (3) failed and was not recovered.
6.
On July 2,1981, tne Brunswick Unit 2 "C" steam line inboard valve stem disk separated from the stem.
Pin (3) was not properly installed.
7.
On July 18, 1981, the Brunswick Unit 2 "D" steam line inboard valve main disk separated from the piston.
Pin (4) was not fully inserted.
These failures have raised concerns regarding (1) the capability of the valve to perform its required safety function and (2) increased challenges to safety systems.
However, it is notes that the failures to date have resulted in the main disk going closed (i.e., not cocking open) with.some uncertainty only as to its leak tightness.
Detailed investigation of the July failures at Brunswick Unit 2 led to the preliminary findings of possible excessive vibrations on valve internals from sceam flow turbulences created by the piping direction changes.
In addition, there was cvidence of loose thread connections.
Further investigations and evaluations are current y in progress.
Preliminary corrective actions by the licensee include increasing the stem nin size from 5/16-inch tu 3/8-inch, using three pins instead of one or two pire. and increasing the hole depth 1/8-inch into the stem.
In addition, corrective actions for the main-disk-to piston connection include adding an extra pin (of the same 1/2-inch size) and increasing the hole depth by 1/8-inch.
This information is provided as notification of a potentially significant matter that is still under review by the NRC staff.
In case the continuing NRC review finds that specific licensee actions would be appropriate, an IE circular or bulletin may be issued.
In the interim, we expect that licensees will review this inforc.u'on for applicability to their facilities.
do written response to this information is required.
If you need additional information regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Attachments:
1.
Figure 1 2.
Recently issued IE Information Notices
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STEM DISK j.
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MAIN DISK 3.
ANTIR0TATION PIN - STEM OISK TO STEM 4.
ANTIR0TATION PIN
. MAIN DISK TO PISTON 5.
STELLITED O!SK GUIDES, 3 RIBS 120* APART (OUT OF SHOWN VIEW) 6.
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IN 81-28 September 3, 1981 RECENTLY ISSUED IE INFORMATION NOTICES Information Date Ji Notice No.
Subject Issue Issued to 81-27 Flammable Gas Mixtures 9/3/81 All power reactor in the Waste Gas Decay
-facilities sith an Tanks in PWR Plants OL or CP 81-26 Compilation of Health 9/3/81 All power reactor Physics-Related Informatiu.7 facilities with an Items OL or CP 81-25 Open Equalizing Valve 8/21/81 All power reactor of Differential Pressure facilities with an Transmitter Causes Reactor OL or CP Scram and Loss of Redundant Safety Signals 31-24 Auxiliary Feed Pump 8/5/81 All power reactor Turbine Bearing Failures facilities with an OL or CP 81-23 Fuel Assembly Damaged 8/4/81 All power reactor due to Improper Positioning facilities with an of Handling Equipment OL or CP 81-22 Section 235 and 236 7/31/81 All power research Amendments to the reactor, fuel Atomic Energy Act fabrication and of 1954 reprocessing, and spent fuel storage licensees and applicants 81-21 Potential Loss of Direct 7/21/81 All power reactor Access to Ultimate Heat Sink facilities with an OL or CP 81-20 Test Failures of Electrical 7/13/81 All power reactor Penetration Assemblies facilies with an OL or cP 81-19 Lost Parts in Primary 7/6/81 All power reactor Coolant System facilities with an OL or CP l