ML20010F165
| ML20010F165 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde, Columbia, Diablo Canyon, San Onofre, Humboldt Bay, Rancho Seco, Washington Public Power Supply System, Satsop, Trojan |
| Issue date: | 09/03/1981 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| NUDOCS 8109090449 | |
| Download: ML20010F165 (1) | |
Text
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k UNITED STATES 4
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~t NUCLEAR REGU' ATORY COMMISSION REGION V E
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,E 1990 N. CALIFORNIA BOULEVARD Q
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- d SUITE 202, WALNUT CREEK PLAZA
- ,,no WALNUT CREEK, CALIFORNIA 94596
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- ,g September 3, 1981
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NOTE T0:
ALL THOSE ON IE INFORMATION TOTICE DISTRIBUTION LIST g
FROM:
IE - REGION V
SUBJECT:
IE INFORMATION NOTICE N0. 81-27, " FLAMMABLE GAS MIXTURES IN THE WASTE GAS DECAY TANKS IN PWR PLANTS IE INFORMATION NOTICE NO. 81-28, " FAILURE OF ROCKWELL-EDWARD MAIN STEAM ISOLATION VALVES The attached IE Information Notices 81-27 and 81-28 were iss.;ed this date to the following licensees:
1.
Arizona Public Service Company (Palo Verde 1, 2 & 3, Docket Nos. 50-528, 50-329 & 50-530).
2.
Pacific Gas & Electric Company (Humboldt Bay Unit 3, Diablo Canyon Units 1 & 2, Docket Nos. 50-133, 50-275 & 50-323).
3.
Portland General Electric Company (Trojan, Docket No. 50-344).
4.
Sacramento Municipal Utility District (Rancho Seco, Docket No. 50-312).
5.
Southern California Edison Company (San Onofre Units 1, 2 & 3, Docket Nos. 50-206, 50-361 & 50-362).
l 6.
Washing?on Public Power Supply System (WNP-1, WNP-2, WNP-3, WNP-4 &
l WNP-5, Docket Nos. 50-397, 50-460, 50-508, 50-509 & 50-513).
l
Enclosures:
1.
Transmittal Letter 2.
IE Information Notice No. 81-27 3.
IE Information Not No. 81-28 i
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i 8109090449 810903 4
PDR ADOCK 05000133 G
s SSINS No.: 6835 Accession No.:
8103300415 IN 81-27 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 September 3, 1981 IE INFORMATION NOTICE NO. 81-27:
FLAMMABLE GAS MIXTURES IN THE WASTE GAS DELAY TANKS IN PWR PLANTS Description t.
Ci rcumstances :
In July 1981, hydrogen ignition occurred in one gaseous waste decay tank at San Onofre Unit I while the plant was in cold shutdown.
This resulted in a j
release of about 8.8 curies of noble gases and minor tank damage.
The cause j
of the hydrogen igrition 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 ir +hr instrument air system is higher than that of the nitrogen system.
These cre : connections had been installed ~.n response to TMI Action Plan requirement tem II.E.1.2 of NUREG-0737.
The nitrogen system provided a backup gas supply to we 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 cri teria.
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 i
air-operated pressurizer relief valves and the -associated block valves.
Following the occurrence, the licensee sampled all_ potentially affected tanks and detennined that most of the tanks had oxygen levels above 10 to 15 percent.
Generally, the gas in pressurized wate: reactor, (PWR) waste gas systems is l
hydrogen rich and the oxygen concentration is controlled to prevent flammable
~
gas mixtures.
Flammable concentration af gas nixtures 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 pro,ide 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 mixtuws were created af ter the primary coolant picked up oxygen from the air during.'efueling and maintenance.
No ignition or explosion was reported.
U v
IN 81-27 September 3, 1981 Page 2 of 2 It appears that licensees need to devote more attention to the potential effects of nitrogen-air system cross connections when systems are modified to use nitrogen i
as a backup to air systems.
If cross connections exist, the potential for the formation of flammable gas mixtures should be evaluated. A sampling program to.
assure that flammable gas mixtures do not exist in tanks should be considered.
No written response to this information notice is required.
If you need additional information with regard to this subject, please contact the Director of the appropriate NRC Regional Office.
Attachment:
Recently issued IE Information Notices t
f' te Attachment IN 81-27 September 3, 1981 RECENTLY ISSUED IE INFORMATION NOTICES Tnformation Date of Notice No.
Subject
_ Issue Issued to 81-26 Compilation of Health 9/3/81 All oower reactor Phys'cs Related Infonnation facilities with an Items OL or CP 81-25 Open Equal.izing 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 81-24 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 Assenblies facilities 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 K = Operating Licenses CP = Construction Permits
h.
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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 N0. 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 "(" 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 Unit 1 and 2, Cooper, Duane Arnold, Fitzpatrick, Hatch Uni t 2, and Vermont: Yankee. 'Of the seven. total reported mechanical failures, five'occurrediat Brunswick ifnit. 2'and,one each occurred at Brunswick Unit 1 and Hatch, Unit:2.
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e
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s The valve components that have failed.are shown..in Figure'll 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 equalization 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 internals. This separation was either at the stem-to-stem-disk threaded connection 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 connection, which in some cases is caused by vibration-induced rotation of the disk so that it becomes disconnected from its threaded mate.
Such rotation is believed to be caused by or aided by the propensity of steam flow to produce vibration and to create turning forces on valve interral components when antirotation restraint is inadequate due to
.a failed or missing pin. Other contributing causes are believed to result from reassembly of the valve af ter disassembly at the site; such reassembly may 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 on 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.
^
IN 81-28 September 3, 1981 Page 2 of 2 2..
'On January 30, 1979, the Br'unswick Unit 2 "A" steam line inboard valve stem disk' separated from the stem. A square pin was used in the round hole at poi nt '(3).
The corners of the pin experienced'high; stress, thereby causing cracking of the pin.
~
3.
On January 15, 1981, the-Brunsw'ick Unit 2_'"C" steam line outboard valve main
~
There' wa'.no evidence that pin (4) was disk separated from the' piston.
s ever inserted.
This_ was' deduced from finding the hole _ not defomed 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 separated from the stem.
Pin (3) failed and was not recovered.
6.
On July 2, 1981, the 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 perfom its required safety-function and (2) increased challenges to safety systems.
However, it is noted 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 l
preliminary findings of possible excessive vibrations on valve internals from steam flow turbulences created by the piping direction changes.
In addition, there was evidence of loose thread connections.
Further investigations and evaluations are currently in progress.
Preliminary corrective actions by the licensee include increasing the stem pin size from 5/16-inch to 3/8-inch, using three pins instead of one or two pins, 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 i
this information for applicability to their facilities.
No written response to this infomation is required.
If you need additional information regarding this matter, please contact the Director of the appropriate NRC Regional Office.
Attachments:
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1.
Figure 1 2.
Recently issued IE Information Notices -
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MAIN DISK 3.
ANTIR0TATION PIN - STEM DISK TO STEM j
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ANTIR0TATION PIN - MAIN DISK TO PISTON s
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Attachment IN 81-28 September 3, lo81 RECENTLY ISSUED IE INFORMATION NOTICES Information Date of Notice No.
Subject Issue Issued to 81-27 Flammable Gas Mixtures 9/3/81 All power reactor in the Waste Gas Decay facilities with an Tanks in PWR Plants OL or CP.
81-26 Compilation of Health 9/3/81 All power reactor Physics Related Information 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 CL or.CP Scram and Loss of Redundant Safety Signals 81-24 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 L'oss of Direct -
"' 7/21/81.
All power reactor Access to Ultimate Heat Sink
~
facilities with an c
OL or CP 81-20 Test Failures of Electrical 7/13/81.
All power reactor Penetration As'semblie's facilities with an i
81-19 Lost Parts in Primary 7/6/81 All power reactor Coolant System facilities with an
-0L or CP OL =. Operating Licenses CP = Construction Permits
-