ML20237G602
| ML20237G602 | |
| Person / Time | |
|---|---|
| Site: | 05000000, LaSalle |
| Issue date: | 11/26/1986 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| Shared Package | |
| ML20237F649 | List: |
| References | |
| FOIA-87-377, RTR-NUREG-0090, RTR-NUREG-90 IEIN-86-047, IEIN-86-47, NUDOCS 8709020326 | |
| Download: ML20237G602 (6) | |
Text
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NUCLEAR REGULATOFtY COMMISSION
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l November 26, 1986 i
MEMORANDUM FOR:
C. J. Heltemes, Jr., Director, Office of Analysis and Evaluation of Operational Data 4
FROM:
James G. Keppler, Regional Administrator, RIII
SUBJECT:
PROPOSED ABNCRMAL OCCURRENCE REPORT -- LASALLE Enclosed is the proposed Abnormal Occurrence Report on the LaSalle pressure level switch event for inclusion in the Third Quarter 1986 Abnonnal Occurrence Report to Congress.
As requested by Paul Bobe of your staff on November 26, 1986, we are preparing a draft report on the University of Cincinnati misadministration incident and will be submitting it shortly.
If you have any questions, please contact Jan Strasma (FTS 388-5674).
l l
James G. Keppler Regional Administrator
Enclosure:
As stated t
cc w/ enclosure:
J. G. Davis, NMSS H. R. Denton, NRR J. J. Fouchard, PA G. W. Kerr, SP R. B. Minogue, RES J. M. Taylor, IE i
G. H. Cunningham, ELD Regional Administrators
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8709020326 070820 PDR FOIA CORDDNB7-377 PDR f/33
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November 26, 1986
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MEMORANDUM FOR:
C. J. Heltemes, Jr., Director, Office of Analysis and Evaluation of Operational Data i
FROM:
James G. Keppler, Regional Administrator, RIII
SUBJECT:
PROPOSED ABNORMAL OCCURRENCE REPORT -- LASALLE Enclosed is the proposed Abnormal Occurrence Report on the LaSalle pressure level switch event for inclusion in the Third Quarter 1986 Abnormal Occurrence Report to Congress, l
l As requested by Paul Bobe of your staff on November 26, 1986, we are preparing a draft report on the University of Cincinnati misadministration incident and will be submitting it shortly.
If you have any questions, please contact Jan Strasma (FTS 388-5674).
1 James G. Keppler Regional Administrator l
Enclosure:
As stated i
cc w/ enclosure-i l
J. G. Davis, NMSS l
l
[
H. R. Denton, NRR J. J. Fouchard, PA i
G. W. Kerr, SP R. B. Minogue, RES J. M. Taylor, IE G. H. Cunningham, ELD l
Regional Administrators l
RIII RIII RIII RIII RIII Strasma/kst Guldemond Norelius Davis Keppler 11/ /86 11/ /86 11/ /86 11/ /86 11/ /86 i
ABNORMAL OCCURRENCE -- LASALLE PRESSURE LEVEL SWITCH EVENT N
Date and place -- On June 1,1986, LaSalle Unit 2 experienced a problem with its feedwater system which caused the water level in the reactor to drop and thea f ricrease before returning to a nonnal level. The LaSalle County Nuclear Power Station utilizes two General Electric Company boiling water reactors.
It is located near Seneca, Illinois. Subsequent licensee reviews determined that the water level had dropped briefly below the point where an automatic reactor shutdown should have occurred. The unit was shut down manually to evaluate the incident.
Nature and probable consequences -- At approximately 4:21 a.m., June 1,1986, a failure occurred in the control circuitry for one of two operating feedwater pumps which pump water to the reactor from the unit's condenser system. The feedwater flow decreased, and reactor water level began to drop. Licensee i
operators reduced reactor power and started a third, motor-driven, feedwater pump to restore the reactor water level.
Following the incident, the licensee determined that reactor water level had dropped below the Technical Specification (license) water level limit where an j
automatic reactor shutdown should occur. This point is 11 inches above a I
level specified as " instrument zero" and is approximately 14 feet above the top of the reactor fuel. A review of level instrumentation indicated that the water level likely went below the water level limit of 11 inches for 1.5 seconds and may have been as low as 4.25 inches.
After these evaluations the licensee declared an alert under its Emergency Plan, and connenced a controlled shutdown, reaching hot shutdown at 9:22 a.m.,
June 2, 1986.
The automatic shutdown is initiated by four differential pressure switches in two pairs of two switches. For shutdown initiation, one switch in each pair l
must actuate. In the June 1 incident, only one switch actuated, and thus no i
automatic shutdown occurred.
l Subsequent testing of the switches led the NRC staff to conclude that, while the switches failed to actuate during the brief period the water dropped below the set point, in all likelihood they would have functioned had the level dropped lower or for a longe period of time. In addition, there are two additional sets of level switches which would have been reached had the reactor water level continued to drop. These switches would have the function of initiating an automatic shutdown and starting certain emergency core cooling system equipment, should it have been needed. Subsequent evaluation indicated that the reactor could have been protected adequately by these switches.
The NRC staff detennined that the reactor operators on duty when the feedwater problem occurred had performed well and that the ensuing operating shift's performance was exceptional in its recognition and persistence in pursuing the water level instrumentation problem.
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, N Cause or causes -- The licensee determined through testing of the water level monitoring switches, that all four Static-0-Ring differential pressure switches failed to actuate at the required set point, although in the June 1 incident, one of the switches did actuate. The testing indicated that even though the switches were calibrated to trip at approximately 13.4 inchas, the actual trip points varied 3.9 inches to 10.2 inches. None of them, however, failed to actuate during the testing.
Further testing by the licensee determined that the switches do not perfom in a totally erratic manner. They appear to undergo a set point shift when exposed to continuous pressure different from the pressure used in calibration. The testing also determined that the set point shift has a limit and does not continue to shift; therefore, the shifting phenomena is reasonably predictable.
In addition to the water level sensing applications of the Static-0-Ring switches, the switches were used elsewhere at LaSalle in flow measuring applications. The switches are used to detect a minimum flow in the discharge line from emergency core cooling system pumps to avoid overheating and possible damage to the pumps. Tests of switches in these flow applications revealed that they too exhibited the nonconservative set point shift characteristic when exposed to operating conditions different from those experienced during calibration.
1 Actions taken to prevent occurrence --
Licensee -- The utility undertook an extensive testing program to evaluate the nature of the Static-0-Ring switch problem. This testing determined that the switches, if properly calibrated to include the predicted set point shift, can continue to be used in their current applications in the interim. The licensee, 4
and the vendor, however, are testing the switches on a more frequent basis over long time periods to assure their continued operability.
NRC -- The licensee's investigation of the water level switch problem was initially monitored by the resident inspectors. An Augmented Investigation l
Team was later dispatched to the site on June 2,1986, to evaluate the incident and the nature of the switch problem and corrective actions. The Office of Nuclear Reactor Regulation reviewed the results of the tests performed by the I
licensee and the vendor and concluded that the Static-0-Ring Model 102 and 103 differential pressure switches could remain in service until the end of calendar year 1986; however, use beyond that point would require additional technical justification on the part of the licensee. That justification has yet to be provided.
Information Notice 86-47 was issued on June 10, 1986, describing the LaSalle incident and the findings at that time. The notice was issued to all nuclear power plants. and included a listing, which hed been provided by the vendor, of other facilities with Static-0-Ring Movel 102 and 103 differential pressure switches. On July 18, 1986, IE Bulletin 86-02 was issued to all nuclear power plants, requiring them to review any applications of the Static-0-Ring Model 102 or 103 differential pressure switches in safety-related systems and systems important to safety and test them where necessary.
I
t REFERENCES Letter frbm Charles E. Norelius, Director, Division of Reactor Projects.
Region III, to Mr. Cordell Reed, Vice President, Commonwealth Edison Company, dated September 17, 1986, enclosing Augmented Inspection Team Report No. 50-374/86-23.
Information Notice 86-47, dated June 10, 1986.
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6 Document Name:
AOR LASALLE Reqbestor's ID:
CAROLG Author's Name:
strasma Document Comments:
lasalle pressure level swtich event Destination Name:
CAROLG Distribution Name:
NRCRIII_ KELLY _0022 Addressee:
Carol Gallaghar, AEOD 24484 Date Sent:
l 11/28/86 l
l Tire Sent:
1 09:09 Message:
TO: PAUL BOBE, AE0D FP0M: JAN STRASMA, RIII, OPA
SUBJECT:
ABNORMAL OCCURRENCE REPORT: LASALLE please note, memo is at the end of document i
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