ML19262A186
| ML19262A186 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/06/1975 |
| From: | Arnold R METROPOLITAN EDISON CO. |
| To: | |
| References | |
| NUDOCS 7910260514 | |
| Download: ML19262A186 (4) | |
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Docket No. 50-289 Operating License DPR-50 In accordance with the Technical Specifications for our Three Mile Island Nucle.tr Station, Unit 1, we are reporting the following abnormal occurrence:
(1) Report Number: A0 50-289/74-32 (2a) Report Date:
JAN 6 1975 (2b) Occurrence Date : December 26, 1974 (3) Facility: Three Mile Island Nuclear Station Unit 1 (TMI-1)
(4) Identification of Occurrence :
Title:
Violation of Containment Integrity at the Reactor Building Access Hatch Type: An abnormal occurrence as defined by the Technical Specifications, paragraph 1.8.e., in that the Violation of Containment Integrity at the Reactor Building Personnel Access Hatch resulted in an abnormal degradation of one of the several boundaries designed to centain the radioactive materials resulting from the fission process.
(5) Conditions Prior to Occurrence The reactor was at steady-state power with major plant parameters as follows :
Power:
Co re : 99.35*:
Elec: 868 MW (Gross)
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6 RC Flow: 142 x 10 lb/hr RC Pressure : 2155 psig 198
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RC Temp. : 579 F PRZR Level:
240 in PRZR Temp.: 648 F (6) Description of Occurrence During personnel egress from the Reactor Building through the Reactor Building Personnel Access Hauch, an individual shut the inner door, but did not properly shut the outer door (it was slammed) which resulted in the door being about 6 inches ajar, and also resulted in (a) an improper indication in the c muol room that the outer door was shut, and (b) a subsequent improper functioning of the outer / inner door interlock. The next individual who exited via this same hatch opened the inner door to gain access to the inner space between the doors, noticed the condition of the outer door, and restored contain-ment integrity by shutting the inner door. The outer door was then cycled open and properly shut.
(7) Designation of Apparent Cause of Occurrence The apparent cause of the occurrence was primarily design la that the limit switch which is used in the control room indication circuit for the position of the outer coor 'orks off the latch bar mechanism of the door,vice the position of the door itself. A possible contributing cause can be attributed to procedure, in that the design condition would not have resulted in the occurrence had procedure required either (a) individuals to visually check the condition of the outer door (vice simply obtaining clearance from the Control Room prior to leaving the area), or (b) a slow closing of the door (in which case (a) operation of the outer door latch bar mechanism does always properly coincide with the position of the outer door, and (b) the outer / inner door interlock (which is supposed to prevent a simultaneous open condition of the two doors) would have functioned properly).
(8) Analysis of Occurrence It is believed that the simultaneous opening of both doors of the Re-actor Building Personnel Access Hatch did not threaten the health or safety of the public as the reactor building represents only one cf three boundaries designed to contain radioactive materials resulting from the fission process ; the violation of containment integrity existed for only several minutes; the Reactor Building would be required to perform its boundary function only if one or more of the other boundaries should fail; and both of the other boundaries were always intact.
(9) Corrective Action Immediate corrective actions we 1 taken as described above to restore containment inte grity. In addition, appropriate personnel were in-structed to visually verify that Reactor Building doors.are fully closed upon access and egress.
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The Plant Operations Review Co=mittee (PORC) reviewed and approved the i= mediate corrective actions, and in addition recommended that as long term preventative actions :
1.
an evaluation be conducted to determine if either the existing limit switch should be relocated, or another limit switch (which would operate with the closing of the outer door itself) be added to provide a positive indication of the position of the outer door, and 2.
revise procedures such that personnel passing through the personnel access hatch wculd be required to both (a) slowly close the outer door, and (b) visually verify proper closure of the outer door prior to leaving the area.
The Station Superintendent concurred with PORC's findings, and has taken steps to ensure implementation of the long term preventative a ctions.
(10)
Failure Data Previous Failures: See Abnormal Occurrence Report A0-50-289/74-11 Equipment Identification:
(a)
Reactor Building Personnel Access Hatch Outer Door Indication Circuit (b)
Reactor Building Personnel Access Hatch Outer / Inner Door Interlock Sincere y,
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R.C.)kYnold Vice President RCA:DNG:tas File:
20.1.1 7.7.3.5.1 cc:
Mr. J. P. O 'Reilly (DORO-Region 1)
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