05000289/LER-2017-003

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LER-2017-003, Primary Containment Declared Inoperable Due to Both Airlock Doors Open Simultaneously
Three Mile Island Unit 1
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications

10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded

10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
2892017003R00 - NRC Website
LER 17-003-00 for Three Mile Island, Unit 1 Regarding Primary Containment Declared Inoperable Due to Both Airlock Doors Open Simultaneously
ML17311A145
Person / Time
Site: Three Mile Island Unit 1, Three Mile Island Exelon icon.png
Issue date: 11/06/2017
From: Callan E W
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
TMl-17-105
Download: ML17311A145 (5)


comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER 1. FACILITY NAME 2017 003 - 00

A. EVENT DESCRIPTION

Plant Conditions before the event:

Babcock & Wilcox — Pressurized Water Reactor — 2568 MWth Core Power Date/Time: September 5, 2017 / 10:00 EDT Power Level: 100% Mode: Power Operation On September 5, 2017 the plant was operating at steady state full power operation. Preparations for a scheduled refueling and maintenance outage were in progress that included planned entries into the Reactor Building primary containment. Three Mile Island Unit 1 (TMI-1) has two primary containment personnel entry pathways, both utilize a double-door airlock that utilizes an interlock linkage to prevent both doors from being opened simultaneously. The event occurred when technicians inside the Reactor Building, were attempting to exit containment via the Inner Door of the Personnel Airlock of the Equipment Hatch (PAEH). Technicians noted prior to operating the Inner Door of the PAEH, that the PAEH Outer Door indicated closed. The Inner Door was opened approximately 18 inches when the technicians saw light in the PAEH and realized that the Outer Door must not be fully closed. The technicians immediately closed the Inner Door to re-establish containment integrity.

Additional maintenance technicians were dispatched to the Outer Door of the PAEH and found the Outer Door open. A visual inspection of the Outer Door of the PAEH was performed and found indications of wear on the interlock linkage and damage to the Outer Door's seal. The Outer Door of the PAEH was closed. The Inner Door of the PAEH was verified closed in accordance with the plant Technical Specifications (T.S. 3.6.12). Direct communications between the operating stations at the Inner and Outer Doors of the PAEH were established in order to verify door positions. All actions required by the plant Technical Specifications were performed to confirm compliance until the event could be fully investigated and repaired during the refueling and maintenance outage beginning in approximately two weeks.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A) due to a principal safety barrier (primary containment) being seriously degraded and, 10 CFR 50.73(a)(2)(v)(C) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material and, 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.ResourceCnrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 003 - 00

B. CAUSE OF EVENT

TMI-1 entered its planned maintenance and refueling outage on September 18, 2017. During the period of time at which containment integrity was not required for the plant condition, technicians were able to repeat the failure of the interlock linkage of the PAEH. Maintenance discovered that the PAEH interlock linkage designed to prevent both doors from being opened simultaneously had failed due to a bent ratchet pawl. A weld repair to the ratchet pawl interlock linkage was performed. The interlock linkage preventive maintenance was performed that included linkage adjustment. Testing of the interlock linkage of the PAEH was performed satisfactorily.

An extent of condition was performed on the remaining airlock designated as the Reactor Building Personnel Hatch Airlock. The surveillance and preventive maintenance activities performed on the Personnel Hatch Airlock were all satisfactory. This included testing of the Personnel Hatch Airlock interlock mechanism which was completed satisfactorily.

C. ANALYSIS / SAFETY SIGNIFICANCE

This event had no significant impact on public health and safety. TMI-1 was operating at full power when the event occurred. The potential for radioactive material release to the environment was evaluated. The reactor building environmental conditions of pressure and airborne radioactivity were well within operating limits at the time of the event. The resulting consequence for this short duration event is negligible.

Control of the Inner Door of the PAEH was maintained throughout the event. However, the Outer Door of the PAEH was not closed that resulted in a loss of a principal safety barrier (primary containment) and is counted as a safety system functional failure (SSFF) since the event could have prevented fulfillment of a safety function.

D. CORRECTIVE ACTIONS

Actions Completed on the Personnel Airlock of the Equipment Hatch Inner and Outer Doors:

1. Reviewed Airlock door operating practices, assigned designated door operators and established backup door indication verification technique prior to re-commencing reactor building entries.

2. Performed a weld repair to the pawl on interlock linkage.

3. Site Maintenance performed PAEH interlock preventive maintenance, including linkage adjustments.

4. Performed interlock door test to verify operability between the two doors.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER 1. FACILITY NAME 2017 003 - 00 5. PAEH Outer Door seal was repaired.

6. Performed Outer Door seal test to verify repairs to door seals.

7. Performed a satisfactory LLRT of the Personnel Airlock of the Equipment Hatch.

E. PREVIOUS OCCURENCES

None.