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On September 5, 2017, Three Mile Island Un … On September 5, 2017, Three Mile Island Unit 1 was operating at 100% power and preparing for a scheduled maintenance and refueling outage. During a planned entry through the primary containment personnel airlock of the equipment hatch, the inner and outer doors were open simultaneously for less than one minute due to a failure of the interlock mechanism. The breach was immediately recognized by the operator and the inner door of the equipment hatch airlock was closed. Exelon determined the opening of both airlock doors constituted a violation of Technical Specification 3.6.12, Personnel or emergency air locks. The event was reported under 10 CFR 50.73(a)(2)(ii)(A) due to a principal safety barrier being seriously degraded, 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 Specification.Corrective Actions: Corrective actions included repairing the affected portion of the interlock mechanism and retesting its operation. An extent of condition was performed on the containment personnel hatch doors resulting in no similar issues. Corrective Action Reference(s): Issue report 04049166</br>Violation: Three Mile Island Technical Specification 3.6.12, Personnel or emergency air locks, states at least one door in each of the personnel or emergency air locks shall be closed and sealed during personnel passage through these air locks.Contrary to the above, on September 5, 2017, at least one door of a Three Mile Island Unit 1 personnel or emergency air lock was not closed and sealed during personnel passage through the air lock. Specifically, as the result of a failure of the interlock mechanism, the inner and outer equipment hatch emergency air lock doors were simultaneously opened for less than one minute. Severity/Significance: For violations warranting enforcement discretion, Inspection Manual Chapter 0612 does not require a detailed risk evaluation, however, safety significance characterization is appropriate. The NRC Enforcement Policy, Section 2.2.1 states, in part, that, whenever possible, the NRC uses risk information in assessing the safety significance of violations. The inspectors determined that finding was of very low safety significance (Green).Basis for Discretion: The inspectors determined that both containment hatch doors opening simultaneously was not within Exelons ability to foresee and prevent. As a result, no performance deficiency was identified. The inspectors assessment considered previous surveillances performed on the equipment hatch doors and interlock mechanisms. The inspectors reviewed all recent surveillances performed on the equipment and personnel inner and outer doors for timeliness and any abnormal results. No abnormalities were discovered and all surveillances were completed within periodicity. The NRC determined that it was not reasonable for Exelon to have been able to foresee and prevent this violation of NRC requirements, and as such, no performance deficiency existed. Therefore, the NRC has decided to exercise enforcement discretion in accordance with Sections 2.2.4 and 3.10 of the NRC Enforcement Policy and refrain from issuing enforcement action for the violation of technical specifications (EA-18-038). Further, because Exelons actions did not contribute to this violation, it will not be considered in the assessment process or the NRC Action Matrix. Inspectors elected to inspect the cause evaluation and corrective action determination related the issue described in LER 2017-003 as a selected annual sample. Exelon evaluated the condition and determined the cause of the event to be the failure of the outer door pawl to engage, providing a false indication that the outer door was closed prior to opening the inner door. The inspectors placed additional inspection focus to evaluate additional maintenance activities on the containment door mechanism, prior to outage activities where the door is cycled on a frequent basis with many new operators on site. Existing procedures and maintenance activities do not specify any subcomponent replacements until there is a failure or indication of damage. In addition to performing repairs to the outer door pawl, Exelon reviewed the current preventative maintenance activities for scheduling adequacy with the focus on high usage periods, evaluating additional maintenance activities that would include preventative subcomponent replacements, and reviewing industry operational experience for similar failures and corrective actions prior to the next refueling outage. Exelon documented the inspectors observation in issue report 04049166.tors observation in issue report 04049166.

Discovered date

23:59:59, 31 March 2018 +

Docket

05000289 +

Event date

23:59:59, 31 March 2018 +

Finding integer

2 +

Finding type

Finding +

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Identified by

NRC identified +

Inspection Manual Chapter

NRC Inspection Manual 0612, Power Reactor Inspection Reports +

Inspection procedure

IP 71153, Event Followup +

Inspection report

IR 05000289/2018001 +

Inspector

Bill Lin +, Ronald Rolph +, Javier Brand +, Joseph Deboer +, Matt Young + and Zachary Hollcraft +

Issue report

AR 04049166 +

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12:59:54, 30 May 2018 +

Person