05000255/LER-2017-001

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LER-2017-001, Inadequate Protection from Tornado Missiles Identified Due to Nonconforming Design Conditions
Palisades Nuclear Plant
Event date: 03-29-2017
Report date: 05-24-2017
2552017001R00 - NRC Website
LER 17-001-00 for Palisades Nuclear Plant Regarding Inadequate Protection from Tornado Missiles Identified Due to Nonconforming Design Conditions
ML17144A289
Person / Time
Site: Palisades Entergy icon.png
Issue date: 05/24/2017
From: Arnone C F
Entergy Nuclear Operations
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
PNP 2017-024
Download: ML17144A289 (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.

PALISADES NUCLEAR PLANT 05000-255 2017 - 00

BACKGROUND

- 001 Enforcement Guidance Memorandum (EGM) 15-002, "Enforcement Discretion for Tornado-Generated Missile Protection Noncompliance," provides guidance to exercise enforcement discretion when an operating power reactor licensee does not comply with a plant's current site-specific licensing basis for tornado-generated missile protection.

Specifically, discretion would apply to the applicable Technical Specification (TS) Limiting Condition(s) for Operation (LCO) that would require a reactor shutdown or mode change in the event a licensee could not meet TS LCO required action(s) within the TS completion time.

Interim Staff Guidance DSS-ISG-2016-01, "Clarification of Licensee Actions in Receipt of Enforcement Discretion Per Enforcement Guidance Memorandum EGM 15-002," provides interim staff guidance to facilitate staff understanding of expectations for consistent oversight associated with implementing enforcement discretion for tornado missile protection noncompliance(s) per EGM 15-002.

Appendix A to DSS-ISG-2016-01 provides guidance for acceptable initial and comprehensive compensatory measures for licensee use in implementing the enforcement discretion outlined in EGM 15-002. The licensee should declare (log) the utilization of EGM 15-002, inform the resident inspector, and enter the issue into the corrective action program. For initial compensatory measures, it is expected that the measures listed are already in place at sites that may be affected by severe weather, such as tornados and/or hurricane force winds. The measures should be verified as current and readily deployable within a very short timeframe.

EVENT DESCRIPTION

On March 29, 2017, during an evaluation of protection of TS equipment from the damaging effects of tornados, nonconforming conditions were identified in the plant design. Specifically, TS equipment did not meet current design basis for protection against potential tornado missile impact. In some systems, both trains of TS equipment are impacted, potentially resulting in the loss of safety functions. The plant was in Mode 1 at approximately 70% reactor power. No Structures, Systems or Components (SSCs) were inoperable when the conditions were identified that contributed to the event.

Six systems containing TS equipment are affected to the extent that an impact on operability was credible. Potential tornado missile impacts could affect the following systems:

  • Service Water (SW) and Fuel Oil (FO) - Ventilator openings in the structure housing portions of the SW and FO systems provide a straight-line path to TS equipment that is part of the systems.
  • Auxiliary Feedwater (AFW) - The steam supply relief valves for the steam turbine driven AFW pump downstream of the steam supply valve are located adjacent to the turbine building siding which is not designed for tornado missile impact. A potential tornado missile strike of either relief valve could cause a loss of steam supply to the pump.
  • Component Cooling Water (CCW) — A wall of the CCW surge tank room may not be adequate protection for the surge tank. A calculation demonstrating the adequacy of the wall could not be located.
  • Control Room Ventilation (CRV) Filtration - The air intake piping for the CRV system is exposed and could cause a loss of air intake to the control room envelope if struck and crimped.

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.

PALISADES NUCLEAR PLANT 05000-255 2017 - 00

CAUSE OF THE EVENT

Due to the historical nature of the issue, a specific cause for the identified vulnerabilities was not determined.

ASSESSMENT OF SAFETY CONSEQUENCES

No actual safety consequence occurred, as Palisades did not experience an actual tornado missile event. As stated in the NRC Enforcement Guidance Memorandum,15-002, the basis for exercising enforcement discretion is a result of a generic risk analysis performed by the Office of Nuclear Reactor Regulation (NRR), Division of Risk Assessment (DRA). The assessment documents a conservative, bounding-type analysis of the risk significance for plant facilities that may not be in compliance with their tornado missile protection licensing basis. The generic analysis assumed that core damage would occur if a tornado hit a plant located in the most active tornado region in the country and that it caused a tornado-generated missile to fail all emergency core cooling equipment at the plant with no ability to recover.

Given this conservative assumption, the core-damage frequency (CDF) associated with tornado missile related to the non-compliances are well below CDFs requiring immediate regulatory action. Some tornado generated missiles may not cause system failures at all or may cause failures that are repairable or recoverable within a reasonable time frame.

In summary, the generic bounding risk analysis performed by NRR DRA has concluded that this issue is of low risk significance. Therefore, enforcement discretion will not impose significant additional risk to public health and safety.

CORRECTIVE ACTIONS

Corrective Actions Completed:

All applicable TS equipment and systems were declared inoperable. Initial compensatory measures were implemented, per the guidance of DSS-ISG-2016-01 Appendix A, within the time allowed by the applicable LCOs.

Subsequently, the affected TS equipment and systems were declared operable but nonconforming.

To establish a heightened level of station awareness and preparedness relative to identified tornado missile vulnerabilities, a description of the nonconforming SSCs and the associated compensatory measures were documented in operations standing orders log.

Corrective Actions Planned:

Establish comprehensive compensatory measures in approximately 60 days of discovery, per the guidance of NRC Interim Staff Guidance DSS-ISG-2016-01 Appendix A.

PREVIOUS SIMILAR EVENTS

None.

- 001