05000261/LER-2016-004
| H. B. Robinson Steam Electric Plant, Unit No. 2 | |
| Event date: | 08-24-2016 |
|---|---|
| Report date: | 10-24-2016 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2612016004R00 - NRC Website | |
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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 H. B. Robinson Steam Electric Plant, Unit 05000- NUMBER NO.
004 00 No. 2 261 2016 -
BACKGROUND
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to the event resulting in an automatic actuation of the Reactor Protection System (RPS) [AA] and Auxiliary Feedwater System (AFW) [BA].
The RPS monitors all parameters related to safe operation of the reactor. The system is designed to protect the core against fuel rod cladding damage caused by departure from nucleate boiling (DNB), and to protect the Reactor Coolant System (RCS) [AB] against damage caused by overpressure. The Turbine Trip/Reactor Trip provides overpressure or overtemperature protection for the RCS on a Loss of Load. This trip occurs when 2 out of 3 Auto- Stop Oil Pressure Signals decrease below the setpoint 40% and automatically blocked below 40%.
On August 24, 2016, at 1338 hours0.0155 days <br />0.372 hours <br />0.00221 weeks <br />5.09109e-4 months <br /> EDT, Event Notification Report #52198 was made to the NRC under 10 CFR 50.72(b) (2)(iv)(B), due to the automatic actuation of the Reactor Protection System, and under 10 CFR 50.72(b)(3)(iv)(A)(B)(6), due to the valid actuation of Auxiliary Feedwater System.
EVENT DESCRIPTION
At the time this condition was identified, RNP Unit 2 was operating in Mode 1 at approximately 100 percent power. No structures, systems or components were out of service at the time of this event that contributed to the event.
At 13:38 hours on 08/24/2016, an automatic turbine trip, and a subsequent automatic reactor trip occurred. Systems Engineering and Operations were performing a visual inspection of the RNP Unit 2 Main Turbine Trip Block. The visual inspection was being performed as a result of a sticking trip block that revealed itself on 8/19/16, during the performance of the Turbine Trip Functional Test (performed Quarterly During Power Operation). As a result of sticking trip block, operations removed the trip block cover and reset the sticking trip mechanism [TBLK] while the turbine trip bypass [JI] was enabled. The removal of the trip block cover was not covered in the Turbine Trip Functional Test. There was no procedural guidance directing the removal of the cover or manipulation of the turbine trip block. Therefore, on 08/24/2016, the act of removing the trip block cover, without the turbine trip bypass enabled, resulted in an automatic turbine trip with a subsequent automatic reactor trip.
This event necessitates a 60-day Licensee Event Report (LER) to the Nuclear Regulatory Commission (NRC), under 10 CFR 50.73(a)(2)(iv)(A) due to the event resulting in an automatic actuation of the Reactor Protection System (RPS) and the Auxiliary Feedwater System (AFW).
CAUSAL FACTORS
An in-depth evaluation of the automatic turbine trip followed by the automatic reactor trip, has concluded the following:
The personnel involved in the removal of the trip block cover had a common understanding of the trip block design and believed the probability causing an automatic turbine trip to be very low to moderate. Therefore, a formal risk assessment was not performed and mitigation capabilities were not integrated into the visual inspection activities. In addition, the unique nature of this particular evolution resulted in the activity receiving inadequate risk review and management oversight. Finally, informal communications conducted amongst station leadership resulted in unclear directions regarding the intended follow up actions which ultimately resulted in inadequate communications to the observers at the work activity level.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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.
2016 H. B. Robinson Steam Electric Plant, Unit No. 2 261
3. LER NUMBER
004 00 05000-
CORRECTIVE ACTIONS
Corrective actions taken to restore compliance with regulations are listed below.
Immediate:
1. Entered event into Corrective Action Program Corrective Actions to Prevent Recurrence (CAPRs) to address the Root Cause:
A comprehensive and clear standard for trip sensitive equipment will be developed and implemented. Associated training and communication will be developed to reinforce use of risk recognition in the decision making process for non-intrusive evolutions, data gathering activities and visual inspections.
There are no outstanding corrective actions required to restore compliance with NRC requirements; restoration of compliance has been met.
SAFETY ANALYSIS
The reactor was operating at full power during the performance of the visual inspection when an automatic reactor trip occurred. The mitigating equipment (RPS and AFW) functioned as expected and plant shutdown proceeded normally without further challenge. The cause of the plant trip is attributed to the absence of a standard that would govern risk assessment and control of work activities around trip sensitive equipment. The trip logic performed as designed and there were no other equipment performance issues. Therefore, the risk consequence of this event was minimal based on a successful reactor trip with no equipment or operational challenges.
ADDITIONAL INFORMATION
An extensive Operating Experience (OE) review was performed. The search phrases used to conduct the internal OE search were "Turbine trip test", "turbine trip from operator error" and "improper risk". The search phrases used to conduct the external OE search were "Turbine trip test", "turbine trip from operator error" and "improper risk". A search conducted on Institute of Power Operations (INPO) revealed approximately 50 hits.
Conclusion — OE Summary The list of OEs referenced above could have been used as part of preparation for a pre job brief of the turbine trip test.
Their relevance only applies to the test being performed and most likely would not be searched for when performing a "visual inspection". Also an OE search would not have been conducted because the Auxiliary Operators (AOs) and engineer believed this was a low risk task. This event has been performed almost identically at other units.
INPO makes information available to aid plant operators in conducting visual inspections. This further enhances awareness of the potential for trips in trip-sensitive systems. The site will benefit from the lessens learned from this event and the available OE for individuals who are accessing the plant. It will further be reinforced that even low risk and routine work should be treated properly, understood and managed.
Energy Industry Identification System (EIIS) codes for systems and components relevant to this event are identified in the text of this document within brackets [