05000219/LER-2017-004
| Oyster Creek Nuclear Generating Station | |
| Event date: | 08-31-2017 |
|---|---|
| Report date: | 02-16-2018 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2192017004R01 - 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.
Oyster Creek Nuclear Generating Station
3. LER NUMBER
2017 - 01 004
Plant Conditions Prior To Event
Event Date: August 31, 2017 Event Time: 10:30 hours ET Unit 1 Mode: Run Power Level: 100%
Description of Event
On August 31, 2017, during a review of industry Operating Experience (FERMI 2 2017-001) for the use of a Reactor Protection System (RPS) test box during main turbine surveillance testing, it was determined that the Oyster Creek station procedures failed to implement the required action specified by Technical Specifications (TS) Section 3.1,1. note (nn) during testing. The surveillance tests associated with the Turbine Trip and Generator Load Rejection functions were revised in 2013 to use an RPS test box to minimize operational risks associated with the receipt of half scram signals during testing. With the RPS test box installed, two of the four required Turbine Trip Scram inputs were bypassed. The action to verify sufficient channels remained operable was not documented as complete within one (1) hour as specified in TS Table 3.1.1, note (nn).
TS Table 3.1.1, Function 11, Turbine Trip Scram, specifies the minimum number of operable channels as four per trip system. The test directed the RPS test box to be installed around the relay that actuates the specific channel in the RPS division that would receive a trip signal when the turbine stop valves closed or the pressure switch that senses low trip system oil pressure for the main turbine was tested.
Cause of Event
The cause has been determined to be insufficient technical rigor during the development of the procedure revision, and the failure to obtain an independent technical review of the procedure changes. The procedure preparer and approver did not identify that installation of the RPS test box resulted in the need to execute the TS action.
Consequently, the Turbine Trip and Generator Load Rejection surveillance test procedures did not direct the performance of the required action.
Analysis of the Event
Since May 2013, Oyster Creek has used an RPS test box to perform the Turbine Trip and Generator. Load Rejection surveillance tests. Each RPS division contains two logic channels that receive inputs from the turbine stop valve limit switches. Two stop valve limit switches are assigned to each RPS logic channel. The assignment of stop valve limit switches varies between the two channels in RPS division 1 and RPS division 2. When the turbine stop valves are less than 90 percent open, a limit switch associated with that valve opens in the RPS logic.
When two stop valve limit switches in one trip channel open, a relay in the RPS logic system (relay 1K11, 1K12, 2K11, or 2K12) is deenergized, causing a half scram signal to be initiated. Installation of the RPS test box during the Turbine Trip and Generator Load Rejection surveillance tests would prevent the relays in the RPS channel from initiating causing the two stop valves assigned to that channel to be rendered inoperable.
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.
Oyster Creek Nuclear Generating Station
3. LER NUMBER
Assessment of Safety Consequences
The RPS has two independent trip systems with two logic channels in each trip system. The use of the RPS test box only impacts one channel in the RPS division being tested. The ability to receive a full scram due to a turbine stop valve closure when the RPS test box was installed for testing was not inhibited since the other channel in the RPS division being tested was unaffected by the installation of the RPS test box.
Corrective Actions
1. All operating procedures using the test box, including the Turbine Stop Valve Anticipatory Scram and Turbine Load Rejection Scram surveillance tests, will be revised to reflect the TS Section 3.1.1. note (nn) requirement prior to next use. The procedures direct sufficient channels remain operable and a log entry made verifying the total amount of time the channel has been bypassed during test box installation is less than the time limit specified in the TS.
2. All station surveillances which implemented test boxes for Station Qualified Reviewer errors were reviewed as part of the extent of condition with no other deficiencies noted.
Previous Occurrences
There have been no similar, previous events resulting from the installation of a test box during surveillance testing at Oyster Creek.
2017 - 01