ML16203A105
| ML16203A105 | |
| Person / Time | |
|---|---|
| Site: | U.S. Geological Survey |
| Issue date: | 07/07/2016 |
| From: | Timothy Debey US Dept of Interior, Geological Survey (USGS) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 52054, 52062 | |
| Download: ML16203A105 (4) | |
Text
EUSGS science for a changing world Department of the Interior
- US Geological Survey PO Box 25046 MS 974 Denver, CO 80225-0046 July 7, 2016 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555-0001
Reference:
Event Number 52054 and 52062
Subject:
Written report of Equipment Failure and Resulting Technical Specification Violation at U.S. Geological Survey TRIGA Reactor (GSTR), Docket 50-274, License R-113 Sirs:
Details of the two equipment failures and resulting Technical Specification violations at the GSTR are enclosed. Please contact me if you have questions about this matter.
Sincerely,
~U-B~
Tim DeBey USGS Reactor Supervisor I declare under penalty of perjury that the foregoing is true and correct.
Executed on 7/7/2016 Enclosure Copy to:
Vito Nuccio, Reactor Administrator, MS 911 USGS Reactor Operations Committee
Report of Self-Identified Technical Specification Violations (Loss of safety circuit)
At 0712 on 6/30/16 a routine GSTR startup and ascent to 900 kW was initiated after successful completion of the daily prestart checks and an excess reactivity check. At 0715, as power was passing through "'200 kW it was clear to the operator that one of the three power instruments (the NPlOOO) was not functioning since it was still reading 0% when it should have been reading
"'20%. The reactor was then shutdown, Reactor Supervisor notified, and troubleshooting commenced. Shortly after this, the NPlOOO signal cable was found to have the coaxial cable pulled out of one of the connectors in the signal path (see drawing on last page). It is suspected that this cable was stepped on and/or tripped over by a staff member working in that area.
Repair and testing were performed to resolve the problem. At 0740 a reactor startup was performed to verify function of the NPlOOO but it was still not working correctly. The connector was disassembled, reassembled and checked. At 0804 the reactor was started up, all power instrumentation operated correctly and the scheduled one-hour power operation was performed without further problems. This event was reported to the NRC Operations Center and is documented as Event Number 52054.
Further corrective action taken: The coaxial cables going to the NPlOOO detector were elevated from the floor level near the reactor tank top and suspended on the vertical surface by cable straps. This action will prevent the cables from being stepped on or tripped over by personnel working in that area. (see photo below of new cable positioning)
NPlOOO connectors
At 0914 the next day (7 /1/16} a routine GSTR startup and ascent to 900 kW was initiated after successful completion of the daily prestart checks and an excess reactivity check. At 0919 as power was passing through ~so kW it was clear to the operator that one of the three power instruments (the NP1000} was not functioning since it was still reading 0% when it should have been reading >5%. Since the reactor was on a positive period, power reached ~25% (250 kW}
before the increase was stopped. The reactor was scrammed, Reactor Supervisor notified, and troubleshooting commenced. Shortly after this, the NP1000 signal cable was found to have an intermittent connection through a tee connector that was installed at the instrument box. This tee connector was installed in April 2014.
Corrective action taken : The tee connector was replaced to resolve the problem and the connector circuit was tested satisfactorily. The new connector has a slightly different physical configuration to eliminate a 90 degree bend in the signal cable near the connector site, which may have been a contributing factor. (see photo below} At 1050 the reactor was started up again. All power instrumentation operated correctly and the daily power operation was performed without further problems. Power operations were performed again on 7 /5/16 with no further problems in the NP1000 instrument. This event was reported to the NRC Operations Center and is documented as Event Number 52062.
Evaluation: The problems identified on 6/30/16 and 7 /1/16 were open circuits in the signal line from the ion chamber detector to the input of the NP1000 instrument. (see wiring drawing
below} This signal line normally carries a small DC current ranging from zero to 0.0011 ampere, which corresponds to a reactor power from zero to 100% (1 MW}. An open circuit has the same indication as a shutdown reactor. The routine checks performed on the NPlOOO instrument for high power scram and loss of high voltage' scram are done by injecting signals into the instrument and these tests do not check or verify the functionality of the detector or the cables and connectors going to the detector. The only method for performing a complete, valid test of the detector, cables, and connectors is to expose the detector to a sufficiently high neutron flux and confirm a correct response. This can only be done by starting up the reactor and raising power into the kW power range.
The NPlOOO is a required safety instrument for operation of the reactor, so malfunction of the instrument is a violation of the facility's Technical Specifications. The facility's other two power instruments were functioning correctly during this event, providing correct power indications and also providing high power scram protection from the NPPlOOO instrument. There was never any threat to the staff, public, or environment from this event.
Specifically, Specification E.7 states: "The type and minimum number of safety systems which shall be operable for reactor operation are shown in Table I." Table I requires the NPl OOO to provide a high power scram at 110% power, but the cable connector problems would have prevented the high power scram from occurring in that instrument.
NPlOOO connectors Coaxial cables (2) ~25 ft long for high voltage and NPlOOO wiring from ionization chamber detector to power instrument box Reactor tank; 25 ft deep; 8 ft dia.
Ionization chamber in reactor tank Root cause on 6/ 30/16