ML18064A794
| ML18064A794 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 06/07/1995 |
| From: | Haas K CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9506130378 | |
| Download: ML18064A794 (3) | |
Text
KurtM. Haas consumers Power Plant Safety and Licensing Director POWERING MICHIGAN"S PIUllillESS Palisades Nuclear Plant: 27780 Blue Star Memorial Highway, Covert, Ml 49043 June 7, 1995 U S Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT ADDITIONAL INFORMATION TO SUPPORT NRC INSPECTION REPORT NO. 50-255/95002(DRP)
NRC Inspection Report 95002, dated March 6, 1995, contained a Notice of Violation concerning the failure to follow procedures for the independent verification of installation steps for a temporary modification. This violation stemmed from an event on January 11, 1995, during which the installation of a temporary modification resulted in the illumination of the loss of load bistable trip indicating lights on two of the four loss of load trip channels.
Section 5 of the Inspection Report contains ~ summary of the maintenance and surveillance activities that were reviewed during the inspection. Section 5 also contains a detailed description of the investigation of the events
- surrounding the temporary modification which led to the conclusion that a violation of our procedural controls had occurred.
This description was consistent with our understanding of the event at the time we communicated it to the Resident Inspector.
As we continued our investigation after the Inspection Report was completed, however, our understanding of the event and our conclusions changed.
Our violation response dated April 5, 1995, reflected this new understanding.
It is
. appropriate that we provide additional clarification in specific response to some of the statements made in the Inspection Report.
During the Resident Inspector's review of the events that resulted in the violation, discussions were held concerning what the loss of load bi-stable trip lights, referred to as tell-tale lights, indicate.
The tell-tale lights are generally viewed as on~ indication of a reactor trip.
As a result, the NRC Inspection Report states that the bistable trip lights provide one 9506130378 950607 PDR ADOCK 05000255 Q
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2 indication of a reactor trip and the Notice of Violation contained a statement that the event resulted in an indicated reactor trip with the plant at 100%
power.
Our response to the Notice of Violation stated that we had determined that these tell-tale lights are not an "indicated reactor tr1p" but are actually from loss of load auxiliary trip unit trips, which obtain their input from turbine t~ip circuits. The tell-tale portion of the auxiliary trip unit circuit is not the part which outputs a trip signal to the reactor protection system.
They only indicate an input from the turbine trip control circuitry.
In addition, the electronic tell-tale circuits are much faster responding than the relays which provide the trip signal to the RPS and, therefore, they are much more prone to spurious illumination from system generated noise.
The tell-tale lights are illuminated when a turbine trip occurs and could, therefore, be an indirect indication that the reactor tripped.
Interviews conducted by the Resident Inspector shortly after the event indicated that some control room operators consider this an indication that a reactor trip occurred.
Our further reviews determined that their function, from a design standpoint, is to indicate when a loss of load (turbine trip) has occurred and is not to be an indication of a reactor trip. This conclusion was conveyed in our violation response.
It is also stated in the Inspection Report that the independent verifjcatioh, if properly iompleted, should hav~ revealed that an incorrect wiring configuration would occur and would have prevented the occurrence.
In our violation response we agreed that the technician performing the work failed to understand that the independent verification activities for a temporary modification are required to be completed concurrent with the modification.
Because of thi~ misunderstanding, the technician was planning to obtain the independent verification following the landing of the first two wires.
Our
- subsequent review of the event determined that, because the instructions for completing the work were *faulty, properly performed independent verification would not have prevented *the event. This led to our conclusioD expressed in the violation response that performing an independent verification during the modification process would not have prevented the situation from occurring.
This is contrary to our original understanding and what we had discussed with the Resident Inspector.
In summary, our initial investigation of the event resulted in incorrect statements being made to the Resident Inspector.
These statements were subsequently incorporated into Inspection Report 95002.
As we learned more during our continuing investigation, we were led to conclusions somewhat different from those we and the Resident Inspector had originally reached.
The changes in our conclusions were briefly conveyed in the violation response to assure accuracy, but we did not provide a detailed explanation within the violation response to explain the differences between the NRC description of the event and our final conclusions. These differences should not be construed as implying that the NRC description of the event was faulty, as this is not the case.
The NRC description of the event in the Inspection Report was consistent with our understanding at the time the Inspection Report was written.
- We trust that this explanation clarifies why our April 5, 1995 repiy to the Notice of Violation differed from some of the statements in Section 5 of Inspection Report 95002.
SUMMARY
OF COMMITMENTS This letter contains no new commitments and no revisions to existing commitments.
Kurt M Haas Plant Safety and Licensing Director CC Administrator, Region III, USNRC NRR Project Manager, USNRC NRC Resident Inspector - Palisades 3