05000423/LER-2013-001
| Millstone Power Station - Unit 3 | |
| Event date: | 02-19-2013 |
|---|---|
| Report date: | 04-15-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4232013001R00 - NRC Website | |
1. EVENT DESCRIPTION
On February 15, 2013,at 2313 hours0.0268 days <br />0.643 hours <br />0.00382 weeks <br />8.800965e-4 months <br />, with Millstone Power Station Unit 3 (MPS3) operating in Mode 1 at 100 percent power, operators discovered that the insulating cover installed over 3MSS*PT526, "B" Steam Generator [SG] Pressure Transmitter (SGPT) [MON] Channel 3, was not properly secured. When the problem was found, it was incorrectly assessed as not impacting equipment operability. However, on February 19, 2013, upon further review by the Electrical Equipment Qualification (EEQ) program engineer, it was determined that without the insulation box fully secured in place, the transmitter would not be adequately protected from a postulated high energy line break (HELB). Therefore, 3MSS*PT526 was declared inoperable per Technical Specification (TS) 3.3.2, Engineered Safety Features Actuation System Instrumentation, on February 19, 2013, at 1122 hours0.013 days <br />0.312 hours <br />0.00186 weeks <br />4.26921e-4 months <br />.
Information exists that 3MSS*PT526 was inoperable on February 15, 2013, when the problem was initially discovered. Since the condition existed for longer than allowed by TS 3.3.2, Action 20 (i.e., for more than six hours without the bistable being placed in trip), this is a reportable condition per 10 CFR 50.73 (a)(2)(i)(B) as an event or condition which was prohibited by the plant's Technical Specifications.
Operations subsequently closed and secured the insulation box to restore the correct Equipment Qualification (EQ) configuration on February 19, 2013, at 12:04, and the TS Action Statement was exited at 1310 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.98455e-4 months <br />. Because 3MSS*PT526 was restored to an operable condition less than six hours after it was declared inoperable, the bistable was not required to be placed in the trip condition as required by TS 3.3.2, Action 20. The insulation box limits the internal transmitter box ambient temperature to a peak temperature of 293 degrees F during a postulated HELB per Calculation US(B)-330, Revision 6 and Equipment Qualification Report (EQR) 134-1-4. Without the insulation box completely enclosing the transmitter, equipment qualification was not maintained because the maximum allowed qualification temperature of 318 degrees F would be exceeded during a HELB, and therefore the instrument operability could not be assured.
After the identification of the improperly secured enclosure on 3MSS*PT526, the other 11 MPS3 SGPTs were walked down and inspected on February 19, 2013. The inspections determined the enclosures were closed and intact, and therefore were in a condition such that the pressure transmitters were OPERABLE.
2. CAUSE
Lack of awareness of the purpose of the enclosure boundary combined with the lack of clear labeling identifying the HELB enclosure resulted in a delay in declaring the equipment inoperable.
3. ASSESSMENT OF SAFETY CONSEQUENCES
The twelve steam generator pressure transmitters (SGPTs) provide input to the main steam line isolation (MSLI) signal that closes the fast acting main steam isolation valves (MSIVs) located on each main steam line downstream of the four steam generators (SGs). Three transmitters are provided for each of the steam generators. Sustained uncontrolled steam release from more than one SG is prevented following a postulated steam system piping failure (SLB) by the automatic trip of the MSIVs.
For a SLB inside containment, MSLI is activated by either high containment pressure or low steam line pressure, or manual operator action from the control room. For a SLB outside containment, manual operator action from the control room would be taken to isolate the SG if the SGPTs failed to automatically provide inputs for MSLI.
In this instance, one of three transmitters provided for activating the MSLI for a steam generator was found inoperable. With one SGPT inoperable, the other two operable transmitters can perform the safety function if needed. The two operable SGPTs would have functioned to support identifying and isolating a faulted steam generator due to either a steam line break or a feed line break in the main steam valve building.
Therefore no loss of safety function is assumed. Regarding long term monitoring, the remaining operable SGPTs would have provided their post accident monitoring function for the required mission time, i.e., 30 days. In addition, there are alternate indications which could have been used, including SG level, auxiliary feedwater flow and reactor coolant system temperature if one or more SGPTs were to fail. Therefore, the safety consequences for this event are low.
4. CORRECTIVE ACTION
Operations created and installed a new label for the insulating box around each of the Steam Generator Pressure transmitters that indicates the box is a HELB barrier and is part of the EQ boundary for the transmitter.
Other actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES
MPS3 LER 2012-001-00, Main Steam Line Pressure Transmitters Declared Inoperable, reported a condition where the MPS3 SGPTs were declared inoperable because gaskets in Litton-Veam connector seals were not replaced after maintenance was performed in January 2012.
Energy Industry Identification System (El IS) codes are identified in the text as [XX].