05000338/LER-2002-002

LER-2002-002,

Event date:	08-16-2002
Report date:	10-11-2002
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3382002002R00 - NRC Website

1.0 DESCRIPTION OF THE EVENT On August 16, 2002 during a review supporting Improved Technical Specification (ITS) implementation, it was discovered that the procedure tolerance band for the Low Temperature Overpressure Protection System (LTOPS) setpoints could result in a noncompliance with the TS limit. Specifically, the review of Licensee Event Report 50- 338, 50-339/2002-001-00 regarding an incorrect alarm setpoint for the Waste Gas Decay Tank (WGDT) Oxygen Analyzer (EIIS System WE, Component AA) prompted a review of the design and licensing basis regarding procedure tolerance bands. This review identified the LTOPS pressure and temperature concern.

Prior to ITS implementation, on August 20, 2002, the Unit 1 and 2 Technical Specifications (TS) 3.4.9.3 for the LTOP System required two Pressurizer Power Operated Relief Valves (PORV) (EIIS System AB, Component RV) to be operable with lift settings of (a) s 500 psig (Unit 1), s 415 psig (Unit 2) whenever any RCS cold leg temperature is 235 degrees F (Unit 1), s 270 degrees F (Unit 2) and (b) 5_ 395 psig (Unit 1), 375 psig (Unit 2) whenever any RCS cold leg temperature is 150 degrees F (Unit 1), s 130 degrees F (Unit 2). This was applicable in MODE 4 when the temperature of any Reactor Coolant System (RCS) cold leg is 235 degrees F (Unit 1), 270 degrees F (Unit 2), and in MODE 5 and MODE 6 when the head is on the reactor vessel and the RCS is not vented through a 2.07 square inch or larger vent. Current ITS requirements are worded slightly different, but the overall requirements are unchanged.

An example of the instrument calibration procedure (ICP) scaling for pressure and temperature for the LTOPS setpoints is described below. For an ICP setpoint of 500 psig, the scaling for the pressure instrument comparator is 0 - 3000 psig which is equivalent to 0 - 10 VDC, 500 / 3000 psig (rounded to 0.1667 times 10 VDC equals an ICP setpoint of 1.667 VDC; 0.1667 times 3000 psig equals a TS trip point of 500.1 psig). For an ICP setpoint of 235 degrees F, the scaling for the RCS Wide Range Temperature is 0 - 700 degrees F which is equivalent to 0 - 10 VDC, 235 / 700 degrees F (rounded to 0.3357 times 10 VDC equals an ICP setpoint of 3.357 VDC; 0.3357 times 700 degrees F equals a TS trip setpoint of 234.99 degrees F). The standard tolerance applied to Westinghouse comparators at North Anna is +/- 25 mVDC. This allows the technicians to leave the actual setpoint in non-compliance with TS.

On August 30, 2002, the review of completed instrument calibration procedures for the last three years, on Units 1 and 2, identified six occasions where the pressure or temperature settings were outside the TS limits. This could have prevented the PORVs from lifting at the TS limit. However, in each case the PORVs would have lifted at a pressure and temperature within the Safety Analysis Limit. Although the TS limit was exceeded, the PORVS would have performed their design function. A summary of the out of specification setting is provided below.

Pressure lift settings were identified out of specification as follows:

Unit 1 1

PORV

1455C 1455C TS Trip Point .500 psig psig ICP As-Found ICP As-Left Setpoint S Setpoint 1.667 VDC 1.668 VDC 1.667 VDC 1.669 VDC Actual 500.4 psig 500.7 psig Date 08/23/01 01/07/00 Temperature enable settings were identified out of specification as follows:

Unit PORV TS Trip Point ICP As-Found ICP As-Left Setpoint S Setpoint Actual Date 2 2456 >270°F 3.857 VDC 3.856 VDC 269.92 09/17/99 2 2455C >270°F 3.857 VDC 3.853 VDC 269.71 09/30/99 1 1455C >150°F 2.143 VDC 2.140 VDC 149.80 01/07/00 1 1455C >150°F 2.143 VDC 2.140 VDC 149.80 08/23/01 Therefore, this event is being reported as a condition prohibited by TS in accordance with 10CFR50.73(a)(2)(i)(B).

2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The LTOP System controls RCS pressure at low temperatures so the integrity of the reactor coolant pressure boundary is not compromised by violating the LTOP System design basis pressure and temperature limit curve. As designed for the LTOP System, each PORV is signaled to open if RCS pressure exceeds a limit determined by the LTOP actuation logic. The LTOPS actuation logic monitors both RCS pressure and temperature and determines when a condition is not acceptable. The wide range RCS temperature indications are auctioneered to select the lowest temperature signal. The lowest temperature signal is passed to a comparator circuit, which determines the pressure limit for that temperature. The pressure limit is then compared with the indicated RCS pressure from a wide range pressure channel. If the indicated pressure meets or exceeds the calculated value, the PORVs are signaled to open (on a staggered basis).

The Safety Analysis Limit (SAL) for the enabling temperature is 219.8 degrees F (Unit 1) and 254.3 degrees F (Unit 2). The margins between the Technical Specification allowable values for LTOPS temperature enable and the Safety Analysis Limit equals 15.2 degrees F (Unit 1) and 15.7 degrees F (Unit 2). This margin is greater than the currently applicable channel statistical accuracy of 13.5 degrees F. Available margin for Unit 1 is 15.2 degrees F minus 13.5 degrees F equals 1.7 degrees F. Available margin for Unit 2 is 2.2 degrees F. Thus, Unit 1 can accommodate a non-conservative LTOPS temperature enable by as much as 1.7 degrees F, while Unit 2 can accommodate a non- U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1)

DOCKET

05000 - 338 LER NUMBER (6) conservative LTOPS temperature enable by as much as 2.2 degrees F, while still meeting the requirements of the safety analysis. The actual temperature enable settings were within the SAL limits.

The Safety Analysis Limit (SAL) for the pressure lift setting is 560.54 psig (Unit 1) and 499.60 psig (Unit 2). PORV pressure lift settings, taking into account the TS allowed value plus instrument uncertainty, were calculated to be 553.5 psig (Unit 1) and 468.5 psig (Unit 2). The margins between the Safety Analysis Limit and actual PORV pressure lift settings equal 7.04 psig (Unit 1) and 31.1 psig (Unit 2). Thus, Unit 1 can accommodate a non-conservative PORV pressure lift setting of 7.04 psig, and Unit 2 can accommodate a non-conservative PORV lift setting of 31.1 psig while still meeting the requirements of the safety analysis. The actual PORV pressure lift settings were within the SAL limits.

The PORVs for both units were able to perform their design function. Therefore, the health and safety of the public were not affected by this event.

3.0 CAUSE The cause of the event is attributed to personnel error that resulted in calibration procedures with tolerance limits so close to the TS requirements for pressure and temperature settings that a very small variance would cause the TS limits to be exceeded.

The development of the calibration procedures were based on the channel statistical analysis and the safety analysis limits for this system without ensuring the TS limits would never be exceeded.

4.0 IMMEDIATE CORRECTIVE ACTION(S) An information action statement was entered on August 16, 2002, to recalibrate the instrument loops prior to entry in to MODE 4.

5.0 ADDITIONAL CORRECTIVE ACTIONS Procedure revisions were initiated and subsequently completed providing temperature enable settings and pressure lift settings that would prevent exceeding the TS limits.

The corrected Unit 2 LTOP temperature enable and pressure settings were installed for both PORVs on September 4, 2002. The corrected Unit 1 LTOPS temperature enable and pressure lift settings were installed for both PORVs on September 5, 2002.

6.0 ACTIONS TO PREVENT RECURRENCE No further actions are required.

7.0 SIMILAR EVENTS LER N1/2-02-001-00 was written for a similar concern where the procedure tolerance band for the alarm setpoint for the Waste Gas Decay Tank Oxygen Analyzer may allow the tank oxygen to exceed the limit.

8.0 MANUFACTURER/MODEL NUMBER Not Applicable 9.0 ADDITIONAL INFORMATION None