05000220/LER-2008-003

LER-2008-003, Power Supplies for Drywell Pressure Indication not Qualified for Required Post-Accident Operating Duration

Docket Number
Event date:	11-06-2008
Report date:	01-06-2009
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2202008003R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS:

On November 7, 2008, Nine Mile Point Unit 1 was operating steady state at 100% power.

B. EVENT:

During design and qualification basis validation activities for Environmental Qualification (EQ), the power supplies supporting the post accident drywell pressure monitors were determined to be unqualified for the required post-accident operating duration. These power supplies support drywell pressure monitors PI-201.2-483A and PI-201.2-484A. This deficiency is due to the limited radiation levels to which the reactor trip unit cabinet power supplies, in the Analog Trip System (ATS) cabinets are qualified for under LOCA conditions. This condition does not affect the ability of the ATS cabinets to perform their required trip or interlock function(s) following a LOCA or other Regulatory Guide (RG) 1.97 functions when they are required.

The condition was identified based on a revised point-specific dose calculation for the ATS cabinets. Based on the calculation, a Design Bases LOCA will result in the total integrated dose reaching the qualified radiation levels in less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. These instruments are required to function for 100 days post-accident.

Upon declaring the monitors inoperable, TS Table 3.6.11-2, Action 4.b, requires a pre-planned alternate method of monitoring this parameter to be implemented within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Instruments PI-201.2-105A and PI-201.2-106A are wide range drywell pressure indication loops approved as RG 1.97 instruments and are pre-planned alternates for the TS monitors.

THE EVENT:

The power supplies supporting the post-accident range drywell pressure transmitters were determined to be unqualified for the required post-accident operating duration. These power supplies support instrumentation loops for PI-201.2-483A and PI-201.2-484A. This deficiency is due to the limited radiation levels to which the reactor trip unit cabinet power supplies (ATS cabinets) are qualified for LOCA conditions. This condition does not affect the ability of the ATS cabinets to perform their required trip or interlock function(s) following a LOCA or other RG 1.97 functions when they are required.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

September 23, 1981: Nine Mile Point Nuclear Station (NMPNS) informed the NRC that Containment Pressure Monitors as required by NUREG-0737 have been installed (PI-201.2­ 483A and PI-201.2-484A).

April 1, 1985: Drywell pressure monitors added to Unit 1 Technical Specifications as part of License Amendment 72.

July 28, 1989: PI-201.2-483A and PI-201.2-484A specifically identified as wide range drywell pressure monitors in NMPNS response to NUREG-0737 Supplement 1, Section 6.2.

November 6, 2008, 1553: Engineering recognized that drywell pressure monitors PI-201.2-483A and PI-201.2-484A are not qualified for the required post-accident operating duration.

November 7, 2008, 0129: Both channels of wide range drywell pressure monitors declared inoperable because they are not qualified for the required post-accident operating duration.

Implemented use of pre-planned alternative drywell pressure monitors PI-201.2-105A and PI-201.2­ 106A per TS Table 3.6.11-2, Action 4.b.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

No other systems or secondary functions are affected by this condition.

F. METHOD OF DISCOVERY:

The condition was identified based on a revised point-specific dose calculation performed for the ATS cabinets.

G. MAJOR OPERATOR ACTION:

No significant Operator action was required to respond to this condition.

H. SAFETY SYSTEM RESPONSES:

No safety system response was required nor occurred as a result of this condition.

II. CAUSE OF EVENT:

The cause of this event was a historical error in the EQ analysis for the post-accident drywell pressure monitors. The analysis failed to consider the potential impact of post-LOCA radiation levels on the power supplies, which are located inside the Reactor Building, as part of the EQ analysis.

III. ANALYSIS OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition not allowed by Technical Specifications because:

• Technical Specification 3.6.11 requires two channels of drywell pressure indication be operable whenever the plant is in the power operating condition.

• Drywell pressure indication loops PI-201.2-483A and PI-201.2-484A are credited for meeting this requirement.

• It has been determined that the power supply for PI-201.2-483A and PI-201.2-484A are not qualified for the required post-accident operating duration, and therefore are inoperable.

This condition has existed since Unit 1 TS Amendment 72 was issued April 1, 1985.

• Use of a pre-planned alternate drywell pressure monitors was not implemented until November 7, 2008.

Drywell pressure monitors PI-201.2-483A and PI-201.2-484A have not been qualified for the required post-accident operating time since they were installed. The channels are scheduled to be restored to an operable condition no later than April 30, 2011. In the interim, pre-planned alternate drywell pressure monitors PI-201.2-105A and PI-201.2-106A will be relied upon to satisfy TS requirements for monitoring post-accident drywell pressure.

Drywell pressure indication is an Emergency Operating Procedure (EOP) key parameter for design basis conditions. However, other drywell pressure instrumentation than the TS instrumentation, narrow and wide range, is credited in the EOP Bases Documentation as EOP key parameters that provide the same functions. The other drywell pressure instrumentation loops are not affected by this issue. These instruments remain fully capable to meet the required design functions during accident conditions, and provide indication of the full range of expected pressures in the drywell.

These instruments are EOP key parameters.

Technical Specification Section 3.6.11 requires two channels of Drywell pressure to be operable.

Both the normal and wide range instrumentation loops include two channels. Both are fully capable of meeting the required plant conditions through the narrow range (0-4 PSIG) loops supporting indicators PI-201.2-13A and PI-201.2-01B and the wide range (0-75 PSIG) supporting indicators Pl­ 201.2-105A and PI-201.2-106A.

The actual safety significance of this condition is low because the alternative drywell pressure monitors being used, PI-201.2-105A and PI-201.2-106A, are the monitors used in the EOPs and Severe Accident Procedures (SAPs) for monitoring post-accident drywell pressure rather than the TS monitors.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

Use of a pre-planned alternate drywell pressure monitors has been implemented. There is no time limit specified in TS for maximum duration that a pre-planned alternative can be used.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

Actions required to resolve this issue for PI-201.2-483A and PI-201.2-484A include an alternative analysis to determine the best design change solution. Design change options to restore the originally intended monitoring capabilities include, but are not limited to:

a) provide new/different power supplies to PI-201.2-483A and PI-201.2-484A instrument loops, b) change the range of PI-201.2-105A and PI-201.2-106A instrument loops and add recording capability, to meet NUREG-0737, and make them the designated TS monitors, c) install shielding to the existing ATS cabinet power supplies sufficient for Environmental Qualification.

This analysis will be complete and the selected method implemented no later than April 30, 2011.

This activity is being tracked by CR-2008-008383. This completion date is appropriate because:

• An outage is required to implement any of the proposed solutions.

• There is limited time to analyze the options and prepare a design change for installation during the spring 2009 refueling outage. If the modification cannot be completed in the 2009 outage, the next planned outage is in the spring of 2011.

Design and qualification basis validation reviews were recently completed to ensure compliance with 10 CFR 50.49 for all existing Unit 1 EQ components. No other reportable conditions were identified as a result of this review.

A. FAILED COMPONENTS:

No failed components are associated with this condition.

B. PREVIOUS LERs ON SIMILAR EVENTS:

Nine Mile Point Unit 2, LER 2008-001, submitted 04/10/2008, Unqualified Relays Installed Since Original Construction Result in an Unanalyzed Condition C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

THIS LER:

COMPONENT IEEE 803 FUNCTION�IEEE 805 SYSTEM IDENTIFIER�IDENTIFICATION Drywell Pressure Indicator PI� IP Power Supply RJX IP D.SPECIAL COMMENTS:

None