05000266/LER-2007-008, For Point Beach, Unit 1, Non-Conservative Low Temperature Overpressure Protection System Basis

For Point Beach, Unit 1, Non-Conservative Low Temperature Overpressure Protection System Basis

ML073520049
Person / Time
Site:	Point Beach
Issue date:	12/17/2007
From:	Mccarthy J Florida Power & Light Energy Point Beach
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC 2007-0097 LER 07-008-00
Download: ML073520049 (6)

LER-2007-008, For Point Beach, Unit 1, Non-Conservative Low Temperature Overpressure Protection System Basis

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2662007008R00 - NRC Website

text

FPL Energy Point Beach Nuclear Plant December 17, 2007 FPL Energy Point Beach, LLC, 6610 Nuclear Road, Two Rivers, WI 54241 NRC 2007-0097 10 CFR 50.73 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Point Beach Nuclear Plant, Units 1 and 2 Dockets 50-266 and 50-301 Renewed License Nos. DPR-24 and DPR-27 Licensee Event Report 2661301 -2007-008-00 Non-Conservative Low Temperature Overpressure Protection System Basis Enclosed is Licensee Event Report (LER) 2661301 -2007-008-00 for the Point Beach Nuclear Plant, Units 1 and 2. This LER documents the discovery of a non-conservative basis for the low temperature overpressure protection system (LTOP). This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A), as a condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded.

Very truly yours, int Beach, LLC 7

James H. McCarthy Site Vice President I

Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Point Beach Nuclear Plant, USNRC Resident Inspector, Point Beach Nuclear Plant, USNRC PSCW An FPL Group company

(9-2007)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digitstcharacters for each block)

1. FACILITY NAME Point Beach Nuclear Plant Unit 1 NON-CONSERVATIVE LOW TEMPERATURE OVERPRESSURE PROTECTION SYSTEM BASIS

4. TITLE

, the NRC ma!

not conduct or sponsor, and a person is not required to respond to, tht information collection.

1

10. POWER LEVEL 100 This condition was reported via an 8-hour non-emergency report, EN 43750, on October 26, 2007, pursuant to 10 CFR 50.72(b)(3)(v)(D), as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The basis for the report was subsequently re-reviewed and it was determined that it should have been reported, pursuant to 10 CFR 50.72(b)(3)(ii)(A), as a condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded.

2. DOCKET NUMBER 05000266

5. EVENT DATE 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50,73(a)(2)(viii)(A) 20.2203(a)(I) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(~)(1

)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50,36(c)(l)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(~)(2) 50.73(a)(2)(v)(A) 73.71 (a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71 (a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A I - -

NRC FORM 366 (9-2007)

3. PAGE 1 OF 5 MONTH 10

6. LER NUMBER

12. LICENSEE CONTACT FOR THlS LER

CAUSE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFRS: (Check all that apply)

9. OPERATING MODE YEAR 2007 DAY 19 NAME Steve Forsha COMPONENT SYSTEM YEAR 2007

7. REPORT DATE TELEPHONE NUMBER (Include Area Code) 9201755-7793

14. SUPPLEMENTAL REPORT EXPECTED YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

E4 NO NUMBER

- 008 -

MONTH 12

8. OTHER FACILITIES INVOLVED MANU-FACTURER REV NO.

00 FACILITY NAME Point Beach Nuclear Plant Unit 2 FACILITY NAME ABSTRACT (Limit to 1400 spaces, ie., approximately 15 single-spaced typewritten lines)

On October 25, 2007, at 1930 CDT Point Beach Nuclear Plant (PBNP) Unit 1 and Unit 2 low temperature overpressure protection (LTOP) systems were declared inoperable as a result of the determination that the current LTOP actuation setpoint was non-conservative based on new calculation information. Changes were made to operating procedures to delineate operation of reactor coolant pumps and charging pumps during low temperature conditions. These changes provided the guidance required to ensure that the current LTOP setpoints remain conservative. Operability of LTOP was restored for both Unit 1 and Unit 2 on October 26,2007, at 1751 CDT upon issuance of the revised procedures. This issue was discovered as part of the ongoing corrective actions associated with pressure and temperature limit report (PTLR) issues at the plant.

15. EXPECTED SUBMISSION DATE DAY 17 DOCKET NUMBER 05000301 DOCKET NUMBER REPORTABLE TO EPlX YEAR 2007 MONTH

CAUSE

DAY SYSTEM YEAR COMPONENT MANU-FACTURER REPORTABLE TO EPlX

Reportable Occurrence:

J U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

LICENSEE EVENT REPORT (LER)

On October 19, 2007, as part of ongoing corrective actions associated with pressure and temperature limits report (PTLR) issues, an issue with the Point Beach Nuclear Plant (PBNP) Unit 1 and Unit 2 low temperature overpressure protection systems (LTOP) actuation was identified. A recent calculation showed that the maximum actuation setpoint may be non-conservative. Changes to the system parameters inputs were incorporated in the new calculations, which included:

1. FACILITY NAME Point Beach Nuclear Plant Unit 1

1) The mass input from the safety injection pumps was significantly higher (25%) based on the use of a PBNP-specific system flow model versus the previously used generic Westinghouse flow model, 2 ) The previous setpoint calculation did not consider instrument delay times in the opening of the power-operated relief valves (PORV), and

3) Instrument uncertainties had changed.

On October 25,2007, at 1930 CDT, PBNP Unit 1 and Unit 2 LTOP systems were declared inoperable based on the new calculation results. The new calculation resulted in a lower maximum LTOP setpoint of 1420 psig vs. the previous 1500psig. Additional operating restrictions were required to utilize 1420 psig as the maximum LTOP setpoint.

2. DOCKET

6. LER NUMBER 05000266 2007

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00 These operating restrictions are that only one reactor coolant pump may be in operation 1180°F and only two charging pumps may be in operation whenever the LTOP is enabled. These changes were incorporated into the operating procedures. The procedure changes provide the guidance required to ensure that the current LTOP setpoints remain conservative. Based on the issuance of the revised procedures with the recommended restrictions, operability of the LTOP system was restored for Unit 1 and Unit 2 on October 26,2007, at 1751 CDT.

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This condition was reported via an 8-hour non-emergency report, EN 43750, on October 25, 2007, pursuant to 10 CFR 50.72(b)(3)(v)(D), as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident Upon further review, it was recognized that this condition should have been reported pursuant to 10 CFR 50.72(b)(3)(ii)(A), as a condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded. Accordingly, this 60-day written report is submitted pursuant to 10 CFR 50.73(a)(2)(ii)(A).

Initial Conditions:

Units 1 and 2 were in MODE 1 at 100% power.

Description of Occurrence:

J U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

LICENSEE EVENT REPORT (LER)

A new calculation was performed by Westinghouse to update the PBNP PTLR with new pressure-temperature (PT) curves and LTOP setpoints that would be applicable to the end of the Renewed Licenses for Units 1 and 2. This new calculation took into account the additional fluence for the period of extended operation. The new calculation used a different methodology, Master Curve, for adjusted reference temperature (ART) values. It is recognized that the results of this calculation could not be used until the Master Curve methodology had been submitted to the Commission and was approved for use at PBNP.

1. FACILITY NAME Point Beach Nuclear Plant Unit 1 During the operability review of the LTOP systems, another difference between the current and proposed LTOP setpoint calculations was identified. The previous calculation of the maximum allowable reactor pressure at low temperatures used the limiting material properties in the beltline of the reactor vessel. The new calculation uses the 10 CFR 50, Appendix G requirement that the vessel pressure must be less than or equal to 20% of the preservice system hydrostatic test pressure at low temperatures.

The operating restrictions identified by the new calculation are primarily due to the above error. Since the Master Curve methodology was not the source for the operating restrictions, the potential impact on the existing LTOP setpoint was evaluated. The recommended LTOP operating restrictions were then added to plant procedures, and the lower maximum LTOP setpoint was incorporated in the current PT curves.

2. DOCKET 05000266 Apparent Cause:

6. LER NUMBER

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The cause of this event was determined to be personnel error. The previous calculation incorrectly considered the reactor vessel beltline material to be limiting for LTOP setpoints instead of the reactor vessel flange requirement contained in Table 1 of 10 CFR 50, Appendix G.

The previous calculation also contained the following non-conservative inputs/assumptions: 1) Used generic Westinghouse flow model; 2) Did not consider instrument delay times in the opening of the power-operated relief valves (PORVs); and 3) Instrument uncertainties that had changed.

These inputs/assumptions were corrected in the new calculation. The restrictions were implemented in the site operating procedures because the resulting operating restrictions contained in this calculation were not dependent upon the approval and implementation of the proposed Master Curve methodology.

Corrective Action

J U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

LICENSEE EVENT REPORT (LER)

The LTOP maximum setpoint was reduced from 1500 psig to 1420 psig. The actual setpoint of the PORVs remains at 41 5 psig. Two operational restrictions were placed in the operating procedures. When reactor coolant system temperature is 51 80" F, only one reactor coolant pump is allowed to be operating; and when LTOP is enabled, only two charging pumps are allowed to be operating.

1. FACILITY NAME Point Beach Nuclear Plant Unit 1 The change to the maximum pressure setpoint and the operational changes meet the operational requirements in the calculation and ensure that the LTOP setpoint is conservative.

Safety Assessment

2. DOCKET 05000266 The overall safety significance of this event is low. The primary difference between the two calculations (91.5 psig of a total 97.7 psig change) was a result of the 10 CFR 50 Appendix G flange requirements vs.

use of the beltline as the limiting material.

Per WCAP-14040-A, "Methodology Used to Develop Cold Overpressure Mitigating System Setpoints and RCS Heatup and Cooldown Limit Curves," Revision 4, Section 2.9 states:

6. LER NUMBER YEAR 2007

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00 "10 CFR Part 50, Appendix G contains the requirements for the metal temperature of the closure head flange and vessel flange regions. This rule states that the metal temperature of the closure flange regions must exceed the material unirradiated RT,,,

by at least 120°F for normal operation when the pressure exceeds 20 percent of the pre-service hydrostatic test pressure, 3106 psig. This pressure is 621 psig for a typical Westinghouse reactor vessel design.

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"This requirement was originally based on concerns about the fracture margin in the closure flange region.

During the boltup process, stresses in this region typically reach over 70 percent of the steady-state stress, without being at steady-state temperature. The margin of 120°F and the pressure limitation of 20 percent of hydrostatic test pressure were developed using the K,, fracture toughness, in the mid 1970s.

"Improved knowledge of fracture toughness and other issues which affect the integrity of the reactor vessel have led to the recent change to allow the use of K,, in the development of PT curves, as contained in Code Case N-640, "Alternative Reference Fracture Toughness for Development of P-T Limit Curves for Section XI, Division 1."

The discussion given in WCAP-15315, "Reactor Vessel Closure HeadNessel Flange Requirements Evaluation for Operating PWR and BWR Plants," concluded that the integrity of the closure headlvessel flange region is not a concern for any of the operating plants using the K,, toughness. Furthermore, there are no known mechanisms of degradation for this region, other than fatigue. The calculated design fatigue usage for this region is less than 0.1, so it may be concluded that flaws are unlikely to initiate in this region.

PBNP uses K,, in the development of the PT curves, as contained in ASME Code Case N-641, "Alternative Pressure-Temperature Relationship and Low Temperature Overpressure Protection System Requirements for Section XI, Division 1." Use of ASME Code Case N-641 at PBNP was approved by an NRC Safety Evaluation dated October 6, 2000.

J U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

LICENSEE EVENT REPORT (LER)

An evaluation is being performed to determine whether the non-conservative maximum setpoint value posed a concern relating to past operability. A supplemental report may be submitted pending the results of this evaluation.

Additional Information

1. FACILITY NAME Point Beach Nuclear Plant Unit 1 None

6. LER NUMBER YEAR 2007

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2. DOCKET 05000266

Previous Occurrences

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The following licensee event reports have been submitted during the past three years associated with analysis issues:

LER 266-2005-006-00, Calculation Errors in Model for ECCS Long Term Cooling LER 266-2005-005-00, Postulated Faults with Electrical Current in Excess of Maximum Interrupt Ratings and Non-Conservative Degraded Voltage Time Delay Relay Setting Technical Specification LER 266-2005-003-00, Potentially Inoperable Safety Injection Pumps