ML12177A430
| ML12177A430 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 11/09/2012 |
| From: | William Jones NRC/RGN-II |
| To: | Bahadur S Division of Policy and Rulemaking |
| Cruz H | |
| References | |
| TIA 2012-009 | |
| Download: ML12177A430 (23) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II 245 PEACHTREE CENTER AVENUE NE, SUITE 1200 ATLANTA, GEORGIA 30303-1257 November 9, 2012 MEMORANDUM TO: Sher Bahadur, Deputy Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation FROM: William Jones, Deputy Director /RA/
Division of Reactor Projects
SUBJECT:
TASK INTERFACE AGREEMENT (CONCURRENCE) -
OPERABILITY OF BRUNSWICK UNIT 2, REACTOR WATER CLEANUP SYSTEM ISOLATION INSTRUMENTATION WITH THE INLET FLOW ORIFICE INSTALLED BACKWARDS (TIA 2012-09)
1.0 INTRODUCTION
This Task Interface Agreement (TIA) documents the U.S. Nuclear Regulatory Commission (NRC) staffs position that the Brunswick Nuclear Power Plant, Unit 2 (Brunswick-2), Reactor Water Cleanup (RWCU) System Isolation Instrumentation was not operable while the inlet flow orifice was installed backwards. The orifice was installed backwards during the Unit 2 refueling outage in April 2011, until August 2011, when the orifice was oriented correctly. Region II staff issued a licensee-identified violation (LIV) of technical specification (TS) 3.3.6.1 (see ) in Inspection Report 05000325,324/2011004 as a result of the maintenance error.
The licensee initially submitted a Licensee Event Report (LER) for the issue as a condition prohibited by TS 3.3.6.1. After further analysis, the licensee retracted the LER and contested the LIV stating that the error did not render the RWCU isolation instrumentation inoperable (see ). Region II consulted with the Office of Nuclear Reactor Regulation (NRR) staff and has concluded that the LIV of TS 3.3.6.1 is valid. Region II seeks to document this position via this concurrence TIA.
2.0 BACKGROUND
The Brunswick-2 Updated Final Safety Analysis Report (UFSAR), states RWCU System Isolation on Differential Flow-High is provided to detect gross leakage resulting from a pipe or component rupture and initiate automatic isolation that will prevent excessive loss of reactor coolant and release of significant amounts of radioactive material, with the analytical flow rate limit being no greater than 300 gallons per minute (gpm). Flow measurement is a critical component in the measurement of RWCU differential flow to ensure RWCU system isolation functions as designed.
S. Bahadur 2 Technical Specifications require that the RWCU differential flow instrumentation be demonstrated operable by performance of Surveillance Requirement (SR) 3.3.6.1.5, Functional Test once every 184 days, and SR 3.3.6.1.6, Channel Calibration once every 24 months.
RWCU instrument channels are usually considered operable if the SRs verify that the channels are capable of isolating the RWCU System at equal to or less than a value of 73 gpm differential flow. The 73 gpm TS differential flow rate provides an adequate margin considering all instrument uncertainties to ensure that the 300 gpm analytical limit is not exceeded during accidents, transients or anticipated operational occurrences.
In August 2011, the licensee discovered a significant difference between indicated RWCU inlet and return flows. Upon investigation, the licensee found that the inlet flow orifice was installed backwards, causing the inlet flow rate to be approximately 18 percent lower than the expected value when compared to the system return flow rate. This 18 percent error in RWCU inlet flow rate resulted in instrument readings to be 46 gpm non-conservative with respect to actual RWCU differential flow rate. Combining the 46 gpm attributed to the 18 percent error in RWCU inlet flow rate with the nominal 43 gpm RWCU high differential flow instrument readings exceeds the TS Allowable Value (AV) of 73 gpm. This condition was introduced during the Unit 2 refueling outage, which ended in April 2011. Upon discovery of the incorrectly installed flow orifice on August 2, 2011, the licensee declared TS 3.3.6.1 Function 5.a not met and manually isolated the RWCU system.
The licensee also reported the condition in an LER. However, after further review, the licensee concluded that the RWCU differential flow isolation function was Operable with the inlet flow orifice installed backwards, retracted the LER, and formally contested the LIV. Region II staff then held discussions with NRR staff from the Technical Specifications Branch and the Instrumentation and Control Branch and concluded that the LIV is valid.
Licensees Position The licensee contends that the error associated with the incorrectly installed RWCU inlet flow orifice is within the margin to the safety limit of 300 gpm and that the error should be allocated to the available margin between the TS AV (73 gpm) and the safety limit (300 gpm), as opposed to allocating the error to the margin between the nominal setpoint (43 gpm) and the TS AV. The licensee justifies the allocation of the error in this manner by characterizing the error as unmeasurable uncertainties. The term unmeasurable uncertainties is used in the licensees setpoint calculation and is defined as those uncertainties not directly measured or affected by the instrument calibration surveillance. For example, manufacturing tolerances and normal flow element wear are given as examples of unmeasurable uncertainties. Unmeasurable uncertainties are allocated against the available margin between the TS AV and the safety limit in the licensees RWCU high differential flow isolation setpoint calculation. The licensees position is fully explained in their operability determination (Enclosure 3) and the LIV denial letter (included in Enclosure 2).
NRC Staff Evaluation
The NRR staff evaluation included review of the Brunswick-2 UFSAR; Brunswick-2 Technical Specifications for Limiting Conditions for Operation applicability, Surveillance Requirement applicability and Table 3.3.6.1-1, Primary Containment Isolation Instrumentation, Function 5.a,
S. Bahadur 3 RWCU Differential Flow - High; the licensee documentation withdrawing Licensing Event Report 2-2011-001; the licensees operability determination (AR 479248-21) and the regulations under Title 10 of the Code of Federal Regulations (10 CFR) Part 50.36, Technical Specifications.
The licensees contested violation letter BSEP 11-0108, dated December 14, 2011, stated that operability of the RWCU Differential Flow - High instrumentation is dependent upon:
(1) meeting the TS required AV of 73 gpm and (2) the overall ability of the instrument loop to perform its intended safety function. The flow safety function of the instrument loop is met when it can be demonstrated that the analytical limit is met. the staffs evaluation of the information provided by the licensee in Enclosures 2 and 3 confirms that sufficient safety margin was available and the additional error did not prevent the loop from meeting the analytical limit for the RWCU Differential Flow - High function.
Under 10 CFR 50.36(c)(2) Limiting conditions for operation, (i) Limiting conditions for operation are the lowest functional capability or performance levels of equipment required for safe operation of a facility. When a limiting condition for operation is not met, the licensee shall []
follow any remedial action permitted by the technical specifications until the condition can be met. Whether a TS LCO is satisfied cannot solely be determined by the successful performance of licensee surveillance procedures. It is possible that the surveillance procedures are not adequate to demonstrate a system, subsystem, component, or device is capable of performing its specified safety function(s). The surveillance procedures corresponding to the Surveillance Requirements for RWCU System differential flow-high presume that the flow element is installed correctly. SR 3.3.6.1.6 requires performance of a channel calibration once every 24 months. The TS definition for Channel Calibration establishes requirements to verify that channel safety functions will be met. The pertinent part of the definition of Channel Calibration is:
A Channel Calibration shall be the adjustment, as necessary, of the channel output such that it responds within the necessary range and accuracy to known values of the parameter that the channel monitors. The Channel Calibration shall encompass all devices in the channel required for channel Operability and the Channel Functional Test. Calibration of instrument channels with resistance temperature detector (RTD) or thermocouple sensors may consist of an inplace qualitative assessment of sensor behavior and normal calibration of the remaining adjustable devices in the channel.
Thus, the TS AV does not account for an incorrectly installed flow element unless the calibration procedure adjusts the channel output to respond within the necessary range and accuracy to known values of the parameter that the channel monitors.
The NRC staff reviewed the licensees description of the RWCU high differential flow surveillance procedure documents. The procedure for SR 3.3.6.1.6 does not evaluate the channel sensor (flow element), does not compare the calculated flow to a known value of the actual plant flow rate, and does not include an in situ qualitative assessment of sensor behavior similar to the comparison required to be performed for RTD or thermocouple sensors. RWCU high differential flow surveillance procedures neither address an incorrectly installed flow element nor require the TS AVs to be verified to ensure that passing the channel calibration test
S. Bahadur 4 validates that the TS LCO has been satisfied. Therefore, the incorrectly installed flow element created an unaccounted-for error, because the calculated TS AV did not address the condition of an incorrectly installed sensor and no in-situ qualitative assessment of sensor behavior was performed. Furthermore, the Channel Calibration did not compare calculated flow to a known value of actual flow. In this instance, there is a valid argument for stating that the safety significance of this degraded condition is low, because the estimate of the magnitude of the unaccounted for error is small compared to the remaining safety margin after accounting for all identified errors. The regulations under 10 CFR 50.36(b) require plant-specific TSs be derived from the analyses and evaluations included in the UFSAR. The Brunswick-2 TSs AV is the LCO (10 CFR 50.36(c)(2)(i)) and it is the AV that establishes an appropriate margin to the UFSAR Analytical Limit for RWCU system isolation on high differential flow. The purpose of SR 3.3.6.1.6 is to verify that the RWCU Differential Flow - High instrumentation is operable when channel output is such that it responds within the necessary range and accuracy to known values of the RWCU flow to isolate RWCU on a sensed differential flow of 73 gpm.
Region II staff consulted the NRR Technical Specifications Branch and the Instrumentation and Control Branch. NRR concurs with the RII position outlined in this assessment. The assessment, in summary, states that the licensees assertion that the instrument inaccuracy associated with the flow orifice installation error is not applicable to the TS AV is not appropriate because allocation of instrument inaccuracy introduced by maintenance errors is not accounted for in the licensees calculation and should be evaluated as a degraded condition. This degraded condition has a clear and quantifiable impact on the instruments ability to perform its TS-required function of isolating the RWCU system piping with a setpoint of less than or equal to 73 gpm.
3.0 CONCLUSION
Based on the Region II and NRR assessment of the condition of the Brunswick-2 RWCU system with the inlet flow orifice installed backwards, the NRC staff has concluded that TS Table 3.3.6.1-1, Function 5.a was inoperable from the date the orifice was installed backwards during the Unit 2 refueling outage in April 2011 until the date in August 2011, when the orifice was reinstalled correctly. The licensees evaluation of the condition is not correct and the LIV issued by Region II is valid. Furthermore, the condition is reportable as a condition prohibited by TS per 10 CFR Part 50.73(a)(2)(i)(B).
Contacts:
Region II POCs: Phillip Niebaum, Acting Senior Resident Inspector -
Brunswick (910-457-9531)
Randall Musser, Chief, Division of Reactor Projects Branch 4 - Region II (404-997-4603)
Bernard Dittman, Instrumentation & Controls Engineer, NRR David Rahn, Senior Instrumentation & Controls Engineer, NRR Carl Schulten, Senior Reactor Engineer, Technical Specifications Branch, NRR
Enclosures:
- 1. LIV of TS 3.3.6.1 issued in Inspection Report 05000325,324/2011004.
- 2. Carolina Power & Light Company initiated correspondence (LER, LER retraction, and LIV denial letter).
- 3. Carolina Power & Light Company Operability Determination.
ML12177A430 X SUNSI REVIEW COMPLETE OFFICE RII:DRP RII:DRP RII:DRP NRR: DSS/STSB NRR: DE/EICB NRR: DPR/PLPB NRR: DPR/PLPB NRR: DPR: D RMusser for PNiebaum RMusser via WJones via RStattel for NAME via email email email RElliott JThorp HCruz SStuchell (A) SBahadur Date 10/16/12 10/24/12 10/24/12 10/25/12 10/15/12 10/15/12 10/25/12 11/6/12 S. Bahadur 5 Distribution w/encls:
S. Stuchell, NSIR R. Elliott, NRR R. Musser, DRP C. Schulten, NRR H. Cruz, NRR P. Niebaum, DRP M. Catts, DRP D. Rahn, NRR S. Stuchell, NRR S. Bahadur, NRR D. Baxley, NRR P. Obrien, DRP J. Thorp, NRR B. Dittman, NRR RidsNrrDpr RidsNrrLA RidsRgn2MailCenter RidsAcrsAcnwMailCtr RidsRgn3MailCenter RidsRgn4MailCenter RidsNrrDssStsb RidsResOd Resource RidsNroMailCenter Resource RidsRgn1MailCenter
Licensee-Identified Violation Issued By Region II to Brunswick in IR 05000325,324/2011004 Technical Specification (TS) 3.3.6.1, Primary Containment Isolation Instrumentation, requires that the reactor water cleanup (RWCU) high differential flow instrumentation be operable in modes 1, 2, or 3. If the instrumentation is not operable, then TS 3.3.6.1 requires that the RWCU penetration flow path be isolated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Contrary to the above, the licensee identified that the RWCU high differential flow instrumentation was not operable and the penetration flow path was not isolated when the unit entered mode 1 on April 16, 2011 until August 2, 2011, because the RWCU inlet flow sensing element was installed backwards, causing the flow sensing element to be inaccurate. The resulting inaccuracy caused the instrumentation to be unable to isolate within the required TS limit of less than or equal to 73 gallons per minute differential flow. The finding was determined to be of very low safety significance per Appendix A of Inspection Manual Chapter 0609, Significance Determination Process, because the finding:
- 1) did not represent a degradation of the radiological barrier function provided for the control room, auxiliary building, spent fuel pool, or the standby gas treatment system, 2) did not represent a degradation of the barrier function of the control room against smoke or a toxic atmosphere, and 3) did not represent an actual open pathway in the physical integrity of reactor containment. Upon discovery of the condition, the licensee isolated the affected penetration flow path and installed the flow sensing element correctly. The issue is in the licensees corrective action program (CAP) as nonconformance report (NCR) #479248.
Enclosure 1
Initial LER, LER Retraction, and LIV Denial Letter Enclosure 2
2 Enclosure 2
3 Enclosure 2
4 Enclosure 2
5 Enclosure 2
6 Enclosure 2
7 Enclosure 2
8 Enclosure 2
9 Enclosure 2
10 Enclosure 2
11 Enclosure 2
12 Enclosure 2
13 Enclosure 2
Licensees Operability Determination (AR 279248)
Enclosure 3
2 Enclosure 3
3 Enclosure 3