ML070240595

Notice of Enforcement Discretion for Exelon Generation Company LLC Regarding Dresden Nuclear Power Station, Unit 2 (NOED 07-3-01; TAC MD4044)

ML070240595
Person / Time
Site:	Dresden
Issue date:	01/24/2007
From:	Satorius M Division Reactor Projects III
To:	Crane C Exelon Generation Co, Exelon Nuclear
References
NOED 07-3-01, TAC MD4044
Download: ML070240595 (7)

Text

January 24, 2007Mr. Christopher M. CranePresident and Chief Nuclear OfficerExelon NuclearExelon Generation Company, LLC4300 Winfield RoadWarrenville, IL 60555

SUBJECT:

NOTICE OF ENFORCEMENT DISCRETION FOREXELON GENERATION COMPANY LLC REGARDINGDRESDEN NUCLEAR POWER STATION, UNIT 2(NOED 07-3-01; TAC MD4044)

Dear Mr. Crane:

By letter dated January 22, 2007, you requested that the U.S. Nuclear RegulatoryCommission (NRC) exercise discretion to not enforce compliance with the actionsrequired in Technical Specification (TS) 3.1.7, "Standby Liquid Control (SLC) System." Your letter documented information previously discussed with the NRC in a telephoneconference on January 19, 2007, at 3:45 a.m. (All times discussed in this letter refer toCentral Standard Time). You stated that on January 19, 2007, at 5:10 a.m., DresdenUnit 2 would not be in compliance with TS 3.1.7 Required Action B.1 which wouldrequire Exelon to place Unit 2 in Mode 3 (Hot Shutdown) per Required Action C.1 onor before 5:10 p.m. on January 19, 2007. You requested that a Notice of EnforcementDiscretion (NOED) be granted pursuant to the NRC's policy regarding exercise ofdiscretion for an operating facility, set out in Section VII.C of the NRC EnforcementPolicy, and be effective for the period from 5:10 a.m. on January 19, 2007, to 5:10 a.m.on January 22, 2007. This letter documents our telephone conversation on January 19,2007, when we orally issued this NOED at 5:03 a.m. We understand that the conditioncausing the need for this NOED was corrected and you exited from TS 3.1.7 RequiredAction B.1 and from this NOED on January 20, 2007, at 12:15 a.m.The principal NRC staff members who participated in that telephone conferenceincluded: Steve West, Deputy Director, Division of Reactor Projec ts (DRP), RIII;John Lubinski, Deputy Director, Division of Operating Reactor Oversight and Licensing,Office of Nuclear Reactor Regulation (NRR); Mark Ring, Branch Chief, Reactor Projects Branch 1, DRP, RIII; Charles Phillips, Senior Resident Inspector, Dresden; Joe Williams,Project Manager, NRR; David Hills, Branch Chief, Engineer ing Branch 1, Division ofReactor Safety (DRS), RIII; Allen Hiser, Chief, SG Tube Integrity and ChemicalEngineering Branch, NRR; Terence Chan, Chief, Piping and NDE Branch, NRR; HaroldChernoff, Chief, Plant Licensing Branch I-1, NRR; Mel Holmberg, Senior Metallurgical Inspector, DRS, RIII; Sonia Bur gess, Senior Risk Analyst, DRS, R III; and J ohn Kramer,Senior Risk Analyst, NRR.

C. Crane-2-Your staff requested enforcement discretion to preclude a required entry into Mode 3(Hot Shutdown) by 5:10 p.m. on January 19, 2007. To accomplish this, you requestedthat the 8-hour Completion Time for TS 3.1.7 Required Action B.1 be extended by72 hours to 5:10 a.m. on January 22, 2007, to accomplish restoration of the SLC systemto an operable status. With this extended Completion Time, the unit would have beenrequired by TS 3.1.7 Required Action C.1 to enter Mode 3 (Hot Shutdown) by 5:10 p.m.on January 22, 2007, if both SLC subsystems remained inoperable. Technical Specification Limiting Condition for Operation 3.1.7, "Standby Liquid Control(SLC) System," states that "Two SLC subsystems shall be OPERABLE." Thisspecification is applicable in MODES 1 and 2. Technical Specification 3.1.7 Condition Bprovides required actions for two SLC subsystems inoperable. If two SLC subsystemsare inoperable under Condition B, action is required to restore one SLC subsystem tooperable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. Technical Specification 3.1.7 Condition C requires theunit to be placed in Mode 3 (Hot Shutdown) within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> if Condition B is notmet. At 9:10 p.m. on January 18, 2007, your staff determined that a small linear crackleaking on the Unit 2 SLC tank temperature alarm sensor rendered both SLCsubsystems inoperable. This placed Unit 2 in TS 3.1.7 Condition B, "Two SLCSubsystems Inoperable." The 8-hour Completion Time of TS 3.1.7 Required Action B.1expired at 5:10 a.m. on January 19, 2007.

At the expiration of this Completion Time,action was required to place Unit 2 in Mode 3 (Hot Shutdown) within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />(i.e., 5:10 p.m. on January 19, 2007). Your staff provided the following information in your letter: While performing a Senior Manager Overview of Training Activities in the plant,personnel identifi ed sodium pentaborate crystallizati on surrounding thecircumference of the thermowell. The thermowell contains a sensor that inputsto indication only and a main control room annunciator. The cracked componentwas stainless steel. Your staff sus pected that the crystallization was due to acrack on a bushing into which the thermowell was mounted. The SLC tank is astainless steel, American Society of Mechanical Engineers (ASME) Section XIClass 2 structure that is vented to the atmosphere.Technical Specification surveillances consistently confirmed that requirementsfor volume (daily) and concentration (monthly) continued to be met. During Dresden Maintenance Outage Number 12 (D2M12) in November 2006,the SLC atom weight concentration was increased as part of a modification. Aminor leak on the thermowell on a threaded connection was repaired while thetank was drained. You suspected that the repair process in D2M12 initiated aflaw which eventually cracked and led to this leak. However, the root cause ofthe leak will be confirmed through NDE analyses, or possibly by material removalfor offsite analysis.

C. Crane-3-You stated that recent industry issues involving operational leakage in ASMECode components resulted in a heightened awareness that these crystals couldbe symptomatic of a tank integrity concern. Consequently, your staff determined that the Code Class 2 pressure boundary was not intact and the SLC operabilityrequirement per TS 3.1.7 was, therefore, not met. As a result, a repair plan wasdeveloped that will satisfy the ASME Code requirements. The required time toimplement this repair was estimated to be 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. No extent of conditionissues have been identified (walkdowns of the Unit 2 and Unit 3 SLC tanks havenot detected any similar issues).Two repair options were evaluated. The primary option involved an externalrepair, while the secondary option involved an internal repair. The primary optionwas to perform a modification to remove the thermocouple from the well andinstall a pipe cap over the thermowell head and coupling. The new pipe capwould be welded to the boss protruding from the tank. The pipe cap, installed inaccordance with applicable ASME Code requirements, would remove the leakingcoupling from the code boundary. The primary option allows the SLC system toremain available throughout the repair and testing process. The secondary option involved removing the SLC tank from service, draining thetank, and replacing the thermowell. Following thermowell replacement andassociated NDE, the tank would be refilled and the solution parameters restoredto TS limits. During a portion of this repair option, the SLC system would bedrained and unavailable.The decision to abort the preferred, primary option and proceed with thesecondary option would be based on Engineering review of the feasibility of theprimary option. You stated that you would pursue both options in parallel to theextent possible to ensure aggressive execution of the secondary option, should itbe necessary. You stated that based on further engineering review, the decision was made topursue the external option which removed the thermocouple from the well andinstalled a pipe cap over the thermowell head and coupling. Your staff requested this NOED after consideration of the safety significance andpotential consequences of such an action. A bounding risk assessment of operatingUnit 2 with SLC tank unavailable was performed. The results of the risk assessment foroperating for a short duration (i.e., 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) with the SLC tank unavailable showed thatthere would be no net increase in radiological risk to the public.Your staff stated that the baseline risk for Dresden Unit 2 using the zero maintenance probabilistic risk assessment (PRA) model yields a core damage frequency (CDF) valueof 3.69E-6 and a large early release frequency (LERF) value of 5.17E-7. The estimatedincrease in risk for the incremental condi tional core damage probability (ICCDP)associated with a postulated 72-hour extension is 3.2E-8. The ICCDP values for Unit 2are less than the threshold of 5E-7 specified in regulatory issue summary (RIS) 2005-01. In addition, the estimated increase in risk for incremental conditional large early release C. Crane-4-probability (ICLERP) is 1.7E-8. The ICLERP values fo r Unit 2 are also less than thethreshold of 5E-8 specified in RIS 2005-01. These calculated risk increases areconsistent with the site's normal work control levels; and therefore, there is no netincrease in radiological risk to the public. A Region III Senior Risk Analyst reviewedthis risk analysis and determined the values to be appropriate.As for compensatory measures, during the time the SLC system was inoperable, yourstaff committed to the following: (1) the SLC system would be restored to availablestatus within the bounding 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> time period to ensure online risk is maintained withinthe assessment assumptions; (2) both anticipated transient without scram (ATWS)Recirculation Pump Trip systems would be protected; (3) the reactor protection system(RPS) would be protected; (4) all production risk activities would be prohibited; and(5) if the external repair option is utilized, the SLC tank would remain available duringthe entire activity. In addition to the compensatory actions to minimize risk previouslydescribed, your staff committed to the following additional actions during the period ofthe enforcement discretion: (1) provided the repair leaves the SLC available, thefrequency for Surveillance Requirement (SR) 3.1.7.1, which requires verification ofavailable SLC tank volume, would be increased from once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to once per8 hours; (2) systems that impact production risk would not be removed from service forpreventive maintenance; and (3) Nuclear Oversight personnel would oversee the NOEDactivities. The NRC reviewed your written request for enforcement discretion dated January 22,2007, and verified consistency between your oral and written requests. The NRC'sbasis for this discretion considered the information discussed above including: (1) thecompensatory measures tak en to reduce the probability of a plant transient whileassuring the availability of other safety related equipment; and, (2) the qualitative andquantitative risk evaluation of the condition which determined that the calculated riskincreases were consistent with normal work control levels and, therefore, would notincrease the radiological risk to the public. Based on the above considerations, the NRC staff concluded that Criterion B.2.1.1.aand the applicable criteria in Section D.4 to NRC Manual Chapter 9900, "TechnicalGuidance, Operations - Notice of Enforcement Discretion," were met. CriterionB.2.1.1.a states that for an operating plant, the NOED is intended to avoid unnecessarytransients as a result of compliance with the license condition and, thus, minimizepotential safety consequences and operational risks. On the basis of the staff's evaluation of your request, we have concluded that grantingthis NOED was consistent with the Enforcement Policy and staff guidance, and had noadverse impact on public health and safety or the environment. Therefore, we exercisediscretion to not enforce compliance with TS 3.1.7 Required Action C.1 for entry intoMode 3 (Hot Shutdown) by 5:10 p.m. on January 19, 2007, until January 22, 2007, at5:10 p.m. A follow-up license amendment request is not required.

C. Crane-5-As stated in the Enforcement Policy, action will be taken, to the extent that violationswere involved, for the root cause that led to the noncompliance for which this NOEDwas necessary.Sincerely,

/RA by K. Steven West for/Mark A. Satorius, DirectorDivision of Reactor ProjectsDocket No. 50-237License No. DPR-19cc:Site Vice President - Dresden Nuclear Power StationDresden Nuclear Power Station Plant ManagerRegulatory Assurance Manager - DresdenChief Operating OfficerSenior Vice President - Nuclear ServicesSenior Vice President - Mid-West Regional Operating GroupVice President - Mid-West Operations SupportVice President - Licensing and Regulatory AffairsDirector Licensing - Mid-West Regional Operating GroupManager Licensing - Dresden and Quad CitiesSenior Counsel, Nuclear, Mid-West Regional Operating GroupDocument Control Desk - LicensingAssistant Attorney GeneralIllinois Emergency Management AgencyState Liaison OfficerChairman, Illinois Commerce Commission C. Crane-5-As stated in the Enforcement Policy, action will be taken, to the extent that violationswere involved, for the root cause that led to the noncompliance for which this NOEDwas necessary.Sincerely, Mark A. Satorius, DirectorDivision of Reactor ProjectsDocket No. 50-237License No. DPR-19cc:Site Vice President - Dresden Nuclear Power StationDresden Nuclear Power Station Plant ManagerRegulatory Assurance Manager - DresdenChief Operating OfficerSenior Vice President - Nuclear ServicesSenior Vice President - Mid-West Regional Operating GroupVice President - Mid-West Operations SupportVice President - Licensing and Regulatory AffairsDirector Licensing - Mid-West Regional Operating GroupManager Licensing - Dresden and Quad CitiesSenior Counsel, Nuclear, Mid-West Regional Operating GroupDocument Control Desk - LicensingAssistant Attorney GeneralIllinois Emergency Management AgencyState Liaison OfficerChairman, Illinois Commerce CommissionDOCUMENT NAME: C:\FileNet\ML070240595.wpd G Publicly Available G Non-Publicly Available G Sensitive G Non-SensitiveTo receive a copy of this document, indicate in the concurrence box "C" = Copy without attach/encl "E" = Copy with attach/encl "N" = No copyOFFICERIIIRIIINRRRIIIRIIINAMEMRing:dtpSBurgessJLubinski*MARfor per emailGShearMsatorius*KSW forDATE01/24/0701/24/0701/24/0701/24/0701/24/07OFFICIAL RECORD COPY C. Crane-6-DISTRIBUTION

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