ML102870077
| ML102870077 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 10/13/2010 |
| From: | Cowan P B Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TMI-10-102 | |
| Download: ML102870077 (8) | |
Text
10 CFR 50.55a TMI-10-102 October 13, 2010 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Three Mile Island Nuclear Station, Unit 1 Renewed Facility Operating License No.DPR-50 NRC Docket No.50-289
Subject:
Submittal of Relief Request RR-10-01 Concerning Control Rod Drive Housing Examinations Associated with the Third Inservice Inspection (lSI)Interval Attached for your review is a relief request associated with the third Inservice Inspection (lSI)interval for Three Mile Island Nuclear Station (TMI), Unit 1.TMI, Unit 1 is requesting relief from Table IWB-2500-1, Examination Category B-O, Item Number B14.10, which requires volumetric or surface examination of the pressure retaining Control Rod Drive (CRD)butt welds in 10%of the peripheral CRD housings.The third interval of the TMI, Unit 1 lSI program complies with the American Society of Mechanical Engineers(ASME)Boiler and Pressure Vessel (B&PV)Code,Section XI, 1995 Edition, 1996 Addenda.We request your approval by October 13, 2011.There are no regulatory commitments in this letter.If you have any questions concerning this letter, please contact Tom Loomis at (610)765-5510.Respectfully, Pamela B.Cowan Director-Licensing&Regulatory Affairs Exelon Generation Company, LLC
Attachment:
Relief Request RR-10-01 cc: Regional Administrator, Region I, USNRC USNRC Senior Resident Inspector, TMI USNRC Project Manager, TMI ATTACHMENT Relief Request RR-10-01 Relief Request RR-10-01 for Alternative Control Rod Drive Housing Examinations in Accordance with 10 CFR 50.55a(a)(3)(i)
IC<!l*,......1 of 1.ASME Code Component(s)
Affected Code Class:
Reference:
Examination Category: Item Number:
Description:
Component Number: 1 Table IWB-2500-1 B-O B14.10 Selection of Control Rod Drive (CRD)housing welds for examination Various 2.Applicable Code Edition and Addenda The Inservice Inspection (lSI)program is based on the American Society of Mechanical Engineers (ASME)Boiler and Pressure Vessel (B&PV)Code,Section XI, 1995 Edition, 1996 Addenda.3.Applicable Code Requirement Table IWB-2500-1, Examination Category B-O, Item Number B14.10 requires volumetric or surface examination of the pressure retaining CRD butt welds in 10%of the peripheral CRD housings.4.Reason for Request Pursuant to 10 CFR 50.55a(a)(3)(i), relief is requested on the basis that the proposed alternative will provide an acceptable level of quality and safety.TMI, Unit 1 has sixty-nine (69)CRD locations which have four butt welds each (shown in Figure RR-10-01.1
-welds"A","B","C", and"0").Twenty-four (24)of these CRD locations are categorized as"peripheral" per Examination Category B-O.Ten percent of the peripheral CRD housings equates to an examination of three (3)CRD locations.
Peripheral housing welds with the"0" designator in Figure RR-10-01.1 are accessible for NDE examination through access ports in the reactor vessel closure head service structure and are not applicable to this relief request.CRD housing welds with an"A","B", or"C" designator as shown in Figure RR-1 0-01.1 are only accessible for examination when a CRD is removed from the reactor vessel closure head.As shown in Figure RR-10-01.2, the"Service Structure" surrounding the CRDs causes interferences that result in the peripheral CRD housing welds being inaccessible for examination unless the CRD is removed to gain access.Literal compliance with Table IWB-2500-1, Examination Category B-O requires that only welds on the peripheral CRD locations can be credited for meeting the code requirements.
It is believed that the intent of this requirement was to provide greater flexibility in meeting the code by requiring examination of the peripheral locations as compared to the inner locations.
Typically, examination of welds on non-peripheral CRD locations is limited due to access restrictions.
However, the code did not account for some plants, such as TMI, Unit 1, that have a Service Structure that makes examination of the peripheral CRD locations more difficult.
Relief Request RR-10-01 for Alternative Control Rod Drive Housing Examinations in Accordance with 10 CFR 50.55a(a)(3)(i)(Page 2 of 6)Over the course of a ten-year lSI interval, a small population of CROs (though often not peripheral in location)are removed for various purposes which allows an opportunity to perform examinations.
At this time, no peripheral CROs are expected to be removed during the upcoming outage (Fall 2011).The Fall 2011 outage is the last outage in the third lSI interval.Duringthe third interval in the first period (2001), six (6)CROs not in the periphery were examined and no indications were identified.
There were no examination limitations reported for these welds.A review of lSI data for examinations of welds"A","B", and"c" completed since 1986 identified no degradation.
Visual examination of the flange region of all CROs is completed using remotevideoeach outage to assure there is no leakage from the mechanical joint.Small leakage from the welds above the flange that might not be evident during the normal Section XI VT-2 examination pressure tests would likely be observed during the flange video examinations.
The cost for removal and reinstallation of three peripheral CROs in order to meet the literal compliance with this code requirement is estimated to be greater than$80,000.The estimated dose for removing and re-installing three control rod drive mechanisms to perform the inspection is greater than 1.3 Rem.A review of the operating conditions between the interior and peripheral CRO locations shows that the difference in operating temperatures is not significant.
The motor tube (RCS pressure boundary)weldments (welds"A","B", and"C")are located above an internal thermal barrier which results in the welds being at a lower operating temperature as shown in Figure RR-10-01.3.
The thermal barrier restricts the thermal circulation of hot, primary coolant and acts as an insulator between the reactor vessel and the drive.The maximum steady state operating temperature for the internal components above the thermal barrier is 470°F.Welds"A" and"B" are located slightly above the internal rotor assembly (further away from the top of the reactor vessel head)so their operating temperature is slightly lower.Additionally, an external water cooled stator-water jacket assembly is installed over the motor tube region of welds"A" and"B" for all 69 drives which leads to a relatively consistent temperature.
Weld"c" is located approximately 165" above weld"B" and is the coolest of the three welds based on the lack of flow and distance from the RV closure head.Accordingly, an examination sample of welds from interior drive locations is essentially equivalent to a sample of welds from the peripheral drive locations and will adequately represent the condition of the Examination Category B-O welds.5.Proposed Alternative and Basis for Use As a proposed alternative, TMI Unit 1 will credit the examinations of the"A","B", and"c" designator welds on three non-peripheral (3)CRO housings, performed in the first period of the third interval.The examinations performed met the requirements of Table IWB-2500-1ExaminationCategory B-O for NOE methods, area examined, and acceptance.
Relief Request RR-10-01 for Alternative Control Rod Drive Housing Examinations in Accordance with 10 CFR 50.55a(a)(3)(i)(Page 3 of 6)Examination of the CRO housing welds on any of the 69 CRO locations provides an equivalent level of quality and safety.TMI, Unit 1 will complete the examination of the"0" designator welds shown in Figure10-01.1 on three (3)peripheral CRO housings in accordance with Table IWB-2500-1 requirements.
TMI, Unit 1 will perform an ASME Section XI, Category B-O examination of the"A","B", and"c" welds on at least one peripheral CRO housing during the first period of the fourth lSI interval and complete the remaining examinations during the interval as required by ASME Section XI.As an alternative to the first period examination, TMI, Unit 1 may replace the current population of CROs with new CROs during the first period of the fourth lSI interval and complete the subsequent fourth lSI interval examinations in accordance with ASME Section XI.6.Duration of Proposed Alternative Relief is requested for the third ten-year lSI interval for TMI, Unit 1.The third ten-year interval began on April 20, 2001.7.Precedents (Optional)
None.
Relief Request RR-10-01 for Alternative Control Rod Drive Housing Examinations in Accordance with 10 CFR 50.55a(a)(3)(i)(Page 4 of 6)FIGURE RR-10-01.1 CRD Housing Weld Locations (Excerpt from TMI drawing 1 D-ISI-RC-011
)
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SI%.blfGh Relief Request RR-10-01 for Alternative Control Rod Drive Housing Examinations in Accordance with 10 CFR 50.55a(a)(3)(1)(Page 5 of 6)Approximate elevation of welds A and B Removed CRD Location and RV Head Penetration Top Flange TypicalPeripheral CRD Locations FIGURE RR-10-01.2 CRD Housings and Weld Locations Photograph from Top of Service Structure Looking Down Relief Request RR-10-01 for Alternative Control Rod Drive Housing Examinations in Accordance with 10 CFR 50.55a(a)(3)(i)(Page 6 of 6)FIGURE RR-10-01.3 CRD SchematicandMaterials SA 182 F304 Or SA-479 TP-304 SA-312 TP-304 Stator-Water Jacket Assembly SA-508 Class 2 ERNiCr-3 Thermal Barrier I Assembly I I SA-182 F304 Reactor Vessel Head Nozzle Flange