ML082530250
| ML082530250 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 08/29/2008 |
| From: | Laughlin G Constellation Energy Group, Nine Mile Point |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC 61181, TAC MC3272, TAC MC3273 | |
| Download: ML082530250 (9) | |
Text
- Constellation Energy-Nine Mile Point Nuclear Station P.O. Box 63 Lycoming, NY 13093 August 29, 2008 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION:
SUBJECT:
Document Control Desk Nine Mile Point Nuclear Station Unit No. 1; Docket No. 50-220 Request to Utilize an Alternative to the Requirements of 10 CFR 50.55a(g) for the Repair and Inservice Inspection of Control Rod Drive Stub Tubes for the License Renewal Period of Extended Operation
REFERENCES:
(a) Letter from R. Auluck (NRC) to C. V. Mangan (NMPC) dated March 25, 1987, Request to Utilize an Alternative to the Requirements of 10 CFR 50.55a(g) (TAC 61181)
(b) Letter from J. A. Spina (NMPNS) to Document Control Desk (NRC) dated November 30, 2005, Amended License Renewal Application (ALRA) -
Responses to NRC Requests for Additional Information Regarding ALRA Parts 1, 2, and 3 (TAC Nos. MC3272 and MC3273)
By letter dated March 25, 1987 (Reference a), the NRC approved an alternative for the repair of control rod drive (CRD) penetrations (stub tubes) for Nine Mile Point Unit 1 (NMP 1) pursuant to the provisions of 10 CFR 50.55a(a)(3). The alternative allowed relief from the requirements of 10 CFR 50.55a(g) and American Society of Mechanical Engineers (ASME) Code,Section XI, IWA 5250(a) to allow for the use of a roll repair for leaks found in the CRD penetrations during a system pressure test. The approved alternative included allowable leakage rates for the rolled penetrations.
No duration for use of the alternative was specified by the NRC in this approval.
On October 31, 2006, the NRC issued the Renewed Operating License for NMP1, with an expiration date of August 22, 2029. As part of the application for the renewed operating license for NMP I (Reference b),
Nine Mile Point Nuclear Station, LLC (NMPNS) committed to implement a permanent zero leakage roll repair method for leaking CRD penetrations utilizing ASME Code Case N-730, "Roll Expansion of Class 1 Control Rod Drive Bottom Head Penetrations in BWRs,Section XI, Division 1," as conditioned by the NRC for the 20-year period of extended operation.
Since this Code Case has not been generically approved for use through inclusion in NRC Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," at this time, NMPNS requests NRC approval to utilize Code Case N-730 (with a variation) as described in the attached 10 CFR 50.55a Request Number IISI-02.
Document Control Desk August 29, 2008 Page 2 This request would allow use of the proposed alternative for the license renewal period of extended operation (i.e., from August 23, 2009 to August 22, 2029).
NMPNS has previously roll repaired 33 CRD penetrations. The inservice inspection requirements of the proposed alternative would be applied to these penetrations, as well as to any new penetrations roll expanded during the period of extended operation. Roll expansions completed in accordance with the previously approved alternative will not be retrofitted to the repair requirements of this new proposed alternative.
NMPNS requests approval of this request for alternative by regulatory commitments.
Should you have questions regarding the information in Licensing Director, at (315) 349-5219.
August 22, 2009. This letter contains no new this submittal, please contact T. F. Syrell, Gafy Jay Laughlin Manager Engineering Services GJL/JJD
Attachment:
Nine Mile Point Nuclear Station, Unit 1 - 10 CFR 50.55a Request Number IISI-02 cc:
S. J. Collins, NRC R. V. Guzman, NRC Resident Inspector, NRC
ATTACHMENT NINE MILE POINT NUCLEAR STATION, UNIT 1 10 CFR 50.55a REQUEST NUMBER IISI-02 Nine Mile Point Nuclear Station, LLC August 29, 2008
Nine Mile Point Nuclear Station, Unit 1 10 CFR 50.55a Request Number 11SI-02 Proposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(a)(3)(ii)
A.
COMPONENT IDENTIFICATION:
System:
Control Rod Drive (CRD) Bottom Head Penetrations Code Class:
Quality Group A, ASME Code Class 1
==
Description:==
Use of Variation of Code Case N-730, "Roll-Expansion of Class 1 Control Rod Drive Bottom Head Penetrations in BWR's, Section Xl, Division 1" Components Affected:
Reactor Vessel Control Rod Drive (CRD)
Bottom Head Penetrations B.
APPLICABLE CODE REQUIREMENTS:
The applicable ASME Code, Section Xl, for the Nine Mile Point Unit 1 (NMP1) fourth 10-year in-service inspection interval as currently referenced in 10CFR50.55a is the 2001 Edition through the 2003 Addenda. The fourth 10 year interval Will begin on August 23, 2009, concurrent with the NMP1 license renewal period of extended operation.
ASME Code Case N-730, "Roll-Expansion of Class 1 Control Rod Drive Bottom Head Penetrations in BWRs, Section Xl, Division 1," is applicable from the 1989 Edition through the 2004 Edition with the 2006 Addenda of ASME Section X1. All references provided in ASME Code Case N-730 to the ASME Code apply to 2004 Edition. (Reference 1)
ASME Section Xl, 2001 Edition through 2003 Addenda, IWA-4000, "Repair/Replacement Activities," requires that all repair and replacement be performed in accordance with the provisions of IWA-4000. Additionally, IWB-3142, "Acceptance," provides acceptance criteria for components, which includes removal of the relevant condition.
C.
REASON FOR REQUEST FOR RELIEF:
The NRC staff informed Nine Mile Point Nuclear Station, LLC (NMPNS) during the License Renewal Application process that the staff did not consider the currently approved plant specific roll repair process to be acceptable for permanent repair (Reference 2). As a result, NMPNS has committed to implement ASME Code Case N-730 during the license renewal period commencing August 23, 2009. Although ASME has approved Code Case N-730 and NRC ASME participants' comments were incorporated into the final version of the Code Case, the Code Case has not yet been approved for general use by the NRC and added to Regulatory Guide (RG) 1.147 (Reference 3). Hence, NMPNS is requesting relief to use Code Case N-730 at NMP1.
Pursuant to 10 CFR 50.55a(a)(3)(i), NMPNS requests to use ASME Code Case N-730, as an alternative to the requirements of ASME Section Xl, applicable edition and addenda, IWA-4000
("Repair/Replacement Activities") and IWB-3142 ("Acceptance") for the repair of Control Rod Drive Bottom Head Penetrations utilizing the mechanical roll expansion technique to eliminate leakage from Class 1 CRD bottom head penetrations. NMPNS has determined that the proposed alternative described below provides an acceptable level of quality and safety'and satisfies the requirements of 10 CFR 50.55a(a)(3)(i).
Additionally, NMPNS requests approval to vary from paragraph 6.6 of Code Case N-730, which requires a VT-2 visual examination in conjunction with a system leakage test in accordance with IWB-5000 for CRD housings subjected to roll expansion following completion of the post-roll-ISI 02-1 of ISI 02-6
Nine Mile Point Nuclear Station, Unit I 10 CFR 50.55a Request Number 11SI-02 expansion UT examination.
The justification below demonstrates that compliance with the specified code case requirement would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety per the requirements of 10 CFR 50.55a(a)(3)(ii).
D.
BASIS FOR RELIEF AND ALTERNATIVE EXAMINATIONS:
IA. Proposed Alternative:
In accordance with 10 CFR 50.55a(a)(3)(i), NMPNS requests the use of ASME Approved Code Case N-730, "Roll-Expansion of Class 1 Control Rod Drive Bottom Head Penetrations in BWRs, Section X1, Division 1," for repair of CRD housing penetrations.
Currently, NMPNS has roll expanded thirty-three (33) CRD housings as approved by the NRC as an alternate to ASME Section XI pursuant to 10 CFR 50.55a(a)(3) in a safety evaluation (Reference 4).
NMPNS is requesting approval of the code case as an alternative permanent repair for any additional CRD housing penetrations that may exhibit leakage during the License Renewal Period commencing August 23, 2009 or for the re-roll expansion of any previously roll expanded CRD housing that exhibits a repeat occurrence of leakage.
Additionally, NMPNS will perform future volumetric (UT) and system leakage tests on the thirty-three existing roll-expansion repairs in accordance with requirements of ASME Code Case N-730 to provide added assurance of CRD housing structural integrity and a zero leakage acceptance criteria, respectively.
lB. Basis for Relief:
The technical basis for the Code Case is provided in the Code Case N-730 Technical Basis Report, XGEN-2005-10, Revision 3, "Technical Basis for ASME Code Case N-730 Roll-Expansion of Class 1 Control Rod Drive (CRD) Bottom Head Penetrations in BWRs" (Reference 1).
The CRD penetrations in a BWR are located on the bottom head of the vessel. The NMP1 BWR CRD penetrations used a stub tube to which the CRD housing is welded. The CRD housing is approximately 6 inches in diameter and is made of Type 304 stainless steel. The CRD housing encloses the control rod drives. There are 129 CRD penetrations. The use of the stub tube allows the stainless steel housing to be welded to the stub tube after post-weld heat treatment (PWHT) of the vessel. Like the CRD housing, the stub tube was also made of Type 304 stainless and was welded to the bottom head prior to PWHT.
The subsequent vessel PWHT caused furnace sensitization of the stub tube making it susceptible to Intergranular stress corrosion cracking (IGSCC) with exposure to the high temperature BWR water environment. The stub tubes are attached to the vessel bottom head by inconel 182 welds which are also susceptible to IGSCC. Cracking in either the stub tube or the inconel 182 welds would typically be identified by lower plenum in-vessel visual inspections or by leakage identified on the CRD housing during the under vessel leakage inspections. A stub tube is depicted in Figure 1.
NMP1 has CRD penetrations that have leaked due to stress corrosion cracking in the furnace sensitized stainless steel stub tubes and/or potentially in the stub tube-to-vessel attachment welds. Code Case N-730 applies to these locations. A roll-expansion repair method to stop the leakage has been implemented at NMP1 since 1984 (Reference 4).
Leakage from the CRD penetration cracking prior to roll repair expansion has been minimal with the maximum measured leak rate being approximately 80 drops/min. The observed leakage prior to roll expansion has been a small fraction of system make-up capability. Following roll repair, a zero leakage condition was observed in all cases. To date 33 CRD penetrations have been roll-expanded to a nominal 4% wall thinning. Of the 33 roll-expanded CRD penetrations, only one of the penetrations (50-19) has been re-roll expanded to 6% wall thinning due to repeat occurrence of leakage. Zero leakage has been observed at this penetration since it was last roll expanded in ISI 02-2 of ISI 02-6
Nine Mile Point Nuclear Station, Unit I 10 CFR 50.55a Request Number 11SI-02 2005. NMPNS implemented Hydrogen Water Chemistry and Noble Metals Chemical Addition (HWC/NMCA) in 2000. To date, only one new CRD penetration has exhibited leakage following commencement of HWC/NMCA.
That was in early 2001 indicating the crack likely originated prior to HWC/NMCA.
The inspection results demonstrate that NMPNS can effectively and repeatedly roll-expand CRD bottom head penetrations to achieve a zero leakage condition and that HWC/NMCA has been an effective method to mitigate further cracking and leakage. As such, the NMPNS roll repair history along with the XGEN-2005-10 technical basis provide adequate basis for the proposed alternative to use ASME Code Case N-730 for future roll repairs, if required, at NMPNS.
2A. Proposed Alternative:
NMPNS proposes to follow Code Case N-730, paragraph 6.6 with regard to performing the VT-2 visual examination for leakage from previously roll expanded CRD housing penetrations in accordance with IWB-5000.
In the future, if a new CRD housing penetration leak is detected during the leakage test required by IWB-5000, then during that outage the CRD housing would be roll expanded in accordance with Code Case N-730. However, as an alternative to the rated test pressure required by IWB-5000, NMPNS proposes to perform the post-roll expansion VT-2 examination at approximately 900 psig prior to returning the Unit to full power operation.
2B. Basis for Relief:
Historically, CRD stub tube leakage is detected at the end of a refueling outage during the performance of the non-nuclear heat-up ASME Class 1 System Leakage Test performed using an external pressure source prior to returning the Unit to service.
Under the current roll repair program, NMPNS would be required to disassemble the CRD housing support grid (shoot-out steel), TIP tubing, remove the CRD mechanism and CRD thermal sleeve, perform the roll repair and post-roll UT prior to plant startup from the outage. This historically has extended a refueling outage by at least one day. After completion of the post-roll repair UT, NMPNS has performed the post-maintenance test (PMT) leakage examination of the roll repaired penetration at cold static head conditions and repeats the leakage examination during the final drywell entry during plant startup typically with Reactor Pressure Vessel (RPV) pressure at, approximately 900 psig.
ASME Code Case N-730 step 6.6 requires the rolled penetration to be visually (VT-2) examined for leakage in conjunction with a system leakage test in accordance with ASME XI 2004 edition, IWB-5000. IWB-5000 requires that the system leakage test be conducted at a pressure not less than the pressure corresponding to 100% rated power. Assuming the leakage is first detected during the performance of the non-nuclear heat-up ASME Class 1 System Leakage Test at the end of a refueling outage, this code case requirement would mandate that after performance of the roll expansion, NMPNS either: 1) repeat the non-nuclear heat-up ASME Class 1 System Leakage Test using an external pressure source; or 2) attempt to perform the leakage exam at power at approximately 1030 psig.
In accordance with 10CFR50.55a(a)(3)(ii), NMPNS proposes to provide an acceptable alternative which is to perform the PMT VT-2 visual examination at approximately 900 psig during the final drywell entry prior to power ascension, which is consistent with NMP1's past 20-year practice.
Justification for this position follows:
i)
NMPNS has roll expanded 33 CRD penetrations to date. The Post-Maintenance Test (PMT) visual leakage examinations were performed during plant startup at reactor pressures between 500-900 psig.
No evidence of leakage was identified during these examinations.
During the non-nuclear heat-up ASME Class 1 System Leakage Test performed immediately following the outage in which. the CRD penetration was roll expanded and prior to the unit's return to service, no evidence of leakage was detected. This confirms that if the non-nuclear heat-up ASME Class 1 System Leakage Test was repeated following each roll repair during the outage in which the leakage was detected and corrected, the leakage would have been ISI 02-3 of ISI 02-6
Nine Mile Point Nuclear Station, Unit 1 10 CFR 50.55a Request Number 11SI-02 zero. These inspection results demonstrate that NMPNS can effectively and repeatedly roll expand penetrations to achieve a zero leakage condition, such that repeating the non-nuclear heat-up ASME XI Class 1 leakage test in the same outage is'not necessary.
ii) Inspections of CRD stub tu bes for leakage during a system leakage test at the nominal operating pressure (-1030 psig) associated with 100% rated reactor power cannot be performed during a normal plant startup, due to the excessive temperature and radiological exposure conditions to which the NDE examiners performing the visual VT-2 examinations would be exposed in the primary containment. Furthermore, NMP1 Technical Specification 3.3.1 requires the primary containment atmosphere oxygen concentration to be reduced to less than four percent by volume within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of the reactor being placed in the run mode, thereby also potentially requiring the NDE examiners to wear breathing apparatus.
iii)
The CRD penetrations are not isolable from the reactor vessel. The entire primary system will have to be pressurized in order to perform the non-nuclear heat-up Section XI system leakage test.
During implementation of the non-nuclear heat-up ASME Class 1 System Leakage Test extensive valve manipulations, system lineups, and procedural controls are required in order to heat up and pressurize the primary system to establish the necessary test pressure during plant outage conditions, without the withdrawal of control rods. This is done in order to perform the necessary system leakage test without exposing the examiners to the excessive temperature and radiological exposure conditions described in the paragraph above. This special test usually takes one full day of plant outage time, and the additional valve lineups and system reconfigurations necessary to support this special test impose an additional challenge to the affected systems.
A normal plant startup then occurs after completion and subsequent recovery from the test procedure at which time the visual VT-2 examination of the roll repaired penetration can be performed at approximately 900 psig.
Therefore, repeating the non-nuclear heat-up ASME Class 1 System Leakage Test after a roll repair is not necessary.
iv) During a normal plant startup, operators are required to perform final drywell entry walk-down inspections of the primary containment at approximately 900 psig.
The roll-expanded penetration can be visually inspected by a qualified visual VT-2 examiner during these final drywell entry walk-down inspections at approximately 900 psig.
During the next refueling outage, the roll-expanded connections are re-examined for signs of leakage during the non-nuclear heat-up ASME XI in-service leak test at a pressure not less than the pressure corresponding to 100% rated power.
v)
CRD penetration leakage rates are expected to be proportional to the square root of the test pressure ratio as noted in Table 1, Note 1, of Reference 4. Using this correlation, a 25 drop per minute leak detected at 1030 psig would be approximately a 23 drop per minute leak at 900 psig. Furthermore, the sensitivity of leakage detection is not expected to decrease due to temperature because the reactor temperature difference between 900 psig and rated pressure (1030 psig) is less than 20 0F. Therefore, leakage identified at nominal operating conditions should be detectable at 900 psig.
vi) The roll repair process has been qualified in mockups and tested for leakage at pressures much greater than that required by IWB-5221(a) in the mock-up qualification. The roll expanded mockups were hydro-tested 1.8 times greater than the nominal operating pressure and no evidence of leakage was detected.
vii) This position is essentially consistent with the BWRVIP-146 position (Reference 5), section 4.3, that indicates repeating the non-nuclear heat-up ASME Class 1 System Leakage Test is not essential and instead performance of the leakage exam at a minimum of 90% normal operating pressure is sufficient to detect leakage.
Nine Mile Point Nuclear Station, Unit 1 10 CFR 50.55a Request Number 1ISI-02 E.
IMPLEMENTATION SCHEDULE Pursuant to 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(a)(3)(ii), NMPNS requests relief for the NMP1 License Renewal Period from August 23, 2009 to August 22, 2029.
NMPNS has demonstrated that CRD Bottom Head Penetrations that have been repaired by roll-expansion can achieve a zero leakage condition. Therefore, the requested duration of the proposed alternative is justified.
F.
PRECEDENT:
NRC Safety Evaluation, Oyster Creek Nuclear Generating Station - Relief Request, Application of Draft ASME Code Case N-730, TAC No. MD1070, October 6, 2006 G.
ATTACHMENTS:
None.
H.
REFERENCES:
- 1. Report XGEN-2005-10, Revision 3: "Technical Basis for ASME Code Case N-730 Ro II-Expansion of Class 1 Control Rod Drive (CRD) Bottom Head Penetrations in BWRs," dated August 2006.
- 2.
Letter from N. B. Le (NRC) to J. A. Spina (NMPNS), "Request for Additional Information for the Review of Nine Mile Point Nuclear Station, Units 1 and 2, Amended License Renewal Application (TAC Nos. MC3272 and MC3273)," dated November 2, 2005.
- 3.
NRC Regulatory Guide 1.147, Revision 15, "Inservice Inspection Code Case Acceptability, ASME Section Xl, Division 1," dated October 2007.
- 4.
Letter from R. Auluck (NRC) to C. V. Mangan (NMPC), "Request to Utilize an Alternative to the Requirements of 10 CFR 50.55a(g) (TAC 61181)," dated March 25, 1987.
- 5.
BWRVIP-146, "BWR Vessel and Internals Project Technical Basis for ASME Code Case N-730, Roll-Expansion of Class 1 Control Rod Drive Bottom Head Penetrations in BWRs,"
dated November 2005.
Nine Mile Point Nuclear Station, Unit I 10 CFR 50.55a Request Number 11SI-02 Figure 1 Stub Tube (Typical)
TYPICAL CRACK LOCATI SA 182 F304 STUB TUBE (FURNACE SENSITIZED)
INCONEL 182 WEL 304 SS CLADDING-ALLOY CARBON STEEL VESSEL (SA 302 GRADE B)-
LEAK PATH D
ISI 02-6 of ISl 02-6