IR 05000245/1992030
| ML20128A397 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/11/1993 |
| From: | Gray E, Lohmeier A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20128A364 | List: |
| References | |
| 50-245-92-30, 50-336-92-32, 50-423-92-29, NUDOCS 9302020208 | |
| Download: ML20128A397 (10) | |
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U.S. NUCLEAR REGULNI"ORY COMMISSION
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REGION 1 REPORT / DOCKET NOS, 50-245/92-30 50 336/92-32 50 4?.3/92-29 LICENSE NOS.
DPR-21 DPR-65 NPF-49 LICENSEE:
Northeast Nuclear Energy Company P.O. Box 270 Hartford, Connecticut, 06141-0270
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FACILITY 'NAME:
Millstone Nuclear Power Station Units 1,2, and 3 INSPECTION AT:
Berlin and Waterford, Connecticut INSPECTION DATES:
November 16 20,1992 and December 14-18, 1992
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-INSPECTOR:
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A%hmeier Sr. Reactor Engineer, Dat6 Materials Section, EB, DRS
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APPROVED BY:
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E. Harold Gray, Chief, Materials Section,
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Engineering Branch, DRS Areas Insoccted: The inspection related to.the retention and evaluation of records for the
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duration of the facility lifetime of transients or operational cycles for those facility components designed for a limited number of transients or cycles at Northeast Nuclear -
Energy Company Millstone' Nuclear Power Station Unit Nos li 2, and 3. Also included in -
the inspection was the response of Northeast Nuclear Energy Company in providing the required information of Generic Letter 92-01 relating to reactor vessel belt-line material-adequacy expressed in 10 CFR 50 Appendices G and H.
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9302020200 930126
{DR ADOCK 05000245~
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Enults: Inspection of Millstone Unit 3 revealed an operating system for tracking and evaluation of the numbers of operational cycles and transients of components designed for a
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limited fatigue life. On Millstone Units 1 and 2, however, there was no system to' convert records of transient or operational cycles to the fatigue life assessment of components.
While the operational data is recorded in accordance with Technical Specification Section
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6.9.1.6, the data had not been applied toward assessment of fatigue life of components designed for a limited number of transients or cycles. Furthermore, on Millstone Unit No.'
1, on the basis of calculations performed in 1982, estimates of present fatigue' life usage factor approach the allowab'e value of 1.0 in the reactor basin seal skirt.
Northeast Nuclear Energy Company engineering is considering installation of a computerized
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system for transient cycle monitoring in 1993 for Millstone Units 1 and 2. It was requested that Northeast Nuclear Energy Company provide analytic justification that the design of the basin seal skirt of Unit I would not reach end of fatigue life during the anticipated life of the facility.
The response of Northeast Nuclear Energy Company to Generic Letter 92-01 comprehensively discussed reactor vessel belt-line material surveillance in relation to requirements of 10 CFR 50 Appendices G and H.
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3 1.0 SCOPE OF Tile INSPECTION 1.1 llackground and Purpose of Inspection Operational Cycle Monitoring Design of primary pressure vessel components in accordance with ASME Boiler and Pressure Vessel Code Section 111 for Nuclear Vessels requires analysis of the vessels subjected to a predicted lifetime histogram of cyclic operation during which the temperature and pressure k)adings vary. The stresses throughout the components change in accordance with the cyclic pressure and thermal loadings and cause fatigue of the component material. In the design of the components, this Code requires computation of the ranges of strain cycling ai critical points in the vessel and comparison of these strain ranges with the design fatigue strength of the material. The predicted strain cycles at each critical location are compared with results of a design fatigue curve based on the results of fatigue tests of these materials. The exhaustion of uscable life of the material is reflected in a " Cumulative Usage Factor" (CUF) which is the cumulative value of the ratio of fatigue cycles to be experienced under the predicted strain cycles to those cycles after which failure would occur at those strain levels. The design rules allow for a factor of safety within the design fatigue curve.
The Equipment Specification for each component contains the lifetime prediction of temperature and pressure variation transients to which the components are to be designed by t!:: equipment manufacturer and these are reflected in the Final Safety Analysis Repori (FSAR). For each operational transient (such as start-up, shut down, hydro-test, loss of feedwater, etc.), the temperature and pressure changes with time are given together with the number of cycles of application of the transient predicted over the component lifetime.
The Technical Specification for each unit provides for the retention of records of the transient cycles. Millstone Units No. I and 2 require in 6.10.2(f) that " records shall be retained for the duration of the facility lifetime," including " records of transients or operational cycles for those facility components designed for a limited number of transients or cycles." Millstone Unit No. 3 requires in 6.10.3 (e) that " records shall be retained for the duration of the operating license" including " records of transient or operational cycles for those unit components identified in Table 5.7-1." Section 5.7-1 states that " components identified in Table 5.7-1 are designed and shall be maintained within the limits of Table 5.7-i." Table 5.7.1 describes the number of cycles and nature of each transient for which the component is designed.
it was the purpose of the inspection to assess the monitoring of operational cycles by Northeast Nuclear Power Company through retention of operating records for those components designed for a limited number of transients or cycles and evaluation of the fatigue life usage of these components on a continuous basis.
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Reaetor Belt-Line Matedal - Response to Generie Irtter 92 -01 It was the purpose of the inspection to review the response of Northeast Nuclear Energy l
Company in providing the required information of Generic-Letter 92-01 relating to reactor.
vessel belt line material adequacy expressed in 10 CFR SO Appendices G and H.
2.0 FINDINGS 2.1 Trnuslent or Operational Cycle Monitoring
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Millstone Unit No.1 Millstone Unit No. I began commercial operation on December 28,1970. The construction permit was issued May 19,.1966. It's operating license would have expired on May 19,2006, but an extension was granted to extend the operating license expiration to October 6,2010. This plant has been operational for 22 years.
The inspector reviewed the reactor vessel stress analysis of October 27,1981, and the reactor vessel usage factor update program. The program tabulated the operating transients each year of plant operation through 1982. The usage factor was determined from equations
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derived from the reactor pressure vessel stress analysis (CENC-1126).
The transients considered in the analysis included the following:
Transient Cveles (12 vrs)
through 1982 Design / Hydro Bolt-Up
Design Hydro-test
Quarter Power Hydro 0=
Normal Shut Down
Loss of feedwater/ Scrams
Vessel Over-pressurization
Initiate Condensate Isolation
A comparison of cumulative usage factors at the end of 1982 with those for which the vessel was designed (for 40 years), is shown as follows:
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Region Namt C1E Cl!E (40 yrs)
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Vessel Closure Region
.046
.021-
Closure Region Bolts
.823
.108
Vessel Shell -
.238
.110
Bottom head Support Skirt
.032
.01_2
Fecelwater Nozzle (Shield Replaced)
Core Spray Nozzle
.271-
.221
CRD Return Nozzle (Plugged)
Recire. Nozzle Inlet
.133-
.038
Recirc. Nozzle Outlet
.339
.052
Vent Nozzle
.027
.006
Head Spray Nozzle
.012
.003
Steam Outlet Nozzle Region
.230
.083
Shroud Bracket
.045
.017
Jet Pump Attachment
.025
.009
Basin Seal Skirt
.921
.522
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The feedwater nozzle had been found to have developed cracks and was repaired and replaced with an improved feedwater sparger design that precluded the fluid stratification effect found to be the cause of cracking.
In reviewing the list of cumulative usage factors for the Millstone Unit No.1 Reactor, the inspector noted that none of the design cumulative usage factors exceeds the limiting value of 1.0. As a result of the evaluation of usage factors in 1982 (when the reactor vessel had been operating for 12 years), an extrapolation of approximately 4 times the cumulative usage factor would not result in values in excess of 1.0, with the exception of the basin seal skirt, which at the present time is approaching the limiting value of 1.0. This' area warrants re-evaluation to ascertain that the fatigue usage factor limit.will not exceed 1.0 during the -
expected life of the facility. This estimate is based on the assumption that the applied transients were of equal magnitude and nature as those experienced during the first decade of operation.-
The licensee has been recording the operating transients in accordance with the requirements of Technical Specification 6.9.1.6, which requires submittal of operations and shutdown data.:
The inspector reviewed the monthly reports of the operational' data to USNRC. At the present time, reactor vessel fatigue monitoring is mandated by the Nuclear Review Board ofi Northeast Utilities, using a cycle counting approach. The CUF has been determined from
. data compiled through 1982, and although operating data are being compiled on a regular basis, consistent with Technical Specification Section 6.9.1.6, numbers of operational transients acting on components designed for specific numbers of cycles for componer.ts designed for limited cycles have not been evaluated since 1982.
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The inspector found that Northeast Nuclear Energy Company engineering is considerink installation of a computerized system for transient cycle monitoring in 1993 that would provide for monitoring of components designed for a limited number of transients or cycles on Millstone Units 1 and 2. In discussion of this matter with members of the engineering department on December 18,1992, it was requested that Northeast Nuclear Energy Company provide analytic justification that the design of the reactor basin seal skirt of Millstone Unit I would preclude fatigue failure during the anticipated life of the facility. This issue is considered as unresolved item URI 50-245/92-30-01.
Millstone Unit No. 2 Millstone Unit No. 2 began commercial operation on December 26,1975. The construction permit was issued December 11,1970. The operating license would have expired on-December 11,2010, but an extension was granted to extend the operating license expiration to July 31, 2015. This plant has been operating for 17-years.
The inspector reviewed a list of reactor vessel components for which stress analysis was performed, including the estimated end of life usage factor for each component. The following results were noted:
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Component Usage Factor -
End of Life Closure Head & Vessel Flange Region
.737 CRDM Nozzles
.00253 Instrument Nozzle
.005 Vent Tube
.0001 q
Inlet Nozzle
.0504 Outlet Nozzle
.08172 Vessel Supports
'.0009 Vessel Wall Transition
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Surveillance Specimen Holder
.05926 Core Stabilizer Lugs
.0 Vessel Shell & Bottom Head
.0098 Flow Baffles -
.0033 The foregoing data was based on stress reports CENC 1177,1177A, and 1236.
It is noted that the only arca with a significant fatigue usage level after 40 years operation is in the closum head and vessel flange region. The usage factor, however, is less than the limit of 1.0. - The numbers of operational transients acting on components designed for
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In report C ENPSD-633-P, May 1991, a comprehensive evaluatio. was completed that identified 12 fatigue sensitive components. The evaluation also identified 10 major transients -
that must be tracked for fatigue monitoring of. sensitive components. Consideration is being j
given by the licensee to put in place a fatigue monitoring and evaluation system during 1993-
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that would provide for monitoring transient cycle operation on equipment designed for limited numbers of cycles. The absence of fatigue data evaluation is an unresolved item
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(URI 50-336/92-32-01).
j Ml!! stone Unit No. 3 Millstone Unit No. 3 began commercial operation on April 23,1986. The construction permit was issued December 11,1970. The operating license was granted to' expire
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November 25, 2025. This plant has been in operation for 6 years.
The inspector visited the control room facility where the cyclic operation is electronically recorded. The inspector reviewed a monthly report in which the current value of cycles is compared to the number of cycles for which the components were designed.
The report for October included the following transients:
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Current Design Cyclic Operating Mode Cycles.
Cycles RCS Heat-ups & Cool downs
200 Pressurizer Heat-up & Cool-down 38.
200-Pressurizer Spray Nozzle 2556 30400 RC Pump A Starts / Stops-
1900 Charge Nozzle Transients Loop 1
200 Salety injection Actuation
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Full Core Off-Load 4-
RCS Leak Tests
.2 200 RCS Hydro test 2.
A S/G Leak Tests
80 A S/G Hydro Tests -
-10 Contaimnent FW Iso Valves 103 250-
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The inspector reviewed a list of reactor vessel components for which stress analysis was performed, including the estimated end of life usage factor for each component. The following results were noted:
Component Usace Factor Closure Head & Vessel Flange Region 478-CDRM Housing
.1093
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Instrument Nozzle
.318 Inlet Nozzle
.074 Outlet Nozzle
.101 Vessel Supports
.081 Vessel Wall Transition
.012 Core Support Guides
.0612 Vessel Shell & Bottom Head'
.007
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The foregoing data was based on stress reports CENC 1282,-1282Al,1398,1672, and 1708.
Three areas with significant predicted lifetime fatigue usage factor level after 40 years operation are Closure Head Region (.478), CDRM Housing (.1093), Instrument Nozzle (.318), and Outlet Nozzle (.101). None of these exceed the allowable value of 1.0.
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2.2 Reactor Vessel Belt-Line Material-Response to Generic Letter 92-01 Millstone Unit Nos.1. 2. and 3 The inspector reviewed the surveillance program for reactor vessel belt-line material integrity and reviewed the response of the licensee to Generic. Letter 92-01, Revision 1.
Northeast Nuclear Energy Company, on behalf of the Millstone Nuclear Power Station, Unit Nos.1,2, and 3 provided for the response to the required information section of the Generic Letter in a letter of July 6,1992, to the USNRC.
Tiie review covered the licensee response to NRC questions related to the existence of a surveillance program meeting 10 CFR 50, Appendix H. This includes the charpy upper shelf energies (USE) of belt-line plate and weld surveillance materials, heat treatment received by all belt-line plate, weld, and surveillance materials, hea! numbers for all plate and weld _ wire, lot number for flux " sed for belt-line and surveillance v< eld, chemical composition of. weld-metals used in reactor and surveillance test welds, embrittlement effects at lower than-
_ operating temperature, and approach to consideration of surveillance test results. After review of the responses to the Generic Letter questions, the. inspector finds the responses _to be comprehensive. Where the licensee could not provide the appropriate response, an
- alternate method was proposed, together with justificatica for review and acceptance.
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9 3.0 UNRESOLVED ITEMS
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Unresolved items are matters about which more information is required in order to ascer'ain whether they are acceptable items, violations or deviations. Unresolved items disclosed during the inspection are discussed in Section 2.1.
4.0 SUMMARY Millstone Unit 3 has in opemtion a Stigue monitoring system for tracking the numbers of operational cycles which allow engineering to evaluate the fatigue life usage of those facility
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components designed for a limited number of transients or cycles.
Millstone Units 1 and 2 do not have an operating fatigue monitoring system for evaluating records of transient or operational cycles on components designed for a limited number of transient cycles.
Millstone Unit No.1, on the basis of calculations performed in 1982, has a fatigue life usage factor at present approaching the allowable value of 1.0 in the reactor basin seal skirt. The licensee will provide an analytic justification that the cumulative usage factor of the reactor.
basin seal skirt will not exceed 1.0 during the lifetime of the facility (URI 50-245/92-30-02).
A system for tracking the numbers of operational cycles is under development for application to Millstone Units 1 and 2.
The response of Northeast Nuclear Energy Company to Generic Letter 92-01 was co'uprehensive.
MANAGEMENT MEETINGS The inspector met with licensee representatives at the entrance meeting on November 16, 1992, and at the exit meeting on November 20,1992, at Northeast' Nuclear Energy Company in Berlin, Connecticut, The names oflicensee personnel contacted is
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- shown on Attachment 1. Those names having an asterisk attended the exit meetin.
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ATTACIIMENT 1
- The 'following persons were contacted during the course of the inspection (asterisk * indicates -
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attendance at the exit meeting):
Hollhcast Utilities Service Company (NUSilQ)
- N. Azevedo Senior Mechanical Engineer NUSCO Engineering.
- P. Godha Principal Engineer NUSCO Engineering
- M. Kupinski Manager - Mechanical Engtg.
NUSCO Engineering _
- P. Lutzi Licensing Engineer NUSCO Licensing P. Mine-Licensing Engineer (MP-1)
NUSCO Licensing G. van Noordennen Licensing Supervisor NUSCO Licensing
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