05000245/LER-1996-009-01, :on 960109,isolation Condenser Makeup Water Temperature Below Design Basis Limit,Determined.Caused by Inadequate Design Specification.Preliminary Assessment of non-ductile Failure of Isolation Condenser Sys Performed

:on 960109,isolation Condenser Makeup Water Temperature Below Design Basis Limit,Determined.Caused by Inadequate Design Specification.Preliminary Assessment of non-ductile Failure of Isolation Condenser Sys Performed

ML20141G523
Person / Time
Site:	Millstone
Issue date:	05/19/1997
From:	Robert Walpole NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20141G504	List: 05000245/LER-1996-009-01, :on 960109,isolation Condenser Makeup Water Temperature Below Design Basis Limit,Determined.Caused by Inadequate Design Specification.Preliminary Assessment of non-ductile Failure of Isolation Condenser Sys Performed
References
LER-96-009-01, LER-96-9-1, NUDOCS 9705220396
Download: ML20141G523 (4)

LER-1996-009, on 960109,isolation Condenser Makeup Water Temperature Below Design Basis Limit,Determined.Caused by Inadequate Design Specification.Preliminary Assessment of non-ductile Failure of Isolation Condenser Sys Performed

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
2451996009R01 - NRC Website

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FACIUTV NAME (1)

DOCKET NUM8ER (2)

PAGE (Ji Millstone Nuclear Power Station Unit 1 05000245 1 of 4 TITLE (4).

Isolation Condenser Makeup Water Temperature Below Design Basis Limit EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR FACiUTY NAME DOCKET NUMBER NUMBER NUMBER 01 09 96 96 009 01 05 19 97 FAGiuTY NAME DOGEET NUMBER i

OPERA DNG THIS R EPO0T IS SUBMITTED PURSUANT TO "HE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11) i MODE (9) 20.2201(b) 20.2203(aH2)(v) 50.73(aH2Hi) 50.73(aH2)(vm)

POWER 20.2203(aH 1) 20.2203(aH3)b) 50.73(a)(2)(u) 50.73(aH2)(x) 20.2203(a)(2)(i) 20.2203(aH3Hu) 50.73(aH2Hm) 73.71 l

20.2203(aH2Hn) 20.2203(aH4) -

50.73(aH2)bv)

OTHER or in NRC Form 366A 20.2203(aH210v) 50.36(cH2) 50.73(aH2)(vn)

LICEN! EE CONTACT FOR THIS LER (12)

N4.M E TELEPHONE NUMBER (mcaude Asea Codel Robert W. Walpole, MP1 Nuclear Licensing Manager (860)440 2191 l'

1 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

C SYSTEM COMPONENT MANUF At JRER R POPTAB.

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M 5 TEM COMPONENT M ANUFACTURE R R PORT BE S JPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY YEAR SUBMtsSION YES V

NO (If yes, complete EXPECTED SUBMISSION DATE).

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On January 9,1996, with the plant shutdown and the reactor in the COLD SHUTDOWN condition, the Millstone Unit No.1 design basis verificatian team determined that the isolation condenser may have been operated with makeup water colder than that perrnitted by the design basis. On February 5,1996, after an extensive review of the design basis involving the structural integrity of the isolation condenser, it was determined that makeup water as l

cold as 50 degrees F has been used. This is contrary to the design basis makeup water temperature of 70 degrees F.

This event is reportable pursuant to 10CFR50.73(a)(2)(ii)(B) as a condition outside the design basis of the plant.

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Additionally, this event was promptly reported pursuant to 10CFR50.72(b)(2)(ii)(B) as a condition outside the design

- basis of the plant, No immediate operator actions were required at the time of discovery. There were no safety consequences as a

,f result of this event.

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LICENSEE EVENT REPORT (LER) i TEXT CONTINUATION FACILITY NAME (t)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) 05000245 YEAR SEQUENTIAL REVISION Millstone Nuclear Power Station Unit 1 NUMBER NUMBER 2 of 4 96 009 01 TEXT (11more space is reqwred, use additionalcopies of NRC form 366Al fil)

- 1.

Description of Event

On January 9,1996, with the plant shutdown and the reactor in the COLD SHUTDOWN condition, the i

Millstone Unit No.1 design basis verification team determined that the isolation condenser may have been operated with makeup water colder than that permitted by the design basis. On February 5,1996, after an extensive review of the design basis involving the structural integrity of the isolation condenser, it was l

determined that makeup water as cold as 50 degrees F has been used. This is contrary to the design basis makeup water temperature of 70 degrees F.

This event is reportable pursuant to 10CFR50.73(a)(2)(ii)(B) as a condition outside the design basis of the plant.' Additionally, this event was promptly reported pursuant to 10CFR50.72(b)(2)(ii)(B) as a condition outside the design basis of the plant, i

No immediate operator actions were required at the time of discovecy. There were no safety consequences as a result of this event.

II. Cause of Event

The cause of this event is an inadequate design specification. Since the make-up water source is specified to be either the condensate storage tank or the fire protection system, the design specification should have specified an isolation condenser makeup water temperatum limit consistent with the Condensate Storage Tank temperature or the potable water supply temperature in Connecticut. A temperature lower.than.50 degrees F would have been appropriate. Additionally, inadequate operating procedure at Millstone Unit No 1 did not properly ensure that the 70 degrees F design limit on the make-up water temperature design limit was met.

Ill. Analysis of Event A systematic design basis verification is being performed to provide assurance that the plant is being operated within its design basis. As part of this effort, on January 9,1996, it was determined that the isolation condenser may have been operated outside its design basis. Following an evaluation and a review of the plant equipment operator (PEO) logs, it was determined that makeup water as cold as 50 degrees F has been used for the shell (secondary) side of the isolation condenser. The plant design basis is a makeup water temperature of 70 degrees F. This event is reportable pursuant to 10CFR50.73(a)(2)(ii)(B) as a l

condition outside of the design basis of the plant. Additionally, this event was promptly reported, pursuant to 10CFR50.72(b)(2)(ii)(B) as a condition outside the design basis of the plant.

Preliminary analysis (Calculation 96-SDS-1445M1, Rev. O) showed that there is no apparent degradation of l

the isolation condenser due to this design inadequacy. The use of colder,50 degree F water does not pose a non-ductile failure concern. The fatigue analysis performed on the affected shell (secondary) side components of the isolation condenser shows that the use of lower temperature makeup water (as low as 40 degrees F) does not have an adverse effect on compliance with the original ASME 111 fatigue design requirements, it must be noted, however, that the external piping loads were not included in this preliminary evaluation of 40 degree F makeup water because they were not included in the original design basis analysis of record for MC Ff AM 366A (4-95)

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DOCKET NUMBER (2)

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the make-up nozzle. The makeup water piping is low pressure and low temperature piping which had not been rigorously enalyzed previously.

The existing isolation condenser make-up piping has been since analyzed rigorously (Calculation 96-SDS-

'1520M1, Rev. 0) to demonstrate compliance with Millstone Unit No.1 piping design bases. The analysis results showed that this piping was not operable. LER 96-051-01, " Seismic Qualification Deficiencies Found in Safety Related Piping," reported this deficiency in the isolation condenser piping (3" IC-12). Additional l

piping supports were required to demonstrate compliance with Millstone Unit No.1 piping design bases.

The nozzle loads determined from this rigorous piping analysis with additional supports were used in the analysis of the isolation condenser shell/ nozzle region. The design basis stress and fatigue analysis of the makeup nozzle has been revised to include a lower bound makeup water temperature of 32 degrees F as well l

as the piping imposed loads.

The stress analysis of the isolation condenser makeup nozzle has been completed using the ANSYS finite element computer code. A 2-D axisymmetric model representing the geometry of the shell makeup nozzle including sufficient region of the isolation condenser vessel shell is created. A sufficient length of the shell is modeled as a flat plate. Since the curvature of shell is much larger than the makeup nozzle (132 inch Vs 3.5 inch) the flat plate approximation is considered appropriate.

Heat transfer coefficients are calculated for the nozzle inside and outside diameters to simulate the makeup fiow addition at 32 degrees F and used in determining the transient temperature distribution in the nozzle and the shell. Transient temperature distributions due to a step change from 250 degrees F ( shell side maximum operating temperature) to 32 degrees F are calculated and used to perform thermal stress analysis at several time steps. The nozzle and shell are analyzed for nominal as well as corroded wall thickness and for the design as well as throttle condition flow rates. The cross-section, flow rate and time step with the largest nodal stress intensity is selected to be combined with other loading conditions such as pressure and external mechanical loads.

In addition to ' internal pressure, the axisymmetric and non-axisymmetric external loads are applied to the nozzle using harmonic functions as unit load cases as discussed in ANSYS Users Manual.

The stresses are. categorized based on Table N-413 in ASME Section ill, Subsection A,1965 Edition.

Accordingly, the membrane stresses due to nozzie external loads are categorized as P for the nozzle and t

shell. All O category stresses are categorized as secondary stresses for the nozzle and the shell. The stresses due to through the thickness thermal gradient in the vessel wall are considered peak stresses to be included in the fatigue assessment.

The nodal stresses from ANSYS analysis are converted into P and P stress categories as defined in ASME m

I Code. Automated conversion feature of ANSYS post processing routine is used at several cross-section slices to determine these stresses. Note that the cross-section has to pass through free surface at both extremities for appropriate results.

The ASME Code stress check is performed for the design condition (including faulted) as well as for the i

operating conditions. Fatigue usage factor for 800 design number of cycles (as specified in General Electric l

Design Specification 21 A1609) for the addition of makeup water at full power is also calculated and shown to be below 1.0.

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PAGE (3) 05000245 YEAR SEQUENTIAL REVISION

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TEXT (If more space is required, use additional copies of NRC form 366A) (17}

Brittle fracture of the nozzle /shell region due to thermal shock from makeup water addition at 32 degrees F was addressed qualitatively. Both the nozzie and shell material are suitable for service up to -20 degrees F per ASME Section Vill, 1965 Edition, (Para. UCS 65), with no fracture toughness (RTnor) - testing requirements Additionally, the thickness of the components involved is less than 0.625 inch and the maximum expected pressure is only 15 psig. Based on relatively thin cross-section thickness of the nozzle I

and shell, material suitability to service temperature as low as -20 degrees F, and minimal pressure and j

service loads, a failure due to thermal shock is believed to be highly unlikely.

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With new support installation, the isolation condenser shell side make-up piping will be restored to full I

compliance with Millstone Unit No.1 design basis.

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IV. Corrective Action

A preliminary assessment of non-ductile failure of the isolation condenser system was performed in 1996 without identifyin0 any concerns. Additionally, a fatigue analysis was also performed on the affected isolation condenser components, which confirmed that 50 degree F makeup water has had no adverse effect on compliance with the original ASME lit fatigue design requirements. However, neither the original analysis j'

for 70 degrees F make-up water nor the preliminary analysis with 40 degrees F make up water include any l

nozzle loads because these loads were unavailable.

The nozzle loads have been since determined from rigorous piping analysis. This analysis concluded that the existing piping in as-is condition was in-operable. LER 96-051-01 was issued to report this deficiency.

The LER 96-051-01 committed to restore the piping system to design basis requirements prior to startup for j

operating Cycle 16.

I The isolation condenser shell/ nozzle junction analysis has been completed using the augmented nozzle loads l

and 32 degrees F makeup water. This analysis shows thei the nozzle complies with applicable ASME Code l

requirements provided new supports are instailed.au Ngned such that nozzle loads are not impacted.

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The Updated Final Safety Analysis Report will be revised to incorporate 32 degrees lower bound for the isolation condenser makeup water temperature, based on the results of the isolation condenser shell analysis prior to startup for operating Cycle 16, Since the makeup water temperature of 32 degrees F has been found to be acceptable, procedural controls are not necessary.

V.

Additional informaticq l

Similar Events

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l Manufacturer Data -

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None, 4c F)RM 366A (4 953 l