ML20209C157

Forwards Response to NRC RAI Re SCE Submittal Dtd 980710,re GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design-Basis Accident Conditions

ML20209C157
Person / Time
Site:	San Onofre
Issue date:	07/02/1999
From:	Scherer A SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-96-06, GL-96-6, NUDOCS 9907090187
Download: ML20209C157 (14)

Text

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J EDISON E=b am, An LDISON INTERNAlIONAL"* Company i

July 2,1999 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington D.C. 20555 Gentlemen:

Subject:

Docket Nos. 50 361 and 50-362 Additional Information Regarding Generic Letter 96-06: " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions" San Onofre Nuclear Generating Station, Units 2 and 3

Reference:

Letter dated July 10,1998, from J. L. Rainsberry to Document Control l Desk (NRC),

Subject:

Docket Nos. 50-361 and 50-362, Generic Letter 96-06: " Assurance of Equipment Operability and Containment Integrity '

During Design-Basis Accident Conditions," San Onofre Nuclear Generating Station Units 2 and 3 p Provided as an Enclosure is information requested by the NRC in a telephone conversation on June 11,1999. The NRC requested additional information regarding Southern California Edison's (SCE's) submittal dated July 10,1998, regarding Generic Letter 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions." SCE agreed to provide a sample calculation, for the staff's information only, to demonstrate how the requirements of the acceptance criteria in Section 2 of the enclosure to the July 10,1998 letter have been met.

9907090187 990702 PDR ADOCK 05000361 p PDR P. O. Box 128 Sam Clemente, CA 92674-0128 949-368-7501 Fax 949-368-7575 080021

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Document Control Desk July 2, 1999 If you have any additional questions on this subject, please feel free to contact me or Jack Rainsberry at (949) 368-7420.

Sincerely, l

Enclosure .

1 cc: E. W. Merschoff, Regional Administrator, NRC Region IV l J. A. Sloan, NRC Senior Resident inspector, San Onotre Units 2 & 3 L. Raghavan, NRC Project Manager, San Onofre Units 2 and 3

f:

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ENCLOSURE RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION Generic Letter 96-06:

Assurance of Equipment Operability and Containment Integrity J During Design-Basis Accident Conditions

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I Acceptance Criteria l As noted in Section 2, Acceptance Criteria, of the enclosure to Southern California

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Edison's (SCE's) July 10,1998 letter, the stress limits in the ASME Code,1989 Edition, no Addenda, Appendix F, Article F-1331 were used. A finite element based analysis was performed to determine the thermal-structural response of containment penetrations and the attached piping in order to calculate the trapped water pressure and the stresses resulting from a loss of coolant accident (LOCA) as a function of time.

This approach was adopted in lieu of the alternative simplified, and more conservative, approach / stress and pressure limits given in Article'F-1430. The application of the acceptance criteria of choice, as defined in Article F-1331, is further discussed below.

F-1331.1(a). General Primary 9mbrane Stress Intensity (Pm l '

The stress limit on the general primary membrane stress intensity, Pm , is based on Appendix F, Article F-1331.1(a). The value of Pm was based on the results of the finite element analysis, and acceptability was determined based on Pm s lesser of 2.4 Smand 0.7 S u-where Smis the allowable stress intensity, and S uis the ultimate tensile strength. Both values were obtained from Appendix 1.

For a pipe, Pmis calculated due to internal pressure only as defined in Table NB-3217-

2. In this case, Pm is given by Pm =lS-Sl i 3 where S3 = hoop stress S3 = radial compressive stress F-1331.1(c). Primary Membrane (General or Local) Plus Primary Bendina Stress Intensity (P t P) 3 The trapped water pressure was calculated as a function of time during a LOCA using  ;

the finite element method. To simplify the analysis, the finite element model did not include the external bending loads due to deadweight (DW) and design basis earthquake (DBE). The bending loads are available from existing stress calculations of the piping attached to the analyzed penetrations. These loads were used to calculate the combined bending stress, S3, due to DW and DBE.

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l It should be noted that stresses due to thermal expansion were excluded since they are classified as secondary and peak stresses (classifications P., O and F in Table NB-3217-2). Per Article F-1310, only limits on primary stresses are prescribed.

Results of the finite element analysis showed that the local primary membrane stress intensity, Pt , evaluated at the discontinuity formed by the weld attaching the .ed head to the penetration's neck extension, is bounded by the general primary membrane stress , Pm. This can be explained based on the stiffening effect of the flued head, which constrains the penetration's neck extension radial deformation due to pressurization. Figure 1 in the attachment shows the components of the penetration and the weld location.

The value of the combined bending stress was compared to the axial stress, S , due to the pressurization of the trapped water. In all cases, the calculated S3 was less than S,.

In one case only, S3 was about equal to S., i.e.,

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So s S.

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Accordingly, it was concluded that the combined bending stress plus axial pressure stress is 2 0.

The state of stress can be represented schematically as, a

S, (hoop stress) l e 7 S, + S (axial stress)

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V Since S, = W the hoop stress, it was also concluded that S, + So s S, < P m where P is less than or equal to 2.4 Smper F-1331.1(a). It follows that the higher allowable of F-1331.1( c) is also met. A Mohr's circle representation of the following i loadings is attached in Figure A: '

2

(a) Internal pressure only, (b) Internal pressure plus bending moment, on the tension side of the bending moment, (c) Internal pressure plus bending moment, on the compression side of the bending moment.

The stress intensity is enveloped by P in all cases.

A bounding simplified check was performed to evaluate Pt + P . Using the equation from F-1430(b) for calculating the combined pressure plus bending stress (S + S )

provided a simplified, and conservative, check of the Pt + P3 limit given in F-1331(c). In ;

this confirmatory check of Pt + P , the allowable stress of 3.0 S per F-1430(b) was  !

used for this evaluation, and no credit was taken for the higher allowable stress of 3.6 Smgiven in F-1331(c).

A detailed numerical example of the calculations described above is attached for penetrations 45 and 46.

Nomenclature DBE = design basis earthquake DW = deadweight F = peak stress intensity P,. = primary bending stress intensity P, = expansion stress intensity Pt = local primary membrane stress intensity Pm = general primary membrane stress Intensity Q = secondary stress intensity S, = pressure stress in the axial direction Se = bending stress Sm = allowable stress intensity Su = ultimate tensile strength j i

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TA $/

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(a) Internal Pressure Only T l /

la+Sg p+ Ss y S

cr e y-  :.

(b) Internal Pressure + Bending, (c) Internal Pressure + 8ending, Tension Side Compression Side Figure A Mohr's Circle Representation 4 I i

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Attachment i

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Detailed Example - Penetrations No. 45 and 46 5

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Desian Data Figure 1 shows a drawing of containment penetrations No. 45 and 46. A summary of the design input used in the annlysis for this penetration is given below.

System description  : Chilled water inlet (penetration 45 - chilled water inlet)

Chilled water outlet (penetration 46 - chilled water outlet)

Penetration location  : elevation 31'-6" (penetration 45 - chilled water inlet),

elevation 31'-6" (penetration 46 - chilled water outlet),

Penetration type :4 Penetration material . SA-106 Gr B Head diameter  : 18" Line No.  : 1513ML698 (penetration 45 - chilled water inlet) 1513MLO41 (penetration 46 - chilled water outlet)

Pipe size  : 8" sch 40 Design Pressure  : 150/125 psi (inlet / outlet)

Design Temperature  : 95'F (penetration 45 - chilled water inlet)

95'F (penetrahoa 46 - chilled water outlet)

Operating Pressure  : 80 psi (penetration 45 - chilled water inlet)

Operating Temperature  : 44*F (penetration 45 - chilled water inlet)

Operating Pressure 12 psi (penetration 46 - chilled water outlet)

Operating Temperature  : 60*F (penetration 46 - chilled water outlet)

Pipe material SA-106 Gr B Isolation valves HV9900 (penetration No. 45, inside containment)

HV9920 (penetration No. 45, outside containment)

HV9971 (penetration No. 46, inside containment)

HV9921 (penetration No. 46, outside containment)

Calculation of the Maximum Pressure Due to LOCA A finite element analysis was performed to calculate the overpressure in the penetration due to a LOCA. This analysis was performed using the general purpose ,

finite element analysis program ANSYS. An axisymmetric finite element (FE) model of

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the penetration was generated, as shown in Figure 2. The analysis was performed in i the following two steps:

Step 1 A thermal transient analysis was used to calculate the temperature time history of the pipe, penetration, and the trapped water. The model was generated using ANSYS element type PLANE 55, which can be used to solve two-dimensional axisymmetric heat transfer problems. In addition to the penetration, the model shown in Figure 2 include.= the inboard and outboard isolation valves, and pipe segments extending a distance of several pipe '

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diameters beyond the inboard isolation valve to account for the heat transferred to the trapped water via the adjacent piping. The model also includes the containment wall and the containment carbon steel lining.

The moden. boundary inside containment is exposed directly to the accident environment, and appropriate heat transfer coefficients were calculated as a function of time. These coefficients include the effect of condensation. A typical natural convection value of .2 BTU /hr ft *F was applied to the boundary outside containment.

The thermal transient analysis was performed in several time steps starting at the onset of the LOCA (t=0) to t=10 seconds.

Steo 2 A structural analysis was used to calculate the stresses and the trapped water pressure using the results of the thermal transient analysis. The finite element model in this case has identical geometry to the thermal analysis model.

The structural model uses ANSYS element type FLUID 79 for the trapped water and PLANE 42 otherwise.

The pressure calculation methodology using the finite element method was verified by hand calculation for a simple geometry, and was shown to be very accurate. The difference between the FE results and hand calculations was on the order of only 0.24%.

Table 1 gives a summary of the trapped water pressure time history due to a LOCA.

The maximum pressure, Pmo, of 3,194 psi occurs at 300,000 seconds.

l Table 1 Pressure Time History for Penetrations No. 45 and 46 Time Pressure Time Pressure (seconds) (psi) yseconds) (psi) 300 1 40,000 964 500 2 60,000 1,435 1,000 5 100,000 2,132 3,000 25 300,000 3,194 10,000 156 500,000 3,100

, 20,000 416 1,000,000 2,845 l 7

Calculations The maximum general membrane stress intensity, P , per the detailed finite element analysis results (see below)is P, = 41,520 psi < S,% (=42,000 psi) l where S,% = the lesser of 0.7 So and 2.4 S.

= 0.7 So (< 2.4 S, of 48,000 psi)

= 42,000 psi (for SA-106 Gr B at 200*F) 4 The maximum P, corresponds to the maximum pressure of 3.194 psi.

Maximum Membrane Stress per FEA Results j 1

• • • • • POST 1 LINEARIZED STRESS LISTING *****

INSIDE NODE = 68 oUTSIDE NODE = 50 i LOAD STEP 16 SUBSTEP= 3 TIME = 83.333 LOAD CASE = 0 l l l ** AXISYMMETRIC OPTION ** RHO = .32791E+12

) THE FOLLOWING X,Y,Z STRESSES ARE IN SECTION COORDINATES. i

• • MEMBRANE **

SX SY SZ SXY SYZ SXZ

-1403. -1761. .3974E+05 -99.54 .0000E+00 .0000E+00 S1 S2 S3 SINT SEQV

.3974E+05 -1377. -1787 !41525+05 .4132E+05 The following bounding deadweight moments were obtained from the piping stress calculations:

I M,.ow = -444 ft-lb My .ow = 239 ft-Ib M,e y = 2,816 ft-Ib 1

Similarly, the DBE moments are M,.o.e = 1,799 ft-Ib My.o e = 486 ft-Ib 8

M,.o e = 2,826 ft-lb The resultant moment M,, is M, = M,.ow + M,.ose 2 2 2

= (M,.ow + M y.ow + y,,0w )x + (M,.o e 2+ M .o 2 y e + yz-DBE )

= 2,861 + 3,385

= 6,246 ft-lb The section modulus, Z, is Z = nR,2t

= 17.43 in 8 The axial stress due to internal pressure, S., is combined with the bending stress due to deadweight +DBE stress, So, l 1

i Bi PD/2t + B2 M/Z = S, + S.

l = 0.7.5x3,194x8.625/(2x0.322) +

) 1.5x6,246x12/17.43 38,533 < 3.0 S (=60,000 psi) where the stress indices are given by Bi = 0.75 1 B2 = 1.5 In the above equation, the right hand side consists of two terms:

S, = 0.75x3,194x8.625/(2x0.322) l

= 32,083 psi l S. = 1.5x6,246x12/17.43 i

= 6,450 psi l Since the value of So is less than S , the combined stress is tensile in the penetration.

Furthermore, it is noted that the value of S, + S is less than the value of P, calculated j previously.

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