ML20246N849

Rev 3 to Oyster Creek Nuclear Generating Station Mark I Containment Long Term Program,Addendum to MPR-734 Plant- Unique Analysis Rept Torus Attached Piping

ML20246N849
Person / Time
Site:	Oyster Creek
Issue date:	12/31/1988
From:	MPR ASSOCIATES, INC.
To:
Shared Package
ML20246N836	List: ML20246N832 ML20246N849
References
MPR-999, MPR-999-R03, MPR-999-R3, NUDOCS 8909080283
Download: ML20246N849 (25)

Text

.. . - _ _ - _ - _ _

- MPR ASSOCIATES, INC.

OYSTER CREEK NUCLEAR GENERATING STATION MARK I CONTAINMENT LONG-TERM PROGRAM ADDENDUM TO MPR-734 PLANT-UNIOUE ANALYSIS REPORT TORUS ATTACHED PIPING MPR-999 .

Revision 3 n.

4 '

t Prepared for:

General Public Utilities Nuclear <

Parsippany, NJ .

December 1988 .

l l

I 1050 CONNECTICUT AVENUE, N.W. WA&MINGTON. D.C. 20036 202 659 2320 .

8909080283 890830 -

FDR ADOCK 05000219 F FDC

M P R ASSOCIATES. INC.

,TS.BLE OF CONTENTS

1.0 INTRODUCTION

2.0 REANALYSIS RESULTS 2.1 Vacuum Relief Piping 2.2 Containment Spray Test Return 2.3 Core Spray Test Return 2.4 SRV Discharge Piping 2.5 Small Bore Piping i

l

MPR ASSOCIATES. INC.

1.0 INTRODUCTION

The Oyster Creek Nuclear Generating Station uses a containment structure for the boiling water reactor (BWR) nuclear steam supply system desig-nated as the Mark I containment system. The containment structure con-sists of a drywell, torus suppression chamber, and connecting vent system. Is August of 1982, MPR prepared a report, MPR-73", documenting the results of ar.alyses performed on piping systems attached to the torus suppression chamber. These analyses were performed in accordance with the Mark I Containment Long-Term Program, as documented in MPR-734 MPR-734 documented that the piping systems attached to the torus suppression chamber would satisfy the Mark I Containment Long-Term Pro-gram provided that certain modifications were made. Subsequent changes to the piping and support arrangements made it necessary to reanalyze some of these piping systems to reconfirm that they satisfy Mark I Program acceptance criteria and to redefine the needed modifications.

The purpose of this report is to document the reanalyses of torus attached piping systems which were performed for the reasons discussed above. Because this report is an addendum to the original Mark I Long-l Term Program analysis report, only the information that differs from the original report, i.e., the reanalysis results, is included in this report.

1.1

MPR ASSOCIATES. INC.

2.0 REANALYSIS RESULTS 2.1 VACUUM RELIEF PIPING 2.1.1 Torus-to-Reactor Building Vacuum Breaker Line The original MPR-734 Mark I Program analysis of the Torus-to-Reactor Building Vacuum Breaker Line (TRB) included supports which had pre-viously been engineered, but not yet installed, as part of a Containment Vent / Purge System Upgrade, a program unrelated to the Mark I Program.

This upgrade also included the proposed installation of supports on a branch line, the Nitrogen Purge Line, in the vicinity of its connection to the TRB. Subsequently, it was determined by GPUN that there was no need for the Containment Vent / Purge system upgrade. The question then arose as to which of the supports were essential to ensure that the TRB satisfied the Mark i Long-Term Program acceptance criteria. A preliminary fielo check of the proposed supports revealed that certain of these supports could not be installed as originally designed due to interferences. For these reasons, GPUN requested that MPR reanalyze the TRR in order to:

Determine which of the original seven TRB supports are required to satisfy the Mark I long-Term Containment Program piping criteria.

• Recommend needed changes to the support designs and any other TRB modifications required to satisfy Mark I Program Criteria.

Determine updated design loads for any new supports required and for the existing floor support (the floor support had been shown to require modification in the original MPR-734 analysis).

2.1

The reanalysis of the TRB is based on the support arrangement shown in Figure 2.1-1, which supersedes Figure 6.1-4 in MPR-734. This support arrangement requires installation of three of the additional supports which were originally proposed. The method used for this reanalysis is the same as that used originally, except for the summation method used to combine dynamic loads, which is based on square root sum of the squares (SRSS) combination of independent dynamic loads. This approach was approved by the NRC for use in Mark I analyses as documented in NUREG-0484, Rev.1. " Methodology for Combining Dynamic Responses," and -

NEDE-24632, " Mark 1 Contair. ment Program Cumulative Distribution Functions for Typical Dynamic Responses of a Mark I Torus and Attached Piping Systems," which was forwarded to the USNRC on behalf of the BWR Mark 1 Owners Group by GE letter MFN-147-82.

With this support arrangement the piping stresses satisfy all Mark 1 Containment Program Acceptance Criteria. Maximum and allowable stresses for the TRB piping are shown in Table 2.1-1, which supersedes the results shown in Table 6.1-2 in MPR-734 for the TRB (Azimuth 180'). The most limiting occasional loading stress is 8,000 psi, 22% of the allowable stress. For the thermal and sustained load piping stresses, the most limiting calculated stress is 19,000 psi, 84% of the allowable stress.

Support and hanger stresses are bounded by the stresses and loads reported in MPR-734, except for the floor support O'0Z-2-H30), which is '

being modified to meet Mark I Acceptance Criteria. The most limiting stresses for the modified floor support are as follows: (i) Level A/B '

Loading - 16,920 psi, 78% of the allowble stress, (ii) Level C Loading -

27,960 psi, 97% of the allowable stress. gg The following actions which result in the TRB satisfying the Mark 1 Pro-gram criteria are being taken:

l 2.2

• Installation of three additional supports.

Reinforcement of the existing f.oor support at elevation 26'-6". '

1 2.1.2 Containment Exhaust Line The original MPR-734 Containment Exhaust Line Mark I Program analyses were performed including the effects of a proposed modification:

replacing 200 lb butterfly valves with 1325 lb valves and adding a dead-weight support. GPUN has determined that this modification is not nec-essary; therefore, the original analysis results do not correspond to the as-built condition of the line.

To verify the adequacy of tne piping without this modification, the ori-ginal MPR-734 calculations were reviewed. These calculations contained ,

scoping analyses which included analyses using the existing 200 lb valves.

It was, therefore, possible to compare results for the as-built piping with results obtained for the piping with the proposed, heavy valves.

From these comparisons, it was concluded that the analysis results for the original analysis (with the proposed, heavy valves) bound the results for the as-built configuration of the Containment Exhaust Line (with the light valves). Furthermore, there is no change in the conclusion that the Containment Exhaust Line as-built configuration meets the requirements of the Mark i Long-Term Program. Accordingly, no structural modifications are required.

2.3

TABLE 2.1-1

SUMMARY

OF MAXIMUM AN0 ALLOWABLE STRESSES TORUS-TO-REACTOR BUILOING VACUUM RELIEF PIPING AT AZIMUTH 180" Occasional Loading Stresses - ASME Equation (9)

Load Case (Note 1) Maximum Stress (ksi) location (Note 3) Allowable Stress (ksi) la 4.0 (Note 4) Elbow G 18.0 lb 4.0 (Note 4) Elbow G 27.0 II 5.3 Elbow G 36.0 III 8.0 Elbow G 36.0 IVa 4.0 (Note 4) Elbow G 27.0 IVb 4.0 (Note 4) Elbow G 36.0 Va 4.0 (Note 4) Elbow G 27.0 vb 4.0 Elbow G 36.0 Thermal and Sustained Loading Stresses - ASME Equation (10)

Load Case (Note 1) Maximum Stress (ksi) Location (Note 2) Allowable Stress (ksi)

I 17.1 Tee E 22.5 II & III 19.0 Tee E 22.5 IV & V 27.2 (Note 3) Tee E 35.3 Notes:

1. Load cases defined in MPR-734,

2. Maximum stress locations defined in Figure 2.1-1.

3. Case IV and V evaluated in accordance with ASME Equation (11).

4 Pipe stresses for these occasional load cases are conservatively taken as the stress for Load Case Vb.

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f 2.2 CONTAINMENT SPRAY' TEST RETURN PIPING

~ The original' Mark I Program analysis of the Containment Spray and Test Return' Piping was performed using a model which contained a proposed modification: rerouting the two Test Return Lines such that they would penetrate ~ the torus ttirough their own nozzles, instead of penetrating through the torus-to-dryweH vacuum relief piping, which is external to

' the torus. Reanalysis waslequired by a change in the routing planned by GPUN for.these lines, and the addition on one of the lines of a

. special branch connection <and support for returning temporary torus water clean-up flow to the torus.

I As described above, each of the two containment spray and test return piping lines will continue to be connected to the torus through a torus-to-drywell vacuum relief assembly. The coupled nature of these systems j made it necessary to include the vacuum relief piping in the containment l spray piping analysis models. Figure 2.2-1 shows the model of vacuum  ;

assembly G used for this. analysis, and supersedes Figure 6.3-1 in MPR-734 The model for vacuum assembly B is shown in Figure 2.2-2.

The method used for this reanalysis is the same as that used originally, except for the summation method used to combine dynamic loads, which is based on square root sum of the squares'(SRSS) combination of independent dynamic loads. This approach was approved by the NRC for use in Mark I analyses as documented in NUREG-0484, Rev.1, " Methodology for Combining Dynamic Responses," and NEDE-24632, " Mark I Containment Program Cumulative Distribution Functions for Typical Dynamic Responses of a Mark I Torus and Attached Piping Systems," which was forwarded to

- the USNRC on behalf of the BWR Mark I Owners Group by GE letter MFN-147-82.

2.6

Previous analyses of the south containment spray loop, in which the modified support at the torus water cleenp line (H0327) was conservatively modeled as a rigid pinned support, resulted in calculated peak stresses for Load Cases Ib and II which exceeded the allowable stresses by less than 4%. A reanalysis of the line for these load cases. in which support H0327 is more accurately modelec :o account for l the actual stiffness of the support, confirmed that the previous analysis was conservative. The peak calculated stresses for the north and south containment spray test return lines are summarized in Table 2.2-1 hlong with the Mark I Containment Long-Term Program allowable stresses. As shown in the table, the peak stresses in these lines satisfy the Mark I Program acceptance criteria for all load cases. The stresses shown in Table 2.2-1 for the north loop at Assembly G supersede the Out-of-Torus stress results contained in lable 6.3-1 cf MPR-734.

I Although the purpose of the containment spray piping analysis effort was tc account for the changa in the planned routing of the cortaiment spray -

3 piping, the stresses in the adjacent vhcuum relief pi;dng were evaluated l

as well. It was found thr.t the stresses in vacuum relief piping calculated with the coupled containment spray / vacuum relief piping l mode?s are bounded by the original analyses of the vacuum relief piping discussed in MPR-734 All support and hanger stresses are within the Mark I requirements except as noted below. For the remaining supports, the maximum calcu-lated support stress is 14,300 psi, 79% of the allowable stress. The maximum calculatad hanger load is 290 pounds, 94% of the allowable load specified by the hanger manufacturer.

2.7

To meet the Mark I criteria, the following support modifications were and are being made:

1. The torus spray header supports were modified to withstand Mark I loads. The design loads and requirements for these supports did not change as a result of the reanalysis.

2. The existing support at the torus water cleanup line connection on the south containment : pray test return line at vacuum relief assembly B (Azimuth 72') was modified to withstand Mark I loads.

The support is located at Elevation 25 feet and is designated D in Figure 2.2 2 (H0327).

3. One existing spring hanger support on the north conwinment spray test return line located at vacuum relief assembly G (Azimuth 288 )

will be replaced with a rigirl vertical strut. Tnis support is 1ccated at Elevation 14 feet ans ;s :ksignated G in Figure 2,2-)

(N0-2-H43). Yhe v. modification ,os recoirect becaust the existing l

j spring hanger was unabic to atioquately restrain oscillatica of the combined test return line and vacuum relief assembly G. The exist-ing arrangement resulted in unacceptable stresses in both the con-tainment spray test raturn line and ir, vacuum relief piping at i

assembly G.

The existing vertical support on the north containment spray and test

! return line at vacuum relief assembly G ( Azimuth 288 ), is currently i

gapped in all directions. This support is located at Elevation 30 feet, and is designated S in Figure 2.2-1 (NQ-2-H39). During analysis, displacements were calculated at this support to determine if the limits of the gap would be reached. It was determined that the gap would not

) close during any Mark I loading combinations and therefore the support L may be removed without affecting the Mark I analysis results documented in this report. It is not mandatory that the support be removed to 2.8

satisfy the Mark I Program requirements. It should also be noted that the seismic restraint on the north containment spray and test return line designated R in Figure 2.21 (NQ-2-RI), at Elevation 28 feet, 3 inches, is also gapped. Using a similar approach, it was determined l that the gap limits would not be reached. Thus, this support may also be removed without affecting the Mark I analysis results documented in this report.

The vacuum relief piping assemblies to which the containment spray and test return lines are connected each have two nozzles: one connected to the torus and one connected to the vent line external to the torus. The stresses for each load combination evaluated for the torus nozzles of both vacuum relief assemblies (B and G) were less than those computed for the original load combinations. Also, all stresses calculated for the B and G vacuum relief piping assembly vent line nozzles were within l

the allowable stress values. The revised analyses snow that the i limiting load combination results fron the bounding postchug combination l rattier than the bounding condensation oscillation load combination, which was limiting in the on :'ginal analyses; however, the calculated stress to allowable stress ratio remains the same. Accordingly, the results contained in MPR-734 Lre representative of the structural design l margins of the piping and it is not necessary to revise those results.

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\ 2.9

TABLE 2.2-1

SUMMARY

OF MAXIMUM PlPING STRESSES FOR CONTAINMENT SPRAY PIPING Occasional Leading Stresses - ASME Ecuation (9)

North Loop at Assembly G South Loop at Assembly B

(

Load Case Maximum Stress Location Maximum Stress Location Allowable Stress (Note 1) (kst) (Note 2) (ksi) (Note 3) (ksi) la 10.0 D 12.6 A 18.0 lb 23.0 D 2$.5 A 27.0 18 27.7 0 34.5 A 36.0 111 30.4 D 34.4 A 36.0 IVa 12.7 D 19.9 A 27.0 Ivb 24.0 D 30.6 A 36 .0 Va 17.5 D 24.7 A 27.0 l

Yb 26.2 D 33.4 A 36.0 1

Thermal and Surialned Loadina Stresses - ASME Equation (II) l North Loop at Assembly G Sou+h toop at Assembly tf n

Load Case Maximum Stress locatlan Maximua Stress Locatice. Alicaabte Stress (Note 1) (ksi) (Not e 2) (ksi) (Note 3) (ksl>

I , 27.1 0 21.9 A 37.50 1I & III l 35.2 0 32.3 A 31.50 l V lt V 28.6 D 23.5 A 35.25 I i Notes :

1. Load cases are bounding combinations of those presented in MPR-734

2. Locations defined in Figure 2.2-1 f 3. Locations def ined in Figure 2.2-2.

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2.3 CORE SPRAY TEST R[ TURN PIPING The original Mark I Program analysis results from MPR-734 indicated that an existing support on the Core Spray Test Return piping which connects to Vacuum Relief Piping Assembly F (NZ-2-R13A) was overstressed and required modification. (MPR 734 identified this support location as being near Assembly 0; however, the actual support location is near Assembly F.) An MPR field check of this support in April and July 1985 indicated that the as-built support NZ-2-R13A differed in both configuration and orientation from the Burns and Roe (B&R) design draw-ing of the support. The original Mark I analyses documented in MPR-734 were based on the configuration of this support as shown in the B&R drawing. Since those analyses were performed, the USNRC approved the Square Root Sum of the Squares (SRSS) method of combining independent dynamic loads for use in the Mark I Long-Term Program. In order to cor. firm the effects that the as-built support configuration and SRSS summation method have on the support and piping stresses, a partial computer reanalysis was performed.

I Reanalysis of the existing support NZ-2-R13A using the es-built config-uration ar.d SRSS summation confirms that stresses are acceptable for Mai-k I Long-Term Program loads. The modeling of the actual support con-figuration resulted in a change in the dynamic response of the piping system. As a result, calculated inads in su? port N1-2-R13A were creatly reduced, thus reducing the loss of Coole.nt Accident (LOCA) induced lead' on the support. The reduced support stiffness, however, caused an increase in the calculated seismic loads on the support. The net effect, including the SRSS summation of independent seismic and LOCA loads is that the support stresses are acceptable for Mark I long-Term i Program loads. Therefore, support NZ-2-R13A does not require modifica-tion to satisfy the Mark I Containment program acceptance criteria.

2.13

The resulting piping stresses in the line were also affected as a result of the change in this support. The as-built support configuration caused a shift in the maximum stress location in the piping for some load combinations. Nevertheless, all piping stresses are within Mark I Containment Long-Term Program stress limits for all loading conditions, as shown in Table 2.3-1, which supersedes the Vacuum Breaker F stresses given in Table 6.4-1 in MPR-734 Likewise, Figure 2.3-1, which shows limiting stress locations, supersedes Figure 6.4-1 in MPR-734 The maximum calculated occasional load piping s:ress required to meet the 18,000 psi Level B allowable stress is 8,100 psi, 45% of the allow-able stress. The maximum calculated occasional load piping stress for the 27,000 psi Level B(3) allowable stress is 18,600 psi, 69% of the allowable stress. The maximum calculated thermal and sustained load piping stress of 11,700 psi is 52% of the allowable stress. The SBA post-chug thermal and sustained load case (Load Case V) is required to meet a reduced allowable stress, due to the number of effective cycles (up to 14,000). The maximum calculated piping stress of 11,300 psi is 56% of this allowable.

All support and hanger stresses were within the Mark I requirements

?xcept fur one support on the core spray test return piping at assembly D (Nl ? R41Ai, whicii is being replaced so as to satisfy these require-ment 9.. For tht: remaining supports, the maximum chlculated tuppoet stress is 23,162 psi, 80% of the allowable stress. Tho maximum calcu-laced hanger load is 1,000 pounds, 81% of the allowable load specified by the hanger manufacturer.

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2.14

TABLE 2.3-1

SUMMARY

OF MAXIMUM AND ALLOWABLE STRESSES CORE SPRAY TEST RETURN PIPING AT VACllVM BREAKER F Occasional Loading Stresses - ASME Equation (9)

Maximum Allowable Load Case Stress Location Stress (Note 1) (ksi) (Note 2) (ksi) la 7.7 Elbow B 18.0 lb 15.5 Elbow B 27.0 II 14.9 Branch C 36.0 III 16.7 Branch C 36.0 IVa 7.0 Elbow B 27.0 IVb 10.1 Elbow B 36.0 Va 8.4 Elbow B 27.0 Vb 16.1 Branch C 36.0 Thermal and Sustained Loading Stresses - ASME Equation (10)

Maximum Allowable Load Case Stress Location Stress (hote 1,' (ksi) (Note 2) (ksi)

--=-

I 1 7.8 Elbow A 22.50 11 & III 9.4 Elbow B 22.50 IV & V 8.7 Elbow A 20.25 Notes:

1. Load cases defined in MPR-734,

2. Maximum stress locations defined in Figure 2.3-1.

MPR ASSOCIATES F-8 3 11 4/13/8 7-MODEL TERMINATED ELEVATION 67 FT-0 IN 6-INCH W

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j AZIMUTH 144 ELEVATION 15 FT-0 IN l

l FIGURE 2.3-1 l LIMITING STRESS LOCATIONS CORE SPRAY RETURN PIPING -

AT VACUUM BREAKER F s

2.4 SRV DISCHARGE PIPING The original Mark I Containment Program analysis of the drywell SRV pip-ing restraints resulted in loads that would require major structural modifications to most of the pipe restraints and the supporting drywell structure. A partial reanalysis which had been performed for the in-torus SRV discharge piping (MPR-772) using a more detailed analysis technique resulted in more realistic (and significantly lower) dynamic pipe responses. In order to obtain a more realistic assessment of the restraints for the out-of-torus SRV South Header and North Header drywell piping, this same detailed analysis technique was used to reanalyze this piping.

The original analysis of the SRV piping was performed with a response spectrum analysis technique in which the response of the structure for each mode is determined independently. These responses were then added assuming random phasing between the input for each mode. The response for each anchor point was considered separately and the results combined I using an absolute summation method. The revised analysis used a time history approach based on the harmonic analysis technique. This tech-nique accurately accounts for the phase relationship between the responses of each mode to the various components of anchor point excita-tion. In addition, the original analysis combined the independent load l contributions by summing the absolute value of the components. The revised analyLis load cnbinations are based on the Square Root Sum of the Squt,res (SP.SS) of the independent dynamic loads.

The following approach was used in the evaluation of the SRV drywell

, piping restraints: the standard components of the pipe restraints (e.g., snubbers) were evaluated by comparing the support rating to the revised support design load. The stresses in the support / pipe and the support / anchor attachment assemblies were calculated for the revised I support loads using the as-built support dimensions obtained in the 1

2.17 1

November 8, 1985 field check of the supports. These stresses were com-pared to the allowable stress level specified in the ASME Code Sec-tion !!I, Subsection NF. For the north SRV header, the maximum calcu-lated support stress was 17,560 psi, which is 84% of the allowable stress. For the south SRV header, the support stress closest to the allowable was 12,120 psi, which is 87% of the allowable stress. These analyses demonstrated that no modifications are required for any of the SRV discharge drywell piping or piping supports to satisfy the require-ments of the Mark I Containment Long-Term Program.

1 l

2.18 4

1

2.5 SMALL BORE PIPING AND CORE SPRAY SUCTION STRAINERS The original Mark I Containment Program analysis concluded that addi-tional structural supports were required for certain branch lines to ensure that each piping natural frequency is above 50 Hz so that exces-sive amplificat1on of the LOCA acceleration loads does not result. The affected branch lines are:

Torus level reference line at vacuum relief assembly E, Containment spray pump minimum flow return lines at torus-to-drywell vacuum relief piping assemblies B and G (north and south sides of the Reactor Building), and Air test line on north containment spray test return piping (at vacuum relief assembly B).

The purpose of the new calculations was to quantify the number of struc-tural supports required for each of the branch lines identified above.

LOCA acceleration loads and allowable piping stresses used in these cal-culations were as specified in the original MPR-734 analys is It was concluded from these calculations that a minimum of two supwrts are required for each branch line in order to limit piping stresses to allowable values for Mark I loadings.

Originally, GPUN had planned to remove the torus level reference line piping and cap the connection to the core spray suction header. GPUN subsequently decided to leave the torus level reference line installed.

Accordingly, the lire required analysis for Mark I loads.

2.19

The torus level reference line is connected to the top of the torus through torus-to-drywell vacuum relief assembly E and to the bottom of the torus through the core spray suction header. Both of these connections provide dynamic excitation and thermal expans'an loads to this piping as a result of torus LOCA loads. Additionally, the torus level reference line is located in close proximity to the torus room wall. As a result, supporting the line induces thermal stresses in the line due to the radial thermal growth under LOCA conditions of the torus, core spray suction header and vacuum relief assembly E. Although other small bore and branch piping lines were analyzed using hand cal-culations, the complexity of this line with its two excitation points and thermal growth restrictions dictated the use of a finite element computer code. The piping stress analysis was performed using the analysis and evaluation methods documented in MPR-734 All piping stresses for the torus level reference line are acceptable for both LOCA loads and torus thermal expansion, in accordance with the Mark 1 Containment Program acceptance criteria. The new stresses for the torus level reference line are shown in Table 2.5-1, which super-sedes the stresses for this system given in Table 6.7-2 in MPR-734 The new analysis determined that a total of four supports must be added to the lir.e. The supports are located so as to accommodate loads from torus thermal expansion as well as Mark I loads.

Analysis results for an additional branch line, the nitrogen purge line, are shown in Table 2,5-1. This line is connected to the torus to reactor building vacuum relief piping (TRB) at a location some distance from the TRB connection to the tores. This branch line was not a Mlyzed as part of the original Mark 1 Containment Program because Mark I loadings from the TRB line at the purge line connection were insignificant. This line was analyzed, however, as part of the TRB reanalysis described in Section 2.1.1 of this report, because the change in the TRB support configuration increased the loads at the purge line branch connection.

2.20

The response spectrum analysis of the torus-to-reactor building vacuum relief piping resulted in a calculated stress at the nitrogen purge line branch connection (location H in Figure 2.1-1) for Occasional Load Case III of 38,700 psi. This stress is approximately 8% in excesses of the allowable value of 36,000 psi. This calculated overstressed condition was judged to be acceptable due to the conservatism in the response spectrum analysis method. To confirm the acceptability of the nitrogen purge line branch connection, a more realistic time history analysis of the stresses at this location due to the main contributor to Load Case III stresses, DBA(CO) hydrodynamic loads, was performed. The time history analysis resulted in a calculated stress at the branch connection of only 19,200 psi for Occasional Load Case III. The new most limiting stress at the branch connection, therefore, is due to Occasional Load Case II. The Load Case Il calculated stress at the branch connection, based on the response spectra method, is 27,300 psi, which is less than the allowable stress of 36,000 psi. Thus, the nitrogen purge line branch connection satisfies the Mark I Program acceptance criteria.

The most limiting calculated to allowable stress ratio for the '

redesigned strainers occurs at the flange, where the calculated stress is 15.0 ksi, 97% of the 15.5 ksi allowable stress. This value supersedes the strainer stress results shown in Table 6.7-1 of MPR-734. The redesigned stainers thus satisfy the Mark I Program acceptance criteria.

2.21 E __

TABLE 2.5-1

SUMMARY

OF MAXIMUM AND ALLOWABLE STRESSES IN BRANCH PIPING Stresses (psi)

Occasional Load Combination II to V (Note 1)

Piping Line Maximum Allowable Torus Level Reference Line <9,100 27,000 9,100 36,000 Nitrogen Purge line <27,000 27,000 27,300 36,000 Notes:

1. Load Case I was evaluated and the 18,000 psi allowable was met.

Thermal expansion stresses were evaluated for Load Cases I to V using ASME Equation 11 for the Torus Level Reference Line, and ASME Equation 10 for the Nitrogen Purge Line. The allowable stresses of 35,220 psi and 37,500 psi for Equation 11 and 22,500 psi for Equation 10 were met.

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_ _ _ _ _