Review of Stress Analysis Results According to Decoupling Criteria Change and Suggestion of Alternative Solution

18th International Conference on Structural Mechanics in Reactor Technology (SMiRT 18) Beijing, China, August 7-12, 2005 SMiRT18-F05-6

REVIEW OF STRESS ANALYSIS RESULTS ACCORDING TO DECOUPLING CRITERIA CHANGE AND SUGGESTION OF ALTERNATIVE SOLUTION

Joong-Kyo Shin * Kyoung-Mo Yang Korea Power Engineering Company, inc. Korea Power Engineering Company, inc. 360-9 Mabuk-ri, Guseong-eup, Yongin-si, 360-9 Mabuk-ri, Guseong-eup, Yongin-si, Gyeonggi-do, 449-713, Korea Gyeonggi-do, 449-713, Korea Phone: 82-31-289-3737, Phone: 82-31-289-3636, Fax: 82-31-289-4109 Fax: 82-31-289-4105 E-mail: [email protected] E-mail: [email protected]

ABSTRACT For OPR 1000(Optimized Power Reactor 1000) which was called as KSNP(Korean Standard Nuclear Plant), if moment-of-inertia ratio of run to branch pipe (Ir/Ib) is larger than 7 to 1, or diameter ratio of the run to the branch pipe (Dr/Db) is larger than 3 to 1, the branch pipe could be decoupled from the run pipe in piping stress analyses. But, EPRI URD and WRC Bulletin 300 criteria, Ir/Ib ≥ 25, are more difficult to accommodate the design sequence and designers’ convenience, than Ir/Ib ≥ 7. If the branch pipe, branching off the run pipe, cannot be decoupled in a piping stress analysis according to the criterion, Ir/Ib ≥ 25, the design sequence of the branch pipe should be parallel with that of the run pipe. However, in general, the design process for run pipe always precedes the process for the branch pipe, because the works for run pipe closely interfaces with other works such as calculation of penetration loads and size of embedded plate for the pipe support design. Although, OPR 1000 adopts its own decoupling criterion, the difference between the two existing criteria and thereafter the effects on the piping design process are not yet investigated in detail. Therefore, the difference between the two criteria was intensively reviewed and the impact on the piping design process was investigated. To do these, the three representative piping systems in the OPR 1000 having a branch pipe and 7 < Ir/Ib <25 were selected. In order to compare the effect of including the branch pipe in the stress analysis, two type of stress analyses were also performed for each piping system; that is, one is to carry out an analysis by including the branch pipe in the run pipe analysis whereas the other is by excluding it. Analysis results show that although pipe stresses, equipment nozzle loads and piping support loads increase when using the criterion of Ir/Ib ≥ 25, almost all stresses and loads satisfy the design requirements. However, it is thought that some parts of current piping design procedure have to be modified. Based on these results, recommendations are made to develop more appropriate guideline for piping stress analysis of OPR 1000.

Keywords: Decoupling Criteria, Run Pipe, Branch Pipe, Moment of Inertia, Pipe Diameter

1. Introduction The purpose of decoupling the branch pipe from the run pipe is to overcome the functional limitation of stress analysis program and to increase the efficiency in design and construction processes for nuclear power plant (NPP). Especially, there is a big difference in design schedule between large-bore piping (2inch over in diameter) and small-bore piping (2inch and less in diameter). The large-bore piping design always precedes the small-bore piping design in design schedule. For the design sequence between large- and small-bore piping, the layout and stress analysis of large-bore piping are performed first in connection with large-bore piping spool RTM (Release to Manufacture). And it is

difficult to conduct the design of large and small-bore piping simultaneously because the analysis results of a run pipe are reflected in design of small-bore piping. Although the small-bore pipe design has been partially completed, when it interferes with works for large-bore pipes, electrical cables, ducts or any other systems, the possibility of design change is high for the reason that the design change of the small-bore pipe is much easier than that of large-bore pipe. For the above-mentioned reasons, the stress analysis of large and small-bore piping is separately performed. It is an essential condition in analyzing the run and the branch pipe separately that the effect of the branch pipe on the run pipe can be negligible. Whether the branch pipe gives a negligible impact on the run pipe is determined by the stiffness ratio of the run to the branch pipe. If the stiffness ratio of the run to the branch pipe meets the design requirement, then the stress analysis of the run pipe can be performed separately from the branch pipe. However, if the design requirement is not met, the branch pipe has to be analyzed separately with intentionally setting up anchors on pipe so that the branch pipe may not influence a severe effect on the run pipe. Seismic category buildings such as the containment building and auxiliary building have available structures which consist of concrete and beams for easy installation of piping restraints and supports; therefore, this kind of intentional design is possible. For non-seismic category buildings, such as the Turbine Generator building, it is difficult to perform the decoupling analysis due to the difficulty in installing anchors. In case of being not feasible for anchor installation as stated above, piping stress analyses of the run and branch pipe have been performed, respectively, in accordance with the unconservative criteria. Namely, OPR 1000 Standard [1], EPRI URD [2] and WRC Bulletin 300 [3] have been used as decoupling criteria in piping stress analysis. The major difference between these criteria is the moment of inertia ratio of the run to the branch pipe (Ir/Ib): OPR 1000 Standard is at least 7, EPRI URD and WRC Bulletin 300 is at least 25. Although, OPR 1000 adopts its own decoupling criterion, the difference between the two criteria and thereafter the effects on the piping design process are not yet investigated in detail. In this paper, therefore, the difference between the two criteria was intensively reviewed and the impact on the piping design process was investigated. To do these, the three representative piping systems in the OPR 1000 having a branch pipe and 7 < Ir/Ib <25 such as main steam piping system, component cooling water piping system and chemical and volume control piping system were selected. In order to compare the effect of including the branch pipe in the stress analysis, two type of stress analyses were also performed for each piping system, that is, one is to include the branch pipe in the run pipe analysis and the other is not to include it. Analysis results show that although pipe stresses, equipment nozzle loads and piping support loads increase when using the criterion of Ir/Ib ≥ 25, almost all stresses and loads satisfy the design requirements. However, it is thought that some part of current piping design procedure have to be modified. Based on these results, recommendations are made to develop more appropriate guideline for piping stress analysis of OPR 1000.

2. Decoupling Criteria The standards or guides, which are generally used for decoupling criteria in piping stress analysis, are OPR 1000 Standard, EPRI URD and WRC Bulletin 300. According to these standards or guides, the piping stress analysis of the run pipe has to be performed by integrating or overlapping the branch pipe, when the decoupling criterion is not satisfied.

2.1 OPR 1000 Standard In case of Dr/Db ≥ 3 or Ir/Ib ≥ 7, the branch pipe can be decoupled from the run pipe in the piping stress analysis. If these criteria are not satisfied, the overlapping analysis should be performed. For overlapping analysis, branch (or run) pipe at least up to two restraints in each orthogonal direction from branch connection should be included in the modeling of run (or branch) pipe for seismic category I and II piping. For seismic category III cold piping, two vertical supports should be included in the modeling of run (or branch) pipe. Then, the higher values of stress, restraint load, etc. are taken from the two overlapping analyses.

2.2 EPRI URD Criteria In case of Dr/Db ≥ 3 or Ir/Ib ≥ 25, the branch pipe can be decoupled from the run pipe in the piping stress analysis.

2.3 WRC Bulletin 300 Criteria Although the branch pipe can be decoupled from the run pipe in case of Ir/Ib ≥ 25, it should not be applied under the following conditions:

- If anchors or restraints on the branch pipe are located near the run pipe and significantly restrict the

movement of the run pipe, the branch pipe up to the anchor points should be included in the run pipe analysis. - If accurate load evaluations are required at equipment nozzles, penetration, etc., the branch pipe should be included in the run pipe analysis to consider the effect of the branch pipe.

3. Impact on the Piping Design due to the Change of Decoupling Criteria Table 1 shows the diameter and the moment of inertia ratio of the run to the branch. If EPRI URD and WRC Bulletin 300 criteria (Ir/Ib ≥ 25) are applied to the decoupling criteria, the branch pipes of 1~2 inch in diameter can not be decoupled from the run pipes of 2.5~4 inch in diameter. That is, the branch pipe should be included in the run pipe analysis because the stiffness of the branch pipe influences on that of the run pipe. Therefore, the design of the run and the branch pipe should be simultaneously performed to include the effect of branch pipe on the run pipe. In this case, the design of branch pipe with small-bore cannot progress smoothly because the construction sequence of the small-bore pipe is always behind the design of run pipe with large-bore and the design information for the small-bore pipe is insufficient until the large-bore piping design is completed. Although the small-bore piping design is completed, the possibility of design change always exists when there is some interference with other disciplines under given site conditions.

Table 1. Dr/Db and Ir/Ib for Large-bore Run Pipes and Small-bore Branch Pipes Run Pipe Branch Pipe Ratios Acceptable Diameter(inch) Diameter(inch) (Yes or No) Dr/Db Ir/Ib 6 ≤ 2 ≥ 3.0 ≤ 25.0 ≤ Yes 2 2.0 8.3 ~ 11.1 No 4 1.5 2.7 18.5 ~ 23.3 No 1 ≥ 3.0 ≤ 25.0 ≤ Yes 2 1.5 4.3 ~ 4.5 No 3 1.5 2.0 7.7 ~ 9.7 No 1 ≥ 3.0 ≤ 25.0 ≤ Yes 2 1.3 1.8 ~ 3.5 No 1.5 1.7 3.9 ~ 6.0 No 2.5 1 2.5 14.5 ~ 17.5 No 0.75 ≥ 3.0 ≤ 25.0 ≤ Yes 2 1.0 1.0 No 1.5 1.3 1.7 ~ 2.7 No 2 1 2.0 6.3 ~ 8.2 No (L/B Scope) 0.75 2.7 14.9 ~ 19.4 No 0.5 ≥ 3 .0 ≤ 25.0 ≤ Yes

4. Design Status and Case study

4.1 Design Status For OPR 1000, the piping stress analysis has been performed on the basis of Ir/Ib ≥ 7. Table 2 and Table 3 show the total number of piping systems to be analyzed and number of piping subsystems for each building and also show whether Ir/Ib ratio of the run to the branch pipe exceeds 25. For the piping systems in Table 2, consisting of the large-bore run pipe and the large-bore branch pipe, there are many cases in the Turbine Generator building that don’t meet the decoupling criteria (Ir/Ib ≥ 25). And for the piping systems in Table 3, consisting of the large-bore run pipe and the small-bore branch pipe, there are many cases in the auxiliary and Turbine Generator building that don’t meet the same decoupling criteria. The reason why there are many cases that don’t meet the decoupling criteria in the Turbine Generator building is thought that the non-seismic category Turbine Generator building consists of steel structures and has wide inner space, which makes it difficult to install restraints and anchors.

Table 2. Building Status of Ir/Ib Ratio for Large-bore Run Pipes and Large-bore Branch Pipes

Ir /Ib ≥ 25 Building Q’ty Remark Yes No RCB 4 4 0 Reactor Coolant Building FHB 2 2 0 Fuel Handling Building CCW 3 3 0 Component Cooling Water ACB 7 7 0 Access Control Building PAB 17 15 2 Primary Auxiliary Building SAB 11 7 4 Secondary Auxiliary Building TGB 75 59 16 Turbine Generator Building Total 119 97 22 -

Table 3. Building Status of Ir/Ib Ratio of Large-bore Run Pipes and Small-bore Branch Pipes

Ir /Ib ≥ 25 Building Q’ty Remark Yes No RCB 12 8 4 Reactor Coolant Building FHB 6 0 6 Fuel Handling Building EDG 4 2 2 Emergency Diesel Generator PAB 68 16 52 Primary Auxiliary Building SAB 87 73 14 Secondary Auxiliary Building TGB 74 41 33 Turbine Generator Building Total 251 140 111 -

4.2 Case Study Among the piping subsystems in OPR 1000, which don’t meet the criteria of Ir/Ib ≥ 25, three subsystems were selected and the stress analyses results for two cases, including and excluding the branch pipe in the run pipe analysis, were compared with each other. The three piping systems to be analyzed and the size of the run and the branch pipe are as follows: Main Steam Piping System (48″×26″), Component Cooling Water Piping System (14″×6″), and Volume Control Piping System (3″×1.5″).

4.2.1 Case 1 The scope of analysis for Main Steam Piping covers from the outside anchor wall of Main Steam Isolation Valve Room to High-Pressure Turbine Nozzle in the Turbine Generator Building through the Primary Auxiliary Building. The piping systems in the Primary Auxiliary Building are seismic category II and those in the Turbine Generator Building are non-seismic category ASME B31.1 piping. The seismic analysis is not required for the piping in Turbine Generator Building. However, if the non-seismically designed piping is broken and subsequently affect on the seismically designed piping in case of earthquake, the seismic analysis should be performed for the non-seismic category piping. The decoupled point between the run and the branch pipe is 48″×26″ tee that Ir/Ib is 11 as shown in Fig. 1 and Fig. 2, which can’t meet EPRI URD coupling criteria (Ir/Ib≥ 25); therefore, the run pipe analysis should be performed including the branch pipe. Table 4 shows the comparison of stress analysis results for two cases, including and excluding the 26” branch pipe in the run pipe analysis, and shows the piping stress ratio for the decoupling and the coupling cases at the node points near the connection of the run and the branch pipe. As shown in Table 4, it is thought that the effect of including the branch pipe in the run pipe analysis in accordance with Eq. 11 and 12 in ASME B31.1 code [5] is insignificant. Table 5 shows the comparison of the turbine nozzle loads for two cases, including and excluding the branch

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pipe in the run pipe analysis. Forces and moments of directional component increase by 10~20 percent, but these are all within the allowable load range. Table 6 shows the comparison of the support loads for two cases, including and excluding the branch pipe in the run pipe analysis. As shown in Table 6, although the support loads increase by maximum of a thirty percent, they are all within the allowable load range for the piping component support.

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Fig. 1 Run Pipe Isometric Dwg. of Case 1

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Fig. 2 Branch Pipe Isometric Dwg. of Case 1

Table 4. Comparison of Pipe Stresses between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Decoupling Coupling Equation Node Max Allowable Ratio Max Allowable Ratio (A/B) Stress (A) Stress (B) (A/B) Stress (A) Stress (B) 580M 10100 15000 0.67 10200 15000 0.68 585M 10100 15000 0.67 10100 15000 0.67 11 570M 9470 15000 0.63 9620 15000 0.64 595M 9450 15000 0.63 9270 15000 0.61 560T 7160 15000 0.48 8380 15000 0.55 580M 13500 18000 0.75 13100 18000 0.73 585M 13900 18000 0.77 13000 18000 0.72 570M 12400 18000 0.70 11900 18000 0.66 12 595M 12800 18000 0.71 11800 18000 0.66 560T 8690 18000 0.48 11000 18000 0.61 595M 11800 18000 0.66 12800 18000 0.71 560T 11000 18000 0.61 8690 18000 0.48

Table 5. Comparison of Nozzle Loads between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Service Force (lbs) Moment (lbs-ft) Node Remarks Level Fx Fy Fz Mx My Mz A -1981 -11448 -1684 37116 -31318 9772 Decoupling B 18124 -46888 -12141 109975 -70740 133263 (I) D 28167 -64355 -17921 153226 -96172 206836 A -1905 -9063 2128 -27678 -25921 -11089 Coupling 135L B -18840 -41684 12243 -99380 -64969 -136746 (II) D -29456 -57723 18161 -143587 -90950 -212784 A 1.0 1.3 0.8 1.3 1.2 0.9 B 1.0 1.1 1.0 1.1 1.1 1.0 Ratio(I/II) D 1.0 1.1 1.0 1.1 1.1 1.0 A 1983 -11454 -1689 37177 31259 -9761 Decoupling B 16722 -46294 -12288 110706 68397 -127019 (I) D 25914 -63435 -18234 154582 92804 -196724 A 1927 -9017 2165 -28437 27707 11205 Coupling 305L B 17739 -43396 12460 -101108 64790 134294 (II) D 27639 -60313 18527 -145897 89797 208242 A 1.0 1.3 0.8 1.3 1.1 0.9 B 0.9 1.1 1.0 1.1 1.1 0.9 Ratio(I/II) D 0.9 1.1 1.0 1.1 1.0 0.9 A -1595 25931 -6282 148637 -12819 -33612 Decoupling B -15292 46959 -17069 291726 -39643 -180957 (I)

D -22633 56432 -22821 370515 -55896 -260687 A -1407 25789 6662 100790 -13424 -31451 Coupling 190L B -12463 46867 17543 245252 -39698 -158019 (II) D -18689 56415 23426 325405 -56360 -229927 A 1.1 1.0 0.9 1.5 1.0 1.1 B 1.2 1.0 1.0 1.2 1.0 1.1 Ratio(I/II) D 1.2 1.0 1.0 1.1 1.0 1.1 A 1597 25931 -6283 148658 12818 33629 Decoupling B 14119 47068 -17209 292828 40387 172248 (I) D 20630 56590 -23048 372280 56811 245752 A 1456 25793 6666 100449 15966 32018 Coupling 240L B 13253 46977 17637 245663 42540 165147 (II) D 19682 56572 23579 326296 59402 238619 A 1.1 1.0 0.9 1.5 0.8 1.1 B 1.1 1.0 1.0 1.2 0.9 1.0 Ratio(I/II) D 1.0 1.0 1.0 1.1 1.0 1.0

Table 6. Comparison of Support Loads between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Support Decoupling (I) Coupling ( II ) Ratio (I/II) Remarks Dir. I.D A B D A B D A B D (lbs) HMS205- Load Y 71424 113123 164602 84058 149485 220950 0.8 0.8 0.7 006R Increase Load X 22381 114760 151905 24943 117535 155707 0.9 1.0 1.0 HMS205- Increase 005G Z 21276 117451 158501 18218 115770 158408 1.2 1.0 1.0 - HMS205- Load Y 71477 106663 155398 75229 162584 232287 1.0 0.7 0.7 012R Increase Load X 21331 108059 147014 22145 115350 157887 1.0 0.9 0.9 HMS205- Increase 011G Load Z 22357 105977 138631 28392 117041 153516 0.8 0.9 0.9 Increase

4.2.2 Case 2 This case is for the component cooling water system piping in the Turbine Generator building, which is ASME B31.1 piping and, therefore, the seismic analysis is not required. The diameters of the run and the branch pipes are 6 and 14 inches, respectively, as shown in Fig. 3 and their schedules are 40. The ratio of Ir/Ib is 10 and it doesn't meet ERPI URD decoupling criteria (Ir/Ib ≥ 25). Therefore, piping stress analysis is performed again after including the branch in run pipe analysis. Tables 7, 8 and 9 show a summary of the comparison results for piping stresses, equipment nozzle loads and pipe support loads between including and excluding the branch pipe in the run pipe analysis, respectively. As shown in Table 7, the effect of including the branch pipe in the run pipe analysis in accordance with Eq. 11, 12 and 13 in ASME B31.1 code [5] is insignificant. Although equipment nozzle loads increase due to the including the branch pipe in the run pipe analysis, all loads are within the allowable range, as shown in Table 8. Also shown in Table 9, support load of HWT 412-001R increases by 3.3 times when the branch pipe is included in the run pipe analysis. The reason seems that the half weight of run pipe span between support I.D. HW406-005G and HW406-006N is imposed on HWT 412-001R, which is located on the branch pipe as shown on Fig. 3. Therefore, based on these results, pipe supports has to be considered on the run pipe near the connection of branch, when decoupling the branch pipe in run pipe analysis by the criteria of Ir/Ib ≥ 7.

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Fig. 3 Run Pipe and Branch Pipe Isometric Dwg. of Case 2

Table 7. Comparison of Pipe Stresses between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Decoupling Coupling Equation Node Max Allowable Ratio Max Allowable Ratio Stress(psi) Stress(psi) (%) Stress(psi) Stress(psi) (%) C360 5800 15000 38.7 5800 15000 38.7 D360 5600 15000 37.3 5600 15000 37.3 325 4950 15000 33.0 4950 15000 33.0 E360 4820 15000 32.1 4820 15000 32.1 433 4660 15000 31.1 4660 15000 31.1 11 400 4520 15000 30.1 4520 15000 30.1 550 4220 15000 28.1 4220 15000 28.1 360 4190 15000 27.9 4190 15000 27.9 200 4130 15000 27.5 6460 15000 43.1 486 4080 15000 27.2 4080 15000 27.2 12 C360 5800 18000 32.2 5800 18000 32.2 D360 5600 18000 31.1 5600 18000 31.1 325 4950 18000 27.5 4950 18000 27.5 E360 4820 18000 26.8 4820 18000 26.8 433 4660 18000 25.9 4660 18000 25.9 400 4520 18000 25.1 4520 18000 25.1 550 4220 18000 23.4 4220 18000 23.4

360 4190 18000 23.3 4190 18000 23.3 200 4130 18000 22.9 6460 18000 35.9 486 4080 18000 22.7 4080 18000 22.7 205 2410 34796 6.9 2430 34796 7.0 210 2370 32567 7.3 2410 32567 7.4 857 2160 30000 7.2 2160 30000 7.2 856 2080 30000 6.9 2080 30000 6.9 N228 1730 30000 5.8 4520 30000 15.1 13 580 1590 30000 5.3 1630 30000 5.4 486 1580 30000 5.3 1580 30000 5.3 N223 1540 30000 5.1 4100 30000 13.7 576 1450 30000 4.8 1490 30000 5.0 565 1390 30000 4.6 1430 30000 4.8

Table 8. Comparison of Nozzle Loads between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Equipment Decoupling Coupling Ratio Allowable Nozzle CH04(I) CH05(II) CH04(I) CH05(II) CH04(I/II) CH05(I/II) Load (lbs) Level A A A A A A A DIR. Fx 86 48 155 54 0.6 0.9 1000 Fy 908 397 944 399 1.0 1.0 3500 Fz 105 412 157 413 0.7 1.0 1000 Mx 1887 891 2167 909 0.9 1.0 4600 My 532 1515 663 1457 0.8 1.0 2600 Mz 194 190 141 180 1.4 1.1 2400

Table 9. Comparison of Support Loads between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Service Level(A) Support I.D DIR. Ratio(I/II) Decoupling(I) Coupling(II) HWT406-003R Y 2007 1937 1.0 HWT406-004R Y 1456 1413 1.0 Y 2820 2911 1.0 HWT406-005G Z 3091 3507 0.9 HWT406-006R Y 6814 6863 1.0 Y 5187 5138 1.0 HWT406-007G Z 122 119 1.0 HWT412-001R Y 2508 8063 0.3 X 22 123 0.2 HWT412-002G Z 67 205 0.3

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4.2.3 Case 3 This case is for the chemical and volume control piping system, which is ASME Class 2 piping located in Containment Building. The diameters of the run and the branch pipes are 3 and 1.5 inches, respectively, and their schedules are 40. Figures 4 and 5 show isometric drawings for these piping systems. The ratio of Ir/Ib is 10, and doesn’t meet the EPRI URD criteria (Ir/Ib ≥ 25).

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Fig. 4 Run Pipe Isometric Dwg. of Case 3

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Fig. 5 Branch Pipe Isometric Dwg. of Case 3

Table 10 shows the comparison of piping stresses for 10 node points among the piping nodes analyzed in accordance with Eq. 8, 9, 10 and 11 in section III of ASME B&PV code [4]. As shown in this table, the effect of including the branch pipe in the run pipe analysis is insignificant. Table 11 shows the effect of including the branch pipe in the run pipe analysis on piping restraint loads in accordance with service level A and D. The support loads of HCV103-005G for the case of including the branch pipe in the run pipe analysis increase by maximum of thirty percent. However, the effect of including the branch pipe in the run pipe analysis is insignificant, because the increased loads are all within the allowable range of piping support loads.

Table 10. Comparison of Pipe Stresses between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Decoupling Coupling Code Stress Allowable Ratio Stress Allowable Ratio Equation Node Node (psi) Stress (psi) (%) (psi) Stress (psi) (%) 156 7060 24600 28.7 156 7220 24600 29.3 227 6850 24600 27.8 227 6840 24600 27.8 412 5780 24600 23.5 550 5860 24600 23.8 550 5760 24600 23.4 412 5570 24600 22.6 320 4930 24600 20.0 435 5460 24600 22.2 8 146 4730 24600 19.2 320 4930 24600 20.0 A227 4120 24600 16.7 146 4790 24600 19.5 435 4110 24600 16.7 A227 4120 24600 16.7 149 3590 24600 14.6 149 3630 24600 14.8 E205 3250 24600 13.2 E205 3250 24600 13.2 156 29500 43200 68.3 156 29700 43200 68.8 435 26600 43200 61.6 435 29600 43200 68.5 550 21700 43200 50.2 550 21900 43200 50.7 320 21300 43200 49.3 320 21300 43200 49.3 227 17000 43200 39.4 227 17000 43200 39.4 9D 205 16700 43200 38.7 205 16500 43200 38.2 F435 14800 43200 34.3 D435 14200 43200 32.9 D435 14600 43200 33.8 F435 14100 43200 32.6 E435 14000 43200 32.4 E435 13400 43200 31.0 411 13500 43200 31.3 412 13400 43200 31.0 114 19100 27600 69.2 114 19200 27600 69.6 146 16000 27600 58.0 146 16000 27600 58.0 149 15900 27600 57.6 146 15800 27600 57.2 146 15300 27600 55.4 149 15600 27600 56.5 105 13500 27600 48.9 105 13600 27600 49.3 10 113 12900 27600 46.7 113 12900 27600 46.7 147 10700 27600 38.8 147 10300 27600 37.3 148 9800 27600 35.5 148 9730 27600 35.3 156 9530 27600 34.5 K440 9550 27600 34.6 105 8670 27600 31.4 156 9480 27600 34.3 11 114 19800 44000 45.0 114 19800 44000 45.0 149 19600 44000 44.5 149 19400 44000 44.1 146 18300 44000 41.6 146 18600 44000 42.3 146 18000 44000 40.9 146 18400 44000 41.8

105 14300 44000 32.5 105 14400 44000 32.7 113 14000 44000 31.8 113 14000 44000 31.8 147 12800 44000 29.1 147 12400 44000 28.2 156 11800 44000 26.8 156 11900 44000 27.0 148 10300 44000 23.4 K440 10700 44000 24.3 113 9850 44000 22.4 150 10400 44000 23.6

Table 11 Comparison of Support Loads between Cases including and excluding the Branch Pipe in the Run Pipe Analysis Decoupling(I) Coupling (II) Ratio(I/II) Support I.D Dir. Service Level Service Level Service Level A D A D A D HCV103-003G X 614 2817 614 2833 1.0 1.0 HCV103-003G Z 100 432 100 447 1.0 1.0 HCV103-004R Y 171 390 176 406 1.0 1.0 X 35 335 49 404 0.7 0.8 HCV103-005G Y 114 521 123 435 0.9 1.2 HCV103-006X Z 339 2005 342 2028 1.0 1.0

4.3 Discussion The moment-of-inertia ratio considered in this paper has the range of 7< Ir /Ib<25. The branch pipes were decoupled in the run pipe analysis, because it met the decoupling criteria of OPR 1000 Standard (Ir/Ib ≥ 7). However, they may not be decoupled, when EPRI URD criterion (Ir/Ib ≥ 25) apply. But, the application of Ir/Ib ≥ 25 gives difficulty the piping design in terms of project schedule and designer’s convenience. In order to find out the impact of the application of severer criteria, three cases of run pipe analyses including the branch pipe were performed and their results were compared with the cases of excluding the branch pipe in the run pipe analysis from the viewpoint of piping stresses, piping restraint and equipment nozzle loads. As a result of the comparison, the following summary is obtained:

1) In terms of piping stress, the effect of whether the branch pipe is included in the run pipe analysis is insignificant. 2) In terms of the equipment nozzle loads, the force and moment components of the turbine nozzle loads increase by 20 and 10 percent for the main steam piping system, respectively. However, the increased equipment nozzle loads are all within the allowable range. 3) In terms of the support loads, supports loads located near the branch connection are increased, but the increased support loads in three cases are within the allowable range of the component support except one case, which is for the support I.D. HWT 412-001R in the Component Cooling System. The reason is thought that there is no consideration of locating the support on the run pipe near the branch connection when decoupling the branch pipe. Therefore, a half of the run pipe weight has to be imposed on that support located on the branch pipe.

5. Conclusions In this paper, the difference between the two criteria was intensively reviewed and the impact on the piping design process was investigated. To do these, the three representative piping systems in the OPR 1000 having a branch pipe and 7 < Ir/Ib <25 were selected. In order to compare the effect of including the branch pipe in the stress analysis, two type of stress analyses were also performed for each piping system; that is, one is to carry out an analysis by including the branch pipe in the run pipe analysis whereas the other is by excluding it. Based on the analysis results, the following conclusions are obtained:

1) When decoupling analysis has to be performed based on the OPR 1000 standard, which is Ir/Ib ≥ 7 or Dr/Db ≥ 3, it is considered to be desirable to afford a margin of about thirty percent in design of piping restraints near the branch pipe. 2) Piping restraint should be placed on the run pipe near the branch pipe, which is to minimize the effect of the run pipe loads on the branch pipe

3) If the displacement of the run pipe is restrained because anchors or restraints on the branch pipe are located near the run pipe, the branch pipe up to the anchor points should be included in the run pipe analysis. 4) When the exact evaluation is required for the loads at equipment nozzles and penetrations, the branch pipe should be included in the run pipe analysis in order to consider the effect on the branch pipe.

REFERENCES 1. OPR 1000 Standard, DS-P-2201, 1997, Piping Stress Analysis Standard. 2. Electric Power Research Institute (EPRI), 1995, Utility Requirement Document Rev.7. 3. Welding Research Committee, 1984, Bulletin 300. 4. ASME, 1992, Boiler and Pressure Vessel Code, Section III. 5. ASME, 1995, Power Piping Code, B31.1