ML21278A232
| ML21278A232 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 09/07/2021 |
| From: | Exelon Generation Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML21278A102 | List:
|
| References | |
| NEI 99-04 | |
| Download: ML21278A232 (5) | |
Text
CALVERT CLIFFS UFSAR 10A.2-1 Rev. 47 10A.2 MAIN STEAM TO AUXILIARY STEAM GENERATOR FEED PUMP TURBINES Main steam (normally at 900 psig and 550F) is supplied to the two auxiliary steam generator feed pump (SGFP) turbines automatically upon low level in the steam generator or by remote manual control from the Control Room.
Each turbine has a manually set governor for controlling turbine speed. Once set for a certain speed, the governor holds the speed constant even if the steam pressure decreases to a minimum of 50 psig.
Main steam drives the AFWP turbine as long as the pressure is equal to or greater than 50 psig.
Should the steam pressure in both of the steam generators drop below 50 psig, the steam supply can be switched to the auxiliary boiler steam system.
The branch line from the MS lines to the CVs (1/2-CV-4070, 4071, 4070A and 4071A) before the auxiliary SGFP turbines, will normally contain high energy fluid (MS). A bypass line is provided around each CV station in order to allow for a single failure of the valves. The bypass valves can be actuated by an extended remote manual operator.
Based on the level of quality control, periodic ISI, the low usage factor, the short time this system exceeds 200F and 275 psig, and the strict administrative control of the system, a break in this system between the CVs and the AFWP turbines is not considered credible.
10A.2.1 PIPE WHIP The MS line to the auxiliary SGFP turbine contains high energy fluid (above 275 psig and 200F) only from the MS lines to the CVs and manual bypass valves. Therefore, pipe whip protection will be provided in this area.
10A.2.2 PIPE BREAK LOCATIONS The criteria used for determining the location of pipe breaks has been presented in Section 10A.1.2. The pipe break locations are shown on Figures 10A.2-2A and 10A.2-2B.
10A.2.3 PIPE BREAK ORIENTATION The criteria used for determining the orientation of pipe breaks has been presented in Section 10A.1.3.
10A.2.4
SUMMARY
OF DYNAMIC ANALYSIS 10A.2.4.1 Location and Number of Design Basis Breaks The location and number of design basis breaks are chosen in accordance with criteria discussed in Section 10A.1.2, except that one break in a line with a run less than 5 pipe diameters was postulated on Unit 1.
10A.2.4.2 The Postulated Rupture Orientation The longitudinal break is assumed to be parallel to the pipe axis and oriented at any point around the pipe circumference. The circumferential break is assumed to be perpendicular to the pipe axis. A further discussion of the break area and jet impingement forces is provided in Section 10A.1.4.2.
10A.2.4.3 Description of the Forcing Function and the Mathematical Model A forcing function is assumed to be a straight line with changes so slow that the variation, up to the time of maximum response, is negligible.
CALVERT CLIFFS UFSAR 10A.2-2 Rev. 47 The dynamic analysis method, used in pipe restraint design for this line, is similar to the one used for the MS line which is described in Section 10A.1.4.4. The mathematical model is shown in Figure 10A.1-5.
10A.2.4.4 Unrestrained Motion of the Ruptured Lines Except for the horizontal runs at the break location upstream of 2-CV-4070, there will not be any unrestrained motion of the MS to auxiliary SGFP turbine line to damage structures, systems, and components important to the plant safety.
Movement of this line is restricted by adjacent structures (evaluated as adequate restraint).
10A.2.5 PROTECTION AGAINST PIPE WHIP, JET IMPINGEMENT, AND REACTIVE FORCES 10A.2.5.1 Pipe Whip Restraints and Sleeves All break locations in the MS to auxiliary SGFP turbine lines up to the bypass and CVs, are restrained and/or sleeved to prevent any pipe whip, jet impingement, or reactive forces from damaging structures, systems, and components important to plant safety following a longitudinal or circumferential break. Sleeves meet the criteria for the encapsulations referenced in Section 10A.1.5 and are securely anchored to surrounding permanent structures to prevent movement. An exception to this statement is the piping at valve station 2-CV-4071. A longitudinal break at this location could result in a jet which could impact the motor bonnet yoke of feedwater isolation valve 2-MOV-4517. An evaluation using the guidelines in Section 10A.1.4 was conducted. This evaluation determined that, due to the construction and configuration of 2-MOV-4517, a protective barrier is not required.
Adequate venting is provided in the MS piping Penetration Room to prevent compartment pressurization from a break or crack in the 6" MS line to the auxiliary SGFP turbines from causing damage to safety-related structures and components.
The jet impingement force due to a critical crack in the 6" MS to auxiliary SGFP turbine lines is 526 lbs. This force is not large enough to cause damage to any safety-related structures, systems, or components. The structures and equipment in the area of these lines have been evaluated for the much greater jet impingement forces resulting from a crack in the 34" MS line.
10A.2.5.2 Separation Provisions Redundant features of the MS line to the auxiliary SGFP turbines are separated by a combination of sleeves and properly placed restraints. A break or crack in one MS line to the auxiliary SGFP turbines will not affect the integrity of the other steam generator if the CVs 1/2-CV-4070/4071 and 1/2-CV-4070A/4071A and bypass valves are closed. Further redundancy is included with a check valve downstream of each CV.
10A.2.5.3 Description of a Typical Pipe Whip Restraint The pipe whip restraints are provided in the vicinity of the postulated full break locations to control the pipe whip impact and axial movement due to a full postulated break.
Description of a typical pipe whip restraint is given in Section 10A.1.5.5.
CALVERT CLIFFS UFSAR 10A.2-3 Rev. 47 10A.2.6 EVALUATION OF SEISMIC CATEGORY I STRUCTURES 10A.2.6.1 Method of Evaluating Stresses Category I structures were evaluated for structural adequacy following a postulated rupture using the design bases shown in Appendix 5A. Ultimate strength design method was used in the structural evaluations. All Category I structures and structural components were found to be adequate against the loadings due to the postulated break.
10A.2.6.2 Allowable Design Stresses Design stresses are proportioned such that the combined stresses are within the limits established in Appendix 5A.
10A.2.6.3 Load Factors and Load Combinations Load factors and load combinations used in the design are discussed in Appendix 5A.
10A.2.7 STRUCTURAL DESIGN LOADS The design loads used to evaluate the adequacy of Category I structures or structural components are discussed in Section 10A.1.7 of the Updated Final Safety Analysis Report (UFSAR).
10A.2.8 REVERSAL OF LOADS ON THE STRUCTURES The forces causing reversal of loadings, due to the postulated accident, on the Category I structures or structural components are:
- a.
Jet Impingement Forces
- b.
Compartment Pressurization
- c.
Reactions from Pipe Whip Restraints Since the MS to Auxiliary SGFP Turbine line is sleeved at the postulated pipe break locations, the sleeved pipe will resist the jet impingement forces, and protect the structures, systems and components important to the plant safety. Where encapsulation was not used, jet impingement effects on structures were reviewed at the break locations shown on Figures 10A.2-2A and 10A.2-2B.
The pipe whip restraints are supported from the existing structural components. When the restraint loads cannot be sustained by the existing structure or structural components, these loads are transferred to the foundation level using additional supports.
10A.2.9 STRUCTURAL EFFECTS OF NEW OPENINGS The vent is discussed in Section 10A.1.9.
10A.2.10 EFFECTS OF STRUCTURAL FAILURE There will not be a failure of any structure, including Category II (non-seismic Category I) structures, due to the accident, that could cause failure of any other structure in a manner to adversely affect:
- a.
Mitigation of the consequences of the accident; and
- b.
Capability to bring the unit(s) to a cold shutdown condition.
CALVERT CLIFFS UFSAR 10A.2-4 Rev. 49 10A.2.11 VERIFICATION THAT PIPE RUPTURE WILL NOT AFFECT SAFETY Verification that a rupture in the MS line to auxiliary SGFP turbines will not affect safety is presented in Section 10A.1.11.
10A.2.12 EFFECT ON CONTROL ROOM The results of the analysis presented in Section 10A.2.20 show that the Control Room will not be affected by a break in the MS lines to the auxiliary SGFP turbines.
10A.2.13 ENVIRONMENTAL QUALIFICATION OF AFFECTED REQUIRED EQUIPMENT Section 10A.1.13 discusses environmental qualification of affected required equipment in the area of the MS lines including the lines to the auxiliary SGFP turbines.
10A.2.14 DESIGN DRAWINGS Figure 10A.2-1 shows a piping schematic diagram for the MS line to the auxiliary SGFP turbines.
Figures 10A.2-2 and 10A.2-3 show the routing of the MS line to the auxiliary SGFP turbines.
Figures 10A.2-2A and 10A.2-2B show line break locations and whip restraint locations.
10A.2.15 FLOODING The postulated break in the MS line to the auxiliary SGFPs will release high quality steam, which will be vented to prevent damage to vital equipment or structures. Any moisture separated from the escaping steam or formed by condensation on cold surfaces can be adequately handled by the floor drainage system in the Auxiliary Building and Turbine Building, so that no flooding will occur.
10A.2.16 QUALITY CONTROL AND INSPECTION PROGRAMS The quality control and inspection programs are presented in Section 10A.1.16.
10A.2.17 LEAK DETECTION Temperature sensors are located within the MS line Penetration Room, which will alarm and will alert the operator to abnormally high temperatures that could result from the release of steam from a break or crack in the MS line to the auxiliary SGFP turbines.
10A.2.18 EMERGENCY PROCEDURES Emergency Procedures are discussed in Section 10A.1.18.
10A.2.19 SEISMIC AND QUALITY CLASSIFICATION The MS lines to the auxiliary SGFP turbines are designed and constructed to meet ANSI B31.7, Class II requirements from the MS line through 1/2-CV-4070/4071 and 1/2-CV-4070A/4071A, and their manual bypass valves. The rest of the lines from these valves through to the auxiliary SGFP turbines are designed and constructed to meet ANSI B31.1 requirements with additional non-destructive examination requirements as follows:
- a.
Either MT, PT, or radiography for all circumferential butt-welds; and
- b.
100% MT or PT for 4" and under welded branch connections and all socket weld pipe and fittings (FCR 89-26 and future modifications).
CALVERT CLIFFS UFSAR 10A.2-5 Rev. 47 These lines are designed to withstand a SSE in combination with normal design loads.
10A.2.20 DESCRIPTION OF ASSUMPTIONS, METHODS, AND RESULTS OF ANALYSIS FOR PRESSURE AND TEMPERATURE TRANSIENTS IN COMPARTMENTS All the postulated breaks in the MS to AFWP turbine lines are located in the MS Penetration Room (Figure 10A.2-2). The largest postulated break is a 6" circumferential break. The pressure and temperature effects of a break of this size in the MS Penetration Room are presented in Section 10A.1.20.3.
10A.2.21 INTEGRITY OF THE CONTAINMENT STRUCTURE AND A PIPE RUPTURE OUTSIDE THE CONTAINMENT Since the MS to Auxiliary SGFP Turbine line is only 6" in diameter, any forces acting upon the Containment Structure will not be significant enough to impair the integrity of the prestressed concrete Containment Structure.