ML20116B346
| ML20116B346 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 04/12/1985 |
| From: | Devincentis J PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| To: | Knighton G Office of Nuclear Reactor Regulation |
| References | |
| SBN-790, NUDOCS 8504250241 | |
| Download: ML20116B346 (34) | |
Text
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SEABROOK STAT 10N Engineering Of fice April 12, 1985 Pub 5c Service W New HampsNro SBN-790 T.F.
B7.1.2 New Hampshire Yonkee Division United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention:
Mr. George W. Knighton, Chief Licensing Branch No. 3 Division of Licensing Re ferenc es :
(a) Construction Permits CPPR-135 and CPPR-136, Docket Nos. 50-443 and 50-444 (b) PSNH Letter SBN-761, dated February 7,1985, " Elimination of Arbitrary Intermediate Pipe Breaks", J. DeVincentis to G. W. Knighton (c) PSNH Letter SBN-764, dated February 19, 1985, " Elimination of Arbitrary Intermediate Pipe Breaks; Re-Transmittal of Attachment D, Potential for Stress Corrosion Cracking",
J. DeVincentis to G. W. Knighton
Subject:
Elimination of Arbitrary Intermediate Pipe Breaks in the Feedwater System
Dear Sir:
The New Hampshire Yankee Division of Public Service Company of New Hampshire has previously submitted a request for " Elimination of Arbitrary Intermediate Pipe Breaks" [ Reference (b)] that sought your approval to eliminate from design consideration the postulation of Arbitrary Intermediate Breaks (AIBs). That request specifically petitioned relief from postulating AIBs in all high energy piping, excluding the Feedwater System.
We are now requesting elimination of arbitrary intermediate pipe breaks in the Feedwater System at Seabrook Station, Units 1 and 2.
This request includes the exclusion of all dynamic effects associated with AIBs (i.e., pipe whip, jet imping ement, and compartment pressurization loads). The break selection criteria currently utilized is derived from NRC Branch Technical Position MEB 3-1, which is described in Section 3.6(B) of the Seabrook Station l
Final Safety Analysis Report (FSAR).
In support of the Staff's review of our proposed elimination of Feedwater System AIBs from the Seabrook Station design bases, we have included six l
l gpo P.O. Box 300 Seobrock, NH 03874. Telephone (603) 474-9521 1
I I
8504250241 850412 PDR ADOCK 05000443 A
PDR L
s' United States Nuclear Regulatory Commission
' Attention:
Mr. George W. Knighton Page 2 enclosures.to this letter which address the evaluations the Staff requires prior to the granting of break criteria revisions:
Enclosure Subject A
Benefit Summary B
Technical Justification C
Transient Forces and Vibrational Effects D
Potential for Stress Cracking in PWR Piping E
Breaks to be Eliminated F
Proposed FSAR Revision We note that in order to facilitate and expedite your review of this request, the structure and format of this submittal is identical to that of Reference (b).
In summary, it is our strong belief that the elimination of AIBs in the Feedwater Piping System will in no way compromise overall plant safety or structural design. Staff acceptance of our request would result in substantial benefits in terms of reduced occupational exposure and cost savings over = the forty year plant life. Due to the advanced stage of design,
. and construction of Unit 1,~ the realization of these potential benefits will be severely tempered if our request is not granted in a timely manner.
We, therefore, request a decision on this proposal no later than May 17, 1985.
If I can be of further assistance, or if a meeting with the staff is
'f
' deemed beneficial, do not. hesitate to. contact me.
y Very truly yours, J. DeVincentis, Director Engineering and Licensing Attachments f-cc:. Atomic Safety and Licensing Board Service List d
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1
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c ENCLOSURE A r.-
SEABROOK STATION BENEFIT
SUMMARY
ELIMINATION OF ARBITRARY INTERMEDIATE PIPE BREAKS IN THE FEEDWATER SYSTEM 1.
Improved access for inspection, Improve quality of inservice inspec-maintenance and operation.
tion.
Reduce radiation exposure during ISI.
Reduce plant down-time during ISI outages. A savings of approx. 60 man-rem / unit is estimated over the 40 year plant life.
-2.
Engineering, fabrication and Estimate S.85 million/ unit (1985 Installation of 16 pipe rupture dollars).
restraints and jet shields.
T 3.
Reduction of heat loss and Relatively minor, but real savings.
elimination of expensive Min-K Delicate Min-K insulation may be re-insulation of pipe restraint placed by durable sections, designed locations.
to be removable for ISI.
4.
Improvement in overall plant Eliminate potential for uninten-safety (NUREG-CR-2136).
tional restricted piping movement.
O lD ENCLOSURE B SEABROOK STATION JUSTIFICATION FOR THE ELIMINATION OF ARBITRARY INTERMEDIATE PIPE BREAKS IN THE FEEDWATER SYSTEM We feel that sufficient technical justification exists for the elimination of the arbitrary intermediate pipe breaks required to be postulated in High Energy, ASHE Code Section ill Piping to comply with Standard Review Plan 3.6.2.
Our justification is as follows:
1)
Operating Experience Does Not Support the Need for the Criteria The combined operating history of commercial nuclear plants, both domestic and foreign, has not shown the need to provide protection from the dynamic effects of arbitrary intermediate breaks.
2)
System Piping Stresses Are Well Below ASME Code Allowables Branch Technical Position MEB 3-1 requires the postulation of intermediate breaks in Class 2 piping where the streeses exceed 0.8 (1.2 Sh + S )*
A This is only 80% of the ASME Code allowabic stresses.
Intermediate breaks for Seabrook Station were postulated in the Class 2 Feedwater piping where stresses exceeded 0.8 (Sh+SA), which provides additional conservatism.
Welded attachments are generally not located near (approx. 5 pipe diameters) arbit ra ry intermediate breaks. Any arbitrary intermediate break located near welded attachments, such as shear lugs, will not be deleted. Therefore, local bending stresses f rom these attachments will not af fect tt.e stress levels at the arbitrary break locations being deleted.
Deletion of pipe rupture restraints associated with the arbitrary inter-mediate breaks wilI reduce possible unanticipated thermal restraint of piping.
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{p 3)
Arbitrary Intermediate Breaks Complicate the Design Process Since the design of p'iping systems is generally an iterative process, the location of the highest stress points usually change several times as the design evolves. The alternate criteria of - SRP 3.6.2 (NUREG 0800) provides little relief from moving arbitrary break locations, as the revised break locations must still be evaluated as to their effects on essential equip-ment and structures.
4)
Substantial Cost Savings The elimination of pipe whip restraints and jet shields is the primary cost benefit realized by the elimination of the arbitrary intermediate breaks.
Plant operation costs will tlso be reduced, as reduced manhours for in-service inspection and maintenance will result. The cost benefit for Seabrook Station is provided in Attachment A.
5)
Improved Inservice Inspection Pipe whip restraints are normally located adjacent to or surrounding the welds at changes in pipe direction. The dismantling and reinstallation of portions-q' of the restraint structures associated with arbitrary breaks to gain proper access for the performance of inservice inspection would be eliminated.
Also, the absence of structural framing will allow for better inspection technique and quality.
6)
Reduction in Radiation Exposure The elimination of pipe whip restraints and jet shields associated with ar-bitrary breaks, and the large structures necessary to support them, will result in more efficient maintenance, inspection and decontamination operations. Im-proved access for firefighting will also be gained.
A reduction in the time required to perform all of these activities will result in a significant reduc-tion in personnel exposure to radiation over the 40 year plant life.
Attach-ment A provides an estimate of the man-rem benefit to be realized if the ar-bitrary breaks are eliminated.
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7)
Improved Operational Efficiency The elimination of pipe whip restraints associated with arbitrary breaks will preclude the requirement for cut back insulation or special insulating assem-blies near the close fitting restraints and will reduce the heat load in plant buildings, especially inside containment.
8)
Proper System Design and Operating Procedures The Mechanical Engineering Branch, in Branch Technical Position MEB 3-1, re-cognizes that "... pipe rupture is a rare event which may occur only under unanticipated conditions such as those which might be caused by possible design, construction, or operation errors; unanticipated loads or unantici-pated corrosive environments." For Seabrook Station, there are many ways in which those unanticipated conditions may be detected. The system transient (water-hammer) and vibrational stress testing portions of the preoperational as discussed in Attachment C, minimize unanticipated and startup test programs, conditions arising from design, construction or operation errors and also from unanticipated loads, while control of water chemistry and materials used during fabrication, installation, startup testing and operation minimize exposure to potentially corrosive environments, as discussed in Attachment D.
Once Seabrook station begins operation, an extensive In-Service Inspection (ISI)
Program will continue to provide that assurance and will detect any system
' degradation before unsafe conditions develop.
9)
Adequacy of Equipment Qualification The elimination of arbitrary intermediate breaks will not downgrade the environ-mental qualification levels of Class IE equipment. The break postulation for environmental ef fects is performed independently of break postulation for pipe whip and jet impingement.
ENCLOSURE C SEABROOK STATION TRANSIENT FORCES AND VIBRATIONAL EFFECTS ASSOCIATED WITH ARBITRARY INTERMEDIATE BREAKS IN THE FEEDWATER SYSTEM Discussion of Transient Forces Because of the susceptibility of Main Feedwater (MFW) Systems in other plancs to water hammer, PSNH has incorporated several water hammer prevention features into the design of the FW piping at the Seabrook Station.
The steam generators are Westinghouse Model F type steam generators in which feedwater enters each unit at an elevation above the top of the U-tubes through the 16-inch feedwater nozzle. The water is distributed circumferentially within the steam generator by means of a feed ring. The feedwater enters the ring via a welded thermal sleeve connection and leaves it through inverted "J" tubes located at the flow holes which are at the top of the ring. The "J" tubes are arranged to distribute the bulk of the colder feedwater to the hot leg side of the tube bundle. The feed ring is designed to minimize conditions within the steam generator which could result in water hammer occurrences in the feedwater piping.
Westinghouse has conducted a number of investigations into the causes and consequences of water hammer events. The results of these investigations have been reflected in design interface requirements and recommendations to assure that water hammer events initiated in the BOP secondary systems do not compromise the performance of the Westinghouse-supplied safety-related systems and components.
Each steam generator nozzle utilizes a 90 elbow connected immediately to a near vertical run of pipe to minimize potential steam voids.
Under normal operating conditions, the feedwater flow arrangement ensures that l
the line is kept filled with water; steam is thereby prevented from leaking back into the feedwater piping. This routing of the feedwater piping is in compliance with Westinghouse recommendations.
Feedwater Control Valves (FCV) instabilities have been minimized by ensuring that all components in the system are compatible. A small bypass control line is provided to stabilize operation at low power levels.
, The Feedwater System arrangement and components are carefully evaluated under normal and upset conditions to assure that the water hammer pulses propagated to the steam generator are within the appropriate limits. Water hammer pressure pulses could be generated in the Main Feedwater System as a result of feedwater isolation or control valve closure / opening, check valve closure, pump start /stop, and hydraulic resonance. The pressure pulse magnitudes listed for startup and shutdown are intended to include those pulses associated with normal unit loading and unloading such as the startup and shutdown of pumps, and the switchover f rom bypass to main feed control valve and vice versa. The spurious closure of a feedwater isolation valve could generate a large water hammer pulse. A steamline break could also result in a high flow rate to the faulted steam generator, due to single failure considerations, and consequently the maximum water hammer pulse is expected to occur for this transient. After evaluating the above cases, and any other cases which could generate large pressure pulses, the results of these analyses are utilized when specifying the feedwater isolation valve load requirements. The feedline break is analyzed to estimate the' reverse pressure differential and flow against which the check valve will close so that the water hammer pulse magnitude can be estimated. Again, this information is used to develop the specifications for the check valve. As recommended by Westinghouse for this case and implemented by PSNH, the check valves are specified as slow closing valves. The piping / supports are designed to accommodate the loads resulting from these transients. The associated valves are also periodically checked for leaks.
For the Seabrook plants, the functions of auxiliary feedwater supply are fulfilled by the Startup Feedwater System during startup, hot standby, and hot shutdown conditions and the Emergene; 'eedwater System during loss of normal feedwater flow. The Startup Feedwater System also:
Provides a supply of feedwater to the steam generators during plant a.
startup to fill and pressurize the steam generators; l
b.
Provides sufficient feedwater flow to the steam generators to allow steam to be utilized for turbine plant warm up, and turbine operations up to 5% of full load, prior to operation of the main feed pumps;
. _ > - c.
Provides sufficient feedwater flow to the steam generators to allow the reactor plant tc operate at low load (hot standby) while the turbir.e plant is not operating; and d.
Minimizes thermal transients in the steam generator feedwater lines.
The startup feed pump is started f rom the Main Control Room for startup ope rations. During normal power operation, the startup feed pump will automatically start if both steam-driven feed pumps trip.
During the normal operations of heatup, cooldown, and hot standby (rated flow less than 15% and temperatures less than 250 F), feedwater is supplied only through the startup feed pump. The plant operator is instructed to feed continuously rather than intermittently as much as possible. This practice reduces the likelihood of steam backleakage and, therefore, water hammer.
Startup feedwater flow to the steam generators is controlled by the feedwater control bypass valves, either manually or automatically, using a steam generator level signal. Control of feedwater flow to the steam generators uses a portion of the same narrow-range steam generator level channels used during normal feedwater operation.
The plant has the capability for preheating startup feedwater which will decrease the likelihood of the thermal stratification and stripping problem occurring at the steam generator feedwater nozzle under low flow conditions.
Feedwater preheating is accomplished by supplying auxiliary steam to the sixth point heaters (E26A and E26B).
The Emergency Feedwater System ptovides the capability to remove heat from the Reactor Coolant System during emergency conditions when the. Main Feedwater System is not available, including small LOCA cases.
The design and operation of the EFW System has been reviewed regarding the
-y occurrence of hydraulic instabilities, characterized as water hammer. The EFW System is connected to the Main Feedwater System through stop-check valves outside the containment. The flow regulating valves in each.EFW line are normally open, and are sized to pass the required flow under accident conditions.
s., An analysis of the EFW System has established that its function and performance is not affected by the common causes for loss of flow resulting in water hammer, such as pump trip, or rapid valve closure. A pressure transient in the Main Feedwater System resulting from a pipe treak, pump trip, and/or valve closure would be dissipated before flow is established in the EFW System. Both EFW pumps discharge to a common header with branch lines to each SC.
A trip of one pump will not affect the capability of the other pump to provide flow to the intact SGs.
The only automatic valve closure in the EFW System would occur in the line to a faulted SG.
During operation of the EFW System, the plant operators can initiate any changes in flow to each SG, as required.
During all modes of plant operation, including startup, hot standby, and normal operation up to full power load, the EFW System is depressurized and has zero flow.
Consideration has been given in the choice of materials used in those regions of the Feedwater Systems that are exposed to dynamic loadings. All Class 2 and Class 3 pipe, valves, and fittings are fabricated from materials that are listed in Appendix I of Section III of the ASME Code as follows:
o SA-106, Grade B (normalized, fine grain) o SA-234 o
SA-105 o
SA-193, Grade B7 o
SA-194, Grade 7, 2H, 4, or 3 The test methods and acceptance criteria used to verify the fracture toughness of the ferritic materials used in the Class 2 and 3 components of the Feedwater Systems are in accordance with applicable requirements of Articles MC-2300 and MD-2300 in Section III of the ASME Boiler and Pressure Vessel Code, 1974 edition.
s a.
The feedwater isolation valves, containment penetrations, and the piping between containment penetrations and isolation valves have been reviewed for compliance with General Design Criterion 51 and found to be acceptable.
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. b.
The Feedwater System pipe and fittings inside containment and outside containment up to the check valve beyond the isoIation valve have been fabricated from the materials listed above. All welds are examined radiographically to ensure minimum defects. The piping material, SA-106, was heat-treated to improve impact properties.
Impact tests were performed on seven of the eight heats of piping
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material and met code requirements at the minimum emergency feedwater injection temperature of 50 F.
The condensate storage tank water inventory will be maintained at 50 F minimum temperature in order to assure material fracture toughness limits are not violated.
The recommendations of Regulatory Guide 1.37, " Quality Assurance Requirements for Cleaning of Fluid Systems and Associated Components of Water Cooled Nuclear Power Plants", and ANSI N45.2.1-73, " Cleaning of Fluid Systems and 4
. Associated Components for Nuclear Power Plants", are complied with for cleaning and handling of all Class 2 and 3 components.
4 The preheat temperatures used for welding low alloy steel are in accordance with Regulatory Guide 1.50, " Control of Preheat Temperature for Welding of
.; Low-Alloy Steel".
The preheat temperatures used for welding carbon steel materials are in accordance with ASME Code,Section III.
The Feedwater System components are provided with sufficient accessibility such that standard welding procedures are utilized. Non-destructive examination procedures used for tubular products conform to applicable requirements of the ASJE Code.
The design and operation of the Feedwater System and the confirmatory analyses performed provide assurance that the piping and supports can withstand any anticipated dynamic events, as well as precluding or minimizing the potential for a water hammer event from occurring in the Feedwater Piping Systems.
These systems have been reviewed in light of the findings in NUREG-0927, and are believed to cope adequately with the problems that have been experienced at operating plants.
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. Discussion, of Vibrational Effects The pre-operational vibration testing program at Seabrook will help minimize the potential for vibration fatigue. During the testing, both transient and steady-state vibration of Feedwater System piping will be monitored and evaluated. A listing of the areas which will be monitored for vibration during pre-operational and startup testing is contained in FSAR Table 3.9(B)-1, and is included herein.
For the vibration tests, the Feedwater System will be visually inspected and sections to be investigated will be identified, with special attention paid to piping between supports, instrument connections, vent and drain connections, and valve operators. Displacement, frequency, and acceleration will be measured as applicable.
If measured parameters exceed acceptable tolerances, the effect of the vibration on the system design will be evaluated by analysis. The analysis will consider piping stresses based on vibration amplitude, and combined stresses due to other applicable loads including vibration. The evaluation will determine fatigue life based upon stress level, frequency, and endurance limit.
In addition, the evaluation will take into account the operability of any in-line components based on the measured accelerations compared to the component qualification and also the operability and accuracy of instruments connected to the piping.
i Acceptance criteria for steady-state vibration will limit peak vibratory stress to a conservative limit based upon material type; that limit is selected well below the material fatigue endurance limits defined in the ASME Code.
In conclusion, we expect that Seabrook Station will not experience problems due to transient forces or vibrational fatigue in the Feedwater System piping containing arbitrary breaks.
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4 ENCLOSURE D SEABROOK STATION POTENTIAL FOR STRESS CORROSION CRACKING IN FEEDWATER SYSTEM PIPING CONTAINING ARBITRARY BREAKS Carbon steel piping materials, including the materials generally.used for PWR Plant Feedwater Systems are considered immune to stress corrosion. This is because their overall corrosion rate in aqueous environments typical of PWR system service is high compared to the stainless steele and copper base alloys. A metal or alloy will be subject to the highly localized form of attack known as stress corrosion cracking
}
. only if the overall corrosion rate in the subject environment is low.
The overall corrosion rate of carbon steel piping materials is minimized at Seabrook by careful control of the water chemistry, with the intent to minimize the oxygen level, which is the primary contributor to overall corrosion.
During plant operation the secondary-side water chemistry is carefully monitored to assure compliance with the specification requirements shown in Table D-1.
In addition, the oxygen and pH control agents have been carefully selected to assure compatibility with the piping materials.
It is therefore concluded that Seabrook Station Feedwater System is not susceptible to stress corrosion cracking.
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.g TABLE D-1 SEABROOK STATION WATER CHEMISTRY SPECIFICATIONS FOR FEEDWATER-LINES CONTAINING ARBITRARY BREAKS-OPER-MAX.
NO. OF ATING HYDROCEN MAX.
CHLORIDES &
ARBITRARY ASME PIPE TEMP.
-CONCEN.
OXYGEN FLUORIDES pH pH CONTROL 02 CONTROL SYSTEM BREAKS CLASS MAT'L ( F)
(cc/kg H 0)
(ppm)
(ppm)
(0 25 C)
AGENT AGENT 3
2 CS 450 0.005 8.8-9.2 Morpholine Hydrazine (PRIMARY LINES)
FEEDWATER TO 14 2
CS 450 0.005 8.8-9.2 Morpholine Hydrazine AUX. EQUIP.
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- L.
ENCLOSURE E SEABROOK STATION ARBITRARY INTERMEDIATE BREAKS TO BE ELt."NATED IN THE FEEDWATER SYSTEM
=
EST. NO. OF DEVICES ELIMINATED NUMBER OF BREAKS WHIP JET SYSTEM LOCATION
4 0
8 4
FEE 0 WATER TO OC (MS&FW Pipe Chase) 4" 14 0
0 AUX. EQUIPMENT
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22 12 4
TOTALS N
O IC - Inside Containment OC - Outside Containment
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ENCLOSURE F Proposed FSAR Changes - Section 3.6(B)
PROTECTION AGAINST DYNAMIC EFFECTS ASSOCIATED WITH THE POSTULATED RUPTURE OF PIPING a.
Introduction General Design Criterion 4 of Appendix A to 10CFR50 requires that structures, systems and components important to safety be protected against the dynamic ef fects of piping failures. This section dis-cusses the design bases and design measures employed to ensure that all essential structures, systems and components located inside and outside the reactor containment, including the components of the reactor coolant pressure boundary, have been adequately protected against the effects of possible blowdown jet and reactive forces and pipe whips resulting from postulated rupture of piping located both inside and outside of containment.
The required information is furnished in two sections:
1.
Sections 3.6(B).1 and 3.6(B).2 and respective subsections address all piping systems inside and outside containment, exclusive of the reactor coolant loop piping.
2.
Section 3.6(N).2 and subsections, which have been furnished by the NSSS supplier, address only the reactor coolant loop piping inside the reactor containment and the loops' support system.
The criteria used in postulating pipe rupture and leakage locations in high and moderate energy piping systems located outside containment correspond with the guidance set forth in the NRC's Branch Technical Position APCSB 3-1.
The criteria employed for identifying high energy fluid piping, and for postulating pipe break locations, break orientations and break flow areas inside containment are consistent with the criteria established in Regulatory Guide 1.46, " Protection Against Pipe Whip Inside Containment". The Westinghouse Topical Report, WCA?-8082,
" Pipe Break for the LOCA Analysis of the Westinghouse Primary Coolant Loop", is referenced as the basis concluding that the reactor coolant piping system will provide an equivalent level of protection, as recommended in Regulatory Guide 1.46.
The Seabrook Station coolant system piping is consistent with the design considered in WCAP-8082, which has been approved by the NRC Staf f, b.
Definitions High Energy Fluid Systems or Lines - Fluid systeme or lines which, during normal plant conditions, are either in operation or main-tained pressurized under conditions where either or both of the following conditions are met:
3.6(B)-1
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- Maximus' operating temperature exceeds 2000F,
- Maximum operating pressure exceeds 275 psig.
Moderate Energy Fluid Systems or Lines - Fluid systems or lines which during normal plant conditions, are either in operation or maintained pressurized above atmospheric pressure under conditions where both the following conditions are met:
- Kaximum operating temperature is 200 F or less, and
- Maximum operating pressure is 275 psig or less.
Normal Plant Conditions - Plant operating conditions during reactor
~
start-up, operation at power, hot standby or reactor cooldown to cold shutdown conditions.
Upset Plant Conditions - Plant operating conditions during system transient conditions that may occur with moderate frequency during plant service life and are anticipated, operational occurrences, but not during system testing.
Essential Systems and Components - Systems and components required to shutdown the reactor and mitigate the consequences of a postulated piping failure without offnite power.
I-Postulated Piping Failure - Longitudinal and circumferential breaks in high-energy fluid system piping and through-wall leakage cracks in moderate energy fluid system piping posultated according to the provisions of Subsection 3.6(B).2 below.
for thermal expansion as defined in SA-Allowable stress range
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subarticle NC3600 of the ASME Code,Section III, 1971 Edition, with Addenda up to and including Winter, 1972.
Sjy - Al-lowable stress at maximum temperature.
-~~S,- Design stress intensity defined in subarticle NB-3600 of the ASME Code.
Single Active Component Failure - Malfunction or loss of function of a component of an electrical or fluid system. A failure of an active component of a fluid system is not considered to include loss of component structural integrity. The direct consequences of a single active component failure are considered to be part of the single failure.
Terminal Ends - Extremities of piping runs that connect to struc-tures, component s. (ves sels, pumps, valves) or pipe anchors that act as rigid constraints to thermal expansion. A branch connection to a main piping run is a terminal end of the branch run.
3.6(B)-2
FL.
SB 1 & i Amendment 47 FSAR September 1982 Intersections of runs of comparable size and fixity need not be considered terminal ends when so justified by the analysis. Terminal ends, for the purpose of postulating breaks, should be selected at points located immediately outside or beyond the required pipe whip restraints located inside and outside containment at penetration In piping runs that are maintained pressurized during areas.
normal plant conditions for only a portion of the run (up to the first normally closed valve), a terminal end of such runs is the piping connection to this first valve.
Five Degree Restraint - A device which restrains the pipe in such a way that only axial loads can be transmitted past the restraint.
3.6(3).1 Postulated Piping Failures in Fluid Systems Outside of Containment 3.6(B1.1.1 Design Bases a.
Equipment Potentially Susceptible to Effects of Piping Failure Systems and components important to plant safety or shutd:<n (herein referred to as essential systems and components), located pr aimate to high or moderate energy piping systems, and which are potentially susceptible to the consequences of piping systems breaks and cracks, are listed in Table 3.6(B)-1.
The identification of this equipment i
is related to predetermined piping failure locations, determined in accordance with the methodology discussed in Section 3.6(B).2.
N Figures 3.6(B)-1, 3.6(B)-2 and 3.6(B)-5 through 3.6(B)-38b show the locations of the postulated pipe ruptures, locations of pipe whip restraints, and relative locations of potentially affected essential components.
The limiting acceptable conditions for, and the measures taken to 47 protect the essential systems and components, are listed in the pipe rupture analysis summary sheets in Appendix 3A.
b.
Design Criteria for Protection Against Piping Failures The following. criteria were utilized as guidelines during the station design to assure the protection of essential equipment from potential failure of nearby piping systems:
1.
Piping Systems Containing High Energy Fluids Piping systems are to be isolated by adequate physical a.
separation, and remotely located from essential systems and components required to shut down the reactor safely and maintain the station in a cold shutdown condition.
3.6(B)-3 i
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Where isolation by remote location is considered imprac-tical, piping systems, or portions of the systems, are enclosed within structures suitably designed to protect adjoining essential systems and components from postulated piping failures within the enclosure.
Where both isolation by remote location and enclosure in c.
protective structures are considered impractical, the piping systems or portions of the systems are provided with restraints and protective measures such that the operability and integrity of the structures, s a fe ty systems and components would not be impaired.
d.
Protective enclosures for the piping systems a e designed as seismic Category I structures capable of withstanding the combined ef fects of a postulated pipe break, the dynamic effects of pipe whipping, the jet impingement forces and the compartment pressurization resulting from discharging fluids in combination with the specified seismic event of the Safe Shutdown Earthquake and norral operating load.
Piping systems containing high-energy fluids are designed e.
so that the ef fects of a single postulated pipe break will not initiate unacceptable failures of other pipes or compon-ents.
In addition, any systems, or portions of systems, that are designed to mitigate the consequences of a postula-ted pipe failure and place the reactor in the cold shutdown condition, are provided with design features that will
. ensure the performance of their safety function, assuming a single active component failure.
f.
For a postulated pipe f a ilu r e, an escape of steam, water and heat f rou structures enclosing the piping shall not preclude:
- 1) the accessibility to surrounding areas important to the safe control of reactor operations, 2) the habitability of the control room, 3) the ability of instrumentation, electric power supplies, and components and controls to initiate, actuate and complete a safety action.
In this regard, a loss of redundancy is considered permissible, but not the loss of function.
g.
The design measures employed for the protection of struc-tures, systems, and components important to safety will not prevent inservice examinations of ASME Class 2 and J pressure-retaining components, as required by the rulas of ASME B&PV Code,Section XI, " Inservice Inspection of Nuclear Power Plant Componenta".
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3.6(B)-4 l
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SB 1 & 2 Amendment 44 FSAR February 1982 2.
Pipi'ng Systems Containing Moderate-Energy Fluids Piping systems containing moderate-energy fluids are a.
designed to comply with the criteria applied to high-energy fluid piping systems, as. stated above, except that the piping is postulated to develop a limited-size through-wall leakage crack instead of a pipe break.
b.
For each postulated leakage condition, design measures are provided that will provide protection from the ef fects of the resulting water spray and flooding.
3.
Exceptions Measures for protection against pipe whipping or jet impingement resulting from the breaks postulated in Subsection 3.6(B).2 are not provided for piping where any of the following applies:
a.
Piping is physically separated or isolated from any essential system or cosponent necessary for plant sa fe ty or shutdown by means of barriers, or is restrained from whipping by plant design features such as encasement.
b.
The broken pipe cannot cause unacceptable damage to t
any essential system or component.
c.
The energy associated with the whipping pipe can be demonstrated to be insufficient to impair to an unacceptable level the safety function of an essential system or component. For example, a whipping pipe is considered unable to rupture an impacted pipe of equal or larger nominal pipe size and equal or heavier wall thickness.
3.6(B).1.2 Description High energy lines are listed in Table 3.6(B)-2; moderate energy lines include all other lines not listed in this table. For a complete li* ting of all high and moderate energy lines, see the Seabrook line designation j
tabulation, Appendix 3B.
Relative to possible dynamic effects of pipe failure iri the Seabrook plant l
layout, essential systems and components are protected from the dynamic effects of rupture of high energy piping primarily by separation and redundancy. Routing of high energy lines has been arranged to provide the maximum amount of protection by utilizing plant structural elements, such as walls or columns, and routing the high energy lines as far as practicable from essential components.
In cases where separation is not possible, pipe whip restraints are used to prevent uncontrolled whipping of the high energy piping. Compartments of primary interest are the containment structure, the main steam and feedwater pipe tunnels, and the containment enclosure building and its attached compartments.
44 1
3.6(B)-5
bM...
SB 1 & 2 Amer.doent 44 FSAR February 1982 In the case of the control. room, there are no high energy lines in the area which could af fect habitability as a result of pipe whip. The main steam and feedwater lines on the pipe bridge are separated from the control room by the seismic Category I control building wall, which has been reinforced to protect the control room environment from postulated breaks in, or whip loads from, the main steam and feedwater lines. Control roo2 dsbitability systems are discussed in Section 6.4.
The high energy lines outside containment whose breaks or cracks could have the greatest ef fect on environment within the structures housing components essential for safe plant shutdown are listed below:
1.
Primary Auxiliary Building Steam generator blowdown lines a.
b.
Auxiliary steam and condensate lines Chemical and volume control system letdown line c.
d.
Hot water heating lines 2.
Fuel Storage Building Hot water heating lines a.
b 3.
Containment Enclosure and Connec ted Buildings a.
Het water heating lines 4.
Main Steam and Feedwater Pipe Cha se Main steam lines a.
b.
Fee dwa t.e r lines 5.
Diesel Generator Building a.
Hot water heating line 6.
Control Building a.
Hot water heating line 7.
Emergency Feedwater Pumphouse a.
Hot water heating line 8.
Service Water Pumphouse a.
Hot water heating lines Table 3.6(B)-1 lists the essential components located outside containment which are potentially susceptible to the ef fects of high and moderate energy piping ruptures.
AL 3.6(B)-6
e n,
SB 1 & 2 Amendment *5 FSAR June 1982 Table 3.9(B)-23 ta,bulates all active valves, including those in zones outside containment, whose function must be unimpaired in the event of a pipe rupture accident.
3.6(B).1.3 Safety Evaluation Appendix 3I summarizes the environments in each of the structures housing essential components which result from postulated rupture of the high energy lines.
An analysis of the potential effects of missiles is discussed in Section 3.5.
Pressure rise analyses of structures and compartments due to piping breaks are discussed in Sec tions 3.7 and 6.2.
A summary of the results of failure or leakage from high energy or moderate energy lines on nearby safety systems (failure modes and effects analysis),
presented in Appendix 3A, verifies that the consequences of failures of high and moderate energy lines will not a f fec t the ability of the plant to be shutdown safely. The analyses considered the effects of single active component failures occurring in required systems concurrent with the postulated event.
44 3.6(B).2 Determination of Break Locations and Dynamic Effects Associated with the Postulated Rupture of Piping
/
This section dcscribes the design bases for locating postular< d breaks and cracks in piping situated both inside and outside of containment, the proce-m dures used to define the jet thrust reaction at the break or crack location, and the jet impingement loading on adjacent safety-related structures, equip-ment, systems and components.
3.6(B).2.1 Criteria Used to Define Break and Crack Location and Configuration The criteria employed for defining break and crack locations and configuration's in primary loop piping inside containment is discussed in Subsection 3.6(N).2.1.
This section discusses all other piping.
The criteria are provided for those high and moderate energy piping systems for which separation or enclosure cannot be acnieved,
'High Energy Piping a.
1.
ASME Section III Code Class I Piping Breaks were postulated to occur at the following locations in each piping run or branch run:
(a) Terminal ends.
l 3.6(B)-6a
y c
Sh I&2 Ami.niles est 4's FSAR Jasnc 1987 (b) 'At all intermediate locations where the maximum stress range as calculated by Eq(10) and either (12) or 13) exceeded 2.4 Sm; based upon. Subsection NB-3600 of Section III of the ASME B&PV Code, 1977 Edition, up to and including the Summer, 1979 Addenda. The load-ings considered were all Level A and B loads including an operating basis earthquake.
(c) At all intermediate locations where the cumulative usage factor derived from the piping f atigue analysis under the loads described above exceeded 0.1.
A A
2.
ASME Section III Code Class 2 and 3 Piping Breaks were postulated to occur at the following locations for each piping run or branch run which does not penetrate the containment:
(a) Terminal ends.
(b) Any intermediate locations between termtnal ends where either circumferential or longitudinal stresses derived by elast'ic methods under the loadings associated with opera-A tional plant conditions and an operating basis earthquake exceed 0.8 (S
+S)-
A g
-=
See below for piping penetrating the containment.
3.
Non-Nuclear Piping-Breaks in non-nuclear piping were postulated at the following locations in each piping run or branch run:
(a) Terminal ends.
(b) Each structural discontinuity (elbows, tees, reducers, valves).
4.
Piping Penetrating Containment All piping penetrating the containment is ASME Section III, Code Class 2.
All high energy, high temperature lines pene-trating containment make use of integrally forged flued heads.
A detailed discussion of the design of these flued heads is given in Reference 1.
3.6(B)-7
'nH SB I&2 Amendment 49 FSAR Hay 1983 s
For main s' team and feedwater piping penetrating containment, no breaks were postulated between the first whip restraint inside the containment and the five-degree restraint outside containment, since the following conditions are met:
(a) The maximum stresses, as calculated by the sum of equa-tions (9) and (10) in paragraph NC-3652 of Section III*
of the Code, considering normal and upset conditions S }-
and an OBE event, do not exceed 0.8 (1.2 Sh*
A (b) The maximum stress, as calculated by equation 9 of paragraph NC-3652 under the loadings resulting from a postulated piping tailure of fluid system piping beyond these portions of the piping, does not exceed 1.8 Sh.
(c) The number of circumferential and longitudinal weld points in piping have been minimized.
Al length of those portions of piping have been reduced (d) The to the minimum practical.
(e) The design of pipe restraints and anchors have not generally required welding direct ly to the outer sur face of the pipe.
Where anchors or restraints were needed, forgings were used to avoid welding to the surface of the ptpe.
Where lugs were used for riser clamps, a detailed analysis was made
,j to assure compliance with stress limits stated above.
Lug attachments welded to Class 2 and 3 pipes are qualified by a procedure whose methodology is equivalent to, but more conservative than, that presented in Code Case N-318.
Local stress levels in the pipe resulting from applied lug loads are obtained by multiplying the nominal stress in the lug at the lug / pipe interface by the appropriate B or C index (as defined in Code Case N-318) for each individual loading condition. The local stresses are superimposed upon the general pipe stress as determined from program ADLPIPE to establish the total stress level in the pipe for that loading condition.
Loading conditions required to be considered for Plant Normal, Plant Upset. Plant Emergency, and Plant Faulted Operating Condition are defined (per appropriate FSAR section), and total stress in the pipe is obtained frois summing the stresses for each individual 1,oading condition that must be considered.
Local stress levels determined using B indices are added to the general stress levels f rom ADLPIPE and this sua is 4T
- For piping design, the pplicable Code edition is the 1971 Code, with addenda up to and including Winter 1972.
3.6(B)-8
SB 1 & 2 Amendment 49 FSAR May 1983 compared against allowable limits to demonstrate struc-tural integrity. For the pipe wall, local stress levels
. determined using C indices are added to the general stress levels from ADLPIPE, and this sua is compared against the allowable range of stress (S +Sa)-
h Finally, weld stress is evaluated considering the absolute sua from all loads, independent of the operating condition, and compared against allowable stress from Table NF329.1-1, Subsection NF, ASME III.
4F The terminal ends of these portions of piping are considered to originate at a point adjacent to the restraints located inside and outside containment which are:
(a) Located reasonably close to the isolation valve.
(b) Capable of withstanding the loadings resulting from a postulated pipe rupture beyond this portion of the piping, such that neither valve operability nor the leaktight integrity of the containment is impaired.
Details of typical containment piping penetrations showing location of process pipe welds, anchorage and points of dis-continuity are shown in Figures 3.6(B)-3 and 3.6(B)-4 Inservice inspection of Code Class 2 components, including penetrations, is discussed in Section 6.6.
1 t
l l
I l
3.6(B)-8a i
f
r
~
r#'.
Moderate Energy Piping Through-wall leakage cracks are postulated to occur in seismic Category I and non-nuclear fluid system piping located within or outside and adjacent to protective structures, with the following exceptions:
1.
Fluid system piping between isolation valves, provided they meet the requirements of ASME Section III, subarticle NE-1120, and are designed such that the maximum stress range does not exceed 0.4 (1.2 Sh+S) for ASME Class 2 piping.
A 2.
Fluid system piping located in an area in which a break in a high energy system is postulated, provided a break in a moder-ate energy fluid system does not result in a more limiting condition than the break in the high-energy system.
3.
Seismic Category I fluid systems in which the maximum stress range in Class 2 or Class 3 or non-nuclear piping is less than 0.4 (1.2 Sh + S )*
A The cracks were postulated to occur in those locations that result in the maximum ef fects from flood spraying or flooding.
Through-wall leakage cracks were postulated instead of breaks in the piping of those systems that qualify as high energy fluid systems for only short operational periods, but qualify as moderate energy fluid systems for the major operational period. These systems include containment spray, safety inj~ection and residual heat removal.
An operational period is considered short if the fraction of time that the system operates within the pressure-temperature limits specified for a high-energy system is 2 percent or less of the time that it operates as a moderate energy fluid system.
c.
Type of Breaks The following types of breaks and cracks were postulated to occur in high-energy and moderate energy piping as described below:
1.
High Energy Piping (a) Circumferential breaks were postulated to occur in high-energy piping larger than one inch nominal pipe size.
Circumferential breaks are presumed to occur at right angles to the axis of the pipe, to completely sever the pipe within one millisecond and to separate the 3.6(B)-9
~
a4 m
SB 1 & 2 FSAR ends of the pipe to permit a flow area equal to the flow area of the pipe. See Subsection 3.6(N).2.1 for exception for RCS piping.
(b) Longitudinal splits were postulated to occur in high-energy piping four inches or larger nominal pipe size.
The area of the longitudinal split was assumed to be equal to the flow area of the pipe, and the split was assumed to be parallel to the axis of the pipe. Crack orientation was selected on the basis of the most serious effects.
(c) Certain long'.tudinal break orientations were excluded on the basis of the state of stress at the location considered. Specifically, where the maximum stress range in the c.xial direction is at least one and a half times that in the circumferential direction considering upset plant conditions, then only a circumferential break was postulated.
tulated to occur in (d) Longitudinal breaks were not pe piping at terminal ends where the piping contains no longitudinal welds or at intermediate locations where the criteria for a minimum number of break locations were satisfied.
5 2.
Moderate Energy Piping Through-wall leakage cracks were postulated to occur in moderate energy piping larger than one ir.ch n_ominal pipe diame ter, and to have openings up to one-hal f ' pipe diameter by up to one-half the pipe wall thickness.
d.
Jet Impingement Force Criteria The criteria used to evaluate jet impingement forces are described in Appendix 3C, Procedure for Evaluation of Jet Impingement Loads f rom High Energy Piping Failures. After jet forces imposed on structures or equipment have beer. deter =ined, the capacity of the structures or equipment to support these loads without d amage is investigated using conservative methods. Jet impingement loads are considered to be f aulted condition loads and are so evaluated.
3.6(B).2.2 Analytical Methods to Define Forcing Functions and Response Models This section presents a description of the methods used to define forcing functions and response models for pipe whip analysis. For RC Loop piping, see Subsection 3.6(N).2.2.
3.6(B)-10
s n+. '
N.
Forcing Functions 1.
Time Dependence The normal steady-state operating conditions of the plant were assumed prior to postulating a pipe rupture.
When circumferential ruptures were postulated, the through-wall crack was assumed to develop across the circumference of the pipe instantaneously, and the ruptured pipe was assumed to separate to the full flow area (e.g., double ended rupture) in one millisecond.
When longitudinal ruptures were postulated, the time for a longitudinal rupture to open to its maximum length was assumed to be one millisecond.
2.
System Friction Loss Dependence full credit In calculating forces acting on the piping system, may be taken for any restrictions or line losses between the break and the pressure reservoir (s).
For Seabrook, however, simplified conservative analyses did not consider friction the losses.
3.
Closed-Ended Lines g;
For the closed end of a line (dead end or normally-closed valves) when it was obvious that the fluid dynamic forces could not be sustained, pipe whip response was not considered.
4.
Discharge Coefficient For flashing or nonflashing flow through circumferential C, of 1.0 and longitudinal breaks, a discharge coef ficient, d
was used to determine the flow rate through the break, Cd AV Q
=
flow rate through break where: Q
=
break flow area A
=
velocity V
=
Od=
discharge coefficient 5.
Options The jet thrust reaction, forcing function at the break locations
- However, may be generated from a dynamic fluid system model.
a simplified approach was used, applying a maximum thrust value defined for discharge of non-flashing liquid or for discharge of saturated or superheated vapor as:
3.6(B)-11
$4
> ~:.
K1 (K2 P
-P)
A T
=
o Where: T represents the thrust force P
represen*, vessel pressure (psig) o A
reprencats break flow area Kg,K2 represents th rus t coe fficients P.
pressure of ambient outside system (psig)
Representative values of K reported by Moody (2) are:
(a) Saturated and superheated vapor, Kg = 1. K; = 1.26 (b) Subcooled liquid - non flashing, Kg - 2, K2*1 Other values may be used when substantiated; however, the Moody coefficients have been used for pipe rupture analysis on this project.
For circumferential breaks, direction of thrust was assumed to be along the centerline of the pipe in a direction opposite the jet flow.
For longitudinal breaks, thrust was assumed in a direction opposite jet flow.
Y.,y For all breaks, maximmn thrust was assumed to occur within I millisecond and to be a steady state condition thereafter.
3.6 (B ). 2.3 Dynamic Analysis Methods to Verify Integrity and Operability a.
Dynamic Analysis Methods The analysis of a piping system and its restraints under pipe rup-ture conditions requires consideration of the interaction effects o f both piping and restraints. The magnitude and distribution of loadings depends upon such parameters as the restraint load-deflec-tion gaps between piping and restraint, piping flexibility, break location, etc.
1.
Energy-Balance Analysis In this method, kinetic energy generated during the first quarter cycle movement of the ruptured pipe is imparted to the piping / restraint system through impact and is converted into equivalent strain energy. Deformations of the pipe and the restraint are compatible with the level of absorbed energy.
For applications where pipe rebound may occur upon impact of the rgstraint, an additional amplification factor 1.5 was used to establish the magnitude of the forcing function in order to determine the maximum reactor force of the restraint af ter the first quarter cycle of response. Amplification factors other 3.6(B)-12
r;s SB 1 & 2 Amendment 45 FSAR June 1982 than 1.5 may be used if justified by more detailed dynamic analysis. Appendix 3D presents the procedure used for calcula-ting piping / restraint system loads by the energy balance method.
2.
Quasi-Static Analysis In order to satisfy the system capability requirements, a dynamic analysis is the preferred method. In the event a dynamic analysis is not possible or feasible for a piping and restraint system, a quasi-static analysis may be possible if it is shown to give more conservative results.
Two design considerations are required as in the dynamic ant. lysis. The system must be capable of supporting both the dynamic and the steady-state blowdown loads.
[
If a constant, conservative blowdown force is assumed, the system is independent of the dynamic event occurrence time.
Since the dynamic inertia effects are therefore unknown, the load-sharing relationship between the pipe and the restraints, etc., cannot be determined.
The jet force can be represented by a conservatively amplified static loading, and the ruptured system is analyzed statically.
The amplification factor that is used to establish the magnitude of the forcing function is a conservative value obtained by com-parison with the factors derived from detailed dynamic analysis performed on comparable systems. Appendix 3E presents the en procedure used for calculating piping / restraint system loads by the equivalent static analysis method.
b.
Design Considerations Pipe rupture locations and orientation were determined as stated in Subsections 3.6(B).2 and 3.6(N).2.
Effects of each rupture were evalusted and, if necessary, whip restraints were located to protect the essential systems or components.
Pipe whip restraints for the reactor coolant system piping were designed to limit the motion of the ruptured piping and to restrict the ficw area of the breaks in order to limit jet thrust forces.
For other Code Class 1, 2 or 3 piping, the whip restraints were designed to prevent unrestrained whipping of the piping, but at the same time permit unrestrained thermal movement of the piping.
In some cases, such as on the main stesa and feedwater lines in the penetrations and piping tunnel areas, it was appropriate to use pipe whip restraint steel as intervening elements or as supplementary steel for the attachment of seismic restraints.
Wherever this was done, the boundary between PWR steel and ASME Class 2 seismic restraints was defined by showing the PWR steel and the seismic restraints on separate fabrication and installation drawings. All Code Class supports and restraints are identified on the drawings as N-Stamp Items.
~45 3.6(B)-13
n Q..
7'n'
~.
SB 1 & 2 Amendment 45 FSAR June 1982 s
After the whip restraints were located, the following information was developed:
(a) Jet thrust force (b) Pipe seismic displacement (c) Pipe thermal displacement (d) Maximum allowable pipe travel (e)
Insulation thickness Minimum gap between pipe and restraint is determined froc consider-ation of (b), (c) and (e) above.
Reatraint stiffness is determined from (a) and (d).
Where the whip restraint is also a seismic restraint, the following values for stiffness were used:
106 or 107 lb/ inch.
(a) For piping larger than 8" nominal diameter:
10, 106 or 5
(b) For piping from 2h" to 6" nominal diameter:
107 lb/ inch.
10, 105 or 106 lb/ inch.
4 (c) For piping up to 2" nomina 1' diameter:
show that a change Analyses of representative piping configurations in stiffness of one order of magnitude in either direction will not change pipe stresses significantly, so that the designers generally used the lowest values for stiffness in the ranges given, unless pipe deflection is the critical parameter.
In the design of the whip restraints, the energy absorption capacity of the pipe was not considered.
For structural steel whip restraint me mb e r s, when elasto plastic design methods were used, the stress l
44 limit for design is 90% of the yield stress value shown in the AISC Steel Construction Manual. When elastic design methods were used, the stress limit for design is 63% of yield.
In general, for pipe whip restraints, elastic design criteria were used.
In cases where elasto plastic design criteria were used, was also uned as an intervening element and the pipe whip restraint for attachment of pipe supports or restraints, it was first designed a whip restraint using elasto plastic criteria, and was then aschecked to verify its ability to support the pipe support / restraint loads using elasto plastic criteria.
45 In order to determine the adequacy of a system, including pipes and restraints, following postulated pipe rupture accident, two design considerations must be evaluated:
1.
Dynamic Response Upon the occurrence of the postulated pipe rupture, the system of pipe restraints structure, etc., will respond dynamically to the suddenly applied blowdown thrust, FB (t).
This thrust 3.6(B)-14
,r E"
will move the pipe so that it impacts against the restraint with an impulse equal to the pipe mass times the impact velocity.
F, and the time after this The product of blowdown thrust, B
impact until motion ceases, t, will be an additional impulse on the system.
Static Equilibrium 2.
Following the occurrences of the dynamic event (when motion ceases), the system must be able to support the active applied forces (the blowdown thrust). Therefore, the system mus t satisfy the requirements of a static analysis.
For a conservative static analysis, each component (i.e.,
pipe, restraint) is capable of supporting the total load (or it is shown which component (s) support the load). When this is done and the components will have the load capacity to support the steady-state blowdown, the system design is considered to be conservative.
Design Loading Combinations c.
Pipes which have been identified in accordance with Subsection 3.6(B).1 as those which could cause adverse effects due to pipe movement were provided with means of controlling their motion, if barriers, separation, or some other acceptable method was not 1s used for protection.
I'.
Piping The pipe will be subjected to dynamic forces following a An evaluation was made to insure postulated pipe break event.
that the load carrying capability of the pipe is not exceeded.
(a) Adequacy Requirements is in order for the motion of pipes to be controlled, it the load on the pipe during the dynamic necessary that event be less than the load capacity of the pipe. The dynamic load capacity of the pipe can be determined by test or by a suitable analytical model.
l Without testing, the load capacity for analysis is limited f
to the bending associated with a maximum fiber strain of j
50 percent of the ultimate strain of the pipe material.
Ultimate attain is defined as the value of strain which I
corresponds to the maximum stress on the engineering stress-strain diagram. For a given material where there I
is a range of values due to statistical variation, the l
guaranteed minimum value of ultimate strain is used.
6 3.6(B)-15
- r.. -
tr,- >
. 0; SB 1 & 2 Amendment 49 FSAR May 1983 s
t The second requirement, to insure that the motion of pipes is controlled, is for the moment-carrying capacity of the pipe to be greater than the applied moment af ter the occurrence of the dynamic event. An ultimate moment, that the pipe cross Mu, is defined as the maximum momentIf the applied moment, M, defined section can support.
a as a force times lever arm is numerically smaller than M, uncontrolled rotation of the pipe will not occur.
y (b) Mayerial Properties Careful cona:d ation was given to the piping material The rapid loading conditions due to properties pipe rupture may require the consideration of high strain-in addition to strain-rate effects on material behavior, hardening considerations.Section III of the ASME Code provides tabulations of material properties which may be The values of yield strength used for er>me evaluations.
for example, are minimum values for static at temperature, loadings. In calculating the allowable span distance between restraints, use of minimum values is conservative.
which could be exerted In calculating the maximum moment on an anchor point, the use of minimum values would be unconservative. The applied moments, M,,
during the steady state blowdown will be no greater than 90 percent capacity of the pipe based on minimum pipe q
of the moment material properties determined from test, applicable specifications, or codes.
2.
Restrainta provided to maintain For BOP piping, pipe whip restraints are the motion of the ruptured pipe within controlled limits.
The limit of pipe motion is the area within which no essential component would be affected by impact or jet impingement.
49 The primary function of a restraint is to control pipe motion As used in this context, upon the occurrence of a pipe rupture.
a restraint is considered to be different from a support. In certain instances, a restraint may also function as a support, and is designed according to the f aulted conditions rules of Subsection NF of ASME Code,Section III.
Typical whip restraints consist of heavy structural members extending from the building structure to the pipe, and a structural box or a series of U-bolts which surround the Unless the restraint acts pipe to restrain lateral motion.
also as a thermal or seismic restraint, contact between the pipe and the whip restraint is prevented by means of a suitable air gap. Where it is necessary to reduce pipe impact loads on critical structures, energy-absorbing devices are used between the pipe and the structure.
3.6(B)-16
s SB 1 & 2 Amendment 49 FSAR May 1983 (a) Design Limits s
Pipe restraints are designed for one-time usage, and as such may be allowed to have greater distortion, plastic deformation, etc., than normally permitted for support design.
For elasto plastic system analysis, wherein the ef fects of 4T strain-rate, strain-hardening, etc., are included, the permanent strain in metallic ductile materials is limited to 50 percent cf the uniform strain. When a crushable energy-absorbing material is used, the deformation is limited to that corresponding to 50 percent of the total energy absorption capacity of the crushable material.
(b) Material Properties Materials selected for restraints designed to significant strain levels must have well-known dynamic mechanical properties. Assurance was provided by material inspection.
3.6(B).2.4 Guard Pipe Assembly Design Criteria Guard pipes are employed in th'e following locations: a) on the main steau and feedwater lines to prevent pressurization of the annulus in the event of a pipe rupture; b) on the main steam lines just north of the main steam and i
feedwater pipe chase to protect the main steam isolation valves from missile damage due to jet impingement of the pipe chase north wall; and c) on the main steam line in the pipe bridge area to protect the control building wall um from jet impingement. The guard pipes in the containment enclosure were design'ed as a part of the flued head penetrations for the main steam and feedwater lines.
41 A discussion of the design criteria and analysis of the high energy contain-ment penetrations is given in Reference 1.
The purpose of the penetration assemblies is to permit penetration of the containment by process pipes with-out jeopardizing containment integrity. Where they are used as guard pipes, they also serve to prevent overpressurization of the containment enclosure and annulus. No other lines in this area require guard pipes.
Penetra-In general, all process pipes penetrating containment are seamless.
tion assemblies for large high temperature lines are integrally forged flued head design. Penetration assemblies for cold lines or small lines (under 1" nominal diameter) are seamless pipe welded to fist plate heads which All in turn welded to sleeves anchored in the containment structure.
are penetration sleeves are seal welded to the steel containment liner, and leak test channels are provided for periodic testing of containment leak-tightness.
There are no process pipe welds located within the protective assemblies, with the exception of the 2" diameter steam generator blowdown lines.
The process pipe welds for these lines do not require inservice inspection (Ref. IWC-1220d of ASME XI).
Moment-limiting restraints have been provided for all penetrations carrying high energy piping in order'to maintain process pipe stress levels below the limits defined in Equation 8 of NC3652 for maximum stress range considering s
all upset design transients in combination with OBE.
3.6(B)-17
d 4-o 7':Q.
m.
S-SB 1 & 2 FSAR s
3.6( B).2.5 Material to be Submitted for the operating License Review The results of the analyses performed on high and moderate energy piping systems and their supports to determine the loadings from postulated pipe breaks and cracks, as well as the procedures used, are presented in the following appendices:
Appendix 3A Pipe Break Analysis Srmma ry Shee t s Line Designation Tabulation (Seabrook Line List)
Appendix 3B Appendix 3C Procedure for Evaluating Jet Impingement Load s from High Energy Piping Failures Procedure for Calculating Elasto-Plastica 11y Designed Appendix 3D Pipe Whip Restraint Loads by the Energy Balance Method Procedure for Calculating Elastica 11y-Designed Pipe Whip Appendix 3E Restraint Loads by Equivalent Static Analysis Method 3.6(B).3 References for High Energy Piping Penetrations for PSNH-Seabrook 1.
" Stress Report Station Units I and 2", Stres s Report No. 9763-325-1, dated September, Inc.
"\\,
1976, United Engineers & Constructors 2.
Mood y.
F.J., " Prediction of Blowdown Thrust and Jet Forc e s",
Paper No. 69-HT-31, presented at the ASME-AICHE Heat Transfer Conference, Minneapolis, Minnesota, August 3-6, 1969 3.6(B)-18
.