ML19308E098
| ML19308E098 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 09/01/1973 |
| From: | US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19308E092 | List: |
| References | |
| NUDOCS 8003200822 | |
| Download: ML19308E098 (14) | |
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DOCUMENT (B)
STRUCTURAL DESIGN CRITERIA FOR EVALUATING THE EFFECTS OF HIGH-EtlERGY PIPE BREAXS ON CATEGORY I STRUCTURES OUTSIDE THE CONTAIflMElli t
CONTENTS A. - Introduction B.
Loads, definition o.f terms and nomenclature Acceptable load combinations and allowable lim'its for Category I C.
concrete structures D.
Acceptable load combinations and allowable limits for Category I steel structures E.
Acceptable procedures for determination of the effect of an impacting whipping pipe on concrete and steel structures F.
Acceptable procedures for design of structural pipe restraints t
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A
_2-A.
INTP.0 DUCTION General Design Criterion 4 of Appendix A to 10 CFR Part 50, " General Design Criteria for Nuclear Power Plants," necessitates that structures important to safety, classified.as Category I' structures, shall be designed to accommodate the ef fects of, and to be~ compatible with, the environmental conditions associated with normal operation, maintenance, testing and postulated accidents. Thess structures shall be appro-Priately protected against dynamic effects, including the effects of missiles, pipe whipping, and discharging fluids associated with postu-lated high-energy pipe rupture accidents and f' rom events and conditions outside the nuclear power unit.
i This document presents a set of acceptable criteria.for evaluating and assuring the required protection.
It is assumed that the follow-ing steps, which are not structural in nature and are thus not within the scope of this document, have already been performed 'and the neces-sary design parameters already defined:
4 1)
Systems in which pipe breaks are postulated and for which pro-tection against the effects of such breaks should be proviaed, have been defined,
- 2) Locations of postulated breats and type and orientation of each break, guillotine or longitudinal, have been determined, l
1 3) Protection criteria for each postulated becak have been estab-lished. This should identify the structurcs, systees and com-ponents to be protected from the effects of the break, and
- 4) All induced loadings for each postulated break are defined, including:
a) Differential pressure across compartments, if any, as a function of time, b) Jet impingement force, if any, on a protective barrier, as a function of time, and c) Whipping pipe impact parameters, if any, on a protective barrier or a pipe restraint, including the equivalent mass, impact area and impact velocity.
B.
LOADS, DEFINITION OF TERMS AND NOMENCLATURE The following nomenclature and d.efinition of terms will apply to all the criteria that follow in this document.
t All the major loads to be encountered and/or to be postulated during a high-energy pipe rupture event are listed. All the loads listed, however, are not necessarily applicable to all the structures and their elements in a plant. Loads and the applicable load combinations for which each structure has to be checked and evaluated will depend on the conditions to which that particular structure could be subjected, l
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-3 3.1 NO:UfAL LOADS Normal loads are those loads to be encountered during normal plant operation. They include the following:
D - Dead loads and their related moments and forces, including any permanent equipment loads, and prestressing Icads, if any.
3, L -- Live loads, present during the pipe rupture event, and their related moments and forces.
T, Thermal loada during normal operating conditions.
R, -
Pipe reactions during normal opera' ting,canditions.
B.2 SEVERE ENVIRONMENTAL LOADS Severe environmental loads are those loads' that could infrequently be encountered during the plant life.
Included in this category are:
Fego -k.oadsgeneratedbythe0peratingBasisEarthquakeor,if an OBE is not specified, loads generated by half the Safe Shutdown Earthquake. If both are specified, they shall be the largest of the two.
B.3 EXTREME ENVIRO:C! ENTAL LOADS Extreme environmental loads are those leads which are credible but are highly improbable. They include:
Feqs - Loads generated by the Safe Shutdo.ra Earthquake.
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. B.4 ABN0?J'AL LOADS _
Abnormal loads are those loads generated by a postulated high-energy pipe break accident withi.n a building and/or cccpartment thereof.
Included in this category are the foll'oving:
P, --- Pressure equivalent static load within or across a compart-
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ment and/o'r building, generated by a postulated break, and including an appropriate dynamic factor to account for the dynamic nature of the load.
T, Thermal loads under thermal conditions ' generated by a postulated break and including T,.
Pipe reactions under th' rmal' conditions generated by a e
E, postulated break and including R.
o Y,
Equivalent static load on a structure genereted by the reaction on the. broken high-energy pipe during*a postulated 1
treeak, and including an appropriate dynamic factor to account for the dynamic nature of the load.
g Y
.Tet impingement equivalent static load on a structure gen-
.1 ersted by a postulated break, and including an appropriate dynamic factor to account for the dynamic nature of the load.
static load on a structure gen-Y, --- Missile i= pact equivalent erated by or during a postulated break, like pipe whipping, and including an appropriate dynamic factor to account for the dyna =ic nature of the load.
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and In determining an appropriate equivslcat static load for P ' Y ' Ij a
r Y,, einsto-plastic behavior may be assumed with appropriate ductility ratios and as long as excessive deflections will net result in loss of function.
B.5 OTHER DEFT.!ITIONS For structural steel, S is the required section strength S
based on the elastic design methods and the allowable stresses defined in Part 1 of the AISC " Specification for the Design, labrication and Erection of Structural Steel for Buildings,"
February,12, 1969.
U For concrete structure's, U is the section strength required to res'st design loads and based on methods described in ACI 318-71.
T For structural steel, Y is the section strength required to resist design loads a'nd based on plastic design methods described in Part 2 of AISC " Specification for the Design, Fabrication and Erection of Structural Steel for Buildings," February 12, 1969.
C.
LOAD COMBINATIONS AND ACCEPTANCE CRITERIA FOR CATECORY I CONCRETE STRUCTURES _
The following presents an acceptable set of load combinations and allowable limits to be used in evaluating and checking Category I cencrate structures outside the contain=ent for the effects of
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high-energy pipe breaks, Concrete barriers, used to provide a shis!d against the ef fects of high-energy pipe breaks, will have to maintain-their structural integrity under all credible loading conditions. To assure that the structural integrity will be maintained, limits on the required strength capacities are recommended.
C.1 LOAD COMBINATIONS The following load combinations should be satisfied:
j 1)
U=D+L+T
+R
+ 1.5 P a
a a
2)
U=D+L+T
+R
+ 1.25 P + 1.0 (Y
+Y
+ Y ) + 1.25 Feqo a
a a
r m
3)
U=D+L+T
+R
+ 1.0 P + 1.0 (Y
+Y
+ Y ) + 1.0 Fegs a
a
.a r
a The maximum values of P,, T,, R,, Y), Y a d Y, including an appro-r priate dynamic'. factor, shall be used unless a time-history analysis is performed to justify otherwise.
Both cases of L having its full value, possibly present during the
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I pipe rupture event, or being completely absent should be checked for.
For combinations (2) and (3), local stresses due to the concentrated loads Y,, Y) and Y,, may exceed the allowables provided there will be no loss of function of any safety-related system.
E::isting structures will have to be checked and evaluated for the above three co=binations. The failure capacity of concrete structures
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-S-The combined loads cay be checked by using the " Yield Line Theory."
In such should not exceed 907 of the calculated failure capacity.
situations, however, it should be verified that neither excessive deflections nor excessive cracking, will result in the loss of func-tion of any safety-related system.
- LOAD COMBINATIONS AND ACCEPTANCE CRITERIA FOR CATECORY I STEEL D.
STRUCTUPIS Category I steel structures outside the containment, whose function is to provide protection against the effects of high-energy pipe' breaks, will have to maintain their structural integrity under all credible loading conditions. To assur,e this, limits on resulting stresses or required strength capacities are recotcmended.
D.1 LOAD COMBINATIONS 7 m) If elastic working stress design methods are used:
1) 1.6 S = D + L +'T
+R
+P a
a a
+Y
+ Y ) + Feqo
_2)
- 1. 6 S = D + L + T, + R, + P, -t-1.0 (Y r
m 3) 1.6 S = D + L + T
+R
+P
+ 1.0 (Y
+Y
+ Y ) + Fegs a
a a
r n
b)
If plastic design methods are used:
1)
.90 Y = D + L + T
+R
+ 1.5 P a
a a
2)
.90 Y = D + L + T
+R
+ 1.25 P + 1. 0 (Y
+Y
+ Y ) + 1.25 Feqo a
a a
r a
3)
.90 Y = D + L + T
+R
+ 1.0 P, + 1.0 (Y. + Y + Y ) + 1.0 Fegs j
r m
a a
o In co abinations D.1(a) and (b),therrtal loads can be neg1ceted when it can ba sha en that they are secondary and self-limiting in nature and whara the catarial is ductile.'
b g.
In combinations (1), (2) and (3), the maximum values of P,, T, R,,
Y), Y and Y,, including an appropriate dynamic f actor, shall be used unless a time-history analysis is performed to justify otherwise.
1 Both cases of L having its full value, possibly present during the pipe rupture event, or being completely absent should be checked for.
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For combinations (2) and (3), local stresses due to the concentrated and Y, may exceed the allowables provided there will be loads Y,, Y3 no loss of function.
Furthermore, in computing the required section strength, S, the plastic section modulus of ste'el shapes may be used.
Existing structures will have to be checked and evaluated"for the above three combinations. The.0.90 reduction factor applied en the
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required section strength, Y, car, b'e increased to 1.0.. In such situa-tions, hcwever, it should be verified that excessive deflections will not result in the loss of function of any safety-related system.
E.
,/.CCEPTABLE PROCEDURES FOR DETEP?IINATION OF THE EFFECT OF AN DIPACTING_
kHIPPING PIPE ON CONCRETE AUD STEEL STRUCTURES If pipe whipping is permitted and if the whipping pipe can impact a barrier whose structural integrity has to be maintained during and after the event of the pipe rupture, the barrier will have to be designed to resist that impact.
Essentially, the impacting pipe can be considered as a missile for which the follo::ing parameters can be defined:
impact velocity, impact equivalent area and equivalent
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.. mass of the missile.
Procedures used in deter =ining these parameters are outside the scope of this docunent. Missile barriers, whccher concrete or steel, should have. sufficient strength to stop the pos:u-lated missile. To accomplish this objective, prediction of local and overall damage due to missile impact is necessary.
P Local da= age prediction, in the i= mediate vicinity of the impacted area, includes estimation of the depth of penetration and whether secondary missiles might be generated by spalling in case of concrete targets. Overall damage prediction includes ed.timation of the struc-tural response of the target to the missile impact, including struc-tural stability and deformations.
E.1 LOCAL DAMAGE PREDICTION a)
In Concrete There are several empirical equations available to. estimate missile penetration into concrete targets. The cost commonly W
used is the modified Petry equation, as given by A. Amirikian in
" Design of Protective Structures," Bureau of Yards and Docks, NP-3726 (1950). This equation, having been widely used, is presently acceptable.
Should other equations, however, be used, the level of conservatism in these equations should be co= parable to that of the modified Petry equation.
Actual testing for deter-cining penetration in concretc is acceptable.
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. b)
In Secel~
Extensive series of tests were conducted by the Stanford Research The Institute on penetration of missiles into steel' plates.
results of these_ tests were sunmarized by W..B. Cottrell and A. W. Savolainen in Chapter 6 of Vol. 1 of U. S. Reactor Contain-"
ment Technology, ORNL-NSIC-5. Equations for penetration of missiles into steel plates presented in this chapter,'having been widely used, are presently acceptable.. Should other equations, however, be used, the level of conservatis,m in these equations shall Actual testing for be comparable to that of those mentioned above.
determining penetration in steel is acceptable.
E.2 OVERALI, DAMACE PREDICTION The response of a structure to a missile impact depends largely on the location of impact, e.g., midspan of a slab or near the support, on the dynamic properties of the target and missile and on the
, kinetic energy of the missile.
In general, it will be conservative to absorb all the missile kinetic energy into structural strain energy in the target. Ecwever, energy losses due to missile deforma-tion and local penetration cay be accounted for.
After a check has been =ade on whether the missile will penetrate the barriar or not, an equivalent static 1 cad can be determined fro =
which the structural response, in conjunction with other loads that
might be present, can then be evaluated using conventional methods.
Im acceptable procedure for such an analysis is presented in a paper by U1111c= son and Alvy, of Holmes and Narver, Inc. entitled " Impact Effects of Fragments Striking Structural Elenents," NP-6515 (1957).
Should other methods be used, however, the level of conservatism in these methods should be comparable to that of those mentioned above, a
F.
ACCEPTABLE PROCEDURES FOR DESIGN OF STRTICTURAL PIPE RESTRAINTS Protection of Category I structures, systuns and components frez the dynamic effects of postulated high-energy pfpu~ ruptures can be accomplished 'in some situations by' providing pipe restraints in critical locations on the piping systems. These restraints should function uinly by preventing the ruptured pip % or portions thereof, from becoming a missile that might impact and d===ge other critical systems, and by preventing the ruptured pipe from whipping and impact-ing critical systenar not. capable of resisting such' an impact.
The strestraints may be independent of dead and live load supports and of seismic restraints. However, should a pipe whip restraint be intended to function also as an operating dead load and/or seismic restraint, 1
all applicable loads should be considered in the design of the restraint.
?.1 M*ALYSIS METHOD The structural analysis of pipe restraints may consist of an energy-bal2nce approach, where a potential collapse mechanism is first 4
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established. The displacement of this c,echanism will reach its licit.,
by conservation of energy principles, when the external work avaiLGle eruals the internal work done on the restraint.
External work expressions may include kinetic expressions where cass and velocity of the ruptured pipe are known.
Internal work expressions are graphically represented by ti.e aina under a resisting force-displacement curve.
F.2 ALLOWABLE YIELD STRENGTH Due to the high rate of strain that the struct6ral restraint would experience af ter pipe rupture, and partly due to the strafn-hardening effects, the static yield strength of the material used may be increased by 15%.
F.3 ALLOWABLE STRAINS In general, strains of up to 50% of ultimate strain are acceptable,
' provided there is no loss of function. Where buckling is critical t
in compression members, the load on the members should be limited to 90% of the buckling load.
F.4 CAP EFFICT Where gaps are provided between pipes and restraints, the kinetic anergy of the pipe impacting the restraint may be crirical and shc.sid I
not be ignored.
Moreover, tha kinetic energy of the pipe after I
rebound may be core critical and should also be considered.
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F.5~ ANCHOR DESICN
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Pipe restraints should be anchored in concrete and/or steel _ structures.
Strains and/or stresses induced in the structure by loading the rescraint' h ld be considered and the design of.the structure should be checked
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- in accordance with criteria already presented in this document.
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