ML19319D545

Structural Design Criteria for Evaluating Effects of High- Energy Pipe Breaks on Category 1 Structures Outside Containment.

ML19319D545
Person / Time
Site:	Crystal River
Issue date:	07/23/1973
From:	FLORIDA POWER CORP.
To:
Shared Package
ML19319D541	List: ML19319D545
References
NUDOCS 8003170667
Download: ML19319D545 (14)

Text

- - . _ _ - . . . , . - . . . . . .

q-p.J

.. r DOCUMENT (B)

STRUCTURAL ENGINEERING BRANCH DIRECTORATE OF LICENSING STRUCTURAL DESIGN CRITERIA FOR EVALUATING THE

' EFFECTS OF HIGH-ENERGY PIPE BREAKS ON CATEGORY I STRUCTURES OUTSIDE THE CONTAINMDiT CONTENTS A. Introduction B. Loads, definition of terms and nomenclature C. Acceptable load combinations and allowable limits for Category I concrete structures D. Acceptable load combinations and allowable limits for Category I steel structures E. Acceptable procedures for decernination of the effect of an impacting whipping pipe on concrete and steel structures F. Acceptable procedures for design of structural pipe restraints 8 003170 d?j ( <

n.s... __ , _ _ .

] *j,

-- - .,- .r-~,, . . ,

. .~ i

. o; n 1

- 2- ,.

A. INTRODUCTION 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 l

environmental conditions associated with nor=al operation, maintenance,

' testing and postulated accidents. These structures shall be appro-i priately protected against dynamic ef f ects, including the effects of missiles, pipe whipping, and discharging fluids associated with postu-lated high-energy pipe rupture accidents and from events and conditions outside the nuclear power unit.

This document presents a set of acceptable criteria for evaluating i

and assuring the required protection. It is assumed that the follow-ing steps, which are not structural in nature and are thus r.ot within the scope of this document, have already been performed and the neces-sary design parameterc already defined:

1) Systems in which pipe breaks are postulated and for which pro-taction against the effects of such breaks should be provided, have been defined,

2) Locations of postulated breaks and type and orientation of each break, guillotine or longitudinal, have been determined, f

• e e + a ==r' pr. y=. e-. ==-+-e = ==

• s.am.-s a,<--.- w-aw e e a w# =-

4 ts .

t

(*,

().*

3) Protection criteria for each postulated break have been estab-lished. This should identify the structures, systema 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 protectiva barrier or a pipe restraint, including the equivalent mass, impact area and impact velocity.

P. LOADS, DEFINITION OF TERMS AND NOMENCLATURE The following nomenclature and definition of terms will apply to all the criteria that follow in this document.

All the major loads to be encountered and/or to be postulated during All the loads listed, a high-energy pipe rupture event are 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.

' *^* W As aw ,* w, n em - ,m,,.m4,,,,, _

. - _ _ _ _ . _ ..m __ _ . _ .

~

f,

.3 *

'r, #'

B.1 NORMAI 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 loads, if any.

Live loads, present during the pipe rupture event, and their L - - -

related moments and forces.

T --- Thermal loads during normal operating conditions.

R ---- Pipe reactions during normal operating conditions.

E.2 SEVERE EN'/IRO:T','TAL L0i"S Severe environmental loads are those loads that could infrequently be encountered during the plant life. Included in this category are:

Fego Loads generated by the Operating Basis Earthquake or, 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 E E RONMENTAL LOADS Extreme environmental loads are those loads which are credible but are highly improbable. They include:  ;

Feqs a Loads generated by the Safe Shutdown Earthquake.

~

l i

1 t'

~~~+=r=~-w~~~w_nw .., _, _ __ _

. . ~, ,y;

< * ' ~w ^- ~ 'r$ o y ' Q.% ~ 'g .

, , 2 4

h (l.

s u. C.

B.4 ABNOR&\L LOADS Abnormal loads are those loads generated by a postulated high-energy pipe break accident within a building and/or compartment thereof.

Included in this category are the following:

static load within or across a compart-P, --- Pressure equivalent mnrt and/or building, generated by a postulated break, and for the including an appropriate dynamic factor to account dynamic nature of the load.

T, --- Thermal loads under thermal conditions generated by a postulated break and including T .

R, --- Pipe reactions under thermal conditions generated by a postulated break and including R .

Y -- Equivalent static load on a structure generated by the reaction on the broken high-energy pipe during a postulated break, and including an appropriate dynamic factor to account for the dynamic nature of the load.

Y - - - Jet impingement equivalent static load on a structure gen-erated 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 impact equivalent erated by or during a postulated break, like pipe whipping, and including an appropriate dynamic factor to account for the dynamic nature of the load. l

-a

- s

- ~}.

and In determining an appropriate equivalent static load for P , Y , Y3 Y ,, elasto-plastic behavior may be assumed with appropriate ductility ratios and as long as excessive deflections will not result in loss of function.

B.5 OTHER DEFINITIONS S ---- For structural steel, S is the required section strength based on the elastic design methods and the allowable stresses defined in Part 1 of the AISC "Specificat.on for the Design, Fabrication and Erection of Structural Steel for Buildings,"

February 12, 1969.

U ---- For concrete structures, U is the section strength required to resist design loads and based on metheds described in ACI 318-71.

Y ---- For structural steel, Y is the section strength required to resist design loads and 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.

I 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 concrete structures outside the containment for the effects of w

.t ~.

m o

Q' : Q high-energy pipe breaks.

Concrete barriers, used to provide a shield against the ef fects of high-energy pipe breaks, will have to maintain To their structural integrity under all credible loading conditions.

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:

1) U=D+L+T +R + 1.5 P a a a

2) U=D+L+T +R a

+ 1.25 Pa + 1.0 (Y r +Y j + Y m) + 1.25 Fego a

3) U=D+L+T +R a + 1.0 Pa + 1.0 (Y r +Y j + Ym) + 1.0 Fegs a

The maximum values of aP , Ta , Ra , Y,, Y and Y , including an appro-

r priate dynamic factor, shall be used unless a time-;tistory analysis is performed to justify otherwise.

Both cases of L having its full value, possibly present during the 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

+

no loss of function of any safety-related system.

Existing structures will have to be checked and evaluated for the The failure capacity of concrete structures above three combinations.

i x = ~- g- -- , , :. . ,, . ; , . , _ _ . , _ _ _ _

77;7pm 3

~), r' v .

s may be checked by using the " Yield Line Theory." The combined loads should not exceed 90% of the calculated failure capacity. In such situations, however, it should be verified that neither excessive deflections nor excessive cracking, will result in the loss of fune-tion of any safety-related system.

D. LOAD COMBINATIONS AND ACCEPTANCE CRITERIA FOR CATEGORY I STEEL STRUCTL'RES 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 assure this, limits en resulting stresses or required strength capacities are reconmended.

D.1 LOAD COM3INATIONS a) If elastic working stress design =cthods are used:

1) 1.6S=D+L+T +R +P a a a -

2) 1.6S=D+L+T +R a

+P a

+ 1.0 (Y +Y r

+ Y ) + Feqo m

a

3) 1.6S=D+L+T +R a

+P a

+ 1.0 (Y +Y r

+ Y ) + Fegs m

a b) If plastic design methods are used:

1) .90 Y'= D + L + T a +R a + 1.5 P a

2) .90 Y = D + L + T a +R a + 1.25 Pa + 1. 0 (Yj+Y r + Y m) + 1.25 Feqo

3) .90 Y = D + L + T,+ R,+ 1.0 P + 1.0 (Y +Y + Y ) + 1.0 Feqs

- Jn combinations D.l(a) and (b), thermal loads can be neglected when it can be shown that they are secondary and self-limiting in nature and where the material is ductile.

_ . . . - m,_ _ _ ._ _ __ _- .

~ - -

~; .

. y--

c u

mass of the missile. Procedures used in determining these parameters are o'utside the scope of this document. Missile barriers, whether concrete or steel, should have sufficient strength to stop the postu-lated missile. To accomplish this objective, prediction of local and overall damage due to missile impact is necessary.

Local damage prediction, in the i= mediate vicinity of the impacted

-area, includes estimation of the cepth of penetration and whether secondary missiles might be generated by spalling in case of concrete targets. Overall damage prediction includes estimation of the struc-tural response of the target to the missile impact, including struc-tural stability and deformations.

E.1 LOCAL DAMAGE PREDICTICM a) In Concrete There are several empirical equations available to estimate missile penetration into concrete targets. The most co=monly 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 comparable to that of the modified Petry equation. Actual testing for deter-mining penetration in concrete is acceptable.

U l

l

~ ~ *~~ -~ ~ ~ ~- ,. - _ , _ . __

4

. y n b) In Steel Extensive series of tests were conducted by the Stanford Research The Institute on penetration of missiles into steel plates.

results of these tests were summarized 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 Should other equations, been widely used, are presently acceptable.

however, be used, the level of conservatism in these equations shall Actual testing for be comparable to that of these mentioned above.

determining penetration in steel is acceptable.

E.2 OVERALL DAMAGE PREDICTION The response of a structure to a missile impact depends largely on the location of impact, e.g., cidspan of a slab or near the support, on the dynamic properties of the target and =issile 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. However, energy losses due to missile deforma-I tion and local penetration may be accounted for.

After a check has been made on whether the missile will penetrate the barrier or not, an equivalent static load can be determined from

- which the structural response, in conjunction with other loads that I

1 e- .. ,

J 3 (,

might be present, can then be evaluatal using conventional methods.

An acceptable procedure for such an analysis is presented in a paper "I= pact by Williamson and Alvy, of Holmes and Narver, Inc. entitled Eff ects of Fragments Striking Structural Elements," NP-6515 (1957).

4 Should other methods be used, however, the level of conservatism in these methods should be comparable to that of those mentioned above.

F. ACCEPTABLE PROCEDURES FOR DESIGN OF STRUCTURAL PIPE RESTRAIN Protection of Category 1 structures, systems and components from the dynamic effects of postulated high-energy pipe ruptures can be accomplished in some situations by providing pipe restraints in critical locations on the piping systems. These restraints should function mainly by preventing the ruptured pipe, or portions thereof, from becomJng a missile that might impact and damage other critical systems, and by preventing the ruptured pipe from whipping and impact-The ing critical systems not capable of resisting such an impact.

restraints may be independent of dead and live load supports and of seismic restraints. However, should a pipe whip restraint bc intended to function also as an operating dead load and/or seismic restroint, all applicable loads should be considered in the design of the restraint.

F.1 ANALYSIS METHOD The structural analysis of pipe restraints may consist of an energy-balance approach, where a potential collapse mechanisa is first

• ~ ~'*w=e - m n y e. ,,,_, ,,

-r-

• ^ '

( .: b

- 14 -

F.5 ANCHOR DESIGN Pipe restraints should be anchored in concrete and/or steel structures.

Strains and/or stresses induced in the structure by loading the restraint should be considered and the design of the structure should be checked in accordance with criteria already presented in this document.

.m p**= v.ww-. . .-+*ps~,v we*- ,w - ,

,;[ -- g..,+,,, .,_y _,..,,.ww ,e _ , . - , , , _.%,

m

Oj p established. The displacement of this mechanism will reach its limit, by conservation of energy principles,4when the external work available equals the internal work done on the restraint.

External work expressions may include kinetic expressions where mass and velocity of the ruptured pipe are known. Internal work expressions are graphically represented by the area under a resisting force-displacement curve.

F.2 ALLOWABLE YIELD STRENGTH Due to the high rate of strain that the structural restraint would experience after pipe rupture, and partly due to the strain-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 in compression members, the load on the members should be limited to 90% of the buckling load.

F.4 _ GAP EFFECT Where gaps are provided between pipes and restraints, the kinetic energy of the pipe impacting the restraint may be critical and should not be ignored. Moreover, the kinetic energy of the pipe after rebound may be more critical and should also be considered.

'f* 'W P