Regulatory Guide 7.6

Stress Allowables for the Design of Shipping Cask Containment Vessels

ML13350A219
Person / Time
Issue date:	02/28/1977
From:	Office of Nuclear Regulatory Research
To:
References
RG-7.006
Download: ML13350A219 (4)

• . .:..G) .(ou@ U.~...I NUCLEAO REG"LATORY

COMMISSION'"

n e l eibruaryh1977

• OFFICE OF STANDARDS

DEV ELOPM ENT-REGULATORY

GUIDE-7.8 STRESS ALLO WABLES FOR THE DESIGNOF:SHIPPING.

CASK CONTAINMENT

VESSELS'

A. INTRODUCTION

aind thev allowthe use, of superposition in stimmingloaiding týffcfls.

De~sign stress ifltefsitiesar dL usel.Se.'tions

7 a.35:and

,,1136 Of 10 CFR Part 7.. h-bCauseLestablished naterial V tlutsfor this use ist,...ackaging..of Radioactive

.NMtaterial for Tranisport.

-in',Iih4 th 1 E'.d. C and,.bccause this impproach is...: Tr tnsport of b icUd aeon hI i niaxixmunif shear stress the~or-...'h;i6 Cert

a. un reqirementst

"t h"huni sh0,"n to .he ia cnserv ivL cSt mainttcLfthe stress"" Oi.ekaAsusd:i6?

tr'amsp0r.

radi'active materials,;-:z tha-iUep istic de re it v, ,-must."mt:

under~normal- and.hypothettcal',accident.

,to,,cxerimntal data- ,,:::: :*0h iti5sUTis uid nios tmib es'd sign criteria ac- :' '," ...-.: ..." "" -'= -, .." ".con ition

s. This

-gudd rtei C,*. .ceptah.to

.the.,N.RCstaforuse the structura

.'In current designs for the nent issels ol th:Icontainment vessels of-type B fuel casks. the nature or t d pressure:p ickages:

u sed to transpo r t irradiated nuclear :fuel. loads and the y.c.l i ,,,i (stainle.s MAlternativedesign criteria may"be used if judged ac, steel) re such tha c rle fracture ru not.cptah!-,by the NRC.staff in meeting the structural considered to p I P let Thermal ratchetting requirementsofli§7L.35 and 71.36of 10CFR Part 71. is nol consi ere Iau. I ficulies in cyindrical

B. DISCUSSION

I*N o ' "ions 3 and 7 ensure that failureAt nresent.

there are no desien standards thatican

.'e;tt~r ined vieldint.

hlid ket,* 0..,;.he directly used toevaluate the structurhl integrity or f:Affil ticcur. Secondarv stresses (i.e.. stiesse:the -contairieinnt

%lessels of shippingcaksfrr not considered to cause....radiated ruecls. How-vcr.

"Section AIl or~he. A E ""-T~l' ieidingar

'ni nsiee oc'sradiated.fuel.

H eergro s unrestrained Ni-ldbng-hut.

are :considered inBoiler*and Pressure Vessel Code.* n a fatiuu and shakedow n .mnlmls*ments.for thi design of nuclear power it. n cormnents. "The staff has.adaptcd pbrtions of S tion lOf Regulatory Position

4 ensures that fatigue failure"r d csnt Positio 5n cmtr ensure.,the to'form acceptabled eria oe notoccur and Reulat Position..for shippiing c, k containment.:vessels.

In I.I guide. .that- the structureswill shake down to elastic behavior criteria for.s mcask containment Vest :after afew c\ cles. Both of these positions deal only*.st~ls ~r..normal conditii

( fined in 10 CFR Part ..ithehstress rane of normal operation.

A reduc-71). are'.similar Ntgcdi r ctr, ia-in Section III of tion. in the aIIowitble stress for-lire exceeding.10'

-cv-the ASME.Co fo 'as. components under nor- : ces is specificd:in, Reulator, Position

4 since:use of* al condj* n and I de ign criteria for.* accident the~ 10:Cvclycvalue for greater lives* mnia not preservecondit'fr those for-faulted conditions an amdequate design margin for all cases.inw the ý' Co .. a, :) :': :The desit criteria

.presented hcre arc basedprimnarily on lin ear elastic analyses.

Linear..

elasticanalyses are simpler than truc elastic-plastic analyses.

"'Copies may be obtained;

from. the American.

Society orMechanical Engineers, United Engineering Center. 345 East 47thStreet. New York. N.Y. 1001

7. Regulatory Position

8 places a limit on the extremerance of.tht tot ilstresses due to initial fahrication and the norial: opr ating and accident states ol" thecontainment vesseLThe followking terms are presented with the delini-tions used in this guide:U N CREGULATORY

G IDES, t~i C~lnik'tn

011411IdW

-1 14.1~ , 111:- Slwict..9l v I IN Ot,:t.'-.'

icfJ;.'tt.

thu~itr ie l! iý" ~totE ,git,,meine!

jiý tiaks~e a uiart~.t the pulcmethodss~

faluly o40tt4ih"llI

.,2blA-1-1D~

!";--11S1

1tS t ottt Jet4 lt .iii ffl ttvttil In, the. 4 fl4in to aliln Slc ii Rt, ittn Gublern.;a'! nut ast.etit uvts fto re04llt tons, antl 0.tintI.iflrp wilth tt14Cm isno, rftwified.

1. I'owl,- flea Jtu% I.. Pttoijur'l v1,1 tiltsoulno4s dif1levent front thousi %410nutin itte,?quitil"

will ile .IVcet.t

2. Rnse..11t It,%. Tlst R,,ictms

7. T ,s~~ttc,A .bif .th tI~novie a~~, I t,,u In, the Instltitjs mln~us~tp

4 tho tim sulatee or conflniiunce

3., Fuets ntrol Maim ,,ts F itte a .de ocuil.outn.t11 Iat peri or jw., Ir itm Coirmivor,

-..4, Env,,tinnwntatl anti Sitirnl 9, Anfn,,ttstH'

Corntnnts an'l %urfgvit tris Inimpntfltewtflit%-

iti ttiev- Otatidi .14 encautav.id at allfim. and.rpotle.

o ,nflf.ix:t.,u, t*-4. tlnnt ti1av. Cotl -nimiatS

cieihls d R...ttess It, Is~nifle.

1r-o1nýIII-W

ii-0 swet ll t 4wr % As,,rh 116v, Iii4.!~w,'it t 41 .to 1,41 lectri" Inom to orniwrrv.

Ho 'w .C4 1t n on th is q idjif men!,t 0n .40 *tunslntiidtt t i lml4.1 4ti Ii timtli SI t. tt,, , ilIthlefittS

nett.autt ott tt,. t.4eil tor an .6irv s.it,. W.0st~o .. U.C, 205!bg. Al ttrit-ri

., -U,. ,twt .ofit Dot T11i.111en

11:.1,oo,,

0 .

I. Stress intensity'

is defined as twice the maximumshear stress and is equal to the largest algebraic dif-ference between any two of the three principal stres-ses.2. A primary stress is a stress that is necessary tosatisfy the laws of equilibrium of forces and momentsdue to applied loadings, pressure loadings, and body(inertial)

loadings.

Primary stresses are not self-limiting because local yielding and minor distortions do not reduce the average stress across a solid sec-tion.3. A secondary stress is a stress that is self-limiting.

Thermal stresses are considered to be secondary stresses since they are strain-controlled rather thanload-controlled, and these stresses decrease asyielding occurs.The bending stress at a gross structural discon-tinuity, such as where a cylindrical shell joins a flathead, is generally self-limiting and is considered to bea cecondary stress. However.

when the edge momentat the shell and head junction is needed to prevent ex-cessive bending stresses in the head, the stress at thejunction is cons'idered to be a primary stress. Thebending stress at a joint between a rectangular shelland a flat head is unrestrained by hoop effects andwill be considered to be a primary stress.4. Primary membrane stresses are the average nor-mal primary stresses across the thickness of a solidsection.

Primar.1 bendingk stresses are the components of the normal primary stresses that vary linearlyacross the thickness of a solid section.5. The alternating stress intensity.

Salt- is definedas one-half the maximum absolute value of S 12, S,).,S'I. for all possible stress states i and j where oa., a02and u3 irc principal stresses andSC2= (Oi -frlj) -(o2i -'2j)S!3 = (a -a2j )" (03i -a3)Sit. (3i -a3j)-(ali

-Or1j)* 1, etc., follow the principal stresses as their direc-tions rotate if the directions of the principal stressesat a point change during the cycle.6. The phrase stresses caused b ' stress concentra- tions refers to increases in stresses due to localgeometric discontinuities (e.g., notches or local ther-mal "hot spots").

These stresses produce nonoticeable distortions.

7. TIpe B quantitv isdefined in §71.4(q)of

10CFRPart 71. Normal conditions of transport andhypothetical accident conditions are defined in Appen-dices A and B, respectively, to 10 CFR Part 71.8. Containmeni vessel is defined as the receptacle on which principal reliance is placed to retain theradioactive material during transport.

C. REGULATORY

POSITIONThe following design criteria are acceptable to theNRC staff for assessing the adequacy of designs forshipping cask containment vessels in meeting thestructural requirements in §§71.35 and 71.36 of 10CFR Part 71.I. The values for material properties.

design stressintensities (Sil), and design fatigue curves for Class Icomponents given in Subsection NA of Section III ofthe ASME Boiler and Pressure Vessel Code should beused for the materials listed in that subsection.

Formaterials not listed there, the method discussed inArticle 111-2000

of Subsection NA should be used toderive design stress intensity values. ASTM materialproperties should be used, if available, to derivedesign stress intensity values. The values of materialproperties that should be used in the structural analysis are those that correspond to the appropriate temperatures at loading.2. Strain-rate-sensitive material properties may beused in the evaluation of impact loading if the valuesused are appropriately considered in a dynamic time-dependent analysis and can be suitably justified in thelicense application.

When strain rate sensitivity is considered in thestructural response to a combination of static anddynamic loads, the static portion of the stresses andstrains should be analyzed separately using staticmaterial properties and should meet the static designcriteria.

The total stress and strain state resulting from both static and dynamic loads should meet thedesign criteria for which strain-rate-sensitive materialrroperties (e.g., yield strength)

are substituted forstatic values.3. Under normal conditions the value of the stressintensity resulting from the primary membrane stres-ses should be less than the design stress intensity, Sm,and the stress intensity resulting from the sum of theprimary membrane stresses and the primary bendingstresses should be less than 1.5Sm.4. The fatigue analysis for stresses under normalconditions should be performed as follows:a. Salt is determined (as defined in the "Discus-sion"). The total stress state at each point in the nor-mal operating cycle should be considered so that amaximum range may be determined.

b. The design fatigue curves (Figures

1-9.0) ofSection III of the ASME Boiler and Pressure VesselCode should be used. These curves include the max-imum mean stress effect.7.6-2 c. Salt should be multiplied by the ratio of themodulus of elasticity given on the design fatiguecurve to the modulus of elasticity used in the analysisto obtain a value of stress to be used with the designfatigue curves. The corresponding number of cyclestaken from the appropriate design fatigue curve is theallowable life if only one type of operational cycle isconsidered.

If two or more types of stress cycles areconsidered to produce significant stresses, the rulesfor cumulative damage given in Article NB-3222.4 ofSection III of the ASME Boiler and Pressure VesselCode should be applied.d. In the analysis of high cycle fatigue where thenumber of cycles exceeds 104 cycles, the ASMEdesign fatigue curves should be extended using a 4%decrease in the allowable stress per decade, startingfrom the IO0 cycle value. High cycle fatigue could be apotential problem due to vibration during transpor- tation.e. A value of 4 should be used as the maximumstress concentration factor in regions where this fac-tor is unknown.5. The stress intensity, Sn, associated with therange of primary plus secondary stresses under nor-mal conditions should be less than 3Sm. The calcula-tion of this stress intensity is similar to the calculation of 2Salt; however, the effects of local stress con-centrations that are considered in the fatigue calcula-tions are not included in this stress range.The 3Sm limit given above may be exceeded ifthe following conditions arc met (these conditions can generally be met only in cases where the secon-dary bending stresses are a substantial portion of thetotal stress):a. The range of stresses under normal condi-tions excluding stresses due to stress. concentrations and secondary bending stresses yields a stress inten-sity, Sn, that is less than 3Sm.b. The value Sa used for entering the designfatigue curve is multiplied by the factor Ke, where:Ke = 1.0 (Snr < 3Sm)(I-n) (Sn _ I=1.0+ n(m- ik3Sm 1_(3Sm<Sn<3mSm)=1 (Sn -.3mSm)n nSn is as described in a.The values of the material parameters m and n aregiven for the various classes of materials in the fol-lowing table:Low Alloy SteelMartensitic Stainless StecCarbon SteelAustenitic Stainless SteelNickel-Chromium-Iron m n Trnax.0 F2.0 0.2 7002.0 0.2 7003.0 0.2 7001.7 0.3 8001.7 0.3 800c. The temperatures do not exceed those listedin the above table for the various classes of materials.

d. The ratio of the minimum specified yieldstrength of the material to the minimum specified ultimate strength is less than 0.80.6. Buckling of the containment vessel should notoccur under normal and accident conditions.

7. Under accident conditions, the value of thestress intensity resulting from the primary membranestresses should be less than the lesser value of 2.4Smand 0.7Su (ultimate strength):

and the stress intensity resulting from the sum of the primary membranestresses and the primary bending stresses should beless than the lesser value of 3.6Sm and Su..8. The extreme total stress intensity range betweenthe initial zero stress state, fabrication, normal opera-tion. and accident conditions should be less thantwice the adjusted value (adjusted to account formodulus of elasticity at the highest temperature)

ofSa at 10 cycles given by the appropriate design fatiguecurves.A value of 4 should be used as the maximumstress concentration factor in regions where this fac-tor is unknown.9. In some cask designs.

shielding materials applyloads through differential thermal expansion or supp-ly additional strength to the containment vessel. Insuch cases, shielding materials that have low yieldstrengths (e.g., lead) may be structurally analyzed us-ing an elastic-plastic technique while the inner shell isanalyzed by a linear elastic analysis.

When uranium isused for shielding and is needed to add strength to thecontainment vessel, the fracture behavior of theuranium shielding should he considered.

7.6-3 Ii .D0

J. IMPLEMENTATION

1I,-pUrp'os o N his section.

is to provide infornma-

16n , .:ppIIýl Ints:- lien ezs rardingj the N RCstahrt~.

plan wror Lil.i n .this regulatory guide.I w.-.cpt in thl %L t.s case i n h~ich thL dfplpic nt 'oricnu proposes

.mndmet.ptatl ahk letrilativt method.t'or conilpI\

ing;wtth

,pecified portions ol*.tht Conmris%I.J)NITED

STATES* NUCLEAR REGULATO11Y

COMMISSION

INAS H IN rTON; D. C. 20555* OFFICIAL

BUSINESSPE~NALTY

IFOR PRIVATE USE. S300sions regulahtions.,

the design criteria described herein%, ill be used bh the starr mter October I .1977. in as-.se.sing the. adequacy or designs.

ur coiltainnient:.,ces-

" LI 0l" packages for shipping irradiated fuel withrespect to the structural rcquiremcnis in and7.1-36 .of I..CI"R.

Part7 71. When alternative criteria.roposed...ti.applicant or licensee shoulddenitinrtr tl'heir use satisfies the: requirements of -§,7 T3 5mAnd 71 36 o 1 10 CF R Part .71.POSTAOE AND FEEs PAID I*NUCLAR RC.ULA.ORV

COMMISSION

'00