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 DESIGN OF:SHIPPING.

CASK CONTAINMENT

VESSELS'

A. INTRODUCTION

aind thev allowthe use, of superposition in stimming loaiding 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 Certa.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 failure At 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's radiated.fuel.

H eergro s unrestrained Ni-ldbng-hut.

are :considered in Boiler*and Pressure Vessel Code.* n a fatiuu and shakedow n .mnlmls*ments.for thi design of nuclear power it. n corm nents. "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 preserve condit'fr those for-faulted conditions an amdequate design margin for all cases.inw the ý' Co .. a, :) :': : The desit criteria :.presented hcre arc based primnarily on lin ear elastic analyses.

Linear.. elastic analyses are simpler than truc elastic-plastic analyses."'Copies may be obtained;

from. the American.

Society or Mechanical Engineers, United Engineering Center. 345 East 47th Street. New York. N.Y. 10017.Regulatory Position 8 places a limit on the extreme rance of.tht tot ilstresses due to initial fahrication and the norial: opr ating and accident states ol" the containment vesseL The 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 re 0 4 llt 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 I at 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 all fim. 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.4 eil 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 maximum shear 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 to satisfy the laws of equilibrium of forces and moments due 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 than load-controlled, and these stresses decrease as yielding occurs.The bending stress at a gross structural discon-tinuity, such as where a cylindrical shell joins a flat head, is generally self-limiting and is considered to be a cecondary stress. However. when the edge moment at the shell and head junction is needed to prevent ex-cessive bending stresses in the head, the stress at the junction is cons'idered to be a primary stress. The bending stress at a joint between a rectangular shell and a flat head is unrestrained by hoop effects and will be considered to be a primary stress.4. Primary membrane stresses are the average nor-mal primary stresses across the thickness of a solid section. Primar.1 bendingk stresses are the components of the normal primary stresses that vary linearly across the thickness of a solid section.5. The alternating stress intensity.

Salt- is defined as one-half the maximum absolute value of S 12, S,)., S'I. for all possible stress states i and j where oa., a02 and u 3 irc principal stresses and SC2= (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 stresses at a point change during the cycle.6. The phrase stresses caused b ' stress concentra- tions refers to increases in stresses due to local geometric discontinuities (e.g., notches or local ther-mal "hot spots"). These stresses produce no noticeable distortions.

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

10CFR Part 71. Normal conditions of transport and hypothetical 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 the radioactive material during transport.

C. REGULATORY

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

design stress intensities (Sil), and design fatigue curves for Class I components given in Subsection NA of Section III of the ASME Boiler and Pressure Vessel Code should be used for the materials listed in that subsection.

For materials not listed there, the method discussed in Article 111-2000 of Subsection NA should be used to derive design stress intensity values. ASTM material properties should be used, if available, to derive design stress intensity values. The values of material properties 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 be used in the evaluation of impact loading if the values used are appropriately considered in a dynamic time-dependent analysis and can be suitably justified in the license application.

When strain rate sensitivity is considered in the structural response to a combination of static and dynamic loads, the static portion of the stresses and strains should be analyzed separately using static material properties and should meet the static design criteria.

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

are substituted for static values.3. Under normal conditions the value of the stress intensity 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 the primary membrane stresses and the primary bending stresses should be less than 1.5Sm.4. The fatigue analysis for stresses under normal conditions 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 a maximum range may be determined.

b. The design fatigue curves (Figures 1-9.0) of Section III of the ASME Boiler and Pressure Vessel Code should be used. These curves include the max-imum mean stress effect.7.6-2 c. Salt should be multiplied by the ratio of the modulus of elasticity given on the design fatigue curve to the modulus of elasticity used in the analysis to obtain a value of stress to be used with the design fatigue curves. The corresponding number of cycles taken from the appropriate design fatigue curve is the allowable life if only one type of operational cycle is considered.

If two or more types of stress cycles are considered to produce significant stresses, the rules for cumulative damage given in Article NB-3222.4 of Section III of the ASME Boiler and Pressure Vessel Code should be applied.d. In the analysis of high cycle fatigue where the number of cycles exceeds 104 cycles, the ASME design fatigue curves should be extended using a 4%decrease in the allowable stress per decade, starting from the IO0 cycle value. High cycle fatigue could be a potential problem due to vibration during transpor-tation.e. A value of 4 should be used as the maximum stress concentration factor in regions where this fac-tor is unknown.5. The stress intensity, Sn, associated with the range 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 2 Salt; however, the effects of local stress con-centrations that are considered in the fatigue calcula-tions are not included in this stress range.The 3 Sm limit given above may be exceeded if the following conditions arc met (these conditions can generally be met only in cases where the secon-dary bending stresses are a substantial portion of the total 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 3 Sm.b. The value Sa used for entering the design fatigue curve is multiplied by the factor Ke, where: Ke = 1.0 (Snr < 3 Sm)(I-n) (Sn _ I=1.0+ n(m- ik3Sm 1_(3 Sm<Sn<3 mSm)=1 (Sn -.3 mSm)n n Sn is as described in a.The values of the material parameters m and n are given for the various classes of materials in the fol-lowing table: Low Alloy Steel Martensitic Stainless Stec Carbon Steel Austenitic Stainless Steel Nickel-Chromium-Iron m n Trnax.0 F 2.0 0.2 700 2.0 0.2 700 3.0 0.2 700 1.7 0.3 800 1.7 0.3 800 c. The temperatures do not exceed those listed in the above table for the various classes of materials.

d. The ratio of the minimum specified yield strength of the material to the minimum specified ultimate strength is less than 0.80.6. Buckling of the containment vessel should not occur under normal and accident conditions.

7. Under accident conditions, the value of the stress intensity resulting from the primary membrane stresses should be less than the lesser value of 2.4Sm and 0.7Su (ultimate strength):

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

of Sa at 10 cycles given by the appropriate design fatigue curves.A value of 4 should be used as the maximum stress concentration factor in regions where this fac-tor is unknown.9. In some cask designs. shielding materials apply loads through differential thermal expansion or supp-ly additional strength to the containment vessel. In such cases, shielding materials that have low yield strengths (e.g., lead) may be structurally analyzed us-ing an elastic-plastic technique while the inner shell is analyzed by a linear elastic analysis.

When uranium is used for shielding and is needed to add strength to the containment vessel, the fracture behavior of the uranium 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 RC stahrt~. plan wror Lil.i n .this regulatory guide.I w.-.cpt in thl %L t.s case i n h~ich thL dfplpic nt 'or icnu 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 BUSINESS PE~NALTY IFOR PRIVATE USE. S300 sions 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 with respect to the structural rcquiremcnis in and 7.1-36 .of I..CI"R. Part7 71. When alternative criteria.roposed...ti.applicant or licensee should denitinrtr 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

'0 0