Regulatory Guide 7.8: Difference between revisions

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{{Adams
{{Adams
| number = ML003739501
| number = ML13350A233
| issue date = 03/31/1989
| issue date = 05/31/1977
| title = (Task Ms 527-4 and Ms 804-4), Load Combinations for Structural Analysis of Shipping Casks for Radioactive Material
| title = Load Combinations for the Structural Analysis of Shipping Casks
| author name =  
| author name =  
| author affiliation = NRC/RES
| author affiliation = NRC/OSD
| addressee name =  
| addressee name =  
| addressee affiliation =  
| addressee affiliation =  
Line 10: Line 10:
| license number =  
| license number =  
| contact person =  
| contact person =  
| document report number = MS 527, MS 804-4, Reg Guide 7.8, Rev 1
| document report number = RG-7.008
| document type = Regulatory Guide
| document type = Regulatory Guide
| page count = 7
| page count = 5
}}
}}
{{#Wiki_filter:U.S. NUCLEAR REGULATORY  
{{#Wiki_filter:U.S. NUCLEAR REGULATORY  
COMMISSION  
COMMISSION
Revision 1 March 1989 REGULATORY  
May 1977 REGULATORY  
GUIDE OFFICE OF NUCLEAR REGULATORY
GUIDE OFFICE OF STANDARDS
RESEARCH REGULATORY  
DEVELOPMENT
GUIDE 7.8 (Tasks MS 527-4 and MS 804-4) LOAD COMBINATIONS  
REGULATORY  
GUIDE 7.8 LOAD COMBINATIONS  
FOR THE STRUCTURAL  
FOR THE STRUCTURAL  
ANALYSIS OF SHIPPING CASKS FOR RADIOACTIVE
ANALYSIS OF SHIPPING CASKS  
MATERIAL


==A. INTRODUCTION==
==A. INTRODUCTION==
Section 71.71, "Normal Conditions of Trans port," and Section 71.73, "Hypothetical Accident Conditions," of 10 CFR Part 71, "Packaging and Transportation of Radioactive Material," describe normal conditions of transport and hypothetical acci dent conditions that produce thermal and mechanical loads that serve as the structural design bases for the packaging of radioactive material for transport.
Appendix A, "Normal Conditions of Transport," and Appendix B, "Hypothetical Accident Con-ditions," of 10 CFR Part 71, "Packaging of Radioac-tive Material for Transport and Transportation of Radioactive Material Under Certain Conditions." describe normal conditions of transport and hypothetical accident conditions that produce ther-mal and mechanical loads that serve as the structural design bases for the packaging of radioactive material for transport.


Initial conditions must be assumed before analy ses can be performed to evaluate the response of structural systems to prescribed loads. This regulatory guide presents the initial conditions that are consid ered acceptable by the NRC staff for use in the struc tural analysis of Type B packages used to transport radioactive material in the contiguous United States. Any information collection activities mentioned in this regulatory guide are contained as requirements in 10 CFR Part 7 1, which provides the regulatory ba sis for this guide. The information collection require ments in 10 CFR Part 71 have been cleared under OMB Clearance No. 3150-0008.
However, initial conditions must be assumed before analyses can be performed to evaluate the response of structural systems to prescribed loads.This regulatory guide presents a set of initial condi-tions that is considered acceptable by the NRC staff for use in the structural analyses of type B packages used to transport irradiated nuclear fuel in the con-tiguous United States. The values in this set supple-..:
ment the normal conditions and the hypothetical ac-cident conditions of the regulations in forming-r.a..
more complete basis from which structural intigrity.
 
may be assessed.


==B. DISCUSSION==
==B. DISCUSSION==
To ensure safe structural behavior of shipping casks used to transport radioactive material, specific load conditions must be established that will encom pass the static, dynamic, and thermal loadings that may be experienced by the casks during transport.
To ensure safe structural behavior of shipping casks used to transport irradiated nuclear fuel, specific load conditions must be established that will encompass the static, dynani-ic, and thermal loadings that may be experiencl.d,by.:the.casks during trans-port, This regulatory.guide presents initial conditions that can be used ididddition to parts of Appendices A and B of 10 CER Par "ý7.1 to fully delineate thermal and mechanicalibad combinations for purposes of structural.'analysis'7.4tis intended that this guide be used in conjunction with Regulatory Guide 7.6,"Stress All0owiobles for the Design of Shipping Cask Containment Vessels," for the analytic structural evaluation of the heavy (i.e., several tons in weight)casks used to transport irradiated nuclear fue
 
This regulatory guide presents initial conditions that USNRC REGULATORY
GUIDES Regulatory Guides are issued to describe and make available to the pub lic methods acceptable to the NRC staff of Implementing specific parts of the Commission s regulations, to delineate techniques used by the staff In evaluating specific problems or postulated accidents, or to pro vide guidance to applicants.
 
Regulatory Guides are not substitutes for regulations, and compliance with them Is not required.
 
Methods and solutions different from those set out in the guides will be acceptable if they provide a basis for the findings requisite to the issuance or continu ance of a permit or license by the Commission.
 
This guide was issued after consideration of comments received from the public. Comments and suggestions for improvements in these guides are encouraged at all times, and guides will be revised, as ap propriate, to accommodate comments and to reflect new information or experience.
 
Written comments may be submitted to the Regulatory Publications Branch, OFIPS, ARM, U. S. Nuclear Regulatory Commission, Washing ton, DC 20555.can be used in addition to parts of §§ 71.71 and 71.73 of Part 71 to fully delineate thermal and me chanical load combinations for purposes of structural analysis.
 
This guide should be used in conjunction with Regulatory Guide 7.6, "Design Criteria for the Structural Analysis of Shipping Cask Containment Vessels," for the analytical structural evaluation of the heavy (i.e., weighing several tons) casks used to transport irradiated nuclear fuel.  Regulatory Position 1.1 of this guide addresses initial environmental conditions.


The external ther mal environmental limits for which a shipping cask must be designed are stated in § 71.71 as being 100'F (38'C) in direct sunlight and -40*F (-40'C) in shade. The regulations specify that these two nor mal conditions are to be applied separately from the other normal conditions.
====l. USNRC REGULATORY ====
GUIDEStL' ait: tiueci ii tit cl-1 0,- h itl1110 P ,Ae wmlablv to the 1)U.btl mrithth$ds awM~l to , hi WINC %tallci itIneit li ~ all'ci .W~n rl i,'Corv ~ so rf.ev %h,0)r1s.


For the other conditions of § 71.71 and for the hypothetical accident conditions, this guide presents a range of ambient temperatures from -20*F (-29°C) to 100'F (38QC) as a part of the initial conditions.
to tfhl0 .lct' defltn s umit ty tht, .f th I i:j.tl i , gceýIw ic tobwmtceri Wi twIl uittil aCCciil'nl%.
4 t, i t mlrivctdi quid.-ur t m .i i , it fleq, s lixu,, G jKles, Me ,lot u l fw,, timlln.licllfl. '.nlri fthii ' ivutim thetn is riot ,etaclmI 't- .M,'llhotis Indl Qilufirrtms ifihll ont trall. thos' set owi it, the qultu? m. Il tvi .lhe Cctl.dblbe I ti-V 1ri uviltv .) ts.oSl for the lrndiiii l.ui to the or COfli liuWarCC of a pmemil or licenw bv On Corrrnit n anrd Surpj t,! li iin% fant l OVei irit itI t i i. i rqii ides are eicouiaqd at e11 f1M. , aril guilt tihl Ih' r..v.lt. a ,lcitrt)a wo l-ate. to .t: ioiii e.i1irieits  t0 itect t ~,," l ii.tilot itO -iii ' t. t 'ne,. Ho,,,etm'vm
.cornilmiit IIti thus gimlti',il ecrivei( imitt.... .i lw.' t t in tht .0ell. ,, its Will tIw icutllly I1 '.is4 itw Regulatory Position C.I.a of this guide mentions environmental initial conditions.


In the contiguous United States, there is a 99.7 percent probability that any hourly temperature reading will fall within this range.' Regulatory Position 1.3 addresses initial pressure conditions.
The external ther-mal environmental limits for which a shipping cask must be designed are stated in Appendix A of 10 CFR Part 71 as being 130°F (54 0 C) in direct sunlight and -40°F (-40'C) in shade. These limits are applied without an)y additional loading. For the other condi-tions of Appendix A and for tht hypothetical acci-dent conditions, this guide:presents a range of am-bient temperatures.


The pressure inside the containment vessels and neutron shields of irradiated fuel shipping casks depends on several factors. These factors include prepressurization of the vessels, the cask I M. B. Gens, The Transportation and Handling Environment, SD-DC-72-1386, Sandia Laboratories, Albuquerque, New Mexico, September
from -20°F (-29 0 C) to 1000F (38'C) as a part of the initial conditions.
1972.The guides are Issued in the following ten broad divisions:
1. Power Reactors 2. Research and Test Reactors 3. Fuels and Materials Facilities
4. Environmental and Siting 5. Materials and Plant Protection
6. Products


===7. Transportation ===
In the con-tiguous United States.there Is a 99.7 percent probability that, any hourly temperature reading will fall within this range (Ref. l).The insolation data provided in'.the International Atomic Energy Agency's safet)"standards (Ref. 2) have been adopted for this guide.because they have sufficient conser-vatism When. compared with other solar radiation data (RCf. 3)..- Regulatory Position C. I.c mentions initial pressure c.,,onditions.
8. Occupational Health 9. Antitrust and Financial Review 10. General Copies of issued guides may be purchased from the Government Printing Office at the current GPO price. Information on current GPO prices may be obtained by contacting the Superintendent of Documents, U.S. Government Printing Office, Post Office Box 37082, Washington, DO 20013-7082, telephone
(202)275-2060
or (202)275-2171.


Issued guides may also be purchased from the National Technical infor mation Service on a standing order basis. Details on this service may be obtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 22161.
It should be noted that the pressure inside."the containment vessels and neutron shields of ir-radiated fuel shipping casks depends on several fac-tors. These factors include pre-pressurization of the vessels, the cask temperature distributions associated with the ambient temperatures and the decay heat of the fuel rods, and any gas leakage from the nuclear fuel rods.Regulatory Position C. .e states that the values for initial conditions given in this guide are maximums or minimums.


temperature distributions associated with the ambient temperatures and the decay heat of the irradiated fuel, and any gas leakage from such fuel. Regulatory Position 1.5 addresses the possibility that fabrication and installation stresses may result during cask construction.
However, intermediate values could pos-sibly create a more limiting case for some cask designs. For example, a seal design might be more susceptible to leakage at a pressure less than the max-imum internal pressure, or a local structural response might be greater during an impact test if the weight of the contents was less than the maximum.Appendices A and B of 10 CFR Part 71 outline re-quirements for packages used to transport type B quantities of radioactive materials.


These stresses depend on many different processes and should be considered when evaluating the casks. Regulatory Position 1.6 states that the values for initial conditions given in this guide are maximums or minimums.
Some of these re-AII -11-ts' %bo1ullf % l lH ie. n 4 I.t.'t .!tfq tt { .,;"11 " &'itw llt u ........... ,U S .t#,4 , l' l -*' vi 3. I ueli tol Mitet .,I, F.it'ilit=.e II Oiicc.it~u~llul~
IW.:.lrth 2. tA.ttet dc -il L ,%i m Pii. tT ... tO. ( ,mutt....v..Jit $ lit h iii I ., 1"t , i l e it ... U .. N &l li. i.iii ci Cif J- m tnI  V~ij-tiiri t.uti .C. ?055S,. Api t ii D--11-11i1ucicc m. ~im'i i.imii quirements do not pertain to irradiated fuel shipping casks, however, because of the heaviness of the casks or because the requirements are not structurally significant to cask design. Casks that are designed to transport one or. more commercia'
fuel assemblies weigh many tons because of the large quantities of structural and shielding materials used. This mas-siveness causes a shipping cask to have a slow ther--Mal response to sudden external temperature changes such as those that might be produced by quenching after a thermal exposure.


However, intermediate values could pos sibly create a more limiting case for some cask de signs. For example, a seal design might be more sus ceptible to leakage at a pressure less than the maxi mum internal pressure, or a local structural response might be greater during an impact test if the weight of the contents were less than the maximum.
The NRC staff feels that the water immersion test of Appendix B and the water spray test of Appendix A are not significant in the structural design of large casks. Therefore, they are not discussed in this guide. (Note, however, that these conditions may be significant to criticality and other nonstructural aspects of cask design.)Similarly, the corner drop and the compression tests of Appendix A are not discussed because they pertain only to lightweight packages.


Sections 71.71 and 71.73 of Part 71 outline re quirements for packages used to transport Type B quantities of radioactive materials.
The penetration test of Appendix A is not considered by the NRC staff to have structural significance for large shipping casks (except for unprotected valves and rupture disks) and will not be considered as a general re-quirement.
 
However, some of these requirements do not pertain to irradiated fuel shipping casks because of the massiveness of the casks or because the requirements are not structurally significant to cask design. Casks that are designed to transport one or more commercial fuel assemblies weigh many tons because of the large quantities of structural and shielding materials used. This massive ness causes a shipping cask to have a slow thermal response to sudden external temperature changes such as those that might be produced by quenching after a thermal exposure.
 
The NRC staff feels that the water immersion test of § 71.73 and the water spray test of § 71.71 are not significant in the struc tural design of large casks. Therefore, they are not .discussed in this guide. (Note, however, that these conditions may be significant to criticality and other nonstructural aspects of cask design.) Similarly, the corner drop and the compression tests of § 71.71 are not discussed because they per tain only to lightweight packages.
 
The penetration test of § 71.71 is not considered by the NRC staff to have structural significance for large shipping casks (except for unprotected valves and rupture disks) and will not be considered as a general requirement.


C. REGULATORY  
C. REGULATORY  
POSITION The load conditions given here are considered acceptable to the NRC staff for use in the analytical structural evaluation of shipping casks used to trans port Type B quantities of radioactive materials.
POSITION The load conditions given here are considered ac-ceptable to the NRC staff for use in the analytical structural evaluation of shipping casks used to trans,-port type B quantities of irradiated nuclear fuels.I. General Initial Conditions To Be Used for Both Normal and Hypothetical Accident Conditions a. All initial cask temperature distributions should be considered to be at steady state. The normal and hypothetical accident conditions should be con-sidered to have initial conditions of ambient temperature at -20°F (-29°C) with no insolation and of ambient temperature at 100 0 F (38 0 C) with the maximum insolation data given in Table 1. Excep-tions to the above are made for the hot environment and cold environment normal conditions (which use other steady state values) and for the thermal acci-dent condition (which considers the higher thermal initial condition but not the lower one).b. The decay heat of the irradiated fuel should be considered as part of the initial conditions.


Table 1 lists the load combinations that should be used. Analyses should combine the initial conditions with both the normal conditions and the hypothetical accident conditions.
Generally, the maximum amount of decay heat should be considered in combination with the ther-mal environmental conditions of Regulatory Position C.l.a. In addition, the free-drop and vibration parts of the normal conditions and the free-drop and punc-ture parts of the accident conditions should consider the case of no decay heat and the cask at -20OF (-29'C). These initial thermal conditions are sum-marized in Tahle 2.c. The internal pressure used in evaluating normal and hypothetical accident conditions should be con-sistent with the other initial conditions that are being considered.


1. GENERAL INITIAL CONDITIONS
d. The release of all of the pressurized gases inside the fuel assemblies should be considered in determin-ing, the maximum containment vessel pressure.e. It is the intent of this guide to specify discrete in-itial conditions that will serve as bounding cases for structural response.
TO BE USED FOR BOTH NORMAL AND HYPOTHETICAL
ACCIDENT CONDITIONS
1.1. All initial cask temperature distributions should be considered to be at a steady state. The nor mal and hypothetical accident conditions should be considered to have initial conditions of ambient tem perature at -20'F (-29 °C) with no insolation and of ambient temperature at 100'F (38'C) with maxi mum insolation.


Insolation should be in accordance with paragraph
Maximum or minimum values of initial conditions are given. However, if a larger structural response is suspected for an initial condi-tion that is not an extreme (e.g., an ambient temperature between -19 0 F (-28 0 C) and 99 0 F (37 0 C)), intermediate initial conditions should also be considered in the structural analysis.2. Normal Conditions of Transport Each of the following normal conditions of trans-port is to be applied separately to determine its effect on the fuel cask.a. Hot environment-The cask should be struc-turally evaluated for an ambient temperature of 130°F (54°C) in still air and with maximum insola-tion (see Table I). If the cask has auxiliary cooling systems for the containment or neutron shield fluids, these systems should be considered to be inoperable during the hot environment condition.
71.7 1 (c) (1). Exceptions to the above are made for the cold environment normal condition (which uses -40'F) and for the thermal accident condition (which considers the higher thermal initial condition but not the lower one). 1.2. The decay heat of the radioactive material should be considered as part of the initial conditions.


Generally, the maximum amount of decay heat should be considered for the hot environment and no decay heat should be considered for the cold envi ronment. These conditions should include the insola tion considerations of Regulatory Position 1. 1. In ad dition, the free-drop and vibration parts of the nor mal conditions and the free-drop and puncture parts of the accident conditions should consider the cases of maximum decay heat with an ambient temperature of 100'F (38'C) and of no decay heat with an ambi ent temperature of -20'F (-29QC). 
b. Cold environment-The cask should be evaluated for an ambient temperature of -401F (- 40°C) in still air and with no insolation.
1. 3. The internal pressure used in evaluating nor mal and hypothetical accident conditions should be consistent with the other initial conditions that are being considered.


Minimum internal pressure should be taken as atmospheric or, for designs where inter nal pressures are less than atmospheric, the appropri ate negative value. 1.4. For commercial nuclear power plant fuels, the release of all the pressurized gases inside the irra diated fuel should be considered in determining the maximum resultant containment vessel pressure.
The case of maximum fuel heat load and maximum internal pres-sure should be considered in addition to the case of no internal heat load. The possibility and conse-quence of coolant freezing should also be considered.


1.
c. Minimum external pressure-The cask should be evaluated for an atmopheric pressure 0.5 times the standard atmospheric pressure.d. Vibration and fatigue-The cask should be evaluated for the shock and vibration environment normally incident to transport, This environment in-cludes the quasi-steady vibratory motion produced by small excitations to the cask-vehicle system and also intermittent shock loads produced by coupling, switching, etc., in rail transport and by bumps, potholes, etc., in truck transport.


===5. Fabrication===
Repeated pres-surization loads and any other loads that may con-tribute to mechanical fatigue of the cask should be considered.
2 and installation stresses used in evaluating transportation loadings should be consis tent with the joining, forming, fitting, and aligning processes employed during the construction of casks.  Unless subsequent steps are taken to eliminate these stresses, they should be considered in determining the maximum resultant vessel stress.  2 Fabrication means the assembly of the major components of the casks (i.e., the inner shell, shielding, outer shell, heads, etc.) but not the construction of the individual components.


Thus, the phrase fabrication stresses includes the stresses caused by in terference fits and the shrinkage of bonded lead shielding dur ing solidification but does not include the residual stresses due to plate formation, welding, etc.7.8-2 L
Factors that may contribute to thermal fatigue should also be considered.
Table 1 Summary of Load Combinations for Normal and Hypothetical Accident Conditions of Transport Applicable Initial Condition Ambient Internal Fabrication Temperature Insolation Decay Heat Pressure 2  Stresses 3 100°F -20'F Max.1  Zero Max. Zero Max. Min.  NORMAL CONDITIONS (Analyze Separately)
Hot environment:
100°F ambient temp. X X X X Cold environment:
-40'F ambient temp. X X X X Increased external pressure:
20 psia X X X X X Minimum external pressure:
3.5 psia X X X X X Vibration and shock 4: X X X X X normally incident to the mode of transport X X X X X Free drop: X X X X X 1-foot drop X X X X X ACCIDENT CONDITIONS (Apply sequentially)
Free drop: X X X X X 30-foot drop X X X X X Puncture:
X X X X X drop onto bar X X X X X Therma l: fire accident X X X X X 'See Regulatory Position 1.1.  2 See Regulatory Positions
1.3 and 1.4.  3 See Regulatory Position 1.5.  4 See Regulatory Position 2.5.  5 Evaluations should be made 30 minutes after start of fire and at postfire steady-state conditions.


7.8-3  
These factors should in-clude the thermal transients encountered in the loading and unloading of irradiated nuclear fuel.7.8-2
1,6. It is the intent of this guide to specify dis crete initial conditions that will produce bounding cases of structural response.
* e. Free drop-The cask should be evaluated for a one-foot free drop onto a flat unyielding surface. The cask should contain the maximum weight of contents and should strike the impact surface in a position that is expected to inflict maximum damage.3. Hypothetical Accident Conditions The following hypothetical accident conditions are to be applied sequentially in the order indicated to determine the maximum cumulative effect.a. Free drop-The cask should be evaluated for a free drop through a distance of 30 feet (9 meters)onto a flat unyielding horizontal surface. It should strike the surface in a position that is expected to in-flict maximum damage and should contain the max-imum weight of contents.In determining which position causes maximum damage, the staff currently requests evaluations of drop orientations where the top and bottom ends, the top and bottom corners, and the sides are the cask impact areas. The center of gravity is usually con-sidered to be directly above these impact areas.However, evaluations of oblique drop orientations are requested when appropriate.


Maximum or minimum values of initial conditions are given. However, if a larger structural response is suspected for an initial condition that is not an extreme (e.g., an ambient temperature between -20'F (-29°C) and 100°F (38°C)), intermediate initial conditions or other combinations of initial conditions should also be con sidered in the structural analysis.
b. Puncture-The cask should be evaluated for a free drop of 40 inches (I meter) onto a stationary and vertical mild steel bar of 6 inches (15 cm) diameter with its top edge rounded to a radius of not more than 0.25 inch (6mm). The bar should be of such a length as to cause maximum damage to the cask. The cask should contain the maximum weight of contents and should hit the bar in a position that is expected to inflict maximum damage.* c. Thennal-The cask should be evaluated for a thermal condition in which the whole cask is exposed to a radiation environment of 1.475OF (800 0 C) with an emissivity coefficient of 0.9 for 30 minutes. The surface absorption coefficient of the cask should be considered to be 0.8. The structural response of the cask should be considered up to the time when the temperature distributions reach steady state. The possibility and consequence of the loss of fluid from the neutron shield tank should be considered for casks that use this design feature.Table 2 summarizes the loading combinations given above.


===2. NORMAL CONDITIONS ===
==D. IMPLEMENTATION==
OF TRANSPORT
The purpose of this section is to provide informa-tion to applicants and licensees regarding the NRC staffs plans for using this regulatory guide.This regulatory guide will be used by the staff after January 1, 1978, in assessing the structural adequacy of designs for irradiated fuel shipping casks with respect to the requirements in 10 CFR Part 71,§§71.35 and 71.36. Alternative methods that satisfy the requirements in the Commission's regulations will also be considered acceptable.
Each of the following normal conditions of trans port is to be applied separately to determine its effect on the fuel cask. These normal conditions are also to be combined with all the initial conditions as shown in Table 1.  2.
 
===1. Hot environment ===
-The cask should be structurally evaluated for an ambient temperature of 100'F (38'C) in still air and with maximum insola tion (see Regulatory Position 1.1). If the cask has mechanically operated auxiliary cooling systems, these systems should be considered to be inoperable during the hot environment condition.
 
2.
 
===2. Cold environment ===
-The cask should be evaluated for an ambient temperature of -40'F (-40'C) in still air and with no insolation.
 
The case of no internal heat load and minimum internal pres sure should be considered.
 
The possibility and conse quence of coolant freezing should also be considered.
 
2.3. Increased external pressure should be evaluated for an external 20 psia (140 kilopascal). 
2.4. Minimum external pressure should be evaluated for an external 3.5 psia (24.5 kilopascal).
-The cask pressure of -The cask pressure of 2.5. Vibration and fatigue -The cask should be evaluated for the shock and vibration environment normally incident to transport.
 
This environment in cludes the vibratory motion produced by small excita tions to the cask-vehicle system and also intermittent shock loads produced by coupling, switching, etc., in rail transport and by bumps, potholes, etc., in truck transport.
 
Repeated pressurization loads and any other loads that may contribute to mechanical fatigue of the cask should be considered.
 
Factors that may contribute to thermal fatigue should also be considered.


These factors should in clude the thermal transients encountered in the load ing and unloading of irradiated nuclear fuel from the cask and any restraint against thermal expansion that may be provided by the tiedown system. 7.8-4 Although there are a number of different load combinations that could occur during normal trans port and for which separate fatigue analyses may be performed, this evaluation should be based on the most unfavorable initial conditions for the specific design consistent with a credible spectrum represent ing the life-cycle for normal shock and vibration envi ronments, Table 1 identifies the cases that the staff believes are the most unfavorable.
REFERENCES
I. M.B. Gens, The Transportation and Handling En-vironment, SC-DC-72-1386, Sandia Laboratories, Albuquerque, New Mexico, Sept. 1972.2. International Atomic Energy Agency, Safety Series No. 6, Regulations for the Safe Transport of Radioactive Materials, 1973.3. Department of the Army, Research, Development.


2.6. Free drop -The cask (assuming a weight of over 30,000 pounds (13,600 kg)) should be evalu ated for a 1-foot free drop onto a flat unyielding sur face; it should strike the surface in a position that is expected to inflict maximum damage. Impacts with maximum and minimum weights of contents should be considered.
Test, and Evaluation of Material for Extreme Climatic Conditions, AR 70-38, May 1969.7.8-3 TABLE 1 MAXIMUM INSOLATION
 
DATA Form and location Insolation for 12 hours of surface per day Flat surfaces transported horizontally:
===3. HYPOTHETICAL ===
Base None Other surfaces 800gcal/cm
2 (2,950 Btu/ft 2)Flat surfaces not transported horizontally:
Each surface 200 gcal/cm 2 (737 Btu/ft 2)*Curved surfaces 400 gcal/cm 2 (1,475 Btu/ft'2)*',Alternati'ely, a sine function may be used. adopting an absorptioncoefficientand neglecting the effects of possible reflection from neighboring objects.7.8-4 TABLE 2 SUMMARY OF LOAD COMBINATIONS
FOR NORMAL AND HYPOTHETICAL  
ACCIDENT CONDITIONS  
ACCIDENT CONDITIONS  
The following hypothetical accident conditions are to be applied sequentially to the same cask in the order indicated (dropped, then punctured, then ex posed to fire) to determine the maximum cumulative effect. These hypothetical accident conditions are also to be combined with the initial conditions as shown in Table 1. 3.1. Free drop -The cask should be evaluated for a free drop through a distance of 30 feet (9 m) onto a flat unyielding horizontal surface. It should strike the surface in a position that is expected to inflict maximum damage. Impacts with the maximum and minimum weights of contents should be considered.
OF TRANSPORT Applicable initial condition Normal or accident condition Ambient temperature Insolation Decay heat U a.I-U 0 Y I 4 1 LL.a 0 r'j*C0 C0 Normal conditions -I _ i _ i Hot environment
 
-130°F ambient temp.X x x Cold environment
In determining which position causes maximum damage, applicants should consider impact orienta tions in which the cask strikes the impact surface on its top end, top corner, side, bottom end, and bottom corner and the center of gravity of the cask is directly over the point of impact. If the design of the cask is such that an intermediate oblique orientation could be more damaging, the applicant should also evaluate the impact of the cask in those orientations.
-x x x-40*F ambient temp. x x x Minimum external pressure -x x x x 0.5 at
 
These latter evaluations should include impacting on appur tenances that are part of the cask design such as those used for handling, tiedown, or for other func tions during transport.


3.2. Puncture -The cask should be evaluated for a free drop of 40 inches (1 m) onto a stationary and vertical mild steel bar of 6 inches (0.15 m) di ameter with its top edge rounded to a radius of not more than 0.25 inch (6 mm). The bar should be of such a length as to cause maximum damage to the cask; however, it should not be less than 8 inches (0.2 m) long. The cask should hit the bar in a posi tion that is expected to inflict maximum damage, and impacts with maximum and minimum weights of con tents should be considered.
====m. x x x x Vibration ====
 
& shockt -x x x x Normally incident to x x x x the mode of transport x x x x Freedrop -x x x x x I foot drop x x x x x x x x x x Accident conditions x x X x X Free drop -x x x x 30 foot drop x x x x x Puncture -x x x x x Drop onto bar "_ x x x x x__ __ __ __ __ __ _ _ _ K _ x _ _ x x x Thermaitt
3.3. Thermal -The cask should be evaluated for a thermal condition in which the whole cask is exposed to a radiation environment of 1,475 0 F (800-C) with an emissivity coefficient of 0.9 for 30 minutes. The surface absorption coefficient of the cask should be considered to be 0.8. The structural response of the cask should be considered up to the time when the temperature distributions reach steady state. The possibility and consequence of the loss of fluid from the neutron shield tank should be considered for casks that use this design feature.
-Fire accident'See Table I."*See Regulatory Position C.I.c and C.I.d.tSce Regulatory Position C.2.d for "Vibration and fatigue." ttEvaluations should be made 30 minutes after start of fire and at post-fire steady-state conditions.
 
Table I summarizes the loading combinations given above.
 
==D. IMPLEMENTATION==
The purpose of this section is to provide informa tion to applicants and licensees regarding the NRC staff's plans for using this regulatory guide. Except in those cases in which an applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commis sion's regulations, the NRC staff will use the methods described in this guide in evaluating applications for new package designs and requests for existing pack age designs to be designated as Type B packages for all applications and requests.7.8-5 REGULATORY
ANALYSIS A draft regulatory analysis was published with the second proposed Revision 1 to Regulatory Guide 7.8 (Task MS 804-4) when the draft guide was published for public comment in September
1988. No changes were necessary, so a separate regulatory analysis for the final guide has not been prepared.


A copy of the draft regulatory analysis is available for inspection and copying for a fee at the Commission's Public Document Room at 2120 L Street NW., Washington, DC, under Task MS 804-4.7.8-6 UNITED STATES NUCLEAR REGULATORY
7.8-5}}
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Load Combinations for the Structural Analysis of Shipping Casks
ML13350A233
Person / Time
Issue date: 05/31/1977
From:
NRC/OSD
To:
References
RG-7.008
Download: ML13350A233 (5)
v • d • e


U.S. NUCLEAR REGULATORY

COMMISSION

May 1977 REGULATORY

GUIDE OFFICE OF STANDARDS

DEVELOPMENT

REGULATORY

GUIDE 7.8 LOAD COMBINATIONS

FOR THE STRUCTURAL

ANALYSIS OF SHIPPING CASKS

A. INTRODUCTION

Appendix A, "Normal Conditions of Transport," and Appendix B, "Hypothetical Accident Con-ditions," of 10 CFR Part 71, "Packaging of Radioac-tive Material for Transport and Transportation of Radioactive Material Under Certain Conditions." describe normal conditions of transport and hypothetical accident conditions that produce ther-mal and mechanical loads that serve as the structural design bases for the packaging of radioactive material for transport.

However, initial conditions must be assumed before analyses can be performed to evaluate the response of structural systems to prescribed loads.This regulatory guide presents a set of initial condi-tions that is considered acceptable by the NRC staff for use in the structural analyses of type B packages used to transport irradiated nuclear fuel in the con-tiguous United States. The values in this set supple-..:

ment the normal conditions and the hypothetical ac-cident conditions of the regulations in forming-r.a..

more complete basis from which structural intigrity.

may be assessed.

B. DISCUSSION

To ensure safe structural behavior of shipping casks used to transport irradiated nuclear fuel, specific load conditions must be established that will encompass the static, dynani-ic, and thermal loadings that may be experiencl.d,by.:the.casks during trans-port, This regulatory.guide presents initial conditions that can be used ididddition to parts of Appendices A and B of 10 CER Par "ý7.1 to fully delineate thermal and mechanicalibad combinations for purposes of structural.'analysis'7.4tis intended that this guide be used in conjunction with Regulatory Guide 7.6,"Stress All0owiobles for the Design of Shipping Cask Containment Vessels," for the analytic structural evaluation of the heavy (i.e., several tons in weight)casks used to transport irradiated nuclear fue

l. USNRC REGULATORY

GUIDEStL' ait: tiueci ii tit cl-1 0,- h itl1110 P ,Ae wmlablv to the 1)U.btl mrithth$ds awM~l to , hi WINC %tallci itIneit li ~ all'ci .W~n rl i,'Corv ~ so rf.ev %h,0)r1s.

to tfhl0 .lct' defltn s umit ty tht, .f th I i:j.tl i , gceýIw ic tobwmtceri Wi twIl uittil aCCciil'nl%.

4 t, i t mlrivctdi quid.-ur t m .i i , it fleq, s lixu,, G jKles, Me ,lot u l fw,, timlln.licllfl. '.nlri fthii ' ivutim thetn is riot ,etaclmI 't- .M,'llhotis Indl Qilufirrtms ifihll ont trall. thos' set owi it, the qultu? m. Il tvi .lhe Cctl.dblbe I ti-V 1ri uviltv .) ts.oSl for the lrndiiii l.ui to the or COfli liuWarCC of a pmemil or licenw bv On Corrrnit n anrd Surpj t,! li iin% fant l OVei irit itI t i i. i rqii ides are eicouiaqd at e11 f1M. , aril guilt tihl Ih' r..v.lt. a ,lcitrt)a wo l-ate. to .t: ioiii e.i1irieits t0 itect t ~,," l ii.tilot itO -iii ' t. t 'ne,. Ho,,,etm'vm

.cornilmiit IIti thus gimlti',il ecrivei( imitt.... .i lw.' t t in tht .0ell. ,, its Will tIw icutllly I1 '.is4 itw Regulatory Position C.I.a of this guide mentions environmental initial conditions.

The external ther-mal environmental limits for which a shipping cask must be designed are stated in Appendix A of 10 CFR Part 71 as being 130°F (54 0 C) in direct sunlight and -40°F (-40'C) in shade. These limits are applied without an)y additional loading. For the other condi-tions of Appendix A and for tht hypothetical acci-dent conditions, this guide:presents a range of am-bient temperatures.

from -20°F (-29 0 C) to 1000F (38'C) as a part of the initial conditions.

In the con-tiguous United States.there Is a 99.7 percent probability that, any hourly temperature reading will fall within this range (Ref. l).The insolation data provided in'.the International Atomic Energy Agency's safet)"standards (Ref. 2) have been adopted for this guide.because they have sufficient conser-vatism When. compared with other solar radiation data (RCf. 3)..- Regulatory Position C. I.c mentions initial pressure c.,,onditions.

It should be noted that the pressure inside."the containment vessels and neutron shields of ir-radiated fuel shipping casks depends on several fac-tors. These factors include pre-pressurization of the vessels, the cask temperature distributions associated with the ambient temperatures and the decay heat of the fuel rods, and any gas leakage from the nuclear fuel rods.Regulatory Position C. .e states that the values for initial conditions given in this guide are maximums or minimums.

However, intermediate values could pos-sibly create a more limiting case for some cask designs. For example, a seal design might be more susceptible to leakage at a pressure less than the max-imum internal pressure, or a local structural response might be greater during an impact test if the weight of the contents was less than the maximum.Appendices A and B of 10 CFR Part 71 outline re-quirements for packages used to transport type B quantities of radioactive materials.

Some of these re-AII -11-ts' %bo1ullf % l lH ie. n 4 I.t.'t .!tfq tt { .,;"11 " &'itw llt u ........... ,U S .t#,4 , l' l -*' vi 3. I ueli tol Mitet .,I, F.it'ilit=.e II Oiicc.it~u~llul~

IW.:.lrth 2. tA.ttet dc -il L ,%i m Pii. tT ... tO. ( ,mutt....v..Jit $ lit h iii I ., 1"t , i l e it ... U .. N &l li. i.iii ci Cif J- m tnI V~ij-tiiri t.uti .C. ?055S,. Api t ii D--11-11i1ucicc m. ~im'i i.imii quirements do not pertain to irradiated fuel shipping casks, however, because of the heaviness of the casks or because the requirements are not structurally significant to cask design. Casks that are designed to transport one or. more commercia'

fuel assemblies weigh many tons because of the large quantities of structural and shielding materials used. This mas-siveness causes a shipping cask to have a slow ther--Mal response to sudden external temperature changes such as those that might be produced by quenching after a thermal exposure.

The NRC staff feels that the water immersion test of Appendix B and the water spray test of Appendix A are not significant in the structural design of large casks. Therefore, they are not discussed in this guide. (Note, however, that these conditions may be significant to criticality and other nonstructural aspects of cask design.)Similarly, the corner drop and the compression tests of Appendix A are not discussed because they pertain only to lightweight packages.

The penetration test of Appendix A is not considered by the NRC staff to have structural significance for large shipping casks (except for unprotected valves and rupture disks) and will not be considered as a general re-quirement.

C. REGULATORY

POSITION The load conditions given here are considered ac-ceptable to the NRC staff for use in the analytical structural evaluation of shipping casks used to trans,-port type B quantities of irradiated nuclear fuels.I. General Initial Conditions To Be Used for Both Normal and Hypothetical Accident Conditions a. All initial cask temperature distributions should be considered to be at steady state. The normal and hypothetical accident conditions should be con-sidered to have initial conditions of ambient temperature at -20°F (-29°C) with no insolation and of ambient temperature at 100 0 F (38 0 C) with the maximum insolation data given in Table 1. Excep-tions to the above are made for the hot environment and cold environment normal conditions (which use other steady state values) and for the thermal acci-dent condition (which considers the higher thermal initial condition but not the lower one).b. The decay heat of the irradiated fuel should be considered as part of the initial conditions.

Generally, the maximum amount of decay heat should be considered in combination with the ther-mal environmental conditions of Regulatory Position C.l.a. In addition, the free-drop and vibration parts of the normal conditions and the free-drop and punc-ture parts of the accident conditions should consider the case of no decay heat and the cask at -20OF (-29'C). These initial thermal conditions are sum-marized in Tahle 2.c. The internal pressure used in evaluating normal and hypothetical accident conditions should be con-sistent with the other initial conditions that are being considered.

d. The release of all of the pressurized gases inside the fuel assemblies should be considered in determin-ing, the maximum containment vessel pressure.e. It is the intent of this guide to specify discrete in-itial conditions that will serve as bounding cases for structural response.

Maximum or minimum values of initial conditions are given. However, if a larger structural response is suspected for an initial condi-tion that is not an extreme (e.g., an ambient temperature between -19 0 F (-28 0 C) and 99 0 F (37 0 C)), intermediate initial conditions should also be considered in the structural analysis.2. Normal Conditions of Transport Each of the following normal conditions of trans-port is to be applied separately to determine its effect on the fuel cask.a. Hot environment-The cask should be struc-turally evaluated for an ambient temperature of 130°F (54°C) in still air and with maximum insola-tion (see Table I). If the cask has auxiliary cooling systems for the containment or neutron shield fluids, these systems should be considered to be inoperable during the hot environment condition.

b. Cold environment-The cask should be evaluated for an ambient temperature of -401F (- 40°C) in still air and with no insolation.

The case of maximum fuel heat load and maximum internal pres-sure should be considered in addition to the case of no internal heat load. The possibility and conse-quence of coolant freezing should also be considered.

c. Minimum external pressure-The cask should be evaluated for an atmopheric pressure 0.5 times the standard atmospheric pressure.d. Vibration and fatigue-The cask should be evaluated for the shock and vibration environment normally incident to transport, This environment in-cludes the quasi-steady vibratory motion produced by small excitations to the cask-vehicle system and also intermittent shock loads produced by coupling, switching, etc., in rail transport and by bumps, potholes, etc., in truck transport.

Repeated pres-surization loads and any other loads that may con-tribute to mechanical fatigue of the cask should be considered.

Factors that may contribute to thermal fatigue should also be considered.

These factors should in-clude the thermal transients encountered in the loading and unloading of irradiated nuclear fuel.7.8-2

  • e. Free drop-The cask should be evaluated for a one-foot free drop onto a flat unyielding surface. The cask should contain the maximum weight of contents and should strike the impact surface in a position that is expected to inflict maximum damage.3. Hypothetical Accident Conditions The following hypothetical accident conditions are to be applied sequentially in the order indicated to determine the maximum cumulative effect.a. Free drop-The cask should be evaluated for a free drop through a distance of 30 feet (9 meters)onto a flat unyielding horizontal surface. It should strike the surface in a position that is expected to in-flict maximum damage and should contain the max-imum weight of contents.In determining which position causes maximum damage, the staff currently requests evaluations of drop orientations where the top and bottom ends, the top and bottom corners, and the sides are the cask impact areas. The center of gravity is usually con-sidered to be directly above these impact areas.However, evaluations of oblique drop orientations are requested when appropriate.

b. Puncture-The cask should be evaluated for a free drop of 40 inches (I meter) onto a stationary and vertical mild steel bar of 6 inches (15 cm) diameter with its top edge rounded to a radius of not more than 0.25 inch (6mm). The bar should be of such a length as to cause maximum damage to the cask. The cask should contain the maximum weight of contents and should hit the bar in a position that is expected to inflict maximum damage.* c. Thennal-The cask should be evaluated for a thermal condition in which the whole cask is exposed to a radiation environment of 1.475OF (800 0 C) with an emissivity coefficient of 0.9 for 30 minutes. The surface absorption coefficient of the cask should be considered to be 0.8. The structural response of the cask should be considered up to the time when the temperature distributions reach steady state. The possibility and consequence of the loss of fluid from the neutron shield tank should be considered for casks that use this design feature.Table 2 summarizes the loading combinations given above.

D. IMPLEMENTATION

The purpose of this section is to provide informa-tion to applicants and licensees regarding the NRC staffs plans for using this regulatory guide.This regulatory guide will be used by the staff after January 1, 1978, in assessing the structural adequacy of designs for irradiated fuel shipping casks with respect to the requirements in 10 CFR Part 71,§§71.35 and 71.36. Alternative methods that satisfy the requirements in the Commission's regulations will also be considered acceptable.

REFERENCES

I. M.B. Gens, The Transportation and Handling En-vironment, SC-DC-72-1386, Sandia Laboratories, Albuquerque, New Mexico, Sept. 1972.2. International Atomic Energy Agency, Safety Series No. 6, Regulations for the Safe Transport of Radioactive Materials, 1973.3. Department of the Army, Research, Development.

Test, and Evaluation of Material for Extreme Climatic Conditions, AR 70-38, May 1969.7.8-3 TABLE 1 MAXIMUM INSOLATION

DATA Form and location Insolation for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of surface per day Flat surfaces transported horizontally:

Base None Other surfaces 800gcal/cm

2 (2,950 Btu/ft 2)Flat surfaces not transported horizontally:

Each surface 200 gcal/cm 2 (737 Btu/ft 2)*Curved surfaces 400 gcal/cm 2 (1,475 Btu/ft'2)*',Alternati'ely, a sine function may be used. adopting an absorptioncoefficientand neglecting the effects of possible reflection from neighboring objects.7.8-4 TABLE 2 SUMMARY OF LOAD COMBINATIONS

FOR NORMAL AND HYPOTHETICAL

ACCIDENT CONDITIONS

OF TRANSPORT Applicable initial condition Normal or accident condition Ambient temperature Insolation Decay heat U a.I-U 0 Y I 4 1 LL.a 0 r'j*C0 C0 Normal conditions -I _ i _ i Hot environment

-130°F ambient temp.X x x Cold environment

-x x x-40*F ambient temp. x x x Minimum external pressure -x x x x 0.5 at

m. x x x x Vibration

& shockt -x x x x Normally incident to x x x x the mode of transport x x x x Freedrop -x x x x x I foot drop x x x x x x x x x x Accident conditions x x X x X Free drop -x x x x 30 foot drop x x x x x Puncture -x x x x x Drop onto bar "_ x x x x x__ __ __ __ __ __ _ _ _ K _ x _ _ x x x Thermaitt

-Fire accident'See Table I."*See Regulatory Position C.I.c and C.I.d.tSce Regulatory Position C.2.d for "Vibration and fatigue." ttEvaluations should be made 30 minutes after start of fire and at post-fire steady-state conditions.

7.8-5


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