ML20195B280
| ML20195B280 | |
| Person / Time | |
|---|---|
| Site: | 07109205 |
| Issue date: | 05/23/1986 |
| From: | Macdonald C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | |
| Shared Package | |
| ML20195B262 | List: |
| References | |
| NUDOCS 8605290165 | |
| Download: ML20195B280 (12) | |
Text
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' 4lf* *c%qi UNITED STATES
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' NOCLE AR REGULATORY COMMISSION s
c wasmorow. o. c. 20sss Safety Evaluation Report
'Teledyd'e Energy Systens Model No. SENTINEL SS Packace
~ Docket No. 71-9205 SUPARY By application dated October 16, 1985, as supplemented, Teledyne Energy Systens requested design approval of the liedel No. SENTINEL 55 shipping package (radioisotope themoelectric generator (RTG)).
Based on the statements and ' representations contained in the application and the conditions listed below, w have concluded that the tiodel No.
SENTINEL 55 package rneets the perfomance requirements of 10 CFR Part 71.
REFERENCES 1.
Teledyr.e Energy Systens application <iated October 16, 1985.
2.,
Supplement dated February 24, 1986.
3.
Supplement dated May 7,1986.
opm Inns The packaging tis constructed in accordance with Teledyne Energy Systems figu res 1. (, 1. l a, 1. l b, 1.lc, 1,2, 1. 3a, 1. 3b, 1. 3c, 1.3d, 1. 3e, 1. 4a,
1.45, 1.5, 1. 7a, 1. 7b, 1. 7c, 1.8a,, 1.86, 1.8c, 1.9a, 1. 9 h, 1.9c, and 1.9d.
DESCRIPTION The packaging contains a themoelectric generator with 32,900 ci of strentium 90 fluoride meeting the requirements of special fom radio-active material.
The double encapsulated fuel is held inside a depleted uranium biological shield (7.3-inch OD x 8.85-inch) which is provided with a stepped plug lid and secured with 6,1/4-inch x 1.25-inch long steel bolts. The depleted uranium shield is held in position within the generator's aluninum housing by sized Min-K thermal insulation. A retaining ring is used to preload the Min-K and to dampen any vibrational loads.
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During shipment, th'e finned aluminum housing of the thermoelectric generator is contained within an inner shipping container which is provided with stepped lid and secured with 12, 3/4-inch steel bolts which are recessed.
Movement of the generator is restricted by an RTG Preload Assembly within the inner vessel.
The inner container is constructed of ASTM A-181 forged steel and a lid fabricated of A-36 s teel.
The inner container dimensions are 26.1-inch ID x 21.7-inch high x 36.53-inch OD x 32.2-inch high plus 2-inch thick aluminum bumper pad (spacer) located on the top lid.
The outer shipping container is fabricated from 3/8-inch thick 304L stainless steel (SS) with a 3/4-inch thick bottom plate. The top lid is joined to the bottom of the outer container by 12, 3/4-inch steel bolts and nuts through 2, 3/4-inch thick SS flanges. The closure flanges are gasketed to preclude entry of rain water.
The outer package is reinforced by 4, 3/8-inch thick SS stiffener ribs (external). The lid stiffener ribs contain 4, 2-1/8-inch diameter lifting / tie-down holes.
The bottom plate is welded to 2, 4-inch I-beams.
The gross weight of the package is 8,460 pounds which includes the 276-pound weight of the thermoelectric generator.
' CONTENTS (1) Type and form of material Strontium fluoride (90SrF ) doubly encapsulated in Hastelloy C-276 which meets the requiremekts of special form radioactive material.
(2) Maximum quantity of material per package 32,900 curies.
1.
General Standards for All Packaging (10 CFR 671.43)
Minimun /ackage Size The smallest external dimensions of the Model No. SENTINEL SS Shipping Package is much greater than 4 inches.
Therefore, the Model No. Sentinel SS shipping package meets the requirement by having greater than 4 inches smallest overall dimension.
-3 Tamperproof F_e_ature One of the shipping cask outer (outer container) bolt heads is wired to the structural rib on the head. The wire is sealed in a standard lead security seal.
A broken seal would give evidence of tampering by unauthorized persons.
Positiye_ Closu_r_e, The outer container lid is bolted to the body with 12, 3/4-inch bolts and nuts. The inner container lid is bolted to the body with 12, 3/4-inch square head steel bolts which go through the lid into tapped holes in the cask body.
The square head bolts are recessed 3/4-inch below the top surface in a hole whose diameter precludes the use of a standard socket wrench. Therefore, the ibdel No. Sentinel SS shipping package cannot be inadvertently opened.
Chemical and Galvanic Reactions The materials used in the construction of the Model No. SENTINEL SS shipping package are stainless steel, carbon steel, epoxy painted aluminun alloy and depleted uranium.
There will be no significant chenical or galvanic action between any of these components, nor will there be any chemical or galvanic action between these canponents and the package contents.
4 B.
Lifting and Tie-Down Standards for All Packages Lif ting Devices (10 CFR 971.45(a))
The 4 lifting eyes located on the lid of the outer container are shown by analysis to be capable of lifting three times the maximum package weight.
By comparison of the safety factors for stresses in the lifting eyes, stress in the outer container shell and flange interface due to a lifting load, and stresses in the 12 bolts at the flanges, the staff ccncluded that the weak link for a lifting eye is the tear-out limit of the lifting eyes.
Thus, under excessive load, the lif ting eye would fail in shear without canpromising the flodel No. SENTINEL SS shipping package.
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Tie-Down Devices (10 CFR 971.45(b))
The tie-down arrangement for the Model No. SENTINEL SS shipping package uses the same 4 attachment points as for the lifting configuration.
The applicant has shown by analysis that these tie-down devices are adequately designed to meet the requirenents stipulated in 10 CFR 971.45(b).
As in the analysis for lifting devices, the tear-out limit of the lifting eyes appear to have the smallest safety factor.
Thus, excessive loading would fail a lifting eye in shear with no jeopardy to the Model No. SENTINEL SS shipping package.
C.
Normal Conditions _ of Transport (10 CFR 671.71)
Heat-Under conditions of still ambient air at 100*F, the derived temperatures for the innermost canponents of the RTG installed within the inner and outer ocntainers are lower than the RTG operational tenperatures of the same components given the same fuel inventory.
Thus, the thermal stresses generated under the normal heat condition of transport are within the design operating conditions for the RTG.
Cold Since the outer container is fabricated from Type 304 stainless steel, it can withstand a tenperature of -40 F and meets the brittle fracture toughness recanmendations of NUREG/CR-1815.
Reduced External Pressure and Increased External Pressure The Model No. SENTINEL SS shipping package is shown by analyses to be capable of withstanding pressure differentials greater than produced by reduced external pressure of 3.5 psia and increased external pressure of 20 psia without loss of structural integrity.
i Vibration The vibration loading is judged not to have significant effects on the package safety.
Llater Spray Since the outer container is constructed of steel, exposure to water spray will have no effect on the Model No. SENTINEL SS shipping package.
. Free Drop The applicant used analytical techniques and reasoned argenent to evaluate the Model No. SENTINEL SS shipping package for free drop requirements associated with normal transport conditions. The results indicate that the "thickwalled" low carbon steel inner container would not be stressed beyond the minimum yield strength of 35 ksi in any of the 4-foot free drop orientations.
The stainless steel outer container would be ductile enough to naintain a continuous envelope for the inner container after each of the 4-foot free drop orientations.
Thus, the transportability of the flodel No. SENTINEL SS shipping package would not be effected since the two major components for the normal transport conditions, viz, inner and outer containers, remain intact after the 4-foot free drop test.
Corner Drop Not applicable for this design case.
Compression The Model No. SENTINEL SS shipping package is shown by analysis to be capable of withstanding a load of 5 times the package weight without generating stress in any naterial of the packaging in excess of their yield strength.
Penetration The NRC staff judges that a 13-pound rod dropping from a height of 40 inches would have no significant effect on the exterior of the fiodel No. SENTINEL SS shipping package.
D.
Hypothetical Accident Conditions (10 CFR 971.73)
Free Drop The applicant's evaluation of the ibdel No. SENTINEL SS shipping package to neet the 30-foot drop test of 10 CFR Part 71 is based on the results of analyses using analytical techniques.
The analyses did not take credit for the structural integrity of both inner container and outer container.
Forces generated from the 30-foot drop test were applied directly onto the RTG installed within the inner and outer containers.
~ The applicant has evaluated the RTG for top end drop, bottom end drop, and side drop.
Corner drop was not evaluated directly.
However, because of the high rigidity of the inner container, damage on the aluminun RTG housing cannot be due to deformation of the inner container. Any potential damage to the aluminum RTG housing is more likely to cone from direct impacts against the inner container.
Thus, a corner drop orientation for the RTG can be considered as a combination of the side and end impacts.
The results of the analyses indicated that, although some cooling fins outside the aluminun RTG housing might be damaged during the hypothetical side drop test, the aluminum RTG housing itself would not be breeched in any of the 30-foot free drop orientations. The shield / fuel capsule assembly within the h,ousing would remain intact because a significant portion of the available kinetic energy from the shield / fuel capsule assembly during impact would be absorbed by o
the liin-K insulation surrounding them. As for the fasteners which y
hold the shield lid to the body, the applicant has elected to assume no credit for them during the 30-foot bottom end drop test.
The fuel capsule was assumed to be in a position such that radiation streaming path would exist through a gap between the plug and the shield body.
Infonnation presented in the shielding evaluation section indicated that the inner and outer containers would provide adequate shielding for the Accident Condition of Transport.
In summary, it is concluded that the fuel containment capability of the RTG would not be breeched after the 30-foot drop test.
The inner and outer containers would provide radiation protection after the 30-foot drop test.
Punctu r_e The applicant's evaluation of the tiodel No. SENTINEL SS shipping package to meet the puncture test is based on analytical methods recommended in ORNL-NSIC-68. The result of the calculation indicates that the unprotected RTG housing would not be penetrated during a t
40-inch drop onto the puncture pin per 10 CFR Part 71.
Furthemore, the inner container is made of steel with higher tensile strength and thicker than the aluminun RTG housing.
It is capable of resisting puncture to a higher degree than the aluminum RTG housing. Thus, reduction of shielding effectiveness or loss of radioactive material as a result of the puncture test is not expected.
f Thennal The applicant's evaluation of the Model No. SENTINEL SS shipping package indicates that the maxinun temperatures of individual components resulting from the hypothetical accident thermal conditions of 10 CFR Part 71 would be below their respective naterial nelt tempera tu res.
Internal pressures which may result within the primary fuel containment member are below the capability of the individual components within the RTG.
Furthermore, although materials with different coefficients of thermal expansion are used within the RTG, adequate clearances would still exist.
Interferences would not be developed as a result. Thus, the Model No. SENTINEL SS shipping package would retain its integrity during exposure to the hypothetical fire test of 10 CFR Part 71.
Immersion - Fissile Material Not applicable, fissile packages only.
Immersion - All Packages The Model No. SENTINEL SS shipping package is a sealed Onit. The stainless steel outer container uses a silicon rubber seal between its body and lid.
This seal is capable of preventing ingress of water under the 21 psig pressure. The same pressure would have no effect on the body of the outer container.
THERNAL The Model No. SENTINEL SS shipping package contains a maximum thennal loading of 220 watts (751 Btu /hr). The strontium 90 fluoride fuel is doubly encapsulated to meet special form requirements and is the primary containment vessel.
Decay heat from the radioactive fuel is transmitted to the internal shield assembly which surrounds it and is then directed by the thermal insulation upward through the thermoelectric module. The heat must be dissipated by the generator housing and fins to the ambient.
. The generator is nomally filled with pure argon gas and sealed with Vi ton 0-rings.
The. purpose of the gas fill is to reduce the heat losses through the insulation by about 10%.
This is important to the efficient operation of the module since the high temperature " Min-K" insulation is only able to direct 60% of the decay heat output through the themoelectric nodule.
If the generator seal is lost, there will be a gradual replacement of the argon gas with air and a corresponding increase in the heat losses through the side insulation.
This will not effect the safety of the package since the higher heat loss through the package would result in lower internal temperatures, in the shipping configuration, the SENTINEL SS RTG is loaded within an inner container fabricated from carbon steel.
The inner container is then housed within an outer container of Type 304L stainless steel.
In
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analyzing the thermal behavior of the SENTINEL SS RTG package, the applicant assumed that the outer and inner containers provided no themal protection during hypothetical accident conditions.
The bare shield / fuel capsule assembly was assumed to be exposed directly to the 1475 F radiation environment of 10 CFR Part 71.
Under actual conditions, the inner and outer containers would be expected to provide additional themal protection for the RTG unit and prevent any appreciable melting of the RTG housing or fins.
The analysis presented by the applicant represents the worst case scenario from a themal standpoint and demonstrates that the package meets the themal requirements of 10 CFR Part 71.
Nomal Conditions of Transport The applicant used a finite element computer code (ANSYS) to evaluate the package's themal behavior for normal transport conditions. An ambient temperature of 100*F and decay heat load of 220 watts (751 Btu /hr) were used in the analysis.
The full solar load which the package would experience was distributed unifomly over the entire package surface. The naximun predicted temperatures were:
Critical Predicted Max.
Component Temperature Temperature Hastelloy C276 Liner 2320*F 1321*F Hastelloy C276 Capsule 2320*F ll43*F Biological Shield (Depleted Uranium -0.75% Ti Alloy) 2075*F 1070*F Generator Housing (6061 T.6 Aluminum) 1080*F 222 F Shipping Cask (Carbon Steel) 2500*F 175*F Under nomal " cold" conditions, ambient air at -40*F and shade, the average shipping cask outer container temperature is about -19 F and the average RTG surface temperature is about 60*F for the maximun fuel loading of 220 watts.
In this temperature range, there were no appreciable problems with either material properties or themal stresses.
_g.
Hypothetical Accident Conditions The ANSYS program was also used to simulate the package's 30-ninute exposure to a 1475 F fire radiation environnent. The model also assumed that the themoelectric module failed electrically open as a result of the free drop.
This was a conservative assumption since the capsule temperatures would increase with an open circuit condition due to a lack of Pelties effect cooling at the nodule hot,iunction.
The maximum decay heat loading of 220 watts was used. The maximun temperatures which were predicted were:
Critical Predicted Max.
Component Temperature Tenperature Liner, Hastelloy C-276 2320 F 1510 F Capsule, Hastelloy C-276 2320 F 1390*F
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Shield, (Depleted Uranium 0.75% Ti) 2075 F 1383*F Shield Clad (321 Stainless Steel) 2550 F 1402*F Generator Housing (6061-T6 Aluminum) 1080 F MELTS FINS (6061-T6 Aluminum) 1080*F MELTS The generator housing and fins (6061-T6 aluminum) reached their melt temperature,1080 F, approximately one minute into the hypothetical fire.
Another 2.5 minutes were needed to melt these components completely.
However, the applicant has shown that the bare shield / fuel capsule assembly is capable of surviving the 30 minute fire without compromising fuel containment or shielding.
The shield and capsule do not exceed their melt temperature during or after the fire.
It should be emphasized that the applicant in modeling the package's thennal behavior used a model which incorporated several conservative assumptions. These assumptions included the use of maximum fuel loading and the assumption that the themal environment of the hypothetical accident sequence was applied directly to the shield and enclosed fuel capsule. Therefore, no credit was taken for the cask, generator housing, or themal insulation.
Under actual conditions, the shipping cask's outer and inner container would provide additional thermal protection during the hypothetical accident.
The staff has concluded using independent calculations based on HTAS1/ HEATING 6 that the average temperature of the generator housing would reach approximately 450*F for fire accident condi tions. The housing would be prevented from reaching higher temperatures by the insulating effects of the 0.14-inch clearance (air gap) between the inner carbon steel container and outer stainless steel container and by the air gaps between the RTG unit itself and the inner container.
Only the fins would be in direct contact with the inner container and any melting which would occur would be limited to the fin's edges in contact with possible " hot" spots on the surface of the inner container.
The generator housing itself would not be expected to experience melting, as the melting point of 6061-T6 aluminum is approximately 1080*F.
Compliance With 10 CFR @71.43(g)
The requirements of 10 CFR 671.43(g) state that "a package must be designed, constructed, and prepared for transport so that in still air at 38"C (100 F) and in the shade, no accessible surface of a package would have a temperature exceeding 50*C (122*F) in a non-exclusive use shipment." The naxinun temperature calculated at the package's surface for these conditions using a 220 watt heat load was 113 F.
Maximum Internal Pressure The naximum internal pressures (within the shield-clad gap) results from the volumetric expansion of the argon gas during normal RTG operations and from the temperature increase during hypothetical fire accident conditions.
Pressures for these conditions were calculated by staff and are summarized in the following table:
Argon Gas Pressure in Shield-Clad Gap Temp.
Pressure Loading 70 F 14.7 psi Normal Transport Condi tion 1154 F 44.7 Fire Accident 1331*F 49.67 Pressure may also develop within the primary fuel containment (fuel capsule) during nomal and fire accident conditions.
However, the fuel capsule has been tested to an external pressure of 1000 bars (14,500 psi).
The naximum pressure predicted by the applicant for fire accident conditions was 43.3 psi as compared to staff's calculation of 49.7 psi. The difference results from the applicant's use of an " Average" argon temperature in the shield-clad gap of approximately 1100*F. Staff used 1331*F which was the maximum temperature predicted by the ANSYS program.
Summary and Conclusions The themal analysis presented by the applicant assumed that the generator housing melted during the hypothetical accident condition.
This assumption was made by ignoring the presence of the cask's inner and outer containers.
The applicant has demonstrated for this case that even the loss of the generator housing did not appreciably effect either shielding or source containment, as the depleted uranium - 0.75% titanium shield can withstand temperatures of 2,075*F before melting.
In addition, an independent analysis performed by the staff showed that the generator housing would a
not be expected to experience melting because of the positioning of the RTG unit within the cask's inner and outer containers.
Therefore, the applicant has demonstrated that the liodel No. SENTINEL SS shipping package meets the themal requirements of 10 CFR Part 71.
This conclusion is limited to the shipments with a maximum decay heat loading of 220 watts.
CONTAlfNENT_
The 32,900 curies of strontium fluoride is doubly encapsulated in Hastelloy C-276 and meets the requirenents of special form radioactive material.
The outer container is provided with a gasketed closure to preclude the entry of rain water into the package.
SHIELDING for nornal conditions of transport, the applicant calculated the highest surface dose rate for the package to be 40 mren/hr (bottom).
(Regulatory limit - 200 mrem /hr at the surface of the package.)
For accident' conditions of transport, the applicant calculated the highest dose rate to be 746 nren/hr one neter from the botton surface of the package. This calculation assumed the depleted uranium was not effective (possible brittle fraction or loss of lid bolts).
(Regulatory limit - 1000 nirea/hr at one neter from the surface of the package.)
The NRC staff is in agreement with the applicant's calculations.
_0PERATING ACCEP TANCE,,A,N D,JiAI N,TE,N_Aji,C E, t
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General operating procedures for use of the package are provided in Section 7 of the application.
O The acceptance tests and maintenance programs are described in Section 8 of the application. The Acceptance Tests (Section 8.1) describes visual inspections, fuel capsule structural and leak tests, component tests, and test for shield integrity.
The Maintenance Program (Section 8.2) describes "swip" tests, visual inspections, gasket replacement, and inner / outer container maintenance.
CONDITION In addition to the reoutrements of Subpart G of 10 CFR Part 71, each package nust meet the Acceptance Tests and Maintenance Program of Section 8.0 of the application.
CONCLtGION, Based on our review, the statenents and representations contained in the application and the condition listed above, we find that the Model No.
SENTINEL SS package meets the requirenents of 10 CFR Part 71.
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Charles E. MacDonald, Chief Transportation Certification Branch Division of Fuel Cycle and Material Safety, NtiSS Date: MAY 2 3 'saan
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