ML19276D949
| ML19276D949 | |
| Person / Time | |
|---|---|
| Site: | 07109120 |
| Issue date: | 01/31/1979 |
| From: | Goldmann K TRANSNUCLEAR, INC. |
| To: | Macdonald C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| E-1515, NUDOCS 7903020014 | |
| Download: ML19276D949 (5) | |
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January 31, 1979 Mr. Charles E. MacDonald:
Chief, Transportation Branch Division of Fuel Cycle and Material Safety Nuclear Regulatory Commission Washington, D.C.
20555
Subject:
Docket No. 71-9120 Fracture Toughness for TN-12 Steels
Dear Mr. MacDonald:
In accord with your request during our January 10 meeting for information on the suitability of TN-12 containment vessel steels from a fracture toughness point of view, we offer the following:
A.
DESIGN 1.
Material Acceptance Criteria The containment vessel of the TN-12 is basically a cylinder made of 12 inch thick ferritic steel which is internally overlayed with stainless steel. It is provided with welded trunnions made of the same ferritic material.
Brittle failure at low temperature should be considered in its design.
In the absence of specific regulations or industry standards on fracture toughness criteria for spent fuel shipping casks, Transnuclear, Inc. proposes for fracture toughness of the material for the TN-12 containment vessel, the following acceptance criteria:
Maximum yield strength at room temperature: 50 KSI Minimum yield strength at -20F: 35.7 KSI RTNDT: not exceeding -40F (Ref. AEME BPV Code,Section III, Paragraph NB-2331).
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Maximum ultimate strength of trunnion material at -20F: 85.7 KSI Maximum depth of flaws:
1 inch generally inch in region of trunnion attachment We show hereaf ter that the above criteria protects the cask body against non ductile fracture using the approach of Appendix G of ASME Code,Section III, which apply, in particular, to dynamic loading.
2.
Origin of Stresses During normal conditions of transport at low ambient temp-eratures, stresses in the containment vessel are low and brittle failure is not likely.
The hypothetical accident condition which is considered to be the most adverse for brittle failure is a horizontal drop of the cask from a height of 30 feet on a set of trunnions at an ambient temperature of -40F, Due to the absence of pressure, there is no large energy stored in either the vessel walls or in the internal fluid to sustain tensile forces that would assist propagation of a crack.
There will also be no extensive residual stresses to act as crack drivers since the vessel will be stress relieved.
In the further absence of thermal stresses under the postulated conditions, the propagation of a flaw would be driven only by the transient forces generated by the impact.
3.
Applicability of Linear Elastic Fracture Mechanics As during drop tests of the 1/3 scale model of the TN-12 no gross yielding occurred in shell (no change of cavity diameters) the principles of linear elastic fracture me-chanics apply to the present analysis.
4.
Maximyn Trunnion Reaction ( R)
Trunnions showed no visible strain of their inner segment (diameter 50/120 mm).
We may assume that the peak trunnion reaction does not exceed the product of the cross section area of that segment by the material ultimate strength.
For the full scale cask, the trunnion reaction is limited to R: 5.05 x 107 N.
(1.11 x 107 LB),
Note: Body acceleration corresponds not only to trunnion reaction but also to reaction of drum, rim and fins.
5.
Calculation of K caused by reactijon R.
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Using the methodology of Appendix G, S e'c tion III, ASME B & PV Code, one obtains the results given in the fol.1~ving table.
Axial Cask Center of Impact Trunnions Location Gravity Circumferential Lower Surface Mid Plane Lower Surf Location (8 inch fr Trunnion A.
Loading Bending Bending Shear Sm 15.65 10.26 27.30 T
11.93 10.35 8.26 Sm/Sy 0.48 0.29 0.78 Mm 3.34 3.05 2.95 K
(For a = T/4) 52. 27 31.'29 80.55 7
K, (For a = lin. )30. 3 19.5 7
K (For a =
in.)
39.64 Im where Sy: Yield strength, 35 KSI T:
Wall thickness, in, a:
Maximum depth of typical flau, in.
Sm: Membrane tensile stress, KSI bh: given by Fig. G-2214-1, Appendix G,Section III.
6.
Calculation of KIR From the equation given in Para G-2110, one obtains a required K
= 43.41 psi @
IR 7.
Conclusion We conclude that K does not exceed K for a 1 in. flaw generally and a IE. flaw in the vicin!ty of the trunnion.
The proposed acceptance criteria permit the use of material normally used for thick pressure vessels which precludes possible unforseen fabrication problems as may be antici-pated for higher grade steels.
B.
ADDITIONAL DROP TESTS OF THE 1/3 SCALE MODEL AT LOW TEMPERATU l.
Scope Additional drop tests of the 1/3 scale model will be per-formed at a test temperature of -40F to verify the frac-ture toughness requirements for the material which has been selected for the TN 125 packaging.
The model to be utilized for these tests was previously subjected to a series of nine drops in accordance with the testing requirements for the 10 CFR 71 hypothetical accident conditions.
The model, test conditions and test results will be described in the revision to the SAR.
2.
Inspections and Preparations Prior to Testing 2.1 A pre-test dimensional inspection will be performed tc measure the internal diameters of the shell in and near the planes of the redundant trunnion and the impact points for the two other tests and to check the dimensions of the redundant welded trunnion which will be the point of impact for the 9m drop test.
2.2 The model's internal surfaces will be dye penetrant inspected.
2.3 The model will be placed in an insulated box with dry ice for a sufficient period of time to assure that a temp-erature of -40F or lower is achieved throughout the model.
A preliminary test will be performed to determine the temperature increases experienced when the model is at
-40F and then exposed to ambient air.
2.4 The temperatures of the shell and redundant welded trunnion will be measured by thermocouples and recorded during the test to confirm that the test temperature of
-40F will not be exceeded.
If required, local thermal insulation may be placed over the trunnion and other points of impact and removed just prior to drop.
If necessary, the model will be cooled again to -40F, between drop tests.
2.5 Closure bolts will be properly torqued to their speci-fied values.
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3.
Test Operations Three additional drop tests of the 1/3 scale model will be performed in a drop test facility of the Commissariat h l'Energie Atomique (CEA) at Moronvilliers, France.
These tests are as follows:
a.
A 9m drop test onto an essentially unyielding surface will be performed first.
The model will be in a horizontal
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position and oriented so as to impact on the redundant welded trunnion.
b.
Two lm punch drop tests will be perf rmed onto a circular steel bar 2 inch in diameter.
The first punch drop test will be performed with the model in a horizontal position with the center of gravity vertically above the punch.
The necond punch drop test will be performed with the model in the horizontal position and oriented so as to impact the punch on the body close tc the redundant welded trunnion.
4.
Post-Test Inspections 4.1 The torque required for untightening the closure bolts will be measured and recorded.
4.2 All dimensional measurements made during the pre-test
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inspection will be repeated.
Dimensional data on failures
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will be taken and recorded.
l 4.3 Movies and still pictures will be taken before, during and after the teste.
4.4 A dye penetrant inspection of the models' internal surfaces will be repeated.
4.5 A test report will be prepared describing the test conditions, measurements and results.
5.
Acceptance Criteria The drop test results will be acceptable if the. variations in the internal diameters measured before and a.f.ter testing are not greater than the accuracy of the measurements and no through wall cracks are found in the post-test dye pene-trant examination.
If you have any questions concerning the above, please contact _me.
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Very truly yours, - ~ ~ ~
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lL:tJdW Kurt Goldmann
/wa Chief Engineer