ML20206A308
| ML20206A308 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 03/03/1987 |
| From: | CIM CORP. |
| To: | |
| Shared Package | |
| ML20206A297 | List: |
| References | |
| DR-03415-1, DR-3415-1, NUDOCS 8704070484 | |
| Download: ML20206A308 (34) | |
Text
C MEXJRP DR-03415-1
- FUEL DROP ACCIDENT LOAD REASSESSMENT ANALYSIS REPORT for the MAINE YANKEE SPENT FUEL STORAGE RACKS Prepared for:
Maine Yankee Atomic Power Company Edison Drive Augusta ME 04336 (Maine Yankee P.O. 45409-00) wo Prepared by b ,- /-v - Date F, &, ,/997 Checked by N #>'- N4" Date 3,/3/87 ,
Rsvision No Date 8704070484 870331 PDR ADOCK 05000309 O PDR CIMCORP!nc. 899 West Highway % Shoreview, MN 55126 Telephone:(612)484-7261 Telefax:(612)483-2689 A Wartsila Company k
DR-03415-1 REV pcco 11
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REVISION RECORD i
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DR-03415-1 REV Paga 111 REVISION STATUS
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PAGE REV PAGE REV PAGE REV PAGE REV PAGE REV i 11 iii iv 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 l 16 17 18 19 20 l 21 22 23 24 25 26 27- 28 !
Appendix A A-1 A-2 l
1 l
1
_ . . _ _ . _ - _ _ . _ . , _ . - 4
DR-03415-1 REV Paga iv 1.0 SCOPE . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 STRUCTURE DESCRIPTION . . . . . . . . . . . . . . . 1 2.1 Canister Design . . . . . . . . . . . . . . . . . 1 3.0 ANALYTICAL APPROACH . . . . . . . . . . . . . . . . 2 3.1 Methodology . . . . . . . . . . . . . . . . . . . 2 3.2 Buckling Load Assessment . . . . . . . . . . . . . 3
~
3.3 Finite Element Model . . . . . . . . . . . . . . . 4 4.0 LOADING . . . . . . . . . . . . . . . . . . . . . . 4 4.1 Applied Forces . . . . . . . . . . . . . . . . . .4 4.2 Boundary Conditions . . . . . . . . . . . . . . . 5 5.0 RESULTS . . . . . . . . . . . . . . . . . . . . . . 6 5.1 Fuel Drop Accident Impact Loads . . . . . . . . . 6 5.2 Buckling Mode Shapes . . . . . . . . . . . . . . . 6 5.3 Prebuckled Stresses . . . . . . . . . . . . . . . 6 5.3.1 Top Impact . . . . . . . . . . . . . . . . . . . . 7 5.3.2 Corner Impact . . . . . . . . . . . . . . . . . . 8
6.0 CONCLUSION
S . . . . . . . . . . . . . . . . . . . 8
7.0 REFERENCES
. . . . . . . . . . . . . . . . . . . . 10 LIST OF FIGURES APPENDIX A FUEL DROP ACCIDENT LIMIT LOADING A.1 ENERGY ABSORPTION . . . . . . . . . . . . . . . . A-1 -
A.2 LOAD CALCULATIONS . . . . . . . . . . . . . . . . A-1 9
4
i DR-03415-1 REV . Paco 1 l
1.0 SCOPE l I
l 1
! This report summarizes reassessment of the fuel drop accident impact '
s j loads used for the structural qualification of the Maine Yankee spent .
l fuel storage racks furnished in accordance with References 1 and 2. The original loads were reported in Reference 3. The reassessment comprises recomputation of the buckling loads for load cases la and 2 of Reference 3, to include the effect of the flared canister top. The recomputation I
i is based on linear elastic plate buckling theory, and was performed with the ANSYS finite element program. Neither post-buckling effects nor plasticity are included, in accordance with the original load computation. The finite element model is a detailed representation of .
the canister structure, of sufficient extent to isolate pertinent local buckling mode,s. Only the buckling load and the corresponding penetration distances are recomputed.
- 2.0 STRUCTURE DESCRIPTIOli i
The fuel rack structure comprises an array of canisters supported on an
- open gridwork which in turn rests on adjustable feet located near the corners. Figure 1 shows some fuel storage rack design details.
2.1 Canister Design The inside of each canister is 8.75 inches square, except at the top and bottom which flare to an outside dimension of 10.25 inches square. The cenisters are made from stainless steel sheet 0.105 inches thick. Figure 2 shows the canister design. The canisters are welded to each other at l
- the top and bottom and welded to the lower gridwork. The canisters at i
DR-03415-1 REV Pecs 2 the outside of the array are further secured by a 4 in X 3/8 in perimeter bnr welded around the top of each rack. In the following report the term
- ' top' denotes the 10.25 in sq x 4 in deep section at the top of each canister; the ' flare' is the 3.5 in deep transition between the top and >
the 8.75 in square section forming the remainder of the storage cavity.
Roference 2 contains further descriptive material. Only the canister itself is included in this analysis, since the potential damage from fuel drop accident loadings is confined to the impact zone.
3.0 ANALYTICAL APPROACH The local effects of the fuel drop accidents allow the overall rack assessment to proceed as though the loading were applied statically, using forces derived from conditions at the impact point. Pertinent yielding and elastic buckling loads are taken as limit loads which do work during the accident equal to the drop energy.
3.1 Methodology Loads and stresses are developed from energy considerations, as follows:
- 1. An arbitrary dummy load, Fd, is applied statically at the impact point. i
- 2. The maximum element stress under the dummy load is noted.
- 3. The impact load Fcr is taken as the lower of the following: '*
O
DR-03415-1 REV Poco 3
- a. The load at the onset of yielding found by noting the maximum stress in the impacted component under the dummy load and taking the impact load, Fcr, as Fcr = Fd x Yield stress / Maximum element stress
- b. The load required to cause elastic buckling in the impacted ,
j component 4
- 4. The canister is assumed to deform locally under the impact at a constant load equal to Fcr which does work on the dropped fuel bundle equal to the kinetic energy acquired in the drop.
The kinetic energy is the product of the fuel bundle weight and the drop height.
The computed rack loading is taken as the appropriate multiple of the canister limit load if more than one canister is involved. _
Elastic strain energy is negligibly small, but the effects are included
- for consistency with Reference 3. This approach ignores energy absorbed j
1 by the pool. floor and by deformation of the object being dropped.
3.2 Buckling Load Assessment ANSYS buckling analysis uses the displacement response to the dummy load to compute a stress stiffening matrix. Eigenvalues are then computed in the form of multipliers which are applied to the dummy load to figure the ,
i buckling load. Postbuckling and plasticity effects are not considered.
A buckling eigenvector is aiso computed which defines the buckled shape.
The pre-buckled stress and displacements are taken as the stress and displacement response to the dummy load times the buckling load .
multiplier.
0
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DR-03415-1 REV Pcco 4 3.3 Finite Element Model Two finite element models were used in the reassessment. Figure 3 shows the model used to compute buckling loads for the canister top impact, and .
Figure 4 shows that used to assess corner impact. The model used to essess impact along the top edge takes advantage of appropriate symmetry; no such symmetry exists for the corner impact, so the entire canister periphery is included. The models are a detailed representation of the canister using dimensions taken from Reference 4 except that corner bend radii are not included. ANSYS STIF43 and STIF63 plate elements are used 1 throughout. The model is of sufficient extent and detail to include all pertinent local buckling modes. Loading and boundary conditions are .
discussed in Section 4.0 4.0 . LOADING The fuel drop accident loadings from Reference 3 to be reassessed both involve impact on the canister top. Following the terminology of Reference 3, Load Case 1 considers the impact loading distributed over one side of the canister, and Load Case 2 concerns impact directly on the i
canister corner. Load Case 1 is termed the ' top' impact, and Load Case 2 is the ' corner' impact.
4.1 Applied Forces 1 1
I Reference 3 does not distinguish separate response mechanisms for the two loading cases, but the corner is clearly a 'hard spot,' so loading is carried differently from loading taken on a single canister side. As a result, loading is applied uniformly to one canister side for the top C
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DR-03415-1 REV Pass 5 inpact and as a point load for the corner impact. As noted above, the cnalysis begins by determining the response to a dummy load which is taken arbitrarily as 1000 lb.
4.2 Boundary Conditions Symmetry conditions applicable to the top impact permit the model to comprise only half the canister with appropriate restraints applied at the cut edge. Vertical restraint is applied at the bottom edge of the model. The corner impact loading allows for no such symmetry, so the entire canister periphery is included in the corner impact model.
Horizontal and vertical restraint imposed by welds to the adjoining .
canisters is ignored.
Conditions imposed along the top edge of the canister profoundly affect the character of buckling. The top edges of all canisters are restrained to a degree against motion normal to the canister surface: interior canisters are restrained by adjoining canisters; outer canisters are restrained by the top perimeter bar. Buckling loads for the top impact are determined with and without outward top edge restraint, although the
- presence of outward restraint is more realistic. For the corner impact loading the outward restraint imposed by the perimeter bar is ignored and buckling loads are computed assuming that the top edge is unrestrained.
The loading computation provided in Reference 3 presumes the existence of complete outward restraint. l t
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DR-03415-1 REV Page 6 5.0 RESULTS Primary results are computed impact loads and penetration distances, for both load cases. Additional material, provided in support of the conclusions, includes the buckling mode shapes and pre-buckled stress i
distributions.
5.1 Fuel Drop Accident Impact Loads Table 1 summarizes the fuel drop accident impact loads and penetration distances. Summary results for the top impact are provided only for the more probable case of outward restraint on the top edge. Appendix A ^
chows complete calculations including results for both edge restraint conditions evaluated for the top impact loading.
i 5.2 Buckling Mode Shapes
- Figures 5 and 6 show buckling mode shapes for Load Case 1 with and without outward restraint at the top edge of the canister. Figure 7 shows the buckled shape for corner impact. Since elastic buckling does i
I not obtain for the corner impact and when outward restraint is imposed on the canister edge, elastic buckling mode shapes for these two loading conditions are provided strictly for cultural value.
- 5.3 Prebuckled Stresses ..
Stress contour plots were generated using the ANSYS post processing routines. Up to buckling the stress distribution is assumed proportional to the load; the stress is therefore equal to the stress under the dummy load times the ratio of the limit load to the dummy load. Stress contour
DR-03415-1 REV Poso 7 values are noted on each plot in kai units.
Since the stress plots are based on linear, elastic action they are-clearly inaccurate in buckled areas or areas subject to yielding;
- nevertheless the stress contour plots provide insight in the loading mechanisms and illustrate the local nature of the impact loading response.
5.3.1 Top Impact - Figures 8-12 show the pre-buckled stress states for Load Case 1 computed for outward restraint at the top edge. Figures 13-15 apply to Load Cas.e 1 without outward restraint. Figures 8 and 9 show stress oriented lengthwise along the canister at the outer and ~
mid-surfaces of the canister plating. The stress distribution on the mid-surface refleczs direct load'ing; the outer surface contours show the combined direct and membrane bending stress contribution. Figures 10 and 11 show stress oriented peripherally, again at the outer and mid-surfaces. Figure 12 shows the maximum stress intensity at the outer surface; this plot shows the extent of yielding in the top of the canister. Figures 13-15 apply to the top impact when outward edge restraint is absent. The figures show outer surface lengthwise stress contours; mid-surface peripheral stress contours and mid-surface stress intensity contours. The close-up view of Figure 14 shows details of the l paripheral stress near the bend line.
Stresses are distributed in similar fashion regardless of the restraint **
conditions at the edge; differences between the stress contour plots for either edge condition reflect only different limit loads, not differences in loading mechanisms.
G
' ' ' ~~
l DR-03415-1 REV PcSa 8 5.3.2 Corner Impact - Stress contour plots for the corner impact are shown in Figures 16-17. The stress under this loading is clearly confined to the impacted corner and clearly dissimilar to the stress distributions for impact along the canister edge.
6.0 CONCLUSION
S
- 1. The top impact fuel drop accident assessment of Reference 3 somewhat overestimates the impact load and slightly underestimates the penetration distance of the dropped bundle.
Any similarity is entirely coincidental, since the loading mechanism assumed in Reference 3 is not realized.
- 2. The assumption of purely compressive load transfer through the
~
canister top is incorrect. The lack of support at the bend line forces vertical load to be carried in transverse bending by the canister top to the corners of the flared section into the lower portion of the canister. The plotted peripheral stress distributions are clearly typical of transverse bending.
- 3. Yielding at the flare bend line results from the biaxial stress distribution. One of the principal stresses is compressive and the other is tensile, so yielding occurs before either stress reaches the yield point by itself.
- 4. Evidently, the flare actually reduces the tendency toward buckling by forcing the compressive loading to be carried by the inherently stiffer canister corners. Loading at the flare bend line, is largely statically redundant, with the applied loads
DR-03415-1 REV Paco 9 being carried elsewhere.
Outward restraint offered by the flare itself and by tensile peripheral stresses is sufficient to preclude elastic buckling.
In the actual rack structure, the welds connecting adjacent canisters and the generous flare bend radius provide additional restraint and suppress buckling even further.
- 5. The ' free edge' assumption leads to unrealistically low buckling load estimates by ignoring restraint imposed by the nearby
~
unloaded portion of the rack. Loads are shared by the adjoining cans and the perimeter bar which substantially stiffens the -
l canister top and forces the canister to yield locally before buckling.
- 6. Under fuel drop accident loads the canister top fails by yielding near the flare corners. The extent of yielding is quite small, and clearly will not affect the fuel separation distance to any great degree.
- 7. The failure mechanism under the corner impact load is yielding directly under the load. The corner is stabilized against elastic buckling by the remainder of the canister top which is substantially unloaded. Yielding under this impact loading is quite local and can have no significant effect on fuel separation.
e
. 6
DR-03415-1 REV Para 10 i
7.0 REFERENCES
- 1. Maine Yankee Specification EDCR 81-13-S1.
- 2. GCA/ par Systems Document DC-9016-1, ' Design and Fabrication .
Criteria...'
- 3. GCA/ par Systems Document DR-9016-4, ' Equivalent Fuel Impact Static Load Analysis...,' Feb 11, 1982.
- 4. par Systems drawing AD-32352-D, ' Cavity Weldment.'
TABLE 1 - MAINE YANKEE FUEL DROP ACCIDENT IMPACT LOADING Load Case 1 2 -
Top Impact Point Edge Corner Fuel Weight - Wf (1b) 2500 2500 Drop Height - H (in) 18 18 Impact Energy - E (in-lb) 45000 45000 Canister Limit Load - For (lb) 22500 15000 Fuel Rack Load - (lb) 45000 30000
- Crushing Distance - (in) 0.970 1.480
)
l 1
l
DR-03415-1 REV Pcco 11 LIST OF FIGURES
- 1. Fuel Rack Design
- 2. Storage Cavity Design
- 3. Canister Finite Element Model for Top Impact
- 4. Canister Finite Element Model for Corner Impact
- 5. Buckling Mode: Top Impact With Outward Edge Restraint
- 6. Buckling Mode: Top Impact With No Outward Edge Restraint
- 7. Buckling Mode: Corner Impact
- 8. Lengthwise Mid-surface. Stress: Top Impact
- 9. Lengthwise Outer Surface Stress: Top Impact
- 10. Peripheral Mid-surface Stress: Top Impact
- 11. Peripheral Outer Surface Stress: Top Impact
- 12. Mid-surface Stress Intensity: Top Impact
- 13. Lengthwise Outer Surface Stress: Top Impact (Free Edge)
- 14. Peripheral Mid-surface Stress: Top Impact (Free Edge)
- 15. Mid-surface Stress Intensity: Top Impact (Free Edge)
- 16. Lengthwise Outer Surface Stress: Corner Impact
- 17. Mid-surface Stress Intensity: Corner Impact I
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DR-03415-1 REV Pagb 22
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1 I
APPENDIX A FUEL DROP ACCIDENT LIMIT LOADING A.1 ENERGY ABSORPTION The energy of the dropped bundle is assumed to be absorbed by the work done by elastic deformation and in subsequent crushing under constant load. .A dummy load is applied to the structure and the maximum stress intensity noted. Particularly high stress gradients under the load are excluded from this maximum, since highly local stress does not ~
determine the elastic limit load. At the same time the ANSYS-computed clastic buckling load is also found.
Assuming proportionality of load and stress up to'the yield point, an olastic limit load is found by multiplying the dummy load by the ratio of the yield stress to the maximum stress intensity. This limit load is compared with the elastic buckling load and the lower.value is taken as the canister crushing load. The fuel drop accident impact load may be a multiple of the individual canister crushing load if more than one canister is struck.
A.2 LOAD CALCULATIONS I
j Following Reference 3, the energy acquired by the dropped fuel bundle is equated to the sum of the elastic strain energy in the rack and the energy expended in crushing the impacted canister as follows:
Bundle kinetic energy
= Bundle weight x drop height ,
= WfH i Rack strain energy -M
= elastic strain energy + limit load x penetration distance
- = Fer gie/2 + Fcr eip Noting that
Fcr = Ksie l
DR-03415-1 REV i
PMo A-2 The penetration distance becomes:
Ap = WH/Fer - Fer/2K Where: -
Wf - Fuel bundle weight H - Drop height the - Elastic rack displacement
, tkp - Penetration distance
. K - Static rack stiffness (given as 760.28 K/in in .
! Reference 3)
For - Canister Limit load Table A-1 shows the results of this calculation. The figures should bo considered quite conservative, since no account is taken of elastic strain energy, friction or energy absorbed by the fuel bundle itself.
TABLE A MAINE YANKEE CANISTER IMPACT REASEZSSMENT IMPACT LOAD CALCULATION
~
i Load Case 1 1 2 Impact Point Top Top Corner Top Edge Restraint Condition Pinned Free Free
- Dummy Load - Fd (lb) . 1000 1000 1000 Maximum Stress - a (psi) 2000 2000 3000 l
Canister Yield Stress - a (psi) 45000 45000 45000 Elastic Buckling Load - Fe-(1b) 46238 11014 435970 Load to Yield - Fy (1b) 22500 22500 15000 Canister Limit Load - For (lb) 22500 -11014 15000 Fuel Weight - Wf (1b) 2500 2500 2500 Drop Height - H (in) 18 18 18 Impact Energy - E (in-lb) 45000 45000 45000 Canisters Involved 2 2 2*
Fuel Drop Accident Load - (1b) 45000 22027 30000 Elastic Stiffness - K (lb/in) 760280 760280 760280 i Crushing Distance - dap (in) 0.970 2.028 1.480
- - Perimeter bar load resistance taken as equal to an additional !
j canister edge.
t i $
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