1 Demonstration Drop Test and Design Enhancement of the CANDU Spent Fuel Storage Basket in MACSTOR/KN-400 Woo-Seok Choi *, Jae-Yeon Jeon, Ki-Seog Seo(KAERI) Jung-Eun Park (KHNP) Demonstration Drop Test and Design Enhancement of the CANDU Spent Fuel Storage Basket in MACSTOR/KN-400 Woo-Seok Choi *, Jae-Yeon Jeon, Ki-Seog Seo(KAERI) Jung-Eun Park (KHNP) International Conference for Spent Fuel Management from Nuclear Power Reactors May 31- June 4, 2010, Vienna, Austria IAEA-CN-178/08-04 International Conference for Spent Fuel Management from Nuclear Power Reactors May 31- June 4, 2010, Vienna, Austria IAEA-CN-178/08-04

2 Contents 1. Introduction 2. Demonstration test 3.1 Devices to measure an impact velocity 3.2 Accelerometers and strain gauges 3.3 Leak test 3. Drop test results 3.1 Deformations 3.2 Impact velocity 3.3 Leak rate 4. Design enhancement 5. Conclusion

3  A dry interim storage facility named MACSTOR/KN-400 for CANDU type spent fuels has been constructed at the Wolsung Power Plant(WSPP) in Korea.  The MACSTOR/KN-400 has 7 modules.  400 cylinders/module, 10 baskets/cylinder  Under the process of licensing this facility, KINS(Korea Institute of Nuclear Safety) recommended the demonstration drop test of the basket in this facility.  KAERI(Korea Atomic Energy Research Institute) conducted this test with the support of KHNP (Korea Hydro & Nuclear Power Co.).  A dry interim storage facility named MACSTOR/KN-400 for CANDU type spent fuels has been constructed at the Wolsung Power Plant(WSPP) in Korea.  The MACSTOR/KN-400 has 7 modules.  400 cylinders/module, 10 baskets/cylinder  Under the process of licensing this facility, KINS(Korea Institute of Nuclear Safety) recommended the demonstration drop test of the basket in this facility.  KAERI(Korea Atomic Energy Research Institute) conducted this test with the support of KHNP (Korea Hydro & Nuclear Power Co.). 1. Introduction A drop test facility consisting of a cylinder and tower A basket test model Macstor/KN-400

4 1. Introduction (Performance requirements)  Drop Conditions  Dropping a basket into a cylinder  Dropping a basket onto the other basket loaded in cylinder  Performance requirements  Deformation requirement is for the retrievability.  Leak rate requirement is for maintenance of containment boundary.  Geometric dimension  Inner diameter of cylinder : 1,117.6 mm  Outer diameter of basket : 1,066.8 mm  Drop Conditions  Dropping a basket into a cylinder  Dropping a basket onto the other basket loaded in cylinder  Performance requirements  Deformation requirement is for the retrievability.  Leak rate requirement is for maintenance of containment boundary.  Geometric dimension  Inner diameter of cylinder : 1,117.6 mm  Outer diameter of basket : 1,066.8 mm Performance requirement Allowable criteria 1. Deformation < 1,102 mm (for outer diameter of basket) 2. Leakage rate< atm·cm 3 /sec (He) Schematic drawing of a drop test facility and drop conditions

5 2.1 The first device to measure an impact velocity  Two devices invented and installed to measure the impact velocity of a basket  The first device uses two laser displacement sensors installed with a distance difference.  Calculates the time difference between the measured times when the basket passes over each sensor  The distance difference divided by the measured time difference yields the impact velocity.  Two devices invented and installed to measure the impact velocity of a basket  The first device uses two laser displacement sensors installed with a distance difference.  Calculates the time difference between the measured times when the basket passes over each sensor  The distance difference divided by the measured time difference yields the impact velocity. Schematic drawing for the laser sensor arrangement Arrangement of two installed laser sensors

6  The second device uses a fan shaped rotation device and a laser displacement sensor.  The invented device is installed above the cylinder.  A fishing string is rolled around the circulated object and one end of string is attached to the top of a basket.  When the basket starts to drop, the string becomes unfolded and the object starts to circulate. A laser sensor acquire the pulse data when it circulates.  From this pulse data, the RPM of the circulated object is calculated.  Consequently, an impact velocity is calculated from this RPM.  The second device uses a fan shaped rotation device and a laser displacement sensor.  The invented device is installed above the cylinder.  A fishing string is rolled around the circulated object and one end of string is attached to the top of a basket.  When the basket starts to drop, the string becomes unfolded and the object starts to circulate. A laser sensor acquire the pulse data when it circulates.  From this pulse data, the RPM of the circulated object is calculated.  Consequently, an impact velocity is calculated from this RPM. 2.2 The second device to measure an impact velocity Schematic drawing for the second device Arrangement of the second device

7 2.3 Accelerometer and strain gauge  Accelerometers and strain gauges are attached to basket only.  Accelerometers: 4 each  On spacer pad blocks by the space of 90 degree  Impact acceleration acquisition  Evaluate which bottom region drops first  Strain gauges: 8 each  4 strain gauges attached to the neighborhood of an upper welded part between the top plate and the post.  4 strain gauges to the neighborhood of a lower welded part between the side wall and the bottom plate.  Strain acquisition before and after impact  Accelerometers and strain gauges are attached to basket only.  Accelerometers: 4 each  On spacer pad blocks by the space of 90 degree  Impact acceleration acquisition  Evaluate which bottom region drops first  Strain gauges: 8 each  4 strain gauges attached to the neighborhood of an upper welded part between the top plate and the post.  4 strain gauges to the neighborhood of a lower welded part between the side wall and the bottom plate.  Strain acquisition before and after impact

8  Measuring the leakage rate after drop test  Procedure  Basket is charged with helium gas  A Sniffer test is conducted.  After basket is kept for 15 minutes, a leakage rate is measured by the helium mass spectrometer.  Measuring the leakage rate after drop test  Procedure  Basket is charged with helium gas  A Sniffer test is conducted.  After basket is kept for 15 minutes, a leakage rate is measured by the helium mass spectrometer. 2.4 Leak test Basket under charging helium gasLeakage test by helium mass spectrometer

9 3.1 Drop test results (deformation) BeforeAfter Diameter (0º-180º) Diameter (90º-270º) Height (0º) Height (90º) Height (180º) Height (270º) Dropping basketLoaded basket BeforeAfterBeforeAfter Diameter (0º-180º) Diameter (90º-270º) Height (0º) Height (90º) Height (180º) Height (270º)  After the drop test, both of the dropped basket and the loaded basket were withdrawn by a grappler.  The retrievability of both baskets was maintained.  After the drop test, both of the dropped basket and the loaded basket were withdrawn by a grappler.  The retrievability of both baskets was maintained. Dimension of a basket before/after the first drop test Dimension of a basket before/after the second drop test

10 Drop test Using 2 laser sensors Using rotation device case 1 1 st drop test 9.43 m/s9.26 m/s case 1 2 nd drop test 9.42 m/sN/A Drop test Using 2 laser sensors Using rotation device case 2 1 st drop test 9.15 m/s9.17 m/s case 2 2 nd drop test 9.22 m/sN/A 3.2 Drop test results (impact velocity)  Case 1: Drop to the cylinder bottom  Theoretical free drop velocity: m/s  Velocity reduction: 22.3% ~ 23.7%  Case 1: Drop to the cylinder bottom  Theoretical free drop velocity: m/s  Velocity reduction: 22.3% ~ 23.7%  Case 2: Drop onto the other basket  Theoretical free drop velocity: is m/s  Velocity reduction: 21.0% ~ 21.6%  Case 2: Drop onto the other basket  Theoretical free drop velocity: is m/s  Velocity reduction: 21.0% ~ 21.6%

11 Impacted area to the post of stacked basket (45 degree) Dropped basket figure 1Dropped basket figure 2 Loaded basket figure 1Loaded basket figure 2 Leak happening region (PT) Leak from welding part between the top plate and the post (225 degree) Leak rate: 1.5×10 -2 atm· cm3/sec (HE) 3.3 Drop test results (leak rate)

12 4. Design enhancement  Clear understanding of the problem has been done by drop analysis.  Drop analysis showed that a large plastic strain happened locally at the welding part.  Clear understanding of the problem has been done by drop analysis.  Drop analysis showed that a large plastic strain happened locally at the welding part. The bottom plate of a dropping basket impacts to the post of a loaded basket

13  Direction of design enhancement (1) To enhance the welding performance of welding region itself (2) To afford the deflection of the bottom plate of the dropped basket (3) To increase the bending rigidity of the top plate of the basket (4) To increase the bending rigidity of the bottom plate of the basket  Six revised designs based on the design direction were generated  Direction of design enhancement (1) To enhance the welding performance of welding region itself (2) To afford the deflection of the bottom plate of the dropped basket (3) To increase the bending rigidity of the top plate of the basket (4) To increase the bending rigidity of the bottom plate of the basket  Six revised designs based on the design direction were generated The revised basket designs Revised designs Design direction 1. Increase of the welding thickness at top welding region(1) 2. Addition of extra spacer pads and increase of rib height(2) 3. Increase of the thickness of side wall(4) 4. Increase of the thickness of bottom plate(3) 5. Increase of the thickness of top plate(4) 6. Decrease of the height of central post(2) 4. Design enhancement (Cont’d)

14  Among 6 proposed designs, the final revised design was achieved by the evaluation of many FE analysis and the specimen test.  The final revised design was the one, which is decreasing the height of the central post.  And the revised design was achieved by the minimum design change from the original design.  Demonstration test with the revised basket satisfied all the performance requirements.  Among 6 proposed designs, the final revised design was achieved by the evaluation of many FE analysis and the specimen test.  The final revised design was the one, which is decreasing the height of the central post.  And the revised design was achieved by the minimum design change from the original design.  Demonstration test with the revised basket satisfied all the performance requirements. Post of the revised basket Post of the previous basket 4. Design enhancement (Cont’d) Revised designsEnhancement Strain (%) (Previous:28.07%) 1. Welding thickness increase ▲ Addition of extra spacer pads and rib height increase ▲ Side wall thickness increase ▲ Bottom plate thickness increase △ ※△ ※ Top plate thickness increase ▼ ※▼ ※ Over than elongation 6. Central post height decrease ▲ ※ Collision between fuel dummy and top plate

15 Deformation Basket impact velocity Acceleration history Strain history Design Enhancement Needed Demonstration test with the revised basket satisfied all the performance requirements. Evaluation of FE Analysis and Specimen Test Comparison between Test and Analysis Results Data Acquisition During Test Performance Requirements 5. Conclusion Deformation (Retrievability) criteria satisfied Leak rate criteria not satisfied for the loaded basket Verification through PT

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