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Demonstration Drop Test and Design Enhancement of the CANDU Spent Fuel Storage Basket in MACSTOR/KN-400 Woo-Seok Choi *

International Conference for Spent Fuel Management from Nuclear Power Reactors May 31- June 4, 2010, Vienna, Austria IAEA-CN-178/08-04. 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)

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Demonstration Drop Test and Design Enhancement of the CANDU Spent Fuel Storage Basket in MACSTOR/KN-400 Woo-Seok Choi *

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  1. International Conference for Spent Fuel Management from Nuclear Power Reactors May 31- June 4, 2010, Vienna, AustriaIAEA-CN-178/08-04 Demonstration Drop Test and Design Enhancement of the CANDU Spent Fuel Storage Basket in MACSTOR/KN-400Woo-Seok Choi*, Jae-Yeon Jeon, Ki-Seog Seo(KAERI) Jung-Eun Park (KHNP)2010. 6. 2

  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. 1. Introduction • 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 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 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. Schematic drawing for the laser sensor arrangement Arrangement of two installed laser sensors

  6. 2.2 The second device to measure an impact velocity • 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. Arrangement of the second device Schematic drawing for 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

  8. 2.4 Leak test • 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. Basket under charging helium gas Leakage test by helium mass spectrometer

  9. 3.1 Drop test results (deformation) • 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 second drop test Dimension of a basket before/after the first drop test

  10. 3.2 Drop test results (impact velocity) • Case 1: Drop to the cylinder bottom • Theoretical free drop velocity: 12.13 m/s • Velocity reduction: 22.3% ~ 23.7% • Case 2: Drop onto the other basket • Theoretical free drop velocity: is 11.67 m/s • Velocity reduction: 21.0% ~ 21.6%

  11. 3.3 Drop test results (leak rate) Impacted area to the post of stacked basket(45 degree) Dropped basketfigure1 Dropped basket figure2 Loaded basket figure1 Loaded basket figure2 Leak rate: 1.5×10-2 atm· cm3/sec (HE) Leak from welding part between the top plate and the post(225 degree) Leak happening region (PT) Leak happening region (PT)

  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. The bottom plate of a dropping basket impacts to the post of a loaded basket

  13. 4. Design enhancement (Cont’d) • 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

  14. 4. Design enhancement (Cont’d) • 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 previous basket ※Collision between fuel dummy and top plate Post of the revised basket

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

  16. Thank You

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