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ENHANCEMENT IN THE STORAGE CAPACITY OF KANUPP SPENT FUEL STORAGE BAY

ENHANCEMENT IN THE STORAGE CAPACITY OF KANUPP SPENT FUEL STORAGE BAY. By Sohail Ejaz Abbasi and Tasneem Fatima Karachi Nuclear Power Plant (KANUPP). Introduction to KANUPP. CANDU Reactor In operation since 1972 Under water storage of spent fuel bundles in spent fuel storage bay

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ENHANCEMENT IN THE STORAGE CAPACITY OF KANUPP SPENT FUEL STORAGE BAY

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  1. ENHANCEMENT IN THE STORAGE CAPACITY OF KANUPP SPENT FUEL STORAGE BAY By SohailEjazAbbasi and Tasneem Fatima Karachi Nuclear Power Plant (KANUPP)

  2. Introduction to KANUPP • CANDU Reactor • In operation since 1972 • Under water storage of spent fuel bundles in spent fuel storage bay • Completed 30 years design life in the year 2002 • By refurbishment & safety upgrades, KANUPP operational life extended up to 2019

  3. KANUPP Spent Fuel Bay (SFB) • 11 spent fuel bundles stored in one storage tray • Storage Layout : 120 stacks of trays each consisting of 18 tiers of trays • Design Storage capacity: 23,760 spent fuel bundles • Total Water Depth : 5.94 m • Water Shield thickness: 3.96 m • 8.7E-3 mSv/hr is maintained at 30.5 cm (1 foot) above the water surface

  4. KANUPP Spent Fuel Bay • The KANUPP SFB is divided into four areas. • Storage area • Inspection area • Shipping cask area • Decontamination area • Designed for 20 years of operation with 80% capacity factor

  5. Existing Layout of Spent Fuel Storage Bay

  6. Storage Problem in KANUPP SFB • Almost complete its design capacity • Current SFB Inventory ~ 23151 spent fuel bundles (up to 1st January, 2010) • A dry storage facility is being planned as an ultimate solution of storage problem • An alternate short term remedy is to enhance the storage capacity of existing SFB

  7. Enhancement in Storage Capacity • Increase in no. of layers / stack • Place cooler bundle tray at top of stack • Reserve space for handling / storage of freshly discharged bundles

  8. Analysis for Enhancing Storage Capacity • Computation of thickness of water column for shielding • Analysis of cooling capacity of bay water • Criticality assessment • Seismic Analysis

  9. Computation of Water Shield Thickness • Evaluation of Source Term • Source term of spent fuel bundles is evaluated by employing ORIKAN computer code (modified version of ORIGEN 2 for KANUPP core) • The maximum value of 9000 MWD/TeU is selected as representative burnup • It provides envelope for all average discharge burnup variations

  10. Burnup Variations During 1972 – 2009

  11. Computation of Water Shield Thickness • Shielding Calculations • Contribution of all spent fuel bundles stored in storage bay is modeled • The rate of decrease of activity & decay heat of spent fuel is very fast within 10 years of cooling time; slows down after wards • 10 years cooling period is considered in the shielding Calculations

  12. Computation of Water Shield Thickness • More than 72% of total spent fuel bundles have cooling time greater than 10 years

  13. Computation of Water Shield Thickness • 2.13m water column thickness is sufficient to maintain required dose rate ~ 8.7E-3 mSv/hr • The active height of stack with 24 fuel trays is about 2.44 m • 3.51 m water column is still available to shield the spent fuel • The dose rate with 3.51m water column comes out as 2.8E-6 mSv/hr

  14. Dose Rates • Dose rates due to 10 years, 5 years and 1 year cooled spent fuel bundles are tabulated as:

  15. Analysis of Bay Cooling Capacity • Design total heat removal capacity of bay cooling system is 1.8 MWth • 0.21 MWth decay heat will be generated in the spent fuel storage bay due to overall 31680 spent fuel • 0.27 MWth decay heat is calculated due to unloading of in-core fuel bundles (assuming 3 months cooling) • The calculated total decay heat 0.48 MWth is well in limits of design heat removal capacity of bay cooling system

  16. Criticality Assessment • The spent fuel placed in HDTR in proposed layout in the spent fuel storage bay will remain subcritical in operational and accidental conditions • Use of steel in spent fuel trays, racks and liner in the surrounding walls of the bay make Keff even lesser

  17. Seismic Analysis • A seismic analysis enabled to assess the stability against seismic event (ground acceleration 0.2g) • The result of analysis reveals that overturning will not take place under the specified seismic loading • Sliding will take place, however much less than the clearance available b/w two adjacent racks or between a rack and bay wall • Stress analysis ensured that the axial, bending and shear stresses are within the allowable limits

  18. Proposed Amendment in Existing Storage Pattern • Storage capacity of SFB enhanced by increasing tray stack height from 18 layers to 24 • Seismic stability will be attained by placing these trays in a “High Density Tray Rack” • Two columns each consisting of 24 layers of trays will be loaded into one rack • 60 racks could be arranged in layout of 10 x 6 in the storage area of SFB

  19. Proposed Amendment in Existing Storage Pattern • Each rack will hold 528 spent fuel bundles • 7920 more spent fuel can be stored • Overall 31680 spent fuel can be accommodated • The development and implementation of HDTR System at KANUPP will enhance 1/3rd of design storage capacity • Expected to get relief by mid of 2017 assuming 72% RP and 75% availability factor

  20. Proposed Amendment in Existing Storage Pattern

  21. Comparison b/w Existing and Enhanced Storage Scheme

  22. High Density Tray Rack • The high density tray rack is a seismically and structurally qualified stainless steel frame to be placed in storage area of spent fuel storage bay.

  23. High Density Tray Rack

  24. HDTR System Operation • The HDTRs placement in the spent fuel bay and tray loading operation has been commenced in the month of April 2010 • At first step, five adjacent stacks of trays were transferred from their storage position to the inspection area • By using service building hatch and crane, a rack was brought into the shipping cask loading area of spent fuel storage bay • The bay crane picked the rack and placed in the predefined location in the storage area

  25. HDTR System Operation • 12 spent fuel trays with least cooling period were loaded at the bottom of the rack; six in each column of the rack • These trays were covered by loading 22 – 23 years cooled 36 trays; 18 trays in each column • Two high density tray racks have been successfully loaded so far in the presence of the IAEA Safeguards inspectors • Two more HDTRs will be filled during forthcoming IAEA Safeguards inspection

  26. HDTR System Operation

  27. HDTR System Operation

  28. HDTR System Operation

  29. IAEA Safeguards • KANUPP fuel is under IAEA Safeguards • High density tray rack and its top cover have been designed to facilitate the provision for IAEA safeguards seal • Two seals have been incorporated on to the top cover of each rack by the IAEA safeguards inspectors • Clearance ~ 100 mm b/w two adjacent racks and b/w rack & bay wall will be available to accommodate the Collimator used for annual spent fuel verification measurement carried out by IAEA inspectors

  30. Conclusions • By implementing HDTR system, the storage capacity of KANUPP SFB would be enhanced for about 7920 more spent fuel bundles • Augmentation in bay storage capacity will provide the enough time to build an interim spent fuel dry storage facility for KANUPP

  31. Future Plan • To achieve ultimate solution for spent fuel storage space problem in existing bay, an interim spent fuel dry storage facility has been planned to construct within plant premises • Operation of HDTR will be stopped, once the dry fuel storage facility would be operational

  32. THANKS

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