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By Sohail Ejaz Abbasi 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 The KANUPP SFB is divided into four areas. Storage area
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 ~ 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


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

14 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

15 Available Water Shield Thickness (m)
Dose Rates Dose rates due to 10 years, 5 years and 1 year cooled spent fuel bundles are tabulated as: Dose Rates (mSv/hr) w.r.t. various cooling periods at available shield thickness Cooling Period (Years) Dose Rates (mSv/hr) Available Water Shield Thickness (m) 3.51 3.20 10 2.78E-06 4.35E-06 5 6.09E-05 7.22E-05 1 1.22E-03 1.48E-03

16 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 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

17 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

18 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

19 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

20 Proposed Amendment in Existing Storage Pattern
Each rack will hold 528 spent fuel bundles 7920 more spent fuel can be stored Overall 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

21 Proposed Amendment in Existing Storage Pattern

22 Comparison b/w Existing and Enhanced Storage Scheme
Parameters Existing Storage Enhanced Storage (HDTR System) Single Storage Unit in Bay 18 Fuel Trays Stack 48 Fuel Trays Rack (2 x 24 trays) Number of Bundles in Single Unit 198 528 Array in Bay 12x10 10x6 Number of Bundles in Bay 23760 31680 Fuel Storage Advantage (%) - 33.3 Available Water Shielding (cm) 396 351 Seismic Qualification (0.2 Ground Acceleration) Not Qualified Qualified

23 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.

24 High Density Tray Rack

25 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

26 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

27 HDTR System Operation

28 HDTR System Operation

29 HDTR System Operation

30 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

31 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

32 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



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