By
Sohail Ejaz Abbasi and Tasneem Fatima
Karachi Nuclear Power Plant (KANUPP)
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CANDU Reactor
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In operation since 1972
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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
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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
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Total Water Depth : 5.94 m
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Water Shield thickness: 3.96 m
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8.7E-3 mSv/hr is maintained at 30.5 cm (1 foot)
above the water surface
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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
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5
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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
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Increase in no. of layers / stack
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Place cooler bundle tray at top of stack
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Reserve space for handling / storage of freshly
discharged bundles
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Computation of thickness of water column for
shielding
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Analysis of cooling capacity of bay water
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Criticality assessment
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Seismic Analysis
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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
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1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Average Discharge Burnup (MWD/TeU)
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
Years
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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
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Source Term Evaluated Over Cooling Period of 100 Years at
Different Burnups
1.0E+17
3000
1.0E+16
6000
Photons / sec
9000
1.0E+15
12500
1.0E+14
1.0E+13
1.0E+12
1.0E+11
0
10
20
30
40
50
60
70
80
90
100
Cooling Time (Year)
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More than 72% of total spent fuel bundles have
cooling time greater than 10 years
No. of Spent Fuel Bundles w.r.t. Various Cooling Time
9000
No. of Spent Fuel Bundles

8000
7000
6000
5000
4000
3000
2000
1000
0
>30
30-20
20-10
<10
Cooling Years
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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
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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
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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
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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
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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
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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
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Each rack will hold 528 spent fuel bundles
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7920 more spent fuel can be stored
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Overall 31680 spent fuel can be accommodated
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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
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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 Not Qualified
Acceleration)
Qualified
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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.
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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
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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
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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
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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
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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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THANKS
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