Indian Experience in Commissioning, Operation and Safety of Wet type Spent

Fuel Storage Facilities

B Shreekumar and Kailash AgarwalFuel Recycle Group

Bhabha Atomic Research centreINDIA

PHWR FUEL BUNDLE

URANIUN OXIDE PELLETS19 PIN CLUSTERZIRCALLOY CLAD

AVERAGE BURNUP-7000 MWD/Te

SPENT FUEL STORAGE TRAY

A6

TRAY NO. B1

B2B3

B10

B9

B8

B7

B6

B5

B4

TRAY NO. A1

A2

A3

A10A9A8A7

A5A4

o

o

o

o

BANK B

BANK A

Arrangement of 2x10 fuel trays inside shipping cask

SPENT FUEL STORAGE

KEY PLAN - FUEL POOL BULDING

SECTIONAL ELEVATION-POOL BUILDING

Fuel Storage : Important parameters

Water quality (pH 6.8 to 7.2, Sp Cond 1uS/Cm, Turbidity < 1 ppm)

Pool water activity < 185 Bq/ml

Pool water level > 3.0 m above top most fuel

Pool water Temp < 45 deg C

CONSIDERATIONS IN DESIGN OF STORAGE

Layout : To consider vehicle air locks for entry and exit

of trailer Separation of active and in-active services and

equipment Maximum utilization of fuel pool area for

storage Capacity : Fuel burn up and stacking density Shielding: Water depth and wall thickness

CONTD.

Provision for leak detection and collection either from liner failure or RCC wall failure

Ventilation system : To maintain negative pressure inside pool area, filtered supply, HEPA in exhaust side, RCC stack

Pool water polishing system : To keep pool water activity low and maintain pool water chemistry

Pool water cooling system : To keep pool water temperature below 45oC

CODES AND GUIDES ON THE SUBJECT

AERB Safety Guide No.: AERB/ SG /D-24 Design of Fuel Handling and Storage Systems For Pressurized Heavy Water Reactors

ANS 57.7 – 1988: Design criteria for an independent spent fuel storage installation ( water pool type)

IAEA Safety Series No. 116 1994: Design of spent fuel storage facilities

IAEA Safety Series No. 117 1994: Operation of spent fuel storage facilities

IAEA Safety Series No. 118 1994: Safety assessment for spent fuel storage facilities

IAEA Technical Report Series No. 240 1991: Guidebook on spent fuel storage

DMWATERPLANT

EXHAUSTVENTILATION

POLISHINGUNIT

SYSTEM

SPENT FUELSTORAGE POOL

WATER SYSTEMCOOLING

VENTILATIONSYSTEM

SUPPLY

EOT CRANE

CASK FORSPENT FUEL

MAKE-UP

SPENT FUEL STORAGE FACILITY

STACK

REPROCESSING

BY 75 Te

FEATURES PROVIDED IN SFSFs

OBE design of pool and building structure Use of HPC with micro-silica and box type water

proofing of walls & raft Design load - 30 stack of trays Leak detection & collection system having 50 zones Infiltration gallery for maintaining water table below

pool raft with 200% stand by pumps on DG 3 mm SS lining on walls, 6 mm on floor and 20mm for

cask seating area Single failure proof 75 Te EOT crane for cask

handling Mix of regenerated type MBU & disposable Cation Provision for handling of trays and fuel bundles on

pool bridge on both sides

FEATURES Contd.

Tray locators to avoid sliding and for automation Pull-pull ventilation around pool VFD drives for ventilation fans for better control &

energy saving A direct viewing facility from control room for cask

loading / unloading operations On-line monitoring of pool water chemistry Monitoring of all critical parameters in SFSF control

room and also in nearby reprocessing plant control room

FEATURES Contd.

Redundancy in Polishing system, ventilation system, Cooling system

Waste storage( LLW and ILW) facility and effluent transfer system

75 Te Crane, cooling system, exhaust fans ,lighting on class-III supply and HP monitors and critical instruments on class-II/UPS

SS LINING, LEAK DETECTION &COLLECTION SYSTEM

INFILTRATION TRENCH

MATERIAL HANDLING SYSTEMS1) 75/5 Te EOT CRANE2) 2 Te POOL BRIDGE3) 10 Te EOT CRANE

SINGLE FAILURE PROOF CRANE

Failure of any single component in load path shall not lead to uncontrolled movement of critical load.

Two load paths; each consisting of gear box, rope drum, brakes and hooks

Seismically designed girders with anti-toppling lugs and end stoppers

Analysis for swing of load Galvanized steel core wire rope VFD drives for smooth control of speeds

POOL BRIDGE

Rack and Pinion drive VFD drives for LT,CT and Hoisting Provision for Tray handling Provision for Bundle handling Safety interlocks for safe handling under min

water level Provision for automation

POLISHING SYSTEM

POOL COOLING SYSTEM

MUCK CLEANING SYSTEM

VENTILATION SYSTEM

SFSF POOL BUILDING VENTILATION

SAFETY ANALYSIS

1. NORMAL OPERATION

Radiological safety Liner leakage Accidental fall of fuel bundles during handling of

trays Siphoning of fuel pool water Build up of activity & personnel exposure Area contamination / Air contamination Class-IV Power failure

2. OFF-NORMAL CONDITION

Black-out scenario Cooling system failure Ventilation failure Swing of 75 Te crane holding the load in seismic

event A storage tray falling on a stack of spent fuel

bundles Accidental fall of shipping cask in pool Fall of stack of trays and bundle failure Accident management plan is in place in the

event of any seismic event.

STEP-BY-STEP COMMISSIONING PROCEDURE• The fuel pool leak tight integrity has been checked

before and after lining.• The leak detection and collection headers, SS liners

have been 100 % checked for weld integrity by dye-penetrant test and vacuum box tests.

• The fuel handling equipment like 75 tonne and 10 tonne EOT cranes and Pool Bridge have been load tested after installation.

• The fuel handling devices and tools are tested under water with simulated loads to meet design intent.

• The ventilation system is checked for flow balancing and filters bank efficiency.

COMMISSIONING EXPERIENCE

COMMISSIONING PROCEDURE contd…•The low level and intermediate level liquid lines for waste transfer are tested with hydrostatic pressure and flow checks.•All the safety equipment and control room instruments are calibrated and tested in the field condition prior to start of operation.• The shipping cask with tractor-trailer, waste transfer casks and fuel bundle handling operation trials are carried out to ascertain the crane reaches and handling equipment compatibility.• The class –IV power failures and automatic switch over to class-III power mode are also tested with main loads.• The training of operators has been carried out through classroom lectures and field training during construction and commissioning phase.

PROBLEMS EXPERIENCED DURING COMMISSIONING

• Early replacement of HEPA filters due to dust accumulation in construction phase

• Failure of pool bridge shaft due to misalignment of rails during first few consignments of shipping casks

• Stuck up of cask lid with body in water and it’s remote retrieval.

Some of the important Operation and Maintenance activities in Spent Fuel Storage Facility

•Receipt, handling and storage of Spent fuel from PHWR’S as per the approved check list.•Monitoring of the fuel pool water level, temperature and recording in log book.•Maintaining pool water level.•Maintaining pool water temperature below 450 C by Operation of Fuel pool cooling system and recording various parameters of Primary cooling water pumps, Secondary cooling water pumps, Heat exchangers and Cooling tower.•Maintaining pool water activity below 185 Bq/ml by operation of Pool water polishing system and recording of various parameters including Pump discharge pressure, water inlet/out flow rate, DP across Cartridge filter, Cation cartridge and MBU etc.

Operation Contd…

•Operation of Muck cleaning unit to clean the floor of the fuel pool.•Regular sampling and analysis of Pool water, make up water, Infiltration well water.•Physical inspection inside leak detection and collection bay and ensuring no water collection inside.•Local verification of alarm status in Area gamma monitors and Continuous air monitors. Spot air sample analysis around fuel pool. Changing filter papers for all the Continuous air monitors. Swipe survey taken at various floor areas and checking of contamination level. Radiation survey carried out at various areas.•Monitoring and recording of supply and Exhaust fans status including Speed, Bearing temperatures, current, Pressure drop across HEPA and Prefilter banks etc..

Operation Contd…

•Monitoring and recording of low level and medium level liquid waste levels in the tanks.•Collection, segregation, packing and transportation of CAT-I (Mops, Shoe covers, hand gloves etc) , CAT II / CAT III ( Cartridge filter & Cation cartridge of Pool water polishing unit, HEPA filters of E2 system and muck cleaning filters) solid wastes to Waste management facility for safe disposal.•Pumping and disposal of liquid wastes CAT-I & II arising from active floor drains, cask decontamination wastes, CAT III (MBU regenerant waste of Polishing unit) through waste transfer pipelines to waste management facility.

Operation Contd…

•Operation of DM water plant for fuel pool make up and also for cask decontamination unit.•Operation of Infiltration well pump and recording the hour meter readings.•Surveillance of Various systems including Health Physics monitors, Pool water level and temperature instruments, EOT Cranes, DG sets, Battery banks, Public address system, Exhaust filter bank efficiency, Air receiver pressure testing , fire fighting system and functional checks of logic of ventilation system and infiltration system as per the technical specification.

Major documents Preserved DBRs Preliminary Safety Analysis Report Design Reports (DRs) for civil design for pool, building

& stack DRs for piping, cooling system and ventilation system Safety manual QA manual GA drawings Technical specifications Commissioning procedures & Commissioning reports O&M manuals Emergency preparedness procedures Fire order