Post Fukushima Up-Grades

in

Prototype Fast Breeder Reactor Project

BHARATIYA NABHIKIYA VIDYUT NIGAM LIMITED

(BHAVINI)

INDIA

Prabhat Kumar * & P. Chellapandi**,

*Chairman & Managing Director , BHAVINI,

& Distinguished Scientist, Department of Atomic Energy, india

**Dir REG, IGCAR, & Distinguished Scientist, Department of Atomic Energy, india

PFBR Flow Sheet

2

Sectional View of PFBR

Reactor Assembly

3

1 Main Vessel

2 Core Support Structure

3 Core Catcher

4 Grid Plate

5 Core

6 Inner vessel

7 Roof slab

8 Large Rotatable Plug

9 Small Rotatable Plug

10 Control Plug

11 Absorber Rod Drive Mechanism

12 Transfer Arm

13 Intermediate Heat Exchanger

14 Primary Sodium Pump

15 Safety Vessel

16 Reactor Vault

PFBR Layout

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Secondary Sodium

Main Circuit

5

Sodium Piping system designMany safety precautions have been taken to prevent sodiumleakage and fire.

• Guard pipe is provided around primary sodium piping.

• Leak detectors & guard pipe nitrogen cooling.

• Leak collection trays are provided for the secondarysodium piping.

• All pipe lines are of welded construction & 100% NDE

• No valves in primary main circuit.

• Sodium fire fighting system using Dry Chemical Powder(NaHCO3) is established.

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Reactor protection system

• Two diversified systems – CSRDM (Control & Safety Rod Drive

Mechanism) and DSRDM (Diverse & Safety Rod Drive

Mechanism) are provided to shut down the reactor. During

the Reactor trip, all the control rods will drop by gravity into

the reactor to make it shut down (subcritical)

• Any one of the above system is sufficient to shut down the

reactor

• Both the systems are seismically qualified

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• There are four safety grade

decay heat removal systems in

PFBR.

• Four dedicated diverse sodium

to sodium heat exchangers

immersed in sodium pool will

transfer the heat from sodium to

air heat exchanger by natural

circulation itself.

• Heat from sodium to air heat

exchangers placed at elevated

locations will be dissipated to

ambient air, by natural circulation.

• These systems do not demand

external power supply

Safety Grade Decay Heat Removal Circuit

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Operation Grade Decay Heat Removal System• Decay Heat Removal through Steam Water System.

• Used when at least one secondary loop and steam water system areavailable.

• In addition to removing decay heat, OGDHRS fulfills the following:

• Decreases sodium system temperature uniformly at 250 C/h

• Maintains primary sodium temperature at hot shut down up to8 hours at 3500 C.

• Maintains plant at cold shut down up to 30 days at 200 0 C.

• Variable pressure steam condensers each of 5 MWt rating.

• Condensate recirculation pump (0.21 m3/s of saturated water at 170kg/cm2(a)

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lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll

SCHEMATIC FLOW SHEET OF OGDHR SYSTEM

Na in

Na out

MAIN FEED WATER PIPE

MAIN STEAM PIPEWW

STEAM

GENERATOR

STEAM

SEPARATOR

DECAY HEAT

REMOVAL

CONDENSER

BLOWER

ERVs

AIR

FLOW

ISOLATION

VALVES

RECIRCULATION

PUMPS

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Largest Raft 100mX100m

Pour – II Concrete In Progress

Multi-Well Point Dewatering System

Membrane Waterproofing below NICB Raft

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Tsunami strikes PFBR site onm26th December 2004

• First layer of NICB raft pour was commenced on 15-12-2004 andcompleted on 18-12-2004.

• Second layer of NICB raft pour was commenced on 24-12-2004 and 90% concreting was completed.

• Tsunami tide struck the site on 26-12-04 at 9.15 AM when Secondpour of concreting was going.

• Approximately 3,20,000cum.of water, sand, slush accumulated in

the pit.

• Shore protection was not available.

• Compound wall on sea side was not designed for tsunami force12

P O U R -1 3

P O U R -8 A

P O U R S E Q U E N C E & L A Y E R D E M A R C A T IO N

45°

1000

100 0

625

625 E L 9500

E L 11500

P O U R -9

P O U R -11

P O U R -10

P O U R -12

P O U R -4

P O U R -7 P O U R -8 BP O U R -6

P O U R -5

P O U R -3

P O U R -2

P O U R -1

P O U R N O .R E -B A R (M T )

Q T Y

C O N C R E T E Q T Y

c u .m

2 6 2 0

2 6 9 0

2 9 4 0

2 5 0 0

2 5 0 0

3 3 0 0

3 0 5 0

1 5 8 0

2 8 9 0

2 8 5 0

2 8 5 0

2 8 5 0

3 5 0

3 4 6 0 0

1

2

3

4

5

6

7

8A + 8B

9

10

11

12

13

T O T A L

N O T E : 1

1 5 5 0

7 0

7 2

3 6

3 6

4 2

4 5 2

1 3 0

7 4

7 4

5 8 7

5 8 0

-

3 6 9 8

P O U R S C H E D U L E

N

4470

625

3 50

66 0

31200 3 08 00

35 00

13

Tsunami struck

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Constitution of Expert Committee

• A high power committee consist of National experts wasconstituted to review the chances of occurring Tsunami ofsimilar nature.

• The committee after detail study concluded that the nearestepicenter is 1300KM away from West coast & earthquakeoccurred of severity 9.1 magnitude which is the highest so farseen. With this severity, the damage was minimum &earthquake of similar or lesser magnitude will not damage thenuclear plants in India.

• Sea surface Bathymetry studied various other organizations &it was established that along with East cost the median waveheights are found to be less than 4m.

15

Design Status Against Flood:

Finished Floor Level (FFL) Elevations of Important Plant buildings

above Mean Sea Level (MSL 6.096m)

• Nuclear Island Connected Building (NICB)

(RCB, SGB-1 &2, FB,CB ,EB-1&2, and RWB) : 9.7 m

• DG Buildings : 9.7 m

• Service Water Pump house : 9.7 m

Shore protection

Shore protection having for a length of around 1600 M and cross

section width of 30 M which runs parallel to the sea shore has been

provided. The top of the shore protection level is 3.37m above MSL.

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Design Upgrades after 2004 Tsunami

• The finished floor level of Safety related Buildings were raised

to 9.7 metres above Mean Sea Level (MSL). It may be noted:

• During the Tsunami the maximum water level rise observed

was 4.1 to 4.7 metres above MSL (6.096m).

• Design Basis Flood Level is 6.7m above MSL.

• The higher finished floor levels precludes any water entry to

Safety related Buildings, Emergency Diesel Generator Buildings,

and Power island

• Shore protection and Tsunami bund were constructed at sea

shore.

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SECTION OF

TSUNAMI PROTECTION BUND

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Shore

protection

Tsunami bund

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Lessons Learnt From 2004 Tsunami and

upgrade effected

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• Tsunami warning system has to be available

• Plant design has to undergo modification to account for tsunami

caused by 9.1 Rechitar Scale earthquake which resulted in

Wave Surge and Run-up of 4.1 to 4.8 meters at different places

in the plant: Finished grade level needs to be raised

• Shore has to be protected (shore line got altered and breached

the proposed outfall areas (Engineered shore Protection

System was introduced.)

• Tsunami wall has to be constructed

• Storm water drains were designed for one way flow by

constructing gates across the discharge point in order to avoid

back flow during floods.

• In Township RCC Tsunami Protection boundary wall was

constructed with Boulders, Sand dunes & Coastal Plantation.

• Tsunami Warning System was established to alert the residents

and the community around in case of any Tsunami event,

cyclone etc.

• Community development and awareness was made a part of

the Social development program for the neighboring villages .21

Design Upgrades/ Actions after 2004 Tsunami

Rehabilitation of PFBR site after 2004 Tsunami

• Removing sea water and sludge from pit was a large

challenge successfully accomplished in one month (approx.

3.2 Lakh Cum. 7m deep sludge)

• Debris clearing work was started within 3 days of tsunami

strike & was completed in months time

• All fallen trees were cut & approach roads were made

ready.

• Eroded areas of pit was backfilled by massive earth filling,

electrical cables were relayed, ground faults rectified &

power supply established

• Multi stage well point Dewatering system was restored. 22

Reconstruction of NICB with new Raft started in FEB 2005

• After Regulatory Board clearance BHAVINI management

decided to reconstruct new raft on the 2 layers already done

as:

• Chipping of 10mm top concrete having high chloride deposit.

• 100 mm PCC layer (using flyash) concrete on the second layer

of raft which was done before tsunami.

• Water proofing membrane was laid on the new PCC.

• And the new raft height was increased by 2.5m to enable

new FGL 9.7 meter above MSL.23

Drilling for core sampling

Core from rebar congestion in NICB raft bottom Layer

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10mm concrete was chipped off on exposed

portion of NICB Raft. Water proofing layer

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Post Fukushima Actions

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Constitution of Task Force

Immediately after the Fukushima Daiichi nuclear accident, aTask Force was constituted to conduct stress test on PFBR.Major areas covered were:

1. Model study to assess maximum height of futuretsunami and study the consequences on the plant andsystems: Modify design to account for such rise of water

2. Study Prolonged Station Black Out.

3. Study Beyond Design Basis Events (BDBE) of naturalorigin.

4. SSSB integrity and cooling of spent fuel27

The scope of the Task Force is on following areas:– Guides of “Safety Analysis”, “Safety Classification”,

– Further Technical Specification, such as:

• Reactivity features of SFR reactor core...

• Design conditions (incl. events lists...)

– Total Approach and Measures, such as:

• Sodium fire,

• Sodium-water reaction,

• In-service inspections

• Capability of Reactor shut down, maintaining shut down condition and corecooling.

• Affect on storage facilities of Spent fuel assemblies in Spent SubassemblyStorage Bay

• Availability of Diesel Generators beyond design basis scenario

• Additional DG back up in the event of emergency DG not available

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The scope of the Task Force is on following areas:

• Accident Management strategy and EmergencyPreparedness

• Radiological impact at site and public domain

• Adequacy of approach to handle emergency scenariofollowing DBA

• Entry of water inside the buildings due to water splash

• Approach road to site

• Multi unit concepts

• Communication

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Increasing the Tsunami Protection Bund Height :

• At present the Tsunami bund height is 5.4m above MSL which is

being increased to 9.4m above MSL and constructed on south of

the existing bund also covering total PFBR site from East, north

and south sides.

• Enclosing the SWPH: Flood retaining wall around Sea water

pump house up to the height of 9.7m above MSL is under

constructed to prevent water entry to pump house.

• Shore protection, sand dune and vegetation created along the

coast.30

Emergency Diesel Generators

4Nos. Diesel Generators are provided to meet the emergency

power requirement when the normal power supply fails.

However 2 DGs are sufficient to meet the Station requirement

during normal power failure.

All the 4 Diesel Generators are located at a higher elevation of

9.7m above MSL. All 4 DGs are in separate buildings, 2 are in

East side and 2 are in the West side of NICB.

Day tank capacity was increased from one hour to four hour

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Diesel Generator

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Additional Diesel Generators Air cooled (2 X 500 KVA)

• 2Nos. Truck mounted Additional Diesel Generators

capacity 500KVA,415V, installed & provision has been

made to connect to the existing battery chargers if

power does not resume in 4 hours.

• This will cater to the Emergency power needs in case all

the 4 Emergency DGs at PFBR become unavailable due

to the event.

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Additional Diesel Generator

500 KVA, 415V – 2 nos.

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Spent Subassembly Storage Bay (SSSB)

• SSSB has been designed with the pool in a pool concept,

where the concrete leak tight structure of the bay is situated

in another concrete leak tight structure with gap all around

including from bottom for regular inspection & leakage

monitoring.

• SSSB is qualified for Safe Shutdown Earthquake (SSE)

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Spent Subassembly Storage Bay (SSSB)

• The storage bay is lined with 5mm thick SS 304L plates with

inbuilt leak detection and collection arrangement below the

liner.

• Pumping back facility of leakage water to pool is available

• All the EOT cranes are Single Failure Proof (SFP) cranes & so

designed that the single failure will not result in the loss of

capability of the system to safely retain the load.

• Water seal tight doors to prevent splashing of water

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Spent Subassembly Storage Bay (SSSB)

Any Beyond Design Basis hypothetical external event can

initiate failure of SSSB & can cause a fall in water level in

bay due to following:

• Extended station blackout

• Leak in the Spent Fuel Storage Bay

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Spent Subassembly Storage Bay (SSSB)

• The system is provided with 3 pumps and 3 heat exchangers.

2 heat exchangers and pumps are sufficient to remove

maximum heat load of 800 kW of decay heat during full core.

• Station blackout whose maximum duration is expected to be

14 hours is considered as design basis which is a Category 4

event. Under this situation, the pool temperature will rise to

42oC under normal storage and 52oC under full core unloading,

after 14 hours.

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Spent Subassembly Storage Bay (SSSB)

• DM water tank of 45 m3 capacity is available for make-up

• Nearest Fire water hydrant is hooked up to SSSB incase DM

water make up is not available

• All piping penetrations are provided from top of the bay such

that complete draining is not possible.

• Syphon break arrangement is provided to limit the fall in

water level by 250 mm only from the normal level.

• If leak is observed in one compartment of the bay the Fuel

Subassemblies can be transferred to the other compartment.

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Bore wells for emergency water requirement to SSSB

• 3 nos. Bore wells (10m3/hr) are made to ensure water additionto SSSB incase of water leakage from SSSB .

• In case DM water & Fire water is not available, water from theBore wells will be pumped to SSSB.

• Spare portable Diesel motor pumps are kept ready forconnecting to bore wells, so that water can be supplied to theSSSB to maintain level even under conditions of station blackout.

• The Bore well motors are also power by emergency dieselgenerators.

40

Spent Subassembly Storage Bay (SSSB)

• 4 nos. of portable Diesel generator operated pumps of capacity

10 m3/h are positioned at safe locations in the plant for

emergency in place of fire water pumps and bore well pumps.

• In case of insufficient availability of water from all other sources,

Sea water will be pumped to SSSB to maintain the water level.

The portable DG operated pumps will be used for this purpose.

• Additionally, Fire tenders will be used for pumping water.

41

Instrumentation in SSSB

• Additional diverse instrumentation for Level and Temperaturemeasurements of Spent Subassembly Storage bay, independentof the main plant instrumentation system is provided.

• Simple float type level indicators, with level markings in thepool and suitable mechanical set-up to transmit the indicationto the exterior is designed in case of failure of main plantinstrumentation

• Provision has been made to take field measurement oftemperature.

42

Water seal tight Doors for preventing Water Splash

• Water seal tight doors at all major openings of NICB & FuelBuilding are under manufacturing & will be installed forpreventing the splashing of water during tsunami.

• All cable terminal boxes/junction boxes located outside NICB &Power Island on the east side are properly sealed against thesplash of water.

• All cable trenches are covered from top & sealed to preventwater seepage during flooding.

• Dewatering pumps installed at all major locations & inside thetrenches.

43

Radiation Emergency Handling Procedure & Infrastructure

• Approved procedure for handling of plant & site emergency

conditions available at PFBR along with other units

IGCAR,MAPS,FBTR,CWMF,BARCF for Multi units, duly approved

by District Collector .

• Operating crew for normal shift operation & emergency

conditions are available as per approved procedure.

• Site Emergency exercise drill is conducted once in a year in

PFBR, Kalpakkam along with other units.

44

Radiation Emergency Handling Procedure & Infrastructure

• Additional store built away from site

• Radiation protection instruments, equipment, batterypowered portable communication facilities , emergencylights, portable saw & other tools required to handle theemergency situation in is available in Emergency ControlCentre.

• Emergency response center is being made at plant site withSeismically qualified structure, having adequate radiationprotection equipments, emergency equipment, tools anddedicated communication facility with outside agencies isunder construction.

45

Radiation Emergency Handling Procedure & Infrastructure

• arrangements is made for continuous staying of crew working

round the clock

• New approach road has been constructed to plant site away

from sea shore with sufficient height.

• Alternate approach road is available incase of flooding of

existing road.

• Solar powered lights at important locations have been installed

in plant site & township.

• Kalpakkam Management Committee comprising of all units

heads is available to deal with all normal & emergency

conditions.46

• Key Viewpoints for future SFRs

– Robustness in power supplies, cooling functions, heat transportation system

including final heat sink

– Instrumentation to identify status of reactor core and containment vessel

– Independency and diversity of safety systems

• General aspects

– Passive safety functions

– Protection measures with adequate margins

• SFR specific aspects

– Attention to flooding in buildings with sodium equipment

• Note on stress tests

– Evaluate safety margins against severe plant conditions & extreme external

hazards.

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THANK YOU

Presented by:

Chenna Keshava B K Chief Engineer / Scientific Officer - H