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kknpp koodankulam nuclear power plant INPLANT TRAINING REPORT -KKNPP

INTRODUCTION

Nuclear Power Corporation of India (NPCIL) is a Government of India organization, under which the Kudankulam Nuclear Power Project (KKNPP) is being constructed. India is one of the largest producer of electricity. Two units each of 1000 MWe capacity are constructed in Kudankulam, Tamilnadu. This project is in collaboration with Russia. Design and equipments are supplied by Russia. Indian scope is the construction and commissioning of entire plant with Russian technical support. This is a Light Water Reactor (LWR).

A Nuclear power plant operates basically the same way as a fossil fuel plant, with one difference: the source of heat.  The process that produces the heat in a nuclear power plant is the fission or splitting of nucleus of any fissile material in the Nuclear Reactor. The part of the plant where the heat is produced is called the reactor core.  

The heat generated by Nuclear fission is carried by a medium which in turns transfer it’s heat energy to water in steam generator thus generating steam.

This steam drives the turbine-generator, just as in a fossil fuel plant. Generator produces the electricity.

Nuclear fuel used in this reactor is slightly enriched Uranium-235. Inside the reactor self sustained chain reaction goes on thus generating heat energy continuously. In this process a fraction of fissile material is consumed. Control rods are used to regulate the rate of chain reaction. Water is used as a heat transfer medium.

ABOUT THE SITE

Kudankulam is a small village in Radhapuram taluk, Tirunelveli district, located about 30 km north east from kanyakumari in the Gulf of Mannar. Kudankulam site area is rock type with high mineral content in an otherwise plain region. Plant area is about 2 km². 2/3^rd of the area covered by the sea.  This place before occupation was barren land.

                                      

We were accompanied to take familiarization about the equipments housed in the Reactor building, Turbine building, Pump house etc.,

Some of the points given during our in-plant training, site visit are listed below:

REACTOR SYSTEM                                   

VVER is the acronym for the Russian designed “water cooled, water moderated energy reactor”.  The VVER reactors belong to the family of Pressurized Water Reactors (PWRs).

Reactor plant consists of a Reactor Pressure Vessel, four circulating loops each containing a Horizontal Steam Generator and a main Reactor Circulating Pump. All the primary circuit pipelines are made up of SS material.

Pressurising system (Pressuriser) and Emergency Core Cooling System (Safety system – pumps, Hydro-accumulators etc.,) are also connected to the Reactor.

The Reactor plant also consists of Reactor Protection system, Auxiliary systems etc.

Salient features of the KKNPP are presented below:

Reactor rated thermal power, MWth            3000

Output (gross power), MWe                         1000

Fuel                                                             enriched UO₂ (average.2.5%)

Average fuel burn up, MWD/Ton of U         43,000

No. of fuel Assemblies in core                     163

Refueling is done once a year.

It is a three-circuit system:

·         Primary circuit (closed loop) contains Borated water radioactive coolant.

·         Secondary circuit (closed loop) is a DM (DeMineralised) water non-radioactive circuit steam.

·         Third circuit (once through) is non-radioactive circuit sea water.

Absorber Rod (Control Rod):

Control and Protection System Absorber Rods (Control Rods) move within the guide tubes in each of the Fuel Assembly. The absorbing material is Boron carbide (B₄C).

To arrest quickly the nuclear chain reaction all the electromagnets are de-energized, the latches are unlocked and the Absorber Rods falls in to the reactor by gravity within 2 to 4 sec and makes Reactor sub critical (Stops the chain reaction).

Reactor Circulating Pump:

The reactor coolant pumps serve to circulate the reactor coolant in the closed loops through the Reactor Pressure Vessel, the Reactor coolant piping and the Steam Generators.  It is centrifugal pump.

Pressuriser:

The Pressuriser serves to build up and maintain the necessary pressure in the Reactor Coolant System. Pressure is controlled by electrical heaters and water sprays.

Steam Generator:

The Steam Generators serve to produce steam required for the operation of turbine by transferring heat from primary coolant (tube side) to secondary side feed water (shell side).  It is shell & tube type.

Safety System (Emergency Core Cooling System):

Borated cooling water is injected into the Reactor core to remove the decay heat by High pressure and low pressure Safety system pumps (active system which requires power supply) and Borated water filled stage-I and stage-II Hydro-accumulators (passive system which do not require power supply).

They are provided to do safety function incase-of abnormal conditions by quick shutting down the reactor and making it sub-critical, fast cooling down, and continuous decay heat removal from core, confining radioactivity release from the core and safeguarding integrity of various systems.

The Containment Spray System through the spray headers provided in the top condenses the steam and quickly reduces the pressure buildup inside the containment during pipeline break and containment integrity is assured.

The Passive Heat Removal system (PHRS) removes the core residual heat in the event of complete loss of normal (grid power) and Diesel Generator power supply.  Hot primary coolant is cooled by atmospheric air in this PHRS heat exchanger.

Core catcher has been provided to confine the molten core if melting of the reactor core happens and prevents radiation release to the outside environment.

Hydrogen recombining system provided inside the primary containment.  They recombine Hydrogen and Oxygen molecules and change to water.  By this it prevents Hydrogen explosion and integrity of the containment structure is assured.

Note:

• In case of normal power supply fails, Diesel Generator will start and power supply will be restored back.
• In case of DG fails, supply will be through Battery bank.

Reactor containment System:

The Reactor building has a double containment structure.

The primary containment is a cylindrical structure made of pre-stressed reinforced concrete, with 8 mm carbon steel inner lining and a dome top.  Pre-stressed by Steel wires horizontally and vertically which gives additional compressive and tensile strength to the Primary containment structure.

This sealed enclosure houses main equipments of the primary system

Acts as shielding and protects personnel against radiation under normal and accidental conditions.  Protects equipments located inside against external hazards.

Inside the containments, slightly negative pressure is maintained by separate ventilation systems.  Hence contaminated air (radiation) will not release from the containment to outside atmosphere.

Primary containment is 1200mm thickness and Secondary containment is 600mm thickness.

Airlock (entrance) provided in the Reactor building with two doors.  Only one door can be opened at a time.  By this inside and outside environment are not communicated directly.

REACTOR AUXILIARY BUILDING

          This building houses various mechanical equipments, pumps, tanks etc for operational purposes and for maintaining the chemistry of the Reactor system. Main control room is located in this building annexure. The parameters of Reactor system, Turbine system and other functions are monitored from this building. This building contains lot of rooms, tunnels and shafts for pipelines and electrical cables which come from the Reactor. Fire proof doors, ventilation system and all mechanical equipments are located.

TURBINE BUILDING

Secondary circuit Convert the thermal energy (steam)(3000 MW_th) produced in the Reactor to electricity (1000 MW_e) by using the Turbo – generator.

The Turbine Systems consists of:

• A single, High Pressure turbine with dual flow design.
• A single stage combined Moisture Separator and Re-heater which removes the moisture from the stream after used in High pressure turbine.
• Three Low Pressure turbines with dual flow design.
• Three Condensers to condense the steam after used in the Low pressure turbine.
• Regenerative Feed Heating System contains Heaters heated by steam bled from the turbine.  The set of heaters heat the condensed water collected in the condenser and goes to the de-aerator. Here required chemistry of the Feed water is maintained before supplying to the Steam generator to produce steam.

The turbine rotates with a speed of about 3000 rpm. The turbine is impulse-reaction type. The Turbine and Generator connected in the same shaft.  Electrical power is produced in the Generator is 1000 MW.

The generated output power is transmitted through 400 kV switchyard building to Tirunelveli and thereby to southern grid.

The bearings used in the turbine is Journal bearing. They are lubricated by oil system. The water used to produce steam is de-mineralized (DM) to avoid any corrosion or erosion to the components.

The turbine is mounted on the vibro isolator provided in the turbine building.

    

SALIENT FEATURES OF VIBRO ISOLATORS

• Elimination, transmission of forces, motion resonance effects.
• Can compensate for misalignment of foundation or equipment.
• Ability to take shock.
• Reduces mass of foundation.
• Ability to take up seismic load.

PUMP HOUSE BUILDING

It houses Condenser cooling water circulating pumps (6 nos.).  These pumps circulate sea water which comes from forebay structure and through condensers (3 nos.) go back to the sea.

In Fish catching facility Screens & meshes are provided through this large size fishes cannot enter. And compressed air is given in the entrance. It tends the small size fishes to swim in the upper surface only.  Three stages of curved structures do not allow the fishes through them.  Upper portion of the water is discharged back to the sea. But sea water for the plant purpose is collected from the bottom of this structure through underground tunnels and connected to the fore-bay structure where pump house is connected.

COMMON BUILDINGS

Both Unit-1 and Unit-2 share common buildings for reasons of safety and economy. Orientation and location of these buildings are optimized from topographical consideration.

Common building houses;

·         Chiller building: Chillers for supplying chilled (cold) water for maintaining ventilation.

·         Compressor building: Compressors for giving compressed air for the requirement of the operation of pneumatic valves.

·         Health physics building: For monitoring and controlling the radiation field and radiation workers.

·         Centralised mechanical workshop: Maintenance of mechanical equipments are being done here.

·         Engineering utility building:  All maintenance and operation personnel office is located here.

Desalination plant: It comprises of triple stage process with mechanical vapour compression.  Almost 2/3^rd of the sea water is rejected as brine to the sea and the remaining water is qualified as usable water.  It is free from minerals and salts. 

After this, water is sent to De-mineralising (DM) plant where the ionic impurities are removed through Ion-exchangers and qualified for the use in Reactor and Turbine system.

Water after desalination process is added with calcium dosing to make as domestic (drinking) water.  This is the only water serves for plant usage and township usage.

CONCLUSION

The complete training period has allowed us to learn new things and concepts on how ideas are transferred from paper to the field. Instead of looking concepts from books, observing them first hand at the site is self explanatory.

We have also learnt that safety and quality are to be given prime Importance. We are sure that this training will be of great help to us in the Engineering future.

During this training period, the concepts of nuclear plant and its safety are understood thoroughly. Safety systems provided in the KKNPP makes this plant more safer than other nuclear plants in this world.