How does a NPP operate?
A nuclear power plant (NPP) is a combination of necessary systems, devices, equipment and structures intended to produce electricity. The plant uses Uranium-235 as fuel. A nuclear reactor makes different NPPs from other power plants.
At NPPs three conversions of energy happen.
1. Nuclear energy goes into thermal energy
The reactor is the basis for the plant; is a volume that hosts nuclear fuel and controlled chain reaction. Uranium-235 splits into slow (thermal) neutrons to result in an enormous amount of heat.
2. Thermal energy goes into mechanical energy
Heat is removed from the reactor core by coolant; it may be a liquid or gaseous substance which passes through the core. This thermal energy is used to produce water steam in the steam generator.
3. Mechanical energy goes into electric energy
Steam’s mechanical energy is supplied to the turbine generator where it goes into electricity and further moves to users by wires.
WHAT A NPP DOES CONSIST OF?
A nuclear power plant is a group of buildings which house process equipment. The main building includes the reactor hall where there is the reactor, spent fuel pond, and refueling machine (for recharging nuclear fuel). Operators control all these equipment in the main control room (MCR).
The main component of the reactor is the core(1). It is placed in the concrete vault. Control and protection systems are mandatory components of any reactor which allow for any selected mode of the controlled chain fission reaction, as well as the emergency protection system which promptly stops the reaction in case an accident. All these are assembled in the main building.
There is the second building which houses the turbine hall(2): steam generators and the turbine. Going further down the process flow diagram, there are condensers and high-voltage electricity supply lines which go off-site.
The site includes the building for recharging and storage of spent nuclear fuel in special ponds. Besides, plants are fitted with circulation cooling components, i.e. cooling towers(3) (concrete tower tapering off upwards), cooling pond (natural or artificial water reservoir) and spray ponds.
WHAT NPPs CAN BE?
Depending on the reactor type, NPPs can have 1, 2 and 3 loops for the coolant. In Russia 2-loop plants with WWER (water-water power reactor) reactors are widely used.
NPPs WITH 1-LOOP REACTORS
NPPs with 1-loop reactors are plants where RBMK-1000 reactors are used. The reactor operates together with two condensing turbines and two generators. With that, the boiling-water reactor is the steam generator itself that provides for 1-loop arrangement. One-loop arrangement is rather simple but in this case radioactivity affects all components of the reactor unit making the biological shielding more complicated.
At present, there are 4 NPPs with one-loop reactors in Russia
NPPs WITH 2-LOOP REACTORS
Two-loop arrangements are used at the plants with water-water reactors of WWER type. Water under pressure is supplied to the reactor core and heated up. The coolant energy is used in the steam generator to produce saturated steam. The second loop is non-radioactive. The reactor unit consists of one condensing turbine of 1000 MW or two turbines of 500 MW each with corresponding generators.
At present, there are 6 NPPs with two-loop reactors in Russia
NPPs WITH 3-LOOP REACTORS
Three-loop arrangements are used at NPPs with sodium-cooled fast neutron reactors of BN type. To exclude contact of radioactive sodium with water, the second loop holding non-radioactive sodium is built. This makes the arrangement three-loop one.
At present, there is 1 NPP with three-loop reactors in Russia
NPPs AS HEAVY-DUTY BASELINE POWER SOURCE
Intensive development of nuclear power can be viewed as a tool to counter global warming. For example, experts estimate that nuclear power plants in Europe prevent emissions of CO2 in the amount of 700 million tons annually. In Russia the existing NPPs prevent release of carbon dioxide in the amount of 210 million tons annually. Therefore, being a heavy-duty baseline electricity source, nuclear power significantly contributes to de-carbonization.
