The pressurized water reactor or REFERENCE MARK ( PWR for Pressurized Toilets Reactor in English) is a technology of Nuclear reactor known as of second generation. It is the most widespread die of nuclear reactors in the world in 2006. The 58 French engines of power under operation use this technology.

The Fuel nuclear of a REFERENCE MARK is Uranium enriched, more precisely of oxide of slightly enriched Uranium: the proportion of fissile isotope U-235 varies from 3 to 5% according to the countries. The fuel is appeared as pastilles piled up and maintained in alloy sheaths of Zirconium which one calls pencil. The fuel pins are arranged in the form of assemblies whose mechanical resistance is ensured by grids. According to the models of REFERENCE MARK, one charges between 120 and 250 assemblies in the tank with the engine.

In the primary education circuit, ordinary water (in opposition to the heavy Water D₂O) under pressure is charged to recover the heat produced by the heart: it is this coolant which circulates within the assemblies between the pencils where the chain reaction occurs. The products of the nuclear reaction (Fission product and Transuranic S) are confined with uranium oxide inside the sheath of the pencils to avoid their dissemination and the contamination of the primary education circuit.

The water of the primary education circuit also acts moderating as : it with the capacity to slow down or thermaliser the neutrons of fission.

Like any type of thermal reactor (nuclear or with flame), a REFERENCE MARK is cooled by a great quantity of cool water pumped in a river or a sea. Near a REFERENCE MARK, one finds also sometimes a Tower cooling to cool and condense the vapor on the outlet side of the turbine.

Operation

The control of the reaction is ensured by the concentration of boron in the water of the primary education circuit and by the height of the control rods inserted in the fuel assemblies.

The typical parameters of operation of the water of the primary education circuit are:

- pressure: 155 bar;

- temperature: 300°C;

- flow: 60.000 m ³ /h.

Several steam generator located in the enclosure of the engine transfers heat from the nuclear boiler (primary education circuit) towards the secondary circuit comprising the turbine.

At exit of the steam generators, the vapor has the following characteristics:

- pressure: 55 bar;

- temperature: 270°C;

- flow: 1500 kg/s.

The vapor high pressure (HP) is slackened in the body HP of the turbine, then resurchauffée before continuing its relaxation in (or them) the body low pressure (BP). The turbine involves a Alternateur which produces electricity. The output of conversion of heat into electricity is approximately 33%.

On the outlet side of the turbine, the vapor passes in a condenser and becomes again of the water, which returns in the evaporator. Part of the heat of the secondary circuit is transferred in a tertiary circuit. The tertiary circuit is:

• is sent in a Tower cooling, where approximately 2% of water evaporate, the remainder condenses then is pumped in the basin located in lower part of the tower. Evaporated water is replaced by water coming from a river.
• is poured in a river or the sea, which increases its temperature at least locally.

The water which is used for cooling of the engine is pumped upstream in the river or the sea.

Neutron balance of a REFERENCE MARK

It is supposed that the only fissile material is ²³⁵U. The numbers indicated are orders of magnitude. 100 fissions of Uranium 235 release on average 250 Neutron S, which give place to the following reactions:

• 100 Neutron S cause 100 new fissions, thus maintaining the chain reaction, and consuming 100 cores of fissile material;
• 70 Neutron S undergoes fertile captures by 70 cores of fertile material ²³⁸U, transforming them into as many fissile cores of ²³⁹Pu;
• 75 Neutron S undergo non-fission captures, either by fissile cores (30 neutrons) or by cores of the cooling agent, structures of the heart, elements of control or fission products;
• 5 Neutron S flees out it heart (to be captured by neutron shieldings).

Structure

A nuclear plant equipped with REFERENCE MARK is organized around several buildings.

Building engine

Combustible building

Building of the auxiliaries of safeguard

This building shelters in particular the power supply emergency of the generators (or ASG). This system makes it possible to supply with water the steam generators after the stopping of the Turbine and the pumps feed normal.

Various types of REFERENCE MARK

• WWER (Russian engine)
• EPR (European engine in project)

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