Heavy components: critical for plant performance
AREVA’s Chalon/Saint-Marcel manufacturing facility is unrivalled anywhere in the world for the manufacture of heavy components, including steam generators, reactor vessels and heads, pressurizers and internal equipment. The design and build quality of these components determines power plant performance. The Chalon/Saint-Marcel plant deploys state-of-of-the-art technologies and precision machining tools to ensure that the most exacting requirements are met.
The primary reactor loop
Vessels, steam generators, and pressurizers are complex components which require high precision machining during their fabrication. Technical operations accurate to one hundredth of a millimeter must be carried out on forged parts weighing several tens or hundreds of metric tons.
Deep drilling operations, executed by 3 boring heads, on steel plates up to 1 meter thick, must be completed with geometric accuracy to 1/100 of a millimeter, for example.
All of the internal component assembly operations are carried out inside contained, sanitized, and rigorously-checked assembly units. For certain parts, precision of assembly is guaranteed by laser guidance.
A shielded room equipped with a linear accelerator is used to perform in-depth radio tests to verify materials quality. Functional simulation tests end the checking and verification process.
During the inspection and testing process, steam generators are subjected to pressures of 250 bars, 1.5 times the pressure that will actually be present in the power plant.
The steam generator (SG) converts the heat produced by reactor core fission into steam. The steam drives turbine blades to produce electricity. Consequently, the basic quality of the steam generator, particularly the tube array and configuration, is critical for nuclear power plant safety and performance.
A few indications of scale:
- weight in excess of 500 metric tons: EPRTM type steam generators,
- height of 24 meters: EPRTM type steam generators,
- 18,000 bores on the Saint-Lucie steam generators,
- 140 kilometers of tubes on a single EPRTM type steam generator.
AREVA has supplied nearly 320 steam generators. Offering an extensive range of models varying in power, size, and capacity, the group can adapt its high-performance steam generators to meet customer requirements at any type of power plant.
The replacement of steam generators eliminates corrosion in pipe arrays, restoring original power levels and extending the overall service life of a power plant.
Since 1998, AREVA has replaced more than 79 steam generators, including half of all replacements commissioned in the entire United States market. The group also provides assistance with design and statutory requirements (licensing) for the commissioning of steam generators all over the world.
Reactor vessels and internal
Multi-dimensional plant integrity
The reactor vessel is the main component of the reactor coolant system. It completely seals the core and the fuel assemblies contained therein.
The internal equipment – a complex network of support rods, plates, guide tubes, shields, and baffles – forms a solid infrastructure for the core and isolates it from vibration.
The thickness of the vessel’s carbon steel wall (at 20 to 30cm) and the stainless steel cladding guarantee the containment of the internal reactions..
A few indications of scale – vessels for type EPRTM reactors:
- a height of 13 meters (including vessel head),
- a diameter of 5.4 meters,
- a weight of 526 metric tons (including vessel head),
- wall thickness of more than 30 cm.
AREVA’s priority is the attainment and maintenance of the highest levels of safety. The group’s experience in the manufacture of reactor vessels and internal equipment is unrivalled: AREVA has already supplied 80 vessels for pressurized water reactors (PWR) and more than 70 arrays of internal vessel equipment, as well as a large quantity of components for new reactors.
Reactor vessel heads
Improved safety and efficiency through vessel head design
Weighing several metric tons and clad in stainless steel, vessel heads form a further protective barrier between the fuel inside the vessel and the outside atmosphere. Precision-machining permits integration of control rod mechanisms into the vessel head to remotely regulate the nuclear reaction.
Vessel heads must effectively and safely guarantee both the integrity of the vessel (by sealing it) and the ability to remotely regulate the nuclear reaction inside it.
To date AREVA has supplied 80 vessel heads. The Chalon/Saint-Marcel plant has a production capacity of 10 to 15 heads per year. It is equipped with the very latest computer tools and equipment which facilitate precision welding, molding, machining, and heat treatment operations.
In 1992 the group was the first in the world to offer vessel head replacement services. Since then it has manufactured and installed more than 64 heads (including the dismantling, fitting, and testing of the units) in America, Asia, and Europe. This represents 78% of the world vessel head replacement market.video
In the heart of an stream generator
Essential components of a power plant, the role of steam generators is to transfer energy in the form of heat from the core to the turbines. Their performance depends on their engineering and construction. Virtual visit in the heart of a steam generator.
Maintaining a constant pressure in the reactor coolant system
The role of the pressurizer is to regulate the water pressure in the reactor coolant system. This key component consists of a vertical steel cylindrical tank, fitted with electric heaters enabling water pressure adjustment in the reactor coolant system. The pressurization of the system at 155 bars maintains water in its liquid state, best suited for efficient heat exchange.
A few indications of scale – pressurizers for EPRTM‑type reactors:
- Weight of 113 metric tons
- Height of more than 13 meters
- Diameter of nearly 3 meters
The Chalon/Saint-Marcel plant has already manufactured and supplied 70 pressurizers for light water reactors. Different models have been designed for power plants of between 900 MWe and 1,450 MWe, and are equipped with 66 to 99 heaters accordingly. A pressurizer for a 900 MWe reactor offers a thermal output of 1,440 kW.
Nuclear power plant operators have come to recognize the economic advantages of a complete pressurizer replacement as compared to multiple repairs programs. Replacement solves all problems linked with the corrosion or cracking found in the alloy 600 heating pipes or in dissimilar metal butt welds.
AREVA anticipates a considerable demand due to engagements made by numerous power plants around the world to replace alloy 600 components with new alloy 690 components. AREVA successfully manufactured and replaced the Sainte Lucie power plant pressurizer in the United States in 2008. This operation was a world first.
Tanks and support structures
The list of auxiliary components contributing to the safety of a nuclear reactor is extensive: accumulators, boron injection tanks, steam generator horizontal and vertical support structures, reactor pumps and vessels, vessel heads and internal lifting platforms, vessel supports, reactor coolant pipe clamps etc. Each item of equipment is manufactured according to strict specifications:
- Conformity with international and local standards and codes
- Application of high-precision machining, welding, and assembly techniques
Manufactures are subject to rigorous hydraulic tests and load tests, performed in the workshop, prior to their entry into service.
The boron injection system is a vital nuclear plant component. Its main function is to add concentrated boron to the reactor coolant system in the event of operating irregularities (such as the breakage of a steam line or secondary cooling system water line). Each tank is equipped with a pump which injects boron into the reactor coolant system. The boron absorbs the neutrons driving nuclear fission, so bringing the reactor to a subcritical state.
AREVA has already manufactured more than 50 injection tanks. The new models enable a reduction in the quantity of boron required to block the nuclear reaction, an innovation reflective of technical progress made in other component domains.
The accumulators also contain boron water which penetrates the reactor coolant system in the event of a drop in standard pressure. This operation compensates for any shortfall in liquid refrigerant flow in the reactor core. AREVA manufactures a full range of accumulators clad in, or made entirely of stainless steel. Each weighs between 32 and 38 metric tons.
Steam generator support structures
These stainless steel internal structures support the steam generator pipes and protect them from vibration and from any risk of displacement. This includes risks associated with external disturbances, such as seismic movements. AREVA support structure strength specifications are the highest in the industry.