Nuclear fusion heat exchanger to become ready for series production for ITER.
Seven nations are currently working together on building a nuclear fusion plant as part of ITER (International Thermonuclear Experimental Reactor), the world’s most extensive fusion experiment. For the first time, the plant is intended to deliver more power than is required for generating and maintaining the plasma. Some of the requirements on the components stretch the limits of what can be achieved with today’s technology. Test scale components from PLANSEE have already proved themselves and have made a significant contribution to the reference design of the forthcoming ITER plant. PLANSEE was recently awarded the contract for manufacturing full-scale prototypes. This final stage before series manufacturing is a serious challenge, and only three companies worldwide were able to qualify.
But let’s start at the beginning. How does nuclear fusion work? Energy is released when hydrogen nuclei fuse to form helium nuclei. That is the simple recipe for success behind this environmentally friendly and sustainable source of energy. The shining example of this process is the sun, which also generates energy on the same principle. But although it may sound simple, it is in fact the result of the complex interplay of many factors. In the nuclear fusion plant, hydrogen gas will be heated to temperatures in excess of 100 million °C. This produces a plasma in which the electrons are separated from the nuclei. At these extreme temperatures, hydrogen nuclei possess sufficient kinetic energy to collide with each other despite the repulsive electric force between them and fuse to form helium nuclei. Recoverable energy is released during this nuclear fusion process.
A magnetic field encloses the hot plasma in order to maintain the fusion process and to protect the components of the plant as well as possible. Only very few components come into contact with the outer regions of the plasma. One area which becomes particularly hot is the divertor. At particular points in the magnetic field, generally near the bottom of the plasma vessel, the helium ions and impurities in the plasma are guided towards the divertor. There, the ions are slowed down and electrically neutralized. In order to prevent the divertor components from melting or even vaporizing, the heat that has been generated must be removed as quickly as possible. If the divertor is unable to withstand the extreme stress, the continuous operation of the fusion plant is simply not possible. As a result, only composites that can withstand an extremely high level of generated heat of up to 20 MW/m2 and are capable of resisting the ceaseless attack of electrons, ions and impurities are used in the divertor. In principle, the divertor is made up of a highly efficient heat sink for dissipating the heat protected by an armor. The armor protects the heat sink from being damaged by the hot plasma during operating conditions. Tungsten and carbon are the materials of choice for this armor. These materials are particularly heat resistant and dissipate heat very efficiently. Unlike carbon, tungsten does not bind a large amount of hydrogen and has a low interaction with the plasma resulting in lower impurity levels of the plasma. This makes tungsten a particularly suitable material in highly loaded areas of the first wall of nuclear fusion plants.
As the undisputed expert for refractory metals, PLANSEE manufactures armor composites for the divertor made from carbon fiber reinforced carbon (CFC) and tungsten monoblocks and joins the armor to the copper/chromium/zirconium-based heat sinks. The particular expertise of PLANSEE lies not only in the resilient materials themselves, but also in the joining technology used within the composite. Once the fusion plant has been taken into operation, any repairs represent a huge outlay in terms of time and money. Any downtime of the plant, no matter how short, is an expensive exercise. Only a perfect joint between the armor and the heat sink prevents overheating and damage to the divertor. PLANSEE has developed and patented its own joining process specifically for the nuclear fusion industry: „active metal casting“. This method ensures that heat is transmitted to the heat sink extremely efficiently and reliably.
Over the course of the coming months, the team from PLANSEE will be working together with a large number of engineers and production staff to construct the first full-scale partial segments of the divertor for ITER. All the individual steps in production must be perfectly coordinated and technically harmonized. Joining some 130 armor blocks to the backing tubes of the heat sink in a single step without the slightest error is just one of the many challenges to be overcome during the project. Traditional quality assurance measures are not appropriate to the complexity of this development task. In order to be absolutely certain, PLANSEE has developed its own non-destructive testing methods for ITER based on thermographic and ultrasound techniques.
Stress testing on all ITER prototypes should be completed successfully by mid-2014. Series production of the ITER components can then start.
PLANSEE High Performance Materials
The Plansee Group is a leader in the field of powder metallurgy, covering the entire production process from the ore right through to customer-specific components.
The corporate division PLANSEE High Performance Materials is an expert for components manufactured from molybdenum, tungsten, tantalum, niobium and chromium. Alloys and composite materials from PLANSEE come into their own in electronics, coating technology or high-temperature furnaces – wherever traditional materials are stretched beyond their limits.
Find out more about PLANSEE and locate your local contact: www.plansee.com
Kontakt:
PLANSEE SE
Nadine Kerber
Metallwerk-Plansee-Str. 71
6600 Reutte
+43 5672 600 2422
nadine.kerber@plansee.com
http://www.plansee.com