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BR1 - Belgian Reactor 1
The BR1 was the first Belgian reactor. It was critical for the first time on May 11, 1956. A critical reactor is a reactor in which an itself maintaining chain reaction occurs. The critical state is a normal state of activity of an operational reactor.
The BR1 is an air-cooled reactor with graphite as moderator. It is a flexible instrument for fundamental research and training.
In 2006 the 50th anniversary of BR1 was celebrated. For this occasion a special BR1 website was created.
In the beginning
After the start-up period, BR1 was mainly used for research in reactor and neutron physics. Until after the start-up of BR2 in 1964, BR1 was also used for the production of radioisotopes for medical applications. The reactor worked continuously, 24 hours a day, 7 days a week.
Two main fans, each consuming 0.8 MW, were necessary to guarantee a sufficient cooling of the reactor (cost: 6,200 €/day). The reactor's thermal power was 4 MW (4,000 kW or 4,000,000W). 1 MW equals one million time the unity of power watt (W). 1 MW = 1,000 kW = 1,000,000 W. For comparison: an iron has 2,500 W.
What now?
The reactor now only works on request of the experimenters, for at most 8 hours a day, at a maximum power of 700 kW (short periods up to 1 MW are also possible). The cooling for this reduced power can be guaranteed by a smaller auxiliary fan (cost: 30 €/day).
What is the reactor used for?
• Neutrography
This is a radiology technique that looks a lot like X-ray photography: a neutron beam is used instead of an X-ray beam. Neutrography "screens" an object with thermal neutrons. Because some elements (like hydrogen) easily absorb neutrons and others (like for instance aluminium) not or nearly, an image will appear, in which different materials can be distinguished, just like with X-ray diagnostics. Since neutrons are not ionising, they cannot form an image on a photographic plate: so, one has to convert the neutrons first into ionising radiation.
To this end, one generally uses gadolinium that strongly absorbs the neutrons and by that generates beta rays, to which a photographic plate is sensitive. However, the image is very different from an X-ray image. You can, for example, easily distinguish synthetic materials (containing quite a lot of hydrogen), because they turn black on the picture. It is less easy to distinguish several metals. In the case of X-rays, the density of the material determines how much radiation will be absorbed: heavier elements will absorb more than light elements.
• Calibration and validation
The instruments used to measure radiations (neutrons, gammas, etc.) need to be calibrated beforehand in reference neutron or photon fields of which the characteristics are well-known. BR1 offers such reference fields used for this application.
• Neutron Activation Analysis (NAA): service stoppped in 2010
Neutron Activation Analysis is a non-destructive analytical technique that allows determining the composition of a sample. If a sample is irradiated with neutrons, all its elements will be activated. By measuring the gamma rays, which are characteristic for each chemical element, it is possible, even if there are very few gamma rays (even 1 part per billion = 1 ppb), to determine the precise composition of the sample.
For a number of elements, the activation analysis is more sensitive than a chemical analysis and it is used for research, industry, archaeology and criminology. The biggest advantage of this technique with regard to chemical techniques is the non-destructive character: the sample remains in its original form and if necessary, it can be measured/analysed again or it can be subjected to other studies.
Future
The continued existence of the reactor is ensured because there are no budgetary or safety problems. The exploitation costs are quite low: we do not have costs for new fuel, because with the actual exploitation regime, we are able to run the reactor for more years with the present fuel. The electricity costs are quite low too, since we work with reduced power.
Also, the personnel expenses are limited. An exploitation team consists of 5 persons: the exploitation engineer, one adjunct, one pilot and two operators. This team is responsible for the exploitation of the reactor on request of our clients (load/unload an experiment, start of the reactor, measurements ...) and they also carry out the periodical controls and maintenance of the reactor and the related installations, so that the reactor is ready at all times for a safe use.
We try to guarantee our different internal and external clients the highest possible flexibility, to offer them stable irradiation conditions and to support them in the development of new experimental devices .
More information about these services can be found in the section 'Our Services'.
Technical specifications
• Nuclear Fuel
The fuel is natural metallic uranium (approximately 25 tons). The uranium is originating from the former Belgian Congo (now Democratic Republic of Congo) where the uranium reserves have played an important role in the development of the nuclear sector in Belgium (see our History Brochure).
A remarkable fact: the current fuel in BR1 is still the original one. After 50 years of working, the burn-up is less than 1% (burn-up: quantity of burnt-out fissile material in comparison with the quantity of fissile material of the fresh nuclear fuel).
• Graphite
The moderator of the reactor is graphite (carbon). A moderator is needed to slow down the energetic fission neutrons (2.5 MeV) until they have a thermal energy of 0.02 eV, for the chance of fission is 600 times higher via thermal energy.
There are 14,500 graphite blocks in the reactor (approximately 500 tons). The reactor is surrounded by a concrete construction of 2 m thick. This construction mainly serves as a biological shield against radiation; thanks to this shield it is possible to perform experiments on and around the reactor without contracting any dose.
• Channels
There are 829 channels (dim. 50 x 50 mm) for nuclear fuel, of which only 569 are loaded. Next to these fuel channels, there are about 70 channels, intended for experimental purposes. These channels are of various dimensions: rectangular ones of 10 x 10 cm, 18 x 18 cm, 24 x 24 cm, and round ones of 8 cm in diameter.
Moreover, the reactor has 2 thermal columns: these are places where the graphite further extends up to the concrete and where specific experimental settings can be installed. In order to load or unload specific samples during the working of the reactor, BR1 is equipped with a number of pneumatic sample dispensers.
• Cooling
BR1 is cooled by air. This occurs by a forced convection with the help of a fan and the removal of warm air via the chimney. There are of course filters in the cooling circuit to prevent for example dust particles from getting in the reactors or to prevent the discharge of radioactive material via the chimney.
• Control
The reactor is controlled by control rods. These are tubes in an alloy of silver-indium and cadmium in an aluminium cover. They are operated by electric motors in vertical channels. In total there are 18 such rods: 6 security rods, 5 pairs of control rods and 2 precision regulation rods. These rods absorb the neutrons, which makes there are less neutrons available to continue the chain reaction, and therefore, depending on their position, slow down or stop the chain reaction.
• Control room
The reactor is operated by the pilot. Once the reactor has reached the desired power, it can automatically be controlled. This makes it able to maintain the power up to 0.2 % precisely. Just like the reactor and the nuclear fuel, a part of the equipment in the control room is still original and operational. As a matter of fact, we have still got the necessary pieces to replace others.
Through the years, the necessary modernisation has been carried out, especially with regard to the electronic nuclear measuring devices and the possibility of data acquisition via pc.
• Safety
The safety of the reactor is followed and ensured via various mechanisms. There is for example a snuff system that measures the released radioactivity if one of the fuel rods is damaged. In the control room they are also constantly monitoring the temperature of various components via thermocouples.
The maximum temperature of uranium may not exceed 250 °C, graphite cannot exceed 104 °C. The power that can be generated is limited by means of alarm levels on the nuclear measuring devices. The reactor and the reactor building are constantly in underpressure, i.e. the pressure in the building is lower than outside to prevent radioactive leaks. The reactor has a negative temperature coefficient. This means that, if the power of the reactor rises, the reactivity will go down as a result of which, if the pilot does not take action, the power of the reactor will automatically decline.
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