THE BUDAPEST RESEARCH REACTOR

ABSTRACT

The research reactor in Budapest was first put into operation in 1959. After a major reconstruction and upgrading the start-up procedure began in 1992. The upgraded reactor can serve for: basic and applied research, technological and commercial applications, education and training: (e.g. involving the IAEA). The full scale reconstruction and upgrading project started in 1986, aiming the substitution of aged components, the enhancement of reactor safety, the increase of reactor power to 10MW. The reactor reached first criticality on 12 December 1992. The regular operation started 25 November 1993. The Budapest research reactor is a tank type reactor, moderated and cooled by light water. The fuel of the research reactor is an alloy of aluminium and uranium-aluminium eutectic with aluminium cladding. About 2000 operational hours per year are foreseen for 2000. Later (when the cold neutron source will be operational) the operation time can be extended. The reactor has 10 horizontal beam tubes (8 radial and 2 tangential). The installation of a cold neutron source equipment is in progress at one of the tangential beam tubes. Irradiations may be carried out by inserting samples into the 51 special vertical channels. The utilisation of the reactor for basic and applied research is considered to be the basic purpose of the reactor, in the fields: condensed matter, radiochemistry, biological irradiations, reactor physics and technology. A lot of technical problems can be solved by means of the reactor as well. These problems can be divided into the following main fields: production of radioisotopes, neutron radiography, activation analyses, pressure vessel surveillance and perhaps later silicon doping by neutron irradiation can be considered too.

C O N T E N T S

1. HISTORY

2. SHORT TECHNICAL DESCRIPTION

3. AGEING

4. APPLICATION IN RESEARCH

5. PRACTICAL APPLICATIONS

5.1 Production of Radioactive Isotopes

5.2 Neutron Radiography

5.3 Activation Analyses

5.4 Pressure Vessel Surveillance

5.5 Silicon Doping by Neutron Irradiation

6. EDUCATION

7. INTERNATIONAL RELATIONS

8. SUMMARY

1. HISTORY

The research reactor in Budapest was in operation from 1959 to 1986. No incident occurred during the 27 years of reactor operation. In this period the reactor played an essential role in establishing nuclear research and technology in Hungary. It served as a basic facility for neutron scattering, nuclear and particle physics, radiochemistry, shielding investigations; for establishing nuclear medical applications providing radioisotopes; for performing pressure vessel surveillance programme for reactor safety studies; and it was an important school of university and postgraduate training.

In 1983 the government made a decision for the reconstruction and upgrading of the reactor according to new trends in nuclear research and applications as well as modern reactor safety requirements. The upgraded reactor can serve for:

1) Basic and applied research: condensed matters, materials science, activation analysis, radiochemistry, nuclear gamma spectroscopy, reactor safety, health physics.

2) Technological and commercial applications: radioisotope production, silicon doping, development of nuclear instrumentation, tests and certification for industry by neutron and gamma radiography etc.

3) Education and training: contribution to university and postgraduate education, training for nuclear engineering, international training courses (e.g. involving the IAEA), popular information (nuclear energetics, research etc).

The full scale reconstruction and upgrading project started in 1986, aiming

- the substitution of aged components,

- the enhancement of reactor safety,

- the increase of reactor power to 10 MW.

The reactor vessel and the primary piping turned out to be much less corroded than previously assumed. Reactor safety has been enhanced by adding some new safety systems and thus satisfying the "Defense in Depth" concept and also by applying more up-to-date and reliable systems. A new safety analysis report taking into account all relevant recommendations of IAEA has been prepared. The increase of reactor power was facilitated mainly by building new cooling towers, permitting a reactor power of 20 MW. However, the characteristics of the VVR-SM fuel do not allow a reactor power higher than 10 MW and the higher power can be achieved only by applying a new type of fuel elements.

The reconstruction was finished in the technical sense by the end of 199 0. Due to the re-organization of KFKI and other non-technical considerations KFKI has not applied for licensing. The newly independent institute KFKI Atomic Energy Research Institute applied for the licensing in 1992. After having got the license for the first period, the start-up procedure of the reactor has been begun in 1992. The reactor reached first criticality on 12 December 1992. The licensing and testing period took nearly a year (physical start-up, measurements at zero power, approaching to nominal and at nominal power). The license for regular operation at nominal power was issued 25 November 1993, without any restrictions. The regular operation started immediately on 26 November 1993.

The institute has fresh VVR-SM fuel for a few years of operation. Spent fuel problems are not solved completely, but very probably the solution applied for the spent fuel of the Paks NPP, Hungary, will be applicable also for the spent fuel of the research reactor.

The Budapest Research Reactor is a tank type reactor, moderated and cooled by light water. The reactor is in a cylindrical reactor tank, made of a special aluminium alloy. The diameter of the tank is 2300 mm, the height is 5685 mm. The heavy concrete reactor block is situated in a rectangular semi-hermetically sealed reactor hall. The area of the reactor hall is approximately 600 m². It is ventilated individually.

The fuel of the research reactor is of the VVR-SM type (Russian product). It is an alloy of aluminium and uranium-aluminium eutectic with aluminium cladding. The uranium enrichment is 36%, the average U-235 content is 39 g/fuel element. The fuel elements contain three fuel tubes, the outer tubes are of hexagonal shape, while the two inner ones are cylindrical. The active length of fuel elements is 600 mm. A fuel element is shown in Fig.1.

The equilibrium core consists of 223 fuel elements, with a lattice pitch of 35 mm. The core is surrounded radially by a solid beryllium reflector. The reactor is equipped with boron carbide safety and shim rods. There is a stainless steel rod for the purpose of automatic power control.

The reactor can be characterized by the following main technical data:

thermal power: 10 MW

mean power density: 61.2 kW/litre

approx. maximal thermal flux: 2.2 x 10¹⁴ n/cm²s

approx. maximal fast flux: 1.0 x 10¹⁴ n/cm²s

cooling water inlet temperature: 54^oC

maximum cooling water outlet temperature: 60^oC

 

Fig.1. VVR-SM Type Fuel Element

 

The reactor cycle will be about 40 effective days (for the equilibrium core), which is followed by a refuelling period of approximately one week. A continuous operation of the reactor is not planned, 3600 operational hours per year are foreseen. However, the timetable should correspond to the various requirements and flexible solutions can be found. The Budapest Research Reactor had a very good reputation before 1986, since timetables were kept in a reliable manner.

The reactor has 10 horizontal beam tubes (8 radial and 2 tangential). The installation of a cold neutron source equipment is in progress at one of the tangential beam tubes. The cold neutron source may start to operate late 2000. Irradiations may be carried out by inserting samples into the 51 special vertical channels. A special computer-controlled irradiation facility is under construction for silicon doping. The reactor staff has a long experience in assisting physical experiments and radioisotope production. The experiments and other applications planned at the research reactor are described below.

During the reconstruction all the primary and secondary components were dismantled and replaced. To increase knowledge about the ageing of the mechanically loaded components some dismantled parts of the reactor were tested or samples were cut and stored for testing. Previously a new aluminium alloy has been developed and tested for production of the main components of the reconstructed reactor. This alloy and its welding had been carefully tested before they were used. The test results also supply information about the ageing of aluminium structures for research reactors.

During the dismantling some of the main components have been hardness tested. Since the main vessel was dismantled and stored in one piece, no specimens were cut from any location. Specimens for destructive mechanical testing were cut only from the inside structural elements like vertical channel pipes, grids etc.

Even though the increase in hardness was high, no cracks were observed. The results obtained on the vessel wall show, that radiation embrittlement of the outer vessel is negligible.

The 26 years' experience can be summarized as:

- The AlMgSi alloy tank didn't lose its integrity, although for the larger part of the time of operation the power was 5 MW instead of 2 MW designed originally, and the design lifetime were extended 30 %.

- Due to the highly effective water purification no type of corrosion destroyed the vessel.

- The ductility of the AlMgSi1 alloy was reduced by neutron irradiation and by low-cycle thermal fatigue, but the remaining toughness of the vessel still satisfied even the most exaggerated safety requirement.

The utilisation of the reactor for basic and applied research is considered by the following means:

- Neutrons produced in the reactor core with an important flux can be guided to the measuring instruments for investigation of elastic and inelastic scattering phenomena i.e. neutrons can probe in condensed matter structural properties in the 0.01 - 1000 Å size range and particle interaction behaviours in the 10^-9 - 1 eV energy range.

- Investigations related to nuclear reactions based on neutron capture (fundamental physical problems, nuclear astrophysics, activation analysis etc).

- The reactor provides experimental basis - as complex irradiation source (neutrons, alpha, beta and gamma rays) - for materials testing, irradiation damage biological irradiation, dosimetric, nuclear safety etc investigations.

Investigations based on neutron scattering are essential in studying the condensed matter structural properties. These studies will get a much improved tool, when the cold neutron source will be put into operation (after 2000).

Investigations of biological objects is an area of growing interest. Especially the influence of low doses on human cells need more detailed studies. The reactor provides with an excellent tool for these investigations, as the biological objects can be irradiated by a complex source (variable combination of gamma rays and neutrons, where the neutron spectrum can also be adjusted to the needs of the investigation). The biological irradiation channel is naturally provided with a dosimetric system as well.

Besides the basic research some problems for possible applications are foreseen, two of them are mentioned here briefly:

- It is of great interest to investigate segregation processes, e.g. determining crystallite orientations by texture analyses and carrying out internal stress analysis by high resolution lattice parameter measurements.

- A very practical use can be the aging calibration of turbine blades by small angel neutron scattering and neutron diffraction.

A lot of technical problems can be solved by means of the reactor. These problems can be divided into four main fields, i.e. radioisotope production, neutron radiography, activation analyses, and pressure vessel surveillance studies. Some other applications, as e.g. silicon doping, might be of some interest as well.

5.1 Production of Radioactive Isotopes

The production of radioactive isotopes can be considered, as one of the main applications of the reactor. The production of ¹²⁵I is the major production. The method used gives the possibility to produce 5 Ci (180 GBq) per week.

The production of the following radioisotopes is performed in small quantities:

- ⁵¹Cr, ⁶⁵Zn, ¹⁴¹Ce, ¹⁷⁰Tm, ⁸²Br, ²⁰³Hg.

The production of some other isotopes, as e.g.

- ¹⁹²Ir for gamma defectoscopy,

- ⁶⁰Co for industrial gamma radiography

can be considered too, but the production of these isotopes needs especially long irradiation times.

5.2 Neutron Radiography

Collimate neutron beam is used to investigate objects in closed volumes. In dynamic radiography moving objects or processes can be recorded. Static radiography provides better resolution. A few examples on the use of radiography: turbine blades, pipelines, compressors of refrigerators, heat-exchangers, valves.

There are two neutron beams used for radiography, one for static and one for dynamic investigations.

5.3 Activation Analyses

Activation by reactor neutrons is a very sensitive analytical method. About 70 various chemical elements can be detected in an extremely wide range of content, i.e from percents to 10^-8 - 10^-10 g/g concentrations.

A pneumatic rabbit system has been constructed to serve the laboratory of activation analysis. The laboratory is capable to analyze 100-150 samples per week.

5.4 Pressure Vessel Surveillance

An extended national programme for the surveillance of the power plant's pressure vessels is going on. As regions, where the flux is higher, than the flux at which the pressure vessel of NPPs is exposed, can easily be found in the research reactor, the neutron induced embrittlement of 20 - 30 - 40 years can be studied after a few month irradiation.

The gamma heated irradiation channel (BAGIRA) gives the possibility of the above investigations in an advanced, NNP-like environment.

5.5 Silicon Doping by Neutron Irradiation

There is a beryllium reflector surrounding the core. Silicon irradiation can be performed in channels in the beryllium. Estimated thermal flux is 10¹³ ncm^-2s^-1, the transmutation yield is 10⁹ cm^-3s^-1. Uniformity of the transmutation will be improved by rotation of the ingot. Maximum length of the ingot is approximately 500 mm. For the measurement of the irradiation dose SPNDs (self powered neutron detectors) are available. There will be a computerized flux and dose evaluating system that will control irradiation. 4 inch diameter is planned.

The demand for high quality doped silicon produced by neutron irradiation has decreased in the last years. On the other hand the irradiation capacity is now bigger, than it was years ago, mainly due to more significant exploration of the capacities in the CIS countries. The situation might change with the time, so the question whether or not to construct the silicon irradiation equipment has to be answered later.

The Budapest Research Reactor is foreseen to fulfil the following aims in the field of education:

- Providing university and postgraduate education opportunities;

- Training for specialists in nuclear industry, shielding, industrial radiography, etc;

- International training courses (e.g. involving IAEA);

- Popular information (nuclear energetics, research, shielding).

The Budapest Research Reactor is considered as Centre of Excellence by the Central European Initiative.

For the utilization of the reactor in the field of basic research the Budapest Neutron Centre (BNC) has been set up, by three research institutes: KFKI Atomic Energy Research Institute, KFKI Research Institute for Solid State Physics and the Isotope Research Institute of the Hungarian Academy of Sciences. The BNC has an international scientific advisory council.

The utilization of the reactor for practical applications can be considered in international cooperation as well.

The main goal of the reactor is to serve neutron research, but applications as neutron radiography, radioisotope production (primarily for medical purposes), silicon doping, pressure vessel surveillance test, etc. are foreseen as well.

The Budapest Research Reactor is operated by the KFKI Atomic Energy Institute, which is responsible for reactor safety and utilisation as well. The institute is prepared for any reasonable cooperation.