VR-1

Plans for the construction of the reactor were already adopted at the beginning of 1960s, but it was Karel Matějka who succeeded in putting them through, in spite of some quite strong opposition from a number of institutions. Even the CTU Administration was in doubt about the project, objecting to high costs of this facility. On the other hand, the then regulatory body was aware of the importance of an installation where future specialists could be trained to gain experience with the reactor operation. The Czechoslovak Atomic Energy Commission of the time had strong influence on and close relations with the Ministry of Education, responsible for the decision and building approval.

Over the years several studies were carried out and requirements for the Faculty training reactor were specified. The main objectives were education and training in reactor operation and control, instruction in experimental reactor physics, and usage as a neutron source. Emphasis was placed on research and development. Finding a suitable site for the reactor was a tricky task. Eventually, an opportunity to build the reactor in the premises of heavy laboratories of the Faculty of Mathematics and Physics of Charles University in Prague 8 was acclaimed. The reactor site was designed to fit a so far unused experimental premises. It was, however, not completely suitable for a nuclear reactor and some restrictions were imposed by, for example, the size of the hall and entrance gate. The hall was fitted with a system of changeable platforms, a crane, engineering network (like waste water liquidation station) and ventilation (like active air conditioning).

The project was joined by the companies Chemoprojekt Praha and ŠKODA JS. The Faculty participated in work coordination, core calculations, safety analysis and the design of reactor control equipment. The main objectives pursued by the FNSPE included reactor implementation, its testing and putting into operation, preparation of experimental methods and sources for introduction of the Reactor VR-1 course into higher education and research programmes. Reactor technology and commissioning were financed from state funds for research and development (project A 01-159-112-08 “School reactor VR-1P“), reactor shielding and reactor hall adjustment were financed by the Ministry of Education. The budget also included first experimental equipment. The Reactor design was progressive, especially in the arrangements of two mutually connectable vessels. Unique solutions consisted of the use of stainless technology, quality assurance policy and the first completely digital control system in the world.

The Reactor went critical for the first time on 3rd December 1990 at 16:25.

The reactor commissioning was immediately followed by trial operation, during which all main parameters and educational experiments were verified. Since January 1992 the Reactor has been in permanent operation. At the time of great political and social changes it was not easy to start operation of the nuclear reactor, develop quality educational methods, procure experimental equipment, and ensure effective use of the Reactor. Miloslav Havlíček, at that time Dean of the Faculty, was an invaluable ally to the staff of Reactor VR-1 who re-established the Department of Nuclear Reactors. During its operation, the Reactor VR-1 became one of the pillars of nuclear education in the Czech Republic, offering experimental training to students of Czech and Slovak Universities as well as to future operators of both Czech nuclear power plants. It also found its place in international projects.

The reactor body is octahedral, manufactured from shielding concrete with cast iron or barite. There are two vessels inside the body, marked H01 and H02. Both vessels are structurally identical, but differ in use. Therefore, their inner equipment is different. The first vessel, marked H01, is the reactor vessel for the reactor core. The second, marked H02, is the manipulation vessel. Their surface has no bushings, as all piping is led at the top, with the exception of the radial and tangential channel in the H01 vessel. There is a third vessel, H03, in the hall, used for storage of demineralized water re-pumped from the H01 or H02 vessels. This arrangement was adopted for better radiation safety and easy manipulation. The inner parts of the reactor vessel include, in particular, a core diagrid, peripheral walkways, a control system carrier, measurement channels, and an operating and measurement pipeline. There is a service platform in the reactor vessel enabling manipulation in the reactor core and around it at lower water level. The manipulation vessel H02 is fitted with a fuel storage unit where fuel elements can be put aside or experiments can be prepared. In case of need, the vessels can be separated with a waterproof gate. This solution is convenient during vessel inspection or major adjustments of the reactor core. 

The reactor core is assembled on a core support plate with a geometry of 8×8 cells in a square lattice. At present fuel type IRT-4M is used, enriched to 19.7% ²³⁵U. The number of fuel elements is between 16 and 24, depending on core configuration. Furthermore the core is equipped with 5 to 7 control rods and experimental channels. An Am-Be neutron source is used to start-up the reactor. This source ensures sufficient level of signal at the output of the power measuring channels from the deepest subcriticalities, and thus guarantees a reliable check of the power during the reactor start-up. The source is placed inside the shielding container below the reactor vessel and is moved pneumatically by pressurised air.

Reactor uses 5-7 absorption rods UR-70 with cadmium absorbers (a cadmium plate sheet wound on an aluminium tube inserted inside a stainless rod) developed by ŠKODA JS. The number of rods in the core depends on the configuration. All rods are identical and their function depends on their assignment in the control system. Rod movement is ensured by rotating the stepper with optional motion speed (maximum speed is limited by limit of positive reactivity insertion in the reactor core). In the event of the safety signal activation, the power supply of the electromagnets that hold the rod in a defined position, is lost and the rod falls freely into the core. The fall is softened by a progressive hydraulic dumper.

Operation power measurement system is secured by four wide-range non-compensated RJ 1300 fission chambers. Independent power protection system is given by four SNM-12 pulse corona detectors that are placed below the vessel H01. Output signals from all detectors are displayed on the panels in the control room. Three detectors are used for evaluation, the fourth one is in hot backup. Evaluation of signals is based on a 2 out of 3 voting logic.