System message


The training reactor VR-1 is a light water, zero power research reactor with enriched uranium. Its design satisfies the requirement of easy accessibility to the reactor core with respect to education students and training qualified staff for nuclear industry. The pool type arrangement assures quick and easy access to the reactor core, easy insertion and extraction of various experimental samples and detectors, simple and safe manipulation with fuel elements. Light water, used at the same time as the moderator, reflector and coolant, functions also as biological shielding, which enables access to the reactor during operation. Because of its low power there is sufficient natural flow to take away the heat released by the fission of uranium in the reactor core without a pump, which has been installed anyway, to ensure better flow of water around fuel element tubes to prevent deposit formation on the fuel surface. The Reactor is operated at an atmospheric pressure at a temperature of about 20 °C (depending on the ambient temperature).


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 configuration. Furthermore the core is equipped with 5 to 7 control rods and several experimental channels. An Am-Be neutron source is used to start up the Reactor. It 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. A neutron source is also used during some experiments. 


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. 

Instrumentation and Control

Reactor uses 5-7 absorption rods UR-70 with cadmium absorbers (a cadmium plate sheet wound on an aluminium insert 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 mounting in the control device and position in the reactor core. The control rod can be hung on a control system carrier or placed inside a tube sheet in the reactor shielding. 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 activating, 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.

Main Parametres

Nominal thermal power 



for a short time (max. 72 h/year) 5 kW 


- type

- fuel mixture

- cladding

- enrichment

- geometry





19,7 % 235U






Reactor core cooling

natural convection



Reactor vessels

- diameter

- height

- wall thickness

- bottom thickness

- volume

- material

- material of inner parts 


2300 mm

4720 mm

15 mm

20 mm

17 m3

stainless steel 08CH18N10T


Reactor shielding

- vertical

- horizontal


approx. 3000 mm H2O

approx. 850 mm H2O + 950 mm extra heavy barite concrete 

Control device

microprocessor control system

Regulation system

5 to 7 absorption rods UR-70 with cadmium absorber

Operating power measurement

4 wide-range non-compensated fission chambers RJ 1300

Independent power protection

4 pulse corona detectors SNM-12  

Thermal neutron flux

1-2×109 n/cm2

Neutron Source

Am-Be, 185GBq, emission frequency 1.1×107n/s