Research Reactor LVR-15

History

The first research reactor in the Czech lands started its operation in 1957 in the Institute of Nuclear Physics (Czechoslovak Academy of Sciences) in Rez near Prague. The reactor’s thermal power was 2 MW. This reactor was in operation until 1987 and then during 1988 – 1989 the reactor underwent  reconstruction from a VVR-S to an LVR-15 type. The reconstruction project was prepared at the beginning of the 1980s and the goal was a power uprate and an increase in safety. Test operations of the LVR-15 reactor commenced in 1989, and the reactor has been operating on full power since 1995.

Reactor Description

LVR-15 is a light water tank-type research reactor placed in a stainless steel vessel under a shielding cover. It has forced cooling, IRT-4M fuel and an operational power level of 10 MWt. Reactor operations run in campaigns. Usually the campaign lasts for 3 weeks, followed by an outage lasting for 10-14 days  for maintenance and fuel reloading. There are also other campaigns which can operate for ‘short-time’ experiments. As a moderator and an coolant, demineralised water is used. A reflector is composed of a water, or beryllium block, depending on the operation configuration.

Technical Parameters

Reactor Vessel

Diameter	2300 mm
Height	5760 mm
Wall thickness	15 mm
Bottom thickness	20 mm
Water volume in the vessel	22 m3
Weight (without water)	7900 kg

Operation Parameters

Maximal thermal power	10 MW
Maximal thermal neutron flux	1014 n×cm-2s-1
Pressure	atmospheric
Temperature	max. 56 °C

Fuel

Type	IRT-4M – tube sandwich-like type
Active length	600 mm
Cladding	Al
Fuel core	UO2 + Al
Enrichment	19,75 % U235

Power control

12 control rods, 3 groups:	compensation (8) safety (3) automatic regulator (1)
Absorber	B4C

Reactor Utilization

The research reactor LVR-15 is used for research and production in cases of:

• Material research (e.g. an irradiation of reactor pressure vessel (RPV) materials)
• Corrosion tests of primary circuit and internal structural materials of nuclear power plants) in experimental loops and probes
• Water chemistry experiments for nuclear power plant primary circuits
• Neutron activation analysis (used to determine materials composition)
• Development and production of new radiopharmaceuticals (¹⁵³Sm, ¹⁶¹Tb, ¹⁶⁵Dy, ¹⁶⁶Hop, ¹⁶⁹Er, ⁶⁰Co, ¹⁹²Ir, ¹⁸²Ta, ¹⁹⁸Au)
• Production of silicon through neutron doping for the electronic industry (the phosphorus doping of silicon utilizing neutron irradiation significantly improves specific resistance homogeneity compared to other methods)
• Irradiation services (production of radioisotopes: ⁹⁹Mo-⁹⁹mTc, ¹¹³Sn-¹¹³mIn, ¹⁸⁸W-¹⁸⁸Re)
• Scientific research into horizontal channel material characteristics (neutron physics and solid phase physics)
• Neutron capture therapy (irradiation of patients with glioblastoma-type brain tumours)

Neutron beams exiting the reactor via horizontal channels are used by scientific staff of the Nuclear Physics Institute of the Academy of Sciences of the Czech Republic and the Faculty of Nuclear Sciences and Physical Engineering of the Czech Technical University in Prague for the following experiments:

• Neutron measurement of structures and textures at room and helium temperatures
• Deep neutron profiling and th study of immediate gamma radiation from neutron radiation capture
• Neutron optics and neutron topography
• Measuring textures in semi-crystalline metal materials.
• Study of structural inhomogeneities using the diffraction and the small-angle neutron scattering methods
• Neutron interferometry
• Study of local tension in polycrystalline materials

Irradiation Services at LVR-15 Reactor and Epithermal Neutron Beam

Irradiation services at LVR-15 reactor and epithermal neutron beam provide:

• Proposal of an irradiation workstation involving neutron source, neutron moderation and filtering; geometric arrangement of the volume under specific conditions and shielding by calculating the transport of neutrons and photons
• Irradiation of material samples by the epithermal neutron beam (flux density 7×108 n.cm^-2.s^-1) in terms of experimentally verified conditions with the possibility of heating the samples up to 300 °C
• Sample irradiation in vertical irradiation channels
• Fission neutron irradiation of samples in vertical irradiation channels located in the beryllium and water displacers
• Production of neutron doped silicon – silicon single crystal irradiation facility in “DONA” device
• Handling and technological operations with ionizing radiation sources in hot cells
• Transhipment of ionizing radiation sources from one cask to another
• Visual control of ionizing radiation sources
• Dose rate measurements at a defined distance from the ionizing radiation sources
• Other manipulations with ionizing radiation sources according to specific customer requirements

Material Irradiation Research and Services

Material irradiation research and services provide:

• Irradiation experiments focused on material behaviour research and influence of radiation and chemical parameters
• Study of structural materials’ behaviour in the aquatic environment under chemical parameters and radiation conditions
• Studies on the compatibility and corrosion behaviour of structural materials in various environments (helium, liquid metals and molten salts)
• Experiments in the experimental facilities of the research reactor LVR-15, including continuous monitoring of experimental conditions (thermohydraulic, chemical and radiological)
• Evaluation of corrosion behaviour of structural materials in steam circuits and liquid metals
• Evaluation of local and surface damage mechanism and the nature of corrosion attack in operational conditions
• Assessment of corrosion damage mechanism under model operational conditions, depending on the level of mechanical stress and composition of the aquatic environment
• Evaluation of corrosion behaviour of fuel cladding materials, including eddy current measurement

Core

The core contains an aluminium baffle, called a separator, into which fuel elements, beryllium blocks, aluminium displacers and irradiation channels are inserted. The centre of the core is located approx. 1.4 m above the bottom of the vessel. The baffle has 8 × 10 positions in a rectangular arrangement with 71.5 mm pitch (see picture with core layout).

From 28 to 32 cells accommodate fuel elements of which,12 fuel elements contain control rods with some cells serving for rig channels. On the periphery of the core there are irradiation channels for experimental loops, rotation channel for silicon irradiation, pneumatic rabbit and vertical irradiation channels. Other cells are filled with beryllium reflectors or water displacers.
Note: The blue Cherenkov radiation visible inside the reactor is an electromagnetic version of an acoustical shock wave. It is created by the decay of fission products. These products decay through beta decay, where beta radiation (i.e. electrons) is responsible for the blue light as the electrons are moving faster than the speed of light in the water.

Fuel

The reactor uses Russian IRT-4M fuel (manufactured by NZCHK Novosibirsk – consortium TVEL) enriched to 19.75 % with 235U. Fuel assemblies are sandwich-like type, with a uranium meat consisting of a UO2 dispersion and aluminium powder. The assemblies are composed of tubes with a square cross-section, concentrically arranged in six and eight-tube assemblies. The fuel assembly is sealed with aluminium caps on both ends. The fuel cladding is also aluminium. The fuel assembly is 880 mm long, with the active fuel part being 600 mm long. Control rods are installed in the central tube of each six-tube assembly. All fuel assemblies are subject to regular inspections according to international agreements. These are performed by inspectors from the IAEA, Euratom and The Czech Regulatory Body (SÚJB).

Reactor control

During the fission of 235U nuclei, each neutron creates 2 to 3 free neutrons – thus the term ‘chain reaction’. In order to be able to safely control the reactor, it must be maintained at ‘critical’, meaning the ratio of neutrons in two following generations should be equal to one,  and excess neutrons must be absorbed. In the LVR-15 reactor, the neutron absorber is boron. Twelve control rods are used to control the fission, hung on a console permanently attached to the vessel superstructure in the upper part of the vessel. Eight rods are compensatory, three are safety rods and one operates as an automatic regulator. The absorptive part of the control rods is made of boron carbide (B₄C).

New safety related control system on LVR-15 reactor

Reactor cooling

The heat generated in the core is channelled through three cooling circuits into the Vltava River. The primary cooling circuit has five main circulation pumps and two emergency auxiliary circulation pumps connected to batteries, ensuring the flow of de-ionized cooling water through the core and heat exchangers. When outage of external electrical power to the reactor occurs, cooling of the core is ensured by one main pump and one emergency pump with each powered by a separate diesel generator. The maximum output temperature of coolant is 56 °C, the input temperature is 45 °C, and maximum flow through the primary circuit is 2000 m³.h^-1.

 

Handling Irradiated Samples

Processing of irradiated capsules and removal of material samples from irradiation probes and water loops takes place in five hot cells. Hot cells are located on the ground floor of the reactor building, below floor level of the reactor hall, as shown in the picture below.

Processing of irradiated capsules and removal of material samples from irradiation probes and water loops takes place in five hot cells. Hot cells are located on the ground floor of the reactor building, below floor level of the reactor hall, as shown in the picture below.

Wet Repository and Wet Temporary Storage

The wet repository is used as a temporary storage facility for spent fuel assemblies removed from the core. It is an aluminium container installed in the floor of the reactor hall, shielded on all sides by concrete and encapsulated in steel plating. The upper edge of the rector vessel is connected to the storage facility with an angled tube that leads to the bottom of the storage facility. The wet temporary storage is used for temporary storage and holding of irradiated rigs, loops and other active materials and for temporary storage of spent fuel assemblies. It is located in the rear part of the reactor building. The storage area is composed of two 7m deep pools made of stainless steel and filled with de-ionized water.

Monitoring

The ventilation system of reactor LVR-15 is used to exhaust the technical area, maintain negative pressure and gather activity into the ventilation chimney for the measurement of released activity. Volume activities of rare gases and beta active aerosols in ventilation branches (radioactive iodine, beta-active aerosols, radioactive gases, alpha-active aerosols, tritium (³H) and carbon isotope ¹⁴C) are all recorded. People, clothing and all waste are also monitored. Workers performing activities in the reactor building are equipped with personal dosimeters for measurement of equivalent dosages of all types of radiation (beta, gamma and neutrons). The operation of the LVR-15 research reactor meets all the basic legislative radiation protection requirements prescribed by SÚJB Decree No. 307/2002 Coll.

Reactor Operation

The LVR-15 reactor is licensed for operation by SÚJB until the year 2020. In December 2001, an INSARR mission from the IAEA was performed to verify the safety of reactor LVR-15. The mission recommended some precautions to increase the safety, which were implemented in the following years. At present, a verification of the influence of external events on the safety is being performed following the accident at NPP Fukushima – Daiichi.

In 2004, the Czech Republic joined the GTRI initiative (Global Threat Reduction Initiative – a global initiative to reduce nuclear danger), which aims  to identify, secure and restructure, or facilitate, the final disposal of high-risk nuclear and radiological materials around the world that could endanger the U.S. and the international community. This initiative was established by the U.S. National Nuclear Safety Agency (NNSA).

One initiative program of the GTRI is the RERTR (Reduced Enrichment for Research and Test Reactors) program and RRRFR (Russian Research Reactor Fuel Return), to which the reactor LVR-15 joined. The RERTR performs the conversion from high to low enriched fuel, and within the RRRFR in 2007 all spent fuel from the reactor site was transferred to Russia for reprocessing as a result of joint efforts of the USA, Czech Republic, Russia and the International Atomic Energy Agency (IAEA).