VTT Centre for Nuclear Safety

Hot Cell laboratory for irradiated specimen testing

The VTT Centre for Nuclear Safety is Finland’s new infrastructure for ensuring safety and efficiency in nuclear power generation and radwaste management. We provide experimental and computational research, development and technical support services to customers internationally, to both the industry and regulators.

VTT Centre for Nuclear Safety

includes research infrastructure and expertise to cover a wide variety of aspects in nuclear energy and waste management

is a national infrastructure accessible for customers internationally

also provides services to industries beyond nuclear energy

The VTT Centre for Nuclear Safety (CNS) in Espoo hosts our brand-new multi-disciplinary laboratories and research facilities, all under one roof.

VTT Centre for Nuclear Safety offers a unique set of sophisticated experimental facilities, analysis and modelling software, and professional staff with multi-technological background and state-of-the-art knowledge from research projects and collaboration with industry.

For the current list of accredited tests, see the website of the Finnish Accreditation Service FINAS. In addition to standard tests, we carry out demanding non-standard studies.

Hot Cell laboratory for irradiated specimen testing

VTT’s Hot Cells were primarily designed for material investigations and failure analysis. Additionally they can be used for other studies that require a radiation shielded facility. The Hot Cells have thick walls of lead bricks, lead glass windows, and the samples inside are accessed using mechanical manipulators. Using the Hot Cells, we offer the following:

  • Instrumented tensile, compression, hardness, fracture toughness, fatigue and impact testing and analysis
  • Mechanical testing of Reactor Pressure Vessel (RPV) surveillance specimens and other RPV materials, including reconstitution and retesting of specimens
  • Assessing radiation induced damages and/or changes in properties
  • Investigations of mechanisms behind radiation embrittlement
  • Fuel cladding creep assessment
  • Customized investigations on active materials

The lightly-shielded protective cells are used for light-optical microscopy examinations as well as for preparing cross-sections and resizing of specimens for microscopy.

The heavily-shielded protective cell at the receiving bay is used for opening the transport cask and capsules. The receiving bay has horizontal and vertical ports for transport casks of different sizes and orientations, weight up to 10 metric tons. The main hall has two lines of heavily-shielded cells: the specimen preparation line and the mechanical testing line.


VTT Centre for Nuclear Safety complements VTT’s microscopy capabilities by an analytical Scanning Electron Microscope (SEM) with Focused Ion Beam (FIB), and an analytical Transmission Electron Microscope (TEM). Using them we can offer the following for non-irradiated as well as irradiated samples:

  • Determination of crack initiation site and fracture mode, crack growth, microstructure, secondary phases, crack path in the microstructure
  • Determination of microstructural metrics: grain size and texture, second phase population distributions, compositional mapping
  • High-resolution compositional mapping intra- and inter-grain features
  • Investigations of microstructural features at nano-scale
  • Determination of radiation-induced defects in materials
  • Microscopy specimen preparation, from light microscopy cross-sections to FIB lift-outs for TEM, from metals to ceramics, concrete and polymers

Fatigue testing in realistic conditions

Fatigue of structural material is a challenge for nuclear power plant’s design and operation. VTT’s solutions reduce uncertainties in plant lifetime management through the assessment of fatigue in simulated reactor conditions.

VTT’s FaBello facility operates using direct strain control. This provides results directly comparable with the design curves, which are determined using similar tests in air. Thus we can report environmental effects valid for design purposes. The FaBello facility is ASTM E606 standard and ASME III design code compliant.

Using the facility we can offer:

  • Assessment of material performance in nuclear power plant components
  • Material characterisation to support plant design and operation
  • Component lifetime assessment based on experiments and analyses
  • Codified stress analysis and design data in realistic conditions

Aerosol laboratory

Environmental safety requires gaseous species identification and concentration measurements, analysis of particle number/mass concentration and size distribution as well as analysis of particle properties, e.g. chemical compounds.

Using the facilities of our aerosol laboratory, we can offer gaseous-species and aerosol-particle measurements and characterisation:

  • Emission measurements, e.g. conventional power plants, and instrument testing
  • Analysis of fission products’ transport and chemistry, in both primary circuit and containment conditions in accident scenarios
  • Assessment of filtration devices’ ability to mitigate releases to the environment
  • Customer-tailored measurements, with sample analysis both on- and off-line

We have a comprehensive set of equipment for the characterization of aerosols in both gas and liquid phases as well as for the characterization of gaseous species.

Radiochemistry laboratory

In our radiochemistry laboratory we can accurately characterize radioactive materials, e.g. decommissioning waste. We offer:

  • Qualitative and quantitative analysis of radionuclides in structural materials, water, food, and other irradiated, contaminated, and natural materials
  • Characterisation of activated and contaminated wastes, such as for decommissioning waste streams (but excluding spent nuclear fuel material)
  • Surface decontamination testing
  • Irradiation of components and materials
  • Sample preparation, including activity detection, mechanical size-reduction, pre-treatment e.g. dissolution, incineration, chemical separation of nuclides etc.
  • Tracer experiments, to evaluate transport mechanisms, surface reactions, release rates

The facilities include Liquid Scintillation Counters for alpha, beta and X-ray emitting nuclides, gamma spectrometers and alpha spectrometers.

Elemental and isotopic analyses

Do you have challenging samples, which are difficult to dissolve or in which the concentrations are below the detection limit of your current analytical technique? We specialise in difficult sample matrices, tailor-made solutions and our limit of detection can be as low as ng/l. We operate in a newly built trace-level metal clean-room which enables us to carry out very low analysis of impurities.

In addition to the tailor-made solutions, we offer:

  • Quantitative multielemental analyses (reference the periodic table below)
  • Qualitative and semi-quantitative analysis of unknown samples
  • Isotopic analyses (e.g. 6Li/7Li, 10B/11B, 229Th/232Th, 235U/238U)
  • Sample preparation in a clean-room ISO5/6 at need
  • Radiochemical analyses
  • Gamma spectrometric analyses

Common sample types:

  • Liquids: impurities in clean water and different aqueous samples
  • Solids: metals and metal alloys, sediments, minerals, biological samples and filters

Our most important tools are high resolution Inductively Coupled Plasma Sector Field Mass Spectrometer (ICP-SF-MS) and Synchronous Vertical Dual View Inductively Coupled Plasma Optical Emission Spectrometer (SVDV ICP-OES).

Impact facility for studying external impacts on structures

Structural integrity of nuclear power plant components and structures is of paramount importance in external hazard events for safe process shutdown. The purpose of the Impact testing facility is to experimentally investigate the possible outcomes of airplane crash scenarios. It also improves the industry’s understanding on external impacts on civil structures.

Experimental impact studies are conducted on scaled specimens that represent structurally relevant parts of a nuclear facility. Various specimen shapes have been tested, including two-way simply supported slabs for the study of punching, combined bending and punching and bending behaviours. Free form complex structures have been studied for vibration propagation after impact and liquid filled missiles to study the effect of jet fuel splash.

The VTT impact test apparatus is can be considered as the world’s largest airgun. The apparatus uses pressurized air to accelerate the projectile to its target velocity. The apparatus can accelerate a 50 kg projectile up to a maximum impact speed of 167 m/s. The projectile diameter can currently be max. 350 mm. The currently used test frame can hold concrete slabs of 2 by 2 meters.

Clay laboratory

Safe permanent geological disposal of radioactive waste requires accurate characterisation of bentonite clay performance. In our clay laboratory, we can assess material performance for the structural design of geotechnical barriers. We offer:

  • Microstructure measurements of clay matrices
  • Chemical analyses of clay matrix
  • Online measurements of pH and Eh from clay materials
  • Analyses of pore water chemistry and phenomena related to diffusion, pH buffering, alteration, cation exchange, dissolution/ precipitation
  • Coupled thermal, hydro-, mechanical and chemical (THMC) measurements of clay barriers, including erosion potential and transport properties
  • Designing, building, maintaining, dismantling and analysis of customised experiments

Our environments with simulated conditions include the following:

  • Controlled atmosphere boxes with oxic or anoxic conditions (gloveboxes)
  • THMC devices including heater, cooler, data acquisition systems, hydration system, sensors
  • Diffusion cells, squeezing cells, hydraulic presses

Our analysis facilities include the following:

  • Small-angle X-ray scattering (SAXS)
  • Nuclear magnetic resonance spectroscopy (NMR)
  • Spectrophotometer
  • Inductively coupled plasma spectrometry (HR-ICP-MS, ICP-OES)
  • Chemistry and radiochemistry laboratories

Our modelling tools include the following:

  • COMSOL Multiphysics
  • Hydrogeochemical modelling tools EQ3/6, PHREEQC
  • Geochemist workbench, PetraSim
  • Molecular modelling LAMMPS

Computational safety analyses

Computational analysis is necessary in all phases of a nuclear power plant installation, where modelling and simulation can rapidly assess operational and structural performance. VTT has a comprehensive set of computational analysis capabilities from neutronics and microstructures to power plant system level.

We can offer:

  • Software tools
  • Engineering simulators, Operator training simulators
  • Safety analyses for licensing support to plant vendors and licensees
  • Independent safety analyses as Technical Support Organization (TSO) to regulatory safety authorities
  • Training and competence development

Our analysis topics and methods include the following:

  • Fuel and reactor core neutronics
  • Radiation shielding
  • Computational Fluid Dynamics (CFD)
  • Transients and design basis accidents, including neutronics, thermal hydraulics, instrumentation and control and electrical systems
  • Severe accidents
  • Release and dose assessment
  • Performance of mechanical components
  • Structural behaviour, Finite Element Method (FEM)
  • Fire spread and evacuation
  • Probabilistic Risk Assessment: levels 1, 2 and 3

We have developed a number of software tools, three of which can be made available for users outside VTT:

  • Apros for design basis accident analysis at plant scale, as well as for engineering, testing and training simulators. A product owned by VTT and Fortum  
  • Serpent for reactor physics
  • FinPSA for Probabilistic Risk Assessment