Just as VTT is decommissioning its nuclear research reactor, which has served faithfully since 1962, it is also creating a new, modern research environment for projects supporting nuclear safety.
VTT has decided to decommission its Finnish Reactor 1 (FiR 1) in Otaniemi, Espoo. VTT no longer has any strategically significant projects for which a research reactor would be needed.
FiR 1 was switched on with all the appropriate pomp and circumstance at the Otaniemi Campus in Espoo on 31 August 1962. The reactor has played a vital part in the training of two generations of Finland’s nuclear experts. Its role in nuclear research has also been substantial.
The high-level waste produced by the reactor is in its core, which contains the nuclear fuel rods immersed in an open pool of water. Once the reactor has been decommissioned, the spent fuel will probably be shipped back to its country of origin, the US. Similar batches of fuel of other Triga-type reactors have been shipped to the Idaho National Laboratory (INL) previously. VTT also continues to liaise with Finnish authorities with regard to this arrangement.
The structural components of the reactor are radioactive, and will need to be disposed of as intermediate-level or low-level waste. Radiation measurements will be taken to determine the nature of the waste after the reactor has been shut down.
No nuclear reactors have been decommissioned in Finland before. However, several research reactors have been decommissioned in other countries, e.g. in Denmark and Germany, and the lessons learned from those projects will be used in the decommissioning of the Otaniemi reactor. The lessons that will be learned from the decommissioning of the Otaniemi reactor can then be used to plan the decommissioning of other TRIGA-type reactors, and also of nuclear power plants.
History of the FiR 1
The FiR 1 reactor is a so-called Triga-type reactor. Triga stands for Training, Research, Isotopes, and General Atomics, and the United States have supplied a total of more than 60 of this type of reactors to institutions around the world.
For the first decade after it was switched on, FiR 1 was used exclusively for training and basic reactor physics research.
This was to lay the foundation for future activities. The key personnel of Finnish nuclear power organisations were trained at the reactor.
The reactor’s thermal power was raised to 250 kW in 1967. The goal was to increase the neutron flux intensity to speed up the irradiation process. In the 1970s, the focus shifted to neutron activation analysis. A rapid irradiation system was developed for determining uranium concentrations in soil and rock samples, which was based on delayed neutron counting. Almost 50 000 samples were analysed annually, and the technology was also exported to other countries. In 1969, FiR 1 had the honour of analysing samples collected by the Apollo 12 lunar mission. The reactor’s control systems were modernised in 1981, in collaboration with the Atomic Energy Research Institute of the Hungarian Academy of Sciences (KFKI).
The reactor underwent several substantial upgrades in the 1990s, when a radiation therapy facility was incorporated into it. The goal was to produce an intensive, pure epithermal neutron beam that could be used to provide boron neutron capture therapy (BNCT). The reactor was used to give radiation therapy to a total of more than 300 cancer patients. The BNCT project turned FiR 1 into an important medical research and training facility. Research in this field covered, for example, dosimetry, radiation modelling, treatment planning, prompt gamma ray imaging, and other physics applications relating to BNCT.
Pioneering research until the end
FiR 1 is the first nuclear reactor to be decommissioned in Finland. The volumes and total radioactivity of the spent fuel and the waste generated by the decommissioning process, are only a fraction (1/10 000) of those associated with power-generating reactors. VTT will, nevertheless, consult external experts during the decommissioning process, with regard to issues such as transporting the spent nuclear fuel, determining the radioactivity characteristics and arranging interim storage of the waste.
The Finnish Nuclear Waste Fund has approximately EUR 10 million for the decommissioning and waste management of FiR 1.
Dismantling of the reactor
To ensure the safety of the dismantling process and efficient nuclear waste management, the following steps will need to be taken: Access arrangements, ventilation systems, and radiation monitoring procedures will be modified. More work space and radiation measurement facilities have to be provided in the reactor building. The estimated radioactivity levels of the structural components of the reactor will be verified, and measuring techniques will need to be developed for decommissioning actions. The reactor fuel rods will need to be detached. The aluminium lightweight internals of the reactor will be removed. The concrete shield structures, aluminium liner and graphite moderator from around the reactor core have to be dismantled. The radioactivity of waste packages will to be measured carefully during the dismantling process. The results have to be recorded in a nuclear waste log.
The dismantling work will be carried out by external specialists, under VTT’s supervision. Dismantling the reactor will take a few months, and the entire decommissioning process, including decontamination and release of the facility, will take approximately two years. The building can then be used for some other purpose.
Nuclear waste management
Nuclear waste management relating to the decommissioning of FiR 1 will mostly consist of the following steps: Coordinating the decommissioning project from start to finish, drawing up contracts for nuclear waste management and liaising with partners in the US, liaising with partners in Finland (TVO, Fortum P&H, and Posiva), drawing up contracts with external dismantling experts, and liaising with other actors.
VTT will draw up a detailed dismantling plan once the project begins, determine the radioactivity and other characteristics of the reactor structures, and establish the suitable packaging of the waste for road transport. VTT will also study the technical alternatives relating to interim storage, as well as final disposal, especially on the basis of the characteristics of the dismantled graphite and aluminium structures, and the BNCT moderator (Fluental™). Issues relating to safety requirements and the drawing up of a safety case will also be examined.
The current plan is for the spent nuclear fuel to be returned to the US, the reactor to be dismantled, and the waste to be managed and placed in interim storage over the next few years. Interim storage will end when final disposal and the associated licensing process begin around the year 2030. It will take several decades before the final repository will be closed and VTT is exempted from its nuclear waste management responsibility. VTT will not be able to influence these long-term timescales.
The later stages of the final disposal process will depend on nuclear power companies’ decisions on whether to extend current intermediate-level waste repositories, the decommissioning of nuclear power plants, and the final disposal of the resulting dismantling waste.
Spent nuclear fuel
The spent nuclear fuel generated by the TRIGA-type reactor in Otaniemi over the years amounts to just over 100 spent fuel rods (approximately 15 kg of uranium, of which 3 kg is uranium-235). According to the programme of the US Department of Energy (DOE), the spent nuclear fuel may be returned to the US if the shipment arrives at the Idaho National Laboratory (INL) by 12 May 2019.
Transporting nuclear materials from Finland requires a national export permit, in addition to authorisation from both the IAEA and Euratom. There is, for example, a Swedish cargo vessel that transports nuclear power plants’ spent nuclear fuel, which has taken similar smaller shipments across the Atlantic in the past. VTT has discussed the practical arrangements for nuclear fuel inspections and the necessary documentation with representatives of the INL.
If the reactor spent fuel could not be returned as planned, VTT will need to engage Posiva Ltd into negotiations concerning the final disposal of the spent nuclear fuel in Finland. VTT and Posiva have signed an agreement in principle, which enables the final disposal of the reactor core in Olkiluoto, as long as Posiva is informed of this within five years of the reactor final shut down. However, the agreement does not provide for interim storage, which is an essential precondition.
Low-level and intermediate-level nuclear waste resulting from the decommissioning project
The waste resulting from the decommissioning of FiR 1 will consist of low-level and intermediate-level nuclear waste. Moreover, the volume of waste will not be particularly high. The final disposal of the waste will need to be coordinated with the schedules of nuclear power plants, which means that the waste will be placed in an interim storage facility measuring less than 100 cubic metres, for a period of nearly 20 years. Primarily the interim storage and final disposal measures needed for the waste generated in the operation of the research reactor over the years, as well as the waste that will result from the decommissioning of the reactor, can be arranged in cooperation with nuclear power utilities in Finland.
VTT has estimated the induced radioactivity of the reactor’s structural materials (see figure 4), based on neutron flux distribution calculations and the reactor’s operating history. What makes Otaniemi’s Triga reactor special is the fact that its original graphite moderator was replaced in 1995 by a radiation therapy station with a Fluental™ moderator, the main components of which are aluminium and aluminium/lithium fluoride. This kind of moderator generates relatively high content of radioactive tritium, most of which, according to current assessment, remains within the moderator material, and therefore represents the main residual radioactivity in the waste.
The waste generated by dismantling of Finnish nuclear power plants contains no reactor graphite and only a small amount of aluminium. VTT has conducted a literature survey on the chemical behaviour of irradiated graphite and aluminium, and their impact on the long-term safety of nuclear waste repositories. VTT has also studied international practices for the final disposal of graphite.
Operation of a nuclear reactor
A nuclear reactor operates by maintaining and monitoring a chain reaction that occurs in the reactor core, in which the uranium atoms in the fuel split into smaller parts. This process is known as nuclear fission. To sustain this chain reaction, a nuclear reactor needs enriched nuclear fuel that generates neutrons to trigger fission, as well as a moderator, which reduces the energy of fast neutrons to increase the likelihood of fission.
The physical properties of the FiR 1 TRIGA-type research reactor make it extremely stable. The concentration of uranium-235 in the reactor is just under 20%, which is approximately five times that of the fuel used in electricity-generating reactors. The fuel in TRIGA-type reactors needs to be changed considerably less frequently than the reactor cores used in power-generating reactors, which need to be reloaded annually.
VTT – towards better nuclear safety
Nuclear safety research at VTT now has a new priority: responding to future needs. The shutting down of the FiR 1 research reactor marks the end of an important era of innovative use of nuclear reactions. A new era is already dawning, however, in the form of a new national research centre, VTT’s Centre for Nuclear Safety.
The Centre for Nuclear Safety will house modern facilities for handling radiation sources, as well as state-of-the-art technology for studying radioactive materials with a view to improving the safety of nuclear power plants and nuclear waste repositories.
The construction of the centre is already well under way, and VTT’s nuclear safety experts can expect to move into their new offices during the first months of 2016. The laboratories will be completed by mid-2016.
VTT has always played an important part in nuclear research in Finland. It has been hosting the Finnish national hot laboratory infrastructure since the first nuclear power plants were constructed in Finland in the 1970s. In addition to infrastructure-intensive facilities for handling radioactive materials, other important test facilities have been built up over the years, and experts have blossomed in many aspects of research and development promoting nuclear safety. Over time the activities have broadened to outgrow both the capacity and capabilities of the existing facilities.
In May 2012, the Ministry of Employment and the Economy published a report by the Committee for Nuclear Energy Competence in Finland, which not only addressed personnel resources, but also included research infrastructure competencies. It specifically endorsed the construction of a whole new facility, with the additional goal of gathering most of the VTT Nuclear Safety research personnel currently scattered around the Otaniemi campus, into a single, compact facility, i.e. VTT’s Centre for Nuclear Safety. In January 2013, the Ministry of Employment and the Economy set up a working group to draw up a research strategy for the nuclear energy industry until the year 2030. Several strategic priorities were identified in the course of the work. VTT’s Centre for Nuclear Safety infrastructure plays an important role in fulfilling those objectives.
VTT’s technological flagship for the nuclear sector
VTT’s new Centre for Nuclear Safety is being built in Otaniemi, Espoo.
The new building provides a common radiological facility housing radiochemistry laboratories, modern microscopy and analytical capabilities, and mechanical testing of radioactive materials. The modern laboratory facilities will raise the level of technological prowess, in tandem with enhancing radiation safety. The technological enhancement enables a higher scientific level in research results.
Constructing a safe and modern radiological facility
The building will be owned by Senate Properties, the state-owned real-estate management enterprise, but VTT is the end-user. Regulation and oversight by the authorities has involved the local municipal government, building department and emergency services, as well as Radiation and Nuclear Safety Authority, Finland-STUK.
The VTT experts who will work in the facility will serve the nuclear sector in areas such as computerized fluid dynamics, process modelling (APROS), fusion plasma computations, severe accidents, core-computations, nuclear waste-management and safety assessments. Meanwhile, in the radiological laboratory, staff will conduct radiochemistry, radioisotope dosimetry, failure analyses, and mechanical and microstructural characterisation of nuclear reactor structural materials in support of nuclear waste management and nuclear reactor safety. Shipping radioactive materials into and out of the facilities in a secure manner is possible via a gated courtyard and covered loading dock at the rear of the building. Since the building is designed according to KATAKRI Level III security requirements, the passive and active safety requirements for radiological facilities are also fulfilled.
Extra-thick concrete at the exterior and interior walls and ceiling of the basement provide passive gamma radiation protection in case of unexpected radiation source exposure, and is also utilized for shielding in some of the handling facilities. The ventilation system of the laboratory wing has also been designed for robustness, with the A-laboratory and the B- and C-laboratory ventilators separate and redundant, and connected to back-up diesel generators. This ensures that the under-pressures in the laboratory are retained even in the event of maintenance or failure of one of the ventilators, or loss of electricity from the grid.
The electrical supply to the laboratory facilities is available as normal electricity, backed-up electricity, and for some needs, as a centralized uninterrupted power supply (UPS). Centralized cooling is also available for connection by individual pieces of equipment as needed.
C-class radiological laboratories for high quality radiochemistry
An entire floor of the laboratory wing is dedicated to C-class radiological laboratories. The C-class laboratory is intended for handling radioactive isotopes with such a low level of activity that a separate radiological control point is not required. Most of the rooms of the C-laboratory facilities are devoted to radiochemistry and to nuclear waste repository research.
A special facility included in the C-laboratory is a high resolution inductively coupled plasma mass spectrometer (HR-ICP-MS), which is a type of mass spectrometer that is capable of detecting metals and several non-metals in solution at concentrations as low as one part in 1012 (part per trillion), even separating elemental isotopes. Compared to atomic absorption techniques, ICP-MS has greater speed, precision, and sensitivity. By locating it in a purpose-built ISO 6 class cleanroom facility, trace contaminants from laboratory ware and reagents is minimized.
B-class laboratories for services requiring enhanced radiological protection
The B-class radiological laboratories can handle a higher level of radioactive isotopes, and thus the entrance to the B-laboratory is a radiation control point where workers are required to change to lab clothing, including shoes and at least a long lab coat. The B-class laboratories include different kinds of activities, each with their own dedicated facilities, including an iodine laboratory, radiochemistry laboratory and gamma radiation spectrometry room.
The iodine facilities are designed to support the nuclear power plant iodine filter laboratory operated by VTT Expert Services Ltd. The main service is testing the efficiency of exhaust air filters of nuclear power plants and the activated charcoal used in them. Since the radioactive methyl iodide gas is a hazardous chemical, the exhaust air of the iodine lab is filtered through a special set of active charcoal filters before release.
The latest microscopy facilities for high resolution analytical imaging of radioactive materials
For the purpose of examining radioactive materials, a suite of microscopes is to be installed. The whole area is designed to provide constant room air temperature and humidity, and to minimize mechanical vibrations and electromagnetic and electrostatic interference. The facilities will house the latest in analytical scanning and transmission microscope technology, enabling high resolution imaging, element mapping, and crystallographic information mapping from irradiated materials.
A-class remote handling facility
Historically the principle radioactive materials handling has been for the mechanical testing of reactor pressure vessel steels, which have a relatively low level of radioactivity.
The new experimental facilities will especially bring the research of irradiated materials to the next level, by providing substantial remote handling capabilities in the hot cell island (see figure 3). The hot cells enclose the research equipment with lead shielding, and operation is carried out remotely using manual master-slave manipulators while viewing through thick, leaded glass windows. A main activity is mechanical testing of neutron-irradiated structural materials, but there are also associated processes such as electric discharge machine cutting, electron-beam welding and specimen preparation that need to be carried out in a shielded fashion. A shielded glove box is planned for metallography and small specimen handling, TEM specimen production, and other activities involving small specimens requiring hand dexterity not easily achievable with manipulators.
Although that new approach in working methods requires practice, the staff will also be increased. At the same time the volume of the research can be increased by offering services to more customers from abroad on topics formerly passed by on account of inadequate facilities.