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The FiR 1 TRIGA reactor on the Otaniemi Campus close to Helsinki, Finland, was permanently shut down in June 2015. The reactor is under the US DOE FRR spent fuel return program, but due to political and administrative reasons, the DOE INTEC facility in Idaho was not allowed to receive the used fuel from FiR 1. In 2020 a new path for repatriation of the fuel to the United States was opened culminating in US Geological Survey (USGS) TRIGA reactor (GSTR, Denver, Colorado) receiving early 2021 all the irradiated fuel from FiR 1. This solution between USGS and VTT was elaborated with the assistance of the Edlow International Company (EIC). It included USGS and DOE agreeing on the disposition of also FiR 1 irradiated fuel inventory and NRC accepting to expand the USGS’s license limits to include the full FiR 1 irradiated fuel inventory. USGS is planning for an intensive use of the reactor during the current operating license valid till October 2036 and is therefore in need of more fuel. USGS has identified that the FiR 1 fuel is suitable to be used in the GSTR and has significant burnup capacity left. VTT contracted EIC to transfer the irradiated fuel from FiR 1 to GSTR. EIC contracted NAC International to carry out the transfer using the NAC-LWT cask and associated fuel-handling systems [1]. Fortum Power and Heat was contracted to establish the local transport and support organization in Finland. Cask loading and road transport in Finland took place under VTT license granted by the Finnish Radiation and Nuclear Safety Authority - STUK. The cask loading took place late December 2020, and on 29th December, the Pacific Nuclear Transport Limited (PNTL) nuclear fuel carrier Pacific Grebe sailed off from the Port of Helsinki. Failed fuel was put into five sealed failed fuel cans. A team from Idaho National Laboratory witnessed this as these cans will be transferred in the future intact to INTEC Idaho. This article describes the arrangements for cask loading in the middle of the Finnish winter along with the actual transfer of the fuel from the reactor tank and the dry pits to the NAC-LWT cask outside the reactor building inside a weather cover tent. The intense two-week operation involved some thirty people in a Finnish-US team.

The Finnish FiR 1 TRIGA Mark II reactor is facing shut-down after more than 50 years of operation. The decommissioning of the reactor is planned to start during fall 2015. The management and final disposal of the decommissioning waste require knowledge about, among other things, the possible waste-related chemical reactions and the effects of such reactions on long-term safety. The above warrants the rationale for the literature survey, which was conducted to collect information on: i) The chemical behaviour of irradiated aluminium and graphite in FiR 1 de-commissioning waste under expected final repository conditions. ii) The international practices concerning the management and final disposal of irradiated aluminium and graphite. iii) The experimental techniques for determining the chemical form (organic or inorganic) of the 14C released from graphite waste. The report describes initially the FiR 1 TRIGA reactor, its associated decommissioning waste and foreseen final disposal conditions. The main part of the report focuses on the chemical behaviour of aluminium and graphite under such conditions. In addition, a few examples are provided concerning available methods for managing irradiated graphitic waste and for measuring the contents of organic and inorganic 14C in irradiated graphite. Finally, the report proposes outlines for some experiments to be conducted at VTT in order to determine the release rates of organic and inorganic 14C from the FiR 1 decommissioning waste.

Purpose: In this work, accuracy of the mcnp5 code in the electron transport calculations and its suitability for ionization chamber (IC) response simulations in photon beams are studied in comparison to egsnrc and penelope codes. Methods: The electron transport is studied by comparing the depth dose distributions in a water phantom subdivided into thin layers using incident energies (0.05, 0.1, 1, and 10 MeV) for the broad parallel electron beams. The IC response simulations are studied in water phantom in three dosimetric gas materials (air, argon, and methane based tissue equivalent gas) for photon beams (60Co source, 6 MV linear medical accelerator, and mono-energetic 2 MeV photon source). Two optional electron transport models of mcnp5 are evaluated: the ITS-based electron energy indexing (mcnp5ITS) and the new detailed electron energy-loss straggling logic (mcnp5new). The electron substep length (ESTEP parameter) dependency in mcnp5 is investigated as well. Results: For the electron beam studies, large discrepancies (>3) are observed between the mcnp5 dose distributions and the reference codes at 1 MeV and lower energies. The discrepancy is especially notable for 0.1 and 0.05 MeV electron beams. The boundary crossing artifacts, which are well known for the mcnp5ITS, are observed for the mcnp5new only at 0.1 and 0.05 MeV beam energies. If the excessive boundary crossing is eliminated by using single scoring cells, the mcnp5ITS provides dose distributions that agree better with the reference codes than mcnp5new. The mcnp5 dose estimates for the gas cavity agree within 1 with the reference codes, if the mcnp5ITS is applied or electron substep length is set adequately for the gas in the cavity using the mcnp5new. The mcnp5new results are found highly dependent on the chosen electron substep length and might lead up to 15 underestimation of the absorbed dose. Conclusions: Since the mcnp5 electron transport calculations are not accurate at all energies and in every medium by general clinical standards, caution is needed, if mcnp5 is used with the current electron transport models for dosimetric applications.

The Finnish TRIGA reactor, FiR 1, started operation in 1962. From early on the reactor created versatile research to support the national nuclear program as well as generally the industry and health care sector. Production of short-lived radioisotopes is still a basic service. Education and training play a role in the form of university courses and training of nuclear industry personnel in the Baltic region. In the 1990’s a BNCT cancer treatment facility was build. Over 200 patient irradiations have been performed since May 1999. FiR 1 is one of the few facilities in the world providing these treatments. A long term strategy is being worked out for FiR 1 by VTT supported by an independent survey. The survey recommends operation of the reactor at least till 2016 to enable continuation of the promising development of BNCT in parallel of developing accelerator based neutron sources for this treatment.

The Finnish Triga reactor, FiR 1, has been in operation since 1962. From its early days the reactor created versatile research to support both the national nuclear program as well as generally the industry and health care sector. The volume of neutron activation analysis was impressive in the 70’s and 80’s. Production of short lived isotopes for tracer studies is still an important application of the reactor with increasing amounts of isotopes produced, normally twice a week. In the 1990’s a Boron Neutron Capture Therapy (BNCT) treatment facility was build at the FiR 1 reactor. The treatment environment is of world top quality after a major renovation of the whole reactor building in 1997. Over 150 patient irradiations have been performed since May 1999. FiR 1 is one of the few facilities in the world providing this kind of treatments. Due to the BNCT project FiR 1 has become an important research and education unit for medical physics. Education and training play also a role at FiR 1 in the form of university courses and training of nuclear industry personnel. A long term strategy is being worked out for FiR 1 by VTT and its proprietor the Ministry of Employment and the Economy supported by an independent survey of an outside consultant. The independent survey recommends operation of the reactor till 2016 to enable continuation of the promising development of the BNCT treatment in parallel of developing accelerator based neutron sources for this treatment.

The meaningful sharing and combining of clinical results from different centers in the world performing boron neutron capture therapy (BNCT) requires improved precision in dose specification between programs. To this end absorbed dose normalizations were performed for the European clinical centers at the Joint Research Centre of the European Commission, Petten (The Netherlands), Nuclear Research Institute, Rez (Czech Republic), VTT, Espoo (Finland), and Studsvik, Nyköping (Sweden). Each European group prepared a treatment plan calculation that was benchmarked against Massachusetts Institute of Technology (MIT) dosimetry performed in a large, water‐filled phantom to uniformly evaluate dose specifications with an estimated precision +-2%-3%. These normalizations were compared with those derived from an earlier exchange between Brookhaven National Laboratory (BNL) and MIT in the USA. Neglecting the uncertainties related to biological weighting factors, large variations between calculated and measured dose are apparent that depend upon the 10 Β uptake in tissue. Assuming a boron concentration of 15 μ gg -1 in normal tissue, differences in the evaluated maximum dose to brain for the same nominal specification of 10 Gy(w) at the different facilities range between 7.6 and 13.2 Gy(w) in the trials using boronophenylalanine (BPA) as the boron delivery compound and between 8.9 and 11.1 Gy(w) in the two boron sulfhydryl (BSH) studies. Most notably, the value for the same specified dose of 10 Gy(w) determined at the different participating centers using BPA is significantly higher than at BNL by 32% (MIT), 43% (VTT), 49% (JRC), and 74% (Studsvik). Conversion of dose specification is now possible between all active participants and should be incorporated into future multi‐center patient analyses.

The Finnish TRIGA reactor, FiR 1, has been in operation since 1962. From its early days the reactor created versatile research to support both the national nuclear program as well as generally the industry and health care sector. The volume of neutron activation analysis was impressive in the 70's and 80's. In the 1990's a BNCT treatment facility was build at the FiR 1 reactor. The treatment environment is of world top quality after a major renovation of the whole reactor building in 1997. Over one hundred patient irradiations have been performed since May 1999. FiR 1 is one of the few facilities in the world providing this kind of treatments. Due to the BNCT project FiR 1 has become an important research and education unit for medical physics. Education and training play also a role at FiR 1 in the form of university courses and training of nuclear industry personnel. Isotopes for tracer studies are produced normally twice a week. The reactor is operated by four reactor operators and five shift supervisors; this in addition to their work as research scientists or research engineers.

The FiR 1 reactor, a 250 kW Triga reactor, has been in operation since 1962. The main purpose to run the reactor is now the Boron Neutron Capture Therapy (BNCT). Although BNCT dominates the current utilization of the reactor, it also has an important national role in providing local enterprises and research institutions in the fields of industrial measurements, pharmaceuticals, electronics, etc. with isotope produc-tion and activation analysis services. The whole reactor building has been renovated, creating a dedicated clinical BNCT facility at the reactor. Close to 30 patients have been treated since May 1999, when the licence for patient treatment was granted to the responsible BNCT treatment organization. The treatment organization has a close connection to the Helsinki University Central Hospital.

Two clinical trials are currently running at the Finnish dedicated boron neutron capture therapy (BNCT) facility. Between May 1999 and December 2001, 18 patients with supratentorial glioblastoma were treated with boronophenylalanine (BPA)-based BNCT within a context of a prospective clinical trial (protocol P-01). All patients underwent prior surgery, but none had received conventional radiotherapy or cancer chemotherapy before BNCT. BPA-fructose was given as 2-h infusion at BPA-dosages ranging from 290 to 400 mg/kg prior to neutron beam irradiation, which was given as a single fraction from two fields. The average planning target volume dose ranged from 30 to 61 Gy (W), and the average normal brain dose from 3 to 6 Gy (W). The treatment was generally well tolerated, and none of the patients have died during the first months following BNCT. The estimated 1-year overall survival is 61%. In another trial (protocol P-03), three patients with recurring or progressing glioblastoma following surgery and conventional cranial radiotherapy to 50-60 Gy, were treated with BPA-based BNCT using the BPA dosage of 290 mg/kg. The average planning target dose in these patients was 25-29 Gy (W), and the average whole brain dose 2-3 Gy (W). All three patients tolerated brain reirradiation with BNCT, and none died during the first three months following BNCT. We conclude that BPA-based BNCT has been relatively well tolerated both in previously irradiated and unirradiated glioblastoma patients. Efficacy comparisons with conventional photon radiation are difficult due to patient selection and confounding factors such as other treatments given, but the results support continuation of clinical research on BPA-based BNCT.

Two clinical phase I/II protocols (P01, P03) on boron neutron capture therapy (BNCT) for the treatment of glioblastoma started at the Finnish BNCT facility in May 1999 (P01) and in February 2001(P03). For the reliability of BNCT it was regarded useful to verify actual patient doses by making comparisons between the doses calculated with the treatment planning programs and the doses measured with independent detectors. In this work the measured and calculated gamma doses and thermal neutron fluences were compared with each other for the 21 patients (18 in P01 and 3 in P03) treated so far. For neutron fluence and gamma dose measurements in vivo activation detectors and thermoluminescent (TL) dosimeters can be used. The methods of measuring gamma doses in BNCT beams have been published in detail elsewhere [1, 2]. Diluted Mn-Al activation foils (1%, Æ 12 mm 0.2 mm, ECN Petten) and wires (2.4 %, Reactor Experiments Inc.) were used for neutron fluence measurements and 7LiF:Mg,Cu,P TL detectors of type MCP-7s (TLD Niewiadomski & Co., Krakow, Poland) for the measurement of absorbed gamma doses. Detector pairs were placed at several points on the beam entry surface on patients' head in order to verify treatment planning. 55Mn reaction rates and gamma dose rates were calculated with two treatment planning softwares, namely BNCT_Rtpe (P01) and SERA (P03) (both INEEL/MSU, USA). In SERA dose planning also the air cavities were included to the head model unlike in BNCT_Rtpe because of SERA's advanced geometry tool and its shorter calculation time. The methods and the results of the comparisons will be presented. [1] C. Aschan, M Toivonen et al, Radiat. Prot. Dosim. 81 (1999) 47 - 56. [2] C. Aschan, M. Toivonen et al, Radiat. Prot. Dosim. 82 (1999) 65 - 69.

The clinical trials of glioma patients with boron neutron capture therapy (BNCT) started in May 1999 at the Finnish Research Reactor (FiR 1). Epithermal neutrons are used with boronophenylalanine-fructose (BPA-F) as the 10B carrier. Before the clinical trials the dose planning system was established. The aim of the study was to 1) determine the FiR 1 epithermal neutron beam model 2) define the most suitable normal brain tissue material for NCT dosimetry 3) verify and normalise the beam model for clinical use 4) study the reliability of computational BNCT dose planning under in vivo conditions. The FiR 1 beam was modelled using DORT (Two Dimensional Discrete Ordinates Transport) code. The beam model was defined for the BNCT treatment planning program BNCT/Rtpe and its new version SERA (both INEEL/MSU, USA). The dosimetric characteristics of PMMA, water and two ICRU brain equivalent liquids as a phantom material were studied with computations to find a most suitable brain tissue sustitute for NCT dosimetry. The spectrum of the neutron beam model was verified in air with activation measurements. The neutron fluence/dose and gamma dose distributions in-phantoms were verified with activation dosimeters, ionisation chambers and TL dosemeters. The beam model of the treatment planning program was normalised to the measurements (activation foils) at the thermal neutron maximum in the PMMA phantom. The uncertainty of calculated reference doses are estimated in the brain with computational methods and around the brain with comparison to the measured values (activation foils and TL dosemeters) under in vivo conditions. The features of the dose planning system developed in the Finnish BNCT project will be exemplified by the treatment plans of the treated patients. [1] T.Serén, I.Auterinen, T.Seppälä, P.Kotiluoto, 15th European TRIGA Conference, (1999) 167. [2] T.Seppälä, T.Serén, I.Auterinen, Frontiers in Neutron Capture Therapy (2001) 219. [3] T.Seppälä, J.Vähätalo, I.Auterinen, A.Kosunen, D.W.Nigg, F.J.Wheeler, Radiat. Phys. Chem. (1999) 239. [4] A.Kosunen, M.Kortesniemi, H.Ylä-Mella, T.Seppälä, J.Lampinen, T.Serén, I.Auterinen, S.Savolainen, Radiat. Prot. Dosim. (1999) 187. [5] C.Aschan, M.Toivonen, S.Savolainen, T.Seppälä, I.Auterinen, Radiat. Prot. Dosim. (1999) 47. [6] T.Seppälä, I.Auterinen, C.Aschan, T.Serén, J.Benczik, M.Snellman, R.Huiskamp, U.Abo Ramadan, L.Kankaanranta, H.Joensuu, S.Savolainen, (under revision).