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The International Network of Nuclear Reaction Data Centres (NRDC) coordinated by the IAEA Nuclear Data Section (NDS) is successfully collaborating in the maintenance and development of the EXFOR library. As the scope of published data expands (e.g., to higher energy, to heavier projectile) to meet the needs from the frontier of sciences and applications, it becomes nowadays a hard and challenging task to maintain both completeness and accuracy of the whole EXFOR library. The paper describes evolution of the library with highlights on recent developments., 4 pages, 2 figures

The simulation of neutron irradiation–induced transmutation using inventory codes is an important part of the research into materials in various nuclear environments, including fusion, fission, med...

The EXFOR database is a collection of experimental nuclear reaction data, maintained by the IAEA on behalf of the International Network of Nuclear Reaction Data Centres (NRDC). The format for the storage of such data was first described in 1969 and while there have been many incremental changes over the years so that the format is now capable of containing a very wide range of measurement results, there is a growing realisation that a major change is required. Consequently the IAEA Nuclear Data Section (NDS) organised a Consultant's Meeting on ‘Further Development of EXFOR’ in 2012. This was an opportunity for a range of international experts to discuss ways of improving EXFOR and while this focused on new formats there was also discussion on ways of storing new data, new output formats and software tools such as editors. This paper will discuss recent and proposed changes to enable new quantities to be stored (such as coincidence measurements and covariances), the range of output formats available (e.g. C4 and X4+) which make interaction with the data more user friendly and the possible use of XML to modernise the database.

The OECD Nuclear Energy Agency (NEA) organizes cooperation between the major nuclear data evaluation projects in the world. The NEA Working Party on International Nuclear Data Evaluation Cooperation (WPEC) was established to promote the exchange of information on nuclear data evaluation, measurement, nuclear model calculation, validation, and related topics, and to provide a framework for cooperative activities between the participating projects. The working party assesses nuclear data improvement needs and addresses these needs by initiating joint activities in the framework of dedicated WPEC subgroups. Studies recently completed comprise a number of works related to nuclear data covariance and associated processing issues, as well as more specific studies related to the resonance parameter representation in the unresolved resonance region, the gamma production from fission product capture reactions, the 235U capture cross section, the EXFOR database, and the improvement of nuclear data for advanced reactor systems. Ongoing activities focus on the evaluation of 239Pu in the resonance region, scattering angular distribution in the fast energy range, and reporting/usage of experimental data for evaluation in the resolved resonance region. New activities include two subgroups on improved fission product yield evaluation methodologies and on modern nuclear database structures. Future activities under discussion include a pilot project for a Collaborative International Evaluated Library Organization (CIELO) and methods to provide feedback from nuclear and covariance data adjustment for improvement of nuclear data. In addition to the above mentioned short-term task-oriented subgroups, WPEC also hosts a longer-term subgroup charged with reviewing and compiling the most important nuclear data requirements in a high priority request list (HPRL)., JRC.D.4-Standards for Nuclear Safety, Security and Safeguards

This paper presents the approach of a combined use of resonance integrals and average Maxwellian cross sections (MACS) at kT = 30 keV to test and validate the resolved resonance range or its reconstructed cross section curve. Based on these two integral measurements a sensitive and energy dependent test can be provided. These two integral quantities cover with their neutron spectra the energy region between En = 0.5 eV up to several hundred keV, respectively, with different weighting. Our principal motivation is to produce a validation tool, sensitive to the lower and upper parts of the resonance region through the difference in the applied 1/E and kT = 30 keV Maxwell–Boltzmann spectra of the resonance integral and MACS data.

The intense neutron flux densities in fusion reactor blankets produce activation in the blanket materials relevant to operational safety, decommissioning, etc. The aim of the present work is to check the European Activation System EASY-2007 for its capability to predict important gamma activities induced in titanium in a fusion neutron field. Many advanced low-activation materials for fusion applications contain titanium, most notably in the breeder material Li 2 TiO 3 . In the present work, a small sample of Ti was irradiated with the intense DT neutron generator of Technical University of Dresden. The gamma-radioactivity following irradiation was measured and nuclide activities were derived. For each of the measured gamma activities, the corresponding value was calculated with EASY, and calculation-to-experiment ratios ( C / E ) were determined. EASY predicted the induced gamma activities, isotopes of scandium, well with some overestimation for 47 Sc. The results of this measurement together with available EXFOR and validated state-of-the-art activation libraries are discussed.

An overview is presented of the state-of-the-art of computational tools, data and models developed for neutronics and activation analyses of the IFMIF neutron source. Significant progress has been achieved in making available computational tools for simulating the d-Li neutron (and photon) source term with the McDeLicious Monte Carlo code and associated d+6,7Li cross-section data, in generating neutronics Monte Carlo geometry models by the McCad conversion software, and in providing the interface programme MCDO to enable coupled 3D Monte Carlo and discrete ordinates shielding calculations. In the field of nuclear data for IFMIF, a major milestone has been achieved with the launching of the FENDL-3 research project co-ordinated by the IAEA. Another major achievement is the production of the European Activation File, version EAF-2007, which has the neutron energy range extended to the needs of IFMIF and also provides calculated data libraries for deuteron and proton induced activation reactions.

Nuclear data are of fundamental importance in studies of nuclear technology such as the design of fission power plants, fusion devices and accelerators. The large amounts of data required are stored in computer readable formats in data libraries and include the general purpose files used for neutronics calculations. The other class of libraries are special purpose ones containing decay data and cross sections for dosimetry and activation. This paper gives examples of available data and discusses some needs for various applications. The focus is on neutron-induced activation with examples of how the reactions of particular importance can be identified. All data should be accompanied by estimates of uncertainty. The climate of budget cuts worldwide means that the greatest nuclear data need is for resources to continue production of compiled and evaluated data essential for nuclear technology.

Two novel tools for the estimation of activation dose in fusion devices based on the rigorous-two-step formalism are discussed and compared. The tools, one in-house and one commercially available, couple transport and activation calculations in an integrated manner and allow for very high spatial resolution. Benchmark exercises are reported; the accuracy of the commercial activation solver has been found to be similar to that of FISPACT. Comparison in a 1D problem with ITER-like irradiation conditions is made. Despite minor differences in input data and isotopic and photon output, activation dose results at several decay times and locations are within 20% of each other. The adequacy and completeness of the nuclear data of the commercial software is assessed against the well-established EAF data; recommendations are given for its improvement for generic fusion applications.

At the International Thermonuclear Experimental Reactor (ITER), a neutron activation system is foreseen to measure neutron fluence on the first wall and to evaluate total fusion power from ITER plasma. This system utilizes the method of counting gamma radiation from the metal sample irradiated by the neutron flux at the irradiation end located near the plasma. Evaluation of the operational radioactivity of the sample, which has been induced during ITER operation, is necessary in order to determine sample material, mass, and the appropriate irradiation time. Neutronic calculations are performed to evaluate operational activity of the sample. Activation of the sample is calculated according to the irradiation time for various sample materials such as Si, Al, Ti, Fe, Nb, and Cu and by assuming that the samples are irradiated at the midplane inboard region where the neutron flux is one of the strongest.

The European Activation System, EASY, includes as the source of nuclear data the European Activation File (EAF). A new version of EAF, EAF-2007, has been developed that contains cross-section data for deuteron-and proton-induced reactions in addition to the traditional neutron-induced data. The main reason for the addition of these data to EAF is to enable activation calculations to be performed for the International Fusion Materials Irradiation Facility, which is a planned materials test facility, and for other accelerator-driven devices with an incident upper energy limit of 60 MeV EAF-2007 has benefited from the generation and maintenance of comprehensive activation files and the development of the processing code SAFEPAQ-II. Cross-section validation exercises against both experimental data and systematics, which were started on the EAF-4 file (1995), enable a comprehensive assessment of the data. Although EAF-2007 is the best-validated activation neutron cross-section library in the world, currently

An extended analysis has been performed of elastic-scattering and reaction cross-sections of deuterons on the Al 27 nucleus, for deuteron energies from 3 to 60 MeV, based on a semi-microscopic optical potential with a double-folding real part and phenomenological imaginary and spin-orbit terms. An increased effort is devoted to the breakup mechanism, the analysis of proton-emission spectra and angular distributions from deuteron-induced reactions on nuclei from Al to Pb, at incident energies from 15 to 80 MeV, providing the energy- and mass-dependence of the breakup mechanism contribution. The corresponding direct-reaction cross-sections within the same energy range has then been analyzed, the improved description of both the elastic-scattering and reaction measured data backing the proper use of these optical potentials for deuteron activation assessment.

Safety and waste management of materials for ITER, IFMIF and future power plants require knowledge of the activation caused by irradiation with neutrons, or in the case of IFMIF, deuterons. The European Activation System has been developed for such calculations and a new version was released earlier this year. This contains a large amount of nuclear data in the European Activation File covering neutron-, deuteron- and proton-induced cross sections. These data are input to the FISPACT code for activation calculations. EASY-2007 is being validated using integral and differential measurements. However, only a minority of reactions have experimental support and a statistical method is described that can test the complete library. Importance diagrams are useful in finding the dominant nuclides formed following irradiation and the reactions responsible for their production. These diagrams now cover energies above 20 MeV and examples of new dominant nuclides and reactions relevant to IFMIF are given.

An assessment of the activation caused by deuteron and proton beam losses in the accelerating components and by the full beam current in the beam dump during the International Fusion Material Irradiation Facility (IFMIF) prototype accelerator testing period was performed. The losses along the acceleration line were calculated by the Monte Carlo codes PARTMTEQM and PARMILA. The activation analysis was performed by the European Activation System EASY-2007 recently upgraded to include charge particle-induced reactions. The deuteron and proton activation cross-sections from this library for the dominant reactions were validated against experimental data demonstrating an acceptable uncertainty. The transport of the decaying gamma-rays and the calculation of the radiation dose rate on the external surfaces of the accelerator tank and beam dump have been performed by the MCNP-5 code. The results show that activation induced by the deuteron and proton beam losses in the accelerating components are below the legal transport and hands-on limits. This is also proved to be the case for the proposed design of the beam dump employing the tungsten as ions stopper to accommodate 1.2 MW beam power.

Excitation functions were measured for the $^{55}$Mn(n,2n)$^{54}$Mn, $^{55}$Mn(n,$\alpha$)$^{52}$V, $^{63}$Cu(n,$\alpha$)$^{60}$Co, $^{65}$Cu(n,2n)$^{64}$Cu, and $^{65}$Cu(n,p)$^{65}$Ni reactions from 13.47 to 14.83 MeV. The experimental cross sections are compared with the results of calculations including all activation channels for the stable isotopes of Mn and Cu, for neutron incident energies up to 50 MeV. Within the energy range up to 20 MeV the model calculations are most sensitive to the parameters related to nuclei in the early stages of the reaction, while the model assumptions are better established by analysis of the data in the energy range 20-40 MeV. While the present analysis has taken advantage of both a new set of accurate measured cross sections around 14 MeV and the larger data basis fortunately available between 20 and 40 MeV for the Mn and Cu isotopes, the need of additional measurements below as well as above 40 MeV is pointed out. Keywords: 55Mn, 63,65Cu, E$\leq$40 MeV, Neutron activation cross section measurements, Nuclear reactions, Model calculations, Manganese, Copper, Comment: 39 pages, 12 figures

Large cross section libraries, such as EAF-2007 used for activation calculations, need to be validated. A traditional approach employs simple systematic formulae based on experimental data and derived at energies such as 14.5 MeV. Such systematics are also used for renormalization of cross sections during library preparation. This approach is gradually being replaced by using results of sophisticated nuclear model calculations. As the energy range of EAF libraries has expanded from 20 to 60 MeV an additional approach is required and the method of ‘statistical analysis of cross sections’ (SACS) has proved to be useful. SACS analyses are carried out for the important charged particle reactions (n,p) and (n,α) in the EAF-2007 and TALYS-6 libraries. TALYS-6 is a calculational library generated by the TALYS model code Version 0.72. SACS considers various reaction statistics such as σmax, Emax and Δ1/2 and plots scatter plots against a parameter such as the asymmetry (s). Trend lines using simple algebraic formulae can be fitted to the data and points discrepant from the trends correspond to reactions that require improvement. A new observation is a ‘step’ in the Δ1/2(s) plot for (n,p) reactions and this has been interpreted as due to competition between (n,p) and (n,n′p) reaction channels. Equations for the various trend curves for EAF-2007 are given.

During radioactive decay of a collection of nuclides the possibility of the total activity increasing is implicit in the standard differential equations. Traditional treatments do not emphasize this possibility so leading to unease when such a rise is observed. Examples of increases in activity for materials following irradiation by neutrons are given, and the phenomenon is explored in a model system of three nuclides. Conditions on the decay constants and the initial number of atoms of the nuclides such that the total activity can increase with time are given.

The main type of activation calculations needed for fusion technology relate to the interaction of neutrons with materials. The roadmap for development of fusion as an electricity producing technology is based on ITER and IFMIF followed by DEMO. IFMIF is a materials testing facility that will qualify the materials needed for DEMO. IFMIF will use intense beams of high-energy deuterons striking a flowing lithium target to produce the neutron field. The neutron spectrum contains significant neutrons with energy up to 55 MeV. In addition, the deuterons will themselves make a contribution to activation especially in the target where they strike the lithium but also due to beam losses in the accelerator. A preliminary deuteron library was released as part of the maintenance release of EAF-2005.1. This was used to calculate the activation in the lithium target due to reactions of the deuterons with the corrosion products. These calculations show that the deuterons are much more important than the neutrons (about a factor of 70) in activating elements other than lithium. The ongoing work to update the library using improved model calculations and available experimental data is described. This new library will form part of EAF-2007 planned for release next year.

Samples of lanthanum, tantalum and erbium which are constituents of structural materials and insulating coatings for blankets of fusion reactor designs have been irradiated in a fusion peak neutron field. The induced gamma activities were measured and the results were used to validate calculations with the European activation system EASY-2005. Good agreement for the prediction of major contributors to the contact dose rate of the materials was found, but for minor contributors the calculation deviated up to 50%.

The possibility of clearance of vanadium–chromium–titanium (V–Cr–Ti) alloys is analysed. These alloys after their service in fusion power plants, have the potential to reach clearance if they are purified from activation products. The extraction part of the technological scheme for radiochemical separation of components of irradiated V–Cr–Ti alloy and their purification from metallic activation products, developed earlier, was tested for the first time in laboratory conditions using activated alloy specimens. The replacement of the acid reextraction of V with peroxide and of acid reextraction of Cr with alkaline improved characteristics of the extraction reprocessing. Duration of the V and Cr reextraction was shortened by about an order of magnitude, the output of these alloy components was increased, V purification from rare-earth metals became two times as great, and Cr decontamination from Co increased by two orders of magnitude. Activation of Be contaminated with trace quantities of uranium is an issue: estimation of Be activation in the blanket of the Power Plant Conceptual Study (PPCS) has suggested that traces of U impurity in Be should be removed – or substantially reduced – prior to use.

The OECD Nuclear Energy Agency (NEA) Data Bank participates in the production of data and their distribution to users including the collection and validation as well as the distribution of the Joint Evaluated Fission and Fusion (JEFF) library. The JEFF project has evolved from two separate projects, namely the European Fusion File (EFF) and the Joint Evaluated File (JEF), with the release of JEFF-3.1, in May 2005. The NEA also provides tools for the EFF project, such as computer codes for nuclear energy and radiation physics applications. Of special interest for fusion applications are the integral experiments collected in the SINBAD database, with radiation shielding and dosimetry experiments including many fusion neutronics shielding experiments. In this paper an overview will be given of the NEA, and some examples of nuclear data services offered, such as the SINBAD database. JANIS, a display program evaluated and experimental data developed at the NEA will be mentioned briefly. The main emphasis will be given to the EFF project including the contents of the new JEFF-3.1 library, released in May 2005. Examples of recent work are given as well as a discussion on the forth-coming evaluation efforts among the EFF collaborators.

The European Activation System (EASY) has been developed for activation calculations within the Fusion Technology programme. It comprises the EAF nuclear data libraries and the FISPACT inventory code. EASY-2005 contains about five times more neutron-induced reactions (62,637) than the previous version; due to an increase in the upper energy limit from 20 to 60MeV. Many measurements of activation in well-defined neutron spectra have been made; these integral results are used to validate EAF. Details of the validation covering 453 reactions are given. Model calculations were used to produce the majority of the data, and the large number of reactions, and the lack of experimental data, make it necessary to develop new checking tools. Within the SAFEPAQ-II code, the new methodology of statistical analysis of cross sections (SACS) has been developed. This enables various quantities such as maximum cross section (σ max ) to be plotted as a function of asymmetry parameter (s) for each reaction type. Such plots show well-defined trends and inconsistent data for a particular reaction can readily be identified. The use of integral data and SACS for improvement are discussed, in relation to the maintenance version, EASY-2005. 1 and the planned new version, EASY-2007.

In the framework of the Broader Approach Bilateral Agreement between European Union and Japan, a number of important projects of common interest for the rapid realization of fusion energy are agreed. Between these projects, the engineering validation and engineering design activities (EVEDA) phase of the International Fusion Materials Irradiation Facility (IFMIF) was included. The objective of the EVEDA phase of IFMIF is to perform reliability tests of key components and to produce a final design to be able to start IFMIF components manufacture as soon as the construction decision is taken. The main technical developments obtained in Europe during the last few years related to the IFMIF design are summarized. Based on this, the main technical issues to be solved during the EVEDA phase are also reviewed in the framework of the present scenario for IFMIF.

In order to minimize the quantity of active materials that require long-term storage, arising during operation and after fusion power plant decommissioning, maximum use should be made of both recycling within the nuclear industry and clearance. For the latter, revised limits have been recently issued at the international level and in the US and Europe. In this paper the implications for fusion materials of these new levels are considered. Concerning recycling, power plant studies have employed criteria based solely on radiological parameters. Reviews of remote procedures currently used within the nuclear industry suggest that these criteria have been unduly conservative and should be revised.

The materials for future fusion devices such as DEMO require testing to high neutron fluence. Such testing is planned to be carried out in IFMIF, an accelerator based facility where the neutrons will have maximum energy of about 55 MeV, but with a broad peak near 14 MeV. In order that activation calculations for IFMIF can be carried out, the nuclear data must contain cross sections covering a similar energy range. A description of the EASY-2005 system is given and it is noted that a new library has been added to EASY to cover another significant source of activation from deuteron-induced reactions. Calculations of the neutron activation of materials in many regions of IFMIF have been carried out. These calculations are reported, and the contribution of neutrons above 20 MeV to the activation is discussed. Preliminary calculations using the deuteron library have been made and the activation from deuterons is discussed.

Several neutron activation cross section libraries have been produced recently with data above the energy of 20 MeV. These are needed because of new applications, such as the International Fusion Material Irradiation Facility (IFMIF) and Accelerator Driven Systems (ADS). A standard validation procedure for such libraries is a comparison with differential and integral experimental data. However, the number of differential data above 20 MeV is relatively small and there are very few integral experiments with neutron spectra dominated by high-energy (>20 MeV) neutrons. Furthermore the size of these libraries (about 775 targets and >60,000 reactions) favours global test procedures. It is shown that the method of ‘Statistical analysis of cross sections’ (SACS) can be used for this purpose. This is based on the assumptions that cross section excitation curves for all targets have a similar (bell) shape shifted by differences in Q -value, and that their properties, such as the maximum of the excitation curve ( σ max ), the incident neutron energy at which σ max occurs ( E max ) and the width of the excitation curve at half its maximum ( Δ 1/2 ) have a pronounced smooth trend as a function of A or s . It will be demonstrated that this method of analysis is a very effective and novel way to validate reaction cross section data, both for their shape and their magnitude. This will be illustrated using the recent European Activation Library EAF-2005, produced within the EFDA Fusion Technology Programme. The majority of the cross section data in the library are based on calculations with the nuclear reaction code TALYS.

Existing neutron cross section libraries such as EAF-2003 contain a large number of reactions. Of these only a small proportion are significant in the production of the nuclides that dominate activation quantities such as activity or γ-dose rate at various decay times. These reactions were identified in a recent extensive set of calculations on all the elements and reported in the ‘Activation Handbook’. These 1340 reactions are considered here and the set of reactions with no differential or integral data are listed and prioritised. A set of 339 reactions with very limited possibility of measurement are given; these require further study by theoretical calculations. A set of 100 reactions with either discrepant or no data, that might be measurable are listed and are recommended to be the subject of future experimental work.

Investigation of current and planned fusion devices, as well as conceptual power plants, requires well-validated tools to predict the activation of materials. This has led to the production of the European Activation System (EASY), which provides such a capability. The version used here, EASY-2003, is widely distributed and has been used to carry out activation calculations on a large number of materials. However, there was also a need for a comprehensive handbook of activation data that could be quickly referred to, rather than resorting to running codes. This paper discusses the process of generating, over a period of 8 months, the data for a handbook that presents the important activation data for all the naturally occurring elements from hydrogen to uranium. The main computational methods are outlined briefly, but the bulk of the paper is focused toward a description of the different ways in which the data are presented, including new presentations of activation data, called ‘importance diagrams’.

Two experiments were carried out and analysed in order to test tools used for the nuclear design of fusion devices. Neutron and photon flux spectra were measured in a thick tungsten assembly during irradiation with D-T neutrons. They were analysed with the Monte Carlo transport code MCNP-4C using nuclear data of the libraries FENDL-2, EFF-2.4 and JENDL-3.3. Small pieces of tungsten were irradiated with D-T neutrons, and the neutron-induced activities measured after the irradiation, were analysed with the inventory code FISPACT using data of the libraries EAF-2003 and FENDL/A-2. Deviations of experimental from calculated results show that an improvement of the tungsten data base is required. Tungsten is widely proposed for use in plasma facing components of future fusion devices.

Yttrium is an element in oxide dispersion strengthened (ODS) steels to be used as structural material at high neutron doses and temperatures. Lead acts as a neutron multiplier and coolant in breeding blanket concepts such as the EU test blanket modules (TBM) with Pb–17Li. Samples of pure Y and Pb were irradiated with D–T fusion neutrons. The radioactivity following irradiation was determined several times during decay by γ-spectroscopy. The results were analysed with the European Activation System. Ratios of calculated-to-experimental values for individual activities are discussed in connection with the expected activation performance of the materials in fusion power plant conditions.

The European Power Plant Conceptual Study (PPCS) reported in the summer of 2004. Several conceptual designs (“Models”) for commercial fusion power plants were developed, spanning a range from relat...

Tungsten is the preferred material for the divertor plates of fusion devices and a constituent of reduced activation structural materials. Samples of pure tungsten were irradiated with D-T fusion neutrons. The radioactivity following irradiation was determined several times during decay by γ-spectroscopy. The results were analysed with the European Activation System. Ratios of calculated-to-experimental values for individual activities are discussed in connection with the expected activation performance of the material on fusion power plant conditions.

CuCrZr is used in high heat flux components of ITER and other fusion reactor designs. A CuCrZr alloy of the European Fusion Technology Programme was irradiated with D–T neutrons, and the γ-activities of all nuclides which are relevant up to the recycling limit of the material were measured. The results were analysed with the European Activation System (versions EASY-2001 and EASY-2003). The calculated total activation property of the material was validated within 10%. The long-term radioactivity was estimated to be well below the hands-on limit with an uncertainty of 19%.

Activation calculations are an essential contribution to understanding the interactions of fusion materials with neutrons. The existing state-of-the-art tools such as EASY-2003 enable calculations to be carried out with neutrons up to 20 MeV. Plans to expose fusion components to high neutron fluxes include the IFMIF materials testing facility. This accelerator-based device will produce neutrons with a high-energy tail up to about 55 MeV. In order to carry out activation calculations on materials exposed to such neutrons it is necessary to extend the energy range of the data libraries. An extension of the European Activation System (EASY) to a new version, EASY-2004, for testing has been completed. The existing reactions have been extended up to 60 MeV and new classes of reactions added using calculated cross sections. Results of preliminary calculations in an IFMIF relevant neutron field are given.

Small platelike clusters of self-interstitial atoms (SIAs) in irradiated metals are extremely mobile. This mobility can be greatly reduced by foreign atoms. Where the plates are large enough to form edge dislocation loops, their immobilization is analysed as a solid solution hardening. The misfitting substitutional solute atoms can significantly reduce the mobility of small SIA loops when in the central cores of their edge dislocation lines. An activation energy is required to unpin a loop from such atoms and this – unlike in conventional solid solution hardening – remains finite even with no applied stress driving the dislocation. In dilute solutions break-away occurs by the thermally activated escape from single atom obstacles on the loops. Application to a proposed fusion power plant alloy (EUROFER 97) shows that the W alloy atoms provide the most severe immobilization, although Mn atoms produced by transmutation run a close second. The contribution of Cr is evaluated.

Neutron transport calculations using MCNP and activation calculations using FISPACT have been carried out to produce a comprehensive dataset to be used in the assessment of materials for fusion power plants. Examples are given to illustrate the useful application of pathway analysis, importance diagrams and the effects of impurities on activation and dose.

The low-activation steel Eurofer was irradiated with D–T fusion neutrons. The radioactivity following irradiation was determined several times during decay by γ-spectroscopy. The results were analysed with the European Activation System (EASY-99). Ratios of calculated-to-experimental values for individual activities and for their sums are discussed in connection with the expected low-activation behaviour of the material in fusion power plant conditions.

The Joint European Torus (JET) machine was built from the beginning to perform DT studies and is for the next decade the only machine with DT capability. JET is thus the tokamak best suited for studies of various nuclear technology issues that will be of importance for future DT fuelled machines. The Active Gas Handling System (AGHS) built for the supply and reprocessing of tritium is still in operation to detritiate the exhaust gases and to provide the necessary ventilation during vessel openings because >1 g of tritium remain in the machine even 4 years after the DTE1 campaign. The tritium is bound in co-deposited layers and flakes formed mainly on the shadowed inner part of the divertor, and in the bulk of tiles. Areas of erosion and deposition are being identified and preliminary models for the material movement developed. Characterisation of the properties of tiles and flakes is very important to develop the best handling techniques. Due to the activation of the machine and the use of Be and T entry to the torus is limited by the need to minimise worker doses and is currently only possible in full pressurised suite. Work inside it is, therefore, performed with remote handling tools where practicable, e.g. the removal of the divertor septum and the collection of dust and flakes from areas below the divertor to achieve a more accurate tritium balance. Techniques need to be developed to reduce the tritium content in waste to permit disposal as low level waste (

The European activation system (EASY) is the complete package of data and codes developed as part of the European fusion technology programme to enable detailed and accurate activation calculations to be carried out for fusion applications. A central part of EASY is the European activation file library of 12 470 neutron-induced cross sections. A major effort to increase the accuracy and confidence in this library has been carried out by a process of validation with integral measurements. Experiments have been carried out in three complementary neutron spectra by irradiating a series of fusion relevant materials. These irradiations can then be modelled by EASY, and the comparison between the calculated (C) and experimental (E) activity values enable C/E ratios to be found for the production of a set of radionuclides. Examples of reactions that can be validated and of discrepant C/E values and the resulting data improvements are given. These studies demonstrate the high level of validation that gives EASY-2001 its status as a first-class activation code and data package.

The radioactivity induced by neutrons in the materials of fusion power plants is a focus of investigations dedicated to safety and environmental assessments of fusion power. The greatest part of the radioactivity is produced by two components of the neutron flux spectrum, by thermal neutrons and by the 14-MeV DT fusion neutrons. The low-activation material SiC and the tritium-generating material Li 4 SiO 4 were irradiated with 14-MeV neutrons, and the γ-activity induced was measured several times during the decay. The results were analysed with the European Activation System EASY-99 with respect to short-term and long-term radioactivity.

Extensive neutron transport calculations have been performed to determine the neutron spectrum at a number of points throughout the JET torus hall. The model has been bench-marked against a set of foil activation measurements which were activated during an experimental campaign with deuterium/tritium plasmas. The model can predict the neutron activation of the foils on the torus hall walls to within a factor of three for reactions with little sensitivity to thermal neutrons. The use of scandium foils with and without a cadmium thermal neutron absorber was a useful monitor of the thermal neutron flux. Conclusions regarding the usefulness of other foils for benchmarking the calculations are also given.

An important aspect of the development of potential structural materials for fusion power plants is their activation by 14-MeV neutrons. At present vanadium alloys of type V–Ti–Cr are considered as promising for this application. Among them the alloys with additions of up to 10% of Ti and of 4–6% of Cr are the most widespread. An activation study of some Russian candidate vanadium alloys was carried out at the SNEG-13 facility. Various samples were studied: three types of vanadium alloy with different additions of Ti and Cr, and the samples of their main components-pure V, Cr, Ti produced by various technologies. All the samples were irradiated in identical conditions in a neutron field with a well certified neutron spectrum. The experimental data are compared to calculations with FISPACT code using the activation data from EASY-99 System.

Safety and environmental assessments have been made of conceptual fusion power plant designs employing silicon carbide composites (SiC/SiC) as the first wall and blanket structure material. These have used similar analysis methods to earlier studies of designs based on vanadium alloy or low-activation martensitic steel, allowing direct comparisons. The very low short-term activation of silicon carbide results in an almost insignificant level of decay heat in postulated loss of coolant accidents, and a lower γ-dose rate on the timescale of relevance to handling for maintenance operations. However on the longer time-scale, of interest in possible recycling operations, decommissioning and waste management, SiC/SiC appears to perform no better than vanadium alloy or low-activation martensitic steel, due in part to the activation of impurities in a realistic composition. Furthermore, its increased neutron transparency may result in higher activation in the vacuum vessel and ex-vessel components, unless costly additional shielding is introduced.

Activation data and inventory codes are a major input to much of the safety related work carried out on fusion devices. The inventory code recommended for European activation calculations is fispact -99; this requires a large amount of nuclear data, which is available in the European Activation File ( EAF -99). The production of an EAF library uses new sources of data, both evaluated and calculated, differential measurements and integral data. In order to store, evaluate, and use all the various data sources an efficient software tool is required. Earlier versions of EAF have been produced using the tools sympal and safepaq , which enabled a large degree of automation as compared with the original construction ‘by hand’. However, these relied on the direct manipulation of the ENDF formatted text files using fortran -77. This is not an efficient approach, as editing of the text files is inconvenient and liable to errors. It was decided to use relational databases to store the data, with data extraction carried out by standard queries written in sql . Other objectives were the provision of a user-friendly graphical interface to allow data to be viewed and manipulated and a high level of QA by logging all data changes. These objectives have been realised by the safepaq -II application; this uses the ideas of the previous tools, but has been designed from scratch using new methods. Visual Basic is used to build the application running under Windows NT 4, which is linked to a series of access databases.