[en] The irradiation materials laboratory of TECHNOFUSION aims to reproduce, with ion irradiation, the neutron damage produced in fusion facilities materials. For this, the laboratory will have different ion accelerators with energies and intensities significant. In this paper, it's analyzed the dose produced outside the irradiation room, assuming that inside there is an iron sample attached to its stand.

[en] The Rigorous-Two-Steps (R2S) is one of the most powerful methods to estimate the Shutdown Dose Rate (SDR) due to material activation in nuclear facilities with intense and spread neutron fields. The most advanced R2S tools couple neutron and photon transport, which are often simulated using Monte Carlo (MC) codes, through an activation simulation using mesh-based techniques to improve the spatial resolution of both the neutron flux and the decay gamma source. One of the problems of the methodology is that the statistical uncertainty of the neutron flux, estimated by the MC transport codes, is not considered by most R2S implementations. Consequently, larger tolerance must be assumed in the design of the nuclear facilities. During the last years, several schemes have been proposed to estimate this uncertainty in R2S calculations, however, all of them assume the so-called 'Single neutron interaction and low burn-up' (SNILB) conditions during the activation step. This limitation significantly limits their applicability because R2S methodology is more relevant in high fluence facilities, where the SNILB conditions are not met. The work performed during my thesis consisted in developing a scheme that enables the calculation of the SDR statistical uncertainty without any additional assumptions than those taken into account by the R2S methodology, particularly without being limited by the SNILB conditions. In addition, the proposed approach is suitable for cell and mesh-based R2S implementations. This methodology, and other features required to calculate the input data needed to use the methodology, were implemented in R2S-UNED code. Among these extra features, it is worth mentioning the capability to calculate the neutron flux uncertainty (covariance matrix) required for the accurate estimation of the SDR uncertainty, because the estimation of this quantity is the step that currently limits the estimation of the SDR stochastic uncertainty in R2S calculations. The principal issue to estimate this matrix is that its size is, in realistic cases, around thousands of GB. Consequently, it can not be calculated during the MC transport calculation as R2SUNED does. For this reason, efforts were dedicated to optimising the R2S simulation to reduce the size of this matrix. As result, a guideline and a methodology were developed to increase the applicability degree of this scheme to realistic cases. Finally, the last part of the work consisted in applying the scheme in different relevant application cases: the ITER benchmark exercise and the SDR estimation in the JET facility after of the last campaign. (authors)

[en] Highlights: • Nuclear data set for the Direct One-step ITER reference tool: D1SUNED. • Applicability for ITER shutdown dose rate analyses in hands-on maintenance areas. • Characterization of the ITER radioactive inventory at 10⁵ and 10⁶ s of cooling time. • ITER recommendations followed in nuclear data set preparation. • Verification of nuclear data set against Rigorous Two-steps (R2S) calculations. ITER will be the largest Tokamak in the world, and it is expected to produce a total of up to 2.8• 10²⁷ neutrons during its operation. The Tokamak infrastructure will become radioactive as the machine operates, which is an aspect that needs to be considered in the design of the planed in-situ maintenance activities. The occupational radiation exposure (ORE) must be accounted for, and an ALARA program must be implemented to minimize it. It requires the determination and analysis of shutdown dose rates fields, the purpose of D1SUNED tool. Common to all Direct one-step-based approaches, this tool needs to be fed with a nuclear data set tailored for each problem and produced ex professo. In this paper, we characterize the radioactive inventory relevant for the ORE of ITER maintenance activities using ACAB activation code. The ITER reference irradiation scenario SA-2 and the cooling times of interest 10⁵ s and 10⁶ s are considered. A comprehensive list of typical materials has been studied with detailed impurities content. The nuclear data set covers 99% of the radioactive inventory of concern, and all the pathways responsible for 99% of its production. It has been prepared following the ITER recommendations of cross-sections libraries and it has been verified against Rigorous-two steps calculations. This batch of nuclear data complements D1SUNED for shutdown dose rate exhaustive analysis for ITER with the perspective of maintenance according to the latest ITER nuclear data standards.

[en] The main nuclear fusion facilities world-wide rely on MCNP to conduct the nuclear analysis activities. It is a computational tool based on Monte Carlo method and probably the most reliable one to solve neutral particles radiation transport problems. The increasing availability of High Performance Computing infrastructure has stimulated the development of tools to translate complex CAD model to MCNP, helping to reduce uncertainties associated with geometry modelling. However, an associated need of RAM memory has emerged, reaching the limits of memory available per CPU in current parallel super computers. Currently, some ITER analyses use models requiring more memory per CPU than available in super computers like Marconi. In these cases the simulations need to reduce the number of CPU used per node, leading to a waste of computational resources. This paper assesses the MCNP memory management related to the geometry and proposes some hints to reduce it acting on the MCNP models. This same study identified the origin of the problem being a coding in MCNP leading to an overestimation of the memory allocation. Modifications in MCNP have been implemented to reduce the memory consumption; these changes have improved noticeably the code performances.

[en] In the IFMIF-EVEDA accelerator prototype, deuterons (with energies up to 9 MeV) interact with the materials of the accelerator components clue to beam losses and in the beam dump, where the beam is stopped. The productions of neutrons/photons together with radioactive inventories due to deuteron-induced reactions are some major issues for radiation protection and safety assessment. Here, we will focus on the proposal of a computational approach able to simulate deuteron transport and evaluate deuteron interactions and production of secondary particles with acceptable precision . Current Monte Carlo codes, such as MCNPX or PHITS, when applied for deuteron transport calculation, use built-in semi-analytical models to describe deuteron interactions. These models are found to be unreliable in predicting neutron and photon generated by low-energy deuterons, typically present in the IFMIF-EVEDA prototype accelerator. In this context, a new computational methodological approach is proposed based on the use of an extended version of current MC codes capable of using evaluated deuteron libraries for neutron (and gamma) production. The TALYS nuclear reaction code is found to be an interesting potential candidate to produce the evaluated data for double-differential neutron and photon emission cross-sections for incident deuterons in the energy range of interest for IFMIF-EVEDA applications. The recently-released deuteron TALYS-based Evaluated Nuclear Data Library, TENDL-2009, is considered a good starting point in the road to achieve deuteron data files of enough quality for deuteron transport problems in EVEDA. Unfortunately, current Monte Carlo transport codes are not able to handle light ion libraries except for protons. To overcome this drawback the MCNPX code has been extended to handle deuteron (also triton, helion and alpha) nuclear data libraries. In this new extended MCNPX version called MCUNED, a new variance reduction technique has also been implemented for the production of secondary particles induced by light ion nuclear reactions, which allow reducing drastically the computing time needed in transport and nuclear response function calculations. Verification of these new capabilities for Monte Carlo simulation of deuteron transport and secondary product generation included in MCUNED is successfully achieved. The existence of the MCUNED code allows testing for the first time the deuteron cross-section TENDL package by simulation of integral experiments. Some preliminary efforts are addressed to compare existing experimental data on thick target neutron yields for copper with those computed by the MCUNED code using TENDL cross-sections. (authors)

[en] This paper describes the local shielding design process of the IFMIF/EVEDA beam dump and the most relevant results obtained from the simulations. Different geometries and materials have been considered, and the design has been optimised taking into account the origin of the doses, the effect of the walls of the accelerator vault and the space restrictions. The initial idea was to shield the beam stopper with a large water tank of easy transport and dismantling, but this was shown to be insufficient to satisfy the dose limit requirements, basically due to photon dose, and hence a denser shield combining hydrogenous and heavy materials was preferred. It will be shown that, with this new shielding, dose rate outside the accelerator vault during operation complies with the legal limits and unrestricted maintenance operations inside most of the vault are possible after a reasonable cooling time after shutdown. (authors)

[en] Highlights: • Scheme to calculate statistical uncertainty due to the calculation method in MC R2S. • It does not add additional assumptions to those considered in R2S calculations. • It includes the calculation of the statistical covariance matrix of the neutron flux. • Application to SDR ITER benchmark shows that covariance of neutron flux is relevant. • Guideline to improve the applicability of the scheme is proposed. The Rigorous-Two-Steps (R2S) is one of the most useful methods to estimate the Shutdown Dose Rate (SDR). The most advanced R2S tools couple neutron and photon transport, which are often simulated using Monte Carlo (MC) codes, through an activation simulation using mesh-based techniques to improve the spatial resolution of the neutron flux and the decay gamma source. One of the problems of the methodology is that the statistical uncertainty of the neutron flux due to the MC method used by the transport codes is not considered by most R2S implementations. Consequently, larger tolerance must be assumed affecting to the design of the nuclear facilities. This article describes a scheme allowing the calculation of the SDR statistical uncertainty without any additional assumptions than those used in the R2S methodology. The approach proposed in this article is suitable for cell- and mesh-based R2S implementations. In this work, the methodology was implemented in the R2S-UNED code. The accurate application of the methodology requires the full the neutron flux uncertainty (covariance matrix) as input data. MCNP was modified to calculate this matrix, although, it cannot be calculated for most of the realistic R2S simulations due to its size. If that is the situation, we propose a guideline to reduce the size of the covariance matrix to be calculated according to its element contribution to the SDR. When this guideline cannot be applied, the methodology still allows calculating the upper and lower SDR uncertainty bounds. In this article, the guideline is applied to the calculation of the SDR uncertainty in the computational benchmark of ITER. In addition, we also study the possible impact of the neutron flux correlation degree on the SDR uncertainty in this benchmark.

[en] In this work, two different atomic models (ANALOP based on parametric potentials and IDEFIX based on the dicenter model) are used to calculate the opacities for bound-bound transitions in hot dense, low Z plasmas, and the results are compared to each other. In addition, the ANALOP code has been used to compute free-bound cross sections for hydrogen-like ions

[en] The decay heat has a strong impact in the design of the fusion facility due to its importance on safety, remote handling and waste management among others. For these applications, the energy deposition due to alpha and beta particles can be considered local, since the mean free path of these particles is small. On the contrary, the photons can travel longer distances affecting to the distribution of the heating, and consequently, on the temperature. Nowadays, most of the advanced tools dedicated to simulate accurate decay photon fields in fusion facilities do not estimate the decay heat, because alpha and beta heating is not coupled to photon heating. This article proposes a methodology, suitable to advanced mesh based R2S, which enables the estimation of the decay heat in each material with high spatial resolution. The aim to develop this methodology is to consider the accurate 3D decay photon field in the estimation of the decay heat. Furthermore, this methodology incorporates ELMER FEM code to calculate the temperature field taking into account the decay heat. This methodology was applied to a pre-conceptual DEMO blanket to quantify the importance of the photon transport in the estimation of the decay heat distribution as well as the temperature field.

[en] We present an experimental study devoted to measuring the opacity of bound-bound transitions in ultra-dense, hot, low Z plasmas, which are at the extreme limit for conditions of both emission spectroscopy and absorption spectroscopy. In this work, we develop an absorption spectroscopy experiment specially adapted to high-density diagnostics, using newly designed structured targets and an ultra-high resolution spectrograph. An aluminum plasma is chosen as the first candidate and the opacity of the He-like 1s²-1s2p (Heβ) and 1s²-1s3p (Heγ) transitions are measured