[en] A specific aim of the EUROTRANS Integrated Project, partially financed in the European 6. Framework Program (by EU), is to demonstrate the conceptual feasibility of high rate Minor Actinides transmutation in an Accelerator Driven System. This concept reactor, called European Facility on Industrial scale Transmuter (EFIT), is fuelled by U-free (Pu, MA)O_2-x + MgO innovative Cer-Cer fuel type with high MA content and is cooled by lead. The design of the sub-critical core is based on the so called '42-0' transmutation rate approach, characterized by zero Pu net balance and maximum MA transmutation rate of 42 kg/TWh_th together with reduced BU reactivity loss (∼200 pcm/year). An essential requirement for the EFIT reactor is that it remains sub-critical in any plant condition. To avoid unwanted returns to criticality, the sub-criticality level and the reactivity coefficients should be known with high accuracy. In this paper, the sensitivity of the K_eff and of the reactivity coefficients from the nuclear data was studied in stochastic approach. Results of these analyses show the need of additional work for uncertainties reductions in order to obtain recommended nuclear data for the neutron core design. (authors)

[en] An epithermal facility for treating patients with brain gliomas has been designed and is under construction at the fast reactor TAPIRO at ENEA Casaccia (Italy). The calculational design tools employed were the Monte Carlo codes MCNP/MCNPX together with the DSA in-house variance reduction patch. A realistic anthropomorphic phantom ('ADAM') was included to optimise dose profiles and in-phantom treatment-planning figures-of-merit. The adopted approach was to minimise the treatment time whilst maintaining a reasonable therapeutic ratio. It is shown that TAPIRO, in spite of its low power of 5 kW, is able to provide an epithermal beam that is of good quality and of sufficient intensity to allow a single beam patient irradiation, under conservative assumptions, of 50 min

[en] European R and D for Accelerator Driven System (ADS) design and fuel development in the 6th EC Framework Programme is driven by the Integrated Project EUROTRANS [1]. In EUROTRANS two ADS design routes are followed, the XT-ADS and the EFIT. The XT-ADS is designed to demonstrate the concept of ADS with a subcritical core combined with an accelerator. The longer-term EFIT development (European Facility for Industrial Transmutation) aims at a generic conceptual design of a full transmuter. This paper will concentrate on the EFIT core, which has a thermal power of about 400 MWth. The main goal of the EFIT design is to achieve an effective transmutation rate of the Minor Actinides (MAs) and respect important operational requirements as e.g. a low reactivity swing, a low power peaking, reasonable beam requirements and guarantee a high safety level. In order to have a sufficient subcriticality level, EFIT design is postulated to have a keff of 0.97. The risk of an accidental over-(the maximum) current does not exist in EFIT because, due to the very small burn-up reactivity swing, EFIT will work in the whole cycle with the maximum current allowed by the accelerator. A so-called 42-0 approach [2] is finally proposed by ENEA and adopted in the EFIT core design. With this 42-0 strategy, the EFIT core will be able to transmute about 42 kg/TWhth of MAs and keep a near zero net mass balance of Pu. The current EFIT core is loaded with a CERCER U-free fuel with MgO as the matrix. The 9Cr1MoVNb (T91) steel is used for the clad, which has a maximum temperature limitation of 550 C at the normal full power operation condition. Lead is used as the core coolant. It has an inlet temperature of 400 C and an outlet temperature of 480 C [3]. The temperature of 400 C at core inlet provides a margin to avoid lead freezing, and the temperature of only of 480 C at the core outlet offers many advantages in terms of reduced structure corrosion rates, improvement of the mechanical characteristics (making negligible creep of the structures), and reduces thermal shocks at transient conditions. Moreover at this 480 C nominal average core outlet temperature, the fuel clad temperature can be maintained below the limit of 550 C during the normal operation condition. Some core design data will be presented in the following section. For EFIT safety studies, the defence-in-depth concept has been applied [4]. The demonstration of the adequacy of the design with the safety objectives is structured along three basic conditions: (1) The Design Basis Conditions (DBC - structured into 4 Categories). The design of the plant results essentially from the analysis of these events. It must be shown that their consequences are very limited and, in any case, the risk of a whole core accident initialed by these events is very low. (2) Design Extension Conditions (DEC - limiting events, complex sequences and severe accidents) evaluated for licensing purposes independently of their occurrence frequency. The consequences of these accidents are analyzed and their consequences in the environment have to be demonstrated to be lower than the limiting release targets. (3) Residual Risk situation. The consequences of these situations are not analyzed since they are postulated to be unacceptable. The prevention measures regarding their occurrence have to be demonstrated to be sufficient. The safety principles and safety guidelines have been elaborated For EFIT within EUROTRANS and a comprehensive and representative list of transients has been established to test the safety behavior of the reactor plant. For innovative reactors such as EFIT, cliff-edge effects should be identified and excluded. For safety analyses, fuel parameter limits related to the different accidental categories have been determined on the basis of recent experimental evidences. Due to existing uncertainties, fuel melting or disintegration may only be allowed in the DEC category. In this paper, based on the current EFIT core design, a first transient analysis of the Unprotected Loss of Flow (ULOF) accident will be reported together with the steady state analysis performed by the SIMMER-III code [5, 6]. SIMMER-III is a two-dimensional, multi-velocity-field, multi-phase, multicomponent, Eulerian, fluid-dynamics code system coupled with a structure model including fuel-pins, hexcans etc., and a space-, time- and energy-dependent transport theory neutron dynamics model. The overall fluid-dynamics solution algorithm is based on a time-factorization approach, in which intra-cell interfacial area source terms, heat and mass transfers, and the momentum exchange functions are determined separately from inter-cell fluid convection. In addition, an analytical equation-of-state (EOS) model is available to close and complete the fluid-dynamics conservation equations. The code has originally been allocated in the severe accident domain of fast sodium cooled reactors. However, the philosophy behind the SIMMER development was to generate a versatile and flexible tool, applicable for the safety analysis of various reactor types with different neutron spectra and coolants, up to the new accelerator driven systems (ADS) for waste transmutation. (orig.)

[en] A flexible fast spectrum research reactor MYRRHA able to operate in subcritical (driven by a proton accelerator) and critical modes is being developed in SCK-CEN. In the framework of IP EUROTRANS programme the XT-ADS model has been investigated for MYRRHA. This paper reports the comparison of the sensitivity coefficients calculated for different calculation models and the uncertainties deduced from various covariance data for the discussion on the reliability of XT-ADS neutronics design. Sensitivity analysis is based on the comparison of three-dimensional heterogeneous and two-dimensional RZ calculation models. Three covariance data sets were employed to perform uncertainty analysis. The obtained sensitivity coefficients differ substantially between the 3D heterogeneous and RZ homogenized calculation models. The uncertainties deduced from the covariance data strongly depend on the covariance data variation. The covariance data of the nuclear data libraries is an open issue to discuss the reliability of the neutronics design. The uncertainties deduced from the covariance data for XT-ADS are 0.94% and 1.9% by the SCALE-6 44-group and TENDL-2009 covariance data, accordingly. The uncertainties exceed the 0.3% Δk (confidence level 1σ) target accuracy level. To achieve this target accuracy, the uncertainties should be improved by experiments under adequate conditions such as LBE or Pb moderated environment with MOX or Uranium fuel

[en] In the last years an international effort has been pursued for the development of the Advanced Lead Fast Reactor European Demonstrator (ALFRED) in line with the vision of the Gen-IV initiative for the LFR concept. This article - dealing with the ALFRED core design - analyses the global and local effects due to the accidental withdrawal of one control rod during the nominal plant state, by evaluating its impact in terms of reactivity balance and power distribution. Starting from the steady state neutronic results obtained with the ERANOS deterministic code, a detailed 3D power map of the core was evaluated (through a specific procedure) at the level of single fuel pins and used as input for accurate transient and thermal-hydraulic studies made by the RELAP5 system code and ANTEO+ sub-channel code, respectively. The ANTEO+ code, developed and validated by ENEA, was adopted to evaluate the temperature distributions in all the pins and surrounding sub-channels at key instants of the transient. It permitted the assessment of the new thermal conditions of the hot fuel assembly, in order to verify the compliance with the safety limits of the MOX fuel and the steel clad even in a completely unprotected scenario. (author)

[en] Recently the BNCT (Boron Neutron Capture Therapy) Scientific Community renewed the interest in the development of compact neutron sources for in hospital BNCT in order to skip the problems related to the use of nuclear reactors and to increase the number of treated patients. This paper presents a feasibility study for the exploitation of a high power D-D compact neutron facility, designed at Lawrence Berkeley National Laboratory (Ca, USA), for the treatment of tumours with diffuse metastases, such as liver cancer. The MCNP code is used to carry out an accurate study of the epithermal column and to assess both the free beam parameters and the in phantom figures of merit to evaluate the beam effectiveness. Various Beam Shaping Assemblies are tested using different materials and geometrical shapes in order to optimize the therapeutic ratio. Finally, the dose profiles are calculated along the beam axis in the anthropomorphic phantom 'ADAM'. (author)

[en] In the last years an international effort has been pursued for the development of the Advanced Lead Fast Reactor European Demonstrator (ALFRED) in line with the vision of the Gen-IV initiative for the LFR concept. This article - dealing with the ALFRED core design - analyses the global and local effects due to the accidental withdrawal of one control rod during the nominal plant state, by evaluating its impact in terms of reactivity balance and power distribution. Starting from the steady state neutronic results obtained with the ERANOS deterministic code, a detailed 3D power map of the core was evaluated (through a specific procedure) at the level of single fuel pins and used as input for accurate transient and thermal-hydraulic studies made by the RELAP5 system code and ANTEO+ sub-channel code, respectively. The ANTEO+ code, developed and validated by ENEA, was adopted to evaluate the temperature distributions in all the pins and surrounding sub-channels at key instants of the transient. It permitted the assessment of the new thermal conditions of the hot fuel assembly, in order to verify the compliance with the safety limits of the MOX fuel and the steel clad even in a completely unprotected scenario. (author)

No abstract available

[en] Accelerator-Driven-Systems represent one of the possible future strategies for transmuting minor actinides. EFIT, the conceptual industrial burner designed in EUROTRANS IP, is an ADS of about 400 MW_th, fuelled by MA and Pu in inert matrix, cooled by lead (673-753 K) and sustained by a 800 MeV proton of some 15 mA. It features the MA fission (42 kg/TWh_th) while maintaining a zero net balance of Pu and a negligible k_eff swing during the cycle. Three radial zones, differing in pin diameter or in inert matrix percentage have been defined in order to maximize the average power density together with the flattening of the assembly coolant outlet temperatures. Thermal-hydraulic analyses have been performed and show acceptable maximum temperatures: 1672 K peak fuel temperature (disintegration at 2150 K) and 812 K peak cladding temperature in nominal conditions (max 823 K). The behaviour of the core power, the temperature and the reactivity during the Unprotected Loss Of Flow transient (ULOF) has been studied as well by obtaining: a peak fuel temperature of 1860 K, a peak cladding temperature of 1030 K, a power increase of 2% removed by natural circulation. (authors)

[en] In the frame of the FP7 European project MAXSIMA, an extensive simulation study has been done to assess the main shielding problems in view of the construction of the MYRRHA accelerator-driven system at SCK-CEN in Mol (Belgium). An innovative method based on the combined use of the state-of-the-art Monte-Carlo codes MCNPX and FLUKA has been used, with the goal of characterizing complex, realistic neutron fields around the core barrel, to be used as source terms in detailed analyses of the radiation fields due to the system in operation, and of the coupled residual radiation. The main results of the shielding analysis are presented, as well as the construction of an activation database of all the key structural materials. The results evidenced a powerful way to analyse the shielding and activation problems, with direct and clear implications on the design solutions. (authors)