[en] Highlights: • A new copper benchmark experiment will be performed with 14 MeV neutrons. • Pre-analysis is presented for optimization of the experimental setup, including block size and background reduction. • 3-D Monte Carlo calculations of neutron fluxes in a pure copper assembly and reaction rates of activation foils. • A 60 cm × 70 cm× 60 cm copper block results suitable for this experiment. - Abstract: A new benchmark experiment on pure copper assembly is presently underway at the Frascati Neutron Generator (FNG) aimed at testing and validating the recent nuclear data libraries for fusion applications under 14 MeV neutrons irradiation. The Copper block has been designed on the basis of the pre-analysis presented in this work, performed with the MCNP5 Monte Carlo code, using JEFF 3.1.1 nuclear data library for transport and IRDF2002 for activation foils reaction rates. The pre-analysis has been performed in order to define suitable dimensions of the copper block and to optimize the experimental set-up for the measurements. This includes the definition of the detectors positions and the irradiation conditions required to get measurable activities for the activation foils. Furthermore, the design has been optimized to reduce the effect of the background due to the neutrons back-scattered from the FNG bunker walls. A 60 cm × 70 cm × 60 cm copper block, without any shield, results suitable for conducting a “clean” benchmark experiment.

[en] Highlights: • A benchmark experiment was performed using pure copper with 14 MeV neutrons. • The experiment was performed at the Frascati Neutron Generator (FNG). • Activation foils, thermoluminescent dosimeters and scintillators were used to measure reactions rates (RR), nuclear heating and neutron spectra. • The paper presents the RR measurements and the post analysis using MCNP5 and JEFF-3.1.1, JEFF-3.2 and FENDL-3.1 libraries. • C/Es are presented showing the need for deep revision of Cu cross sections. - Abstract: A neutronics benchmark experiment on a pure Copper block (dimensions 60 × 70 × 60 cm"3), aimed at testing and validating the recent nuclear data libraries for fusion applications, was performed at the 14-MeV Frascati Neutron Generator (FNG) as part of a F4E specific grant (F4E-FPA-395-01) assigned to the European Consortium on Nuclear Data and Experimental Techniques. The relevant neutronics quantities (e.g., reaction rates, neutron flux spectra, doses, etc.) were measured using different experimental techniques and the results were compared to the calculated quantities using fusion relevant nuclear data libraries. This paper focuses on the analyses carried-out by ENEA through the activation foils techniques. "1"9"7Au(n,γ)"1"9"8Au, "1"8"6W(n,γ)"1"8"7W, "1"1"5In(n,n′)"1"1"5In, "5"8Ni(n,p)"5"8Co, "2"7Al(n,α)"2"4Na, "9"3Nb(n,2n)"9"2Nb"m activation reactions were used. The foils were placed at eight different positions along the Cu block and irradiated with 14 MeV neutrons. Activation measurements were performed by means of High Purity Germanium (HPGe) detector. Detailed simulation of the experiment was carried-out using MCNP5 Monte Carlo code and the European JEFF-3.1.1 and 3.2 nuclear cross-sections data files for neutron transport and IRDFF-v1.05 library for the reaction rates in activation foils. The calculated reaction rates (C) were compared to the experimental quantities (E) and the C/E ratio with relative uncertainties was assessed.

[en] In nuclear fusion reactors, neutrons produced by the D-D and D-T reactions induce the activation of materials and of components. Even when the machine is not operating significant dose levels can be achieved due to the decay of the radioactive nuclides. The development of reliable methods for the assessment of dose rates is one of the key issues for maintenance and operating nuclear machines, in normal and off normal conditions. In the frame of Fusion Technology a computational tool based on MCNP Monte Carlo code has been developed to predict the dose rate after shutdown: it is called Direct One Step Method (D1S). The D1S is an innovative approach in which the decay gammas are coupled to the neutrons as in the prompt case and they are transported in one single step in the same run. The coupling of the decay gammas to the neutron generating the associated radioactive isotope is carried out using special libraries and modified routines of MCNP. A dedicated benchmark experiment has been thus proposed for the 2005-2006 campaign of JET. Two irradiation positions have been selected for the benchmark: one inner position inside the vessel, not far from the plasma, called the 2 upper irradiation end (IE2), where neutron fluence is relatively high. The second position is just outside a vertical port in an external position (EX). In the present work, experimental background data are compared with the same quantities calculated using D1S approach. Dose rate has been calculated multiplying the gamma fluxes with air-kerma factors to be consistent with calibration procedure of the detectors. The transport of both neutrons and decay gammas emitted as prompt was carried out in a single step, but distinct calculations were needed for DD and DT neutron source, that have different yields and irradiation histories. The calculated doses have been multiplied by time correction factors calculated using FISPACT, after a proper description of DD and DT JET irradiation histories since 1993 to 2004 (total neutron yield 2.37 10²⁰ and 2.22 10²⁰ for DT and DD respectively). An optimal agreement between calculation and measurement has been obtained: the ratio between calculated over measured air-kerma rate (C/E) is 0.89±0.08 in IE2 and 0.75±0.31 in EX. It should be noted that the calculated quantities are generally lower with respect to the measured ones, especially in the external position. The impact of key parameters to the dose rate calculated values is very important to be determined, so the paper beside the C/E values for the background dose rate, will address the following issues: the impact of: details of JET model in the surrounding of external position (EX) around the GM tube and the tube itself, concentration of Co in the steel composition. The use of different activation cross section should be investigated as well

[en] The Helium Cooled Lithium Lead (HCLL) Test Blanket Module (TBM) is one of the European blanket concepts selected to be tested in ITER as an important step towards the development of DEMO blankets. The EFDA organization has planned a work to study the problems related to the irradiation of a TBM in ITER, in order to optimize the test and to have a full extrapolation from ITER to DEMO conditions. A very important issue concerning safety is the activation of HCLL materials induced by neutrons during operation. The flow of LiPb transports activated products outside the Vacuum Vessel, furthermore possible leak or accident can give consequences that should be analyzed to be ready for proper countermeasures to be taken. The products of activation can be chemically corrosive and proper maintenance has to be planned. Some troublesome radioactive nuclides, i.e. ²¹⁰Po, represents high health risk. Hence activation calculation are necessary in support of the safety analysis. The design shall minimize the amounts of radioactive and toxic materials and the hazards associated with their handling. A complete nuclear analysis was recently performed using the MCNP-4C Monte Carlo code, supported with FENDL-2 nuclear data library. The 3-D generic and most updated neutronic model of ITER machine has been completed with the insertion of the last HCLL TBM model in one of the equatorial port. The TBM model was described with sufficient detail to give enough reliability to the results turned to the designers. The neutron fluxes were calculated with MCNP in LiPb breeder units and in the Eurofer cooling plates at various positions inside the module for a D-T neutron yield rate of 1.77 1020 ns^-1 (P_fus=500 MW). The activation calculations were performed using FISPACT (EASY 2005.1 package): activity, nuclear heating and contact dose rate were calculated inside the TBM using as input the neutron fluxes calculated by MCNP. Two irradiation scenarios were considered: 1) scenario representative for the irradiation of the TBM as scheduled for the high duty D-T phase of ITER with a total of 9000 neutron pulses over three (calendar) years period; 2) scenario characterized by an extended irradiation time according to the ITER M-DRG1 irradiation scenario (total first wall neutron fluence of about 0.3 MWa/m²) to arrive at a conservative estimate of the activity and afterheat production in case the TBM would be irradiated longer than initially assumed in the first case. The results of the activation analysis in terms of activity, nuclear heat and dose rate at different times since shut-down till 106 y after at various radial, poloidal and toroidal positions are presented. The effect of impurities on LiPb and Eurofer has been investigated and discussed as well as the impact of the different irradiation scenarios on the activation of TBM. (orig.)

[en] Full text: The FNG facility. The Frascati Neutron Generator (FNG) is a 14-MeV neutron generator based upon the T(d,n)⁴He fusion reaction. It was designed and built by ENEA Frascati for conducting neutronics experiments and to validate nuclear data in the field of thermonuclear controlled fusion. FNG is in operation since 1992. The FNG facility is also used for qualification, calibration, and radiation damage resistance tests of nuclear detectors and components, and for studies on new neutron (and gamma) detectors. The design of the breeding blanket and neutron shield of fusion reactors (e.g. ITER) needs experimental verification of the cross sections used for nuclear calculations and the validation of calculation methods used for the neutron transport. To do so, a special experimental activity is required, namely ''benchmark experiments'' and/or Mock-up experiments. A number of such experiments were successfully carried out at FNG since 1992, all related to Fusion tokamaks. FNG produces up to 1 10¹¹ n/s 14 MeV neutrons in continuous or pulsed mode (minimum pulse length 6 μsec) using a deuteron beam accelerated up to 300 keV impinging on a solid tritiated target. FNG produces a nearly isotropic 14 MeV neutron output (forward anisotropy ∼3%) from point-like source (beam size ∼1 cm²). The neutron production (both absolute and time dependent) is measured and recorded by a number of neutron flux monitors. The absolute neutron yield is measured by using the so-called associated charged particle techniques and provides the absolute yield at ±3.0%. A Silicon detector (SSD type), located inside the beam tube is used. The time dependent neutron yield is recorded by means of a U-238 fission chamber (FC), one scintillator (NE-213) and the SSD too. Both FC and NE-213 detectors are also relatively calibrated respect to the SSD detector. Independent measurement of the neutron yield is also routinely performed by activation techniques using ⁹³Nb(n,2n)⁹²Nb or ²⁷Al(n,α)²⁴Na activation foils. (author)

[en] FLUKA is a general purpose Monte Carlo transport and interaction code used for fundamental physics and for a wide range of applications. These include Cosmic Ray Physics (muons, neutrinos, EAS, underground physics), both for basic research and applied studies in space and atmospheric flight dosimetry and radiation damage. A review of the hadronic models available in FLUKA and relevant for the description of cosmic ray air showers is presented in this paper. Recent updates concerning these models are discussed. The FLUKA capabilities in the simulation of the formation and propagation of EM and hadronic showers in the Earth's atmosphere are shown

[en] In order to investigate the influence of aircraft shielding on the galactic component of cosmic rays, an aircraft mathematical model has been developed by the combinatorial geometry package of the Monte-Carlo transport code FLUKA. The isotropic irradiation of the aircraft in the cosmic ray environment has been simulated. Effective dose and ambient dose equivalent rates have been determined inside the aircraft at several locations along the fuselage, at a typical civil aviation altitude (10 580 m), for vertical cut-off rigidity of 0.4 GV (poles) and 17.6 GV (equator) and deceleration potential of 465 MV. The values of both quantities were generally lower than those in the free atmosphere. They depend, in an intricate manner, on the location within the aircraft, quantity of fuel, number of passengers, etc. The position onboard of crew members should be taken into account when assessing individual doses. Likewise due consideration must be taken when positioning detectors which are used to measure H *(10). Care would be needed to avoid ambiguity when comparing the results of calculation with the experimental data. (authors)

[en] To investigate the influence of the aircraft structures and contents on the exposure of aircrew to the galactic component of cosmic rays, a mathematical model of an aeroplane has been developed. The irradiation of the mathematical model in the cosmic ray environment has been simulated using the Monte Carlo transport code FLUKA. Effective dose and ambient dose-equivalent rates have been determined inside the aircraft at several locations along the fuselage at a typical civil aviation altitude. A significant effect of the shielding of aircraft structures has been observed on the ambient dose-equivalent rates, while the impact on the effective dose rates seems to be minor. Care should be taken in positioning the detectors onboard when the measurements are aimed at validating the codes. (authors)

[en] In nuclear fusion reactors, DD and DT neutrons produced during operation induce the activation of the device components, thus the resulting radioactive nuclides induce high dose levels even when the machine is not operating. The problem of the activation is one of the key issues in Nuclear Fusion Technology for safe operation and maintenance and it is as more critical as the nuclear performances of the fusion machines increase. Hence in the past years many efforts have been made to develop reliable methods to predict the induced activation and the resulting shutdown dose rate. Suitable systems of codes, data and interfaces to predict the shutdown dose rate distributions in full 3D geometry have been recently developed mainly by FZK with the Rigorous 2-Step (R2S) scheme and by ENEA with the Direct 1-Step (D1S) method. These techniques are both based on the combined use of MCNP Monte Carlo code and FISPACT inventory code, but exploit different approaches. The R2S follows a classical approach with Monte Carlo transport calculations for neutrons and decay photons in two sequential steps, whereas in the D1S method neutrons and decay gammas are transported in a single run. Previous benchmarks performed at the Frascati Neutron Generator (FNG, Italy) and at the Fusion Neutron Source (FNS, Japan) facilities showed the effectiveness of both methods to predict dose rate, but the comparison with pre-existing, not-oriented for this purpose, dose rate measurements at JET resulted less satisfactory, therefore a dedicated benchmark experiment has been proposed. The experiment was conducted during the 2005-2007 campaign of JET in order to validate the computational methodologies in a reactor-like configuration. Dose rate levels calculated using D1S and R2S methods were compared with experimental data collected before, during off-operational periods and at the end of 2005-2007 JET campaign in two irradiation positions: close to the vessel with high sensitivity TLDs GR- 200A (natural LiF) detectors and one external position with an active detector of Geiger- Mueller type. In this work the results of the JET benchmark experiment are presented; the impact of the nuclear activation data, coming from different evaluations, the outcome of geometrical and/or materials uncertainties and the reliability of both methods in a real fusion reactors framework are discussed as well. (orig.)

[en] In the framework of the EU participation to JT-60SA project [1], a dedicated simulation tool named after Thermo-hydraulic Mended Tool (TEXTO) was developed at CEA between 2006 and 2007 in order to address in a reliable way the calculation of the magnet conductor temperature increase and temperature margins in different operating conditions. The simulation process is based on three different codes, addressing each specific aspects (MCNP for the 3D nuclear heat calculation, TRAPS for magnetic field, ANSYS for 2D transverse thermal contribution of coil casing), which finally stand as input for the well established code GANDALF (with transient helium properties). Both steady-state operating and disruption transient regimes can be studied with this process and a first application is performed on the basis of the design and operating conditions available at this time on JT-60SA TF magnets, i.e. the first version of the different design stages. The complete analysis is shown together with the associated proposals for the TF conductor layout that could be derived from these studies. (authors)