Development of the safety code AINA for the European DEMO designs

In order to evaluate plasma evolution and in-vessel components strains, a safety code called AINA has been developing during the last ten years for different fusion reactors designs. This work describes the new AINA code which is being adapted for the four European DEMO designs (HCPB, DCLL, HCLL and WCLL) after an in-depth critical analysis of the former AINA versions with the purpose of performing a proper, reliable, versatile and flexible tool for the future safety studies. At this point, a new 0D plasma dynamics approach and a 1D finite-difference thermal model for the DEMO HCPB configuration and the divertor have been developed. By means of the feedback among both blocks, a preliminary safety analysis is carrying out checking the integrity of in-vessel components both when a plasma perturbation induces a Loss Of Plasma Control (LOPC) and a thermo-hydraulic accident takes place in the Plasma Facing Components (PFCs) or in the Vacuum Vessel such as a Loos Of Coolant Accident (LOCA). Initial results show deficiencies in the Blanket design which may be extremely significant when some of the described unexpected scenarios takes place leading the reactor to a melting episode.Peer ReviewedPostprint (published version

Contribution to safety analyses of DEMO HCPB using AINA code

The motivation of the current work, framed under the safety EUROfusion activities to develop DEMO, is to present the conclusions drawn from our contribution to the safety studies of the HCPB DEMO carried out by the team tasked with AINA code development. During 2016 and 2017 a new AINA version was built in order to evaluate plasma evolution and in-vessel components strains inside the European DEMO designs. As a result, AINA is able to foresee several accident scenarios as plasma disruptions or structural meltings due to LOPCs (Loss Of Plasma Control) and in-vessel melt either of FW, blanket structure and/or divertor modules because of thermal stresses due to LOCAs. After due analysis, it has concluded that it would be desirable to carry out a design review focused on ensuring a suitable operating temperature range with a bigger safety margin for all the materials which make up the HCPB BB, as well as the need to guarantee a quick detection and actuation by means of a proper system, depending on the affected equipment, when the most demanding transients take place which may drive the reactor to melting scenarios and very energetic plasma disruptions. These events include an increase of fueling above 50%, a permanent improvement in the confinement time and a punctual impurity increase above 300%. Other perturbations has been studied which provide information on non-dangerous cases, impossible situations or melting processes.Peer ReviewedPostprint (author's final draft

Neutron beam imaging with micromegas detectors in combination with neutron time-of-flight at the n_tof facility at CERN

A bulk micromegas detector with the anode segmented in 2 orthogonal directions and equipped with a neutron/charged particle converter is employed at the neutron time-of-light (nTOF) facility at CERN to determine the incident neutron beam profile and beam interception factor as a function of the neutron energy determined by the time of flight. Discrepancies between experimental results and simulations in the values of the beam interception factor range up to 12 % and are to be ascribed to a defect in the mesh of the bulk. Nevertheless the detector proved to be really useful for checking the alignment of the neutron beam optics of the facility. Measurements with a new pixelized bulk detector for the determination of the beam interception factor are forseen before the end of 2012Postprint (published version

Measurement of the neutron capture cross section of the fissile isotope 235U with the CERN n_TOF Total Absorption Calorimeter and a fission tagging based on micromegas detectors

Actual and future nuclear technologies require more accurate nuclear data on the (n, gamma) cross sections and -ratios of fissile isotopes. Their measurement presents several difficulties, mainly related to the strong fission gamma-ray background competing with the weaker gamma-ray cascades used as the experimental signature of the (n,gamma) process. A specific setup has been used at the CERN n_TOF facility in 2012 for the measurement of the (n,gamma) cross section and alpha-ratios of fissile isotopes and used for the case of the 235U isotope. The setup consists in a set of micromegas fission detectors surrounding 235U samples and placed inside the segmented BaF2 Total Absorption Calorimeter.Postprint (published version

New accurate measurements of neutron emission probabilities for relevant fission products

We have performed new accurate measurements of the beta-delayed neutron emission probability for ten isotopes of the elements Y, Sb, Te and I. These are fission products that either have a significant contribution to the fraction of delayed neutrons in reactors or are relatively close to the path of the astrophysical r process. The measurements were performed with isotopically pure radioactive beams using a constant and high efficiency neutron counter and a low noise beta detector. Preliminary results are presented for six of the isotopes and compared with previous measurements and theoretical calculations.Postprint (published version

Equipment for the continuous measurement and identification of gamma radioactivity on aerosols

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper describes an equipment for continuous measurement and identification of gamma radioactivity in aerosols developed by the Nuclear Engineering Research Group (NERG) at the Technical University of Catalonia (UPC) and Raditel Serveis i Subministraments Tecnològics, Ltd. A spectrometric analysis code has been specially designed for it. Spectrum analysis identifies and determines activity concentration of aerosol emitters captured by a fiberglass paper filter. This new equipment is currently operating in three radioactivity monitoring stations of the Environmental Radiological Surveillance Network of the Generalitat of Catalunya (local Catalan government): two near Ascó and Vandellòs Nuclear Power Plants in the province of Tarragona and one in the city of Barcelona. Two more monitors are expected to be deployed at Roses, Girona, Spain, and Puigcerdà, Barcelona, Spain. Measurements and evolution analysis results of emitters identified at these stations were also provided.Postprint (author's final draft

A new code for spectrometric analysis for environmental radiological surveillance on monitors focused on gamma radioactivity on aerosols

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a new code for the analysis of gamma spectra generated by an equipment for continuous measurement of gamma radioactivity in aerosols with paper ¿lter. It is called pGamma and has been developed by the Nuclear Engineering Research Group at the Technical University of Catalonia - Barcelona Tech and by Raditel Serveis i Subministraments Tecnològics, Ltd. The code has been developed to identify the gamma emitters and to determine their activity concentration. It generates alarms depending on the activity of the emitters and elaborates reports. Therefore it includes a library with NORM and arti¿cial emitters of interest. The code is being adapted to the monitors of the Environmental Radiological Surveillance Network of the local Catalan Government in Spain (Generalitat de Catalunya) and is used at three stations of the Network.Postprint (author's final draft

Experimental neutron capture data of 58Ni from the CERN n_TOF facility

The neutron capture cross section of 58Ni was measured at the neutron time of flight facility n_TOF at CERN, from 27 meV to 400 keV neutron energy. Special care has been taken to identify all the possible sources of background, with the so-called neutron background obtained for the first time using high-precision GEANT4 simulations. The energy range up to 122 keV was treated as the resolved resonance region, where 51 resonances were identified and analyzed by a multilevel R-matrix code SAMMY. Above 122 keV the code SESH was used in analyzing the unresolved resonance region of the capture yield. Maxwellian averaged cross sections were calculated in the temperature range of kT = 5 – 100 keV, and their astrophysical implications were investigated.Postprint (published version

First determination of ß -delayed multiple neutron emission beyond A=100 through direct neutron measurement: the P2n value of Sb 136

Background: ß-delayed multiple neutron emission has been observed for some nuclei with A=100, being the 100Rb the heaviest ß2n emitter measured to date. So far, only 25P2n values have been determined for the ˜300 nuclei that may decay in this way. Accordingly, it is of interest to measure P2n values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such a measurement for nuclei with A>100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition, the decay properties of these nuclei are fundamental for the understanding of astrophysical nucleosynthesis processes, such as the r-process, and safety inputs for nuclear reactors.Postprint (published version

The 236U neutron capture cross-section measured at the n TOF CERN facility

The 236U isotope plays an important role in nuclear systems, both for future and currently operating ones. The actual knowledge of the capture reaction of this isotope is satisfactory in the thermal region, but it is considered insufficient for Fast Reactor and ADS applications. For this reason the 236U(n, gamma ) reaction cross section has been measured for the first time in the whole energy region from thermal energy up to 1MeV at the n TOF facility with two different detection systems: an array of C6D6 detectors, employing the total energy deposited method, and a 4p total absorption calorimeter (TAC), made of 40 BaF2 crystals. The two n TOF data sets agree with each other within the statistical uncertainty in the Resolved Resonance Region up to 800 eV, while sizable differences (up to 20%) are found relative to the current evaluated data libraries. Moreover two new resonances have been found in the n TOF data. In the Unresolved Resonance Region up to 200 keV, the n TOF results show a reasonable agreement with previous measurements and evaluated data.Postprint (published version