High-sensitive colour indicator of absorbed dose of epithermal neutrons radiation

In our study, the high-sensitivity colour indicator of the absorbed dose of radiation of epithermal neutrons with energy 0 to 10 keV for dosimetry of low-energy neutrons was developed. We had been developed an indicator on the basis of the dye solution of arsenazo III and gadopentetic acid, allowing precisely define of absorbed dose in the range 2 to 103 Gy. The properties of arsenazo III as metallic indicator, which changes colour after binding of free ions of metals, were used. Colour of the indicator solution before irradiation and after it is stable enough in time at storage in the dark, at artificial illumination or at scattered sunlight. The developed indicator, consisting of a solution of arsenazo III and gadopentetic acid, allows estimating the absorbed dose of epithermal neutron irradiation with good accuracy and reduces the error of measurement related to changing colour of dye under the influence of other factors (light, temperature etc.) Dosimeter is tissue-equivalent and possesses a high-sensitivity neutron radiation due to the content of gadolinium in solution, which has great neutron capture cross-section. The developed dosimeter persists spectrophotometric characteristics after irradiaion within few weeks that allows to use it for measurement of the absorbed dose, both in real time mode and with the delayed measurement within few weeks.

Recovering the performance of irradiated high temperature superconductors for use in fusion magnets

The magnets confining the plasma in future fusion devices will be exposed to a significant destructive flux of fast neutrons. Particularly, in cost efficient compact reactor designs, the degradation of the superconductor becomes an issue and directly impacts the commercial viability. We report on the influence of neutron radiation on the superconducting transition temperature, Tc, and the critical current density, jc, and discuss possibilities to counteract the degradation by thermal treatments. We found that the degradation in Tc and jc are closely related to each other, likely by the expected loss of superfluid density; thus, Tc is a very useful indicator for the magnets' degradation. It increases linearly with annealing temperature and around 25 % of the decrease can be recovered by annealing at 150 °C and about 60 % at 400 °C, which would more than double the magnet’s life time. However, a loss of oxygen has to be impeded in the latter case.

Review on Steel Enhancement for Nuclear RPVs

The reactor pressure vessel (RPV) is one of the most important elements of a nuclear power plant (NPP). The RPV determines the plant operational lifetime since it is not replaceable economically. The purpose of the RPV steel study and enhancement to increase the NPP’s (Nuclear Power Plants) operation lifetime from the original 30–40 years up to 60–80 years or even beyond. The RPV lifetime limited by ageing of the RPV steels. RPV ageing highly depends on the main environmental effects: fast neutron radiation, thermal effects causing thermal ageing and low-cycle fatigue. Firstly, the chemical composition via aged mechanical properties was studied. Efforts to increase the toughness against the radiation embrittlement was enhanced by the appearance of the modern microstructural testing devices such as APFIM (atom probe field ion microscopy), SANS (small-angle neutron scattering) positron annihilation spectroscopy (PAS), transmission electron microscopy (TEM) and Mössbauer spectroscopy (MS). The information on the effect of alloying and polluting elements for the microstructure allowed us to produce increased ageing toughness of the RPVs, and to enhance the safety and lifetime calculations of them, supporting long-term safe operation (LTO).

SARS-CoV-2 Inactivation Simulation Using 14 MeV Neutron Irradiation

The SARS-CoV-2 virus is deadly, contagious, can cause COVID-19 disease, and endangers public health and safety. The development of SARS-CoV-2 inactivation technology is crucial and imminent in current pandemic period. Neutron radiation is usually used to sterilize viruses because neutron radiation is 10 times more effective than gamma-rays in inactivating viruses. In this work we established a closed SARS-CoV-2 inactivation container model by the Monte Carlo method and simulated the inactivation performance by using several different neutrons sources. To study the effects of inactivation container factors, including the reflector thickness, the type of the reflector material, the SARS-CoV-2 layer area and the distance from the radiation source on the energy deposition of a single neutron particle in SARS-CoV-2 sample, we simulated the neutron energy deposition on a SARS-CoV-2 sample. The simulation results indicate that the saturated thicknesses of reflector materials for graphite, water and paraffin are approximately 30 cm, 15 cm, and 10 cm, respectively, and the energy deposition (radiation dose) becomes larger when the SARS-CoV-2 layer area is smaller and the SARS-CoV-2 layer is placed closer to the neutron source. The calculated single-neutron energy deposition on 10 × 10 cm2 SARS-CoV-2 layer is about 3.0059 × 10−4 MeV/g with graphite as the reflection layer, when the 14 MeV neutron source intensity is 1012 n/s and the SARS-CoV-2 layer is 5 cm away from the neutron source. If the lethal dose of SARS-CoV-2 is assumed as the IAEA recommended reference dose, 25 kGy, the SARS-CoV-2 could be decontaminated in about 87 min, and the sterilization time could be less than 52s if the 14 MeV neutron intensity is increased to 1014 n/s.

An induced annealing technique for SiPMs neutron radiation damage

The use of Silicon Photo-Multipliers (SiPMs) has become popular in the design of High Energy Physics experimental apparatus with a growing interest for their application in detector area where a significant amount of non-ionising dose is delivered. For these devices, the main effect caused by the neutron fluence is a linear increase of the leakage current. In this paper, we present a technique that provides a partial recovery of the neutron damage on SiPMs by means of an Electrical Induced Annealing. Tests were performed, at the temperature of 20°C, on a sample of three SiPM arrays (2×3) of 6 mm2 cells with 50 μm pixel sizes: two from Hamamatsu and one from SensL. These SiPMs have been exposed to neutrons generated by the Elbe Positron Source facility (Dresden), up to a total fluence of 8 × 1011 n1 MeV-eq/cm2. Our techniques allowed to reduced the leakage current of a factor ranging between 15-20 depending on the overbias used and the SiPM vendor. Because, during the process the SiPM current can reach O(100 mA), the sensors need to be operated in a condition that provides thermal dissipation. Indeed, caution must be used when applying this kind of procedures on the SiPMs, because it may damage permanently the devices themself.

Study on the Applicability of Neutron Radiation Damage Method Used for High-Temperature Superconducting Tape Based on Geant4 and SRIM

High-temperature superconducting material is a promising candidate to fabricate superconducting magnet for magnetic confinement fusion reactors. The DPA number of the 1 µm thick superconducting layer in a high temperature superconducting tape under neutron irradiation needs to be calculated to predict the property changes. The DPA cross sections, which ignore the spatial distribution of vacancies caused by PKAs, are commonly used to obtain the results of the damage energy and DPA. However, for geometric models with the thickness as small as 1 µm, the energy and angular distribution of PKAs reveal that a significant number of PKAs with relatively high energy tend to scatter forward and cross the boundary of model, so the thickness of model has the potential to affect the number of displaced atoms. In this paper, we developed a method based on Geant4 and SRIM to evaluate the deviation of the traditional analytic method caused by the thickness. Geant4 is used to obtain the location, direction, and energy of PKAs, while SRIM is used to track every PKA and obtain damage energy and the number of displaced atoms. The radiation damage calculation of simple thin plate models with different thicknesses and the tape model are conducted with the neutron energies from 1 to 14 MeV. The results show that PKAs need to be tracked continuously for models with thickness less than 10 µm and the deviation of the analytic formulas increases rapidly with the decrease of thickness. For the superconducting layer composed of four different elements in the tape, the deviation also depends on the proportion of each atomic species and the neutron-atom interaction cross sections under different incident neutron energy.

Radiation-Hygienic Investigations of Experimental Production of Mixed Nitride Uranium-Plutonium Fuel at JSC SChC. Part 1: Methods and Results

Purpose: To present the methods and results of studies of the factors of radiation exposure to workers involved in the manufacture of mixed uranium-plutonium nitride (MUPN) fuel at the complex experimental installations CEI-1 and CEI-2 of JSC SChC. Material and Methods: Regularities of the formation of external exposure doses have been revealed based on the study of the dynamics of the ambient dose equivalent rate (ADER) of photon and neutron radiation at the CEI-1 and CEI-2 workplaces, as well as instrumental individual dosimetric control of the equivalent doses to workers. In order to assess the inhalation intake and possible doses from internal irradiation, studies of the physicochemical properties of radioactive aerosols were carried out. Results: It has been found that the main sources of penetrating radiation in the premises of CEI-1 are boxes where tablets are pressed, chips and rejected tablets are crushed, as well as temporary storage of products is occurred. The highest ADER values have been measured in those boxes, where the radiation exposure was due to radioactive contamination caused by past activity, and is not associated with fabrication of MUPN fuel. A significant contribution of neutron exposure to individual doses of workers was measured, which exceeded the contribution of gamma exposure at some workplaces of the CEI-1. At CEI-2, a non-functioning exhaust ventilation pipe passing over the premises was found to be a powerful source of external radiation. This pipe contained a significant amount of radioactive material. Assessment of the contribution of gamma exposure from the ventilation pipe to the external exposure of workers reached 85% at some workplaces. Studies of the physicochemical properties of radioactive aerosols have revealed a high reactivity of MUPN compounds, leading to instant oxidation of the thoracic fraction of MUPN fuel aerosols under contact with air. The complex morphological and dispersed composition of aerosol particles in combination with a complex chemical composition caused by the aging processes of aerosols, can lead to a fundamental difference in the biokinetics of MUPN aerosols, the process of dose formation and, consequently, the degree of radiological hazard compared to those adopted in the ICRP models for U and Pu. The results of the current radiation-hygienic research are of a preliminary nature, since the object of this research is an experimental installation, which was used to develop a new technology for the production of MUPN fuel. The instrumental and methodological approaches to assess the factors of radiation exposure to workers tested at these experimental installations, will be used in the future to conduct similar studies during the pilot industrial operation of new modules for fabricating and refurbishing of MUPN fuel.