CFD studies of cylindrical target for neutron generator application

The paper deals with theoretical and experimental investigation of transmutation rates for a number of long‐lived fission products and minor actinides, as well as with neutron spectra formed in a subcritical assembly driven with the following monodirectional beams: 660‐MeV protons and 14‐MeV neutrons. In this work, the main objective is the comparison of neutron spectra in the MOX assembly for different external driving sources: a 660‐MeV proton accelerator and a 14‐MeV neutron generator. The SAD project (JINR, Russia) has being discussed. In the context of this project, a subcritical assembly consisting of a cylindrical lead target surrounded by a cylindrical MOX fuel layer will be constructed. Present conceptual design of the subcritical assembly is based on the core with a nominal unit capacity of 15 kW (thermal). This corresponds to a multiplication coefficient, keff= 0.945, and an accelerator beam power of 0.5 kW. The results of theoretical investigations on the possibility of incinerating long‐lived fission products and minor actinides in fast neutron spectrum and formation of neutron spectra with different hardness in subcritical systems based on the MOX subcritical assembly are discussed. Calculated neutron spectra emitted from a lead target irradiated by a 660‐MeV protons are also presented.

Summary form only given. A D-D neutron generator is being developed for thermal neutron activation applications based on gaseous discharge phenomena. The generator is cylindrical and employs a 0.5' diameter solid cylindrical target held at negative high voltage (cathode). A surrounding cylindrical grid and cylindrical chamber walls provide the ground path for the discharge. The chamber is filled with deuterium gas at pressure on the order of 30 mTorr. Deuterons accelerated towards the solid cathode fuse with deuterium embedded in the cathode metal matrix. Thus, the neutron source region is a line, which can be made to any desired length. This geometry has obvious advantages over point sources for calibrating tokamak diagnostics in large machines, and also has advantages for many of the thermal neutron activation applications. The discharge itself provides a means of deuterium ion implantation in the cathode material and the target is therefore self-replenishing. The source has successfully demonstrated D-D neutron production at rates higher than those of pure gas target electrostatic devices.

This paper is devoted to the computational and theoretical assessment of the physical and technical characteristics of the effect of intense energy fluxes on the target in the magneto-inertial method of plasma confinement. The results of calculating the effect of intense broadband radiation fluxes on a single-layer cylindrical target are presented. Based on these calculations, the possibility of creating compact neutron generators is estimated. The processes of radiation transfer, thermal and electromagnetic processes, including the coefficients of thermal conductivity of electrons and ions and suprathermal electrons, are studied. A new algorithm for the numerical solution of the hyperbolic and parabolic (thermal) parts of the plasma dynamics equations is briefly described.

<span>This research in BNCT has a goal to design a collimator that can be used for cancer therapy. Simulations were carried out by MCNPX software. A collimator is designed by cyclotron 30 MeV as a neutron generator. Independent variables varied were material and thickness of each collimator’s component to get five of IAEA’s standard of the neutron beam. The result is two collimator designs that can pass all IAEA’s standard. Those designs are cyclotron collimator I and cyclotron collimator II. Collimator designs obtained are tube collimator consisting of a cylindrical target </span><sup>7</sup><span>Be length of 1.4 cm and radius 1 cm, a lead wall with thickness 23 cm, cylindrical heavy water moderator (D</span><sub>2</sub><span>O) with radius 3 cm. Filter Cd-nat for cyclotron collimator I with a thickness of 1 mm and a radius 3 cm. Cyclotron collimator II uses </span><sup>60</sup><span>Ni with a thickness of 5 cm as a filter. The radius aperture is 3 cm. These two collimator designs can be used for cancer treatment with BNCT. Dosimetry calculation and manufacture of prototypes are needed to test the application of this design.</span>

It is considered a sub-critical assembly driven with existing 660 MeV JINR proton accelerator. The assembly consists of a central cylindrical lead target surrounded with a mixed-oxide (MOX) fuel (PuO2 + UO2) and with reflector made of beryllium. Dependence of the energetic gain on the proton energy, the neutron multiplication coefficient, and the neutron energetic spectra have been calculated. It is shown that for subcritical assembly with a mixed-oxide (MOX) BN-600 fuel (28%PuO2 + 72%UO2) with effective density of fuel material equal to 9 g/cm 3 , the multiplication coefficient keff is equal to 0.945, the energetic gain is equal to 27, and the neutron flux density is 1012 cm∼2 s∼x for the protons with energy of 660 MeV and accelerator beam current of 1 uA.

Optimization of breeding properties of the spallation neutron source target for ADS

This work presents a numerical investigation into broadband radiation effects (with energy flux densities q < 1014 W/cm2) on a magneto–inertial fusion (MIF) target. The calculation results demonstrate the impact of intense energy fluxes on a multi-layer cylindrical target that provides more uniform and homogeneous compression. All principal dynamic parameters (plasma dynamics and radiative) of the compressed target plasma have been determined. The work performed allows us to draw the following initial conclusion: it is advisable to create compact neutron generators based on the MIF scheme on a multi-layer version of the target (made of “heavy” chemical elements).

The results of calculating the combined effects of intense laer beams and plasma jets on a cylindrical target located in external magnetic field are presented. Parameters of compressed plasma are demonstrated and the capability to create neutron source with combined scheme—the number of neutrons per unit length N fus ≈ 1015 n · cm−1 by the time the exposure is completed, is shown. The conclusion is drawn about the prospects of the combined use of laser radiation and pulsed jets in interaction with a magnetized target.

Minor actinides (MA) present a harmful part of spent nuclear fuel due to their long half-lives and high radio-toxicity. Neutrons produced in spallation targets of Accelerator Driven Systems (ADS) can be used to transmute and burn MA. Non-fissile targets are commonly considered in ADS design. However, additional neutrons from fission reactions can be used in targets made of fissile materials. We developed a Geant4-based code MCADS (Monte Carlo model for Accelerator Driven Systems) for simulating neutron production and transport in different spallation targets. MCADS is suitable for calculating spatial distributions of neutron flux and energy deposition, neutron multiplication factors and other characteristics of produced neutrons and residual nuclei. Several modifications of the Geant4 source code described in this work were made in order to simulate targets containing MA. Results of MCADS simulations are reported for several cylindrical targets made of U+Am, Am or Am2O3including more complicated design options with a neutron booster and a reflector. Estimations of Am burning rates are given for the considered cases.