Steady state investigation on neutronics of a molten salt reactor considering the flow effect of fuel salt

The Molten Salt Reactor (MSR), one of the `Generation IV' concepts, is a liquid-fuel reactor, which is different from the conventional reactors using solid fissile materials due to the flow effect of fuel salt. The study on its neutronics considering the fuel salt flow, which is the base of the thermal-hydraulic calculation and safety analysis, must be done. In this paper, the theoretical model on neutronics under steady condition for a single-liquid-fueled MSR is conducted and calculated by numerical method. The neutronics model consists of two group neutron diffusion equations for fast and thermal neutron fluxes, and balance equations for six-group delayed neutron precursors considering the flow effect of fuel salt. The spatial discretization of the above models is based on the finite volume method, and the discretization equations are computed by the source iteration method. The distributions of neutron fluxes and the distributions of the delayed neutron precursors in the core are obtained. The numerical calculated results show that, the fuel salt flow has little effect on the distribution of fast and thermal neutron fluxes and the effective multiplication factor; however, it affects the distribution of the delayed neutron precursors significantly, especially the long-lived one. In addition, it could be found that the delayed neutron precursors influence the neutronics slightly under the steady condition.     

Thiourea-doped ammonium dihydrogen phosphate: A single crystal neutron diffraction investigation

Thiourea-doped ammonium dihydrogen phosphate (TADP) exhibits nonlinear optical property and the second harmonic generation efficiency of these crystals is three times that of pure ammonium dihydrogen phosphate (ADP) crystal. In this context, the study of structural distortion in the thiourea-doped ADP crystal is significant, hence single neutron diffraction investigations were undertaken. The final R-factors are: R[F ² > 2σ(F ²)] = 0.11, Goodness of fit(S) = 1.15. Though the dopant could not be located from the difference Fourier map, the cell parameters (a = b = 7.531(3) A, c = 7.544(5) Å) were found to be significantly greater than that of pure ADP at RT (a = b = 7.502(1) Å, c = 7.546(1) Å). This indicates that the dopant concentration in the crystals is small but enough to bring changes in the overall average structure.     

SMARTer for magnetic structure studies

SMARTer, a 36-meter small angle neutron scattering (SANS) spectrometer was installed at the Neutron Scattering Laboratory (NSL), National Nuclear Energy Agency of Indonesia — BATAN in Serpong, Indonesia and has performed the experiment for studying the magnetic structures of Cu(NiFe), CuCo and FeSiBNbCu metal alloys. The experiments were conducted at room temperature and up to 1 T (10 kOe) of external magnetic field. At zero fields, isotropic scattering identified as nuclear scattering is dominant. When a magnetic field is applied in a horizontal direction perpendicular to the neutron beam, the response of the magnetic scattering permits extraction of the field-induced re-arrangement of the magnetic moment. With increasing field the distortion is more pronounced and the magnetic scattering dominates the intensity and affects the peak position. Radial and angular averaging from experimental data are given to show the details of magnetic structures.      

Magnetization in permalloy thin films

Thin films of permalloy (Ni₈₀Fe₂₀) were prepared using an Ar+N₂ mixture with magnetron sputtering technique at ambient temperature. The film prepared with only Ar gas shows reflections corresponding to the permalloy phase in X-ray diffraction (XRD) pattern. The addition of nitrogen during sputtering results in broadening of the peaks in XRD pattern, which finally leads to an amorphous phase. The M-H loop for the sample prepared with only Ar gas is matching well with the values obtained for the permalloy. For the samples prepared with increased nitrogen partial pressure the magnetic moment decreased rapidly and the values of coercivity increased. The polarized neutron reflectivity measurements (PNR) were performed in the sample prepared with only Ar gas and with nitrogen partial pressure of 5 and 10%. It was found that the spin-up and spin-down reflectivities show exactly similar reflectivity for the sample prepared with Ar gas alone, while PNR measurements on 5 and 10% sample show splitting in the spin-up and spin-down reflectivity.      

Structural behaviour of AgNO3 at low temperatures by neutron diffraction

Structural behaviour of silver nitrate (AgNO₃) at low temperatures has been investigated by neutron powder diffraction and differential scanning calorimetry (DSC). Analysis showed abnormal changes in the rotations of nitrate (NO₃) anions and thermal displacement parameters of the atoms near 220 K and 125 K. However, the basic lattice is compatible with the orthorhombic symmetry (space group Pbca) till 12 K. The fine, small-scale structural anomalies probably originate from freezing of reorientation of NO₃ ions from high-temperature disordered phase.      

Specular neutron reflectivity and beyond

A polarized neutron reflectometer for vertical samples is available at Dhruva reactor guide hall, Trombay. The reflectometer has been designed for horizontal scattering vector. It uses a position-sensitive detector for obtaining the reflectivity pattern. This arrangement allows one to obtain diffuse or off-specular intensity around any specular peak at one go. We have used this instrument for studying the structure of various metal-metal and metal-semiconductor multilayers by specular reflectometry. We have also been successful in understanding interface morphology of several films through diffuse neutron reflectometry (DNR) on this reflectometer. Some of the recent results are presented in this paper to demonstrate the strength of these two techniques.      

Neutron detectors for scattering experiments at HANARO

Position sensitive detectors (PSD) measure the distribution of scattered neutrons and are essential tools for neutron scattering experiments. Various types of neutron detectors used at neutron diffractometers are conventional tube detectors, 1-D and 2-D PSDs. Korea Atomic Energy Research Institute (KAERI) has been developing various kinds of PSDs to improve the instrument performance and to develop new scattering instruments. Our development work is initiated with 1-D PSD for residual stress analysis spectrometer and finally the technology is extended to development of 2-D PSD with planar and curved geometry. All PSDs are based on multiwire grid assembly with delay line readout method for position encoding, as the response is faster than charge division method and enables higher count rate capability. Design details and operational characteristics of some of the PSDs developed, for application at neutron scattering instruments are presented.      

Investigation on pore structure and small-scale agglomeration behaviour in liquid phase sintered SiC using small angle neutron scattering

Mesoscopic density fluctuations in liquid phase sintered silicon carbide have been investigated using small angle neutron scattering (SANS). The increase in the additives results in the modification in the pore size distribution and to some extent the total porosity. SANS revealed a mass fractal nature of the agglomerated matrix microstructure. The fractal dimension of the matrix does not change appreciably with the additives although the upper cut-off value of the fractal decreases significantly with the increase in the additives. The liquid phase sintering due to the presence of additives helps to achieve higher level of densification. However, the agglomeration hinders achievement of the fully dense pellets.      

非线性中子输运问题的蒙特卡罗模拟

针对考虑中子之间相互碰撞的非线性中子输运方程,提出一种线性化近似处理方法,导出相应的积分输运方程,利用蒙特卡罗方法求解此方程,数值实验表明算法的有效性,为研究超高能中子产生与输运问题提供了必要的模拟工具.     

He accumulation effect in solid and liquid D-T mixture

This article reports the accumulation effect of the ³He originating from tritium β decay; ³He created in solid remains in it, while one in liquid diffuses and goes out to the vapor gas. We observed this effect through the neutron detection from muon catalyzed fusion phenomenon (μCF), and gave it qualitative understanding, by which the muon transfer rate from (dμ) and (tμ) to helium was derived. This revised version was published online in August 2006 with corrections to the Cover Date.