Investigation of BeO as a reflector for the low power research reactor

Calculations of the fuel burnup, core excess reactivity, and the reactivity worths of the top beryllium shim plates for two reflector types (beryllium and beryllium oxide (BeO)) in the Miniature Neutron Source Reactor (MNSR) have been presented in this paper using the GETERA and MCNP4C codes. The results showed that the reactor infinity multiplication factors were 1.7030 and 1.6824, the core unadjusted excess reactivities were 31.9 and 5.0 mk, and the reactivity worths of the top beryllium shim plates were 22 and 19 mk for the BeO and Be reflectors respectively. Finally, using the beryllium oxide instead of the existing Be reflector in the MNSR reactor increased the core excess reactivity and reactor operation time.     

Calculations of fuel burn-up and radionuclide inventory in the syrian miniature neutron source reactor using the WIMSD4 code

Calculations of the fuel burn up and radionuclide inventory in the Miniature Neutron Source Reactor after 10 years (the reactor core expected life) of the reactor operating time are presented in this paper. The WIMSD4 code is used to generate the fuel group constants and the infinite multiplication factor versus the reactor operating time for 10, 20, and 30 kW operating power levels. The amounts of uranium burnt up and plutonium produced in the reactor core, the concentrations and radioactivities of the most important fission product and actinide radionuclides accumulated in the reactor core, and the total radioactivity of the reactor core are calculated using the WIMSD4 code as well.     

Design calculation of an epithermal neutronic beam for BNCT at the Syrian MNSR using the MCNP4C code

This article describes the design calculation of an epithermal neutronic beam for the boron neutron capture therapy at the Syrian MNSR by using the MCNP4C code and ENDF/B-V cross-section library. To produce a high flux of epithermal neutrons at the beam exit, the moderator/filter from Al, Cd, Fluental and Bi was used with Pb as reflector for neutrons along the beam. In addition, the Bi lined collimator with Li₂CO₃-PE and Pb at the end. The calculated beam parameters under 30.0 kW of reactor power at the beam exit are Ф_epi = 2.83 × 10⁸ n/cm² s, D_f/Ф_epi = 7.98 × 10⁻¹¹ cGy cm²/n, D_γ/Ф_epi = 1.70 × 10⁻¹¹ cGy cm²/n, Φ_epi/Φ_the = 0.05 and J_n⁺/Ф_n = 0.77. As well as, the calculated values of the advantage depth and advantage ratio are 7.51 cm and 3.49, respectively. If such beam was built into the Syrian MNSR the scientific applications of the reactor would increase.     

Development of a MCNP5 and ORIGEN2 based burnup code for molten salt reactor

The Molten Salt Reactor(MSR) is one of the six advanced reactor nuclear energy systems for further research and development selected by Generation IV International Forum(GIF),which is distinguished by its core in which the fuel is dissolved in molten fluoride salt.Because fuel flow in the primary loop,the depletion of MSR is different from that of solid-fuel reactors.In this paper,an MCNP5 and ORIGEN2 Coupled Burnup(MOCBurn) code for MSR is developed under the MATLAB platform.Some new methods and novel arrangements are used to make it suitable for fuel flow in the MSR.To consider the fuel convection and diffusion in the primary loop of MSR,fuel mixing calculation is carried out after each burnup time step.Modeling function for geometry with repeat structures is implicated for reactor analysis with complex structures.Calculation for a high-burnup reactor pin cell benchmark is performed using the MOCBurn code.Results of depletion study show that the MOCBurn code is suitable for the traditional solid-fuel reactors.A preliminary study of the fuel mixture effect in MSR is also carried out.     

Calculation of the power distribution in the fuel rods of the low power research reactor using the MCNP4C code

The Monte Carlo method, using the MCNP4C code, was used in this paper to calculate the power distribution in 3-D geometry in the fuel rods of the Syrian Miniature Neutron Source Reactor (MNSR). To normalize the MCNP4C result to the steady state nominal thermal power, the appropriate scaling factor was defined to calculate the power distribution precisely. The maximum power of the individual rod was found in the fuel ring number 2 and was found to be 105 W. The minimum power was found in the fuel ring number 9 and was 79.9 W. The total power in the total fuel rods was 30.9 kW. This result agrees very well with nominal power reported in the reactor safety analysis report which equals 30 kW. Finally, the peak power factors, which are defined as the ratios between the maximum to the average and the maximum to the minimum powers were calculated to be 1.18 and 1.31 respectively.     

基于蒙特卡罗程序的AP1000反应堆堆芯布置方案的模拟

AP1000是美国西屋公司研发的大型压水反应堆,采用先进的非能动安全系统。AP1000反应堆有两种堆芯燃料布置方案:D19和Adv。结合两种设计方案的优点提出了一种新的堆芯燃料布置方案。利用MCNP6(Monte Carlo N-particle 6)程序对D19堆芯和新方案堆芯的首循环进行建模,并主要计算了新堆芯的核设计参数随燃耗的变化。结果表明,新堆芯在首循环寿期内满足AP1000的主要核设计准则。通过大规模并行计算表明,带燃耗计算功能的蒙特卡罗程序MCNP6能够在堆芯设计工作中发挥很好的参考作用。     

Time dependent burn-up and fission products inventory calculations in the discharged fuel of the Syrian MNSR

The Syrian Miniature Neutron Source Reactor (MNSR), a 30 kW, 89.8% HEU fueled (U-Al), went critical in March, 1996. By operating the reactor at nominal power for 2.5 h/day, the estimated core life is 10 years. This paper presents the results of fuel burn-up and depletion analysis of the MNSR fuel lattice using the ORIGEN 2 code. A one-group cross-section data base for the ORIGEN 2 computer code was developed for the Syrian MNSR research reactor. The ORIGEN 2 predicted burn-up dependent actinide compositions of MNSR spent fuel using the newly developed data base show a good agreement with the published results in the literature. In addition, the burn-up characteristics of MNSR spent fuel was analyzed with the new data base. Finally, to study the effect of burn-up on the reactivity, the microscopic cross-sections of the fission products calculated by the WlMS code (using the number densities of fission products generated by the ORIGEN 2 code as a function of burn-up time), were used as an input for the CITATION code calculations. The results contained in this paper could be used in performing criticality safety analysis and shielding calculations for the design of a spent fuel storage cask for the MNSR core.     

Monte Carlo simulation of core physics parameters of the Syrian MNSR reactor

A 3-D neutronic model for the Syrian Miniature Neutron Source Reactor (MNSR) was developed earlier to conduct the reactor neutronic analysis using the MCNP-4C code. The continuous energy neutron cross sections were evaluated from the ENDF/B-VI library. This model is used in this paper to calculate the following reactor core physics parameters: the clean cold core excess reactivity, calibration of the control rod and calculation its shut down margin, calibration of the top beryllium shim plate reflector, the axial neutron flux distributions in the inner and outer irradiation positions and calculations of the prompt neutron life time (_lp$l_p$) and the effective delayed neutron fraction (_βeff${\beta }_{\mathit{eff}}$). Good agreements are noticed between the calculated and the measured results. These agreements indicate that the established model is an accurate representation of Syrian MNSR core and will be used for other calculations in the future.     

Analysis of fuel management in the KIPT neutron source facility

Argonne National Laboratory (ANL) of USA and Kharkov Institute of Physics and Technology (KIPT) of Ukraine have been collaborating on the conceptual design development of an experimental neutron source facility consisting of an electron accelerator driven sub-critical assembly. The neutron source driving the sub-critical assembly is generated from the interaction of 100 KW electron beam with a natural uranium target. The sub-critical assembly surrounding the target is fueled with low enriched WWR-M2 type hexagonal fuel assemblies. The U-235 enrichment of the fuel material is <20%. The facility will be utilized for basic and applied research, producing medical isotopes, and training young specialists. With the 100 KW electron beam power, the total thermal power of the facility is ∼360 kW including the fission power of ∼260 kW. The burnup of the fissile materials and the buildup of fission products continuously reduce the system reactivity during the operation, decrease the neutron flux level, and consequently impact the facility performance. To preserve the neutron flux level during the operation, the fuel assemblies should be added and shuffled for compensating the lost reactivity caused by burnup. Beryllium reflector could also be utilized to increase the fuel life time in the sub-critical core. This paper studies the fuel cycles and shuffling schemes of the fuel assemblies of the sub-critical assembly to preserve the system reactivity and the neutron flux level during the operation.     

Calculation of fuel burn up and radioactive inventory in a CANDU reactor using WIMS-D4 code

A study of fuel burn up and radioactive inventory for the CANDU reactor is carried out to validate the computer code WIMS-D4 for cluster geometry. The infinite and effective multiplication factors are calculated as a function of burn up and compared with the available results. A good agreement is observed among the present calculations and the previous published results. The code is then used to calculate the ²³⁵U and ²³⁸U consumed and the ²³⁹Pu produced in the fuel bundle. The inventories and the corresponding activities of some important fission products are also calculated.     

Monte Carlo simulation of a conceptual thermal column in the Syrian miniature neutron source reactor using MCNP-4C

Based on probabilistic approach, the MCNP-4C code has been used effectively to simulate the Syrian MNSR reactor core and all its surrounding components in three dimensions, including a preliminary conceptual design of a thermal column to be installed later. For verification and validation purposes, reactor calculations include: criticality and control rod worth. Values of these parameters are 1.00517 and 6.54 mk, respectively. The thermal column is to be installed in the water of the reactor pool. Optimal conditions for this thermal column were tested using the already developed model. Optimization focused on the most suitable position for placement of the column in the water pool, dimensions, and material. The aim was to have a thermal neutron flux of 1 × 10⁹ n cm⁻² s⁻¹ in the center of thermal column, and resonant and fast neutron fluxes to be as low as possible as well.     

The effect of temperature and control rod position on the spatial neutron flux distribution in the Syrian miniature neutron source reactor

The effect on the spatial neutron flux distribution for both of water and fuel temperature increase as well as the change in the control rod position are presented in the Syrian miniature neutron source reactor (MNSR). The cross-sections of all the reactor components at different temperatures are generated using the WIMSD4 code. These group constants are used then in the CITATION code to calculate the spatial neutron flux distribution at different water and fuel temperatures and different control rod positions using four energy groups. This work shows that the increase in water and fuel temperatures during the reactor daily operating time does not affect the spatial neutron flux distribution in the reactor. The change in the control rod position does not affect as well the spatial neutron flux distribution in the reactor except in the region around the control rod position.     

Assessment of fuel conversion from HEU to LEU in the Syrian MNSR reactor using the MCNP code

Assessment of fuel conversion from high enriched uranium (HEU) to low enriched uranium (LEU) fuel in the Syrian MNSR reactor was conducted in this paper. Three 3-D neutronic models for the Syrian MNSR reactor using the MCNP-4C code were developed to assess the possibility of fuel conversion from 89.87% HEU fuel (UAl₄–Al) to 19.75% LEU fuel (UO₂). The first model showed that 347 fuel rods with HEU fuel were required to obtain a reactor core with 5.17 mk unadjusted excess reactivity. The second model showed that only 200 LEU fuel rods distributed in the reactor core like the David star figure were required to obtain a reactor core with 4.85 mk unadjusted excess reactivity. The control rod worth using the LEU fuel was enhanced. Finally, the third model showed that distribution of 200 LEU fuel rods isotropically in the 10 circles of the reactor core failed to convert the fuel since the calculated core unadjusted excess reactivity for this model was 10.45 mk. This value was far beyond the reactor operation limits and highly exceeded the current MNSR core unadjusted excess reactivity (5.17 mk).     

EDXRF分析装置的角度布置对荧光计数率影响的蒙特卡罗模拟

在EDXRF分析中,X射线荧光计数率与待测元素种类和含量有密切关系.但X射线荧光计数率又与很多因素有关,其中X光管、样品和探测器的几何位置关系是一个重要的影响因素.为了设计较好计数率的能量色散型X荧光分析仪,采用MCNP4C程序,建立与实际相符的几何模型,模拟了不同入射角和出射角时的X荧光计数率,得到了X光管与样品、探...     

Spent fuel interrogation using delayed fast neutron spectrum at Missouri University of Science and Technology Reactor

Interrogation of nuclear fuel and Plutonium (Pu) and Uranium (U) discrimination was performed using Missouri University of Science and Technology Reactor (MSTR) fuel by non-destructive (NDA) method. Post-irradiated delayed fast neutron spectra were obtained for two pairs of burnt and fresh fuels. Burnup and ²³⁹Pu conversions were calculated based on neutron emission intensity ratios. After 100 kW high power runs, all fuel elements showed three distinct regions of neutron spectra; a distinct low energy peak followed by intermediate energy region without distinct peak but a wide hump, followed by a high energy peak with a long tail. At 10 kW low powers, intermediate energy hump and low energy peak seems to merge together while the high energy peak still remains distinct. Based on data from 10 kW power runs, the burnup values of F1 and F2 fuel elements were estimated to be 149 MWD/T and 196 MWD/T, respectively. ²³⁹Pu conversion since 1992 for low enriched (19.75%) fuel elements was calculated as 0.24 g for F1 and 0.32 g for F2. Results based on high power runs of 100 kW provided comparable burnup of 217 MWD/T for F2. However the results for F1 were approximately 10 times higher perhaps due to unique burnup history and consequently high poison buildup. These experimental burnup results compare well with the reactor burnup calculation as reported to the Nuclear Regulatory Commission (NRC).     

Numerical solutions for the kinematic model of pebble flow velocity profiles and its applications in pebble-bed nuclear reactor

The modular pebble-bed nuclear reactor (PBR) is a candidate Generation IV reactor being developed. The pebble flow in the very slow draining of fuel pebbles draws attention for its implications on core physical design and reactor physics analysis. One of the effective and simplified methods to address this problem is the kinematic model which is based on continuous theory to derive a diffusion equation for vertical velocity. This paper investigates the appropriate numerical solutions for the kinematic model of pebble flow velocity profiles in PBR geometry. Our method is based on a previously proposed transformed Cartesian coordinates and uses the implicit Crank–Nicholson integration scheme with two different treatments of the boundary conditions. Validations show that this numerical solution gives preferable agreements with the experimental results in the reference. Finally, the simulated velocity profiles are applied in the investigation of two pebble burnup-related issues, which are the pebble residence time prediction and the channel scheme in realistic high-temperature reactor pebble-bed modules reactor core geometry.     

Dynamic analysis of the closed-loop transfer function in the miniature neutron source reactor (MNSR)

The closed-loop transfer function of Syrian miniature neutron source reactor (MNSR) has been measured experimentally using the prompt jump approximation technique. Analysing the reactor stability behaviour, a physical model has been formulated based on the open-loop (neutronics) transfer function employing the lumped parameter concept to describe the reactor thermohydraulic characteristics. The reactor kinetics is described by the point kinetic model for one-group of delayed neutrons. Inherent internal feedback effect is considered as a single reactivity feedback that represents the coolant temperature effect. Comparison of the analytically derived transfer-function with the experimental one shows good agreement. Stability analysis of the closed-loop transfer function has been made using the Nyquist criterion and Bode diagram. Routh–Hurwitz criterion has been applied to estimate the stability limit of the MNSR closed-loop. The Nyquist and Bode criteria have shown that the MNSR closed-loop transfer function is indeed stable. The Routh–Hurwitz criterion enabled the estimation of the upper limit of temperature feedback coefficient of reactivity. Results indicate that MNSR has high inherently safety features. Various relationships that govern relation amongst reactor variables such as the isothermal reactivity coefficient of moderator temperature, temperature difference across the core and coolant flow rate of the natural circulation and mean time for heat transfer to the coolant have been concluded.     

The behavior of reactor power and flux resulting from changes in core-coolant temperature for a miniature neutron source reactor

In this work, measurements were performed to verify the theoretical predictions of reactor power and flux parameters that result from changes in core inlet temperature (T_in) and the temperature difference between the coolant inlet and outlet (ΔT) in the Nigeria Research Reactor-1 (NIRR-1), which is a Miniature Neutron Source Reactor (MNSR). The measured data shows that there is a strong dependence of the reactor power on coolant temperature in agreement with the design of MNSR. The experimental parameters were found to be in good agreement with data obtained using a semi-empirical relationship between the reactor power, flux parameters, core inlet temperature, and the coolant temperature rise. The relationship was therefore used to predict the power level of NIRR-1 from its neutron flux parameters to which it has been found to be proportional. The variation of T_in and ΔT with the reactor power and flux was also investigated and the results obtained are hereby discussed.     

Post-shutdown decay power and radionuclide inventories in the discharged fuels of HEU and potential LEU miniature neutron source reactors

Assessment of fission product and actinide content along with the time variation of decay power of discharged fuels of both HEU and LEU cores of MNSRs have been carried out for once-through cycle using the ORIGEN2 computer code. The results for the LEU core have been compared with the corresponding values for the current HEU core of MNSRs. For the HEU and the potential LEU UO₂, U-9Mo discharged fuels, the ORIGEN2 computed isotopic and total activity values have been found in good agreement with the corresponding results obtained by using the WIMSD4 code. All three MNSR fuels show fission product dominated activity behavior for post-shutdown periods up to about 10³ years during which, the total activity decreases by as much as 10⁶ times. The residual actinide activity shows smaller variations as the three discharged fuels decay thru 10⁶ years. The time variation of the decay power follows the same behavior as the corresponding total activity values during the fission product dominated period. A decrease from initial values of 154.76, 162.6,160.39 W to the final values 9.35 × 10⁻⁵, 2.1 × 10⁻³, 1.7 × 10⁻³ W has been found for the standard HEU, and potential UO₂, U-9Mo LEU fuels correspondingly during this time. The standard HEU fuel shows smallest decay power values while the UO₂ and U-9Mo LEU fuels have comparable values for time spans from 10³ to about 10⁶ years.