[en] Oxidation of the metallic components of the reactor core and the interaction of core/concrete will produce hydrogen under severe accident. Hydrogen combustion in the containment building may threaten the integrity of the containment. Deliberate ignition of the flammable gas mixture is a promising hydrogen mitigation measure under severe accident. Approach based on σ criterion and λ criterion to evaluate flame acceleration (FA) and deflagration to detonation transition (DDT) is established. Hydrogen deliberate ignition at early and late stage was analyzed in a single close room. The results indicate that deliberate ignition is an effective way to remove hydrogen, depending on igniter location and first ignition time. The approach can be used to determine number, location and frequency of a safe igniter system for a given dry containment in NPPs. (authors)

[en] To solve the multi-dimensional transient neutron diffusion equations, improved quasi-static Green's function method (IQS/NGFM) is adopted to deal with the temporal problem, which will increase the time step as long as possible so as to decrease the number of times of spatial calculation. The time step of IQS/NGFM can be increased to 5∼10 times longer than that of full implicit differential method. In spatial calculation, the theory of NGFM is used to get the distribution of shape function, with coarse meshes which can be nearly 20 times larger than that of traditional finite differential method. So the IQS/NGFM is considered as an efficient kinetic method

No abstract available

[en] The 10 MW High Temperature Gas-cooled Reactor-Test Module (HTR-10) is a pebble bed experimental reactor built by the Institute of Nuclear Energy Technology (INET), Tsinghua University. This paper introduces the first critical prediction calculations and the experiments for the HTR-10. The German VSOP neutronics code is used for the prediction calculations of the first loading. The characteristics of pebble-bed high temperature gas-cooled reactors are taken into account, including the double heterogeneity of the fuel element, the buckling feedback of the spectrum calculation, the effect of the mixture of fuel elements and graphite balls, and the correction of the diffusion coefficients in the upper cavity based on transport theory. Also considered are the effects of impurities in the fuel elements, in the graphite balls and in the reflector graphite on the reactivity. The number of fuel elements and graphite balls in the initial core is predicted to provide reference for the first criticality experiment. The critical experiment adopts a method of extrapolating to approach criticality. The first criticality was attained on December 1, 2000. The first criticality experiment shows that the predicted critical number of the fuel elements and graphite balls is in close agreement with the experimental results. Their relative error is less than 1.0%, implying the physical predictions and the results of the criticality experiment are much beyond expectations

[en] The mode of fuel management of the HTR-10 was studied, including the simulation of the fuel shuffling process and the measurement of the burnup of a fuel element. The prior consideration was the design of the equilibrium state. Based on this the fuel loading of the initial core and the fuel shuffling mode from the initial core through the running-in phase into the equilibrium state were studied. The code system VSOP was used for the physical layout of the HTR-10 at the equilibrium state and in the running-in phase. For the equilibrium state, in order to lessen the difference between the peak and the average burnup, 5-fuel-passage-through-the-core was chosen for the fuel management. The average burnup of the spent fuel for the equilibrium core is 80000 MWd t^-1, and the peak value of it is less than 100000 MWd t^-1 when the burnup of the recycled fuel element is under 72000 MWd t^-1. The mixture of fuel element and graphite element was used for the initial core loading, the volume fractions of the fuel and the graphite elements were 0.57 and 0.43, respectively. During the running-in phase, the volume fraction of graphite will decrease with the fresh fuel elements being loaded from the top of the core and the graphite elements discharged from the bottom of the core. The fuel shuffling mode is similar to that of the equilibrium state. The burnup limit of recycled fuel element is also 72000 MWd t^-1 and the peak burnup is less than 100000 MWd t^-1. Finally the core will be full of fuel elements with a certain profile of burnup and reaches the equilibrium state. According to the characteristics of the pebble-bed high temperature gas-cooled reactor, a calibrating method of concentration of ¹³⁷Cs was proposed for the measurement of fuel burnup

[en] The Modular High Temperature Gas-Cooled Reactor (HTR) can be used to burn plutonium fuel to reduce Pu stockpiles because of its inherent safety characteristics and ability to burn a variety of fuel mixtures. The equilibrium core is calculated and analyzed for Pu enriched fuel. Fuel spheres with 7 g heavy metal including the civilian grade Pu and thorium are loaded into the reactor. An enrichment of 11% is chosen to provide the desired equilibrium core reactivity. The fuel and moderator temperature coefficients are both negative. The maximum fuel element temperature during normal operation and during a loss of coolant accident is less than 1500 degree C. 92% of ²³⁹Pu will be burnt during normal operation. Therefore, a thorium fuel cycle in the modular HTR is an effective method for burning civilian grade plutonium

[en] The 10 MW high temperature cooled reactor (HTR-10) built in Tsinghua University is a pebble bed type of HTGR. The continuous recharge and multiple-pass of spherical fuel elements are used for fuel management. The initiative stage of core is composed of the mix of spherical fuel elements and graphite elements. The equilibrium stage of core is composed of identical spherical fuel elements. The fuel management during the transition from the initiative stage to the equilibrium stage is a key issue for HTR-10 physical design. A fuel management strategy is proposed based on self-adjustment of core reactivity. The neutron physical code is used to simulate the process of fuel management. The results show that the graphite elements, the recharging fuel elements below the burn-up allowance, and the discharging fuel elements over the burn-up allowance could be identified by burn-up measurement. The maximum of burn-up fuel elements could be controlled below the burn-up limit

[en] The shuffling ways, once through then out and multiple through then out, in HTR-10 MW Test Module are studied. Multiple through then out is better than once through with regard to rational use of the fuel and flattening the power. The behaviour of equilibrium core and loss of coolant accident is analyzed. The results indicate that characteristic features of the multiple through then out could be better to satisfy the demands of safety criterions

[en] Three dimensional temperature field and helium flow field of TBM are simulated using the general purpose computational fluid dynamics (CFD) code FLUENT. The temperature distribution of Be Armor, Be Pebble Bed, Li₄SiO₄ Pebble Bed, Structure Material of TBM, and helium flow field in the cooling pipe are presented. The research indicates that the work temperature of each material is under the material temperature allowed except some places where high temperature should be excluded in the design. The results will provide references for further optimized thermal hydraulic design of ITER China TBM. (authors)

[en] A method used in reactivity worth calculation for control rods of 10 MW high temperature gas-cooled reactor (HTR-10) is described, in which the control rods are located at the reflector and directly near the core. GAM and THERMOS codes are used in the usual way to produce cross sections of core, reflector, materials used in control rods, etc. The two-dimensional discrete-ordinates transport theory code SN is used to calculate a model with clear structure of control rod in (r, θ) system, space and spectrum effects are dealt with at same time in this model. The cross sections in the region that includes control rods and part reflector are homogenized by the weight of fluxes. The K_eff for the situations with control rods fully inserted and fully withdrawn is calculated by using diffusion theory code CITATION in (r,z) system. The reactivity worth of control rods at each phase of HTR-10, including initial, running-in and balance phases, has been calculated by using this method. The integral and differential worth of control rods is also studied