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[en] The Mark 1 Pebble-Bed Fluoride-Salt-Cooled High-Temperature-Reactor (Mk1 PB-FHR) is a small, modular 236MWth graphite-moderated pebble-bed fluoride-salt-cooled, high-temperature reactor, developed by University of California, Berkeley (UCB). One of the most important tasks for the design and assessment of Mk1 PB-FHR performance is to develop system analysis codes. A new version called RELAP/SCDAPSIM/MOD4.1 code has been developed by Innovative System Software (ISS). RELAP/SCDAPSIM/MOD4.1 version is developed by ISS, which is powerful enough to treat liquid molten salts in the presence of non-condensable gases and also can simulate liquid-fuel molten-salt-reactors. The Mk1 PB-FHR design uses three modular 50% capacity DRACS units for emergency decay heat removal, the DRACS are passive and function by natural circulation. Therefore, to determine whether the DRACS system as designed could remove the decay heat during a Station Blackout (SBO) event, RELAP/SCDAPSIM/MOD4.1 code is used to analyze Mk1 PB-FHR SBO transient. Results from the transient calculations show that the maximum temperature of fuel element is 1312K and the maximum salt temperature of the molten salt is 1060 K, which is far below the safety limit temperatures 1873.15K and 1123.15 K. (author)
[en] Highlights: • This is the first Method of characteristics code for pebble bed reactor. • Special geometry modeling is developed for pebble bed reactor. • Special algorithm for ray tracing is optimized pebble bed reactor. - Abstract: The method of characteristics which is an effective method for neutron transport calculation with high flexibility in complex geometry has been applied to high temperature gas-cooled pebble-bed reactor geometry. The MOCP (the Method of Characteristics for Pebble-bed high temperature gas-cooled reactor) code was developed in Institute of Nuclear and New Energy Technology, Tsinghua University to achieve this goal. The first stone standing ahead is the geometry modeling for pebble-bed district. In this work, a solid modeling method called constructive solid geometry (CSG) is introduced to model the pebble-bed district. A universal ray tracing technique is developed to arrange tracks in 3-D cylinder geometry. Furthermore, tree search method is implemented into MOCP to improve the ray tracing efficiency. Automatic meshing is implemented to improve the geometry modeling efficiency. A redundant tree was constructed to mesh the interspace among pebbles. The geometry modeling capability of MOCP is verified by fast converging single group benchmarks.
[en] The plan of construction the high temperature gas cooled reactor (HTGR) in Indonesia closer and come true. The HTGRs have two types of fuel that the prismatic and pebble fuel that using the same fuel particles is called TRISO (tri structural isotropic). TRISO particles composed of fuel kernel with four layers of coating that surrounds it. The preliminary study has done about packing fraction and enrichment for criticality value using SCALE 6.1 code. This study calculates modelling of fuel pebbles are stacked in a infinite square grid with the pitch ball 6 cm. The calculations of kef value increases with increasing the number of fuel particles TRISO and increasing the fuel enrichment. The optimum value of the criticality value on enrichment 5 % and 10 % obtained at 5000 TRISO ball while on the enrichment of 17 % was obtained at 2500 TRISO ball. The selection of the TRISO fraction and fuel enrichment should be in under moderated condition. (author)
[en] Highlights: • The loading pattern of pebbles in the reactor is simulated in the model experiments. • The packing factors in reactor model with different packing heights and diameters were measured. • The geometry of the lower cone reflector may induce large variety of packing factor if the angle of the reflector is small. • The changes of the loading rate and the flow velocity in TMSR-SF have little effect on the packing factor. - Abstract: Many concepts of molten salt cooled pebble bed reactor have been developed in recent decades. The packing factor (PF) of the pebble bed in the molten salt reactor should be investigated because it is of great importance for reactor design. Model experiments based on the solid fuel thorium-based molten salt reactor (TMSR-SF) were performed. Experimental results show that the PF of the pebble bed in TMSR-SF (D = 21d, H = 18d, d is pebble diameter) is about 0.57 ± 0.02. The pebble bed in liquid environment is looser than that in dry condition. The PF increases with the diameter of the reactor core and the height of the pebble bed. The geometry of the lower cone reflector may induce large variety of packing factor if the angle of reflector is smaller than the angle of repose of the pebble bed. The loading rate and flow velocity in TMSR-SF are considered to be of little influence on PF. Results from the experiments will be of reference value for the design of reactors.
[en] Highlights: • PANGU code is developed for pebble-bed reactor physics and fuel cycle simulation. • PANGU employs a new two-step calculation scheme utilizing pre-tabulated constants. • PANGU code is advantaged in simulating multi-type particles and pebbles. • PANGU implements an iteration approach for fast calculating equilibrium cycles. • Numerical tests demonstrate PANGU code’s applicability in pebble-bed HTGRs. - Abstract: PANGU is a modern computer code for pebble-bed High Temperature Gas-cooled Reactor (HTGR) physics analyses and fuel cycle simulations, developed by Institute of Nuclear and New Energy Technology (INET), Tsinghua University. This paper gives a comprehensive review on PANGU code’s features including its calculation scheme, methodologies, models and capabilities. Numerical tests are presented for typical pebble bed reactor cases, to verify PANGU code’s applicability. It demonstrates that PANGU code is promising for physical designs of traditional and new-conceptual pebble-bed HTGRs.
[en] Highlights: • The void fraction distribution in a 1 foot (in diameter) pebble bed reactor was studied. • Data obtained experimentally were used to evaluate the empirical correlations. • Experimental results were in agreement with exponential expression for small pebbles. - Abstract: The structure of the pebbles in the pebble bed nuclear reactors plays an important role in their performance as it affects the neutron streaming and the wall channeling of the coolant flow. In this study, the structure of a one foot diameter pebble bed reactor that was measured experimentally by gamma ray computed tomography (CT) in our laboratory in terms of void cross-sectional distribution and radial profiles has been used to evaluate the predictions of the void fractions of the reported empirical and analytical correlations. It can be seen that there is an agreement between the experimental results and the exponential expression for the void fraction with the use of the smaller spherical pebbles diameter (D/dp = 24) as compared to those of larger diameters.
[en] When optimizing high temperature gas cooled pebble bed reactor cores, three Radec non standard nuclear reactor shapes (a.k.a. hour-glass, flask, and lantern) are proposed, calculated and analyzed using the neutronics Serpent code. Taking into account temperature and burnup reactivity effects the power peaking factor for Radec shapes are compared with a standard cylindrical design. The flask and lantern Radec designs exhibit substantial neutronics improvements compared to the cylindrical core shape. (Author)
[en] The main purpose of the paper is to present the possibility for application of recommended principles and methodology for decommissioning costing of research reactors by using CERREX (Cost Estimation for Research Reactors in Excel) code. For that purposes the model calculation case was developed using the inventory data from Korea Research Reactor 2 – KRR2 (TRIGA Mark III type) and pre-defined set of calculation data implemented to CERREX. To create an interface between the inventory database and CERREX calculation module, the special Excel template was developed taking into account physical (mass, surface) as well as radiological parameters (contamination, dose rates, nuclide vectors, limits and conditions). Finally, the calculated results followed by the results of sensitivity analysis are discussed.
[en] Highlights: • The article provides the methods for pebble loading and defueling in liquid salt cooled pebble beds. • The packing factor in liquid salted cooled beds is measured to be less than that in the gaseous environment due to the liquid. • Flow field, loading rate and vibration significantly affect the pebble bed, while the first two mainly affect the bottom geometry of the pebble bed. - Abstract: Based on the advanced high temperature reactor (AHTR), which is an advanced concept combining attractive attributes by adopting liquid salt and coated particle fuel, more and more reactor designs that use fuel pebbles are developed. The bed structure in liquid salt cooled pebble bed reactor is important for reactor design. To investigate the bed structure in the reactor, the Pebble Recirculation Experiment Device (PRED) and the Pebble Bed Dense Experiment facility (PBDE), which were mock-ups for TMSR-SF (Thorium-based Molten Salt Reactor with Solid Fuel) were developed. Packing experiments were performed under different conditions. The results show that, the packing factor of TMSR-SF is supposed to be about 0.574, which is much less than 0.60 in gaseous environment; the loading rate of pebbles and the velocity of inlet flow has great effect on the bottom shape of the pebble bed; the structure of the pebble bed remains stable during normal operation and changes under accident conditions; loss of the coolant in the core may cause rearrangement of pebble bed; increase in packing factor that caused by strong vibration may induce reactivity in reactor core. The pebble bed behavior under different conditions that investigated in this paper provides the basis phenomenological analysis for reactor design. Moreover, the running of PRED demonstrates the feasibility of the methods for pebble loading and defueling in liquid salted cooled pebble bed reactors.
[en] Highlights: • LB-IB-DEM simulation of pebble bed recirculation in HTGR is conducted. • Velocity, FFT and correlation analyses are used to explore gas-pebble two phase flows in HTGR. • Slow gas-pebble flows in HTGR have intermittent and periodic mass flow pattern. • Gas-pebble interaction follows a simultaneous and linearly-dependent two-phase flow pattern. • Helium-pebble flow in real HTGR is predicted to be dominated by pebble recirculation. - Abstract: The pebble bed is one type of the core of the high temperature gas-cooled reactor (HTGR), which is regarded as the candidate of the generation IV advanced reactor. It is important to explore the gas-pebble flow characteristics and the pebble recirculation under the helium atmosphere. In this work, we presented a lattice Boltzmann (LB) method – immersed boundary (IB) method – discrete element method (DEM) coupled approach to simulate a test facility of pebble bed under the recirculation mode of operation. After model validation by an experiment of sphere sedimentation, the process of pebble recirculated at five constant rates are simulated. The correlations of gas motion and pebble motion in the upper and lower half beds are analyzed to uncover the inter-phase relationships for such intermittent pebble flows. Based on the systematic analyses of the two-phase flows, including the mean field and r.m.s field, the historical variation, inter-correlation, and the spectrum and phase space representations, we found sufficient evidences for the characteristics of intermittency, simultaneity, periodicity, and linear dependence for the inter-phase interaction of gas-pebble flows.