[en] Highlights: • Seismic failure event probability is induced by uncertainties in PGA and in Am. • Uncertainty in PGA is shared by all the components at the same place. • Relativity induced by sharing PGA value can be analyzed explicitly by MC method. • Multi components failures and accident sequences will occur under high PGA value. - Abstract: Seismic probabilistic safety assessment (PSA) is developed to give the insight of nuclear power plant risk under earthquake and the main contributors to the risk. However, component failure probability including the initial event frequency is the function of peak ground acceleration (PGA), and all the components especially the different kinds of components at same place will share the common ground shaking, which is one of the important factors to influence the result. In this paper, we propose an analysis method based on Monte Carlo (MC) simulation in which the effect of all components sharing the same PGA level can be expressed by explicit pattern. The Large LOCA accident in AP1000 is analyzed as an example, based on the seismic hazard curve used in this paper, the core damage frequency is almost equal to the initial event frequency, moreover the frequency of each accident sequence is close to and even equal to the initial event frequency, while the main contributors are seismic events since multi components and systems failures will happen simultaneously when a high value of PGA is sampled. The component failure probability is determined by uncertainties in PGA and in component seismic capacity, and the former is the crucial element to influence the result

[en] The HTR-10 steam generator consists of a series of helical pipes where water/steam flows inside and the helium flows outside. It operates under middle pressure which tends to cause the flow instability. Density-wave Oscillation is a result of the multiple feedback effects in relationship between the flow rate, steam generation and the pressure drop in a boiling channel. Density-wave Oscillation is the most common type of two-phase flow instability in steam generator. This paper presents the research on flow stability for HTR-10 steam generator. The drift flux model is used for two phase flow analysis. The transfer matrix was obtained by using linearized perturbation and Laplace transform on the conservation equations. The flow stability is determined by Nyquist stability criterion. (authors)

[en] Highlights: •Helium permeability and Young’s modulus were measured for samples. •The splint based SiSiC has good hermeticity. •Uncoated fiber reinforced SiSiC is permeable to the helium. -- Abstract: SiC-based ceramic matrix composites (CMCs) are attractive materials for Very High Temperature Gas Cooled Reactor and advanced reactor. The present work is focused on the Helium permeability measurements and Young’s modulus calculation of SiSiC samples. A simple and cost effective test system was designed to complete the tests in the low pressure at room temperature. Four kinds of flat-plate CMCs were used in the tests including two uncoated SiSiC coupons and two coated coupons. The permeability was identified, and SEM examination indicated that microscopic porosity contributes to the permeability and the CVD carbon coating can reduce the porosity. On the other hand, experiments for measuring Young’s modulus were carried out for two samples, providing additional evaluations for those materials.

[en] 10 MW high temperature gas cooled reactor steam generator (HTR-10 SG) is once-through-vertical helical-tubing steam generator, and operates at middle pressure parameters. Two-phase flow instabilities must be paid attention. This paper analyzes two-phase flow density-wave instabilities by means of multi-variable frequency domain method based on Zuber-Findaly type of drift-flux model. The feedback coupling effect between the primary and the secondary circuits is analyzed. The mathematical expressions of multi-input to multi-output transfer matrix of the system are proposed, and the multi-channel feedback system model is deduced. A computer code AFIHTR is derived on above bases. The stability condition of two-circuit-coupled density-wave oscillations in HTR-10 SG is obtained by using this code

[en] Integral test plays a key role in assessing the feasibility of the passive containment cooling system (PCCS) and the accuracy of the calculation model. The scaling analysis for ; mixing in large stratified volumes of PCCS provides the primary theoretical basis for determining the key size of the integral test facility. Based on the mixing in large stratified volumes, the key parameters were obtained by scaling analysis based on the hierarchical two-tiered scaling method. The similarity criteria that ensure the integral test facility can well simulate mixing in the passive containment was obtained. (authors)

[en] To analyze the mixing and heat transfer problems in the passive containment cooling system (PCCS), a new advanced computation model is used, which is based on stratified phenomenon in the large enclosures. It uses one-dimensional differential equations to get temperature and velocity profiles for the ambient fluid, which does not require complex meshing. The model is applied on mixing and heat transfer experiments in a large rectangular enclosure with an injected buoyant jet and a cooled vertical surface, which simulates a break flow for passive reactor containment systems. The new modeling results show good agreement with the previous experimental results. (authors)

[en] Large scale integral test is important for both validation and verification for Passive Containment Cooling System (PCS) and its simulation codes. In this paper, scaling analysis of heat transfer in the containment during LOCA/ MSLB was made. The key sizes of the test facility are determined based on the similarity criteria, the containment dimension, and inner boundary condition. The experimental system has been designed. The research is contributed to the basis for the large passive containment thermal hydraulic tests. (authors)

[en] It is important to accurately predict the pressure in passive containment under LOCA condition both for design optimization and accident analysis. Over-conservative assumptions were used in one-dimensional lumped parameter method. 2-D and 3-D CFD methods require very fine grid resolution to resolve thin substructures such as jets, wall boundaries, which requires a big computational effort. This research uses a Lagrangian approach to solve 1-D transient governing equations for the ambient fluid and analytical models or 1-D integral models to compute jets flow. It can significantly reduce the computational effort and improve the calculation accuracy. The new code has been succeeded in PCCS analysis. This paper presents several models in large enclosures for reactor safety analysis. (authors)

[en] Cu/Cu₂O oxygen sensor was tested on the pool type experimental device for solid-phase oxygen control. Experimental device was cooled from 500℃ step-by-step to 300℃. 95% Ar + 5% O₂ was injected during cooling process. The test indicates that the Cu/Cu₂O oxygen sensor shows good performance in terms of accuracy and responsiveness in the temperature range from 300℃ to 500℃. Oxygen sensors can respond to the changes of oxygen concentration caused by temperature change quickly. The relative deviation between the electromotive force (EMF) of the oxygen sensor and the theoretical EMF remains within ± 3%, and the oxygen concentration relative deviation is maintained within ± 10%. Oxygen sensor signal fluctuation in the test is within 1.7 mV. (authors)

[en] 10 MW high temperature gas cooled reactor steam generator (HTR-10 SG) is once-through-vertical helical-tubing steam generator, and operates at middle pressure parameters. Two-phase flow instabilities must be paid attention in the SG. Two-phase flow density-wave instabilities are analyzed by means of multi-variable frequency-domain method based on Zuber-Findlay type of drift-flux model. The feedback coupling effect between the primary and the secondary circuit is analyzed. The mathematical expressions of multi-input to multi-output transfer matrix of the system are proposed, and the multi-channel feedback system model is deduced. A computer code AFIHTR is derived on above bases. The stability condition of two-circuit-coupled density-wave oscillations in HTR-10 SG is obtained by using this code. (4 refs., 6 figs.)