| As an emerging subcritical nuclear power system which is driven by external neutron source, Z-Pinch driven fusion-fission hybrid reactor (Z-FFR) is now being exploring. Z-FFR integrates the concept of Z-Pinch technology and the subcritical blanket. The Z-Pinch driver generates the high power and short duration electrical pulse. The large current delivery through the tungsten wires generates the intense x-ray source which compresses the high-density plasma to fusion condition to indirectly heat a deuterium and tritium fusion target. The high-energy neutrons liberated from D-T fusion reaction strike the subcritical blanket for energy release and self-sustaining tritium cycle. The characteristic of Z-Pinch driven inertial confinement fusion technology cause the system to run in a pulsed mode with duty period of 10 s. The materials, i.e. nuclear fuel and cladding sustain strong continuous transient heat shock. One of the major issues of developing the system is figuring out the characteristic of thermal hydraulic behavior. Based on the conceptual design of the Z-FFR, the thermal hydraulic and safety characteristics were investigated from local and system scale, by using the computational fluid dynamics software FLUENT and thermal hydraulic system code RELAP5. The dissertation studies mainly consist of the following work.The model of the subcritical blanket was built based on the lumped parameter method. The single channel thermal code was developed by the MATLAB, which dedicated for fuel embed with the cooling pipe. Calculation examples demonstrate the reliability of the single channel code at a certain extent. The preliminary thermal and hydraulic design was carried out to verify the rationality of cooling channel inner diameter. The thermal parameters was confirmed to provide boundary condition for thermal calculation, such as inlet core mass flow of the coolant.The characteristics of flow distribution in the part of blanket model (the U type parallel channel) was performed with FLUENT. The way to improve the flow distribution uniformity was discussed. By enlarging the ratio of the branch pipe longitude and inner diameter or by increasing the ratio of the header pipe inner diameter and the branch pipe inner diameter could improve the uniformity of coolant distribution. On the basic of prototype design, the optimal design was implemented by increasing the inner diameter of the header pipe and enlarging the longitude of the branch pipe. The optimal results showed that flow distribution uniformity was improved.Based on the special structure of fuel component in the subcritical blanket, the three-dimension thermal characteristics were performed with FLUENT. Considering the first wall surface heat flux and nuclear heat, the model of heat source was compiled by user defined functions (UDF) hooked in Fluent. The results showed the temperature of fuel and cladding materials would maintain a certain level after 5 pulse period form start-up at cold state. The peak temperature of fuel was 770 K, when the single period energy deposited at 10 ms. The peak temperature of the first wall material was 710 K. The temperature of fuel and cladding satisfy thermal design criteria, which indicated the thermal design scheme of the Z-FFR is acceptable.According to the design of the Z-FFR and three loops PWR, the system model of the Z-FFR was developed based on RELAP5. The continuous heat source was simulated by using the power table hooked in restart deck. The calculated results showed that the main thermal parameter presented the features of pulsed variation. The minimum departure of nucleate boiling ratio (MDNBR) was 1.6, which satisfy thermal design criteria.Considering no lateral flow in the cooling channel and the channels were very narrow, the conditions of different blocked area in flow blockage accidents were analyzed. The calculated results showed that the MDNBR was below 1.5 when the blocked area surpass 10%. When the blocked area surpass 25%, the fuel would melt. |
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