Core inlet temperature

Reactor pressure vessel Core inlet temperature Core outlet temperature Coolant inlet pressure Coolant flow Core power density Average fuel bumup Refuelii interval Gas turbine cycle type... 

A depressurization accident with a subsequent water ingress was found to not represent an intolerable load upon the pressure-keeping containment in terms of peak pressure and pressure transient. Reactivity transients including false operation of absorber rods, water ingress, or a decrease of core inlet temperature were also analyzed to cause no serious damage to the heat exchanging components, unless both reactor shutdown and helium circulators fail at a time. 

The changes in process parameters resulting in decrease in core inlet temperature causing reactivity transient were studied. The required inlet temperature change to cause the two transients were estimated to be -3.1 and -4.9 C respectively. Extensive tests on the influence of changes in primary, secondary and feed water flow and steam pressure were studied at 9.5 MWt power and the results are given in Table 1. 

Regular power operation is attained by moving the reflector upward at a constant speed of Imm/day to compensate for the reactivity decrease due to the bum-up of the core. Since no feedback system or control system are used, the reflector speed remains constant and the electric output is adjusted by varying the feed water flow rate to control die core inlet temperature. The controllable range of the power level by the water flow is 10% at the rated power, which is limited by the steam generator heat balance. Beyond this range, a back-up control mechanism to adjust the reflector position is installed in the driving mechanism. 

To follow the load, the core inlet temperature is changed by controlling the water flow so that the generator output coincides wiA the load-following control, thus causing the reactor ou ut to follow. 

When the control rods are inserted in variants A, B and C, the core temperatures drop in the following minutes from normal operating temperatures to near uniform temperatures, nearly equal to the core Inlet temperature. During this transient period, the stress fields In the core components go from operating stresses to shutdown stresses. 

In summary The efficiency potential of the gas turbine technology for the conversion of high temperature heat from the HTR into electricity is - in principle - as high as that based on natural gas. Therefore it is proposed here to take the gas-plus-steam-turbine-cycle, GST, into consideration, in particular with a "3-pressure-steam-turbine-cycle". With further improvements, in particular in the gas turbine cycle, and with the assumption that the gas turbine-inlet temperature is 1 OSO (100 K more than AVR in 1974) the calculated net efficiency is 54.5 %. A particular advantage of the GST versus the gas turbine cycle with recuperation is that the core-inlet temperature is smaller at comparable efficiency conditions. 

The gas-turbine-cycle of design B is similar to conventional ones, fig. 3. It has the following temperature data, gas turbine-inlet temperature 1 050 C, and core-inlet temperature 396 C. It can be remarked, that the low core-inlet temperature is an advantage of the GST-cycle compared to the gas turbine cycle with recuperation. 

An important advantage of the "gas-plus steam-turbine cycle" in comparison to the "gas turbine cycle with recuperation" is that the core-inlet temperature is smaller at comparable efficiency conditions. The following comparison can be taken as an example The GT-MHR with 47 % at 850 "C, fig 2, has an core inlet temperature of493 C (919 F), lit. ETZEL-1994, fig. 7, upper part, the HTR-GST with 54.5 % at 1 050 °C, fig. 2, has an core inlet temperature of 396 C, fig 3... 

The major difficulty to limit the higher thermal efficiency of the indirect cycle is the lower core inlet temperature. For the direct cycle, the cold gas leaving the precooler can be extracted to cool the reactor pressure vessel (RPV) and the other steel structures. Therefore the core inlet temperature can be as higher as 500- 600°C. For the indirect cycles proposed before, such as MGR-GTI proposed by Yan and Lidskyl, the core inlet temperature is kept as lower as 310°C in order to cool RPV The plant busbar efficiency of MGR-GTI is about 42.1%. In order to achieve higher power plant efficiency, it seems special designs of RPV cooling should be provided for the indirect gas turbine cycle. 

High plant efficiency is achieved mainly by increasing core inlet temperature to 550 °C... 

Based on the state-of-the-art technology, the current activities of HTR-10 GT-ST combined cycle focus on an independently parallel Combined Cycle in which GT and ST cycle are independently parallel in the secondary side. This selected configuration will make full use of the current MHTGR design with a relatively low core inlet temperature (i.e.,250 300 C), change smoothly from the ST cycle in the first phase to the GT-ST cycle in the second phase. A conventional helical IHX is used the system. 

Fig. 3.13. Pumping power as function of coolant channel size and core inlet temperature.

LEADIR-PS 200 has a graceful and safe response to all anticipated transients. For example, an overcooling event (as could be caused by loss of feedwater control or spurious opening of steam relief valves in combination with control system failure) causes the core inlet temperature (normally 350°C) to fall as the freezing point of 327°C is approached the coolant viscosity increases, coolant flow decreases, and in the absence of any control system action, the negative temperature coefficients of the fuel and moderator reduce reactor power. Heat removal is maintained by natural convection. 

Feed water flow is then gradually increased. The core inlet temperature decreases and the power is increased by reactivity insertion. When the reactor power is increased to equal the house load, the main steam control valve is opened to increase the speed of the turbine to a specified frequency, and then the generator is connected. The reactor power output is increased to 100% by raising the water flow. In the present design, it takes 16hrs to reach 100% power after completion of raising system temperature up to 350 C. 

Coolant medium and inventory H2O/36O m Design coolant mass flow through core 9350 kg/s Cooling mode (forced/natural) forced Operating coolant pressure 7,0 MPa Core inlet temperature 278 °C Core outlet temperature. 286"C... 

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