Outlet coolant temperature

Temperature control is unlikely to be effective for condensers, unless the liquid stream is sub-cooled. Pressure control is often used, as shown in Figure 5.17d, or control can be based on the outlet coolant temperature. 

If the degree of superheat is large, it will be necessary to divide the temperature profile into sections and determine the mean temperature difference and heat-transfer coefficient separately for each section. If the tube wall temperature is below the dew point of the vapour, liquid will condense directly from the vapour on to the tubes. In these circumstances it has been found that the heat-transfer coefficient in the superheating section is close to the value for condensation and can be taken as the same. So, where the amount of superheating is not too excessive, say less than 25 per cent of the latent heat load, and the outlet coolant temperature is well below the vapour dew point, the sensible heat load for desuperheating can be lumped with the latent heat load. The total heat-transfer area required can then be calculated using a mean temperature difference based on the saturation temperature (not the superheat temperature) and the estimated condensate film heat-transfer coefficient. 

Attainment of reactor outlet coolant temperature of 950°C (April, 2004)... 

The HTTR is an experimental helium-cooled 30 MW(t) reactor. The HTTR is not designed for electrical power production, but its high temperature process heat capability makes it worthy of inclusion here. Construction started in March 1991 [47] and first criticality is expected in 1998 [48]. The prismatic graphite core of the HTTR is contained in a steel pressure vessel 13.3 m in height and 5.5 m in diameter. The reactor outlet coolant temperature is 850°C under normal rated operation and 950°C under high temperature test operation. The HTTR has a primary helium coolant loop with an intermediate helium-helium heat exchanger and a pressurized water cooler in parallel. The reactor is thus capable of providing... 

Fujikawa, S., et aL, (2004), Achievement of Reactor-outlet Coolant Temperature of 950°C in HTTR , Journal of Nuclear Science and Technology, 41 (12), pp. 1245-1254. 

S. Fujikawa, et al., Achievement of Reactor-Outlet Coolant Temperature of 950°C in HTTR."... 

Tlie temperature was raised within the rate of 15°C/h (reactor-outlet coolant temperature above 650°C)... 

Figure 4. Operation history during the high-temperature test operation by the single-loaded mode. Maximum reactor-outlet coolant temperature of 950°C had attained on 19 April 2004.

Reactor-outlet coolant temperature and heat balance... 

Tlie core-internal thermal-hydraulic performance of fuel temperature, core-internal structure, and core-internal coolant distribution were confirmed to be appropriate to their design during the full power operation. Tlie maximum temperature of the core support-plate measured at the upper surface of the centre core support-plate was 450°C that was sufficiently below its limited value of 530°C. Also, it was confirmed that other core-internal structure temperatures were well below their design criteria. From the result tliat no core-internal structure temperature measurement showed an abnormal value, it was confinned tliat there was no abnormal leak flow of coolant such as cross and bypass flows between fuel blocks, replaceable reflector blocks, permanent reflector blocks, etc. The maximum fuel temperature was evaluated to be 1 463°C prior to the high-temperature test operation. It was re-evaluated using the measured temperature data i.e. core-inlet and -outlet coolant temperatures and the calculated value of 1478°C does not exceed the normal operation hmit of 1 495°C. 

The HTTR attained its maximum reactor-outlet coolant temperature of 950°C in 2004. The main results of 950°C operation were described. Simulation tests of abnormal transients caused by the nuclear heat utilisation system planned to be connected to the HlTR were proposed in order to contribute to the code validation for both of the HTTR-IS system design and future VHTR design, in addition to summarising the preliminary project plan of the HTTR-IS system. 

In this section, miscellaneous methods of pressure control are reviewed. Figure 17.7a shows a scheme where pressure is controlled by liquid recirculation. Either the inlet or the outlet coolant temperature can be controlled. Inlet temperature control is better if the coolant outlet temperature approaches the distillate temperature. 

Another critical point about this method is the absolute value of the coolant mass flow rate. It must be high enough to ensure a sufGcient cooling capacity vithin the jacket in order to avoid an increase of the internal temperature due to the heat of reaction released and this way to maintain isothermal measuring conditions. This high mass flow rate at the same means a comparatively small residence time of the coolant in the jacket and this way a very small temperature difference between inlet and outlet coolant temperature. This may lead to technical measurement problems. This shall be explained with the help of an example. 

Plateout distributions in die parallel loaded operation at rated power operation, i.e. 850 °C of outlet coolant temperature, are shown in Fig, 5. It is predicted that both l and Cs plateout mainly on die heat transfer tubes of PWC where temperature is relatively low in the primary cooling system of the HTTR. On the other hand, there are very small amounts of plateout FPs on the inner pipe of co-axial double pipe where temperature is very high and therefore, desorption rate is large by its high lattice excitation frequency. From the calculation results, it is predicted that... 

With inlet coolant temperature around ISOC, it can produced the outlet coolant temperature beginning from 250C to 450C. 

The potential advantages were low-neutron absorption by the coolant and high outlet coolant temperatures available at moderate pressures. The disadvantages lay in the relatively poor heat transfer and heaf fransporf properties of CO2. 

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