Thermal Analysis Of HTGR Helical Tube Once Through Steam Generator Using Porous Media Method

The accident on March11,2011at Fukushima, Japan, caused by an earthquakeand tsunami, is the evidence of the necessityof developing safer nuclear reactors. TheHigh Temperature Gas-cooled Reactor (HTGR) has the characteristics of a generationIV reactor; its inherent safety features are especially prominent. The HTGR employs ahelical coil, once through steam generator. The uniformity of the temperaturedistribution in the steam generator is important for its design and operation.The shell side of the HTGR once through steam generator is cross flow over helicaltube bundles. At the inlet of the tube side is single phase water, then it is heated to boilby helium, and finally reaches superheated steam. Due to the complex nature of helicalcoil, once through steam generators, the porous media method provides a good way toanalyze its temperature distribution. The porous media method is fast andcomputationally efficient. A two-dimensional shell side and one-dimensional tube sidemodel was established and a computer code was developed to model the HTGR steamgenerator. The two-dimensional cross flow over the tube bundles in the shell side usesthe porous media method. The shell and tube side equations were discretized using thefinite volume method.The temperature profile of the helium and water by the porous media codeclosely match the CFD results. Using a Peclet number of30, several scenarios weretested with the porous media code. A reduction of the water flow rate by1%for a giventube line caused a temperature rise of about5°C in the outlet steam temperature for thattube line. An increase of the flow rate by1%for a given line caused about a6°Cdecrease in the outlet steam temperature of that tube line. Shitfing a center tube line by1mm decreased the outlet steam temperature of the closer tube line by about3°C andincreased the outlet steam temperature of the tube line farther away by about4°C. Theshitfed tube did not change temperature significantly. Next to the wall however, shitfinga tube caused the shitfed tube to increase or decrease in temperature by2-4°C.Blocking a tube caused a sharp increase in the outlet steam temperature for that giventube line as well as an overall increase for the other tube lines. The highest outlet steamtemperature increase was70°C for line1with one tube plugged and the smallest increase was30°C for line4with one tube plugged.The Peclet number was also found to have a strong influence on the outlet watertemperature profile. Using a Peclet number of50caused the largest difference increasein temperature ranging from36°C to82°C for line4and line1respectively. Using aPeclet number of10, the temperature increase ranged from25°C to50°C for line4and1respectively. The CFD results matched the results from the Peclet number10resultsfor line1,2and3with one tube plugged, while it matched the results from the Pecletnumber30results for line4and5with one tube plugged.Overall, numerical simulation of thermal distribution in HTGR helical coil, oncethrough steam generators is realized using porous media method. The results canprovide guidance for the design and operation of HTGR helical coil once throughsteam generator.