Comparison of lumped parameter models of helical-tube precooler in HTGR Brayton cycle

The precooler is very important equipment as cooling source and helium will be cooled finally down to the lowest temperature in the HTGR with direct Gas Turbine cycle. Three lumped parameter models were developed to research on dynamic performances of the precooler. A lumped parameter model (model 1) neglecting thermal capacity of precooler's metal wall was proposed to study on the precooler's dynamic characteristics and meanwhile, to find out effect of wall thermal capacity to the model. A linear model (model 2) was proposed to study on the precooler's dynamic performance, including wall temperature, bu it failed to obtain correct results because of wrong characteristic temperatures. A modified model to the linear model (model 3) could achieve correct and reasonable results. Comparing the model 1 with model 3, it was found that the model 1 could forecast dynamic performance of the precooler, except for the wall temperature. Loss of cooling water accident, a severe accident related to the precooler was studied with the help of the model 3. When loss of cooling water accident happened, it was very important to maintain cooling water to some degree, which could make the cycle running safely until stop. (author)