ABSTRACT
The methods of coolant loop analysis can be of various levels of complication. For reactor operation and control applications, rather rapid calculation schemes and simplified models are needed. For safety analysis, detailed models particularly of the core may be needed. A number of sophisticated thermal hydraulic codes have been developed for power reactor flow loops including systems codes such as RETRAN, RELAP and TRAC for light water reactors and SSC for the liquid metal reactors. However, loop or system analysis including transients can often be done as in this chapter using a simplified one-dimensional model of a loop with a single, heated channel representing the core and one or more cooled channels representing the heat exchangers. This chapter develops the general, one-dimensional equation for the loop and then presents solutions for steady state, single and two-phase conditions under natural circulation. For the two-phase condition, the stability of loop operation is discussed in detail. The chapter finally treats transients starting with single-phase transients by identifying the major time constants and their controlling physical parameters. For two-phase systems, the major addition to the single-phase system treatment is inclusion of the effect of buoyancy and the needed revised momentum equation.
