Experimental and analytical investigations on core flow distribution and pressure distribution in the outlet header of a PHWR

The Indian pressurised heavy water reactor (PHWR) comprises of a number of horizontal channels containing nuclear fuel bundles. The parallel channels are connected to headers at the inlet and outlet through feeder pipes. The flow distribution between the channels of the PHWR is an important aspect of the design of the core and primary heat transport system. A correct determination of the channel flow distribution is required to evaluate the thermal safety margin. The estimation of the design flow rate in the channels is based on the assumption that the pressure in each header is uniform. Moreover, in the reactor core only sixteen channels out of the 306 channels are provided with flow metering elements. An analytical model has been developed to enable a better prediction of the flow distribution between the different channels and the variation of pressure in the outlet header. The flow rates in the channels and the pressure distribution in the outlet header are predicted from the solution of two first order differential equations (pressure-flow equation set) involving the flow rate and the pressure difference across the headers. The outlet header is divided into four basic combining flow manifolds and an iterative procedure has been adopted to satisfy the flow and pressure conditions at each junction point between two successive manifolds by solving the pressure-flow equation set for each manifold. The model adopted for the analytical studies has been validated against experimental data. The experimental studies were carried out on a one-fourth scale model to determine the channel flow distribution in the reactor core and the pressure distribution in the outlet header at different flow rates, with (i) both the steam generating (SG) branches open and (ii) one of the steam generator branches closed. Air was used as the test fluid. The measured flow distribution in the test model has been compared with the theoretically obtained flow distribution. The pressure variations in the outlet header for different modes of pump operation are compared. The analytical results for the flow distribution are in excellent agreement with the experimental data. Analysis is also performed for the prototype reactor header using the validated model for different modes of pump operation. The analytically obtained results are compared with the plant data. (C) 2002 Published by Elsevier Science Inc.