PARALLEL-PROCESSING OF BOILING WATER-REACTOR CORE ANALYSIS

A parallel processing method for the analysis of a Boiling Water Reactor (BWR) core has been developed to drastically reduce the computation time. In the proposed method, a BWR core is divided into smaller segments, each of which is assigned to one bf the processing elements (PE) working in parallel. The whole computing task is divided into smaller tasks that are distributed to the PEs as equally as possible. To solve the neutron diffusion equations in BWR neutronics calculations, the three-dimensional checker-board block iterative method was adopted. In the thermal-hydraulic calculation, the whole task can be divided into parallel tasks except for the coolant enthalpy distribution calculation along a Row channel. Parallelization efficiency of the proposed method was examined by measuring computing time on a hypercube type parallel processor with 64 PEs. The computation speed gradually degrades with the number of segmentation, because of delay due to communications between PEs and to waiting time caused by unequal amount of tasks among PEs. A 64 PE calculation was found to be from 30 to 50 times faster than the 1 PE calculation. Both the axial and the radial segmentations were found to be effective in reducing computing time. If the BWR core analysis is made with a massively parallel processor consisting of more than 4,500 PEs, computing time will be reduced nearly by an order of three.