SVEA spray cooling test. Summary report

The test programme has been based on a realistic experimental simulation of a large recirculation line break in an external recirculation pump BWR. Variations have been made from this base in order to test more conservative choices of the test parameters. About 50 tests were successfully performed within the project. The experiments have provided data which verify the improved heat transfer characteristics of the SVEA fuel bundle design compared to the standard 8x8 fuel. Tests have been performed at power levels corresponding to average planar heat generation rates up to 45 kW/m with both slightly conservative (ANS-79 + 2σ) and a very conservative (ANS-71 + 20%)power decay curve. With realistic values of other paramaters the peak rod temperature was measured to 994 degrees C and 1093 degrees C for these two decay powers. The influence of total spray flow rate and of spray flow distribution has been investigated in a series of tests. These tests show that with uniform sub-bundle spray flow rates the peak rod temperature is only moderately influenced by a reduction of the total spray flow rate to 45% of the minimum available spray flow rate in a Swedish external pump reactor. Maldistribution tests show no influence of minimum sub-bundle spray flow rate down to 25 g/s and only moderate influence in the extreme case of zero sub-bundle spray flow rate. Variations in other parameters including pressure, initial rod temperatures and steam venting direction have also been made within this project. The resulting changes in peak clad temperature were small, indicating only slight influence of these parameters. The programme has also included radiation tests mainly to provide data for evaluation of surface emissivities. (authors)