Investigations in freon on critical heat flux (KRISTA-program)

An experimental study of CHF in closely spaced 7 rod bundles is performed in the KRISTA test facility. The experiments covered a wide range of parameters of interest to high conversion pressurized water reactors (HCPWR). Under comparable conditions the CHF value in bundles is lower than in tubes. The influence of spacers (grid spacer and wire wrap) on CHF has been found to depend strongly on local steam quality. With regard to the CHF behaviour under HCPWR conditions no noticeable improvement has been achieved in a wire wrapped bundle than in a bundle with grid spacers. (orig.)