Modification to Unal’s Subcooled Flow Boiling Bubble Model

Unal’s subcooled flow boiling bubble model is being used in the best-estimate light water reactor code RELAP5/MOD3. There is a significant discontinuity (by a factor of 2) in the condensation heat transfer coefficient from this model at 1 MPa, which can cause numerical problems in the code. The correlation has been modified (with the approval of Unal) to remove the discontinuity at 1 MPa and to replace it with a form that is continuous to three significant places at 1.1272 MPa.