Assessment of RELAP5 CHF prediction methods against experimental tube data

Under particular conditions, boiling may lead to sudden and catastrophic phenomena called critical heat flux (CHF). Therefore, better CHF predictions by system codes such as RELAP5 are seen to be important for system safety and operations. Hence, a set of 1145 water CHF data points for vertical up flow covering a wide range of different parameters have been used to assess the CHF prediction methods in RELAP5. The RELAP5 code uses two methods: the 1986 AECL-UO critical heat flux lookup table method and the PG-CHF correlations. In addition, results obtained from the recent lookup tables of 1995 and 2006 are included in the plots and used to support the conclusions and to perform a comparative study of the methods used by the code. Compared to the look-up tables and correlations, the present study showed a good agreement with the experimental data for the basic form of the PG-CHF correlations illustrated by a good statistics (99.4% of predictions are within ±20% and with a root mean square error of 6.44%).