Assessment of subchannel code ASSERT-PV for prediction of post-dryout heat transfer in Candu bundles - 14351

Atomic Energy of Canada Limited (AECL) has developed the subchannel thermal-hydraulics code ASSERT-PV for the Canadian nuclear industry. The recently-released ASSERT-PV 3.2 provides enhanced models for improved predictions of subchannel flow distribution, critical heat flux (CHF), and post-dryout (PDO) heat transfer in horizontal Candu fuel channels. This paper presents results of an assessment of the new code version against PDO tests performed during five full-size Candu bundle experiments conducted in 1990's and in 2009 by Stern Laboratories (SL), using 28-, 37- and 43-element (CANFLEX) bundles. The SL experiments encompass the bundle geometries and range of flow conditions for the intended ASSERT-PV applications for Candu reactors. Code predictions of maximum PDO fuel-sheath temperature were compared against measurements from the SL PDO tests to quantify the code's prediction accuracy. The prediction statistics using the recommended model set of ASSERT-PV 3.2 were compared to those from previous code versions. The sensitivity studies quantified the contribution of each PDO model change or enhancement to the improvement in PDO heat transfer prediction. Furthermore, the code convergence improvement was assessed against all selected SL tests as well. Overall, the assessment demonstrated significant improvement in prediction of PDO sheath temperature in horizontal fuel channels containing Candu bundles. (authors)