This publication reports on the second international collaborative intercomparison and validation of computer codes for heavy water reactor (HWR) thermalhydraulic safety analyses. The participants aimed to improve the understanding of important phenomena expected to occur in small break loss of coolant accident transients of HWRs; to evaluate code capabilities to predict these important phenomena, their practicality and efficiency, by simulating integrated experiments; and to suggest necessary code improvements or new experiments to reduce uncertainties. The summary report provides a comparison of the results obtained from six participating countries, utilizing four different computer codes. Lessons learned were summarized, and general conclusions and recommendations were made.