PIRT efforts in support of ACR-700 computer code validation

The Advanced CANDU Reactor (ACR™*) is an evolutionary advancement of the current CANDU 6® reactor, aimed at producing electrical power for a capital cost and at a unit-energy cost significantly less than that of current reactor designs. The ACR retains the modular concept of horizontal fuel channels surrounded by a heavy water moderator. However, ACR uses slightly enriched uranium (SEU) fuel and light water as coolant, compared to the natural uranium and heavy water coolant used in CANDU 6. This achieves the twin goals of improved economics (e.g., via reductions in the heavy water requirements and the use of a light water coolant), as well as improved safety. This paper presents the methodology used in developing two US-style Phenomena Identification and Ranking Tables (PIRTs)for selected ACR events and their results. One of the selected events is a large LOCA which is an ACR design basis event while the other is a severe flow blockage which is a beyond design basis event, and is classified as a limited core damage event under the new, proposed classification method. These PIRTs are based on a well-structured, expert elicitation process relying on the contribution of expert panels that involved designers, analysts, computer code developers and code validators. The paper outlines the design characteristics of the ACR reactor that impact the PIRTprocess and computer code applicability, lists all components and systems that have an important role during the event, and discusses the PIRT process and results.