Development of Phenomena Identification and Ranking Tables for the Advanced CANDU Reactor

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 the current reactor designs. The ACR retains the modular concept of horizontal fuel channels surrounded by a heavy water moderator, as with all CANDU reactors. However, ACR uses low enriched uranium fuel, compared to the natural uranium 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 approach used in developing two phenomena identification and ranking tables (PIRTs) for selected ACR-700 events and their results. One of the two selected events is a large loss-of-coolant accident, which is an ACR design basis event, while the other is a severe flow blockage, which is proposed to be classified as a limited core damage event (beyond design basis event). The paper outlines the design characteristics of the ACR-700 reactor that impact the PIRT process and computer code applicability, lists all components and systems that have an important role during the event, discusses the PIRT process and results, and presents the finalized PIRTs. The ACR-1000 reactor design is currently in detailed design at AECL, and it retains similar design features as the ACR-700 design. Although the PIRTs presented in this paper were developed for the ACR-700 design, they are generally applicable to the ACR-1000 design.