Nuclear Technology / Volume 171 / Number 1 / July 2010 / Pages 14-26
Technical Paper / Reactor Safety
This paper presents a model of the Atucha Unit II pressurized heavy water reactor nuclear power plant (currently in the final construction stage) developed in RELAP5/MOD3.3. The nodalization was implemented in order to comply with the probabilistic safety analysis required in the licensing, commissioning, and operating process.
The reactor is cooled and moderated by heavy water. Though the primary circuit is equivalent to a two-loop pressurized water reactor, the reactor core consists of vertical channels surrounded by a relatively large volume of heavy water acting as a moderator. This moderator is cooled by an independent system and kept at the same pressure but lower temperature than the primary circuit.
The relevant components and systems of the plant are presented and nodalized. The main characteristics of the plant are discussed to achieve a correct representation of the expected physical behavior. Additionally, an integral platform of data management is implemented that processes the geometric and physical data for nodalization and finally generates the code input. Then, a complete tracking of data is possible from the corresponding referenced report to the input deck. This tool facilitates the quality assurance process by independent reviewers. Moreover, the verification of sources and documentation employed can be easily implemented.
Initially, the steady state is analyzed by comparing variables obtained with the model with their respective design values and previous calculations performed with other models. Finally, a case of loss of heat sink caused by an electrical supply failure is analyzed. Relevant aspects of the plant dynamic are analyzed and presented for this case. The standard procedure established in the plant to tackle this initiating event is also discussed considering the triggered signals and the configurations of the main systems.