THE LEVEL 1 PROBABILISTIC SAFETY ASSESSMENT
APPLICATION OF TR-2
In recent years, probabilistic safety assessment has acquired increasing importance. Most of the regulation authorities encourage greater use of this analysis technique to improve safety related decision making and regulatory efficiency.
This study is based on an independent, comprehensive and systematic safety evaluation of the Turkish Research Reactor-2 (TR-2). The probabilistic safety assessment (PSA) has been considered for full power state of the reactor. The TR-2 PSA represents a Level 1 analysis, and was constructed using Systems Analysis Programs for Hands-on Integrated Reliability Evaluations (SAPHIRE). SAPHIRE is a PC-based general purpose tool for performing PSAs (INEEL). It is specifically designed to permit a listing of the potential accident sequences, compute their frequencies of occurrence, and assign each sequence to a consequence. SAPHIRE consists of several modules for fault tree analysis, event tree analysis, and for developing and maintaining component failure rate, and maintenance data.
The TR-2 PSA systematically identified and quantified the frequency of scenarios involving core damage by plant specific data. Scenarios resulting from excess reactivity insertion, loss of flow, flow blockage, loss of coolant, loss of off-site power, super prompt criticality, and earthquake initiating events were analyzed. The resulting total core damage frequency of TR-2 based on the actual time of operation is found ten times higher than the acceptance criteria issued by IAEA for existing plants. Even though this is not a mandatory safety limit, some improvements would be beneficial towards increased safety.