In this project our group was much more involved from the beginning than in SARNET one, since we signed with a project with the same name at the national level, which provide services for the design and development of both the tools and the practical application. This project started due to the interest of CSN to develop a safety margins action plan (SMAP) due to new challenges as; increases in power, life extension or fuel burn involving a challenge for maintaining safety margins requirements of regulatory agencies. These changes could lead the plants near or even beyond the base design limits. New methodologies able to study these problems in an integrated manner should be developed.

ISA methodology and SCAIS are precisely designed to perform such studies in a systematic way and being able to perform a detailed analysis in a much faster way than other methods.

One of the strengths of SCAIS is to be coupled to a “fast-running” integral plant code  as MAAP, where simulations last minutes. The result can be considered qualitatively and if necessary a more detailed study can be developed in the area having problems. There were several accidents that were studied during the course of the project, our group studied a Loss of Auxiliary Feed Water followed by a Seal LOCA.

Five headers were considered from the PSA analysis where the most important ones were analyzed. The Dynamic Event Tree (DET) generated with SIMPROC is studied with SCAIS-MAAP where the operator performed the recovery of SIS (Safety Injection System, High-and Low Pressure Safety Injection) and manual cool down and depressurization of the primary system by means of Steam Generator (following the corresponding EOPs) . They were the stochastic events considered. The accumulators inyection systems was considered a deterministic event.

During the design problem to be simulated, several concepts underlying the TSD and not considered in SARNET appeared as auxiliary stimuli.

In this case it was clear that although security systems are deterministic, they can not be operated until water supply recovery. Concepts began to appear as the previous damage ( area of no return, no matter where they enter systems because it has already achieved some of the defined damage) and the Damage Domain. The evolution of SCAIS was the design and development of component paths for analysis, validation of the Risk Assessment component responsible for the analysis of transient damage generated during the analysis.

SM2A exercise

This application were developed in the framework of the Nuclear Energy Agency project on Safety Margin Assessment and Applications (SM2A). The Damage Domain area of a selected sequence from a loss of Component CoolingWater with a subsequent seal LOCA was calculated. Uncertainty actions were considered:

  1. SG:     Manual cooldown by means of Stem Generator.
  2. RCV:  Recovery of safety injection system, HPSI & LPSI.

The safety variable Peak Clad Temperature (TCRHOT in MAAP code)  shows which simulations leads to core damage and which do not (PCT > 1500 K).

The results achieved shown how the system can be adapted to a wide range of purposes such as Dynamic Event Tree delineation, Emergency Operating Procedures and Damage Domain search.

Simulation results