FP7-Maxsima work package 2 "safety analysis in support of myrrha" main outcome and conclusions

The FP7-MAXSIMA project has been launched in November 2012, for a duration of 4 years. Among the different Work Packages (WPs), the WP2 aims at performing Safety Analysis in support of the MYRRHA reactor licensing process. The MYRRHA-related WP2 activities, divided in three Tasks, span through different fields. The Task 2.1 (Neutronic and shielding analysis) aims at defining the possible working range of the MYRRHA core, by supplying an important envelope for safety calculations and providing the neutronic parameters needed for the thermal-hydraulic safety studies. The 3-D Neutron Kinetics models used for MYRRHA core characterization are used to validate the neutronic models present in System Thermal-Hydraulics (STH) codes and multiphysics coarse mesh codes applied in other Tasks. Shielding analyses for the MYRRHA reactor in critical and sub-critical operational modes are also covered. The Task 2.2 (Transient analyses) working plan involves the use of STH codes (RELAP5 series, TRACE) in order to perform safety studies on the MYRRHA reactor. A wide list of scenarios characterizing the MYRRHA system have been investigated, resulting in a series of enveloping events to be analyzed through STH codes, focusing on inspecting the inherent safety characteristics, the decay heat removal functionality, the overcooling risk and the normal operation plant management risks. Task 2.2 also aims to quantify the uncertainty of crucial output parameters (e.g., fuel and clad temperature) against a number of input data, initial conditions, boundary conditions, correlations and coefficients. The Task 2.3 (Severe accident analyses) objective is to investigate MYRRHA core behavior under hypothetical severe accident conditions. Transients potentially leading to fuel pin failures, clad and fuel melting have been identified and then analyzed with the SIMMER code (multiphysics coarse mesh code). The focus lies on reactivity insertion transients and fuel assembly blockage. The core reactivity and related reactor power variations due to all major reactivity feedback effects, including relocation of core materials under accident conditions, have been assessed. In general, the WP2 analyses aim at the verification of the capability of the safety systems to bring the reactor to a safe shutdown state after a postulated accidental event. The studies will also provide the MYRRHA design team with an extensive set of feedback data to be used for further design advancements and improvements for what concerns robustness of the core and the whole plant. © 2016 Association for Computing Machinery Inc. All Rights Reserved.