The goal of the project is to reduce uncertainties in assessment of (i) debris bed properties and coolability, (ii) steam explosion impact. To achieve the project goal, a collaborative experimental and analytical program is proposed by VTT and KTH. Experimental part of the project is responsible for investigation of key physical phenomena of the debris bed formation and coolability, and producing data for validation of simulation tools. Analytical approach will be utilized to improve prediction of coolability and to assess the uncertainties in modelling of steam explosion impact. Following tasks are addressed in the collaborative effort by VTT and KTH:
Task 1. Investigation of the effect of geometry on coolability in 2D debris bed
Task 2. Investigation of the effect of debris agglomeration on coolability
Task 3. Investigation of the effect of initial pool subcooling on coolability
Task 4. Investigation of particulate debris spreading
Task 5. Investigation of the effect of the heaters’ geometry on the DHF
Task 6. Feasibility studies for development of advanced instrumentation
Task 7. Joint analytical activity on debris bed coolability
Task 8. Analysis of steam explosion in a Nordic BWR containment
Summary of experimental and analytical work at KTH
In 2015 KTH will carry out experimental and analytical activities on debris bed formation and coolability. Joint analytical activity on debris bed coolability will include: code–to–code comparison, development of recommendations and best practice guidelines for simulations, defining reference cases for coolability analysis in plant accident conditions. Post-test analysis and code validation against COOLOCE data (Task 7). Investigations will be carried on particulate debris bed spreading in PDS-C tests, and on particulate debris spreading in a pool in the PDS-P tests (Task 4).
DEFOR-A series of tests with corium simulant material on debris bed formation (Task 2). MC3D and TEXAS-V codes will be used for comprehensive analysis of steam explosion in a BWR containment (Task 8).
Summary of experimental and analytical work at VTT
In 2015, VTT will focus on the post-test analysis of the COOLOCE experiments conducted thus far. A comprehensive assessment of the effect of the debris bed geometry on coolability will be performed based on the six debris bed geometries that have been addressed in the experiments in 2012-2014. The remaining tasks related to the validation and development of the simulation models and codes will be carried out. VTT will participate to the joint analytical activity on debris bed coolability including code–to–code comparisons, development of recommendations and best practice guidelines for simulations, defining reference cases for coolability analysis in plant accident conditions and code validation against experiments (Task 7).
VTT will also focus on the steam explosion task by using the MC3D code to analyze steam explosion in a BWR containment for different melt pouring scenarios and to clarify the effect of uncertainties in modelling (Task 8). Information exchange and comparisons of the results will be done with KTH.