Synthesis on plant calculations (D35), Final COLOSS report : Part 2

B. Adroguer, JP. Van Dorsselaere, N. Alpy, S. Pignet, (IRSN/SEMAR), Bellenfant, B. Chaumont (IRSN/SEAC), G. Azarian, A. Caillaux (FRA-ANP-SAS), H. Plank (FRA-ANP-GmbH), G. Bandini (ENEA), J. Birchley (PSI), W. Hering, G. Schanz (FZK), S. Marguet (EDF), E. Virtaneen (LTKK), Y. Zvonarev, V. Kobzar (KI), Rapport technique SAM-COLOSS-P080, DRS/SEMAR 03/30, juin 2003

The eleven partners of the COLOSS project involved in plant calculations (WP8) form the Plant Analysis Group (PAG) co-ordinated as a stand-alone project by IRSN and Framatome-ANP SAS. The specific objectives were: 

• to assess the ability of severe accident codes to calculate the core degradation and the related gas production, in particular those resulting from the degradation of B4C control rods, 
• to identify the needs for improvement and give recommendations for future code developments, 
• to evaluate safety challenges of selected sequences using results produced by the project.

The main European plants using B4C material were investigated, focussing on the impact of B4C on selected severe accidents (SA) sequences. Some partners were also involved in the calculation of the TMI-2 accident. Mainly the core and, to a lesser extent, the primary circuit were considered in these calculations.
The main SA codes in use in the EU could be assessed, in particular the integral codes ASTEC, MAAP4, MELCOR and the more mechanistic ones ICARE/CATHARE and SCDAP/RELAP5.

The work plan involves three stages:
1/ At the beginning of the project, a 1st set of calculations was performed for key SA sequences selected to promote large core degradation. For this, the input decks were harmonised in order to facilitate code assessment and possible comparisons.
2/ Afterwards, codes were improved using, in particular, experimental results and models produced by the project,
3/ At the end, improved codes were run again (2nd set of calculations) to assess the effect of code improvements on predictions and evaluate safety implications of results.

The following table summarises the plant calculation Work Package 8 (WP8) of the project.

The Plant Analysis Group made a large series of SA plant calculations running main codes in use in the EU. During the 2nd set of calculations performed with improved codes, sensitivity studies and code-to-code benchmarks enabled a more general assessment of codes to calculate core degradation and code uncertainties on B4C-gas, H2 total and rate production and corium formation were evaluated.

This report gives a summary of the plant calculations carried out in the work-package 8 (WP8) and main conclusions.