1. ERMSAR 2012, Cologne, March 21 – 23, 2012 Hydrogen Stratification in Experimental Facilities and PWR Containments – Results and Conclusions of Selected COCOSYS Simulations S. Schwarz, S. Band, M. Sonnenkalb GRS Germany

2. ERMSAR 2012, Cologne, March 21 – 23, 2012 – During a severe accident hydrogen (H 2 ) could be generated in the reactor coolant system (RCS) – In case of a release at an elevated position in the containment -> atmospheric stratification -> high H 2 concentrations above and low H 2 concentrations below the release position – Stratification can be dissolved by different processes – H 2 distribution in containment -> flammability – Experiments, COCOSYS validated: THAI, PANDA, HDR E11.2 – PWR application by COCOSYS 2

3. ERMSAR 2012, Cologne, March 21 – 23, 2012 HDR containment COCOSYS nodalisation 143 nodes inclusive annular compartments and gap E11.2 experiment 0 – 12.5 h: upper steam injection 12.32 – 12.87 h: H 2 /He injection 12.88 – 16 h: lower steam injection 16.25 – 20 h: spraying upper hemisphere after 20 h: natural cooldown, venting 3

4. ERMSAR 2012, Cologne, March 21 – 23, 2012 4 H2/He concentrations experiment, COCOSYS injection phase Hydrogen stratification Light gas cloud (H2/He, air steam) in upper region

5. ERMSAR 2012, Cologne, March 21 – 23, 2012 5 H 2 /He concentrations experiment and COCOSYS during lower steam injection and 1st part of spraying -Concentrations at different elevations -Same elevation -> same color for COCOSYS and experiment Hydrogen stratification in dome Contraction of light gas cloud Simulated by COCOSYS Contraction accelerated during spraying

6. ERMSAR 2012, Cologne, March 21 – 23, 2012 6 H 2 /He concentrations experiment and COCOSYS 2 nd part of spraying and remaining test Mixing of atmosphere Partial dilution of stratification by outside spraying Simulated by COCOSYS

7. ERMSAR 2012, Cologne, March 21 – 23, 2012 7 PWR containment steel shell diameter 56 m equipment compartments separated by doors and rupture elements from rest of containment Passive Autocatalytic Recombiner (PAR) concept with ~60 devices COCOSYS nodalisation: 281 zones inclusive annular compartments and gap

8. ERMSAR 2012, Cologne, March 21 – 23, 2012 8 Core melt scenario “ND*” Loss of SG-feed No ECCS available Release from RCS/Prz. at an elevated position Main events:  1.4 h start steam release from RCS/Prz.  2.2 h start H 2 release from RCS/Prz.  6.4 h start release by MCCI in cavity  17.1 h start melt - sump water contact

9. ERMSAR 2012, Cologne, March 21 – 23, 2012 9 Hydrogen concentrations dome and equipment compartments Hydrogen generation in equipment compartments, difference to E11.2 Mixing of dome, combination of heat sinks and sources, difference to E11.2 Hydrogen stratification in equipment compartments

10. ERMSAR 2012, Cologne, March 21 – 23, 2012 10 Hydrogen concentrations dome and compartments behind missile protection Hydrogen stratification behind missile protection

11. ERMSAR 2012, Cologne, March 21 – 23, 2012 11 Summary, conclusions – COCOSYS was validated successfully against several stratification experiments; here the example HDR E11.2 was shown.. – A hydrogen release at an elevated position can create an atmospheric stratification – high hydrogen concentrations at and above the release position an low concentrations below. – Same for experiments (f.e. HDR E11.2) and the PWR calculation. – PWR in addition: stratification behind missile protection. – The dilution of the stratification as observed in E11.2 cannot be compared with the PWR calculation because the boundary conditions differed strongly between both cases.