ERMSAR 2012, Cologne March 21 – 23, 2012 In-vessel retention as retrofitting measure for existing nuclear power plants M. Bauer, Westinghouse Electric Germany GmbH K. Knebel, European Commission, Joint Research Centre, Institute for Transuranium Elements D. Freis, Westinghouse Electric Germany GmbH

ERMSAR 2012, Cologne March 21 – 23, 2012 Introduction In-vessel melt retention (IVMR) concept : e.g. AP Principle: 1: oxidic melt layer, 2: metallic melt layer, 3: channel for cooling water, 4: reactor pit, 5: rising two-phase mixture, 6: separation of liquid phase and steam at the height of the primary coolant lines Source: Westinghouse Electric Company, AP1000 European Design Control Document, Chapter 39, Pittsburgh, 2009

ERMSAR 2012, Cologne March 21 – 23, 2012 ULPU tests Determination of Critical Heat Flux (CHF) for AP600 (ULPU-III, -IV) and AP1000 (ULPU-V) geometries ULPU-III: simple flow duct, ULPU-IV: improved flow duct ULPU-V: improved flow duct + optimized flow cross section Results: CHF in dependence of surface inclination of RPV 3

ERMSAR 2012, Cologne March 21 – 23, 2012 ULPU setups (left: -III, right: -IV) 4

ERMSAR 2012, Cologne March 21 – 23, 2012 ULPU results: Critical heat flux (CHF) 5

ERMSAR 2012, Cologne March 21 – 23, 2012 CHF and corresponding thermal power 6

ERMSAR 2012, Cologne March 21 – 23, 2012 Possible realization as retrofitting measure 7

ERMSAR 2012, Cologne March 21 – 23, 2012 MELCOR simulations Large PWR (~ 3750 MW) Adapted to simulate the IVMR-system Modified correlation for CHF 8

ERMSAR 2012, Cologne March 21 – 23, 2012 MELCOR simulations: Scenarios Base case: 10 cm 2 SBLOCA, with depressurization of primary side, flow rate 38.4 kg/s Variations: – Reduced flow rate – Without depressurization of primary side – Increased decay heat – 200 cm 2 LOCA – LBLOCA (2A-break) 9

ERMSAR 2012, Cologne March 21 – 23, 2012 Results: Base case – containment pressure 10

ERMSAR 2012, Cologne March 21 – 23, 2012 Results: Base case – number of layers of RPV wall below melt temperature 11

ERMSAR 2012, Cologne March 21 – 23, 2012 Results: Base case – experimental CHF compared to calculated maximum heat flux 12

ERMSAR 2012, Cologne March 21 – 23, 2012 MELCOR simulations: Results In all simulated scenarios: – IVMR worked well:  No RPV failure  No venting of containment necessary Details of modelling and results of simulations can be seen in paper to this presentation. 13

ERMSAR 2012, Cologne March 21 – 23, 2012 Summary – The feasibility of retrofitting IVMR in large PWRs was analyzed, based on the results of the ULPU experiments. – A MELCOR model of a German plant was modified to model an IVMR based on gravity driven flow from the spent fuel pool and pump driven injection to the RPV cavity. CHF correlations of MELCOR were modified to reflect the results of the ULPU experiments. – MELCOR simulations of several severe accident scenarios were performed: In all simulations the melt could successfully be retained in the RPV. – “Take home” message: The simulations showed the usefulness and feasibility of such a retrofit. 14

ERMSAR 2012, Cologne March 21 – 23, 2012 Further work: Physical: Further work should investigate the effect on CHF of forced convection as proposed for the retrofitting in contrast to natural convection as used in the ULPU experiments. Technical: From a practical point of view the possibilities of installing a suitable flow duct in the reactor pit have to be examined, along with the development of appropriate installation procedures and tools (manipulators). 15