Investigation into the Viability of a Passively Active Decay Heat Removal System In ALLEGRO Laura Carroll, Graduate Physicist Physics & Licensing Team, AMEC MSc Physics & Technology of Nuclear Reactors University of Birmingham

2 2 Countries we work in Introduction: My Project at a Glance  To assess a proposed modification of a safety feature of a new type of reactor  Use of RELAP5/MOD3  Steady State (normal operation)  Loss Of Forced Cooling (LOFC) transient (accident scenario)  ALLEGRO: experimental demonstration reactor for the Gas Cooled Fast Reactor

3 3  1 0f 6 designs chosen by Generation IV International Forum (GIF)  Fast spectrum  Helium coolant  High outlet temperature  High power density The Gas Cooled Fast Reactor

4 4 ALLEGRO

5 5 Residual Heat; the need for constant cooling post shutdown  Once a reactor is shut down, its power will fall to approximately 7% of full power and then reduces exponentially thereafter.  The Decay Heat Removal (DHR) system exists to remove this residual heat from the reactor core.  It is currently activated after a reactor trip by a valve sequence

6 6 Loss of Forced Cooling Transient: Existing Design  After 10s Blower begins to run down  The reactor is shut down  When mass flow rate reaches 3% of its original flow, main loop valve closes  Simultaneously, DHR loop valves open

7 Modification: Direct connection and Stratification of Upper Plenum

8 Stratification of the Upper Plenum

9 Stratification of the Upper Plenum: LOFC

10 Conclusions  Results are not ideal  Clad temperatures not as terrible as initially feared  Stratification of Upper Plenum showed great improvement on previous modifications  Substantial Potential for future Research and Development in this area

11 Further Investigations  Develop a removable Decay Heat Removal system heat sink  Add a fluidic diode

12 For more information… A Technology Roadmap for Generation IV Nuclear Energy Systems Dec 2002 U.S DOE Nuclear Energy Research Advisory Committee Vortex Diode Pumps: No Moving Part Pumping Systems, NuVision Engineering Thank you… Any Questions?

13 ParameterOriginalStratification core power (MW) Total mass system (Kg) pressure lower plenum (Pa) pressure upper plenum (Pa) core inlet temp (K) core outlet temp (K) Mass flow out of average channel (Kg/s) Max clad temperature hot channel (K) Max fuel temperature hot channel (K) DHR hot leg mass flow rate (Kg/s) DHR hot leg temperature (K) DHR cold leg temperature (K) Mass flow rate main heat exchanger (Kg/s) Total main heat exchanger flux Total DHR heat exchanger flux

14 1.Region of Blower run down 2.Establishment of Natural Convection 3.Natural Convection LOFC results