Gas Cooled Fast Reactors: recent advances and prospects

Transcription

1 Gas Cooled Fast Reactors: recent advances and prospects C. Poette a, P. Guedeney b, R. Stainsby c, K. Mikityuk d, S. Knol e a CEA, DEN, DER, F Saint-Paul lez Durance, CADARACHE, France. b CEA, DEN, DEC, F Saint-Paul lez Durance, CADARACHE, France. c AMEC Knutsford UK d PSI Villigen Switzerland e NRG Petten Netherlands FR13 Conference, Paris, March 2013 C. Poette, CEA, FR13 Conference, Paris, P. GUEDENEY March 2013P. CEA GUEDENEY CEA 22 Novembre 10 AVRIL CEA PAGE 1 Novembre 2012

2 Gas Cooled Fast Reactors: contents Contents 1) Introduction 2) GFR fuel element 3) Core design optimization 4) System Design 5) Safety Aspects 6) GFR R&D Program 7) Conclusion PAGE 2

3 Gas Cooled Fast Reactors: Introduction GFR : a longer term option allowing to combine Fast spectrum & Helium coolant benefits Safety (Helium coolant) No threshold effect due to phase change, no void reactivity effects, no chemical reaction Optical transparency: potential for In Service Inspection, Temperature measurement capabilities Competitiveness High temperature potential for: - High energy conversion efficiency (45-48%) - A broad range heat industrial applications (process heat, hydrogen, synthetic hydrocarbon fuel production) 850 C 400 C He 70bar 820 C He-N2 65bar 362 C 565 C 535 C 178 C H2O 150bar Electrical grid 32 C Fuel management (fast spectrum) Efficient use of natural resources: Pu generation Potential for ultimate waste minimization: multi-recycling of all actinides PAGE 3

4 Gas Cooled Fast Reactors: Introduction The GFR concept is: Very innovative: no demonstrator has ever been built Challenging : high power densities of FRs and poor cooling capacities of gases (The Helium coolant must be pressurized in normal operation to achieve sensible in core gas velocities with reasonable pumping power) Two major issues The design of a high temperature fuel element, able to retain integrity in case of loss of forced cooling accident, to withstand high fast neutron fluxes, and offering good neutronic performances, Safety and decay heat removal in case of loss of helium pressure Development roadmap the target commercial electricity generating reactor (~ 2400 MWth) and its fuel a moderate power demonstrator, ALLEGRO (< 100 MWth) without electricity generation as a necessary step towards an electricity generating prototype before series production of commercial reactors : MOU signed by Hungary, Czech Republic, Slovakia (2010) and Poland (2012) PAGE 4

5 Gas Cooled Fast Reactors: Fuel element A fuel based on high thermal conductivity and refractory materials: (U, Pu)C & reinforced ceramic composite clad (SiC) Cold operating clad/fuel temperature: 1000/1300 C (margins / accident; favourable thermal-mechanical behaviour) Boundary accidental clad T (DBA, 4th cat.): 1600 C/< a few hours (FP confinement function, 1st barrier) Ultimate accidental clad T (SA prevent.): 2000 C/ < some min?, (no loss of geometry, to keep the core cooling capacity) Fuel element concepts : honeycomb plate and pin type PAGE 5

6 Gas Cooled Fast Reactors: Fuel element Although the plate type concept is attractive, fabrication difficulties appeared which lead to focus first on the more classical pin concept a ceramic matrix composite cladding comprising a sandwich of SiC cladding and a thin internal metallic liner to ensure the leak tightness of the pin, a buffer, porous carbon structure placed between the pellet and the cladding allowing higher heat exchanges and moderate clad/pellet mechanical interaction. PAGE 6

7 Gas Cooled Fast Reactors: Core design optimization Main core characteristics Closed sub-assemblies (hexagonal wrapper tube) Pin lengths limited to 1.50m (transport, handling, fabrication considerations): the total fissile length is made of 2 half pins Power : 2400 MWth, power density : 100 MW/m 3 (to limit the Pu inventory) Self-sustainable core (zero breeding gain) Low core pressure drop (favoring natural circulation capacities) ~ 1.45 bar Pu enrichment 16.3% at equilibrium PAGE 7

8 Gas Cooled Fast Reactors: Core design optimization Current core design optimization process Numerous iterations Optimisation MSPu cycle 5,0 Mathieu Référence FARM : a new tool Coupling the different domains to optimize both core performances and safety characteristics Moyenne acc nonprotégé Pint max 4,0 3,0 2,0 1,0 0,0 Diamètre cœur MRPu Puissance de pompage Tsursis Illustration of core performance parameters and safety indicators for the Mathieu core vs the reference core PAGE 8

9 Gas Cooled Fast Reactors: System design Energy conversion and primary circuit arrangement Indirect combined cycle: He-Gas with a tertiary steam cycle Primary/secondary arrangement: 3 x 800 MWth (IHX-blower unit), gas turbomachineries (auxiliary alternators: 3 x 130 MWe) Tertiary: 1 steam turbine (main alternator 730 MWe) 850 C He 70 bar 820 C He-N2 65 bar 565 C 535 C H2O 150 bar 2 nd pipes with isolating valves prim. isolating valve 400 C 362 C 178 C 32 C Electrical grid Prim. cross-duct blower and motorization High efficiency (~ 45%), compactness of the primary circuit, decoupling of The Nuclear island from power conversion& heat applications PAGE 9

10 Gas Cooled Fast Reactors: Safety aspects Decay heat removal relying on gas circulation in the Primary circuit Using at first normal circuits operated in forced or natural circulation Using dedicated DHR loops operated in forced or natural circulation PAGE 10

11 Gas Cooled Fast Reactors: Safety aspects Integration of primary system and DHR loops in the close containment RHP, blower (0.4-7 MPa) axial mono stage, Ptot < 500 KWe RHP, natural convection capability H1 st + 2 nd 20 m RLP, blower ( MPa) radial or axial technology 3 MWe Close containment Provisional conclusions Encouraging potential of the reactor system (about 50 Initiating events + aggravating events considered) Design improvements are nevertheless recommended to cover some very hypothetical situations like «loss of energy supply combined with failure of the primary circuit reconfiguration» PAGE 11

12 Gas Cooled Fast Reactors: Design improvements Still various open innovative design options Reactor system design: Coupled cycle option (improved grace time in case of large LOCA, less demanding in terms of backup pressure i.e potential suppression of the close containment) Principle scheme of the indirect coupled cycle: the primary circulator is mechanically coupled to the secondary circuit turbo-machine PAGE 12

13 Gas Cooled Fast Reactors: Design improvements Still various open innovative design options DHR system design: the concept of autonomous Brayton cycle for DHR is promising; it should be incorporated in the existing DHR architecture as an extra protection line in the prevention of severe accidents. Principle scheme of the autonomous DHR loop: the primary gas circulation is ensured by a small turbo machine driven by the residual heat of the core PAGE 13

14 Gas Cooled Fast Reactors: R&D program Large R&D needs for the future Fuel and core materials The use of a ceramic material implies to adapt a specific codes & standards approach, connected to appropriate tests and modelling, The SiC behavior in accidental situations must be fully characterized, Beyond the cladding, it is necessary to find solutions for the encapsulation of the pins, these studies being at a very early stage, A program of irradiation of components and of qualification of fuel elements is, of course, also necessary. Helium technology Development of individual components and systems (fuel handling, thermal core instrumentation, compressors able to work in large pressure ranges, valves, check-valves, compact gas/gas heat exchangers, gas quality management, thermal barriers ) use of existing Helium loops demonstration that these components and systems are able to work together especially for the safety demonstration. This requires large helium loops which need to be constructed at mid term. PAGE 14

15 Gas Cooled Fast Reactors: Conclusion GFR : an attractive longer term option allowing to combine Fast spectrum & Helium coolant benefits Innovative SiC fuel cladding solutions were found A first design confirming the encouraging potential of the reactor system Design improvements are nevertheless recommended and interesting tracks have been identified (core & system design, DHR system) The GFR requires large R&D needs to confirm its potential (fuel & core materials, specific Helium technology) ALLEGRO prototype studies are the first step and are drawing the R&D priorities PAGE 15