Introduction: global GFR safety approach 1/2

1. Performance Assessment of Passive Gaseous Provisions (PGAP) - FRA 1Short description of the GFRPart of the slides presented during ICCAP’07 (May 2007, Nice, France)Authors : J-Y. Malo et al. (CEA/DEN/DER/SESI)

2. Introduction: global GFR safety approach 1/2 • Fuel Robustness • - high temperatures, nominal and accidental situations •  Use of ceramics with good thermal conductivity, able to withstand “adiabatic” conditions • Performance of monitoring and protection systems • - detection of fuel failure • - detection of core cooling failure, low pressure, low blower speed, excessive inlet/outlet core temperatures (He transparency)… • - detection of neutronic overpower, reactivity changes… • - reliable shutdown system (CSD, DSD) • - reliable DHR systems (redundant, diversified) •  Based on gas circulation, conduction & radiation (used in HTR) are no longer attractive (high core power density and very limited core thermal inertia)

3. Introduction, main reactor key design options 2/2 • Design • Nominal thermal-hydraulic conditions Fuel S/A (plate type)

4. DHR issue, selection of a strategy : , Fully passive mode, considering Hdriving = 15 m 1 25 bar 29 bar (for TinCore 480°C/TfuelMax 1600°C, Hdriving required : ~15 m) (38 bar) pressure (Bar) pressure (Bar) 5 kWe ~ 10 kWe Fully Fully passive mode (15 m) passive mode 7 bar 12 bar 2 5 ~ 50 kWe kWe Forced convection required during a long time (many months) Backup Backup 7 bar 5 bar ~ 1400 kWe 265 kWe 3 Forced Forced convection convection required required during during a a very very long time long time 1 bar 1 bar 3%PN (~ 5 mn) 0,6%PN (1 day) 75,00% 75,00% 125,00% 125,00% 175,00% 175,00% 225,00% Residual power (ANS+10% : %PN) TinCore = 330°C (480°C) TinCore = 330°C Tfuel < 1600°C Tfuel < 1600°C Based on gas circulation, 3 possible strategies: depending on the primary pressure (backup pressure if depressurization) : Option 2 selected for the design and the benchmark 1 High Pressure strategy (DHR under fully NC) : 30 bar required: concrete guard containment pressurized all the time => too heavy and costly solution Medium Pressure (DHR under mixed FC & NC) : 5-10 bar, metallic guard cont., not pressurized in NCs)=> moderate pumping power: “light” self governing systems Low Press. (DHR under FC only) : no guard cont. => high pumping power required 2 3

5. Main design options, reactor integration principle Guard containment & overall systems arrangement Guard containment spherical metallic structure, enclosing the primary systems Initially: N2, 1 bar Targeted back-up pressure: 5 -10 bar Reactor building, A reinforce concrete containment protection against external hazards includes heavy handlings means ultimate barrier

6. Main design options, DHR systems pool Secondary loop H2 Exchanger #1 Exchanger #2 Primary loop H1 core Guard containment Schematic of the DHR loop (inside the guard cont.): - Secondary pressurized water loop, under natural convection - Water pool as tertiary circuit

7. Main design options, 1st combination of possible systems Blower Blower , , with with batteries if batteries if Blower Blower needed needed (operating (operating (operating (operating under under under under 70 70 70 70 - - - - 5 bar 5 bar 5 bar 5 bar ) ) ) ) • Current reference • - 1st level systems: “light” forced convection systems • - 2nd level systems:possibility to rely on natural convection: • in short term for “high” pressure accidental situations • in a “reasonable” time ( 1 day), after LOCA Normal syst. Normal syst. Current systems specifications: Current systems specifications: Backup Backup syst. ( syst. ( necessity necessity to to be confirmed be confirmed ) ) (primary) (primary) ATM. ATM. press press : : NOMINAL NOMINAL press press : : LOCA: LOCA: small small vs vs large large - - med breaches med breaches (GC (GC depress depress 1 1 day day , , refuelling refuelling 1 1 week week ) ) ?  Transient Transient : 70 : 70 – – 5 bar, Final 5 bar, Final press press : 5 : 5 - - 10 bar 10 bar 70 bar 70 bar 1 bar 1 bar High High DH: DH: >1% >1% Alternative self Alternative self governing forced conv governing forced conv Natural Natural Benchmark : - 1 situation pressurized - 1 situation depressurized syst syst : : Turbopump with Turbopump with accu. ( accu. ( with with convection convection previously gas previously gas injection to injection to reach reach 10 10 bars OR bars OR wilful depress wilful depress if if needed needed ) ) ~1 ~1 day day Blower , with Blower Diesel or elec . . Low Low DH: DH: <1% <1% Natural Natural convection ( convection ( with previously gas with previously gas injection if injection if needed needed ) ) Transient Transient Various Various operation operation modes : modes :

8. Main design options, 1st DHR systems arrangement • 1st global DHR systems lay out, main components pre-sizing • - 1st systems level, “light” forced convection systems, blowers (+ case 1 bar): • 3 x Loop_X (each 100%) in blueand for case 1 bar: 1 x Loop_Y in yellow • - 2nd systems level:“light” forced conv. syst. & natural convection: • 1 x Loop_Y in yellow or 2 x Loop_X (each 100%) in blue, under natural conv. Blowers, 120 kWe, Axial mono stage, Multi  (5-70 bar) Natural convection (70 or 10 bar) H1er+2nd 20 m Blower-turbine or ejector, tbd , gas accumulator (10 bar) Blower, 300 kWe Radial, Multi  ? (1-5 bar) Guard containment

9. DHR systems evaluation, Cathare models CATHARE models : primary, secondary and a part of tertiairy circuits, and DHR systems