EUROTRANS – DM1 Preliminary Transient Analysis for EFIT Design WP5.1 Progress Meeting AREVA / Lyon, October 10-11, 2006 G. Bandini, P. Meloni, M. Polidori Italian Agency for new Technologies, Energy and Environment, Advanced Physics Technology Division Via Martiri di Monte Sole 4, Bologna, Italy

Capability to treat global system behavior coupled with dynamic core response in transient conditions Investigation of whole spectrum of accidental scenarios DBC and DEC conditions ( no severe conditions) Main differences respect to PDS-XADS to address code upgrading and activity planning: Lead instead of LBE as a coolant Large positive reactivity potentials without prompt Doppler Preliminary investigation of safety issues to support core design Transient Analysis with RELAP5/PARCS Planned Approach AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Preliminary thermo-hydraulic simulation of EFIT core and primary circuit Primary circuit lay-out: set of data drawn from ANSALDO presentation “Progress on Design” given at DM1 meeting in Mol (20-21 June 2006) Decay Heat Removal system: further information on provided in September by ANSALDO Core Design: Two-zone core studied by ENEA according to the approach presented in the Mol meeting AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Power [MW]390.Total Pressure Drop [mbar]560 Lead Flowrate [kg/s] Power Normal Operation [Mw] Power DHR Operation Mw] 1 20 Core inlet Tempetature [°C] Core outlet Tempetature[°C] DHR Lead Inlet Temp. [°C]451 Natural Circulation High [m]2.5DHR Lead Outlet Temp. [°C]408 Core Pressure Drop [mbar]350DHR Lead Flow Rate [kg/s]1074 Primary Circuit and DHR Main Parameters

AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting Two Zone Core Main Parameters Thermo-hydraulic conditions Pin geometry Inner/Outer Power [MW th ]100.2/289.8 Inner/Outer Fuel (MgO/ MgO+Fuel %) CERCER 0.625/0.50 In/Out Av. Linear Power [W cm -1 ] In/Out Max. Linear Power [W cm -1 ] 138./ /183.4 In/Out Pin Diameter [mm] 8.72 In/Out T inlet [°C] In/Out T outlet [°C] In/Out Pellet Diameter [mm] 7.2 In/Out Radial Form Factor In/Out Axial Form Factor 1.29/ / In/Out Active length [cm] 90 In/Out Mass Flowrate [t s -1 ] 8.14/24.3Gap thickness [mm]0.16 In/Out coolant velocity [m s -1 ]~1.0Clad thickness [mm]0.6 In/Out Core pressure drop [mbar]350Pitch [mm]13.63

AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting Inner and Outer core simulated: average pin for average and hot SAs modelled with 12 axial nodes to simulate axial and radial power distribution Average and hot channel for Inner and Outer core with equivalent flow area coupled with corresponding pins Outer channels chocked to correctly distribute mass flowrate CERCER Fuel properties for Inner (50%MgO 50%MOX) and Outer (60%MgO 40%MOX) from Sobolev Report Cladding conductivity from Sobolev Report (T91 steel) Gap conductivity tuned with SIM-ADS code Lead heat transfer coefficient Subbotin correlation RELAP5 Model of EFIT Core

AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting Lead mass inventory distribution and major flow paths represented Primary pumps simulated by means of time dependent junction to impose forced flow + parallel flow path with check valve to allow natural convection Steam Generators primary (shell) and secondary side (tubes) completely modelled Boundary conditions for secondary loop Target loop not simulated DHR system simulated by imposing flow path and removed power (as a function of Lead Inlet Temperature) RELAP5 Model of EFIT Primary Circuit

AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting RELAP5 Nodalization Scheme

RELAP5 Calculations Steady state calculation at nominal conditions: 100% Power and Mass Flowrate, SGs nominal capability, DHR low capability, BOC conditions Transient to Unprotected Loss of Flow: 100% Power, Natural Circulation, SGs full capability, DHR low capability, BOC conditions Transient to Decay Heat Removal: Decay Heat Curve, Natural Circulation, no SGs, DHR (3 loops of 4) nominal capability, BOC conditions AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Nominal Conditions Steady State Fuel in Inner and Outer hot SAs has very similar performances: peak fuel temperatures lower than dissolution limit for CERCER (1327 C) Peak cladding temperature in Outer hot SA has a worse situation exceeding of a few degrees the corrosion limit assumed for coated T91 clad (550 C) Main limit of the calculation: hot pin not simulated Possible actions to decrease peak clad Temperature: decrease core temperature drop, flatten radial neutronic flux distribution (eg. 3 zones core), distribute mass flowrate proportionally to linear power within Inner and Outer core (choking schemes) AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Steady State at Nominal Conditions AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting INNER ZONE (Fax = 1.143)OUTER ZONE (Fax =1.133) Max Temperature (°C) Hot FA 1/48 Fr = 1.29 Average FA 47/48 Hot FA 1/174 Fr = 1.45 Average FA 173/174 Central Fuel (*) Surface Fuel (*) Internal clad (**) External clad (**) Lead (**) * At max linear power elevation ** At max core elevation

Nominal Conditions – Inner Zone AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Nominal Conditions – Outer Zone AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Transient to ULOF Conditions ULOF conditions achieved with a sudden stop of pumps (<1s) and simultaneous opening of valve on natural flow path Minimal flowrate of 20% calculated in passing from forced to natural circulation (peak clad temperatures 728 °C and 749 °C in Inner and Outer hot SA) Stable natural convection flowrate of 41% maintains peak clad temperature < 700 °C Main limits of the calculation: pump characteristic have important effect on early part of transient, rough estimation of the primary circuit pressure drop (no pressure drop through pumps), possible increase of power due to positive temperature feedback not considered AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

ULOF transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

ULOF transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

ULOF transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

ULOF transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

ULOF transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

Transient to DHR Conditions DHR conditions achieved with an nearly instantaneous closure of SGs feeding, a sudden stop of pumps (<1s) with a simultaneous opening of valve on natural flow path and decay heat curve setting Stable natural convection attained quickly in the DHR exchanger so removed power matches decay heat, oscillatory behaviour of the core mass flowrate due to alternative flow path through downcomer in counter-flow conditions Peak clad temperatures remain limited during all transient Main limits of the calculation: starting of the natural convection depending on transient scenario and pumps characteristics, natural convection paths in DHR circuit are arbitrary in 1-D model (to be set up on multi-D evaluation) AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

DHR transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

DHR transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting

DHR transient AREVA Lyon October 10-11, EUROTRANS – DM 1 - WP 1.5 Progress Meeting