EFIT (PB) - Design and Preliminary ULOF(ss) Analysis M. Schikorr, D. Struwe (FzK)

EFIT (PB) - Design and Preliminary ULOF(ss) Analysis M. Schikorr, D. Struwe (FzK) • EUROTRANS: DM1 WP1.5 : “Safety” • Lyon , 10-11 October 2006 EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

Topics: • Design Criteria for EFIT (Pb) 2. EFIT (Pb) design Data for Transient Analysis 3. Some EFIT (Pb) results to the ULOF transient EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

1. Some important thermohydraulic EFIT Design Criteria: 1. Use MgO as fuel matrix for the MA-based fuel • Assure an optimal MA burning rate • Operate the system as a sub-critical system (k_eff ~ 0.95 - 0.97) • Account for the relatively low fuel temperatures allowable T_fuel_max < 1600 °C 5. Also use T91 as clad material (as of now). 6. Design core and primary system in such a manner to allow sufficient natural convection flow rate to survive a ULOF transient for at least 30 minutes without „large number“ of pin failures (via gas blowout) EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

EFIT ULOF Design Criteria requires : Assure a sufficiently large natural convection flow rate ( > 25 % nominal flow) under ULOF conditions. This implies : 1. keep pressure drop across the core „low“ (~<0.5 bar) by selecting an appropriate fuel pin / subassembly design 2. minimize pressure losses throughout the primary / DHRS system such that total system pressure loss <~ 0.8 bar 3. assure a height differential between the core midplane and the heat sink midplane of ~ 3.7 m EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

Several EFIT design iterations were performed : Option 1 : • Assume a constant fuel matrix (i.e. 50% MgO) and vary the fuel pin / sub-assembly design in the two core zones in order to flatten the power profile. Several variations in pin diameters and sub-assembly sizes were tried but it was difficult to achieve a satisfactory radial power distribution without excessive radial form factors. Option 2: Assume a uniform geometric pin / SA design for the two core zones but vary the fuel matrix composition. ENEA / ANSALDO decided for Option 2 with the following design : EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

EFIT (Pb) Design Data used: Inner Core Zone CZ1, Fuel 62.5% MgO EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

EFIT (Pb) Design Data used: Outer Core Zone CZ2, Fuel 50% MgO EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

EFIT (Pb) Fuel Design: Inner and Outer Core Zones Source : D1.6 Draft Sept.2006 Source : D1.6 Draft Sept.2006 Source : V. Sobolev Sep. 2006 EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

EFIT (Pb) Data : Inner Core Zone CZ1 EFIT (Pb) Data : Outer Core Zone CZ2 EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

Nominal Conditions Inner Core Zone at BOC : EFIT (Pb) Source : D1.6 Draft Sept.2006 EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

Nominal Conditions Outer Core Zone at BOC : EFIT (Pb) Source : D1.6 Draft Sept.2006 EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

Nominal Conditions Inner Core Zone at EOL : EFIT (Pb) Note that peak clad temperatures exceed 500 °C requiring „coating“ of the T91 clad material. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

Nominal Conditions Outer Core Zone at EOL : EFIT (Pb) Note that peak clad temperatures exceed 500 °C requiring „coating“ of the T91 clad material. There is not much margin to the temperature limit of coated T91 of ~ 550 °C !! Note: Hot spot analysis still pending EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

ULOF (ss) Inner / Outer Core Zone at BOC and EOL : • Natural Convection flow rate of EFIT under ULOFss conditions ~ 43 % !! (much higher than the ~ 25% for XT-ADS) • This leads to lower T91 cladding temperatures ( < 700 °C ) for EFIT (Pb) in comparison to XT-ADS ULOFss temperatures ( 790 – 800 °C ) EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

ULOF (ss) Inner / Outer Core Zone at BOC : Pgas =~10 bar Pgas =~10 bar Clad failure not an issue at these clad temps. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

ULOF (ss) Inner / Outer Core Zone at EOL : Pgas = 178 bar tent. Pgas = 178 bar tent. Clad failure not an issue at these clad temps. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

1.) From the TH point of view the current EFIT(PB) design as proposed by ENEA / ANSALDO is quite viable assuming the cladding is „coated“ as clad temperatures exceed 500 °C under nominal conditions. 2.) The calculations thus far have not assumed a form factor to account for the peak pin within the hottest subassembly (f_peak_pin should be ~ 1.04 instead of 1.0 as has been assumed). This will lead to even higher cladding temperatues of the peak pin, possibly in excess of 550 °C. Conclusions on current EFIT (Pb) TH – design (1/2) : EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

3.) Under ULOF steady state conditions at EOL clad failure times are in excess of 1000 hrs as clad temperatures remain below 700 °C MgO fuel temperatures also remain below 1430 °C ( a limit of ~1500 °C was decided not to be exceeded ) 4.) The design exhibits excellent natural convection characterisitics with w_nat ~ 45 % under ULOF conditions ( low pressure losses < 500 mbar ) 5.) The ULOF transient behavior of the design still needs to be analysed in detail Conclusions on current EFIT (Pb) TH - design (2/2): EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

EFIT (PB) - Design and Preliminary ULOF(ss) Analysis M. Schikorr, D. Struwe (FzK)