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Temperature Limits for XT-ADS Clad Material T-91 M. Schikorr D. Struwe (FzK)

Temperature Limits for XT-ADS Clad Material T-91 M. Schikorr D. Struwe (FzK) EUROTRANS: DM1 WP1.5 : “Safety” Lyon , 10-11 October 2006. Topics:. Lower Temperature Limits of T-91 Clad Material under Nominal Conditions

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Temperature Limits for XT-ADS Clad Material T-91 M. Schikorr D. Struwe (FzK)

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  1. Temperature Limits for XT-ADS Clad Material T-91 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

  2. Topics: • Lower Temperature Limits of T-91 Clad Material under Nominal Conditions 2. Upper Temperature Limits of T-91 Clad Material under Nominal Conditions 3. Temperature Limits of T-91 Clad Material under Transient Conditions EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  3. 1. Lower Temperature Limit of T-91 under nominal plant conditions: See DEMETRA presentation to this issue by Janne Wallenius • There appears to be a lower temperature limit due to EMBRITTLEMT isssues • There are recommendations to keep T-91 > 325 °C DEMETRA recommendation: Del 4.1: Tinlet = 350 °C DTcore = 80 °C EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  4. 2. Upper Temperature Limit of T-91 under nominal plant conditions: • To avoid CORROSION of T-91 one should keep the upper clad temperature < 500 °C 2. FeAl alloy COATING by GESA treatment will improve corrosion resistance and the upper temperature limit increased to about 550°C (L. Mansani). 3. No „coating“ requires that the nominal maximum cladding temperature of the peak pin should be below ~ 490 °C to provide margin to account for hot-spot analyses results. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  5. Implications on the XT-ADS Design : Nominal Conditions 1. Accepting the SPIRE and DEMETRA recommendations leads the core inlet temperature to be : T_in ~ 330 °C • No „coating“ requires that the maximum cladding temperature of the peak pin should be T_clad_peak~ 480 °C. • Allowing for a temperature drop of ~ 23 °C between cladding and coolant for the peak pin at the core outlet (peak clad temp), and • Using a radial form factor of 1.375 for the XT-ADS requires that the heat up of coolant across the core is limited to: DT_core = (480 - 23 – 330) / 1.375 = 92.4 °C We have select : DT_core = 90 °C EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  6. Contraints on the XT-ADS Design : Nominal and Transient Conditions 1. Under nominal conditions abide by the temperature limits stated above, 2. Assure a sufficiently large natural convection flow rate to „survive“ an unproteced loss of flow transient (ULOF) : minimize pin clad failure This implies : 1. keep pressure drop across the core „low“ (~<0.75 bar) by selecting an appropriate fuel pin / subassembly design 2. minimize pressure losses throughout the primary / DHRS system such that total system pressure loss <~ 1.0 bar 3. limit the fission pressure gas buildup at EOL to ~ 50 bar to assure pin integrity under ULOF conditions. This implies designing an appropriate fission gas plenum volume. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  7. Pin/Cladding Failure Conditions under Transient Conditions (1/2) : • There are several different modes of pin cladding failure. • One of the most important is CLAD CREEP failure. • Recent experimental data of unirradiated T-91 material by CIEMAT yielded creep data which indicate that particular attention needs to be paid to this potential clad failure mode under all transient conditions leading to cladding temperatures higher than > 800 °C. This in particular applies to ULOF at EOL conditions when the fuel pins are pressurized by the accumulated released fission gas . 4. For T-91 the clad failure limit is no longer ~ 1000 °C (as we have asssumed in a somewhat generous manner during the PDS-XADS safety study), but it is now in the range ~ 850 °C. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  8. Pin/Cladding Failure Conditions under Transient Conditions (2/2): • The failure time of the cladding due to clad creep is dependent on 3 major parameters, namely: • Type of cladding material selected, • Hoop_Stress, essentially determined by a. the fission gas pressure Pgas, and b. the geometry of the pin design, namely outer pin diameter and cladding thickness, 3. The temperature of the cladding material. EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  9. Most Current T91-Cladding Creep Data from CIEMAT Experiments(data distributed by J. Wallenius) P is known as the „Larson-Miller Parameter (LMP)“ EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  10. T91 Creep Data Analysis 2. Inverting the plotted Data 1. Plotting Data from Table : 3. Curve fitting the data in the critical pressure range (Two equations) EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  11. Creep-Stress Correlations Used in the Analysis Another equation providing simliar results (thin cladding ): EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  12. 1.) Fission gas plenum pressure and hoop stress is dependant on pin geometry, i.e. pin diameter,clad thickness and volume of fission gas plena made available. This implies that clad failure time is dependant on the particular pin design. 2.) Experimental data on CREEP available only up to 700 °C (973 K). Is extrapolation of data into higher temperature ranges ok ??? 3.) Issue of expected fission gas plenum pressure under EOL conditions needs discussion/clarification. Issue : gas release fraction from fuel matrix into gap and plenum, 40, 60, 80, 100% release ?? Have decided to be conservative : assume 100% gas release from fuel Issues Needing Attention : EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  13. T91 Clad Failure Time as Function of Clad Temperature and Fission Gas Pressure for XT-ADS Design : Pin = 6.55mm OD, clad thickness = 0.475mm, 580mm Lower Gas Plenum 1. Design Criteria: Clad Failure ≥30 min under ULOFss conditions at EOL 2. Adopted : 50 bar (5 Mpa) as design fission gas plenum pressure for peak pin at EOL 3. This implies : for peak pin : Tclad_max < 847 °C under ULOFss conditions at EOL EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  14. T91 Clad Failure Time as Function of Clad Temperature and Fission Gas Pressure for XT-ADS Design Variant 1 (Bologna): Pin = 6.55mm OD, 580mm Lower Gas Plenum Peak Pin, Nominal Conditions, EOL Pgas = 39 bar EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  15. Nominal Conditions at EOL : XT-ADS : Pin = 6.55mm OD Pgas = 28 bar T_in = 330 °C Pfriction = 508 mbar spacers = 97 mbar Pin_outlet = 123 mbar Pcore = 729 mbar Psystem = 1.006 bar Pgas = 39 bar H_core_HX = 2.0 m EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  16. ULOFss Conditions at EOL, w_nat = 28.7% nom flow XT-ADS Variant 1 Bologna Design Pin = 6.55mm OD 580 mm Gas Plenum Pgas = 39.6 bar T_in = 330 °C Pgas = 41.6 bar EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  17. T91 Clad Failure Time as Function of Clad Temperature and Fission Gas Pressure for XT-ADS Design Variant 1 (Bologna): 6.55mm OD Pin, 580mm Lower Gas Plenum Peak Pin, ULOFss, EOL, nat_conv_flow = 28.7% of nominal (1233 kg/s) Pgas = 42 bar Under ULOFss steady state conditions : 5.1 hrs to failure for current designs implying large margin to 30 min limit 2. What about transient conditions ?? EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  18. ULOFss Conditions at EOL, assume w_nat decreases to 25% nom XT-ADS Pin = 6.55mm OD 580 mm Gas Plenum Time to Clad Failure hot SA avg Pin: EOC (Pgas=40 bar): 0.64 hrs Time to Clad Failure peak pin: EOC (Pgas=42 bar): 0.17 hrs EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  19. T91 Clad Failure Time as Function of Clad Temperature and Fission Gas Pressure for XT-ADS Design Variant 1 (Bologna): 6.55mm OD Pin, 580mm Lower Gas Plenum Peak Pin, ULOFss, EOL, assume : nat_conv_flow = 25% nominal Pgas = 42 bar Clad Failure Time in XT-ADS very sensitive to nat_conv flow rate under ULOFss conditions since nat. convection already relatively low ( ~ 25 % instead of ~ 45% in EFIT and XADS) EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  20. 1. Available fission gas plenem volume. Currently calculated to be 17 cm3 per pin. A reduction to ~ 13 cm3 (alternative pin design option) will decrease failure time from 5.1 hrs to 2.9 hrs as it will increase fission gas pressure from 42 bar to 54 bar Uncertainty in the pin fission gas temperature calculation needs to be considered Superimposing two of several uncertainties will decrease failure time to < 1 hr All issues associated with the natural convection flow rate 4. Transient conditions: during the ULOF transient there may be significant over- and under-shoots in clad temperatures (see following presentation). Potential Uncertainties : EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  21. 1.) EMBRITTLEMENT makes it advisable to select T_in ~ 330 °C following SPIRE and DEMETRA recommendations. 2.) CORROSION issues require that the maximum clad temperatures of the peak pin are below 500 °C under nominal conditions (unless the clad material is coated thereby increasing the temperature limit to ~ 550 °C) limiting core heat up to 90 °C. 3.) New T91 CREEP Data from CIEMAT should be taken into consideration during all transients especially those leading to clad temperatures > 850 °C. Conclusions on T-91 Material Property Limits (1/2 ) : EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

  22. 4.) Under ULOF steady state conditions max. cladding temperatures between 800 °C – 900 °C should be expected. For T_in = 330 °C, T_clad_max (ULOF) : 800 °C – 865 °C corresponding clad failure time due to creep ranging from 5 hrs to 0.17 hrs For the 30 min limit, the maximum temperature of the clad should not exceed 847 °C 6) The issue of high temperature corrosion still needs to be assessed / evaluated in view of experimental data currently assembled (DEMETRA) 5.) The current design (580mm lower gas plenum) is comfortably achieving the 30 min design goal as clad failure time limit under ULOFss and EOL conditions. Conclusions on T-91 Material Property Limits (2/2) : EUROTRANS WP1.5 Safety Meeting : Lyon, Oct 11-12. 2006

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