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XT-ADS Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety”

XT-ADS Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety” Madrid , 13-14 November 2007. Topics:. Design Criteria for XT-ADS 2. XT-ADS design Data for Transient Analysis 3. Some XT-ADS results to the ULOF transient. 1. Some important XT-ADS Design Criteria:.

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XT-ADS Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety”

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  1. XT-ADS Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety” • Madrid , 13-14 November 2007 EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  2. Topics: • Design Criteria for XT-ADS 2. XT-ADS design Data for Transient Analysis 3. Some XT-ADS results to the ULOF transient EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  3. 1. Some important XT-ADS Design Criteria: 1. Neutron Flux sufficiently high ( ~ 2.0E15 n/cm2/s ) to allow XT-ADS to operate as an irradiation facility (i.e. for MA sub-assembly testing). • Operate XT-ADS at k_eff ~ 0.95 - 0.97 with several (8?) test rig positions. Design currently optimized by Task Force (Struwe). • Design core and primary system in such a manner to allow sufficient natural convection flow rate especially to sustain a ULOF transient for at least 30 minutes without „large number“ of pin failures (i.e. via gas blowdown. Note: this does not mean clad melting !!) EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  4. XT-ADS 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“ (~<0.75 bar) by selecting an appropriate fuel pin / subassembly design 2. minimize pressure losses throughout the primary / DHR system such that total system pressure loss <~ 1.0 – 1.1 bar 3. assure a height differential between the core midplane and the heat sink midplane of at least ~ 2.00 m EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  5. Keeping DP_core in the XT-ADS Design low: • Select an appropriate pin / sub-assembly design by optimizing the pin diameter, pin pitch, wrapper dimensions etc. • Minimize the number of grid-spacers and optimise design (reduce grid spacer thickness to a minimum: 0.25 mm from currently 0.50 mm) • Keep the length of the fuel pin low • Optimize inlet and outlet support structures to keep pressure drops small EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  6. Most current XT-ADS Design Data: 580mm Lower Gas Plenum 580 EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  7. Other XT-ADS Data Inputs: 580mm Lower Gas Plenum Current Grid Spacer Design : Proposed Grid Spacer Design: 580 EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  8. XT-ADS Nominal Conditions at BOC : XT-ADS : Pin = 6.55mm OD T_in = 300 °C 4 Grid Spacers @ 0.50 mm Note: using Ushakov (Zhukov-bundle) instead of Subbotin will reduce clad temps by about 9 °C EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  9. XT-ADS Nominal Conditions at EOC : XT-ADS : Pin = 6.55mm OD T_in = 300 °C 4 Grid Spacers @ 0.50 mm Oxide Layer = 30 um At 1 [W/m/K] oxide layer thermal conductivity At EOC (~ 100 MWd/kg peak burnup): Fission Gas Pressure in peak pin ~ 38.4 bar Degraded thermal fuel conductivity (Philiponneau) EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  10. XT-ADS ULOF-ss at BOC : XT-ADS : Pin = 6.55mm OD T_in = 300 °C No Oxide Layer Current Spacer design: 4 Grid Spacers @ 0.50mm thickness D H (core-HX) = 2.0 m D P_primsystem = 1.56 bar Conclusion: At BOC ULOFss Clad Failure Time of ~ 0.5 hrs for Peak Pin is acceptable !! EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  11. XT-ADS ULOF-ss at EOC : XT-ADS : Pin = 6.55mm OD T_in = 300 °C Oxide Layer = 30 um Current Spacer design: 4 Grid Spacers @ 0.50mm thickness D H (core-HX) = 2.0 m D P_primsystem = 1.56 bar Conclusion: At EOC ULOFss Clad Failure Time of ~ 0.13 hrs for Peak Pin is somewhat less than the 0.5 hrs design goal!! EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  12. XT-ADS ULOF-ss at BOC : XT-ADS : Pin = 6.55mm OD T_in = 300 °C No Oxide Layer Proposed Spacer design: 4 Grid Spacers @ 0.25mm thickness D H (core-HX) = 2.0 m D P_primsystem = 0.977 bar Conclusion: At BOC ULOFss Clad Failure Time of ~ 45 hrs for Peak Pin EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  13. XT-ADS ULOF-ss at EOC : XT-ADS : Pin = 6.55mm OD T_in = 300 °C Oxide Layer = 30 um Proposed Spacer design: 4 Grid Spacers @ 0.25mm thickness D H (core-HX) = 2.0 m D P_primsystem = 0.977 bar Conclusion: At EOC ULOFss Clad Failure Time of ~ 9 hrs for Peak Pin is now ok !! EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  14. XT-ADS Transient : ULOF Assumptions: • Pump Coast down charactersitics taken from Myhrra Report (Draft 2) using a pump rundown halftime = 3.8 sec • Assume a similiar flow transition characterisitics from pump coast down to natural convection as has been assumed for the PDS-XADS design ~3.8 sec Source: Myhrra Report – Draft 2 June 2005 EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  15. Flow transition characterisitics from pump coast down to natural convection under ULOF conditions as has been assumed for the PDS-XADS design TALL experimental data (LBE-loop, KTH) I believe that this XADS transition flow characterisitcs was experimentally valided in Italy (Brasemone) and RELAP was validated using this data EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  16. Benchmarking TRAC and SIM-ADS to TALL Natural Convection Transient TALL Natural Convection Transient Experimental data (LBE-loop, KTH) Source : W. Ma (KTH),et.al., E. Bubelis, P. Coddington (PSI) „TALL Experiments …..“ NED Reference to be completed EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  17. ULOF: BOC, Peak Pin, 4 Spacer @ 0.50mm thickness 2. ULOF: EOC, Peak Pin, 4 Spacer @ 0.50mm thickness, 30 um oxide 3. ULOF: BOC, Peak Pin, 4 Spacer @ 0.25mm thickness 4. ULOF: EOC, Peak Pin, 4 Spacer @ 0.25mm thickness , 30 um oxide XT-ADS ULOF Transient Cases Analysed: EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  18. Case 1 : ULOF, BOC, Peak Pin, 4 Spacer @ 0.50mm thickness, no oxide Conclusion: For current design XT-ADS peak pin clad will fail 32 sec into the ULOF transient already under BOC conditions because of flow undershoot < 20 % nom. flow at 36 sec into transient even though the ULOF-ss limit of 30 min is attained after 60 sec into ULOF. EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  19. Case 2 : ULOF, EOC, Peak Pin, 4 Spacer @ 0.50mm thickness, 30 um oxide Conclusion: For current design XT-ADS peak pin clad will fail 32 sec into the ULOF transient under EOCconditions because of flow undershoot < 20 % nom. flow at 36 sec even though the ULOF-ss limit of ~20 min is attained after 60 sec into ULOF. EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  20. Case 3 : ULOF, BOC, Peak Pin, 4 Spacer @ 0.25mm thickness, no oxide Conclusion: For 0.25cm Spacer design XT-ADS clad will most likely survive without clad failure under BOC conditions even though clad failure time dropped down to ~ 80 sec about 36 sec into ULOF transient. Flow undershoot will recover sufficiently fast. EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  21. Case 4 : ULOF, EOC, Peak Pin, 4 Spacer @ 0.25mm thickness, 30 um oxide Conclusion: For 0.25cm Spacer design XT-ADS peak pin clad will however most likely fail under EOC conditions because clad failure time dropped down to ~ 0 sec about 36 sec into ULOF transient. Avg Pin clad will survive – see next figure. EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  22. Case 4 : ULOF, EOC, Avg Pin, 4 Spacer @ 0.25mm thickness, 30 um oxide Conclusion: For 0.25cm Spacer design XT-ADS avg pin clad will not fail under EOC conditions because clad failure time dropped down to only 800 sec about 36 sec into ULOF transient and thereafter recovers to several hours. EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  23. 1.) This transient is very sensitive to natural convection flow rate conditions and thus all plant and design parameters that influence this parameter. During the transient clad failure times can decrease to a few 10 seconds depending on the transitional flow dynamics (natural convection flow undershoot). 2.) The ULOF-ss (steady state) clad design limit condition of at least 30 min survival time are difficult to abide by under ULOF transient conditions for the current design even if the spacer design of 0.25mm thickness is adopted. Additional design measures are needed such as either decrease in primary system pressure drop or by increasing the elevation of the HX relative to the core above the current 2.0 m differential, or by other means (what are those ?). Current Conclusions on XT-ADS ULOF Transient (1/2) : EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

  24. 3.) The XT-ADS core and primary system designs are currently still a moving target. The most recent design iteration proposal calls for a reduced secondary side pressure to 16 bar allowing for power level dependant core inlet temperature variations between 300°C and 200°C. This calls for a revised MHX modelling (2 phase flow as saturation temperature of 16 bar is 200°C). This implies that under norminal conditions – 300°C core inlet, the secondary side HX is mostly in the vapor state. Who has a 2 phase MHX model going and running stable at all plant conditions ??? Current Conclusions on XT-ADS ULOF Transient (2/2) : EUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007

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