1. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 1 Gas Plenum in XT-ADS Fuel Rod V. Sobolev, B. Arien SCK·CEN, Boeretang 200, Mol, Belgium

2. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 2 1.Introduction During the DM1 Meeting in MOL it was required to adapt the gas plenum of XT-ADS fuel rod to assure the cladding withstand during 30 minutes at ULOF conditions at 100 % FG release. The recommended values for acceptable cladding temperatures and pressures were presented at the same meeting by D. Struwe and W. Pfrang (see next slide).

3. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 3 1.Introduction Best estimate values from the CIEMAT creep experiment with T91 steel (D. Struwe, W. Pfrang, Mol, 20-21 June 2006) Gas plenum pressure 5 MPa 10 MPa Clad failure time Mid-wall clad temperature 10 000 h 955 K 920 K 1 000 h 985 K 955 K 10 h 1065 K 1030 K 1 h 1115 K 1070 K 30 min 1125 K 1080 K 2 min 1180 K 1135 K

4. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 4 2. XT-ADS fuel pin schematics (pre-design of June 2006) Top-cap 600 100 300 (?) 20 1200 (?) 6.55 Bottom- cap Lower reflector- insulator OD=5.40 ID=1.50 Fuel pellet OD=5.40 ID=1.60 Gas plenum 60 Spring Upper reflector- insulator OD=5.40 ID=1.50 Cladding OD=6.55 ID=5.60 SupportSpring chamber

5. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 5 2. XT-ADS fuel pin: Equivalent gas chart Filling gas: Hot stand-by:

6. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 6 3. Pressure within fuel pin Operation at nominal power: In LMFBR: - released fraction of the i-th gas

7. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 7 4. Operation conditions Hottest fuel column: = 201 W/cm, K axial hot = 1.257 Filling gas pressure: 0.2 MPa (He at STP) Coolant:  T inlet = 603.15 K (330 °C)  Nominal operation:  T core = 90 K x K core rad = = 90 K x 1.375 = 123.75 K (°C)  ULOF:  T=472.25 K (°C) determined by natural convection (  H core-HX = 2 m; 60 % core resistance).

8. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 8 5. Temperature field in the hottest pin Nominal operation at BOL (FEMAXI-5.1- mod.SCK; EFR TC )

9. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 9 5. Temperature field in the hottest pin ULOF at BOL (FEMAXI-5.1- mod.SCK)

10. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 10 6. Free volumes and pressure within XT-ADS pin Pressure and free volumes (cm³) within the main segments of the hottest fuel rod SegmentGas plenum * Lower reflector Fuel column Upper reflector Spring chamber ** TotalPressure Index12345void (MPa) Cold conditions: T i = 291.15 K 6.2370.3502.2430.3501.31810.500.20 Hot stand-by: T i = 603.15 K 6.2860.3532.2650.3531.32810.590.41 Nominal regime (BOL)6.2860.3532.1160.3491.33210.440.47 ULOF (BOL) 100%FGR (EOL) 6.2860.3532.0640.3611.34710.41 0.51 7.5 The max. clad temperature at ULOF is 1117 K (844 °C) without clad corrosion, and the allowed pressure (Table on Slide 3, D. Struwe) is lower than 7.5 MPa. Clad corrosion will create more severe situation (see next slide).

11. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 11 7. Temperatures of clad with corrosion layer at ULOF   orr ~85 µm

12. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 12 8. Updated XT-ADS rod design (proposal)

13. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 13 8. Updated XT-ADS rod design (proposal) Segment Gas plenum Lower reflector Fuel column Upper reflector Spring chamber TotalPressure Index12345void (MPa) Length (mm) 5806060010060- - Nominal regime: BOL EOL * 12.15 0.21 2.03 1.63 0.21 1.33 15.93 15.54 0.452 3.94 ULOF at EOL with 100 % FGR 12.150.211.700.221.3515.634.77 It has been postulated that the maximum thickness of the corrosion layer is 10 % of the initial clad thickness, i.e. 47.5 microns

14. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 14 Conclusions  In order to assure the 30-minute cladding resistance of the hottest XT-ADS fuel rod under ULOF conditions, the gas plenum should be increased.  Clad corrosion can play a critical role. Taking into account a large uncertainly in the cladding corrosion, it is proposed to postulate at this stage of design that corrosion is limited to 10 % of the clad thickness.  The updated pin design with a larger gas plenum (580 mm) is proposed as a possible solution.

15. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 15 Transient analysis Transient (protected or unprotected) CommentCode LOFFirst estimationSITHER - RELAP LOH Needs HX and SCS design RELAP LOF&LOHidemRELAP TOP Needs reactivity feedback coefficients SITHER overcoolingStill to be doneRELAP SA blockageStill to be doneSITHER

16. IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 16 Unprotected LOF core inlet T: 330°C  H core-HX: 2m  p core : 0.1 MPa = 60%  p tot Note: ULOF becomes very unlikely is spallation loop pump and PHXs are supplied by the same electrical circuit