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

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 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).

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, Introduction Best estimate values from the CIEMAT creep experiment with T91 steel (D. Struwe, W. Pfrang, Mol, June 2006) Gas plenum pressure 5 MPa 10 MPa Clad failure time Mid-wall clad temperature h 955 K 920 K 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

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, XT-ADS fuel pin schematics (pre-design of June 2006) Top-cap (?) (?) 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

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

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

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

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

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

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 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 = K Hot stand-by: T i = K Nominal regime (BOL) ULOF (BOL) 100%FGR (EOL) 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).

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

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

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

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 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.

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 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

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 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