Gas Plenum in XT-ADS Fuel Rod V. Sobolev, B. Arien SCK·CEN, Boeretang 200, Mol, Belgium
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).
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
Upper reflector-insulator OD=5.40 ID=1.50 Lower reflector-insulator OD=5.40 ID=1.50 Support Spring chamber Fuel pellet OD=5.40 ID=1.60 Cladding OD=6.55 ID=5.60 Gas plenum Spring Bottom-cap Top-cap 6.55 20 60 100 20 600 300 (?) 100 1200 (?) 2. XT-ADS fuel pin schematics (pre-design of June 2006)
2. XT-ADS fuel pin: Equivalent gas chart Filling gas: Hot stand-by:
3. Pressure within fuel pin Operation at nominal power: In LMFBR: - released fraction of the i-th gas
4. Operation conditions • Hottest fuel column: <ql> = 201 W/cm, Kaxial hot = 1.257 • Filling gas pressure: 0.2 MPa (He at STP) • Coolant: • Tinlet = 603.15 K (330 °C) • Nominal operation: DTcore = 90 K x Kcore rad = = 90 K x 1.375 = 123.75 K (°C) • ULOF: DT=472.25 K (°C) determined by natural convection (DHcore-HX = 2 m; 60 % core resistance).
5. Temperature field in the hottest pin Nominal operation at BOL (FEMAXI-5.1- mod.SCK; EFR TC )
5. Temperature field in the hottest pin ULOF at BOL (FEMAXI-5.1- mod.SCK)
6. Free volumes and pressure within XT-ADS pin Pressure and free volumes (cm³) within the main segments of the hottest fuel rod 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).
7. Temperatures of clad with corrosion layer at ULOF dcorr ~85 µm
8. Updated XT-ADS rod design (proposal) It has been postulated that the maximum thickness of the corrosion layer is 10 % of the initial clad thickness, i.e. 47.5 microns
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.
Unprotected LOF • core inlet T: 330°C • DH core-HX: 2m • Dpcore: 0.1 MPa = 60% Dptot Note: ULOF becomes very unlikely is spallation loop pump and PHXs are supplied by the same electrical circuit