Fuel geometry

Fuel type. As currently envisioned, the LS-VHTR uses graphite-matrix coated-particle fuel. This fuel can be made into several geometric forms (prismatic blocks, pebble beds, and stringers with fuel pins), each with somewhat different refueling requirements. Refueling experience exists for gas-cooled reactors for each of these fuel geometries. 

Prismatic graphite-block fuel with traditional refueling. The LS-VHTR would be fueled with prismatic fiiel and refueled when shut down. This particular fuel geometry provides a large latitude for the reactor core designer in the choice of (1) fuel-moderator-coolant ratios and (2) core geometry. 

As currently envisioned, the LS-VHTR uses a graphite-matrix coated-particle fuel. Three major types (prismatic, pebble bed, and assembly) of fuel can be fabricated. Each has different refueling demands. Section 4 discusses the alternative fuel geometries and the implications for refueling and core design. 

PBRs use the coated-particle fuel in a graphite matrix compacted into pebbles— t5 ically about 6 cm in diameter (Fig. 4.8). Current estimates indicate that pebbles have the lowest fabrication cost of any of the three fuel geometry options. The reactor core is a bed of pebbles. The THTR core is shown in Fig. 4.9. The vertical structures are channels for control rods. 

Refueling differences exist between sodium-cooled reactors and the AHTR. For the AHTR, refueling temperatures are somewhat higher, the fuel geometry is different, the power density of the prismatic-block fuel-type SNF is 1 to 2 orders of magnitude lower, the vapor pressures of the liquid salts are much lower than those of sodium, and the liquid salt is transparent whereas the sodium is opaque. This section provides discussions of design considerations for the LS-VHTR fuel-handling system relative to sodium-cooled fast reactors. 

Fig. 3.6. SNL model of the reference AHTR fuel/coolant geometry (left) and a revised annular fuel geometry (right).

Lattice Parameter Measurements for o Concentric Tube Fuel Element, D. E. Wood, K. R. Bimey, and E. Z. Block (GE-HAPO). Lattice parameters have been measured for a concentric tube, natural uranium fueled lattice, moderated by graphite. The experiments were made to test calculatlonal models for lattices with toe complex fuel geometry involved. For toe 10-1/2-in. lattice, k >, t, p, and < were measured with water and air In toe co(dant diannels. For toe 8-3/8-in. lattice, k and f were measured with water coolant only. 

Table I shows the results of both the calculations and experiments over a rather wide geometry change. While optimum lattice spacing for each fuel geometry has been established, only maximum buckling points are used here for comparison. Triangular patterns were used for the fuel arrays because a lower critical mass is attainable with them. One significant anomaly is the poor agree-...

For all LOCAs, the integrity of fuel channels shall be maintained, and fuel geometry shall allow continued coolability of the core by ECCS. 

The reactor will be fueled with metallic uranium fuel elements coextruded in a zircaloy-2 Jacket. The fuel geometry selected Is that of two concentric fuel tubes. Figure 3-10 shows the fuel and process tube assembly. 

Figure 6-1 presents results of experimental studies of burnout with the nPR tube and fuel geometry. At a process tube power of 5000 KW (the maximum expected at a 4000 MW reactor power) tube flows could be reduced about 45 per cent below the design value before burnout would occur This Is an ample margin to accommodate normal transients ... 

The resonance Integral for the K-Reactor fuel geometry is based on the measured integrals of Hellstrand. Althou Hells trand s vorh vas confined to rods and single tubes vith a D2O nK>derator and coolant his results have been extended in an approximate fashion to the N Reactor case of H2O coolant and graphite moderator. 

Ohe funotion (r) muat be obtained firon the aolntlon to the tranaport equation For the II Beaotor fuel geometry (r) cannot be aia Jy expreaaed ... 

The total heat gsneratlon fractions for the 21.6 Ib/ft startup fuel geometry are given in Tkble 9.S. 1. 

Fuel geometry is influenced by fuel temperature and heat transfer considera-... 

W.G. Cook, R.P. Olive, Corrosion product deposition on two possible fuel geometries in the Canadian-SCWR concept, in 3rd China-Canada Joint Workshop on Supercritical Water-Cooled Reactors (CCSC-2012), Xi an, China, April 18-20, 2012. 

Observations of our VI tests in hydrogen indicate that, while extensive fuel-cladding interaction, or "liquefaction", may occur, this physical destruction of the fuel geometry leads to no... 

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