9.4 Fuel Retention in Carbon Materials
171
9.4.3 Estimation of Carbon Deposition and Fuel Retention
in an ITER Scale Full Carbon Reactor Operated
at Around 600 K
Based on the accumulated data on carbon erosion/deposition and retention of H +
D in PFS, tile gaps, bulk and deposited carbon layers in JT-60U, the fuel retention
rates in an ITER scale tokamak with full carbon PFM (referred to as full-C) operated
at around 600 K was estimated in the following.
The temperature rises for the full-C reactor during the plasma discharge were
assumed to be the same as observed in JT-60U indicated in Table 9.2. Both the
deposited C and eroded PFS were assumed to be saturated with fuel and the saturation
concentration is given by Fig. 9.3. Since plasma heat load in ITER is much larger
than that in JT-60U, the estimation based on the fuel retention rates determined for
JT-60U may lead to overestimation of the fuel retention rates of the ITER scale full-C
reactor.
The observed fluence dependence of the fuel retention in each area is extrapolated
to expected higher fluence in ITER as follows.
9.4.3.1 Retention in Eroded Area
Particle fluxes at the divertor region and the first wall including baffle plates were
calculated to be 1 × 10
24 m
−2 s
−1 and 1 × 10
20 m
−2 s
−1 , respectively, and the retention
rate at the eroded surface was assumed to be the same as that for the JT-60U. The
fluence dependences of the fuel retentions of the outer divertor region and the first
wall were assumed to be
0.13 and
0.16 as observed in JT-60U, respectively [10].
The surface areas of the divertor area and the first wall are roughly 55 m
2 (25 m
2 for
the outer divertor and 30 m
2 for the dome) and 750 m
2 including 50 m
2 for the baffle
plate, respectively. Consequently, the estimated retention rate in the whole eroded
area is around 2 × 10
20 s
−1 as given in Fig. 9.5, which largely contributes to the total
fuel retention only in early discharge time.
9.4.3.2 Retention in Deposited Area
Using the estimated C erosion rate for full-C ITER, 6 × 10
21 C s
−1 [4], the carbon
deposition rates in plasma-facing surfaces and plasma shadowed areas were calculated by multiplying the fractions of carbon deposition in each region observed in
JT-60U. Hydrogen concentrations in deposited layers were determined from Fig. 9.3,
to be 0.013 for the inner divertor tile above 1000 K, 0.08 for the dome tile at ~800 K,
0.1 for the tile gaps in the first wall above 700 K, 0.1 for the tile gaps of the divertor
tiles at above 700 K and 0.8 for the remote areas of the divertor structure at 423 K.
By integrating carbon deposition rates multiplied by the hydrogen concentrations in
each region, the total fuel retention build-ups were estimated to be ~5 × 10
20 s
−1 for
ITER scale full-C reactor.
171
9.4.3 Estimation of Carbon Deposition and Fuel Retention
in an ITER Scale Full Carbon Reactor Operated
at Around 600 K
Based on the accumulated data on carbon erosion/deposition and retention of H +
D in PFS, tile gaps, bulk and deposited carbon layers in JT-60U, the fuel retention
rates in an ITER scale tokamak with full carbon PFM (referred to as full-C) operated
at around 600 K was estimated in the following.
The temperature rises for the full-C reactor during the plasma discharge were
assumed to be the same as observed in JT-60U indicated in Table 9.2. Both the
deposited C and eroded PFS were assumed to be saturated with fuel and the saturation
concentration is given by Fig. 9.3. Since plasma heat load in ITER is much larger
than that in JT-60U, the estimation based on the fuel retention rates determined for
JT-60U may lead to overestimation of the fuel retention rates of the ITER scale full-C
reactor.
The observed fluence dependence of the fuel retention in each area is extrapolated
to expected higher fluence in ITER as follows.
9.4.3.1 Retention in Eroded Area
Particle fluxes at the divertor region and the first wall including baffle plates were
calculated to be 1 × 10
24 m
−2 s
−1 and 1 × 10
20 m
−2 s
−1 , respectively, and the retention
rate at the eroded surface was assumed to be the same as that for the JT-60U. The
fluence dependences of the fuel retentions of the outer divertor region and the first
wall were assumed to be
0.13 and
0.16 as observed in JT-60U, respectively [10].
The surface areas of the divertor area and the first wall are roughly 55 m
2 (25 m
2 for
the outer divertor and 30 m
2 for the dome) and 750 m
2 including 50 m
2 for the baffle
plate, respectively. Consequently, the estimated retention rate in the whole eroded
area is around 2 × 10
20 s
−1 as given in Fig. 9.5, which largely contributes to the total
fuel retention only in early discharge time.
9.4.3.2 Retention in Deposited Area
Using the estimated C erosion rate for full-C ITER, 6 × 10
21 C s
−1 [4], the carbon
deposition rates in plasma-facing surfaces and plasma shadowed areas were calculated by multiplying the fractions of carbon deposition in each region observed in
JT-60U. Hydrogen concentrations in deposited layers were determined from Fig. 9.3,
to be 0.013 for the inner divertor tile above 1000 K, 0.08 for the dome tile at ~800 K,
0.1 for the tile gaps in the first wall above 700 K, 0.1 for the tile gaps of the divertor
tiles at above 700 K and 0.8 for the remote areas of the divertor structure at 423 K.
By integrating carbon deposition rates multiplied by the hydrogen concentrations in
each region, the total fuel retention build-ups were estimated to be ~5 × 10
20 s
−1 for
ITER scale full-C reactor.