Dt

D-3He

ß = 100%

104 MW/m3

123 MW/m3

ß = 10%

102 MW/m3

1.2 MW/m3

ß = 1%

1 MW/m3

0.01 MW/m3

lower than that of the D-T reaction. Table B.3 clearly shows that the D-3He reaction becomes interesting only if values of fl above 10% can be achieved.

It should be noted that a limit exists to the neutron power Pn per unit surface that can be tolerated by the first wall before serious degradation of its structural properties occurs. For fusion reactor application, the target specific fluence (power x year/unit area) is PnDT/S ~ 10MWyr/m2 to 15MWyr/m2. This value depends on neutron energy (with the 14MeV of the D-T reaction being the worse situation). The target for first-wall replacement is 5 years at full power. This sets a limit —2 MW/m2 to 3 MW/m2 for specific neutron power. This latter depends on the shape of the reaction chamber. In the case of a spherical chamber of radius rw, it is given by Pn/S = fnPspecrw/3. For a cylindrical chamber of radius rw and length L it is given by Pn/S = fnPspecrw/2. Thus, the limit on neutron wall load imposes a limit on specific power that is more stringent for large chamber radii. Taking as an example 1 year of full-power operation, specific power would be limited by

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