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Fusion Reactions

The most likely fusion reaction to be utilised in a power plant is the deuterium-tritium reaction:

\mathrm{D + T} \Longrightarrow \mathrm{^{4}He + n + 17.6 \,MeV}

20% of the energy produced is given to the alpha particles (^4He). The remaining 80% is carried away by the neutrons, which deposit their energy within the blanket and shield and other reactor components. The fraction of the alpha energy deposited in the plasma is falpha.

PROCESS can also model D-^3He power plants, which utilise the following primary fusion reaction:

\mathrm{D + \text{$^3$He}} \Longrightarrow \mathrm{^{4}He + p + 18.3 \,MeV}

The fusion reaction rate is significantly different to that for D-T fusion, and the power flow from the plasma is modified since charged particles are produced rather than neutrons. Because only charged particles (which remain in the plasma) are produced by this reaction, the whole of the fusion power is used to heat the plasma. Useful energy is extracted from the plasma since the radiation power produced is very high, and this, in theory, can be converted to electricity without using a thermal cycle.

Since the temperature required to ignite the D-^3He reaction is considerably higher than that for D-T, it is necessary to take into account the following D-D reactions, which have significant reaction rates at such temperatures:

\begin{aligned} \mathrm{D + D} & \Longrightarrow \mathrm{^{3}He + n + 3.27 \,MeV} \\ \mathrm{D + D} & \Longrightarrow \mathrm{T + p + 4.03 \,MeV} \end{aligned}

Also, as tritium is produced by the latter reaction, D-T fusion also occurs. As a result, there is still a small amount of neutron power extracted from the plasma.

Pure D-^3He tokamak power plants do not include breeding blankets, because no tritium needs to be produced for fuel.

The contributions from all four of the above fusion reactions are included in the total fusion power production calculation. The fusion reaction rates are calculated using the parameterizations in 1, integrated over the plasma profiles (correctly, with or without pedestals).

The fractional composition of the 'fuel' ions (D, T and ^3He) is controlled using the three variables fdeut, ftrit and fhe3, respectively:

\begin{aligned} n_{\mbox{fuel}} & = n_D + n_T + n_{\mathrm{^{3}He}} \;\;\; \mbox{particles/m$^3$} \\ n_D & = \mathtt{fdeut} \, n_{\mbox{fuel}} \\ n_T & = \mathtt{ftrit} \, n_{\mbox{fuel}} \\ n_{\mathrm{^{3}He}} & = \mathtt{fhe3} \, n_{\mbox{fuel}} \end{aligned}

PROCESS checks that fdeut + ftrit + fhe3 = 1.0, and stops with an error message otherwise.

Constraint equation no. 28 can be turned on to enforce the fusion gain Q to be at least equal to bigqmin.

  1. H.S. Bosch and G.M. Hale, 'Improved Formulas for Fusion Cross-sections and Thermal Reactivities', Nuclear Fusion 32 (1992) 611 ↩