  New analytical expressions for parallel transport coefficients in
multicomponent collisional plasmas are presented in this paper. They are
improved versions of the expressions written in [V. M. Zhdanov. Transport
Processes in Multicomponent Plasma, vol. 44. 10 2002.], based on Grad's
21N-moment method. Both explicit and approximate approaches for transport
coefficients calculation are considered. Accurate application of this closure
for the Braginskii transport equations is discussed. Viscosity dependence on
the heat flux is taken into account. Improved expressions are implemented into
the SOLPS-ITER code and tested for deuterium and neon ITER cases. Some typos
found in [V. M. Zhdanov. Transport Processes in Multicomponent Plasma, vol. 44.
10 2002.] are corrected.
