Address reviewers' comments

[smpark7]

This issue can be closed when the following review comments are addressed:

The stated objective of the paper is to study MSR, but the equation the whole model is based on fails to represent the fundamental aspect of MSR i.e. the movement of precursors. The method can have an interest in general, as it claims to provide improved results in the proximity of CR, but the context of MSR is not supported from the very beginning of the paper.
As 1D slab geometries are considered, it seems from the description of the domains at figure 1 that the slab is taken, presumably, perpendicularly to the axis of the reactor (a mention to MSRE is made) and the heterogeneity of the graphite and CR is therefore represented in this simplified configuration. Anyway, it is difficult to understand why the specific focus on MSR had to be made, as the whole point of the work is not addressing the peculiarity of MSR.
Carefully check the paper for inconsistencies. Some suggestions here below:

• Eq 1, although steady- state, has time dependence in the flux
• Is there a specific reason why in eq 1 the cross section do not have space dependence?
• It can be guessed that psi identifies the angular flux and phi the scalar flux, but the fundamental quantities should be defined
• The text should be improved ... for example "where the 1/Σ factors in the streaming and source terms evaluate to very large values" is an incorrect expression in English