Most books on transport theory are quite old. Some numerical methods are thus somewhat obsolete, but the physics and the mathematics still hold.
G. I. Bell and S. Glasstone, "Nuclear Reactor Theory", Van Nostrand Reinhold Company (1970). My favorite. Not everything is in here, but what is in here is always inspiring.
J. J. Duderstadt and L. J. Hamilton, "Nuclear Reactor Analysis", Wiley (1974). I followed their outline as the most pedagogical.
P. Reuss, "Neutron Physics", EDP Sciences (2008). My student's textbook. This is actually the English translation of "Precis de Neutronique" of 2002.
(In reverse chronological order)
S. Marguet, "La Physique des Réacteurs Nucléaires", Lavoisier (2017). Everything you wanted to know, and more.
A. Hébert, "Applied Reactor Physics", Presses internationales Polytechnique (2009). The exercises are in matlab.
J. J. Duderstadt and W. R. Martin, "Transport Theory", Wiley-Interscience (1979). Not just neutrons.
K. M. Case and P. F. Zweifel, "Linear Transport Theory", Addison-Wesley (1967). Caseology fully explained: how to analytically solve the transport equation for infinite and semi-infinite (planar) systems.