Well, I'm not asking about a particular homework problem because even if I tell you one, a very small change in the equations will change everything. What I'm interested in is if there are some assumption that can simplify the equations in order to get a
qualitative understanding of the phenomena. For example, even if you neglect the changes in the coolant's temperature (you assume it constant) you get a system of equations like this (the most simplified model of PWR I could think of... I don't even know if you can call it a PWR

):
$$\frac {dP}{dt} = \frac {\rho - \beta}{Λ} P + \lambda C$$
$$\frac {dC}{dt} = \frac {\beta}{Λ} P- \lambda C$$
$$ \frac {dT_f}{dt} = \frac P {\tau_f} - \frac k {\tau_f} (T_f - T_c)$$
$$d\rho = \delta \rho_0 + \alpha_f dT_f$$
where ##\tau_f = m_f c_{p_f}##. I'd like to know if there is a way to predict how things will unfold after, for example, a step insertion of reactivity. If ## \rho << \beta## maybe Prompt Jump will help, but what if it is not ? Is there a way to make some predictions at least ?
Back to my original question, I thought that one could neglect the latent neutrons contribution in order to drop an equation, but apparently it is not a very good thing to do. So I guess there are no shortcuts after all! Thanks for the replies anyways! And I'll definitely check the article if I can find it.