Astronauts have an unusually high rate of kidney stone formation, with 1-year post-flight astronauts experiencing incidence rates of 2–7 times that of pre-flight estimates, and in-flight risk estimated to be double that again5. This is of mission critical significance, one Soviet in-flight renal stone episode nearly caused a mission termination due to the severe symptoms, but was relieved by spontaneous stone passage by the cosmonaut just before an urgent deorbit was initiated

It has been demonstrated that spaceflight associated changes in urinary biochemistry favour kidney stone formation

the kidney is an exquisitely radiation sensitive organ; it is the dose limiting organ in abdominal radiotherapy

Our data robustly and orthogonally supports tubular remodelling occurring in microgravity with and without GCR (Galactic Cosmic Radiation). This is highly likely to have functional consequences, as tubular remodelling does in other scenarios39.

Renal remodelling in microgravity (possibly related to the cephalad fluid shift) may therefore be a primary event that causes subsequent dysregulation of serum and urine electrolyte homeostasis. This is supported by the prompt return to baseline of humans on return to terrestrial gravity.

Sounds like GCR is a big concern to Renal functionality due to it's sensitivity to radiation, but they don't think it's the main driver of astronauts subsequent renal dysfunction. Interesting stuff.