One point that is worth considering is that modern civilisation isn't even 10k years old, depending of course on what you mean by civilisation. To put this in context, if we went back that far instead of going forward, you end up in the last ice age.
It is generally said that the difference between Ice Age humans and modern humans is a matter of knowledge and technology; certainly things like the Printing Press seem to have reduced our memory capacity in favour of processing and reasoning ability, but this change is most likely psychological in nature, not physiological.
That said, there was a large society in the past that did deal with toxins in the environment for many generations, and we are now starting to research the impacts it may have had on their civilisation.
The Roman Empire had a massive water collection and distribution system, including some sewers in the more well to do neighbourhoods throughout the Empire. This system was almost exclusively made of lead. The Romans actually had some knowledge of the fact that Lead was toxic to them, but its use was so ubiquitous that even the word Plumbing comes from the Latin meaning 'Leadwork'. Just how much of a consideration this was is still up for some debate, but it was clear that there were some issues with lead poisoning throughout the history of the Empire and that there may have been some systemic physiological effects from this.
My advice? Do some research on Romans towards the end of the Roman Empire, and also look up the effects of lead poisoning, look for correlations. From that, you can look up the impacts of chronic radiation poisoning, and extrapolate out the possible systemic effects.
That said - for my mind, I'd expect to see the following, off the top of my head;
Smaller lifespan, the radiation energy would probably mean that the body would age at a faster rate (essentially a higher energy environment)
Less Stamina, the loss of Vitamin D from sunlight results in muscle and bone fatigue, hair loss etc. (which incidentally sounds like some of the outward manifestations of radiation poisoning)
Smaller Lungs, the radiation in the atmosphere is probably going to generate a lot of Ozone, even at the lower altitudes. This is going to cause a lot of issues (including lung damage) that could impact normal O2 absorption, but by the same token, you'll probably want smaller lungs, not larger, so that less Ozone is taken in. This could be offset by more rapid breathing
Higher infant mortality / increased mutation rate, one would expect that a larger number of pregnancies would prove non-viable due to mutation rates, both in the unborn children, the eggs and sperm of the parents, and in their DNA more generally. Most of the mutations will be unhelpful, and will result in either non-viable children or potentially sterile (or at least undesireable) adults. Those rare few mutations that add a benefit would be impossible to predict in terms of how they would shape human physiology by virtue of the fact that they are mutations.
Generally speaking, I wouldn't expect non-robust people to be valued or even protected in such an environment. For one thing, the distribution network and economic frameworks that allow our civilisation to function with such a small percentage of the population making food or providing protection to the group cannot exist in the world you describe, so I'll assume that we're back to clan based groups that are territorial (to protect crops) and where there are essentially two jobs - providing food or other essentials, or protecting those who do. In such a case, mutations that cause infants to look significantly different are going to be a disadvantage because they'll likely result in the destruction of the child.
All things considered, your post 10k humans are going to be fitter than we are, but only relative to the uppermost capability of their physiology, which will be severely curtailed by the conditions in which they live.