Radioactive material produces ionizing radiation while also increases the risk in case of being used with deadly intentions. There's an index of interaction, numeric, that implies ionizing particles that cause mutations. If you have a ball of uranium in your lunch table, the risk is high so the index increases its value but if you transport the radioactive material to another planet, the index goes lower.
To not understand the risk doesn't look particularly rational and it causes constant health issues. There's a reason why the Sun is outside the atmosphere, or why never to use nuclear energy in the planet's surface. Chernobyl or Fukushima are two examples that still today and for a lot of time are increasing the index of interaction with the life. With it, let's insist how the statistics for mutations are higher.
Any control procedure introduces error factors even from the same personal that works in the field, and anyone could remember the recent aviation case, and going out of control the potential damage simply treating radioactive material without methods to mitigate ionizing radiation could be considered too risky. Other aspects are worse, so an effective international policy is strictly necessary.
First radioactive material, then astronauts.