Does your employer have a occupational health office? I am a biologist and work with radioactive substances every week. When I started, I went through their "Reproductive Risk Assessment" because I was very concerned about the risks I would face if I were to get pg unexpectedly. If you are working with radioactivity, your company should have something like this. You should also have dosimeters that you wear when you are around radioactivity. (whole body badge and rings)
Fortunately enough, the assessment concluded that the amount that I am exposed to annually is far below the OSHA recommended allowance for a declared pregnant woman. (I'm exposed to 50 mrem/yr, the threshold for pg woman is 500mrem/yr) So no additional precautions are necessary from that standpoint. We are exposed to background radiation every day from electronics to the environment, so basically every preg. woman is exposed to it in one way or another. We just need to be more careful and aware since we are also exposed at work. I told the RSO that I needed a report of my dosimeter activity every quarter just for peace of mind. And sure enough, everything he said was right.
I was also worried that my employer would freak out if they found out I was TTC or pg. But in all honesty, my lack of information was the issue. Check with your Occupational Health Service Office. They can't fire you for getting pg. They may not like it, but by law they have put your safety and that of your unborn child first.
Hope this helps! : )