Only a very small amount. They showed no signs of radiation sickness and most went on to live 30+ years. The early radioactive material was barely refined compared to today's standards. The early tests produced around one watt of heat. In comparison, using a bic lighter for a second is more than 80 watts.
https://www.atomicheritage.org/history/chicago-pile-1
https://en.wikipedia.org/wiki/Chicago_Pile-1