With regard to the use of natural gas, according to NCRP report (# 94?) there is an estimated dose of of 5 mrem per year from using natural gas due to the radon in the gas.
Concerning the need for hundreds of TLDs to accurately determine the TMI dose - NO, NOT NEEDED. The dose from the emitted noble gases came from both beta and gamma emissions. The range of gammas in air is quite large so that the TLD does not have to be "touched" by the plume in order to measure a dose. I don't have the info in front of me at the moment so the number I'm about to quote may not be exactly correct. But, I do remember calculating the half-value layer of a 662 KeV gamma (Cs-137) in air and it was on the order of several thousand feet. The number 2200 comes to mind but I'm not exactly sure.
As always, just my own thoughts.
Kjell Johansen, Ph.D.
Wisconsin Electric Power Company
Milwaukee
kjell.johansen@wepco.com