Decontamination and Decommissioning (D&D) of radiologically and/or chemically contaminated facilities at the Nevada Test Site (NTS) are the responsibility of the Environmental Restoration (ER) Project. Facilities identified for D&D are listed in the Federal Facilities Agreement and Consent Order (FFACO) and closed under the Resource Conservation and Recovery Act process. This paper discusses the NTS D&D program, including facilities history, D&D regulatory framework, and valuable lessons learned.

Following Thomson's discovery of stable isotopes in non-radioactive chemical elements, the derivation of atomic weight values from mass spectrometric measurements of isotopic abundance ratios moved very slowly. Forty years later, only 3 1/2 % of the recommended values were based on mass spectrometric measurements and only 38% in the first half century. It might be noted that two chemical elements (tellurium and mercury) are still based on chemical measurements, where the atomic weight value calculated from the relative isotopic abundance measurement either agrees with the value from the chemical measurement or the atomic weight value calculated from the relative isotopic abundance measurement falls within the uncertainty of the chemical measurement of the atomic weight. Of the 19 chemical elements, whose atomic weight is based on non-corrected relative isotopic abundance measurements, five of these are two isotope systems (indium, iridium, lanthanum, lutetium and tantalum) and one is a three-isotope system (oxygen).