Evaluation of the radioactive inventory in, and estimation of isotopic release from, the waste in eight trenches at the Sheffield low-level waste burial site

An inventory has been compiled of the isotopes of half-life >5 years buried in eight of the trenches at the Sheffield low-level waste burial site. This was accomplished through a search of the Sheffield radioactive shipment records (RSRs). Pertinent information from some 3200 fuel cycle RSRs and 1700 non-fuel cycle RSRs has been stored in a computerized data base and used to develop the inventory. Results of the compilation are in disagreement with the two previous estimates for H-3 and for C-14. In particular, non-fuel cycle H-3 inventory for the eight trenches of the present study is approximately a factor of 2 higher than either previous estimate of total site inventory. Modeling of release processes has been carried out in order to obtain estimates of isotopic release rates from waste packages to the trenches. This modeling is highly speculative, but believed to be state-of-the-art. It required information not only on amounts of the different isotopes, but also on the waste forms and containers holding them. Such information was generally not given on the RSRs and had to be obtained by contact with the generators. Estimated numerical release rate data are given for each trench for H-3, C-14, Cs-137, Sr-90, and Co-60. I-129 is expected to have been totally released within a year of container breaching by corrosion. Most of the Pu, in the form of oxide, will probably not be released at a significant rate. However, about 10%, in the form of soluble nitrate, may be considered to be released on first contact with water. 50 references, 9 figures, 61 tables, 5 appendixes