Initial median activity was 118 MBq [4–4188 MBq]. Percentage and half-life of the two components identified are presented in Table 2. The major component, representing 99.7% [85.6–99.8%] of the activity, has a median half-life of 6.6 days [5.7–7.2 days] corresponding to 177Lu. The second, representing only 0.3% [0.2–1.7%] of the activity and having a median half-life of 152 days [104–205 days] corresponding to 177mLu, determines necessary storage times.
Table 2 Data for radioactive decay curves obtained from sequential measurements of the 45 first vials usedER measured in July 2021, in contact with all waste stored for decay since 2018, are presented in Tables 3, 4, and 5.
Table 3 Data for N empty vials and corresponding bags, measured in 2021 to determine (ER/2BKG) ratiosTable 4 Data for N biohazard containers measured in July 2021 to determine (ER/2BKG) ratiosTable 5 Data for N partially used vials discarded in 2 bags, measured to determine (ER/2BKG) ratiosEmpty vials (Table 3): ER of each vial from the first semester 2018 was the local BKG (0.05 µSv.h−1). In contact with the bag of 19 vials, ER was complying with the clearance level 2BKG. This bag was disposed of.
An additional 6 months of storage were necessary for vials of the second half of 2018, 12 months for those of the first semester 2019.
Biohazard containers (Table 4): 97.1% of waste collected in 2018 were disposed of. Only one container of the second half of 2018, with an ER of 0.3 µSv.h−1 (6*BKG), required one additional year of storage.
Ten of the 26 containers of the first semester 2019 (38.5%) were disposed of after 2 years of decay. Others were maintained in storage for 6 additional months.
Partially used vials (Table 5): After a median storage time of 34.6 months, median activity of the 10 vials used in 2018 was 100 kBq [26–165 kBq]. ER were still 4–14 times higher than the clearance level, requiring 2 additional years of decay. When discarded in a bag, total residual activity was about 1 MBq and ER in contact with the bag was 50 times higher than the clearance level. Three additional years of storage were necessary before the bag of 10 vials could be disposed of instead of 2 years if vials were disposed of on an individual basis.
Vials used in 2019 had a median activity of 210 kBq [105–615 kBq], and their ER was 8–41 times higher than the clearance level: 3 additional years of decay were required. ER in contact with the bag of 9 vials confirmed 4 additional years of storage would be necessary before disposal.
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