Abstract
Metallic solid radioactive waste class low-intermediate short lived level waste (LILSL RW) is the main type of radioactive waste generated from decommissioning operations. Transport, storage and disposal regulations require for gamma emitting radioactive waste (mainly by 137Cs isotope), that the dose rate in the proximity of the container should stand below a certain threshold. Also, the conditioning technique (using cementation technique) based on certain matrix with specific ratios should be able to attenuate the gamma radiation activity to the minimum level or to acceptable dosage rate at distance of 1 m from the container. In this paper, in absence of suitable labs for waste package assessment, hypothetical method present to assess dose rate in safe way, assumption based on metallic waste pieces contaminated with (137Cs) were conditioned with cement matrix and contained in carbon steel drum volume 220 L, 60 cm diameter then dose rate measurement applied in vicinity of the container. Instead of real contaminated metallic waste (137Cs, Dº=20 mR/h), gamma radioactive point source was positioned in different places in front of cross section of the cemented free metallic waste and gamma dose rates were measured on the outer side of the drum sample using NaI detector dose meter device. Readings showed good attenuation of gamma radiation activity (low dose rates), efficiency of the cement matrix to decrease the dose rate of (137Cs, 0.662 Mev) gamma radiation lower to acceptable values and with waste acceptance criteria and regulation.
Highlights
Radioactive waste handling activities are hazardous as concern for both contamination and external exposure; strict regulations are applied for radiation protection in this field [1]
Where Aͦ the incident gamma-ray activity and D∘ dose rate, which obtained without inserting any sample between the detector and the source and A, D, when the incident photons obtained for the cement waste bulk of thickness (x)
The attenuation coefficient μ could be calculated in terms of dose rate and activity terms using narrow collimated mono-energetic beam of 137Cs gamma source
Summary
Radioactive waste handling activities are hazardous as concern for both contamination and external exposure; strict regulations are applied for radiation protection in this field [1]. One of the test that should be taken in RW management include cut open the package RW (cemented drum) in horizontal direction in safe-secured conditions to examine the enteric of the cemented RW drum and for gamma attenuation determination (shielding function), the cemented bulk will be head to gamma-ray detector or dose rate device and will be taken in contact to the outer side of the drum for quality and safety assessment. In such tests, risks of highly contamination and exposure will be high (radioactive waste dust dispersed in environment). This estimation method was necessary in absence of suitable labs for cemented waste as sample test while in waste management activities are very costly and the (hypothetic) tests could
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