10.1. Introduction

Short-lived waste is radioactive waste that does not contain significant levels of radionuclides with half-lives longer than 30.2 years. Short-lived radionuclides are present in both HLW and LILW. In contrast to HLW the concentration of short-lived radionuclides in LILW is relatively low. The relative weight content of radionuclides in the waste f (%) can be found from the specific content of radionuclides q (Bq/g) using:

(10.1)

where SA is the specific activity of the radionuclide. Taking a typical maximum content of ¹³⁷Cs in LILW as q ~ 10 ⁷ Bq/g (Table 9.3) and the specific activity of the longest lived short-lived radionuclide ¹³⁷Cs: SA = 86.8 Ci/g (Table 2.2), reveals that the relative weight content of ¹³⁷Cs in LILW is ?0.027%. Hence the physical and chemical properties of LILW can potentially be affected very little by the presence of radionuclides and in practice are determined solely by the non-radioactive constituents. Important short-lived radionuclides in radioactive waste include ³H, ⁹⁰Sr, ⁶⁰Co, ⁶³Ni, ¹⁰⁶Ru, ¹³⁴Cs, ¹³⁷Cs, ¹⁴⁴Ce, ¹⁴⁷Pm, ¹⁵¹Sm and ¹⁵⁴Eu. These are often of radiological concern in performance assessment. Most short-lived radionuclides are formed by the fission of fissile radionuclides in the nuclear fuel although they can also form by nuclear reactions, for example, active ⁶⁰Co and ⁶³Ni can arise from neutron capture of inactive isotopes in structural steels (Chapter 9).

10.2. Tritium

Tritium ( ³H) is...