activity by at least an order of magnitude as against a simplistic non-decayed radionuclide inventory.

Surface to mass ratios for metallic materials To determine the amount of gas a metallic component may produce, it is necessary to know the available surface area in relation to its total mass, i.e., the rate of gas production is much higher from sheets of aluminium foil in comparison to that from aluminium laboratory apparatus support stands (rods).

2.7.3. Secondary data

To have an inventory that can be used to respond to questions, e.g., requests from safety assessors, regulators, etc., in a timely fashion, it is recommended that processing functions are built into any inventory database. The types of secondary data that are required during a repository project are:

Summation over any combination of individual waste types (volume, activities, masses, etc.)

Decay and arisings calculations

Radiotoxicity calculations

Classification of material into chemical groups (e.g., inorganic, low-or high-molecular weight organic, etc.)

Elemental composition

For examples of the various inventories that have been derived in Europe and the US, see Alder and McGinnes (1994), Carlsson (1999), ENEA (2000), Riggar and Johansson (2001), USDOE (2001), Nirex (2002) and McGinnes (2002).

2.7.4. Radionuclides occurring in the nuclear fuel cycle

Within the nuclear fuel cycle, radionuclides arise in three groups: activation products, fission products and actinides.

Activation products: In a reactor, a certain amount of the neutrons produced are absorbed by fuel impurities or by fuel and reactor structural materials. The most common

reaction is where a stable isotope absorbs a neutron and emits a -ray, e.g., 59Co (n, ) 60C or 62Ni (n, ) 63Ni.

Fission products: When a nuclide undergoes fission, the resulting nuclei are termed ‘‘fission products’’. Depending on the nuclide that undergoes fission, a distinct distribution of fission products occurs. In Fig. 2.16, for 235U fission (235U is the initial fissile

component of uranium oxide fuels), it can be seen that certain mass numbers dominate, e.g., A =90(90Sr), A =99(99Tc), A =137(137Cs).

Transuranic (TRU) nuclides are those essentially man-made nuclides occurring after uranium in the actinide element series (see highlighted area in Fig. 2.17).

Table 2.3 identifies the most important sources of radionuclides in light water reactors. For each of these nuclides, it also gives the dominant emission ( , , , etc.), its half-life and, in the case of activation products, which reactor material (steel or concrete).

To put radwaste inventories in perspective, the time for vitrified HLW reprocessing wastes to reach the same activity level as in the initial uranium ore from which the fuel is