RADIATION EFFECTS

There are clearly significant areas of research required to realise the ADS technology. Some broad scope areas are given in Table 13.4. These relate to general requirements needed for most of the different fuel cycles and applications. There are also particular engineering-related materials issues associated with radiation damage, and the need to extend the methodologies developed for critical reactors to the more complicated ADS-coupled transport situation.

Severe radiation damage can occur as a consequence of high current, medium-energy protons being injected into the target (Takahashi and Gudowski, 1997). Neutrons and charged particles are generated at energies reaching those of the protons causing radiation damage to the target and surrounding structural materials. This stems from the

Table 13.4. Research requirements

Transmutation of commercial power plant waste, particularly reactor grade plutonium Deployment of weapons grade plutonium in power production Assurance of proliferation resistant fuel cycle Benefits and utilisation of the thorium fuel cycle

Impact of different ADS options on radiotoxicity of the fuel cycle reduction Materials-related research, e. g. radiation damage of the target regions ADS safety issues and their resolution

Methodologies development for ADS, e. g. necessary developments of critical reactor models

displacement of lattice atoms within the target and from the energy the atom receives following emission of a nuclear particle, e. g. g ray (Wechsler et al., 1995).

The primary concerns on the effects of damage relate to hardening and embrittlement and the changes in mechanical properties and stability. The embrittlement is characterised by radiation defect clusters, helium aggregation to form bubbles, ductile brittle transition effects, and impurities arising from transmutation products.

The areas of particular damage will be surrounding walls and the window, which therefore needs to be replaced frequently in high-energy accelerators. Thus, damage is likely to be worst for a high-power accelerator with a large sub-critical reactor. This may be mitigated by adopting a concept with a smaller current and smaller sub-criticality. Similarly the structural damage in an accelerator driven system might be expected to be higher than in a corresponding critical reactor (Takahashi et al., 1994).

The adoption of suitable materials for the beam window section and the target side walls is a subject for research.

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