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Initial Integration of Accident Safety, Waste Management, Recycling, Effluent, and Maintenance Considerations for Low-Activation Materials

Steven J. Piet, Edward T. Cheng, Steve Fetter, J. Stephen Herring

Fusion Science and Technology

Volume 19 / Number 1 / January 1991 / Pages 146-161


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A true “low-activation” material should ideally achieve all of the following objectives:

  1. The possible prompt dose at the site boundary from 100% release of the inventory should be <2 Sv (200 rem); hence, the design would be “inherently safe” in that no possible accident could result in prompt radiation fatalities.
  2. The possible cancers from realistic releases should be limited such that the accident risk is <0.1 %/yr of the existing background cancer risk to local residents. This includes consideration of elemental volatility.
  3. The decay heat should be limited so that active mitigative measures are not needed to protect the investment from cooling transients; hence, the design would be passively safe with respect to decay heat.
  4. Used materials could be either recycled or disposed of as near-surface waste.
  5. Hands-on maintenance should be possible around coolant system piping and components such as the heat exchanger.
  6. Effluents of activation products should be minor compared to the major challenge of limiting tritium effluents.
The most recent studies in these areas are used to determine which individual elements and engineering materials are low activation. Grades from A (best) to G (worst) are given to each element in the areas of accident safety, recycling, and waste management. Structure/fluid combinations are examined for low-activation effluents and out-of-blanket maintenance. The lowest activation structural materials are silicon carbide, vanadium alloys, and ferritic steels. Impurities and minor alloying constituents must be carefully considered. The lowest activation coolants are helium, water, FLiBe, and lithium. The lowest activation breeders are lithium, lithium oxide, lithium silicate, and FLiBe. Designs focusing on these truly low-activation materials will help achieve the excellent safety and environmental potential of fusion energy.

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