Clean Steels for Fusion

摘要

Fusion energy production has an inherentadvantage over fission: a fuel supply with reducedlong term radioactivity. One of the leading candidatematerials for structural applications in a fusionreactor is a tungsten stabilised 9% chromium martensitic steel. This alloy class is being consideredbecause it offers the opportunity to maintain thatadvantage in the reactor structure as well as providegood high temperature strength and radiation inducedswelling and embrittlement resistance. However,calculations indicate that to obtain acceptableradioactivity levels within 500 years after service,clean steel will be required because the niobiumimpurity levels must be kept below about 2 appm andnickel, molybdenum, nitrogen, copper, and aluminummust be intentionally restricted. Internationalefforts are addressing the problems of clean steelproduction. Recently, a 5000 kg heat was vacuuminduction melted in Japan using high purity commercialraw materials giving niobium levels less than 0.7 appm.This paper reviews the need for reduced long termradioactivity, defines the advantageous properties ofthe tungsten stabilised martensitic steel class, anddescribes the international efforts to produce accetable clean steels.