Status of Cross-Section Data for Gas Production from Vanadium and ²⁶AL from Silicon Carbide in a D-T Fusion Reactor

Current designs of fusion-reactor systems seek to use radiation-resistant, low-activation materials that support long service lifetimes and minimize radioactive-waste problems after decommissioning. Reliable assessment of fusion materials performance requires accurate neutron-reaction cross sections and radioactive-decay constants. The problem areas usually involve cross sections since decay parameters tend to be better known. The present study was motivated by two specific questions: i) Why are the ⁵¹V(n,np)⁵⁰Ti cross section values in the ENDF/B-VI library so large (a gas production issue)? ii) How well known are the cross sections associated with producing 7.4times10⁵ y ²⁶Al in silicon carbide by the process ²⁸Si(n,np+d)²⁷Al(n,2n)²⁶Al (a long-lived radioactivity issue)? The energy range 14–15 MeV of the D-T fusion neutrons is emphasized. Cross-section error bars are needed so that uncertainties in the gas and radioactivity generated over the lifetime of a reactor can be estimated. We address this issue by comparing values obtained from prominent evaluated cross-section libraries. Small differences between independent evaluations indicate that a physical quantity is well known while the opposite signals a problem. Hydrogen from ⁵¹V(n,p)⁵¹Ti and helium from ⁵¹V(n,α)⁴⁸Sc are also important sources of gas in vanadium, so they too were examined. We conclude that ⁵¹V(n,p)⁵¹Ti is adequately known but ⁵¹V(n,np+d)⁵⁰Ti is not. The status for helium generation data is quite good. Due to recent experimental work, ²⁷Al(n,2n)²⁶Al seems to be fairly well known. However, the situation for ²⁸Si(n,np+d)²⁷Al remains unsatisfactory.