Comparison of PCA Versus Tungsten in TIBER-II in-Board Shield and Impact of Nuclear Data Uncertainties on Machine Cost

Abstract

In the initial design of TIBER-II inboard (I/B) shield, multilayers of tungsten shield and coolant were deployed with a total thickness of 48 cm. It was thought during the design process to replace W by PCA. The motivations are: (1) accumulated activation level in the I/B shield at shutdown is larger in the W-shield in comparison to the PCA-shield, and (2) concerns regarding cost/fabrication. This design change required an I/B shield thickness of ∼58 cm to reach the same performance level of the 48 cm W-shield. In this paper a detailed comparison between the two types of shield is given regarding the accumulated radioactivity, biological hazard potential (BHP), and afterheat levels at shutdown and various times thereafter. In addition, a substantial part of the present work is devoted to studying the impact of the present neutron cross-section uncertainties in the prediction of the radiation damage parameters in the S/C magnet. In this regard, an extensive cross-section sensitivity/uncertainty analysis was performed to assess the required increase in the I/B shield thickness in both cases to account for these uncertainties. It was shown that the economic penalty of such an increase is 13-17 M$ in the W-shield case as opposed to 10-14 M$ in the case of the PCA-shield.