RAMI analysis of ITER diagnostic radial neutron camera

RAMI (Reliability, Availability, Maintainability and Inspectability) assessments are mandatory part of the design process for all ITER systems to anticipate possible risks in terms of reliability and availability and support reliability growth program. A RAMI assessment performed on the ITER Radial Neutron Camera (RNC) diagnostic system is presented. The assessment is aimed at evaluating the RNC design capability to provide the neutron emissivity radial profile measurement with required reliability and availability. The RNC is composed by two collimating structures equipped with neutron flux detectors, the In-Port RNC sub-system and the Ex-Port RNC sub-system respectively. Such systems radially view different plasma locations thus enabling the emissivity profile reconstruction. Both In-Port and Ex-Port detection systems (sensors, collimators, shielding) and full acquisition system chain (front-end and back-end electronics) are considered in the analysis. The RAMI performance was assessed by means of reliability block diagrams (RBDs) with respect to required mean inherent availability for 2 years of operations fixed at 99.5% for the Ex-Port system and at 88.3 % for the In-Port system. A set of failure events for each RNC component was defined by means of a failure mode and effect analysis. The resulting unavailability conditions of the systems were then identified. Hence identified groups of events were used to feed the RBDs model definition according to reliability-wise integration of the considered components. The integrated RAMI performance of RNC systems was finally estimated. Considering the current level of design development, In-Port RNC system appears able to meet stated requirement thanks to design redundancy. Ex-Port RNC, which includes Back End Electronics for data acquisition, is still below the RAMI target and requires further design improvement.