AbstractMany important neutronics issues will require testing in a fusion facility such as NET, FER, TIBER, OTR, or ITER. These neutronics issues include demonstration of tritium self-sufficiency, verification of adequate radiation protection of components and personnel, and validation of calculational methods and nuclear data. This paper examines the extent to which these issues can be resolved in a fusion testing facility, and discusses the technical interrelationships between the specialized neutronics tests and other tests for the blanket (e.g., fluid flow, tritium recovery). The most difficult issue appears to be the demonstration of DT fuel self-sufficiency. Direct demonstration requires a complete fuel cycle including full blanket and integrated tritium processing systems. This appears unlikely in the next fusion facility. Therefore, indirect demonstration through synthesis of information from various tests appears to be the only option.Tests for verification of other neutronics parameters can be classified into three categories: (1) dedicated tests; (2) supplementary measurements; and (3) measurements for the basic device. Dedicated tests aim at examining the accuracy of present neutron transport codes, basic nuclear data, and geometrical modeling in predicting key neutronics parameters. These tests would be carried out in large modules specifically designed for that purpose to maintain the appropriate boundary conditions. In addition, these tests would also be performed in various breeding material/coolant test modules to estimate the uncertainties in predicting their key neutronics parameters. Most of these tests require only low fluence (< 0.1 MW y/m2) and short plasma pulses (< 30 s) and are best suited for the early phases of the device operation. Supplementary neutronics measurements are intended to be performed in test modules used for other non-neutronics tests (e.g., tritium-recovery, thermo-mechanics tests, etc.). Goals of this category of tests are to: (1) provide the source terms and their associated uncertainties for the non-neutronics tests, and (2) provide additional supporting information to the dedicated tests. The overall test matrix schedule for the above-mentioned neutronics tests has been defined and the measuring techniques to perform these tests have been identified.