Fig. 9-3 Conceptual structure of neutron pulse irradiation test element Neutron fluence to the irradiating sample is controlled by rotating a neutron absorber with a circular window.

Fig. 9-4 Structure of new type SPND Pt-13%Rh coated cobalt was used as an emitter.

Fig. 9-5 Relative output power of the new type SPND under neutron pulse irradiation New SPND showed high sensitivity to the relative output power and also responded very quickly.

We have developed a small size self-powered neutron detector (SPND), which enables measurement of local transitional changes in thermal neutron flux at a sample portion in an irradiation test element. The irradiation test element is equipped with a window made of hafnium as a neutron absorber, and is used for a simulation of neutron pulse irradiation in order to evaluate tritium formation and resumption characteristics of the blanket during neutron pulse operation of fusion reactors (Fig. 9-3). Hitherto, rhodium (Rh) or cobalt (Co) have been generally used as an emitter material of SPND. The SPND with a Rh emitter has high sensitivity but slow speed response, and the SPND with a Co emitter has high speed response but low sensitivity. We have developed the new type SPND with a Pt-13%Rh coated cobalt emitter which has both excellent characteristics of the two kinds of emitters above (Fig. 9-4). The transient response of the new type SPND during neutron pulse irradiation is shown in Fig. 9-5. It is confirmed that 40% of stationary output power was obtained within 20 ms, and tritium formation and resumption characteristics of fusion reactors were able to be measured at high sensitivity and high speed response.

Reference M. Nakamichi et al., Characterization of Hybrid Self-Powered Neutron Detector Under Neutron Irradiation, Fusion Eng. Des., 51-52, 837 (2000).

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