Design of ITER neutron yield monitor using microfission chambers

We propose a microfission chamber system which will be installed near the first wall region of ITER as the neutron yield monitor. This system has a wide dynamic range of 1010 with a temporal resolution of 1 ms and is easily calibrated by a neutron transport calculation. The 234U (80%) + 235U (20%) fission chamber, the lifetime of which is about four times longer than that of the 235U chamber, can be used in ITER for one third of the ITER lifetime. We expect that these detectors will be operated in a high magnetic field near the first wall of ITER. Four sets of the detectors will be installed in the large side port and three blanket modules. Techniques for the replacement of those detectors are discussed.