**2. Generic description**

ITER NAS measures gamma radiation from samples activated by fusion neutron flux. Encapsulated samples are transferred between irradiation ends and counting station by the driving of nitrogen (or helium) gas. Tubes of diameter 12.7 mm will be used for the transfer lines of the capsule.

NAS consists of the pneumatic transfer system and the counting system (**Figure 1**) Cheon et al. [3]. The pneumatic transfer system includes gas supply, transfer station, transfer line, irradiation ends, counter ends, and disposal bin. It is the subsystem related with the transfer of the encapsulated samples from the loading to the disposal. The PLC-based control system will be harnessed for the accurate operation of the system. The counting system consists of gamma-ray detectors, electronic devices such as high voltage supplies and amplifiers, and tool for neutron source strength evaluation. It is the system for the evaluation of the parameters of the NAS by counting gamma-rays from the activated samples [4].

**Figure 1.** The scheme of neutron activation system for ITER.

Due to the large size and the elongated shape of ITER plasma, multiple positions for the irradiation ends in toroidal section are required for highly reliable measurements. At present, four irradiation end locations per toroidal section (A, B, C and D in **Figure 2**) are planned for ITER NAS considering reliability of the measurement and redundancy of the system.

wall, blanket modules, and divertor cassettes that are located near the irradiation ends. A number of irradiation positions located above and below the plasma as well as on highfield side and low-field side has been selected for the ITER NAS to compensate the strong influence from in-vessel materials such as the diagnostic first wall, blanket modules, and

ITER NAS measures gamma radiation from samples activated by fusion neutron flux. Encapsulated samples are transferred between irradiation ends and counting station by the driving of nitrogen (or helium) gas. Tubes of diameter 12.7 mm will be used for the transfer

NAS consists of the pneumatic transfer system and the counting system (**Figure 1**) Cheon et al. [3]. The pneumatic transfer system includes gas supply, transfer station, transfer line, irradiation ends, counter ends, and disposal bin. It is the subsystem related with the transfer of the encapsulated samples from the loading to the disposal. The PLC-based control system will be harnessed for the accurate operation of the system. The counting system consists of gamma-ray detectors, electronic devices such as high voltage supplies and amplifiers, and tool for neutron source strength evaluation. It is the system for the evaluation of the param-

eters of the NAS by counting gamma-rays from the activated samples [4].

**Figure 1.** The scheme of neutron activation system for ITER.

divertor cassettes.

lines of the capsule.

**2. Generic description**

72 Advanced Technologies and Applications of Neutron Activation Analysis

Transfer tubes of the NAS should be bent many times to reach the irradiation ends from the transfer station. To avoid capsule stuck problem around tube bends, there should be a minimum bending radius of the tube in designing tube route. All bends of the tube should have larger radius than this minimum bending radius. Assuming the capsule of OD 8 mm and L 30 mm, and the tube of ID 9 mm, the minimum bending radius of the tube is about 100 mm. The current design value of the minimum bending radius is 150 mm, with the safety factor 50% applied.

Current port allocation for the NAS is #11 and #18 for the upper port, #11 and #17 for the equatorial port, and #12 and #18 for the lower ports. For points A and B, the irradiation ends will be located inside the port plugs. Other irradiation ends will be installed on the vacuum vessel wall with the pipelines routed through the lower level ports [5]. Allocated ports and port numbers for the irradiation locations are shown in **Figure 2**. Total number of the irradiation ends which will be installed is 12.

Transfer station distributes capsules to the appropriate locations such as irradiation end, counting station, or disposal bin. It consists of capsule loader and distribution machine 'carousel.' When capsule is loaded on the carousel from the loader, the platter inside the carousel rotates to place capsule to the point connected to the designated place. The capsule loader and the carousel are separated by the air lock system to prevent the leakage of the driving gas. At every transfer line ends the air cushion technique, which will be implemented to prevent capsule breakage.

Counting station locates outside the bioshield of ITER where neutron flux effect on the detectors is negligible. Detectors such as HPGe or NaI will be used to count gamma-rays from


**Figure 2.** Distribution of irradiation ends in a toroidal section and allocated port numbers.

the activated samples. The required parameters for the NAS such as neutron fluence will be evaluated from the gamma spectrum considering the location of the irradiation end, sample material and its mass, and irradiation and cooling time.

**Figure 3** shows the MCNP model for the calculation. The cutout of DFW was designed to have a toroidal and poloidal angle of view as large as possible, while minimizing the amount of material in front of the irradiation end to the plasma direction, in order to minimize errors from the plasma movement and neutron transport calculation. Initial values for each dimen-

Neutron Activation System for ITER Tokamak http://dx.doi.org/10.5772/intechopen.75966 75

Calculated activation coefficients are shown in **Figure 4**. When there is no DFW material (upper line) and when there is a cutout in DFW material (lower line). Absolute values of the activation coefficient are reduced by about 10% when the irradiation end is surrounded by

sion are:

• Depth: 130 mm.

• Poloidal angle: 105°. • Toroidal angle: 60°.

• Toroidal width: 30 mm.

**Figure 4.** Comparison of plasma movement effect with and without DFW.

**Figure 3.** MCNP model for calculation: (left) side view and (right) front view.
