1. Preliminary design of specimen and capsule materials and position monitoring methods for ITER NAS
J.J. Dang†, Y. Lee, J. G. Jo and
Y. S. Hwang††
KSTAR Conference 2012 Feb. 23rd 2012 Muju Deogyusan Resort, Jeonbuk, Korea
FUSMA, Dept. of Nuclear engineering, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul , Korea

2. Contents Introduction Neutron Activation Foil Material Study
NAS Capsule Material Study
Development of Capsule Position Monitoring Method
Summary 1

3. Introduction: Motivation and Objectives of Study
ITER NAS Circumstance[1, 2,3]
Neutron power load on the first wall (≥ 0.5 MW/m2) : High melting point materials
High magnetic field (5.3T at 6.2m radius): Non-magnetic materials
Long operation time(10s – 3000s): No activation saturation
Long distance between irradiation ends and detection ends(50m-100m): Transport and monitoring system
Investigation on ITER applicable foil and capsule materials
Development of capsule position monitoring system
[1] M. Shimada, et al., “Chapter 1: Overview and summary,” Nuclear Fusion, 47 (2007) S1
[2] A.J.H. Donné, et al., “Chapter 7: Diagnostics,” Nuclear Fusion, 47 (2007) S337
[3] H.G. Lee, et al., “Status of Design and R&D for the Korean ITER Diagnostic Systems”, Proc. 23rd IAEA FEC Conf., ITR/P1-04 (2010).

4. Introduction: Neutron Activation System in ITER[1]
NAS diagnostics requirements
Measurement
Parameter
Condition
Range or Coverage
Resolution
Accuracy
Time
Spatial
Neutron flux and emissivity
Total neutron flux
1x1014 – 5x1020 n/s
10s
Several poloidal points
10 %
In-situ calibration: neutron flux and emissivity
Before H, DD and DT phases
TBD
Neutron fluence
Neutron fluence on the first wall
0.1 – 1 Mwy/m2
Integral
Figure 1. Irradiation ends in toroidal section view. 7 irradiation ends locates at 1 toroidal section, and 2 toroidal section will be used
Figure 2. Design of sample transfer line
[1] H.G. Lee, et al., “Status of Design and R&D for the Korean ITER Diagnostic Systems”, Proc. 23rd IAEA FEC Conf., ITR/P1-04 (2010).

5. Investigation on major properties: nuclear, material properties
Neutron Activation Foil Material Study: Investigation on specimen materials
Investigation on major properties: nuclear, material properties
- for DD neutrons: In-115, Zn-64, Ni-58
- for DT neutrons: Al-27, Si-28, Ni-58, Cu-63
- Neutron induced activation cross section, atomic mass, density, natural abundance
half-life, gamma abundance (for daughter nuclei)
Expectation on activities of candidates materials
- Based on collected data, activities are calculated.
- Calculation conditions
▪ Neutron flux : 2.2x1013 n/cm2/s (equivalent to 0.5MW neutron power load)
▪ Irradiation time : 100s
▪ Volume of materials : 1cm3 4

6. Neutron Activation Foil Material Study: Activation and γ-ray spectrum Analysis
Indium is most promising materials for DD neutron measurement
- Neutron activation reaction of Indium: 113In(n,γ)114In, 114In(n,n’)115mIn, 115In(n,γ)116In
- Major properties
- Major nuclear levels diagram and decay-scheme
Density
Melting point
Boiling point
Natural abundance
113In
114In
7.31 g/cm3
156.6 oC
2072 oC
4.3 %
95.7 %
116In
54.41m
Ground
β--decay
Eγ keV (2.46 %)
Eγ keV (10.0 %)
115In
4.41 x 1014y
4.486h
336.24
Ground
Eγ keV (45.9 %)
Eγ keV (28.9 %)
Eγ keV (3.29 %)
Eγ keV (56.2 %)
Eγ keV (11.5 %)
2801.7
2390.8
Eγ keV (84.4 %)
Ground
116Sn 5

7. Neutron Activation Foil Material Study: Activation and γ-ray spectrum Analysis(Cont’d)
Irradiation period
Cooling period
(a) (b)
Figure (a) and (b) shows the activities of indium foil irradiated by 0.5MW neutron load. Neutron spectrum is assumed to be mono-energetic 2.45 MeV DD neutrons. The dimension of indium foil is Ø4mm x 1mm. Figure (a) is 10 seconds irradiation, and (b) is 1000 seconds irradiation result. 115mIn (blue line) is a meta-stable isotope and a 336keV γ - ray source. Blue lines are linearly dependent on irradiation time with activation saturation. Therefore, if the activity of 115mIn is measured, the neutron fluence can be expected. However, the activity of 115mIn in (b) exceeds the safety limit(100μCi, dashed black line). Therefore, NAS operators should adjust the foil amount according to the expected neutron fluence.

8. Neutron Activation Foil Material Study: Activation and γ-ray spectrum Analysis(Cont’d)
115mIn
116mIn
116mIn
116mIn
116mIn
116mIn
116mIn
116mIn
(a) (b)
Figure (a) and (b) shows the expected γ - ray spectrums emitted by the irradiated indium foils. 336 keV lines are emitted from 115mIn and the others from 116Sn which is a daughter nucleus of 116mIn. Figure (a) is the spectrum of 10sec irradiated indium foil, and (b) is 1000sec irradiated foil. The intensities except for 336keV may decrease during measurement, because 116mIn has relatively short half-life of minute. Since γ - ray measurement might be conducted over several decades of minutes, the spectrums from 116Sn are difficult to use in the neutron diagnostics.

9. Neutron Activation Foil Material Study: Activation and γ-ray spectrum Analysis(Cont’d)
These calculation results are based on the primary assumption and nuclear data. This study should include the neutron energy spectrum in ITER. Also, Monte Carlo simulation is required to estimate the γ - ray spectrum data.
This study has used FISPACT that is ITER standard in the neutron activation calculation. The neutron spectrum based on the ITER simulation results will be included. Furthermore, using Monte Carlo simulation, the realistic γ - ray spectrum measured by HPGe will be obtained.
If more specific study is to be followed, we can choose NAS operation scenario such as foil material, foil amount irradiation time and location. Then NAS will become more powerful neutron diagnostics. In order to apply NAS operation scenario and simulation results in ITER, this study will be conducted through collaboration with ITER KODA and analysis of KSTAR NAS experimental results.

10. NAS Capsule Material Study: Requirements of Capsule Material
- High heat flux
- High temperature
- High neutron flux
- High magnetic field
First Wall Condition
- High melting point
- No magnetic material
- Low neutron activated
- Low chemical reaction
First Wall Material
Similar condition between 1st wall material and NAS capsule material
- High melting point
- Easy fabrication
- Non-magnetic material
- Not brittle
- Low neutron activation
- Low chemical reaction
- Human dose limit : ~100μCi
- Low cost
NAS Capsule Material Requirements

11. NAS Capsule Material Study: Material Selection Procedure
This figure shows the CFC(Carbon-Carbon) plate penetrated by a nail.
Advanced CFC for high temperature application can be fabricated and machined on request.[1]
Metal, SiC composite, CFC, Reinforced polymer materials
Non-magnetic material
SiC composite, CFC, Reinforced polymer materials
Melting point >300℃
SiC composite, CFC
Easy Fabrication
CFC(Carbon-Carbon)
* Raw material (Ø8x20mm) cost of CFC: 18,000 KRW[1]
[1] SGL group and its Korean vendor, private communication

12. NAS Capsule Material Study: Neutron Activation and Primary Design of Capsule
Carbon has three representative neutron activation reaction.
- 12C(n,2n)11C : Threshold energy of reaction is more than 20 MeV.
- 12C(n,γ)13C : This reaction has large cross section by thermal neutrons, but 13C is a stable isotope and is not chemically different from 12C.
- 13C(n,γ)14C : This reaction has large cross section by thermal neutrons and resonance with MeV neutrons , but the natural abundance of 13C is only 1.11% and half-life of 14C is very long. Half-life of 14C is 5730yr. It means that the disintegration of 1 % of 14C requires more than 80years.
Based on the above investigation, the neutron activation of carbon is negligible or chemically stable.
Primary design of capsule is determined as the left figure. Instead of conventional dualistic structure consisted of capsule and wadding, bullet-shaped screw assembly design has been chosen. This design is expected to prevent leakage even when the foil is melt in the inside.
This design should be followed by experimental studies, such as a mechanical test.

13. Development of Capsule Position Monitoring Method: Position Monitoring Method Using Flow Meter
ITER NAS is designed as long transport line and pneumatic transfer system. In order to secure measurement accuracy and prepare for accidents such as stuck-in capsule, the operators should trace the capsule position in real time. This study has developed two kinds of position monitoring methods.
Experiment results of capsule position monitoring method using flow meter
The flow by pneumatic power is measured during capsule transport. The flow meters are located at the start and the end of the transfer line. This method traces the capsule position from the time-integrated-flow, or the volume consumed in transportation of the capsule divided by the cross section of transfer line. Left graph shows the experimental result. This method is expected to trace the position in real time basis.
Though this method has errors of several meters, thus utilizing flow meter method will be advanced by the experimental improvement, optimization and fluid mechanical analysis.

14. Development of Capsule Position Monitoring Method: Position Monitoring Method Using Ultrasonic wave
The other position monitoring method uses the ultrasonic wave. Ultrasonic wave is generated by the home-made magnetostrictive transducer consisted of the permanent magnet, coil and the ferromagnetic material such as iron and nickel. The transducer and receiver are installed at the front part of the transfer line. Because the distance between transducer and receiver is the known value, the speed of the sonic wave in transfer line can be obtained from time interval as shown in figure (a).
Also, if the travel time of the wave reflected by the capsule is measured, the capsule position can be calculated from the travel time and the speed of wave. (Figure (b))
This study is in basic phase, and the following study will be conducted. This method is expected as secondary monitoring system to prepare the accident such as stuck-in capsule.
Reflected wave
Incident wave
(a) (b)

15. Summary
This study selects several candidates of the activation foil materials. Their nuclear and other properties are collected. Based on the collected data, the neutron induced radio-activities and γ - ray spectrums are calculated.
This study chooses the Carbon Fiber reinforced Carbon as promising capsule material. CFC has superb mechanical and material properties and resistance to the neutron activation. Bullet-shaped screw assembly design is chosen as primary design.
Two capsule position monitoring methods have been developed using flow meter and ultrasonic wave. These development should be improved and optimized. This study is expected that two monitoring system are installed simultaneously. This hybrid type system traces the capsule using flow meter in real time, and the ultrasonic wave method will be used for accident analysis.
Pneumatic power source
Solenoid valve
Oscilloscope
Capsule
Pneumatic transfer tube
Electronic flow meter
Sonic wave transducer
Sonic wave receiver