Yoshitomo Uno

Progress of the ITER central solenoid model coil programme

The worlds largest pulsed superconducting coil was successfully tested by charging up to 13 T and 46 kA with a stored energy of 640 MJ. The ITER central solenoid (CS) model coil and CS insert coil were developed and fabricated through an international collaboration, and their cooldown and charging tests were successfully carried out by international test and operation teams. In pulsed charging tests, where the original goal was 0.4 T/s up to 13 T, the CS model coil and the CS insert coil achieved ramp rates to 13 T of 0.6 T/s and 1.2 T/s, respectively. In addition, the CS insert coil was charged and discharged 10 003 times in the 13 T background field of the CS model coil and no degradation of the operational temperature margin directly coming from this cyclic operation was observed. These test results fulfilled all the goals of CS model coil development by confirming the validity of the engineering design and demonstrating that the ITER coils can now be constructed with confidence.

First test results for the ITER central solenoid model coil

Abstract The largest pulsed superconducting coils ever built, the Central Solenoid (CS) Model Coil and Central Solenoid Insert Coil were successfully developed and tested by international collaboration under the R&D activity of the International Thermonuclear Experimental Reactor (ITER), demonstrating and validating the engineering design criteria of the ITER Central Solenoid coil. The typical achievement is to charge the coil up to the operation current of 46 kA, and the maximum magnetic field to 13 T with a swift rump rate of 0.6 T/s without quench. The typical stored energy of the coil reached during the tests was 640 MJ that is 21 times larger than any other superconducting pulsed coils ever built. The test have shown that the high current cable in conduit conductor technology is indeed applicable to the ITER coils and could accomplish all the requirements of current sharing temperature, AC losses, ramp rate limitation, quench behavior and 10 000-cycle operation.

Development of 46-kA Nb/sub 3/Sn conductor joint for ITER Model Coils

The conductor joint is one of the key technologies for superconducting coils. A butt type joint has been successfully developed for the ITER magnets. The 46 kA Nb/sub 3/Sn conductors are connected by the diffusion bonding technique in vacuum, after the reaction of Nb/sub 3/Sn. The advantage of this joint is low losses against pulse field, because the compacted part is very small compared with other types of joint. 15 butt joints have already been fabricated in the ITER CS Model Coil. According to the test results of the full-size conductor samples, these butt joints will be operated stably in the pulse operation, because the temperature increase due to ac losses and Joule heating by joint resistance is very small and the joint has a sufficiently high temperature margin.

An investigation of the activation of water by D-T fusion neutrons and some implications for fusion reactor technology

Abstract Several fundamental aspects of the activation of water by neutrons in D-T fusion systems have been investigated in this work. The basic physical principles involved and the status of pertinent nuclear cross-section and radioactivity data were reviewed. The integral response of the dominant 16 O(n,p) 16 N reaction was calculated using several evaluated differential cross-section representations and characteristic D-T fusion neutron spectra. The impact of cross-section uncertainties was also assessed in this context. Two integral experiments were carried out at a D-T neutron generator facility to investigate the production and transport of 16 N radioactivity in a D-T fusion neutron environment. Radioactivity yield data were acquired in one of these integral experiments (IE-1) and the measured results were compared with values obtained from calculations which employed both analytical and Monte-Carlo techniques. Measurements on the shielding of high-energy gamma rays from 16 N decay by stainless steel (SS-304) and copper were performed in an additional integral experiment (IE-2) and these data were interpreted by a combination of analytical calculations and Monte-Carlo simulation. Some consequences of neutron-induced 16 N radioactivity in the cooling water of a fusion reactor were examined for two contemporary conceptual designs of the International Thermonuclear Experimental Reactor (ITER). This analysis benefitted from insight acquired through the present integral studies. It was found that this radioactivity generating process would lead to significant biological doses outside the reactor containment vessel and could also deliver potentially damaging radiation doses to superconducting magnet insulators unless care is taken to provide adequate shielding when designing a fusion reactor.

Technical feasibility study on a fusion power monitor based on activation of water flow

As a part of development of nuclear instrumentation for the international thermonuclear experimental reactor (ITER), technical feasibility of a fusion power monitor based on activation of water flow was studied. The fusion power monitor determines D–T neutron yield, i.e., fusion power, by measuring 6.1 and 7.1 MeV γ rays accompanied by disintegration of 16N nuclei that are produced by the 16O(n,p) 16N reactions with 14 MeV neutrons in water. The fusion power monitor consists of a water pipe loop laid from the first wall to the outside of the bioshield and a γ-ray detector, e.g., a BGO scintillator. Fusion power can be measured in an absolute value by this monitor similar to a neutron activation method with a pneumatic tube system; in addition, this monitor has a feature that continuously measures the fusion power with time resolution faster than 1 s. This monitor also has other excellent features in terms of long-term stability, sensitivity only for D–T neutrons and being maintenance free. In order to con...

Integral experiment of induced radioactivity in D-T fusion neutron environment and validation of activation cross section library

Abstract Under ITER/EDA R&D Task T-218, an integral experiment on the induced radioactivity was conducted at the Fusion Neutronics Source (FNS) facility in JAERI. The objective was to provide experimental data for validating the inventory calculation codes and relevant activation cross section libraries to be used in the ITER nuclear design. Sample materials investigated were Al, Mg, Ti, V, Mn, Fe, Ni, SS-316LN, Cu, Zn, Nb, Mo, Ag, In, Sn, Hf, Ta, W and Pb. The corresponding neutron spectra at two locations were calculated by MCNP4A with JENDL-Fusion File based nuclear data library by modeling the experimental assembly precisely. The calculations with currently updated activation cross sections, JENDL-ACT96, FENDL-A1 and FENDL-A2, were carried out to compare the results with the experiment. The results for the comparison between the measurement and calculation of radioactivity are discussed in terms of the adequacy of calculation as far as the D-T neutron dominated neutron field is concerned.

Absolute measurement of D–T neutron flux with a monitor using activation of flowing water

Abstract Neutron activation with water flow based on the 16 O(n, p) 16 N reaction ( T 1/2 =7.13 s) has been proposed for the accurate fusion power monitor with reasonable time resolution in International Thermonuclear Experimental Reactor (ITER)-FEAT. The experiment for validation of the method for determining the neutron flux was carried out at the Fusion Neutronics Source (FNS) facility in Japan Atomic Energy Research Institute (JAERI). The stainless steel (SS316)/Water assembly was utilized to simulate a neutron field in the blanket region of ITER. The closed water loop was laid between the assembly and the shielded measurement area. The γ-rays from the irradiated water were measured by Bi 4 Ge 3 O 12 (BGO) scintillator which was ∼12 m away from the irradiation point. The range of the flow velocity was 2–11 m/s. The neutron spectrum at the probe section in the SS316/Water assembly was calculated by the MCNP-4B code with the FENDL/E-2.0 library. The cross section data of the 16 O(n, p) 16 N reaction was taken from the FENDL/A-2.0 file. The counting response of the BGO detector including the effect of the shielding lead blocks surrounding it was calculated by MCNP-4B. The neutron yield from the water activation has a good agreement with that from associated α particle detector.

Neutronics experiments for ITER at JAERI/FNS

A series of fusion neutronics experiments has been performed at the Fusion Neutronics Source facility at Japan Atomic Energy Research Institute as ITER EDA R&D tasks to find ways of dealing with various nuclear problems originating from 14 MeV neutrons in ITER. Recently three groups of experiments were carried out: (1) straight duct streaming experiments, (2) decay heat experiments, and (3) development of a fusion power monitor utilizing activation of water. The straight duct streaming experiments suggest that the calculation accuracy for straight duct streaming analyses in ITER nuclear designs is ±40%. The decay heat experiments show that the accuracy of the decay heat calculation is within 10% for copper and type 316 stainless steel, while it is ~30% for tungsten. It is demonstrated that a fusion power monitor utilizing activation of water is applicable to ITER.

Overview of straight duct streaming experiments for ITER

Abstract Two straight duct streaming experiments for international thermonuclear experimental reactor (ITER) were performed by using the intense deuterium–tritium (D–T) neutron source at Japan Atomic Energy Research Institute (JAERI) in order to investigate the influence of streaming through ducts on radiation dose and to validate the accuracy of design calculations. One was a small duct streaming experiment for diagnostic ports, the other was a large duct streaming experiment for large ports such as neutral beam injector (NBI) port. The ducts increased the neutron flux above 10 MeV by 10 6 –10 7 times at the ends of the ducts, while the increase of neutron flux below 10 MeV and γ-ray by the ducts was less than a few hundred times. These experiments were analyzed by the MCNP-4A code with three nuclear data libraries: FENDL/E-2.0, -1.0 and JENDL Fusion File. Though the ducts made complicated neutron and γ-ray flux distributions in a cavity region, most of the calculated results agreed within ±40% with the experimental data. It was demonstrated that the MCNP calculations with the nuclear data libraries were accurate enough for predicting nuclear design parameters of ITER even for various duct geometries as far as they were modeled precisely.

Development of a 13T-46kA Nb3Sn conductor and central solenoid model coils for ITER

Abstract Japan Atomic Energy Research Institute (JAERI) is developing the outer module of the central solenoid (CS) model coils. The Nb3Sn strands and cables for the outer module were almost completed. The winding and the heat treatment technique were established by the trial fabrication. The design of the conductor joint was already finalized by the full size sample test. The first layer of the 8-layer module was wound with enough accuracy by using a two-conductor-in-hand technique. The CS model coil will be completed and tested in 1998.