Hayanori Takei

Estimation of acceptable beam-trip frequencies of accelerators for accelerator-driven systems and comparison with existing performance data

Frequent beam trips as experienced in the existing high-power proton accelerators may cause thermal fatigue in accelerator-driven system (ADS) components, which may lead to degradation of their structural integrity and reduction of their lifetime. In this study, acceptable beam-trip frequencies of the ADS accelerator were evaluated and compared with the performance of the ADS accelerator, which was estimated based on the operational data on existing accelerators. Thermal transient analyses were performed to investigate the effects of beam trips on the reactor components, with the objective of determining the feasibility of engineering the ADS and the reliability of the accelerator. These analyses were based on the thermal responses of the following reactor components: the beam window, the fuel cladding, the inner barrel and the reactor vessel. Assuming that the annual plant availability was 70%, our results indicated three acceptable beam-trip frequencies, depending on the beam-trip duration, τ b : 2 × 104 times per year for 0 10 s; 2 × 103 times per year for 10 s 5 min; and 42 times per year for τ b > 5 min. In order to consider methods to reduce beam-trip frequency, we compared the acceptable beam-trip frequency with the performance of the ADS accelerator, which was estimated based on the operational data on existing accelerators. The comparison showed that for beam trips with a duration of 10 s or less, the beam-trip frequency was acceptable. On the other hand, for beam trips with durations of 10 s 5 min and τ b > 5 min, it was necessary to reduce the beam-trip frequencies to about 1/6 and 1/35, respectively.

TEF Beam Window Design and Evaluation of Structural Integrity

To promote R&D for accelerator-driven systems (ADS), the ADS Target Test Facility (TEF-T) is planned under the framework of the J-PARC project. Design of a proton beam window (BW) of a lead-bismuth eutectic (LBE) target is one of key issues for TEF-T construction. The objective of this study is to evaluate of structural integrity of the BW. That is, thermal-fluid behavior of LBE around the BW, structural integrity against thermal stress and internal pressure, and effects of cavitation bubbles generated by pressure waves due to pulsed proton beam injection were evaluated. As a result, the integrity of the BW for the thermal stress and the internal pressure was confirmed, and the candidate of the initial operation condition for the target system was suggested. Furthermore, it was confirmed that the cavitation bubbles would not cause meaningful damages on the target vessel.

Evaluation of mean time between accidental interruptions for accelerator klystron systems based on the reliability engineering method

ABSTRACT Frequent beam trips as experienced in existing high-power proton accelerators may cause thermal fatigue in Accelerator-Driven System components. In order to overcome the beam-trip problem, the beam-trip frequencies were estimated based on operational data on existing accelerators. However, there are at least three methods to calculate the mean time between accidental interruptions (MTBI) for one of the accelerator components, the klystron system. In this study, the four types of MTBI for the klystron systems of an electron/positron injector linear accelerator at the High Energy Accelerator Research Organization were compared based on the same operational data. In the analysis, the stop events of the klystron systems were classified, and the MTBI for the klystron systems was calculated using the Kaplan–Meier (KM) estimation, which is a representative non-parametric reliability method. As a result, the mean value of the MTBI found by the KM estimation was 57.3 ± 6.5 hours. On the other hand, the mean values of the MTBI found by the three traditional methods were 30.9 ± 2.4, 32.0 ± 2.3, and 50.4 ± 5.9 hours. The mean values for the ratios of the MTBI found by the KM estimation, to the MTBI found by the traditional estimation, were 1.67 ± 0.07, 1.58 ± 0.06, and 1.14 ± 0.01, respectively. Although these results are obviously different from traditional results, it appears that the present estimation is suitable for the MTBI for accelerator components.

Present Status of the Laser Charge Exchange Test Using the 3-MeV Linac in J-PARC

The Accelerator-driven System (ADS) is one of the candidates for transmuting long-lived nuclides, such as minor actinide (MA), produced by nuclear reactors. For efficient transmutation of the MA, a precise prediction of neutronics of ADS is required. In order to obtain the neutronics data for the ADS, the Japan Proton Accelerator Research Complex (J-PARC) has a plan to build the Transmutation Physics Experimental Facility (TEF-P), in which a 400-MeV negative proton (H) beam will be delivered from the J-PARC linac. Since the TEF-P requires a stable proton beam with a power of less than 10 W, a stable and meticulous beam extraction method is required to extract a small amount of the proton beam from the high power beam using 250 kW. To fulfil this requirement, the Laser Charge Exchange (LCE) method has been developed. The LCE strips the electron of the H beam and neutral protons will separate at the bending magnet in the proton beam transport. To demonstrate the charge exchange of the H, a preliminary LCE experiment was conducted using a linac with energy of 3 MeV in JPARC. As a result of the experiment, a charge-exchanged H beam with a power of about 5 W equivalent was obtained under the J-PARC linac beam condition, and this value almost satisfied the power requirement of the proton beam for the TEF-P.