Masanori Kaminaga

R & D on mercury target pitting issue

Abstract A technical issue in mercury spallation target development is pitting, which appears on the target vessel in conjunction with the pressure wave. Pitting has been found in off-beam line test by split Hopkinson pressure bar (SHPB) test as well as in the on-beam test of mercury target at WNR of LANSCE. In SHPB tests pressure in mercury was reduced from 80 to 40, 20 and 10 MPa. Specimens made of type 316 stainless steel were inspected before and after the impacting test at ×450 magnification. Results show that over 20 MPa pitting was generated. But at the lowest pressure in mercury, the number of pits was very limited and substantial damage was small. Substantial damage by pitting is characterized by holes where mass is removed from the wall. Depression itself may not be a substantial damage as long as it is not accompanied by holes.

Experimental study on the effects of channel gap size on mixed convection heat transfer characteristics in vertical rectangular channels heated from both sides

Abstract The effects of channel gap size on mixed forced and free convective heat transfer characteristics were experimentally investigated for water flowing near atmospheric pressure in a 750 mm long and 50 mm wide channel heated from both sides. The channel gap sizes investigated were 2.5, 6, 18 and 50 mm. Experiments were carried out for both aiding and opposing forced convective flows with a Reynolds number Re x of 4 × 10 to 6 × 10 6 and a Grashof number Gr x of 2 × 10 4 to 6 × 10 11 , where the distance x from the inlet of the channel is adopted as the characteristic length in Re x and Gr x . As for the results, the following were revealed for the parameters ranges investigated in this study. 1. (1) When the dimensionless parameter, Gr x / Re x 21 8 Pr 1 2 is less than 10 −4 , the flow shows the nature of forced convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. 2. (2) When Gr x / Re x 21 8 Pr 1 2 is larger than 10 −2 , the flow shows the nature of free convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. 3. (3) When Gr x / Re x 21 8 Pr 1 2 is between 10 −4 and 10 −2 for the channel with a channel gap size equal to or larger than 6 mm, the heat transfer coefficients in both aiding and opposing flows become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection, and can be expressed in simple forms with a combination of Gr x / Re x 21 8 Pr 1 2 and the previous correlation for either the pure turbulent forced convection or the free convection along a flat plate. 4. (4) When Gr x / Re x 21 8 { Pr 1 2 is between 10 −4 and 10 −2 for the channel with a channel gap size of 2.5 mm, the heat transfer coefficients in both aiding and opposing flows also become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection. This is considered to be because the acceleration of the main flow originated by the development of the boundary layer in a narrow rectangular channel promotes the heat transfer.

Experiments on mercury circulation system for spallation neutron target

A construction of the spallation neutron source is in progress under the Japan Proton Accelerator Research Complex (J-PARC) Project. A mercury circulation system has been designed to supply mercury to the target stably. In the design of the mercury circulation system, it was necessary to test a mercury pump performance. An erosion rate under the mercury flowing condition and an amount of remaining mercury after draining mercury from the system also must be made clear from viewpoints of evaluating life time of mercury piping. In addition, these data play essential roles in establishing remote handling scenario of components used in the system, because mercury would be highly activated. The mercury pump performance, the erosion rates and the amount of remaining mercury were investigated by using a mercury experimental loop with an experimental gear pump. As a result, it was demonstrated that the discharged flow rates of the pump were sufficient. The flow rate increased linearly with the rotation speed as expected. With conservative assumption, a decreased amount of piping wall thickness was estimated 660 mm after 30-year operation under the rated mercury velocity of 0.7 m/s based on the obtained erosion rate. For the amount of remaining mercury in the loop, remaining rates of weight was estimated to be 50.7 g/m2.

Analytical Study of Volumetric Scroll Pump for Liquid Hydrogen Circulating System

The paper presents analytical results of suction process of a volumetric scroll pump, which will be developed for circulating liquid hydrogen in a cold moderator system. The multi-block grid generation approach has been applied to generate a moving boundaries computational model. The finer mesh patterns have been generated in the near-wall regions. The Low-Reynolds number k-ε turbulence model has been solved for predicting Reynolds stresses and turbulent scalar fluxes. The analysis has been carried out under liquid hydrogen flow conditions. The heat transfer effect is neglected to simplify the study. The analytical results show that at the end of suction process the relative pressures increase significantly in a pocket while decrease continuously in another pocket. This phenomenon might damage scroll pump components if the high-pressure side is too high and/or the low-pressure side is too low until the cavitations occur. Therefore, the pocket should open to the discharge chamber before it closes and separates from the suction chamber in order to prevent the cavitations and extremely high-pressure regions.

Water flow experiments and analyses on the cross-flow type mercury target model with the flow guide plates

Abstract A mercury target is used in the spallation neutron source driven by a high-intensity proton accelerator. In this study, the effectiveness of the cross-flow type mercury target structure was evaluated experimentally and analytically. Prior to the experiment, the mercury flow field and the temperature distribution in the target container were analyzed assuming a proton beam energy and power of 1.5 GeV and 5 MW, respectively, and the feasibility of the cross-flow type target was evaluated. Then the average water flow velocity field in the target mock-up model, which was fabricated from Plexiglass for a water experiment, was measured at room temperature using the PIV technique. Water flow analyses were conducted and the analytical results were compared with the experimental results. The experimental results showed that the cross-flow could be realized in most of the proton beam path area and the analytical result of the water flow velocity field showed good correspondence to the experimental results in the case when the Reynolds number was more than 4.83×10 5 at the model inlet. With these results, the effectiveness of the cross-flow type mercury target structure and the present analysis code system was demonstrated.

Critical heat flux at high velocity channel flow with high subcooling

Abstract A quantitative analysis of critical heat flux (CHF) in heated channels under high mass flux with high subcooling was successfully carried out by applying a new flow model to the existing CHF model of a macro-water-sublayer on the heated wall and steam blankets over it. The CHF correlation proposed could correctly predict the existing experimental data for circular tubes of 0.33–4 mm in diameter with mass flux of 124–90 000 kg (m 2 s) −1 and inlet water subcooling of 35–210 K at 0.1–7.1 MPa, resulting in CHF of 4.2–224 MW m −2 , and for rectangular channels of 3–20 mm gap with a mass flux of 940–27 000 kg (m 2 s) −1 and inlet water subcooling of 13–166 K at 0.1–3.0 MPa, resulting in CHF of 2.0–62 MW m −2 . An error of the CHF correlation has also been estimated.

Prediction of Flow Patterns and Pressure Distributions in Suction Process of Volumetric Scroll Pump

Prediction of Flow Patterns and Pressure Distributions in Suction Process of Volumetric Scroll Pump Phichai KRITMAITREE a , Mitsunobu AKIYAMA a , Ryutaro HINO b , Masanori KAMINAGA b & Atsuhiko TERADA b a Mechanical Engineering Department , Utsunomiya University , Ishii-cho , Utsunomiyashi , Tochigi , 321-0912 b System Engineering Group, Tokai Research Establishment , Japan Atomic Energy Research Institute , Shirakata , Tokai-mura , Naka-gun , Ibaraki , 319-1195 Published online: 07 Feb 2012.

Mercury Target and Its Peripheral Devices for 1 MW Spallation Neutron Source

The Japan Atomic Energy Research Institute (JAERI) and the High Energy Accelerator Research Organization (KEK) are promoting a plan to construct a 1MW neutron source facility at the Tokai Research Establishment, JAERI, under the Japan Proton Accelerator Research Complex (J-PARC) Project. In the facility, 1 MW pulsed proton beam from a high-intensity proton accelerator will be injected into a mercury target in order to produce high-intensity pulse neutrons for use in the fields of life and material sciences. In order to realize such a high-power neutron source, the design activity of a cross flow type (CFT) mercury target and its peripheral devices has continued and the results is reflected in the ordering specifications of the facility construction. The arrangement of each component and their structure was optimized through experimental and analytical studies. In this paper, the present design of the mercury target components for 1MW spallation neutron source including the target vessel, a mercury circulation system, and a target trolley will be reported.Copyright

Hydraulic Experiments and Analyses for Development of the Cold Moderator

The Japan Atomic Energy Research Institute is developing a MW-scale spallation target system under the Neutron Science Project. A cold moderator using supercritical hydrogen is one of the key components in the target system, which directly affects the neutronic performance both in intensity and resolution. Since a hydrogen temperature rise in the moderator vessel affects the neutronic performance, it is necessary to ensure the smooth flow of hydrogen while suppressing the recirculation and stagnant flows which cause hot spots. In order to learn the flow pattern of the impinging jet flow and the flow induced by the jet, the experiments using the acrylic model simulating the moderator vessel, were carried out under water flow conditions with a PIV system. In parallel with the experiments, the hydraulic analyses were carried out with the STAR-CD. Both the experimental and analytical results showed the recirculation flow clearly. And the analytical results agreed well with the experimental results.