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Thermal hydraulic design and thermal stress calculations were conducted for a water-cooled solid target irradiated by a MW-class proton beam for a spallation neutron source. Plate type and rod bundle type targets were examined. The thickness of the plate and the diameter of the rod were determined based on the maximum and the wall surface temperature. The thermal stress distributions were calculated by a finite element method (FEM). The neutronics performance of the target is roughly proportional to its average density. The averaged densities of the designed targets were calculated for tungsten plates, tantalum–clad tungsten plates, tungsten rods sheathed by tantalum and Zircaloy and they were compared with mercury density. It was shown that the averaged density was highest for the tungsten plates and was high for the tantalum cladding tungsten plates, the tungsten rods sheathed by tantalum and Zircaloy in order. They were higher than or equal to that of mercury for the 1–2 MW proton beams. Tungsten target without the cladding or the sheath is not practical due to corrosion by water under irradiation condition. Therefore, the tantalum cladding tungsten plate already made successfully by HIP and the sheathed tungsten rod are the candidate of high performance solid targets. The decay heat of each target was calculated. It was low enough low compared to that of ISIS for the target without tantalum but was about four times as high as that of ISIS when the thickness of the tantalum cladding was 0.5 mm. Heat removal methods of the decay heat with tantalum were examined. It was shown that a special cooling system was required for the target exchange when tantalum was used for the target. It was concluded that the tungsten rod target sheathed with stainless steel or Zircaloy was the most reliable from the safety considerations and had similar neutronics performance to that of mercury.

A solid target is expected to give higher neutron intensity than a liquid target of mercury at a spallation neutron source with a power of around 1 MW. We have studied the neutronic performance of a target-moderator-reflector assembly with a tungsten solid target. It is found that the neutron intensities from moderators were higher in the solid target system than in the mercury liquid target. However, the tungsten target required cladding to prevent tungsten from the corrosion of cooling water. A tungsten target with tantalum cladding has been already developed although tantalum has high decay heat. Therefore, we estimated the decay heat of the target and found that the decay heat of 0.5 mm thick tantalum was still high. We need a thinner tantalum or new cladding materials. It was revealed that adoption of a thinner tantalum or new cladding material such as chrome nitride reduced the decay heat effectively.