Radiation damage in the target area shielding of a facility for Selective Production of Exotic Species ( SPES Project )
The advancement of radioactive ion beam (RIB) science since its advent in the last few decades calls for the development of so-called next generation facilities, able to provide beam intensities several orders of magnitude higher than presently available. Two of them are planned by the European roadmap and are representative of the two main methods by means of which RIBs are produced nowadays: projectile fragmentation and isotope separation on-line (ISOL); the latter, based on the ISOL technique, is the EURISOL project: the plan encompasses the construction of three intermediate facilities, one of which is expected to be built at Legnaro (Padua) INFN Laboratories: the SPES Project (Selective Production of Exotic Species).
Possibility of Radiation-Induced Degradation of Concrete by Alkali-Silica Reaction of Aggregates
The effect of Ar ion irradiation on the reactivity of crystalline and amorphous quartz to alkali has been examined for clarifying whether radiation from nuclear reactors accelerates the degradation of concrete by inducing alkali-silica reaction of aggregates. Distorted amorphous quartz generated on the surface of quartz by irradiation of a 200 keV Ar ion beam is at least 700 times and 2.5 times more reactive to alkali than crystalline and regular amorphous quartz, respectively. The high reactivity of the distorted amorphous quartz indicates that the degradation of concrete by alkalsilica reaction is possible to be induced by nuclear radiation even the aggregates are inert to alkali before the irradiation. The critical radiation doses for the degradation of aggregates containing crystalline quartz are estimated to be 5 × 1019 n/cm2 for fast neutrons with energy >0.1 MeV, and 5×1011 Gy for beta and gamma rays. They are 1×1019 n/cm2 and 0.5tiems;1011 Gy, respectively for aggregates containing amorphous quartz.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.