A coaxial double-pipe structure is to be used in both the main and auxiliary primary coolant systems of the very high-temperature gas-cooled reactor which has been developed by Japan Atomic Energy Research Institute. By using a straight-type model of the coaxial double-pipe structure, the experiment has been carried out to study the following items: Effect of both the pitch of spacers in the axial direction and insulator inserted into the inner pipe on the damping vibration characteristics. These experimental results are compared with calculated values for a parallel-beam model using a structural analysis code COSMOS-7. The followings are the conclusions derived: (1) Damping ratio of a coaxial double-pipe structure increase with decrease of the pitch of spacers in the axial direction. (2) The calculated results of displacement-time response against the impact force almost agree with the experimental ones.
Distribution coefficients (Kd) used for an estimation of radionuclide migration in soil were reviewed. The relation between Kd and soil, water quality and chemical forms in groundwater were examined. The Kd values for generic safety assessment on shallow land burial are proposed as follows on the basis of knowledge of measured Kd values and expected chemical forms in ground-water. Group 1: tritium(Kd=0ml/g); Group 2: Tc, I etc. existing in groundwater as an anion(Kd =0-10ml/g); Group 3: alkali earth elements which form insoluble carbonate and sulfate (Kd=5- 50 ml/g); Group 4: rare earth elements or transition elements which form hydroxide or complex (Kd=10100ml/g); Group 5: actinide elements which form polymer, or elements existing in water as a stable cation such as Cs etc. (Kd=100-1, 000ml/g).
In the 1st paper, improvement of shell and tube heat exchanger efficiency by inserted wound wire net layers (WNL) around the tube bundle is investigated. And in the 2nd paper, the effect of the WNL inserted in a preheating shell and single tube heat exchanger, where shell wall is designed to be cooled by the secondary gas which in turn is preheated, is revealed. In the present study, following the 2nd paper, the preheating type heat exchanger with 12-tube bundle is examined; results show marked improvement in heat exchanger efficiency, which is essentially the same as those of the previous paper. By the WNL inserted exchanged heat in the preheating section decreases, however that in the tube bundle section increases to more than overcome this decrease and the total exchanged heat increases by 14-18%. Comparison of heat exchanger performances examined in the preceding works and in the pre-sent study is also made. It is found that the effectiveness for the present heat exchanger is the highest.