MTR TECHNICAL BRANCH QUARTERLY REPORT

摘要

The progressive surveillance of the effect of fast neutron flux upon the MTR core materials continues to show no evidence of structural weakness. Infor¬mation is now available regarding the change in physical properties up to fast (greater than 100 ev.) neutron exposures of 2.6 x lO22 nvt. Tensile strength, yield strength for 0.2 percent offset, and hardness of 347-stainless steel, 2S-aluminura and QMV beryllium are now changing only very slowly and appear to be reaching saturation values.nPreliminary hydraulic testing of MTR fuel assemblies indicate that local flow velocities may drop about 10 percent below the overall average velocity. The location of the lowest coolant flow is at the edge of the channels adjacent to the side plates, particularly in the outer channels.nTechnical support to the Engineering Test Reactor is becoming a significant part of the work load. A thorough examination of the quality of fabrication of a dummy fuel assembly has been carried out. Corrosion tests on the proposed boron-aluminum cladding metal indicate that this alloy is somewhat inferior to 2S aluminum. More definitive tests are required to establish, its complete suitability. A nondestructive procedure for assaying the boron and U-235 content in an ETR fuel assembly is being evaluated. A chemical procedure for nitrate ion has been developed to monitor the radiation produced nitrate ion concentration which analysis has been unnecessary in the MTR.nIn reactor physics, the major effort has been placed on the calculations related to the SPERT III reactor. The IBM 650 Computer has made it feasible to extend the earlier two group reactor calculations to three groups and to correct the thermal utilization as required by the flux depression in the fuel elements. The data obtained so far are presented for both the stainless steel and zirconium clad fuel plates. In the second sizeable problem, it has been predicted that about 40 grams additional U-235 will be required in an MTR fuel assembly, should the present enrichment be reduced to 20 percent, in order to obtain an equivalent excess reactivity.nIn nuclear physics, the decay scheme of 2.7 hour Sr-°2 has been worked out after an examination of the beta and gamma spectra making use of coincidence counting. The current major effort in the Cross Sections program is the measurement of the fission cross section of U-233 in both the crystal spectrometer and fast chopper energy regions. In this report the total cross sections of cadmium, tellurium, and gadolinium are presented. The cross sections of carbon, lithium, silicon, sulfur, and magnesium have been found to be constant up to 10 kev. Five technical papers were presented at the Physical Society meeting in Eugene, Oregon, June 21, 1956.