摘要:

Several of the contaminants of uranium can be removed or controlled by vacuum melting and liquation. The lower limits of carbon content which can be attained by liquation in urania crucibles are 225 to 250 ppm at 1195°C, 190 to 225 ppm at 1150°C, and 170 ppm at 1138°C. In magnesia crucibles the reaction 3 MgO + UC→UO2+ CO + 3 Mg proceeds to the right in a high vacuum resulting in incomplete carbon removal. Oxygen and nitrogen are rapidly removed by liquation and contents of less than 10 ppm are readily obtained. Iron and silicon are not removed by a simple melting and liquation process. Various crucible materials were investigated and the effect of addition agents such as nitrogen, tantalum, titanium, and zirconium was studied. Under optimum vacuum melting conditions a metal is produced that will contain no more than 130 to 200 ppm total impurities.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25406

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Half-lives of thirty radionuclides are reported. Most of the samples were chemically purified after bombardment. In general, the activity of a given sample was followed for two or more half-lives, employing a gamma ionization chamber, gamma scintillation counter, or a Geiger-Mueller counter. The data were analyzed by the least squares method. Some of the half-life values are significantly different from earlier ones; others merely confirm those already established.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25407

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Three corrosion-resistant uranium-base alloys, U-3 weight per cent Nb, U-5 weight per centweight per cent Nb, and U-3.8 weight per cent Si (U3Si) were irradiated to burnups of 0.1 atomic per cent or less. Observations were made of irradiation-induced length changes in specimens of the alloys as influenced by the method of fabrication and heat treatment, and of changes in aqueous corrosion resistance resulting from irradiation. It was found that the uranium-niobium alloy was unsuitable from the standpoint of dimensional and surface stability, and its corrosion resistance was destroyed by irradiation. The uranium-zirconium-niobium alloy could be nominally stabilized under irradiation and its corrosion resistance was destroyed by between 0.046 and 0.074 atomic per cent burnup. The uranium-silicon alloy was relatively stable under irradiation and showed no increase in corrosion rate at 290°C after 0.090 atomic per cent burnup, although cracking occurred after several days corrosion testing.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25408

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Measurement of the time distribution of pairs of counts due to neutrons originating from a common ancestor in a neutron chain, yields a value for the prompt neutron period of a near-critical system. Such measurements can be used to establish the mass or control increment between delayed and prompt critical and, hence, constitute a reactivity calibration without use of the Inhour relation.Measurements are reported for several simple metal critical assemblies.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25409

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

The distribution of enrichment which makes a natural uranium lattice withk∞<1 critical with the smallest amount of added U235is calculated on the basis of a simple model. The results are generalized to the minimization of total enrichment cost when this cost is a nonlinear function of the added fissionable material.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25410

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

In a reactor of sufficient size and operating at sufficiently high power density, an oscillation in the spatial distribution of power may arise because of interplay between the effect of Xe135on flux distribution and the fact that its appearance after fission is delayed by the decay time of I135. By use of a very simple reactor model the conditions required to establish such an instability are studied; amplitude and frequency characteristics of the oscillation are also investigated.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25411

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Effective reactor capture cross section values for Pu240were calculated both from experimental plutonium isotopic ratios and from the resonance parameters for the 1 ev resonance. Both methods gave values of about 1200 barns for highly dilute Pu as contrasted to values of about 500 barns which have been reported for reirradiated Pu samples. The 1200 barn figure is consistent with a 2200 meter per second cross section of about 340 barns and a resonance integral of about 8300 barns.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25412

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Reactivity measurements on cadmium-clad cylinders of uranium, uranium oxide, thorium, and thorium oxide have been interpreted to yield the following effective resonance integrals. For cylinders all with radii of 1.73 cm and with the listed densities:The results are corrected for nonresonance absorptions of neutrons at energies above cadmium cutoff.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25413

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Concentrated thorium nitrate solution has been proposed as a blanket material in power-breeder reactors. The radiation stability, especially of the nitrate group, is therefore of considerable importance. The radiation-induced decomposition of thorium nitrate solutions was studied as a function of concentration, type of radiation (fission recoils, pile radiations, gamma rays), temperature, and total energy absorbed. The principal products were H2and O2from decomposition of the water, and N2, O2, and oxides of nitrogen from decomposition of the nitrate. Hydrogen yield decreased with increasing thorium nitrate concentration, a behavior similar to that for uranium solutions. Nitrogen yield was independent of temperature, but increased with increasing nitrate concentration and with increasing linear energy transfer along the paths of the ionizing particles. The 100-ev yield of N2in 2.73 molal solution was 0.06 for fission particle decomposition, 0.006 for pile radiation (mixed fast neutrons andγrays) and 0.001 forγradiation alone. The oxide of nitrogen produced with the largest yield was N2O and amounted to about ten per cent of the N2yield. In-pile autoclave measurements indicated little radiation-induced back reaction of the nitrogen.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25414

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor

摘要:

Suspensions of UO2in NaK alloy are being studied as possible reactor fuels. Two loops have so far been constructed of one-half inch stainless steel tubing with a test volume of approximately 150 cc. The Mark I loop was operated for 400 hours between 450 and 600°C, while circulating a slurry of 4.3 volume % UO2(36.0 weight per cent). The radioactive monitor indicated that the slurry was uniformly suspended at a flow rate of 2 ft/sec. It was found that above 500°C the UO2dropped out of suspension, but was immediately resuspended when the temperature dropped below the critical value of 500°C. The effect was reversible and could not be eliminated even at the fastest flows. The Mark II loop incorporated a density measuring device in order to correlate the radioactivity monitor with the density of the slurry. It was found, as previously suspected, that when the counts reached maximum value the density also was a maximum, at the calculated value. One gram of powdered uranium metal added to the loop with the UO2completely eliminated the settling above 500°C observed in the Mark I loop. There was no evidence for corrosion or erosion of the loop, and the particle size of UO2was practically unchanged after operation at the high temperature. The UO2could be resuspended immediately after prolonged settling.

ISSN:0029-5639    

DOI:10.13182/NSE57-A25415

出版商:Taylor&Francis    

年代:1957

数据来源: Taylor