摘要:

AbstractA series expansion method is used to obtain approximate solutions of the velocity-dependent transport equation near a resonant energy. Numerical examples of typical cases are given.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27320

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe perturbation approach to control element evaluation is extended from the work presented in a previous paper. A two-group second-order perturbation expression for control element worth is obtained. This has, as its starting point, the unperturbed fast flux but considers the depression in the thermal flux caused by the control element and then, in turn, considers the perturbation on the fast flux caused by the perturbed thermal flux. Finally, the effect of the perturbed fast flux on the thermal flux is evaluated. It is shown that this process, if continued, converges to the correct answer. The perturbation results are compared to experiments for the case of a weak rod in the reflector region of the Bulk Shielding Reactor. The perturbation results are also compared to exact two-group calculations for a cylindrical rod on the axis of a bare cylindrical reactor. In both cases, excellent agreement is obtained.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27321

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractLoop studies have been made on UO2-NaK slurries at temperatures up to 1050°F. The maximum UO2concentration was 4.15 volume per cent or 35 weight per cent at room temperature. A flow rate of 5.4 ft/sec was required to suspend all of the UO2in this slurry at 1050°F. Lesser flow rates were required at lower temperatures. It was discovered that by installing a static cold trap, which was joined vertically upward from the lower horizontal leg of the loop, the slurry became more stable at the higher temperatures. The function of the cold trap is thought to be that of removing, from the circulating slurry, oxygen contamination which may have rendered previous attempts to maintain a stable suspension above 932°F unsuccessful. In the present study, the UO2could be easily resuspended after prolonged settling.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27322

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractA survey of the experimental methods used in testing the radiation stability of molten salts and their corrosion properties is presented. The effects of irradiation on the corrosion of Inconel exposed to fluoride fuel mixtures and on the physical and chemical stability of the fuel mixtures have been investigated by irradiating in the MTR capsules filled with static fuel and by operating in-pile forced-circulation loops in the LITR and in the MTR. In the many capsule tests and in the three in-pile loop tests made to date, no major changes have occurred in the fuel mixtures that can be attributed to irradiation, other than normal burn-up of uranium. Metallurgical examinations of the Inconel capsules and tubing have likewise shown no changes in corrosion that can be the result of radiation damage. The low corrosion results obtained for the in-pile loops have been confirmed by chemical analyses for corrosion products in the fuel mixtures.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27323

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe spatial and temporal distribution of thermal neutrons in a multiplying assembly following the introduction of a short burst of fast neutrons is investigated by means of an extension of the so-called“asymptotic reactor theory”to the time-dependent case. It is shown that the solution for an nth mode fast neutron source can be reduced to that for an nth mode thermal neutron source, so that only the latter need be considered. A formal solution to the time-dependent thermal diffusion equation with an nth mode thermal source is found for an arbitrary slowing-down kernel. The asymptotic behavior of the flux in the long-time limit is shown to be exponential, with a decay constant satisfying a generalized material buckling equation. The asymptotic behavior following a burst of fast neutrons is also found to be exponential with the same time constant. In a continuous slowing-down model, all neutrons slow down in the same time, implying that the time-dependent part of the time-dependent slowing-down kernel is a Dirac delta-function. In this case, an explicit expression for the flux following a burst can be derived, from which the approach to the asymptotic behavior is clearly seen. The mean slowing-down time (t) is used to find an approximate expression for the asymptotic decay constant. To evaluate (t) for hydrogenous media, it is noted that the Laplace transform of the Boltzmann equation is identical with the time-independent Boltzmann equation if, in the latter,Σa(E) is replaced byΣa(E)+η/υ(E), whereυ(E) is the neutron velocity andηthe Laplace transform variable. The resulting equation can then be solved by standard methods. The infinite medium (B2= 0) result of 0.92µsec for the slowing-down time to 1.4 ev is in good agreement with the value 0.85µsec obtained from Monte Carlo calculations. The validity and application of the method are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27324

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractQuick engineering estimates of nuclear radiation heating effects exterior to reactors are frequently desired in preliminary flight vehicle design. A technique that is useful for such evaluations is presented. Analogies are suggested among the capture, inelastic scattering and neutron-induced charged particle processes; a means is provided for treating neutron interactions giving rise to gamma rays of various discrete energies; and a cosine distribution of the core gamma radiation is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27325

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe total neutron cross section of Pu240has been measured at the 1 ev resonance using a crystal spectrometer with good resolution. A detailed analysis was made of the shape of the resonance to obtain the Breit-Wigner level width parameter. The level width was determined to be (32.3±1.5) mv, and the resonance energy was (1.056± 0.003) ev.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27326

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe spherical harmonics approximation oflth order, applied to the transport equation in slab geometry, leads to 2l+ 1 coupled first order differential equations. These may be transformed into (2l+ 1)/2 second order differential equations similar, in form, to the few-group diffusion equations, and amenable to solution by well-known iterative techniques. The double-P1equations of Yvon may be manipulated and solved in the same manner. This article describes an IBM 704 code which makes use of such a method. Some of the results obtained with the code are discussed, and machine times for typical problems are compared with times required to solve the same problem by the discrete ordinate methods.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27327

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractNeutron leakage through a reactor shield composed primarily of iron is discussed. This is of interest whenever the hydrogen content of a shield is reduced either by design requirements or thermal deterioration. Work done at several sites on individual aspects of the problem is combined to present an over-all description of the neutron streaming. In general there are two different phenomena involved, each determined by the geometry. In the case of a long thin streaming path, such as a structural member penetrating the shield, the leakage consists of neutrons which have suffered no collisions. These neutrons will have energies corresponding to energies at which the iron total cross section is small. Iron has several antiresonances in the interval 25 to 100 kev, with the largest dip apparently at 25 kev, so most of the neutron leakage will be at these energies. The other case involves the attenuation of neutrons by large slabs of iron with little or no hydrogen (or other good moderator) present. The 25 kev neutrons are still present, but they are augmented by a large number of neutrons of energy between thermal and 1 Mev. These neutrons may have collided elastically many times but with only a small energy loss each time. Above 1 Mev, inelastic scattering suppresses the leakage, and below a few volts, absorption removes the neutrons.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27328

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractA fast coincidence technique was employed to measure the relative prompt-neutron yields per fission of U233, U235, Pu239, and Pu241induced by thermal neutrons. The values obtained wereν23/ν25= 1.02 + 0.01,ν49/ν25= 1.23±0.01, andν41/ν25= 1.295±0.02, whereν23,ν25,ν49, andν41designate the prompt-neutron yields of U233, U235, Pu239, and Pu241, respectively.

ISSN:0029-5639    

DOI:10.13182/NSE59-A27329

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor