摘要:

AbstractThe fuel management optimization of a nuclear power plant is separable from the over-all optimum design. It has weak interactions with the core design and poison management which may be expressed by constraints upon the maximum permissible fuel burnup and ratio of peak-to-average power density (power peaking). Each time the reactor becomes subcritical, a decision must be made as to which fuel should be discharged and replaced and to what degree rearrangement is advantageous. This is a multistage decision process whose objective is the minimum power cost over the plant life. A dynamic programing algorithm and a computer program have been developed to optimize the refueling policies of a single-enrichment, three-zone, 1000-MWe PWR core for a minimum unit power cost. The major assumptions necessary for this method are the representation of the fuel composition by the sole parameter, burnup, and the prediction of the system behavior by least-squares polynomial curves fitted to prior calculations. These approximations have been verified and their accuracy is about 3%. Many problems are displayed to demonstrate the application of the method. The cost figures given in the numerical examples are for illustration purposes only and may not reflect current manufacturers' and utilities' policies.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20933

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractHeat transfer and pressure drop characteristics for the flow across banks consisting of plain (unfinned) helical tubes in a multistart arrangement with essentially uniform inclination angles, uniform longitudinal pitches and hence essentially equal heat loads per tube, but with tube pattern changing continuously around the perimeter, have been reduced analytically to the relatively well-known heat transfer coefficients and friction factors for the flow across banks of straight tubes with in-line and regularly staggered tube patterns.For this purpose, correction factors for the effects of tube inclination and of the number of tube rows are introduced. The effective average values of the free flow area—which determine the effective velocity and hence the effective Reynolds number—and the effective arrangement factors are obtained by integration of the local values. The apparent differences of the heat transfer and pressure drop correlations obtained by the two experimental investigations known—the Waagner-Biro experiments on the prototype tube bundle of the steam generators for the OECD High Temperature Reactor Project Dragon and the data of Glaser on regenerator inserts—have been explained quantitatively by the different approach employed for calculating the free flow area. Using the expressions for the effective average free flow area and the correction factors for tube inclination and tube row numbers, agreement of the heat transfer and pressure drop data of both experimental investigations with each other and, what is more, with straight-tube data is achieved.The suggested heat transfer and pressure drop correlations for banks of helical tubes are valid for gases and liquids with Prandtl numbers above 0.1. This range includes applications to steam generators of gas-cooled and liquid-cooled reactors (and cryogenic applications as well). For heat exchangers and steam generators of liquid-metal-cooled reactors—that is for Prandtl numbers of the order of 0.01—a different heat transfer correlation is developed, which is based on available data obtained with liquid metal flowing across banks of straight tubes.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20934

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractAdjoint transport theory is most widely used in perturbation theory. A most common problem here is the determination of the reactivity change in a self-multiplying system due to the insertion of an absorber in a small region.There is, however, a class of problems of the source-detector type where adjoint transport theory proves to be a very effective and fast way of obtaining the desired results. In many practical source problems we want to evaluate the reaction rate, say fissions or absorptions, in a material surrounded by a moderator due to a neutron flux incident on the assembly. Here the main advantage of using the adjoint method as opposed to the conventional real-flux shell-source calculations is a significant reduction in computer time. The reactions induced by each group of source neutrons is obtained from one run of an adjoint problem.To obtain the same information from real-flux calculations we need an individual run for every energy groupg. Computer time savings ranging by a factor of 5 to 30 are representative.The theory previously reported by one of us (H.A.S.) in the classified literature is derived and subsequently applied to the following problems.the fissions induced in a spherical plutonium-detector foil separated by a moderating layer from an incident collimated neutron beam;a neutron-dose-rate detector device consisting of a lithium iodide crystal to register absorptions surrounded by a sphere of polyethylene;the theoretical evaluation of the neutronic coupling coefficient between two reactors, as one might visualize in a clustered-Rover nuclear-reactor rocket-engine system.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20935

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe time dependentP1approximation to the neutron transport equation has been solved for the case of an oscillating source on one face of a finite parallelepiped. An oscillatory solution to the differential equations describes the propagation of neutron waves through the medium. Attenuation lengths of plane neutron waves were identical at low frequencies (ω2νΣtr). Wave lengths and wave speeds for the two approximations were slightly different at low frequencies, identical at immediate frequencies and considerably different at high frequencies. A new method, which considers the transient behavior of a spatially-integrated positive-definite function of flux and current, is used to show that the transient part of the solution decays to zero.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20936

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractAn approximation to the transport equation is presented, which is capable of arbitrary accuracy and yields the exact transport-theory asymptotic behavior in all orders for any geometry. Anisotropic scattering is treated explicitly, and the inclusion of energy and time dependences is straightforward. The approximation, which is very similar to the usual spherical-harmonic (PN) method, is derived by introducing a new truncation scheme into the infinite set spherical-harmonic equations. This truncation method consists of assuming that the higher spherical-harmonic components, equated to zero in thePNmethod, can be related to lower components by assuming the angular distribution to be in an asymptotic distribution. The resulting approximation is very similar in structure to thePNapproximation (in particular, it is no more complex) but has the added advantage of yielding exact asymptotic behavior.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20937

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractReflection and transmission of monoenergetical particles with a known ingoing distribution by a strongly absorbing slab is studied from the numerical standpoint.Various approximation methods based on known theoretical solutions are presented: in section III we propose an approximation based on ChandrasekharXandYfunctions; in section IV we obtain the reflection and transmission by using a variational technique, and we show that a successive-collision technique gives identical results; and in section V we propose a diffusion-like approximation, with adjusted coefficients, of the formThe first approximation gives good results for lowcvalues; the second one, for highcvalues.The diffusion-like approximation, however, is accurate to more than 2% for all values ofcbetween 0.1 and 0.9. Moreover it is far easier to compute than any of the former ones.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20938

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA recent investigation established the technical feasibility and indicated the high degree of safety that could be afforded by the storage of high-level radioactive wastes in unlined vaults excavated in crystalline rock 1500 ft beneath the surface of the Savannah River Plant near Aiken, S. C.The crystalline rock at the proposed site is covered by 1000 ft of unconsolidated sediments conSisting predominantly of sand and clay. A virtually impermeable layer of clay separates the rock from the overlying sediments in which several prolific water-bearing zones occur. The separation of the waters above and below this clay layer is confirmed by their different chemical composition and by the presence of dissolved helium-bearing gas only in the water in the rocks beneath the clay. Based on geologic and hydrologic information obtained in an intensive drilling and testing program, upper limits on the rates of water movement through the crystalline rock are calculated to be 1.5 to 7 ft/year, depending upon the degree of fracturing of the rock. Comparable data on the unconsolidated sediments lead to a calculated maximum rate of water movement of 350 ft/year.The most significant driving force for the migration of radionuclides from the storage site is derived from the natural water movement, coupled with effects due to dispersion and ion exchange. Characteristics of the waste, heat generation, and radiolysis have, by contrast, only small effects on migration. Three barriers prevent migration of the radionuclides: the very low permeability of the rock in which the storage vault is located, the virtually impermeable clay layer separating the rock and sediments, and the ion exchange properties of the sediments. Anyone of these barriers is capable of confining the radionuclides well within the plant boundaries for a time much greater than the 600-year period required to render the wastes innocuous.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20939

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractAsymptotic neutron-energy spectra inside a semi-infinite beryllium block have been calculated by an iteration procedure using for the scattering kernel both the one-phonon scattering cross section and the first term of the Placzek expansion. Different absorptions have been considered. The values of the transport mean free path,λtr(E), have been taken from Bhandari's work. Because of the sudden large variation ofλtr(E) near the Bragg cutoff, the calculated equilibrium flux differs markedly from the Maxwellian, particularly for high moderator absorptions. For a pure beryllium block at room temperature (σa= 0.01 barn), the deviation from Maxwellian is small. Calculations also give the values of the diffusion length at different absorptions, from which data the diffusion constantD0and the diffusion cooling constantChave been evaluated.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20940

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractMetastable isomers of stable isotopes may be formed in a nuclear reactor by inelastic neutron scattering and photoexcitation of the stable isotopes, and by radiative neutron capture and (n,2n) reactions on neighboring stable isotopes. The relative importance of these reactions for the production of Ba137m, Cd111m, Se77m, and Sr87mwas evaluated by the irradiation of normal and isotopically enriched samples of the elements in the mixed radiation field of the Union Carbide Research Reactor. Radiative neutron capture is the most important source of Cd111m, Se77mand Sr87min samples of normal isotopic abundance. Inelastic neutron scattering is the prime contributor to the production of Ba137mand is of considerable importance in the production of Cd111m. The (n,2n) reaction appears to be significant only in the production of Ba137m. The formation of these isomers by photoexcitation by the gamma-ray flux associated with the reactor appears to be insignificant when compared with the production by the other three processes. The cross sections determined in these investigations are generally in good agreement with available published values. Reactions for which cross sections were determined and not found in the literature include: Ba137(n,n′)Ba137m,= 0.22b; Cd111(n,n′) Cd111m,= 0.14b; Se77(n,n′)Se77m,= 0.60b;Sr87(n,n′)Sr87m,= 0.12b; Ba138(n,2n)Ba137m,= 2.0mb; and Cd112(n,2n)Cd111m,= 0.35mb. The data indicate that, for short irradiation periods in the fluxes employed in these studies, the metastable isomers Ba137m, Cd111m, Se77mand Sr87mare the most sensitive activation-analysis indicators for these elements and give detection sensitivities in the low nanogram range.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20941

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE65-A20942

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor