摘要:

To determine fission product-graphite sorption behavior, an experimental and analytical study was conducted to obtain a model which would predict the vapor pressures of mixtures of sorbed fission product metals as a function of temperature and composition.The graphite sorbents studied were SP-1C, a very pure natural flake graphite, and TS-688, a typical needle-coke nuclear-grade graphite. Cesium and rubidium tagged with137Cs and86Rb were the sorbates, and the pseudo-isopiestic method was used to determine sorbate concentrations as a function of temperature and vapor pressure. Three models were examined for their capability in predicting binary mixed sorption behavior.Experiments showed the following: (a) The vapor pressure of a species varies inversely with the fraction of total sorbate metal present at a given sorbate concentration and temperature; (b) thermodynamic and FREVAP models were the most successful in the prediction of binary sorption behavior from single component isotherm data. It is concluded that if the departure from ideal adsorption behavior is not known, either model may be used in the calculation of fission product release.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23232

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

Interactions of neutrons with sodium have been studied by measuring gamma-ray-production cross sections. Spectra were obtained for incident mean neutron energies En= 4.85, 5.4, 5.9, 6.45, 7.0, and 7.5 MeV. Data were obtained at angles of 125 and 55 deg using Ge(Li) detectors. Time-of-flight was used to discriminate against pulses due to neutrons and background radiation.Absolute cross sections for production of gamma rays were obtained for the incident neutron energies quoted above. The data have been compared with previous inelastic neutron scattering results and evaluated cross sections, with good agreement. The spectra were studied for gamma rays which could be associated with deexcitation of nuclear levels having unknown decay modes. Gamma rays were found having energies appropriate for decay of levels at excitation energies Ex= 5762, 5934, 5967, 6115, 6576, and 6866 keV.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23233

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The prompt fission neutron energy spectrum of235U was measured at an incident neutron energy of 0.40 MeV with two samples of different thickness. The data were corrected for flux attenuation in the sample material and for effects due to the energy change of the out-going fission neutrons by inelastic scattering and secondary fission processes. After applying these shape corrections, an average fission neutron energy of 2.06±0.05 MeV was obtained using the Watt and the Maxwellian functions for the energy distribution of the fission neutrons. This result has been compared with the presently available results of other works.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23234

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

Data are presented from critical experiments with mixed PuO2-UO2fuels containing 30.0, 14.62, and 7.89 wt% Pu and having H/X (H:Pu + U) atomic ratios of 47.4, 30.6, and 51.8, respectively. In addition to the experimental results, which can be used directly as integral benchmark checkpoints, derived critical sizes are presented for homogeneous mixtures, at theoretical density, of239PuO2-U(0.71)O2-water in slab, spherical, and cylindrical geometries at the three experimental H/X atomic ratios. These types of data provide the bases for establishing criticality safety control limits.Critical thicknesses of 10.80±0.11, 11.56±0.09, and 14.83±0.60 cm were determined, respectively, for slabs of the 30.0, 14.62, and 7.89 wt% Pu-enriched fuels infinite in two dimensions and fully reflected with 15 cm of Plexiglas. Values ofkeffwithin 8 mk of unity were calculated for these three critical systems using either the diffusion theory code, HFN, or the transport theory code, DTF-IV, with the original GAMTEC-II cross-section data previously used at the Critical Mass Laboratory in correlating plutonium critical experiments with theory. Similar calculations with ENDF/B-II cross-section data yielded keffvalues within 12 mk of unity for these three one-dimensional slab assemblies. Except for the more highly moderated 8 wt% Pu-enriched fuel (H/Pu = 659), calculations with ENDF/B-II data resulted in higher keff values for the critical assemblies than did like calculations using the original GAMTEC-II cross-section library. In the case of the 8 wt% Pu enriched fuel, the computed values for were essentially the same for either of the cross-section sets used.

ISSN:0029-5639    

DOI:10.13182/NSE73-2

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

Experimental criticality data on borated raschig rings in plutonium nitrate solutions are presented for use in establishing criticality safety limits and in verifying calculational methods for these type systems. The data cover the concentration range between 63- and 412-g Pu/liter for borosilicate-glass raschig rings containing 0.5 and 4.0 wt% boron, and stainless-steel raschig rings containing 1 wt% boron.Criticality was possible in all three experimental vessels used (12-, 18-, and 24-in.-diam cylinders, 42-in. high) with no raschig rings. With rings randomly loaded in the vessels only the 24-in. cylinder could be made critical and then only when loaded with the 0.5 wt% borated rings. The minimum critical volume for this system, poisoned with 19.27 vol% borosilicate-glass rings containing 0.5 wt% boron, was determined to occur at about 300 g Pu/liter as compared to 175-to 200-g Pu/liter without the rings. The minimum critical mass occurred at≍110-g Pu/liter with the system poisoned, as compared with 30-g Pu/liter if the system had not been poisoned. Exponential measurements on the subcritical assemblies, loaded with 4 wt% borated rings displacing 18.78 vol% solution, indicated that negative bucklings existed for all plutonium nitrate solutions having concentrations below 391-g Pu/liter. Similar measurements on the subcritical assemblies, loaded with 1 wt% borated stainless-steel rings displacing 27 vol% solution, indicated that negative bucklings existed for all concentrations below 412-g Pu/liter.Comparisons between the experimental data and the results of several calculational methods indicate that the validity of a particular calculational technique may be limited to a small concentration region. By treating the raschig rings as vertical parallel tubes displacing an equal volume of solution and using the Monte Carlo code KENO with GAMTEC-II cross sections averaged over the energy spectrum of the plutonium solution, keff values were calculated to within 2% of unity for the experimental critical assemblies presented in this paper. Other calculational methods and cross-section sets used resulted in values ofkeffdeparting from unity by as much as 12% low to 6% high, depending on the plutonium concentration. The various methods used are discussed in this paper.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23236

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

Polynomial approximations in space are used for solving the integral transport equations for multilayers systems, in one dimensional spherical or cylindrical geometry with scattering anisotropy. These polynomial approximations are applied to the neutron sources (collided neutrons) in each layer, in such a way that the mean quadratic error is a minimum. The form of this approximation allows a less complicated treatment of the anisotropic components of the collided neutron sources than the usual approach (collision probabilities for uniform sources). In order to reduce the number of necessary integral equations when the scattering anisotropy is present, some differential equations relating the spherical harmonics components of the angular flux are used. This is very useful from a numerical point of view, especially when polynomial approximations in space are introduced. A very important link between the scattering anisotropy and the degree of polynomial approximations is also derived. Based on this method the SHADOK code was written. Several numerical examples dealing with multigroup calculations of fast critical assemblies for spherical geometry (FRO-GODIVA-TOPSY-ZPR.43/8) are given. The results show that (a) the large optical dimensions are not a problem for this improved integral method, (b) the scattering.anisotropy (at least PI) does not increase the time of computation, and (c) the heterogeneous systems (reflected cores) can be calculated easily. The calculations with the proposed method are considerably faster than those of the SNmethod.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23237

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The stability of a reactor to xenon-induced spatial power oscillations is generally determined using the first harmonic flux mode alone. This assumption has been tested by including the second harmonic mode in the model and allowing cross coupling between modes. It was found that modal interaction effects are only significant for unstable situations, thus verifying that the use of a single flux mode stability criterion is an adequate approximation to the multimode case.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23238

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

A model is presented which enables us to find the distribution of fuel enrichment that minimizes the fuel cycle cost of a fast reactor, subject to constraints on the enrichment, power, and power density. The reactor is described by a discontinuous one-group diffusion model in slab geometry.Making use of Pontryagin’s Maximum Principle, as extended by Gossez and by Vincent and Mason, the optimal sequence of control (enrichment) zones is founda priori.The latter consists of a central constant power density zone, a maximum enrichment zone, a minimum enrichment zone, and a reflector.The numerical solution of the problem is based on an automatic double iteration search procedure requiring no input trial function.Under the economic conditions considered, it seems preferable to start up the first fast breeder demonstration plants with a core surrounded by reflector elements; radial blanket subassemblies should be inserted only later, and progressively, when fabrication costs decrease and the operational knowledge improves.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23239

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractA development in convenient matrix representation is given for the first four moments of the neutron scattering kernel K(v,v’), for a monatomic Maxwellian gas with arbitrary dependence of the scattering cross section on relative speed. The availability of explicit forms for(x,x’), components of the moments in terms of dimensionless speeds, for n = 0, 1, 2, and 3, as single-integral expressions facilitates the spherical harmonics solution of neutron thermalization problems through the P3-approximation.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23240

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe neutron multiplicities P(n) in the spontaneous fission of246Cm,248Cm, and252Cf have been measured in a3He neutron counter assembly. The efficiency∊for detection of a single neutron was measured to be 0.360, based onν̄(average number of neutrons per fission) = 3.73 for252Cf spontaneous fission. Using this value of∊and assuming a Gaussian distribution p(v) for the emitted neutrons, we fitted our observed P(n), corrected for small background and pile-up effects, to the model by the method of least squares in which the Gaussian widthσvandν̄were the parameters of fit. Values of p(v) were then calculated from the resulting Gaussian function. In the case of252Cf, our values of p(v) agree well with literature values; the p(v) values for the curium isotopes have not been measured previously as far as we know. The values ofν̄for both246Cm and248Cm fall on a straight line through existing experimental values for the nuclides242Cm,244Cm, and250Cm in a plot ofν̄versus mass number; our values were 2.86±0.06 and 3.14±0.06 for246Cm and248Cm, respectively.

ISSN:0029-5639    

DOI:10.13182/NSE73-A23241

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor