摘要:

AbstractThis method, which takes into account the influence of assembly heterogeneity on neutron leakage, is based on the heterogeneous B1formalism, which assumes the existence of a fundamental mode in an infinite and regular lattice of heterogeneous assemblies. A simplified formalism, TIBERE, is presented that allows one to define directional space-dependent leakage coefficients. This method, introduced for two-dimensional x-y geometry in the APOLLO-2 multigroup transport code, uses classical and directional first-flight collision probabilities. One can now define leakage cross sections as additional absorption cross sections that have space and energy dependence, as well as all other cross sections. Hence, one obtains perfectly consistent reaction and leakage rates used in an equivalence procedure, determining cell-homogenized parameters for a whole core calculation. The study of this refined heterogeneous leakage treatment was undertaken because of the insufficiency of the homogeneous leakage model, especially in cases when an assembly contains voided zones or almost voided zones, i.e., zones with a long mean free path, so that the streaming effect may become important. The fission rate comparisons between the EPICURE reactor experimental results and the results of the corresponding whole reactor calculations were accomplished, with leakages calculated by the homogeneous and the TIBERE procedures of the APOLLO-2 code.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21491

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractNeutrons that are produced following antiproton annihilation on uranium nuclei are transported through compressed targets by the SCATTER Monte Carlo code in support of antiproton microfission experiments. The SCATTER code and necessary input data are described. Results show that the high-energy (>20 MeV) component of the source is responsible for the majority of the neutron yield. Results for a wide range of uniformly compressed targets are presented for moderation levels of hydrogen-to-uranium ratios of 0:1, 3:1, and 9:1 in235U targets and238U. Moderation is found to increase neutron yields at a given Uniformly compressed unmoderated238U targets demonstrate 9 to 16% lower yields than235U. Four targets under different, nonuniform compression conditions are considered. The average yield in these cases is∼21.8±0.2 neutrons per source antiproton, an increase of 34% over the 16.3 primary neutrons per antiproton. The average yield of the nonuniform compression cases agrees within error with uniformly compressed targets.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21492

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractContainment and interaction of charged pions in a solid linear implosion system are simulated. Pions are generated from annihilation of antiprotons at the surface of a compressed target. A three-dimensional Monte Carlo code has been developed to simulate the interaction of charged pions with the system. Neutron yields are presented for several 27-g uranium targets compressed under different initial plasma conditions. Effects on neutron yields from the diffused magnetic field and density profiles at peak compression are discussed. Results show that the magnetic field at peak compression significantly increases overall neutron yields.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21493

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA semiempirical formula for neutron detector responses, to be used to infer reactivities in subcriticality measurements, is presented. A formal theory for the multipoint approximation of the Boltzmann operators makes possible the description of a large variety of nuclear fuel systems by means of an equivalent two-point model that regards a whole system as the coupled system made up of an arbitrary number of nuclear fuels. Because the analytic formula includes the fitting parameter associated with the detector configuration and because the removal of spatial effects or higher mode contaminations in the detector responses is accomplished by devising the detector configurations, the conventional point approximation can be used to infer the reactivity of a far-subcritical system. For an example of an application to existing experiments, the current method is used to analyze subcriticality measurements by using the252Cf source-driven neutron noise analysis method.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21494

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractAn estimation of the production of long-lived radionuclides by neutron-induced reactions in potential fusion reactor materials is very important for the development of low-activation materials. Although some measured data of activation cross sections leading to long-lived radioactive nuclides are available, the development of a calculation capability is necessary to provide complete excitation functions of the reactions involved.Calculations are not generally effective when experimental data to determine the parameters used in the model calculation are limited. In the SINCROS-II system, the consistency of the method of calculation is respected, and the parameters used are cross-checked by the available experimental data and the systematic trend of the calculated results. Thus, the SINCROS-II is expected to predict the activation cross sections with good accuracy, even if the cross section is calculated for a radioactive target nucleus. As an example of the cross-section predictions, the activation cross-section calculations are presented up to 20 MeV for neutron-induced production of long-lived radioactive nuclides60Co,59Ni,63Ni,91Nb,94Nb,93Mo,99Mo,108mAg,150mEu,152Eu,158Tb, and186mRe.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21495

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA direct control method is developed to control the spatial xenon oscillations in pressurized water reactors. The xenon and iodine concentration difference between the top and bottom halves of the core is estimated by using the extended Kalman filter (EKF), which is a closed-loop estimation method. The measurement equation used in the observer is the axial offset measurement equation, which reflects the xenon unbalanced effect on the axial offset. Meanwhile, some of the coefficients of the observer are estimated on-line to reduce estimation error resulting from model error, i.e., simplified xenon and iodine dynamics. Therefore, the estimation can be guaranteed to be accurate, and the success of the estimation does not greatly depend on the accuracy of the observer model. The predicted one-step ahead xenon concentration, by using the EKF, was used to calculate the possible axial offset variation, and then the control rod motion was calculated to compensate for it. The simulation results show that the proposed method successfully controls the xenon oscillations.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21496

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe solution of the point-kinetics equations with a neutron source can be expressed in terms of the solution without a source by a simple scaling involving reactivities, with an added constant term. Proof is provided by both the Laplace transform and matrix methods.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21497

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor