摘要:

The cross section measurements of 17 neutron induced reactions using an intense semi-monoenergetic neutron field were recently reported. Neutrons for energies up to 40 MeV were produced by a simple Be target system bombarded by protons of 9 different energies between 20 and 40 MeV.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735110

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

To estimate fast reactor core transient behavior in three-dimensional geometry, we have applied the improved coarse mesh method to time dependent problems. The improved quasistatic approximation is used with the feedback of fuel temperature change and coolant temperature change. The shape function describing flux distribution is calculated using effective cross sections which are functions of mesh intervals and the amplitude function. To allow large axial coarse meshes with control rod partially inserted, a bilinearly weighting method is used to calculate homogenized cross sections. Using these methods KICOM code has been developed. The validity of this code has been checked by comparing with a two-dimensional transient code FX2-TH for the case when a control rod at core center is withdrawn. The KICOM code has been applied to calculate the power change of a prototype fast reactor and a large fast reactor for the case when a core center rod or an off-center rod is withdrawn. For the prototype reactor, the reactor power rapidly changes with time, but the power distribution (shape function) remains almost the same. However, for the large fast reactor, not only the reactor power but also the power distribution remarkably change with time. The mesh effect is also investigated by comparing the results with and without the mesh correction.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735111

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Radiation-hardened MOSFETs were developed, and experimental results on their total dose degradation were collected to evaluate effects of three techniques for radiation hardening. The three techniques are; (1) adding a silicon-nitride layer onto the phospho-silicate glass passivation layer, (2) thinning of the field oxide by increasing resistance of the channel stopper, and (3) annealing the gate oxide at lower temperature. Technique (1) suppressed the leakage current generated by the parasitic MOSFET, because the negative threshold voltage shift of the parasitic MOSFET was compensated by the positive shift due to the interface states generated by hydrogen trapped in the oxide by the silicon nitride deposition. Furthermore, leakage current decreased with technique (2) as well. Technique (3) was not effective because the gate oxide is inherently thin. Results gotten using a linear model for the threshold voltage shift represented well the measured data up to 1.5 kGy(Si) at a dose rate of 5Gy(Si)/h.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735112

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A copper vapor laser (CVL) with 6 cm diameter and 300 cm discharge length has been developed for atomic vapor laser isotope separations. Recently, output power of over 200 W (211 W maximum) has been steadily obtained.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735113

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the Purex process, extraction disturbances are, sometimes caused by the formation, at the aqueous/organic interface, of emulsions stabilized by solids called “crud”. In relation with this phenomenon, we investigate under accelerated conditions the precipitation of fission or corrosion products in a 3M nitric acid/TBP 30%-dodecane system, using electron irradiations. It is shown that only iron and palladium markedly precipitate. Iron behaviour is related to Fe(DBP)3formation, which precipitates for too high HDBP concentrations (3 g.l−1) by comparison with process values. Palladium precipitation is related to dodecane degradation and needs high irradiations (0,20 MGy). Zirconium precipitation is not noticed until 0,25 MGy, irradiations leading only to its extraction in the organic phase. Thus, zirconium precipitation with TBP degradation products has been studied. With HDBP, precipitation is limited and occurs for 1,5<HDBP/Zr<6. With H2MBP, precipitation is marked, without dissolution by excess of H2MBP. So, it is suggested that zirconium precipitation in the process occurs in the organic phase, after extraction of this element by degradation products, this phenomenon occuring in areas of the extractors where solvent is not well mixed. Moreover, it is shown that all these precipitates, which simply form a deposit at the interface, are mainly not effective in stabilizing emulsions and cannot be the simple (or single) cause of “crud”.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735114

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the high temperature gas-cooled reactors (HTGRs), the radial and axial heterogeneity resulted from a combination of fuel rods, burnable poison rods, block end graphite and so on causes local power peakings which increase the fuel temperature locally. An method was developed for calculating the local power and the fuel temperature distributions. This method deals with all heterogeneity effects of a whole core in the radial and axial directions with a design code system including a vectorized 3-dimensional diffusion code. The uncertainty of the method had been evaluated through the analyses of the power distribution obtained by critical experiments with the Very High Temperature Reactor Critical Assembly (VHTRC). The difference was less than between the calculated and measured power distributions. From the results, it was confirmed that this method could predict the local power distribution of the HTGR with high accuracy.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735115

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Characteristics of ZnS(Ag)/NE102A and ZnS(Ag)/stilbene phoswich detectors for simultaneous α and β(γ)-counting have been examined. The pulse-shape discrimination between α- and β(γ)-rays was extremely good (a figure of merit: 8~11) and the tailings from each other were negligibly small (≤0.03%). In order to apply the ZnS(Ag)/NE102A phoswich to practical flow monitoring for actinide solutions, the effects of the radiation energy and Au- and Al-Mylar films for protection of the phoswich on the discrimination were examined in detail. A flow monitoring test was successfully performed for various concentrations of enriched uranium solutions using the phoswich protected with the films.

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735116

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735117

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735118

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0022-3131    

DOI:10.1080/18811248.1994.9735119

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor