摘要:

AbstractThe influence of assembly or cell heterogeneity on neutron leakage has been consistently taken into account in the TIBERE simplified heterogeneous B1model. The assumption adopted within the TIBERE model that neutrons are specularly reflected on the boundary introduces two problems. Calculations with this model may become rather time consuming and even unnecessarily long in the case of a Canada deuterium uranium reactor cell, and the peripheral or total coolant voiding of a pressurized water reactor assembly leads to infinite leakage coefficients. These problems have been overcome by the development of another simplified heterogeneous B1leakage model, TIBERE-2, which has quasi-isotropic reflecting boundary conditions. The TIBERE-2 model uses similar approximations as the TIBERE model and yields an iterative scheme to simultaneously compute multigroup scalar fluxes and directional currents in a heterogeneous geometry. These values enable the evaluation of directional space-dependent leakage coefficients. This new model requires the classical and directional escape and transmission probabilities in addition to the classical and directional first-flight collision probabilities calculated for an open assembly. The TIBERE-2 model has been introduced for general two-dimensional geometry into the DRAGON multigroup transport code. The numerical results obtained by DRAGON show that the TIBERE-2 model represents leakages much better than the homogeneous B1leakage model. Moreover, the TIBERE-2 model yields results that are extremely close to those obtained by the TIBERE model with considerably shorter computing times.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24152

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractAn accurate prediction of the reactor pressure vessel (PV) fast neutron fluence (E>1.0 MeV or E>0.1 MeV) is necessary to ensure PV integrity over the design lifetime. The discrete ordinates method (SNmethod) is the method of choice to treat such problems, and the DORT SNcode is widely used as a standard tool for PV fluence calculations. The SNnumerics and the corresponding DORT numerical options and features offer alternative choices that increase flexibility but also impact results. The effects of SNnumerics based on PV fluence calculations for two pressurized water reactors are examined. The differencing schemes [linear, zero-weighted (ZW), andθ-weighted (TW)] and their interactions with spatial and angular discretization are also examined. The linear and TW (θ= 0.9) schemes introduce unphysical flux oscillations that for certain groups and positions may exceed 10%. The ZW scheme produces smooth results; however, its results differ from the other two schemes. A good compromise for PV fluence calculations is a TW scheme with a smallθvalue (i.e.,θ= 0.3), which reduces the uncertainty to∼3%. Angular discretization and spatial mesh size employed in typical calculations introduce another∼3 and∼2% uncertainty, respectively. The analysis further shows that the fixup is not necessary for the negative scattering source. The pointwise convergence criterion is also not a critical issue in the fast energy range because of a relatively fast convergence rate. Similarly, acceleration parameters impact mainly the execution time and only marginally the results. The root-mean-square combined uncertainty for standard PV fluence calculations due to the options analyzed is∼5%.

ISSN:0029-5639    

DOI:10.13182/NSE96-3

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe variational nodal formulation of the neutron transport equation is generalized to provide spherical harmonics approximations of arbitrary odd order. The even angular parity trial functions within the nodes are complemented by new odd angular parity trial functions at the node interfaces. These are derived from the spherical harmonic continuity conditions presented in the classical work of Rumyantsev. The Yn±nterms are absent for all odd n in the resulting odd-parity trial function sets. This result is shown to be equivalent to requiring the variational nodal matrix that couples even- and odd-parity angular trial functions to be of full rank and yields vacuum and reflected boundary conditions as well as nodal interface conditions within the framework of the variational formulation. Nodal P1, P3, and P5approximations are implemented in the Argonne National Laboratory code VARIANT, utilizing the existing spatial trial functions in x-y geometry. The accuracy of the approximations is demonstrated on model fixed source and few-group eigenvalue problems. The new interface trial functions have no effect on P1approximations and yield P3results that differ very little from those obtained with existing trial functions, even where the P5approximation leads to further improvement. More significantly, the new trial functions allow P5or higher order algorithms to be implemented in a consistent straightforward manner.

ISSN:0029-5639    

DOI:10.13182/NSE96-1

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA new two-dimensional computer model for simulating power and pressure pulses in aqueous fissile solutions has been developed. This model includes a radiolytic gas production model that tracks the number of gas bubbles produced during an excursion. An equation of state has been developed that accounts for the production of inertial pressure due to a lag in thermal expansion and the creation of radiolytic gas bubbles. In addition, a study of various reactivity feedback mechanisms occurring during nuclear bursts has been made. The model’s predicted power and pressure pulses are compared with data from the KEWB and SILENE solution pulsed reactor experiments and have produced results that closely match the experimental data and that exhibit the main features of the experimental power and pressure traces.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24155

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe high-temperature engineering test reactor has been designed whose outlet gas temperature is 950°C. That is the highest temperature in the world for a block-type high-temperature gas-cooled reactor. The power distribution in the core was optimized by changing the uranium enrichment to maintain the fuel temperature at less than the limit (1600°C). Deviation from the optimized distribution due to the burnup of fissile materials was avoided by flattening time-dependent changes in local reactivities. Flattening was achieved by optimizing the specifications of the burnable poisons. Control rod destruction of the optimized power distribution was avoided by limiting the depth of insertion. The insertion depth of the control rods is limited by reducing the excess reactivity of the whole core by the burnable poisons to the minimum value necessary for operations.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24156

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe plutonium that comes from dismantled warheads and that is already stockpiled from commercial fuel reprocessing has raised many proposals for its burning in a safe and economical manner. The utilization is examined of current pressurized water reactors (PWRs) that are partially fed with a nonfertile oxide-type fuel, while the rest of the core is still fed with standard235U-enriched fuel. The unconventional fuel consists of PuO2diluted in an inert matrix, which should be highly radiation resistant, scarcely neutron absorbent, and chemically stable and which allows the final disposal of the discharged fuel without any treatment. Commercial PWRs operating in a once-through cycle scheme can transmute 97 to 99% of239Pu and 71 to 84% of total initially loaded reactor- and weapons-grade plutonium, respectively. The remnant plutonium is in a proliferation-resistant condition. The high initial reactivity of the plutonium-bearing rods causes a high initial rod power peak and continuously decreasing power generation in these rods during the irradiation. A less pronounced rod power peak in UO2rods at end of life has to be addressed. The reactivity coefficients are, in absolute terms, slightly lower than the standard UO2fuel ones.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24157

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWithin the framework of French reprocessing policy, for several years, Electricitéde France has been studying a high-moderating-ratio (HMR) pressurized water reactor that could accept 100% mixed-oxide (MOX) reloads. Total plutonium content is 9% to ensure a discharge burnup of 60 000 MWd/tonne. A high-moderating ratio (2.5 instead of 2.0) is obtained by replacing 36 fuel rods by water holes. This solution combines the advantages of high moderation (better efficiency of soluble boron, control rods, etc.) and technological continuity. The core should contain 241 fuel assemblies for a total thermal output of 4250 MW(thermal). The fuel management is easy, but core control requires the use of10B-enriched boron carbide for the control rods and10B-enriched soluble boric acid for the primary system, thereby ensuring satisfactory core behavior under accident conditions such as control rod ejection and unexpected valve opening on the secondary side. The advantages of this 100% MOX core compared with a 50% MOX core are discussed. This concept is fully compatible with the future European pressurized reactor (EPR). This 100% MOX HMR reactor could be the plutonium version of the EPR.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24158

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractNeutron activation cross sections between 15 and 40 MeV were measured by the activation method using a monoenergetic neutron field based on the7Li(p,n)7Be reaction. Natural samples of carbon and cobalt, and separated isotope samples of30Si,47Ti,48Ti,52Cr and58Ni were irradiated in the p-Li neutron fields generated by 20, 25, 30, 35, and 40 MeV protons. Neutron yields were determined from the amount of7Be induced in the lithium target. The amount of7Be was measured by observing the 0.478-MeV gamma rays of7Be(T1/2= 53.29 days) after the irradiation experiment. Cross sections of12C(n,2n)11C,30Si(n,np)29Al,47Ti(n,np)46m+gSc,48Ti(n,np)47Sc,52Cr(n,2n)51Cr,59Co(n,2n)58m+gCo,59Co(n,3n)57Co,59Co(n,4n)56Co, and58Ni(n,2n)57Ni are reported.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24159

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractShielding related calculations were performed for 230-MeV protons incident upon a stopping-length iron target using the LAHET code system (LCS). Secondary neutrons and photons, produced by proton interactions with the target nuclei, were transported through a spherical concrete shield in which absorbed dose and dose equivalent tallies were produced and attenuation parameters deduced. Comparing calculated results with measurements performed with a similar target, beam, and shielding geometry, the dose equivalent production term is double the measured value. The LCS overestimates measured attenuation values at 0, 22, and 45 deg while correctly predicting the attenuation length at 90 deg. Comparisons of LCS results with HETC calculations and analytical methods indicates that LCS better estimates the attenuation length and dose equivalent production.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24160

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA heavy-ion transport code using Green’s function methods is developed. The low-order perturbation terms exhibiting the greatest energy variation are used as dominant energy-dependent terms, and the higher order collision terms are evaluated using nonperturbative methods. The recently revised NUCFRG database is used to evaluate the solution for comparison with experimental data for 625A MeV20Ne and 517A MeV40Ar ion beams. Improved agreements with the attenuation characteristics for neon ions are found, and reasonable agreement is obtained for the transport of argon ions in water.

ISSN:0029-5639    

DOI:10.13182/NSE96-A24161

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor