[en] Calculations were made using the UKAEA reactor physics code package LWRWIMS/JOSHUA, to provide comparisons with similar calculations on the first two cycles of Sizewell B. In Zion cycle 1, the channel power distributions agree quite well with measurement, but there is less good agreement for low burnups in cycle 2. Core axial power profile calculations for cycle 1 also agree quite well with measurement, although the agreement is less good at intermediate cycle burnups. In cycle 2, these do not show the same trends as the measured axial offset. (U.K.)

[en] Measurements of steam bubble velocities and voidage have been made in the relatively small Core B of Lingen BWR. The results of axial scanning in one radial position have produced experimental values of slip ratio, power (from a travelling incore probe), voidage and coolant mean density over the core height for this position. This one set of distributions has enabled us to test current UKAEA models of subcooled boiling and slip ratio against experiment. From the comparisons, it appears that we can predict the onset of voiding well, but the assumption that a constant fraction of the heat flux forms steam in the subcooled region needs modifying. Of four slip options tested, the current one used by HAMBO and JOSHUA III (Bankoff-Jones) predicts too high a slip ratio. A closer fit to experiment comes from the new Bryce flow-dependent slip option. Any changes in the modelling must be checked, however, with coupled thermal hydraulics-neutronics computations. (author)

[en] The small zero-energy critical reactor VENUS contains a simple light water lattice which is easy to model and designed for testing lattice codes such as LWRWIMS. Experiments were carried out on a series of cold critical configurations of UO₂ fuel with a U-235 enrichment of approximately 4 per cent and PuO₂/UO₂ fuel with a U-235 enrichment of approximately 2 per cent and Pu enrichment of 2.7 per cent. LWRWIMS calculations of strongly absorbing gadolinium rods were compared with reaction rate distributions determined experimentally. Mn-55 reaction rates and power distributions were measured. In a few cases, no absorbing rods were present. The radial leakage was represented explicitly in the LWRWIMS modeling, and axial leakage by a geometric buckling. All core simulations were satisfactorily close to critical. Some significant disagreement remains between the calculations and measurements in the poison pin and at positions adjacent to the radial reflector. The depression of the manganese reactions rates by the gadolinium is overestimated by about 3 per cent while the increase in the reaction rate near the reflector is underestimated by approximately 6 per cent. (U.K.)

No abstract available

[en] A study has been made on a PWR loaded partly and wholly with plutonium to determine the changes in shutdown margin compared with an enriched uranium core. Lattice calculations are used to generate cell constants for core calculations. Three fuel loadings were considered, all uranium, 30% (approximately) of the assemblies plutonium in natural uranium, and all plutonium. The equilibrium fuel management schemes adopted in each case are based on the standard three cycle equal size batch scheme. Detailed calculations of power and irradiation distributions through the cycles have been carried out to provide a starting point for the control rod worth and requirement calculations. Control rod worths are reduced in a plutonium core because of the harder spectrum and higher fuel absorption cross sections. Furthermore, the control rod requirements for shutdown increase because of the increase in fuel and moderator temperature coefficients. This results in a reduction in shutdown margin. The magnitude of these changes is fully analysed in the report. The significance of these reductions depends on the detail of the safety argument but reductions of these sizes are unlikely to be acceptable. The data provided in this report could be used to give a first estimate of the plutonium loading acceptable given the safety assessment of the normal uranium core. (U.K.)

[en] A classical field model is proposed, involving a scalar field interacting with the electromagnetic field, that has discrete particle-like solutions corresponding to any desired mass spectrum, all such solutions having exactly the same electric charge. (author)

No abstract available

[en] Codes developed in the UK for LWR reactor physics calculations are described and examples are given of their use. The codes cover both static and kinetic situations and can be used for fuel management and transient calculations in one, two or three dimensions. The first example describes validation of the static calculations by comparison with many cycles of PWR operation. The second one is a treatment of a difficult problem of double heterogeneity caused by discrete gadolinia particles in poison pins. The final section discusses static shutdown and rod ejection accident calculations to assess the adequacy of the control system in a PWR with the introduction of plutonium recycle. (author)

No abstract available

[en] LWR physics calculation methods have been under development in the UK since 1969. A sophisticated lattice code, LWR-WIMS, is used to derive cross-sections for use in the core simulator JOSHUA. JOSHUA is a three-dimensional two-group coarse mesh diffusion code. The codes are briefly described in the paper. Validation has also proceeded for many years and the results and conclusions from this work are discussed. Specific sections cover reactivity, radial power and flux distribution, axial power shape, control rod worths and reactivity coefficients. The primary source of data for validation is from power reactors and results from ten operating cycles are included. The paper provides a basis for establishing the accuracy of the methods and also points out those areas where coarse mesh correction techniques could give small improvements in accuracy