[en] The neutron physics of an APWR are analysed by single pin-cell calculations as well as two-dimensional whole-reactor computations. The calculational methods of the two codes employed for this study, viz. the cell code SPEKTRA and the diffusion-burnup code DIBU, are presented in detail. The APWR-investigations carried out concentrate on the void coefficient characteristics of tight UO₂/PuO₂-lattices, control rod worths, burnup behaviour and spatial power distributions in APWR cores. The principal physics design differences between advanced pressurized water reactors and present-day PWRs are identified and discussed. (orig./HP)

[en] Some findings on the neutron physics of the homogeneous core of the advanced PWR are presented. The programs developed by LRR (collision probability code SPEKTRA with cross section data based on ENDF/BIV and 1-D diffusion burn-up code DIBU-1) have been successfully tested in experiments which come close to the FDWR parameters. (orig./RW)

[en] Twelve different test zones, Cores 7 to 18, have been studied to date in the Phase II program of LWCHR physics experiments at the PROTEUS zero-power facility. This paper reviews the test lattice configurations investigated, the types of integral measurements carried out, experimental techniques and accuracies, the transferability of results to LWHCR design, as also typical comparisons with calculations based on standard LWR methods. It has been shown that the experimental data base provided is broad - in terms of both high converter design characteristics represented and the types of integral data measured. Thus, the experimental program covers changes in moderation ratio (lattice geometry) and effective fissile-Pu enrichment - with investigations of neutron balance components, moderator voidage effects, influence of lattice poisoning, relative control rod worths and core heterogeneity effects. The importance of having such a broad data base is illustrated by the trends currently reported for the C/E (calculation/experiment) variation for reaction rate ratios with degree of moderation. (author). 18 refs, 3 figs, 6 tabs

No abstract available

[en] The characteristical neutronphysical conduct of a homogeneous advanced-pressurized-water-reactor (APWR) with a high conversion ratio is described. We suggest to use the Plutonium already produced in present light-water reactors as fuel for the APWR which would essentially reduce the demand for natural Uranium. The spectral peculiarities of undermoderated PuO₂/UO₂sub(-)fuel-pin-lattices are discussed. In case of a loss-of-coolant-accident a reload enrichment of 7,5 w% Plutonium-fissile achieves sufficient undercriticality at every burnup-state. The average final burnup in a five-batch-core with annual reshuffling will be approxiametely 45,000 MWd/t heavy metal. Results of calculations indicate the homogenous concept of a high-converting-light-water reactor to be feasible. None the less a critical experiment with actual APWR-parameters ought to be executed in order to check the methods of calculation. (orig.)

[en] One measure to improve fuel utilization in light water reactors is to increase the conversion ratio in a tight, hexagonal PuO₂/UO₂ mixed oxide fuel pin lattice. The PWHCR (pressurized water high converter reactor) is the Siemens/KWU approach towards this kind of tight lattice reactor, with the main characteristics of the actual concept being zirconium-clad fuel rods and an average moderator-to-fuel volume ratio of 1.2. In a recent study, concerning the nuclear core design for the PWHCR, mainly the questions related to the fuel assembly design, the reactivity control system and fuel management strategies have been addressed. Results of the investigations essentially confirmed the concept of the tight lattice PWR to be technically feasible. (author). 5 refs, 8 figs, 4 tabs

[en] Twelve different test zones, Cores 7 to 18, have been studied to date in the Phase II program of LWHCR physics experiments at the PROTEUS zero-power facility. This paper reviews the test lattice configurations investigated, the types of integral measurements carried out, experimental techniques and accuracies, the transferability of results to LWHCR design, as also typical comparisons with calculations based on standard LWR methods. It has been shown that the experimental data base provided is broad - in terms of both high converter design characteristics represented and the types of integral data measured. Thus, the experimental program covers changes in moderation ratio (lattice geometry) and effective fissile-Pu enrichment - with investigations of neutron balance components, moderator voidage effects, influence of lattice poisoning, relative control rod worths and core heterogeneity effects. The importance of having such a broad data base is illustrated by the trends currently reported for the C/E (calculation/experiment) variation for reaction rate ratios with degree of moderation. (author) 6 tabs., 3 figs., 18 refs

[en] Utilities operating LWRs require fuel assemblies and in-core fuel management service, which ensure safe, flexible and cost-effective production of electricity. With the reliability of the fuel having been always the most important requirement, advanced measures to minimize fuel cycle costs are receiving increasing attention in the light of the pressure on costs within the de-regulated power generation markets. The role of in-core fuel management in supporting the goal to minimize fuel cycle costs consists in the development of more demanding core loading strategies, i.e. in the first place more advanced low leakage loading patterns. A prerequisite for this type of loading pattern is the use of an optimized burnable absorber design. Gadolinia as integrated burnable absorber is a very effective means for limiting the critical boron concentration and power peaking factors. Siemens has accumulated extensive experience with Gd-fuel for almost 20 years with e.g. more than 5500 Gd-FA's delivered for PWRs and irradiated up to 65 MWd/kg_HM. Current development efforts for optimizing Gd-fuel are focused on the reduction of the inherent penalties of today's Gd-Fa designs, i.e. reduced average FA enrichment and heavy metal content as well as residual reactivity binding. The most effective way to overcome these drawbacks is the reduction of the Gd₂O₃ concentration to values of approximately 2 w/o, for which according to recent measurements of the heat conductivity of modern Gd-fuels the reduction of the fissile content in the Gd-rods is no longer necessary. Various feasibility studies have been performed to evaluate the consequences of low-Gd designs for both Siemens PWRs and Non-Siemens PWRs, for which more restrictive boundary conditions with respect to critical boron concentration and peaking factors have to be fulfilled. These studies as well as the first realization of an extended reactor cycle using a low Gd-Fa reload design confirm that the in-core fuel management can handle the different Gd burnout characteristics without problems. The economical benefits of low-Gd designs compared to conventional Gd designs are comparable to those achievable by distinctly more costly and complex alternatives like the use of enriched Gadolinia. (authors)

[en] One measure to improve fuel utilization in light water reactors is to increase their conversion ratio. Such high converting light water reactors (LWHCR), mainly advanced pressurized water reactors, have been investigated in Europe and the United States for several years. PWR-related R and D activities at the Technical University of Braunschweig, FRG, started in 1978. This paper deals with some of the burnup characteristics of a homogeneous LWHCR-design with an F/M-ratio of 1.9. As a consequence of the high conversion ratio the reactivity change with burnup is very flat as compared to that for conventional PWRs. The reactivity loss during burnup is caused predominantly by fission-product absorptions, with the relatively low consumption of fissile material being of minor importance. A breakdown of the so-called burnup coefficient, which is a direct measure of the reactivity change with exposure, enables a quantitative discussion of the influence of individual nuclides. The changes in fuel isotopic composition during burnup are characterized by: the decrease of the Pu 239 and Pu 242 content of the fuel and, depending upon their initial concentrations, a slight or moderate increase of Pu 240 and Pu 241. The Pu 239 losses exceed the Pu 241 production, i.e. the plutonium quality, defined as the fraction of fissile isotopes in the Pu, decreases. This decline of plutonium quality is, however, small (e.g. 0.653 at the end of equilibrium cycle (45 MWd/kgsub(HM)) related to 0.673 at BOL), and, from the viewpoint of neutron economy, partly compensated for by a more favourable Pu 241/Pu 239 ratio. The above characteristics of high converting pressurized water reactors, viz. the low net consumption of fissile material as well as the conservation of plutonium quality, confirm that such reactors can be effective in helping to stretch the fissile resources

[en] Tight-lattice light water reactors, with a lower moderator/fuel ratio than that for present commercial PWRs, have been investigated at many installations in recent years. Such reactors have several potential advantages related to improved fuel utilization, i.e. higher conversion ratios and increased flexibility of fissile material use, compared to present commercial PWRs. Besides the tight-lattice PWR designation such designs have other names, e.g. light water high converter reactor (LWHCR), which we will use, and convertible spectral shift reactor (abbreviated ^RCVS for its French name). A safety-related parameter of primary importance, the void coefficient, is appreciably less negative in the LWHCR-type reactors being considered than in present commercial PWRs, and the accurate determination of this coefficient has been the subject of considerable investigation in the PROTEUS critical facility. The impact of this coefficient on the ATWS characteristics of an LWHCR emphasizes the obvious importance of this parameter. This paper describes methods and results of a study of the transferability of safety-related integral information from the PROTEUS experiments to the design of a power reactor of the LWHCR type. The information content of PROTEUS results relevant to LWHCR design is investigated using sensitivity theory and methods used so successfully in the French LMFBR program. This study was supported jointly by the Paul Scherrer Institute, PSI (formerly the Swiss Federal Institute for Reactor Research) and Siemens, KWU within the realm of a trilateral agreement among PSI, Siemens and the Kernforschungszentrum Karlsruhe (KfK). Section 2 gives a summary of the formalism used in this study, while the codes, data and models used are discussed in Section 3. Results are presented in Sections 4 and 5 and Section 6 gives the conclusions