AREVA NP Research Articles

A spatial rehomogenization method in nodal calculations

Infinite medium flux weighted cross-sections used in nodal calculations enable equivalence with the corresponding fine configuration if the following condition is satisfied: the flux shape inside the assembly in the core is close to the infinite medium flux shape (computed in lattice calculations). In presence of big flux gradients this condition is not satisfied and the absence of information about cross-sections distributions inside a node does not permit to predict the reaction rates with the same accuracy attained in ordinary situations. This tendency is amplified in case of high heterogeneous regions where tilting the flux causes big changes in reaction rates. The method presented here uses information coming from the lattice calculations that produced the homogenized cross-sections, in order to predict the right reaction rate even in presence of high tilted flux shapes. This is done in evaluating a variation of the cross-sections equivalent to the variation in reaction rate, but no variation is applied to the discontinuity factors. The accuracy of the method and its limitations are shown in several significant configurations. Its implementation in the Areva NP reactor core simulation system SCIENCE has shown better evaluation of control rod worth in comparisons with experimental results.

The EPR: A clear step forward in dose reduction and radiation protection

For the European Pressurized Water Reactor (EPR) a large effort was made to improve the plant design with respect to radiation protection using the experience gained during the design of former generations of pressurized water reactor (PWR) in France and Germany, and their current operation. Keeping the radiation exposure of personnel to an acceptable level is one of the main objectives of the EPR design. Both the individual and the collective doses are considered.Internationally comparable limits based on recommendations of the International Commission on Radiological Protection (ICRP) have been established for individual doses. These limits describe the framework within which the individual dose shall be kept as low as possible, applying the principles:•Justification: No practice involving exposures to radiation should be adopted unless it produces sufficient benefit to the exposed individuals or to society to offset the radiation detriment it causes.•Optimization: In relation to any particular source within a practice, the magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposures where these are not certain to be received should all be kept as low as reasonably achievable (ALARA), economic and social factors being taken into account.•Limitation: The exposure of individuals resulting from the combination of all the relevant practices is subject to dose limits.The paper describes the design provision and measures introduced in the plant design to achieve the above described goals.They are in essence:•measures to avoid or to reduce sources of radiation;•layout aspects;•provisions made in the component design with respect to ease of operation and maintenance management;•improved possibilities of decontamination;•use of operating experience for design improvements.The radiation protection layout principles compiled on the basis of safe operating experience gained from the existing pressurized water reactors in France and Germany are used to develop an improved plant design with respect to radiation protection aspects and dose optimization.Summary: The European Pressurized Water Reactor is an evolutionary third-generation pressurized water reactor with a rating in the 1600 MWe class. Its development was started in 1992 by Framatome and Siemens, whose nuclear activities were combined in January 2001 to form Framatome ANP, now AREVA NP. Being the product of intense bilateral cooperation the EPR combines the technological accomplishments of the world's two leading PWR product lines—the French N4 reactors in operation at Chooz and Civeaux and the Konvoi reactors in operation at Neckarwestheim, Emsland and Isar in Germany. From the very start, development of the EPR was focused on improving plant safety and economics even further and also a large effort was made to improve the plant design with respect to radiation protection. Keeping the doses received by operating and maintenance personnel to a level far below the limiting values was one of the main objectives of the EPR design. Both the individual and the collective doses are considered in this article.