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И з в е с т и я в у з о в • Я д е р н а я э н е р г е т и к а • № 3 • 2 0 1 4 93

Abstract. The Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD) established the Working Party on Evaluation Co-operation (WPEC) to promote exchange of information on nuclear data activities by its members. One of the WPEC objectives is to assess needs for nuclear data improvements and to stimulate initiatives to fulfill these. The High Priority Request List (HPRL) was established in pursuit of this objective. The HPRL project aims at identifying accuracy targets for the improvement of nuclear data, primarily for application in the nuclear industry. The list therefore provides a guide for those planning new measurements, nuclear model calculations and data evaluation programmes. Since 2004, the HPRL has undergone a major overhaul to better guarantee timeliness and adequate documentation of requests. A new webpage was developed at the NEA to facilitate submission of new requests, and to allow easy inspection. Submitted requests are first reviewed by external referees, before being accepted on the list. Requests are divided into high priority requests, where a quantitative justification is provided and general requests for which the justification is qualitative. The relevance of requests for nuclear energy applications is ensured through periodic reviews by an expert group of the NEA WPEC, involving Europe (JEFF), Japan (JENDL), the United States (ENDF), Russia (BROND) and China (CENDL). The new procedures for submission, review and adoption of requests were recently validated with a first set of entries. Examples of recent updates to the HPRL project are presented. The requirements for providing new requests are also presented, as well as how to justify needs for new nuclear data. Data users around the world are encouraged to formulate their concerns about nuclear data and submit them to the HPRL. The HPRL is maintained by the NEA Data Bank and can be consulted at the following address: http://www.nea.fr/html/dbdata/hprl/.

As is well known, integral experiments on critical piles are useful in verifying neutron data obtained in nuclear physics experiments. The ABBN-78 group constants for 23921'1pu were verified in [l]. New nuclear physics data forming the basis of the new ABBN constants have now been obtained [2]. Having been tested and named ABBN-93, the new system of constants has been recommended as the standard reference data for reactor and shielding calculations [3].On the basis of new methods of evaluating macroscopic experiments and additional experiments on BFS fast critical piles, experimental data useful in verifying and refining the constants of 24~ have been obtained. These data, together with the experiments in [ I, 4], constitute a representative set of experiments allowing the constants of plutonium for the new ABBN-93 system of group constants to be tested.In the present work, theoretical data obtained on the basis of the ABBN-93 constants are compared with experimental data on the ratios of the mean fission cross sections and the ratios of the reactivity coefficients for 239"240"241pu (with respect tO 235U). The characteristics of new critical piles are also briefly presented, along with methods of evaluating experimental data. EXPERIMENTS ON BFS CRITICAL PILESThe structure of the new BFS critical piles (Table 1) is traditional; see [4], for example. In contrast to other piles, the central insert of the BFS-56-1B pile consists of seven actual fuel rods that are similar in composition to those of a fast power reactor with uranium-plutonium fuel based on plutonium extracted from a VVER-1000 reactor. The BFS-56-ITs pile differs from the BFS-56-IA pile in that the uranium dioxide is replaced by graphite. The BFS-58-1 pile is obtained by replacing the empty shells of the sodium pellets with pellets containing sodium.The ratios of the mean fission cross sections fi/f235 are measured by means of fission chambers and the method of calibration through the thermal column. In addition, the ratio of the mean fission cross sections of 240"239pu (f240/f239) is obtained by absolute calculation in chambers with a known quantity of material and a known efficiency of fission fragment recording (-0.99). The ratios of reactivity coefficients of the materials ri/r235 are measured by means of periodic perturbation of pile criticality using small samples. The pile reactivity is recorded by means of a digital reactimeter [5]. All the experimental values are obtained as a result of averaging over the height of the pile's central cell. CONSTRUCTING ADEQUATE THEORETICAL MODELS OF THE EXPERIMENTSBefore comparing the experimental and theoretical data, models of the experiments must be constructed and the experimental data must be reduced to the conditions of these models.The experiments are relatively simple. One-dimensional cylindrical calculation models are chosen. (The leakage at the ends is taken into account in the B 2 approximation.) The systems are brought to a critical state by varying the thickness of the State Scientific Center, Russ...