M. Salvatores

THE PHYSICS OF SUBCRITICAL MULTIPLYING SYSTEMS

In recent years an increasing interest is observed with respect to subcritical, accelerator driven systems (ADS), for their possible role in future nuclear energy scenarios, as actinide (Pu and MA) incinerators, and/or as claimed energy plants with potential enhanced safety characteristics. Important research programs are devoted to the various related fields of research. Extensive studies on the ADS behavior under incidental conditions are in particular made, for verifying their claimed advantage, under the safety point of view, with respect to the corresponding critical reactors. Related medium and long range scenarios are being considered to cope with a number of concerns associated with safety (power excursions, residual heat risk), as well as with fuel flow (criticality accidents, fuel diversion, radiological risk, proliferation). In the present work we shall comment on some issues relevant to these new reactor concepts, with the intent of giving a general view of the present state-of-the-art in the reactor physics domain. Specific calculation methods to be adopted for intercomparison analysis of these systems and experimental data interpretation are also discussed, as well as ongoing and perspective relevant experimental campaigns on experimental facilities.

EQUIVALENT GENERALIZED PERTURBATION THEORY (EGPT)

Based on the well-established generalized perturbation theory (GPT), an equivalent method (EGPT) is proposed. An advantage of this new formulation is that in many circumstances of interest the difficulties in calculating the functions entering into the perturbation expressions can be simplified, in particular, allowing us to reduce the equations governing them from an inhomogeneous to a homogeneous form. After a general derivation of the method, its specialization to a number of different problems is made. Numerical tests for a variety of cases are finally illustrated, confirming the validity of the EGPT methodology.

Physics challenges for advanced fuel cycle assessment

Advanced fuel cycles and associated optimized reactor designs will require substantial improvements in key research area to meet new and more challenging requirements. The present paper reviews challenges and issues in the field of reactor and fuel cycle physics. Typical examples are discussed with, in some cases, original results.

Impact of the Core Minor Actinide Content on Fast Reactor Reactivity Coefficients

A major challenge for future fast reactors could be the recycling of minor actinides (MAs) in the core fuel in order to minimize waste and to meet both the sustainability objective and the reduction in the burden of geological disposal. Although the prevailing issues will be found in the development and validation of the appropriate fuels, the presence of MAs in the core can deteriorate the core reactivity coefficients. However, in this paper, we will show that there is no well-defined physical limit to the amount of MAs in the core fuel, and that a careful physics analysis can indicate the most appropriate measures that reduce the MA impact on the reactivity coefficients, and in particular, for Na-cooled reactors, on the Na void reactivity coefficient.

Future Nuclear Power Systems and Nuclear Data Needs

The improved knowledge of nuclear data will continue to play a crucial role in any scenario of nuclear power development. The purpose of this paper is to give some indications in support of that statement, despite the uncertainties on what type of nuclear power development will prevail in future. [“Q : What do you want to do with this stick ? A : I want to measure the depth of water. Q : But here there is no water. What could you measure ? Chao-chu did not answer. He leant on his stick and went away” Master Dôgen].

Developments in Sensitivity Methodologies and the Validation of Reactor Physics Calculations

The sensitivity methodologies have been a remarkable story when adopted in the reactor physics field. Sensitivity coefficients can be used for different objectives like uncertainty estimates, design optimization, determination of target accuracy requirements, adjustment of input parameters, and evaluations of the representativity of an experiment with respect to a reference design configuration. A review of the methods used is provided, and several examples illustrate the success of the methodology in reactor physics. A new application as the improvement of nuclear basic parameters using integral experiments is also described.

International Integral Experiments Databases in Support of Nuclear Data and Code Validation

The OECD/NEA Nuclear Science Committee (NSC) has identified the need to establish international databases containing all the important experiments that are available for sharing among the specialists. The NSC has set up or sponsored specific activities to achieve this. The aim is to preserve them in an agreed standard format in computer accessible form, to use them for international activities involving validation of current and new calculational schemes including computer codes and nuclear data libraries, for assessing uncertainties, confidence bounds and safety margins, and to record measurement methods and techniques. The databases so far established or in preparation related to nuclear data validation cover the following areas: - SINBAD - A Radiation Shielding Experiments database encompassing reactor shielding, fusion blanket neutronics, and accelerator shielding - ICSBEP - International Criticality Safety Benchmark Experiments Project Handbook, with more than 2500 critical configurations with different combination of materials and spectral indices. - IRPhEP - International Reactor Physics Experimental Benchmarks Evaluation Project The different projects are described in the following including results achieved, work in progress and planned.