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Digital archive of theses discussed at the University of Pisa


Thesis etd-05122006-104030

Thesis type
Tesi di dottorato di ricerca
Franceschini, Fausto
email address
Thesis title
Advanced Fuel Cycles for Light Water Reactors
Academic discipline
Course of study
relatore Prof. Ambrosini, Walter
Relatore Dott. Petrovic, Bojan
Relatore Dott. Carelli, Mario
relatore Prof. Oriolo, Francesco
  • fuel cycle
  • Nuclear
Graduation session start date
Release date
There is a continued interest within the nuclear industry towards improving the fuel cycle, mostly in pursuit of cheaper electricity generation, but also to decrease the volume of radioactive wastes and alleviate concerns related to nuclear proliferation.

In spite of the many variables involved, some common trends in the nuclear fuel cycle can be identified. These involve fuel management strategies with enhanced neutron economy, increased fissile content and spent nuclear fuel discharge burnup, longer cycle length. These trends are mainly promoted by economic considerations via enhanced fuel utilization while respecting safety constrains.

In order for an innovative plant to be successful, it must be economically competitive, if not superior, to its predecessors. Accordingly, its fuel cycle should be able to incorporate and enhance the solutions that the nuclear industry has developed over more than 40 years of commercial operation. An innovative plant gives also the opportunity to make provisions during the design phase for best implementation of the changes in the fuel cycle foreseeable over its life span, for which many of the currently operating LWRs may not be ideally equipped.

One of the objectives for an advanced plant is to achieve cycle lengths significantly exceeding those currently in use for LWRs. This is a feature that gathers wide consensus not only within the U.S. DOE but also among the utilities. An extended cycle length is favored by utilities, since it generally implies simplified operation, reduced O&M costs and improved plant availability. Longer cycles are assumed inherently more proliferation resistant since the fuel has longer residence time than in current plants and thus fewer chances to be diverted. Also, with the enhanced irradiation, the content of 238Pu and other even Pu isotopes increases, thereby making the fuel even less attractive to be used in a nuclear weapon.

This study proposes several solutions through which the cycle length of a LWR can be extended. Different fuel compositions and fuel cycle management techniques will be explored to accomplish this objective. Furthermore, this study aims to propose solutions that can be effectively implemented in the near future. For this reason it was deemed appropriate to verify their effectiveness and viability by applying them to an advanced LWR. The International Reactor Innovative and Secure (IRIS) was selected for this purpose.

The solutions proposed in this study combine proven LWR technology with innovative engineering, therefore enabling IRIS to meet the 2010 licensing schedule without forgoing the key economic and safety requirements for the fuel cycle of an advanced plant. Also, it will be shown that these advanced fuels and management techniques cope well with other advanced operational strategies, including load following through Mechanical SHIM (the capability of performing load following maneuvers using only control rods), and use of UO2-PuO2 mixed oxide (MOX) fuel.