Project No. 09-769 Maximum Fuel Utilization in Fast Reactors Without Chemical Reprocessing ItIntegrat tdUied Universit itPy Programs Dr. Ehud Greenspan University of California, Berkeley Steven Piet, Technical POC Jack Wheeler, Federal POC Maximum Fuel Utilization in Fast Reactors without Chemical Reprocessing Summary Report NEUP Project 09-769 University of California, Berkeley November 28, 2012 Maximum Fuel Utilization in Fast Reactors without Chemical Reprocessing NEUP PROJECT SUMMARY REPORT Covering Period: October 01, 2009 through September 30, 2012 Date of Report: November 28, 2012 Recipient: University of California, Berkeley Award Number: DOE-Battelle project award number 00090622 Project Number: 09-769 Principal Investigator: Ehud Greenspan, 510-643-9983, [email protected] Collaborators: Jasmina Vujic, [email protected] ii Contributing students 1. Florent Heidet, completed his Ph.D. in September 2010; now at ANL 2. Christian Di Sanzo, Ph.D. 3. Staffan Qvist, Completed Master project and working on Ph.D. 4. Remi Cognet, Completed Master project in 2010. 5. Soto Gonzalez, Completing Master project. Additional contributing graduate students: Anselmo Cisneros, Guanheng (George) Zhang, Alejandra Jolodosky, Madicken Munk, Lasshana Huddar, Zachery Beauvais, Guervan Adnet, Christopher Varela, Seungmin Woo Contributing undergraduate students: D.J. Anderson, J.C. Curtis, A. C. Kaplan, S.A. Dionisio, A.J. Dixon, J. Doojphibulpol, N.A. Fischer, A.M. Hernandez, J.A. Miller, C.F. Montegrande, S.S. Parker, A.P. Priest, F.V. Rubio, A.P. Shivprasad, K.C. Tirohn, T.M. Wilks iii Table of Contents Abstract 1 Project summary 3 1. Background and Introduction 3 2. List of Issues Addressed 7 3. Summary of Findings 8 4. Conclusions and Recommendations 24 5. Project Publications 27 Appendices 30 A. Fast Reactors for Maximum Fuel Utilization without Chemical Reprocessing 31 B. Large Breed-and-Burn Core Performance 47 C. Neutron Balance Analysis for Sustainability of breed and Burn Reactors 128 D. A Phased Development of Breed-and-Burn Reactors for Enhanced Nuclear Energy Sustainability 147 E. Feasibility of Lead Cooled Breed and Burn Reactors 167 F. Search For Minimum Volume of Breed and Burn Cores 173 G. Energy Sustainability and Economic Stability with Breed and Burn Reactors 181 H. An Accelerator Driven Energy Multiplier for Doubling Uranium Ore Utilization 188 I. Inherent Safety of Minimum Burnup Breed-and-Burn Reactors 196 J. Assessment of waste characteristics of Breed and Burn reactors 206 iv Project Abstract The overall objective of this project was to identify fast reactor core design and fuel cycle options that could enable to achieve burnups that are significantly higher than 100 GWd/tHM without use of fuel processing technologies that can extract plutonium or can separate the actinides from most of the fission products. Following is a brief summary of the findings (see also Quad Chart below): . It is possible to start implementing the B&B mode of operation without exceeding the already proven cladding dpa levels (200 dpa) by driving a sub-critical B&B blanket with neutrons that leak-out from a critical driver. The blanket (and driver) fuel discharge burnup could be gradually increased as a cladding material that is certified to operate to higher dpa levels becomes available. With a 200 dpa constraint a depleted uranium B&B blanket can generate at least 50% of the total core power. Due to the much smaller cost of unirradiated depleted uranium fuel relative to sodium-fast-reactor (SFR) recycled (after reprocessing) fuel, the fuel cycle cost of such a seed-blanket SFR is expected to be significantly lower than of a conventional SFR. When cladding materials are certified to operate up to 300 dpa, the blanket of the seed-and-blanket SFR could generate ~2/3 of the total power. Hopefully, eventually cladding/fuel materials/design that could safely operate up to ~550 dpa/20% FIMA could be certified so that self-sustaining B&B reactors could be deployed. It is neutronically feasible to establish a self-sustaining B&B mode of operation in large fast reactor cores provided the fuel/clad will be able to safely operate up to an average burnup of at least ~20% FIMA (Fissile per Initial Metal Atom). The uranium utilization of such B&B reactors is ~40 times that of LWR. Fuel discharged from a B&B core at an average burnup of 20% FIMA can be used, after reconditioning, for the “starter” fuel of a new B&B reactor core, thus enabling to expand the fleet of B&B reactors without need for supply of external fissile fuel beyond that required for starting the first generation of B&B reactors. The primary functions of the fuel reconditioning are to remove the gaseous fission products (FP) and encase the fuel rod in a new cladding; no separation of actinides from solid FP is needed. Alternatively, after reconditioning the fuel can be recycled into the B&B reactor and operate up to a maximum possible cumulative average burnup of ~55% FIMA. The corresponding uranium utilization is ~100 times that of LWRs. The depleted uranium stockpiles (“waste”) that will be accumulated in the US until ~2050 will be able to generate, when used in the B&B fast reactors, the total US 2010 demand of electricity for, at least 8 centuries and, if ~50% burnup is attainable, for 20 centuries. No fuel reprocessing and very little (if at all) uranium enrichment will be required. It is possible to design even large low-leakage B&B cores to be passively safe. It is possible to design a B&B core to fit within the reactor vessel of SUPER-PRISM. The amount of TRU and, particularly, fissile inventory in B&B UNF can be smaller, per unit of electricity generated, than that in LWR UNF. If LWR UNF could be economically reconditioned to convert it to the feed fuel of B&B reactors, it will be possible to generate at least twice the amount of electricity the same fuel 1 already generated in LWRs while operating on the once-through fuel cycle. That is, the B&B core could provide a very efficient “interim” solution for the LWR UNF. It is concluded that successful development of B&B reactors and associated fuel re- reconditioning technologies offer promising new options for the nuclear fuel cycle that could provide a great measure of energy security and energy cost stability. This prospect justifies addressing the challenging technological issues that need be solved before B&B reactors. A number of computational methods were developed or improved as a by-product of this project. They greatly facilitate the design of fuel assemblies and the search for optimal fuel shuffling scheme for B&B and other types of fast reactors. The work performed and the findings are described in detail in 8 journal papers, 9 conference proceedings papers, 2 white papers, 22 presentations and one invention disclosure. A couple of white papers on the subject of this project were prepared for the director of the DOE NE. 3 Master and one Ph.D. dissertations were completed and 2 additional students are currently pursuing their Ph.D. work. 9 additional graduate students and 16 undergraduate students did a research project on the subject matter of this NEUP project. 2 Project Summary 1. Background and Introduction Present day commercial nuclear power reactors, mostly Light-Water-Reactors (LWRs), utilize less than one percent of the natural uranium feed: the uranium enrichment level presently preferred by the industry is approximately 4.5% 235U. As natural uranium contains only 0.72% of 235U, it takes 8 to 10 tons of natural uranium to make 1 ton of 4.5% enriched uranium. The remaining 7 to 9 tons of depleted uranium, typically containing 0.2% to 0.3% 235U, is discarded as a waste. Of the enriched uranium that is loaded into the core, only about 5% is actually fissioned, making the overall uranium utilization only ~1/9 of 5% or, approximately, 0.6%. The amount of natural uranium that has been mined so far for fueling the fleet of commercial LWRs that presently generates close to 20% of the U.S. electricity consumption is approximately 700 thousand tons. Out of these, more than 60,000 tons ended up as used nuclear fuel (UNF)—the enriched uranium fuel that was fed into the LWRs and discharged after few percent of the uranium has been fissioned. More than 600,000 tons ended up as depleted uranium “waste”. Additional depleted uranium has been accumulated from the military programs. By using fast breeder reactors it is possible, in principle, to fission close to 100% of the depleted uranium “waste”. However, this high uranium utilization cannot be achieved in a single irradiation campaign because neutron-induced radiation damage effects constrain the burnup level the fuel can withstand to the order of 10% to 15% FIMA (Fissions per Initial heavy Metal Atom), depending on the core neutron spectrum. Consequently, attainment of high uranium utilization also necessitates multiple fuel recycling. Traditionally, fuel recycling includes removal of the fuel cladding, removal of most of the fission products, addition of some depleted uranium make up fuel, fabrication of new fuel elements and reloading them into the reactor core for another irradiation cycle. Although technically feasible, there is a significant objection in the U.S. and other countries towards fuel reprocessing due to economic viability and proliferation concerns. Fast breeder reactors could, in principle, also operate without fuel recycling; that is, using a once-through fuel cycle as do all of the LWRs presently operating in the USA. Although a discharge burnup of 10% to 15% FIMA is 2 to 3 times higher than that of contemporary LWRs, the uranium utilization from a once-through fast reactor is not significantly different from that of a once-through LWR because the uranium enrichment required to fuel the fast reactor is more than twice that required to fuel the LWR.