Research Programs

Nuclear Fuel Cycle

Publications:

  1. Hejzlar P., Driscoll M.J., and Kazimi M.S., “High Performance Annular Fuel For Pressurized Water Reactors,” Transactions of the American Nuclear Society, Vol. 84, Milwaukee, June 17-21, p. 192, 2001.
  2. Kim H.T., Hejzlar P., No H.Ch. and Kazimi M.S. “Performance of Internally and Externally Cooled Annular Fuel in a Loss of Coolant Accident,” International Congress on Advanced Nuclear Power Plants (ICAPP), Hollywood, Florida, June 2002.
  3. Xu Z., Hejzlar P., Driscoll M.J., and Kazimi M.S., “An Improved MCNP-ORIGEN Depletion Program (MCODE) and Its Verification for High-Burnup Applications,” PHYSOR 2002, Seoul, Korea, October 7-10, 2002.
  4. Xu Z., Hejzlar P., and Kazimi M.S., “Reactivity Effects of Internally and Externally Cooled Annular Fuel Concept,” accepted for presentation at American Nuclear Society 2002 Winter Meeting, November 17-21, 2002.
  5. Yuan Y., No H C., Kazimi M.S. and Hejzlar P., “Fuel Performance Modeling of Internally and Externally Cooled Annular PWR Fuel,” “ International Congress on Advances in Nuclear Power Plants ICAPP ‘03, Cordoba, Spain, May 4-7, 2003.
  6. Feng. D, Hejzlar P., and Kazimi M.S. , “Thermal Hydraulic Design of High Power Density Fuel for Next Generation PWRs,” The 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10) Seoul, Korea, October 5-9, 2003.
  7. Hejzlar P., Feng D., Otsuka Y., Xu Z., Lee W.J. and Kazimi M.S., “Annular Fuel for High Power Density PWRs: Neutronic and Thermal Hydraulic Considerations,” Advances in Nuclear Fuel Management III (ANFM 2003), Hilton Head Island, South Carolina, USA, October 5-8, 2003.
  8. Y. Zhao, H.C. No and M. Kazimi, “Mechanical Analysis of High Power Internally Cooled Annular Fuel,” Nuclear Technology , Vol. 146, pp. 164-180, May 2004.
  9. P. Hejzlar, D. Feng, Y. Yuan, M. S. Kazimi, H. Feinroth, B. Hao, E. J. Lahoda, and H. Hamilton, “The Design and Manufacturing of Annular Fuel for High Power Density and Improved Safety in PWRs ,” Proc. of the 2004 International Meeting on LWR Fuel Performance, Orlando, Florida, September 19-22, 2004.
  10. Feng D, Morra P., Lee W.J., Hejzlar P., Saha P., and Kazimi M.S. , “Safety Analysis of High Power Density Annular PWR Fuel,” ICAPP 05’, Seoul, Korea, May 2005.

Investigators :

  • Prof. Mujid S. Kazimi, Dr. Pavel Hejzlar, Prof. Ronald G. Ballinger, Dr. Gordon Kohse, Dr. Zhiwen Xu, Dr. Hee. C. No, Y.Otsuka, Yi Yuan, D. Feng, P. Stahl, D. Carpenter, J. Zhao.

High Performance Fuel Design for Next Generation PWRs

One of the key components in Pressurized Water Reactors (PWRs) affecting safety and economy is nuclear fuel. Recent excellent performance of the U.S. PWR plants and appreciable higher core power levels gained from adding to the licensed power (uprating) are in part due to fuel performance advances. Much larger core power density increments in current and future plants, if realizable, would bring significant benefit to plant economy. Therefore, new fuel geometries in combination with operating parameters changes, which would allow a substantial increase in power density, are being investigated. The geometries under investigation involve annular fuel with internal cooling, minipins, and twisted cross—all having the advantage of larger surface to volume ratio of the fuel, which increases margin to critical heat flux and reduces the operating fuel temperatures.

Most significant progress so far has been achieved with annular fuel development where the objective was to develop and optimize the design of internally and externally cooled annular fuel to achieve a significant increase of core power density while improving the safety margins. The tasks involved are to:

Identify the most promising arrangement of internally and externally cooled annular fuel to achieve significant increase of power density (by at least 30%) while simultaneously maintaining or increasing safety margins, based to a large extent on the extensive PWR fuel database to minimize R&D development expenses and the risks associated with transition to a new fuel.

Optimize the fuel for superior thermal hydraulic and safety performance. Examine the optimum flow distribution, core pressure drop, maximum Departure from Nucleate Boiling Ratio (DNBR), and the resistance against parallel channel instabilities. Perform safety analyses, such as Loss of Coolant Accident (LOCA) to confirm safety benefits expected for the new fuel.

Evaluate the neutronic fuel design with respect to achievement of high reactivity-limited burnup and reasonably long refueling cycle to attain good economic, waste and proliferation resistance indicators. Confirm that reactivity feedbacks and reactivity control aspects are acceptable.

Select a fabrication process to produce annular fuel elements with the required characteristics, including fissile loading, smooth surfaces and high integrity cladding. The process should be capable of eventual scale-up into a low cost, efficient fuel element production that can compete economically with current LWR fuel production processes.

Evaluate fuel performance with the focus on the effects of the new UO2 fuel form and new production technologies different from current US practice (e.g. vibropacked fuel), and new operating conditions (especially very low peak fuel temperature) on fission gas release, and fuel dimensional properties during burnup. Both fuel performance modeling and scoping irradiation tests at the MIT reactor will be used to assess performance of the new fuel.

Optimize the core and plant design to minimize electricity cost when using annular fuel for uprating current Generation II PWRs or in new advanced PWRs.

Various array sizes (11x11 to 15x15) that fit in the fixed dimensions of a fuel assembly were explored and the most promising options were found to be a 13x13 and 12x12 arrays. Because thermal expansion and swelling of fuel pellets during operation are expected to be towards the outer cladding and the 13x13 array accommodates higher heat flux to the outer channel, the 13x13 array appears to be the most promising design. The 13x13 design allows power uprate by 50% in terms of DNBR limit. This is a significant power uprate, raising the extracted power from the same core size to support increasing the plant output from the current 1150MWe to 1750MWe. At this high power, the peak fuel temperature is still about 1300ºC lower than the solid fuel in today’s PWRs. Such a high power uprate requires a proportional increase of core flow rate resulting in larger pressure drop and velocity, which in turn raises vibration and fuel assembly lift-off concerns. However, vibration analyses showed that annular fuel even at 150% flowrates is, due to its high rigidity, more resistant to various modes of vibration than solid fuel. Annular fuel was also found to be resistant to both excursive (Ledinegg) instability and density wave instability. However, hydraulic lift-off forces are several times higher than for the reference fuel and will require design modifications of the fuel assembly and fuel rod holding mechanisms.

Safety analyses of selected accidents, such as Large Break Loss of Coolant Accident (LBLOCA), Loss of Flow Accident (LOFA), mains Steam Line Break (MSLB) and control rod ejection, showed that the proposed fuel will have at 150% power comparable or higher margins to safety limits than the current solid fuel. Also, comprehensive neutronic studies have shown that the annular-fueled high power density cores have comparable steady-state performance, including power distributions and reactivity coefficients, to the reference solid fuel core.

On the fabrication side, two major fuel fabrication routes; the traditional pellet sintering route and the vibration packing (Vipac) route, were investigated. An evaluation showed that existing commercial nuclear fuel cladding manufacturing technology could produce the cladding tubes required by the annular fuel without prohibitively higher costs. AECL produced successfully six annular fuel test specimens for irradiation testing at MIT, using Vipac fuel fabrication technology and 4-foot rods. Feasibility of manufacturing with vipac technology was confirmed, but at smaller densities in longer rods (77% of theoretical). The route of the traditional press and sinter fabrication turned out to be very successful and the most promising. Westinghouse Nuclear Fuel Company in Columbia, South Carolina successfully demonstrated pellet fabrication of the reference 13x13 annular fuel with very low tolerances. Economic analyses by Westinghouse have shown that the annular fuel is economically always superior to current solid fuel and that it is the most attractive for the uprate of currently operating PWRs, where it brings the highest rate of return.

Annular fuel performance behavior during irradiation is predicted using modeling based on FRAPCON-3 computer code. The results confirmed expectations of low fission gas release from the annular fuel due to small fuel temperature, which makes it possible to achieve high burnups. The cladding strain and oxide thickness are within the design limit even at high burnup and at high power density. Two test specimens were irradiated at MIT reactor and post-irradiation measurements of fission gas release are ongoing.

The project is lead by MIT with partners from Westinghouse Electric Corporation, Gamma Engineering Corporation, Framatome ANP and Atomic Energy of Canada Limited.