NSE - Nuclear Science & Engineering at MIT


Long fuel cycles for LWRS

The US industry move toward on-line maintenance stimulated this CANES study in which enhanced economic performance of LWR operations and maintenance was pursued by designing for operating cycles of 4 years and beyond, considerably longer than the current 18 to 24 month operating cycles. Steps to offset the higher fuel costs incurred in single batch cores for these longer cycles by elimination of  shutdown time for fuel reloading and associated downtime labor cost were extensively studied. These included new epithermal LWR core designs for lifetime up to 8 years and strategies for maintenance, which extended the allowable time period between inspections. Testing needs that were found limiting had to be extended by new component design or eliminated by on-line performance.

These cycle length extension strategies are being pursued by Small Modular Reactor (SMR) designers to maximize electric supply reliability and limit access to core to minimize global proliferation concerns.


  1. Galvin, M., N.E. Todreas, and L.E. Conway, "Maintenance Cycle Extension in the IRIS Advanced Light Water Reactor Plant Design" MS #01075, Nuclear Technology, Vol. 143, Pg. 270–280, September 2003.
  2. Saccheri, J., N.E. Todreas, and M.J. Driscoll, “Design and Economic Evaluation of an Advanced Tight-Lattice Core for the IRIS Integral Primary System Reactor,” Nuclear Technology, Vol. 158, No. 3, June 2007, pp. 315–347.

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