Solution for Degrading Neutron Absorbing Material or Power Uprates
Degradation of many early neutron absorber materials used in commercial nuclear power plants wet fuel storage racks is limiting the storage capacities of plants around the world. Fuel storage racks that employ polymeric neutron absorbers have proven to be especially vulnerable to embrittlement, erosion, and gap formation under prolonged exposure to radiation. Degradation of these types of neutron absorber materials is continuous with time, resulting in gaps or severe erosion in nearly all fuel racks containing these materials. Additionally, operating the reactor at higher power levels results in discharged fuel that is more reactive.
Holtec has in-house capabilities to re-qualify the spent fuel pool given the degradation issues or new fuel conditions across all disciplines, including licensing, criticality and structural analyses. In some cases the reactively levels in the spent fuel pool may be beyond the moderation capabilities of the installed spent fuel racks, even with increased credit for fuel burnup, resulting in the need for mitigation measures.
Holtec International’s Device for Reactivity Mitigation (DREAM) insert provides a robust and economical alternative to moderate fuel reactivity without replacing the existing racks. Installing DREAM inserts in the fuel storage pool allows a plant to recover the criticality safety margins lost due to neutron absorber degradation or the enhanced reactivity of fuel following a power uprate. The DREAM insert serves to replace or augment the neutron attenuation function of the existing racks. DREAM inserts use Metamic™ as the primary material of construction. The utilization of Metamic as the neutron absorber will ensure criticality control and continued high margins of safety. Holtec currently has three DREAM insert designs, all utilizing Metamic: DREAM F1, DREAM C2, and DREAM C1.
The number, type, and location of the DREAM inserts are based on detailed criticality evaluations performed by Holtec for each site. Holtec’s DREAM insert projects are carried out under the control and surveillance of Holtec’s Quality Assurance/Quality Control Program, which conforms to the requirements of 10CFR50 Appendix B.