A Novel Cold Spray Method for Repair and Mitigation of Cracks in Spent Nuclear Fuel Storage Canisters

Dry storage of spent nuclear fuel (SNF) is canisters can be threatened by corrosion of the metallic canisters which incur substantial repair and replacement costs and logistical ises.A novel cold spray repair and mitigation approach is proposed to repair corroded SNF canisters and mitigate the corrosion threat for fabricated canisters.The proposed work utilizes a novel cold spray technique whereby a low temperature repair can take place which does not degrade the component chemistry or microstructure.In addition, no sparks are present which could cause reactions with evolved hydrogen gasses and the process can be performed remotely using robotic deposition.Lastly, complex geometries can be repaired, and the technique can also be utilized as a mitigation strategy prior to placing the canisters in the field.During Phase I, the SNF canister base alloy 304SS was sprayed and repaired via cold spray.Three alloys were explored for cold spray, 304SS as a benchmark and two Ni-based alloys: NiCr and Inconel 625.Stress corrosion cracking was investigated via U-Bends placed in boiling MgCl2 containing solution and showed that the cold spray process improved corrosion life by over 100% compared to an unprotected specimen.Furthermore, pre-cracked specimens were tested to simulate repairs, and the corrosion life was extended to that of the non-cracked specimen.Together, these results confirm that the cold spray process can be used as both a SCC mitigation and prevention tool as well as a SCC repair method.Lastly, the repairs were performed utilizing a robotic system which can be integrated into mobile field units for remote repair in unsafe conditions.In Phase II, the cold spray methodology and materials will be further improved to enhance performance in SCC testing by optimizing porosity, surface roughness, thickness, and residual stress.General U-bend SCC testing and a more quantitative crack growth method will be combined to assess the performance of cold-spray repaired coupons.In addition, we will explore methods to integrate cold spray units onto mobile systems for remote repairs.Successful demonstration of the cold spray repair technique for spent nuclear fuel canisters would provide a significant enhancement for the logistics of SNF storage methods where new canisters costs several million dollars.Furthermore, a valid and qualified repair technique would enable higher adoption rates of the dry cask method and provide a trusted storage method for the 50,000 metric tons of SNF in the US.Demonstration of cold spray repair for high risk applications such as SNF storage can enable further exploration in other critical repair areas of nuclear reactors, aerospace applications, and automotive applications.