Dry storage systems and aging management H.Issard, AREVA TN, France IAEA TM 47934 LESSONS LEARNED IN SPENT FUEL MANAGEMENT Vienna, 8-10 July 2014 AREVA TN
Summary Dry storage systems and AREVA Experience Aging management: Deployed systems / inspection mitigation New aging management program in the long term Aging analysis for confirmation of safety of extended interim storage Conclusion IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 2
AREVA Experience dry storage systems Experience of used fuel storage designed by AREVA: Metal cask Metal casks (TN 24): Dual purpose : storage and transport Forged carbon steel shell Bolted lids & metal seals Long Industrial Experience :first cask in 1985 Monitoring: temperature, interlid pressure Inspections and Surveillance records : no significant event Safety review for storage extension. IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 3
AREVA Experience dry storage systems Experience of used fuel storage designed by AREVA : canister system 2014: AREVA has received the license for Nuhoms MP 197HB transportation cask, for the transport of high burnup fuels up to 62 GWd/MTU»Canister based systems (Nuhoms ): Storage System components: Dry shielded canister Horizontal storage module Transfer cask Auxiliary equipment Long Industrial Experience : first system in 1989 Inspections and Surveillance records : no significant event visual inspection monitoring: temperature Safety review for extension: lead canister inspection. IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 4
AREVA Experience dry storage systems Experience of used fuel storage designed by AREVA : vaults Vaults (Cascad type): Vaults: storage only storage pits. UNF are placed in leak-tight welded canisters (single element or multi element). Long Industrial Experience : in operation since 1990 Storage conditions monitored Safety records : no significant event Safety review for extension IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 5
AREVA Experience dry storage systems Leaking fuels Capsule Canister for Handling and Storage of Fuel Rod Capsules Dimension for handling and storage similar to a Fuel Assembly For use at a PWR: loading capacity up to 108 Fuel Rod Capsules AREVA s technology in encapsulation of defective Fuel Rods. Drying method : meet the strict requirements of maximum water content for storage. Can guarantee a reduction of residual water content << 1 g per fuel rod. Transport head Tie rod Spacer plate Corner lining strip Fuel rod capsules Bottom end piece For use at a BWR: loading capacity up to 33 Fuel Rod Capsules Transport head Tie rod Spacer plate Corner lining strip Bottom end piece IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 6
Operational Experience dry storage systems Nuclear operators and cask vendors: broad experience in the world in used fuel storage Aging management program and deployed systems / inspection mitigation Periodical inspections visual for containment corrosion Surveillance of air inlets and outlets dose rate Permanent monitoring Storage parameter measurements : temperature, inter-lid pressure gamma and neutron dose rate Inspections of content after cask opening Seal inspection, Moisture, Fuel integrity Time limited aging analysis : ex. creep or corrosion tests Analysis based on surrogates : ex. He build up Lessons learned : No accident and no event, But very limited experience of cask opening Some aging issues need further justification (influence of drying) IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 7
Dry storage feedback from inspections after cask opening US Post Irradiation Examination (PIE in hot cell) of spent fuel assemblies stored 15 years in Castor-V/21 cask no significant degradation to cask or FA s UK PIE of PWR-UO 2 fuel (58 GW d/tu) stored 20 years under air no change in the cladding oxide thickness Japan Post irradiation examination 2 MOX BWR rods irradiated to 20 GW d/tu were stored for 20 years in an air capsule no release of fission gas/he and no change in fuel/cladding microstructure Integrity inspections at Tokai (with metal cask) and Fukushima-Daiichi (with TN24 cask) performed after 5 and 10 years of storage - 52 BWR assemblies ( 30GW d/tu) No release of inner gas (Kr-85) and no defect observed on the spent fuel assemblies (visual checking) IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 8
Development of new aging management program For years, a storage period of up to 40 years was considered as long-term and sufficient in considering decisions and deployment of back-end fuel cycle and/or final waste management options. Extension of dry storage : Some consider an extension of the storage duration significantly, even beyond one century. Address the need to store used fuel with higher burn ups (62 Gwd/t for PWR or 70 Gwd/t for BWR ) and MOX fuel Used fuel should be retrievable for further use => Safety of interim storage in the long term ; need of new aging management program IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 9
Aging management to assure long term performance Focus on ensuring primary safety functions Criticality control Confinement/containment Shielding Focus on components providing safety functions Canister/cask and transport package= Primary for confinement/containment = Can provide criticality control Concrete storage module = shielding Canister/cask internals and fuel = defense in depth for containment criticality control Focus on activities to provide assurance Monitoring Inspection Mitigation IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 10
Aging management program to ensure long term performance Aging management program (AMP) updated with results of new analysis of degradation of dry storage components: Cask or canister material concrete sealing system coatings neutron shielding materials neutron poison materials Actions Tests, models Inspection program Mitigation IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 11
Aging analysis for confirmation of safety for extended storage Analysis of cask or canister material Main function : containment of used fuel. Submitted to ambient atmosphere and humidity. Most important degradation process : atmospheric Stress Corrosion Cracking (SCC), or Chlorine induced SCC. Inspections performed on existing canisters have shown no signs of SCC. However, investigations are underway for Chlorine induced SCC evaluation for welded canister system in marine environment: amount of Chlorine in ambient atmosphere, assessment of deliquescence of salt, evaluation of corrosion through inspection of existing storage systems, modelling corrosion and SCC. Mitigation techniques (stress reduction), coatings or material changes could be considered for increasing weld durability. IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 12
Aging analysis for confirmation of safety for extended storage Inspection to support Analysis Inspection of cask or canister material for salt deposition Analysis Chlorine induced SCC SaltSmart TM device (Louisville solution, USA) SaltSmart TM delivry tool in dry run on canister surface Tool carrier in use during training IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 13
Aging analysis for confirmation of safety for extended storage Analysis of concrete Main function: radiological shielding and physical protection for the Canister against a wide range of postulated natural hazards. The NUHOMS system provide an independent, passive system with substantial structural capacity to ensure the safe dry storage of used fuel assemblies. The long term concrete degradation is associated with temperatures and radiation levels: chemical degradation, carbonation, corrosion of embedded steel, coupled mechanisms, dry-out and thermal degradation of mechanical properties. Results from nuclear and non nuclear industrial experience and inspection are satisfactory. IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 14
Aging analysis for confirmation of safety for extended storage Analysis of sealing system For metal casks, the function of the metal seals is the containment Long term issues are the corrosion of bolts and the corrosion of metal seals. The behaviour of these components has been studied in storage conditions with satisfactory results by CEA (France) and CRIEPI (Japan). These studies cover long term resistance (leak tightness tests) of metal seals with Al or Ag outer jackets. Corrosion tests on such seals have also shown good resistance. IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 15
Aging analysis for confirmation of safety for extended storage Analysis of neutron shielding materials Function : to protect the public and the operators form the neutrons radiations Industrial experience : no increase of the dose rate during storage. In-service neutron shielding ageing: irradiation or thermal oxidation processes. Accelerated aging tests: various temperatures and O 2 partial pressure To predict the long term properties, a non-empirical model is applied, taking into account the diffusion-limited oxidation. The model simulates very confidently weight losses (which are then converted into hydrogen atoms loss) and oxidation profiles. good agreement between experimental results and simulated data. 35 30 1 year 25 3 years Hydrogen loss (%) 20 15 10 7 years 10 years 20 years 5 0 90 100 110 120 130 140 150 160 170 Temperature ( C) IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 16
Aging analysis for confirmation of safety for extended storage Analysis of neutron poison materials Main function : to prevent criticality. Evaluation of creep : Industrial experience (casks in vertical position) has shown no observation of creep of neutron absorbers due to control of temperatures over extended storage times. Wet corrosion and blistering (for Boral, a porous neutron poison material) water entering pores in the material during loading Vaporization during vacuum drying Blistering may cause dimensional changes affecting criticality considerations Material used now : no corrosion/blistering Thermal aging effects: decrease in tensile and yield strength. Embrittlement due to radiation exposure: unlikely Nowadays neutron poison materials degradation negligible IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 17
Aging analysis for confirmation of safety for extended storage Used fuel behaviour in dry storage: many IAEA technical documents Creep of Used fuel cladding (Zr Alloys) At dry storage temperatures between 300 and 400 C, the cladding undergoes strain due to creep. Temperature decreases continually during dry storage, no significant creep strain expected Creep strain is largely determined by fuel rod internal pressure and fuel rod temperature time history. Provided that the maximum cladding temperature does not exceed 400 C, creep under storage will not cause gross rupture of the cladding. Creep self limiting phenomenon: not a critical threat to used fuel integrity IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 18
Aging analysis for confirmation of safety for extended storage Used fuel behaviour in dry storage: many IAEA technical documents Hydrogen effects embrittlement Storage temperature will decrease to the point that hydrides precipitate in the Zr cladding. Hydrogen uptake depends on material, irradiation history and oxide thickness. Hydrogen uptake and hydride precipitation decrease the ductility of irradiated zirconium alloys. The precipitation of radial hydrides can reduce significantly the ductility. CEA R-6084 IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 19
Aging analysis for confirmation of safety for extended storage Pressure increase due to He-generation Used fuel pellets: production of helium from alpha decay during storage For very long storage periods (hundreds of years), the production of helium in MOX fuel becomes comparable to the amount of fission gases produced during reactor irradiation. For the considered storage duration (several decades), the pressure increase is limited IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 20
New AMP developments and studies Aging/degradation Stressor and risk Solution mitigation Need further work UNF Creep T, P, Bu : rupture Temperature limit No UNF oxydation T, BU, gas composition : rupture in transport UNF H2-effects Clad alloy, T, P, Bu: Rupture in transport UNF DBTT Clad alloy, T, P, Bu : rupture in transport Canister stainless steel Cask closure lid Chlorides, resid stress: SCC rupture Chlorides, resid stress: SCC rupture Inert gas Drying temperature limit Time limit for transport Drying temperature limit Time limit for transport Control, Prevent salt deposit, SCC resistant welds Control, Prevent salt deposit, SCC resistant Concrete Corrosion Temperature limit Material selection Aluminium from basket Creep Temperature limit Material selection seals Corrosion Assessment of corrosion No No Complementary tests Complementary tests New coating, selection treatment New coating, selection treatment No Complementary tests Coatings corrosion Assessment of corrosion Complementary tests Neutron shielding Loss of properties Temperature limit Complementary tests IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 21
Conclusion The overall experience is a safe and reliable storage performance. Aging management plan associated with extension of storage New investigations and tests underway for better understanding and managing the degradation of casks or canister materials Used fuel behaviour is a key issue for the management of the back end of the nuclear fuel cycle. Confirmatory demonstration is needed (already started) with high burn up fuel. Involvement of AREVA in these actions IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 22
This document and all information contained herein is intellectual proprietary to AREVA TN /. They shall not be disclosed, in whole or in part, without its authorisation. IAEA TM 47934 Lessons Learned in Spent Fuel Management Vienna, 8-10 July 2014 23