Milestone 2.8: Preliminary Radiolytic Gas Generation Measurements from Helium-Backfilled Samples

Abstract

The Department of Energy (DOE) is currently managing nearly 13 metric tons of aluminum-clad spent nuclear fuel (ASNF), and some of this ASNF will be placed in helium-backfilled canisters for extended (> 50 years) dry storage. Due to in-reactor and cooling pond conditions, oxyhydroxide corrosion layers have formed on the surface of the ASNF elements. These corrosion layers are susceptible to radiolysis and the formation of molecular hydrogen gas (H 2 ) due to the fuel's inherent radiation field. Consequently, a rigorous evaluation of the effect of helium gas on radiolytic H 2 production is necessary to support the "Technical Considerations and Challenges for Extended (> 50 years) Dry Storage of ASNF" program, especially as previous "Task 2 -Oxyhydroxide Layer Radiolytic Gas Generation Resolution" work demonstrated a significant effect of gas composition on the radiolytic yield (G-value) of H 2 . Here, we report preliminary G-values for the radiolytic formation of H 2 from the gamma irradiation of pre-corroded aluminum alloy 1100 coupons flame sealed in helium environments. Irradiations yielded G(H 2 ) values of (5.1 ± 0.5) 10 -4 and (9.4 ± 0.9) 10 -4 µmol J -1 for pristine coupons, and (10.1 ± 0.4) 10 -4 and (15.1 ± 1.2) 10 -4 µmol J -1 for pre-corroded coupons for 0% and 50% relative humidity, respectively. These helium environment G(H 2 ) values are between 28% and 58% higher than previously reported values for argon environments. This enhancement is attributed to the significant difference in first ionization energy between helium (24.59 eV) and argon (15.76) facilitating additional processes (e.g., Penning ionization). These new preliminary helium environment G(H 2 ) values will be employed by Task 3 -Sealed and Vented System Episodic Breathing and Gas Generation Prediction to model the effect of radiolytic H 2 accumulation in helium environments to evaluate the practicality of extended storage in the DOE Standard Canister. v

Effects of Low-Level Gamma Radiation on Common Nitroaromatic, Nitramine, and Nitrate Ester Explosives

“…It is currently not known whether an inert gas irradiation atmosphere will show the same increase in sensitivity as that observed for vacuum irradiation. It is possible that the surface degradation could actually be enhanced because of Penning ionization, , which could lead to more sensitization. Future experiments aim to study this phenomenon to fully understand the effect of the irradiation environment on the sensitization of HEs since the irradiation environment for explosives in the stockpile or on space shuttles likely ranges from typical atmospheric conditions all the way to the vacuum of space.…”

Radiolytic Gas Production from Aluminum Coupons (Alloy 1100 and 6061) in Helium Environments—Assessing the Extended Storage of Aluminum Clad Spent Nuclear Fuel

“…Quantification of the yield of H 2 was achieved by gas chromatography (GC) using a Shimadzu Co. (Kyoto, Japan) Nexus GC-2030 gas chromatograph equipped with a thermal conductivity detector (TCD) set at 200 °C. Note, preliminary H 2 measurements made using a mercuric reduction gas detector struggled with consistent reproducibility [ 34 , 35 ], the TCD did not.…”

Technical basis for extended dry storage of aluminum-clad spent nuclear fuel

“…The key findings of the conducted work to close the associated technical gap are:  H2 generation can be directly attributed to the presence of corroded aluminum and adsorbed water, and the H2 yields are directly dependent on the absorbed gamma dose, relative humidity, and cover gas composition. 20,21 Further, H2 generation increases with the increasing availability of corrosion products. A positive correlation between the (oxy)hydroxide surface area and H2 generation is suspected, although it could not be confirmed empirically.…”

“…22  Experimentally collected H2 generation data can be used successfully to predict H2 generation in ASNF dry storage configurations. 21  The consequences (e.g., sealed canister pressure and canister atmosphere flammability) of radiolytic H2 generation from (oxy)hydroxide layers on dry-stored ASNF under gamma irradiation can be effectively simulated and evaluated using experimentally derived data, for dry storage periods of 50 years or more. This includes sealed and vented dry storage configurations of ATR and other ASNF types within canisters with different backfill gases, such as He.…”