Initial results from dissolution rate testing of N-Reactor spent fuel over a range of potential geologic repository aqueous conditions

Abstract

This report was not produced under a quality assurance program that satisfies the requirements of the National Spent Nuclear Fuel Program and DOE/RW-O333P, Office of Civilian Radioactive Waste Management Quality Assurance Requirements Description. Therefore, the data in the report are not considered qualified and are not to be relied upon to address safety and waste isolation issues until an accepted qualification process has been completed. DISCLAIMERPortions of this document may be illegible electronic image products. Images are produced from the best available original document. SummaryHanford N-Reactor spent nuclear fuel (HSNF) may ultimately be placed in a geologic repository for permanent disposal. To determine whether the engineered barrier system that will be designed for emplacement of light-water-reactor (LWR) spent fuel will also suffice for HSNF, aqueous dissolution rate measurements were conducted on the HSNF. The purpose of these tests was to determine whether HSNF dissolves faster or slower than LWR spent fuel under some limited repository-relevant water chemistry conditions.The tests were conducted using a flowthrough method that allows the dissolution rate of the uranium matrix to be measured without interference by secondary precipitation reactions that would confuse interpretation of the results (i.e., uranium concentrations were kept below the solubility limit). Similar tests had been conducted earlier with LWR spent fuel, thereby allowing direct comparisons.Six undamaged HSNF test specimens (one of the six specimens was treated to produce a thin oxide surface layer) were tested using 10 different water chemistry conditions. Six tests were conducted simultaneously, and then the water chemistries were changed to conduct the remaining four tests. In addition, two auxiliary tests were conducted to investigate one possible cause of the Stage 2 corrosion noted below.Two distinct corrosion modes were observed during the course of these 12 tests. The first, Stage 1, involved no visible corrosion of the test specimen and produced no undissolved corrosion products. The second, Stage 2, resulted in both visible corrosion of the test specimen and left behind undissolved corrosion products.During Stage 1, the rate of dissolution could be readily determined because the dissolved uranium and associated fission products remained in solution where they could be quantitatively analyzed. The measured rates were much faster than has been observed for LWR spent fuel under all conditions tested to date when normalized to the exposed test specimen surface areas. Application of these results to repository conditions, however, requires some comparison of the physical conditions of the different fuels. The surface area of LWR &el that could potentially be exposed to repository groundwater is estimated to be approximately 100 times greater than HSNF. Therefore, when compared on the basis of mass, which is more relevant to repository conditions, the HSNF and LWR spent fuel dissolve at similar rates. Also, the concentra...

Uranium Metal Reaction Behavior in Water, Sludge, and Grout Matrices

“…As seen in Figure 2.3, the 25°C rates for corrosion of irradiated uranium in flowing aerated waters (Gray and Einziger 1998) are consistent with rates obtained by extrapolating the earlier data from non-irradiated uranium corrosion under stagnant aerated conditions (Draley and English 1944;Mollison et al 1945). However, the 75°C rates for irradiated uranium are about 10 to 100 times lower than those found in the prior studies.…”

“…The observations for ~2,200 MWD/MTU irradiated N Reactor fuel under anoxic conditions (Gray and Einziger 1998), shown in Figure 3.3, are scattered within the rate range expected based on the STP rate (a) The sludge in the K Basins largely arose from fuel irradiated to about 2900 MWD/MTU.…”

“…This test was not continued, however, because of sample fracturing. The behavior of the fuel in the 21-to 28-day interval was ascribed to anoxic corrosion and called "Stage 2" in reference to the similar behaviors observed by Gray and Einziger (1998). As seen in Figure 2.3, the corrosion rates found in the tests under aerated conditions with confined air in the vapor space were lower than would be predicted based on the 1940s tests in open vessels (Draley and English 1944;Mollison et al 1945).…”

“…Overall, the paired findings for the irradiated and non-irradiated N Reactor fuel at 25°C Einziger 1998 andAbrefah et al 2000, respectively) and irradiated and non-irradiated EBR-II fuel at 90°C (Fonnesbeck et al 1998and Fonnesbeck 2000, 2003 show irradiation to increase rates. However, the effects of irradiated fuel crumbling or increased surface area were not investigated.…”

Review of oxidation rates of DOE spent nuclear fuel : Part 1 : nuclear fuel.

“…The similarity between oxidation rates of KW SNF and U metal is also consistent with dissolution rates of irradiated uranium metal fuel reported by Gray and Einziger at PNNL and Fonnesbeck at Argonne National Laboratory-West (ANL-W). 74,75 The effects of irradiation on uranium metal oxidation are summarized as follows. Irradiation does not increase the intrinsic oxidation rate of uranium metal.…”