Initial Results from Dissolution Testing of Spent Fuel under Acidic Conditions
- PDF / 115,148 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 203 Views
CC8.6.1
Initial Results From Dissolution Testing of Spent Fuel Under Acidic Conditions Brady D. Hanson, Judah I. Friese and Chuck Z. Soderquist Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A. [email protected] ABSTRACT Flowthrough dissolution tests using solutions with pH in the range 2 to 7 have been conducted on a moderate burnup Light Water Reactor spent fuel. Such low pH conditions have been modeled as possibly occurring in a failed waste package at the proposed repository at Yucca Mountain. The release of total uranium, 99Tc, 90Sr, 137Cs, and 239&240Pu were measured for up to 90% total reaction of the specimens. The reaction rates, determined both from the cumulative release and the release normalized to surface area, were found to decrease with increasing pH and with increasing extent of reaction. The implications to instantaneous release and long-term behavior in a geologic repository are discussed. INTRODUCTION Recent modeling of waste package and waste form degradation within the proposed repository at Yucca Mountain, Nevada, has conservatively suggested that the pH within a failed waste package can readily be below 5. This acidic pH is the result of the relatively rapid degradation of the carbon steel portions of the waste package. Since no qualified data existed for use in performance assessment modeling, a study utilizing flowthrough tests was initiated. The results of these tests are presented here. Initial results indicate that for each of the conditions tested, important radionuclides such as 137Cs, 99Tc, and 239&240Pu are not released congruently as has been previously suggested [1]. Overall, the data agree favorably with the conclusions of Röllin et al. [2]. EXPERIMENTAL METHOD Flowthrough tests were conducted using stainless steel chromatography columns with 0.5 µm stainless steel frits. The fuel was from the same rod of ATM-106 fuel as used by Gray [3] in previous tests. The approximate burnup, obtained by first comparing the 137Cs activity obtained by full-rod gamma scanning with radiochemical analyses performed by Guenther et al. [4] is 50 MWd kg-1. The fission gas release is rather high at 18%, which accounts for the relatively noisy gamma profile and is indicative of Cs relocation. The fuel was crushed using a screw-type device and the powder was first sieved through a 25 µm sieve and then a 10 µm sieve. The process was repeated to remove fines. In contrast to the method used by Gray [1], the fuel was not washed so the grain boundary inventory and at least part of the gap inventory was present. BET [5] was performed on two separate batches of fuel remaining on the 10 µm sieve and yielded specific surface areas of 0.28 m2 g-1 and 0.29 m2 g-1. The solutions were de-ionized water with enough HNO3 added to obtain the desired pH of 2, 3, 4, 5, 6, and 7. Each solution was continuously stirred and sparged with air containing less than 3 ppm CO2. All solutions were pre-equilibrated for at least three days prior to being moved to the hot cells where the testing occurred.
Dissolu
Data Loading...
