The reaction of reference commercial nuclear waste glasses during gamma irradiation in a saturated tuff environment

  • PDF / 7,126,402 Bytes
  • 22 Pages / 593 x 841.68 pts Page_size
  • 32 Downloads / 208 Views

DOWNLOAD

REPORT


•.INTRODUCTION The Nevada Nuclear Waste Storage Investigations (NNWSI) project is currently evaluating the volcanic tuff beds of Yucca Mountain, Nevada, as a repository for the permanent storage of high-level nuclear waste. A description of the site has been given by Ballou,l and an important consideration in assessing the overall performance of the repository is the extent of radionuclide release from the waste form under conditions that may exist during storage. One concern that has been raised previously in the literature is the uncertain effects of penetrating radiation on the performance of the waste form when in contact with groundwater. For NNWSI, the conditions anticipated for disposal suggest a priori that radiation should have little effect on the performance of the glass. Specifically, since the waste container is to maintain its integrity during the 300-1000 year containment period,2 water will contact the glass only after the radiation exposure rate in the repository has dropped to less than 50 R/h. Also, since the NNWSI site hydrology is unsaturated, the opportunity for contact between standing water and glass will be remote. The most likely reactants would be humid air and glass, or small pockets of transient water and glass. The experiments described in this article address the unlikely, but possible, case where relatively large volumes of liquid water contact glass, and measure the differences that occur in the glass reaction process as a 576

J. Mater. Res. 3 (3), May/Jun 1988

http://journals.cambridge.org

function of exposure rate. Previous studies3"5 raise several issues that may affect the glass performance. These concerns include the following. (1) What reactions occur when repository groundwater is subjected to gamma radiation in the presence of waste package components, and what is the effect on glass performance? It has been established3 that when humid air is subjected to gamma irradiation, nitric acid is produced in the gas phase. When a two-phase air/ water system is irradiated, the nitric acid dissolves in the water and may acidify the pH of the solution, attaining values as low as 3. As the/?H changes, the solubilities of glass components change. The extent of glass reaction may thereby increase because glasses are more reactive in high or low pH solutions but are quite resistant to reaction in neutral pH solutions.6 (2) The radiolytic production of nitric acid in an air/water system increases with the radiation exposure rate according to the relationship established by Burns etal.,3

[ l - e x p ( - \A5XlQ-5xGDt)],

where N is the concentration of nitric acid in the water (moles/liter), Co is the initial nitrogen concentration in the gas phase (moles/liter), R is vol gas /vol liq , G is the number of molecules of nitric acid produced when 100

0003-6951 /88/030576-22$01.75

Downloaded: 17 Mar 2015

(1)

© 1988 Materials Research Society

IP address: 142.58.129.109

Bates eta/.: Reaction of commercial nuclear waste glasses

eV of radiation energy is absorbed by the nitrogen gas, D i

Data Loading...