Modeling Carbonation of High-Level Waste Tank Integrity and Closure

K G Brown,S Sarkar,J Arnold,G Flach,J.C.L Meeussen,H Van Der Sloot,D S Kosson,V L’Hostis,R Gens

doi:10.1051/epjconf/20135605003

Abstract

The Cementitious Barriers Partnership (CBP) is focused on reducinguncertainties in current methodologies for assessing cementitious barrier performanceand increasing the consistency and transparency in the assessment process. Oneimportant set of US Department of Energy challenges is assessing the integrity andclosure of the high-level waste (HLW) tanks that currently store millions of gallons ofhighly radioactive wastes. Many of these tanks are decades past their design lives, haveleaked or been overfilled, and must be emptied and closed to satisfy regulatoryagreements. Carbonation-induced corrosion has been identified as a primary degradationand possible failure mechanism for the HLW tanks prior to closure. After closure theimpact of carbonation (and concurrent oxidation) may be to increase the release andshort-range transport of contaminants of concern. HLW tanks may be significantlyempty for many years (and possibly decades) prior to closure; the performance of theclosed tank over centuries, if not millennia, must be assessed to evaluate the potentialrelease of residual radionuclides to the environment.CBP is developing models to evaluate a representative HLW tank closure scenarioincluding the potential impacts of carbonation on waste tanks prior to and post closure.CBP modeling tools, including LeachXS™/ORCHESTRA, are being used to simulatewaste tank carbonation, major constituent leaching, and contaminant releases to evaluatethe source term and near-field conditions. Simulations presented here include sensitivityanalysis for uncracked concrete to varying input parameters including composition,effective diffusivities, and thermodynamic parameters.

Highlights

A set of important challenges to the U.S Department of Energy (USDOE) is assessing the integrity of and closing the high-level waste (HLW) tanks that store millions of gallons of highly radioactive wastes
Carbonation-induced corrosion has been identified as a primary degradation and possible failure mechanism for the HLW tanks prior to closure
The dramatic lowering of pH to ca. 9 [2] in the concrete pore solution can result in the loss of passivation of embedded steel including rebar, and, in the case of a high-level waste (HLW) tank, the steel liner (Fig. 1); the loss of passivation can lead to corrosion resulting in cracking and increased contaminant release from the tank interior and transport into the environment

Summary

Introduction

A set of important challenges to the U.S Department of Energy (USDOE) is assessing the integrity of and closing the high-level waste (HLW) tanks that store millions of gallons of highly radioactive wastes. Many of these tanks are decades past their design lives, have leaked or been overfilled, and must be emptied and closed to satisfy regulatory agreements. HLW tanks may be largely empty for many years prior to closure; the performance of the closed EPJ Web of Conferences tank over centuries, if not millennia, is required to be assessed to evaluate the potential for residual radionuclides in the tanks to be released and adversely impact human health and the environment

Carbonation of Concrete

Impacts of Carbonation on Concrete

Modeling Carbonation of Concrete

Materials Used in Carbonation Modeling

Findings

Conclusions