Partners:

Nuclear Waste Management Organization of Japan (NUMO), Japan,
Korea Radioactive Waste Agency (KORAD), Republic of Korea,
Nuclear Waste Management Organisation (NWMO), Canada,
Federal Ministry for the Environment, Climate Action, Nature Conservation and Nuclear Safety (BMUKN), Germany,
Nagra, Switzerland

Introduction

The longevity of containers under anoxic conditions has been well assessed based on the corrosion behaviour of base metals of carbon steel and copper in contact with bentonite (e.g., the MACOTE project).

Studies on canister sealing (welds) and corrosion under aerobic/thermal transient conditions, however, are limited.

To measure heterogenous corrosion under transient conditions (i.e., a changing environment), in-situ measuring techniques that allow continuous monitoring of the evolving corrosion rate need to be developed.

The ACS project is a long-term project to develop and evaluate in-situ corrosion monitoring techniques for the purpose of investigating in-situ non-uniform corrosion of welds and corresponding base metals and to study the effects of transient conditions.

The project is divided into three phases, moving from small scale to medium scale to potentially up to 1:1 scale and including an increasing number of transients.

In Phase 1, modules used in the MACOTE project are being redesigned to house sensors (Figure 1). Transient oxic and anoxic conditions will be studied under stable (ambient) temperature.

Figure 1: Schematic of an ACS Phase 1 module.

A major target of Phase 1 will be on testing and refining the in-situ sensors currently being developed in Japan and Germany (Figure 2).

Figure 2: Electrochemical-Impedance Spectroscopy (EIS) sensor being developed for the ACS in-situ test.

Each module contains in-situ corrosion sensor tests and standard test coupons (base metal and welds), Figure 3.

Corrosion rates of the standard test coupons will be obtained from weight-loss measurements.

These corrosion rates will then be compared with the corrosion rates obtained from the in-situ corrosion sensor tests.

Figure 3: In-situ corrosion sensors are embedded in bentonite. Measured corrosion rates obtained from the sensors will be compared with the standard weight-loss measurements of base metals and welds also included in each module.

During Phase 1, modules for Phase 2 will also be designed which will be larger to accommodate additional transients, namely heat and radiation field (Figure 5).

Figure 4: Schematic of a Phase 2 module. The module will be larger than the Phase 1 module to allow testing of more transients, namely heat and radiation.