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Corrosion of Selected Packaging Materials for Disposal of Heat-Generating Radioactive Wastes

Objective

A research programme including laboratory-scale and in-situ corrosion studies has been undertaken to characterize further the corrosion behaviour of some carbon steels and the alloy Ti 99.8-Pd which have been identified as promising materials for heat-generating nuclear waste packaging in a rock-salt repository.
The programme has two main objectives:
- Investigation of the influence of essential parameters on the corrosion behaviour of the materials in disposal relevant salt brines. These parameters are : temperature, gamma radiation and selected characteristics of packaging manufacturing (KfK).
- Investigation of the resistance of carbon steels to stress corrosion cracking in an MgCl2-rich brine at various temperatures and strain rates by means of the slow strain rate technique (ENRESA).
In previous corrosion studies, carbon steels and the allow Ti 99.8-Pd were identified as promising materials for heat generating nuclear waste packagings acting as a barrier in a rock salt repository. The research program seeks to characterize the corrosion behaviour of these materials in more detail by:
investigation of the influence of essential parameters on the corrosion behaviour of the materials in relevant disposal salt brines. These parameters are: temperature, gamma radiation and selected characteristics of packaging manufacturing;
investigation of the resistance of carbon steels to stress corrosion cracking in a magnesium chloride-rich brine at various temperatures and strain rates by means of the slow strain rate technique.

Laboratory scale and in situ corrosion studies were performed on three preselected carbon steels. Corrosion results were obtained for the low alloyed steels for up to one year in three disposal relevant brines at 150C. Furthermore, stress corrosion cracking studies by means of the slow strain rate technique were performed on the steels in a magnesium chloride rich brine. In the in situ corrosion experiments, the influence of selected container manufacturing characteristics on the corrosion behaviour in salt brines was examined.

In general, it can be stated that the corrosion rates obtained so far for the parent materials imply corrosion allowances technically acceptable for the thickwalled packagingsdiscussed here. However, submerged arc welding strongly reduces the corrosion resistance of the steels in magnesium chloride rich brines.
Work programme:

Corrosion studies on the unalloyed fine-grained steel in three salt brines (two MgCl2-rich, on NaCl-rich) at 150 C and gamma dose rates of 1 Gy/h and 10 Gy/h (laboratory-scale immersion tests, KfK).
Corrosion studies of two low-alloyed steels (TSt E 460, 15 MnNi 6.3) in three salt brines at 150 C (laboratory-scale immersion tests, KfK)
In-situ corrosion studies on specimens of Fe-base materials, Ti 99.8-Pd and Hastelloy C4 in rock salt at rock temperature (reference experiments, KfK).
In-situ corrosion studies on tubes of carbon steel, Ti 99.8-Pd and Hastelloy C4 provided with selected container manufacturing characteristics in rock salt/brines at 90 C-200 C (KfK).
Statistical analysis of corrosion data (KfK)
Stress corrosion cracking studies on unalloyed and low-alloyed steels (fine-grained steel, TSt E 460, 15 MnNi 6.3) in an MgCl2-rich brine at various temperatures (25 C, 90 C, 170 C) and slow strain rates (10{-4} 10{-7}s{-1}) (ENRESA/INASMET)

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Forschungszentrum Karlsruhe Technik und Umwelt GmbH
Address

76021 Karlsruhe
Germany

Participants (2)

EMPRESA NACIONAL DE RESIDUOS RADIOACTIVOS S.A.
Spain
Address
7,Emilio Vargas 7
28043 Madrid
Fundación INASMET Asociación de Investigación Metalúrgica del País Vasco
Spain
Address
12,Camino De Portuetxe
20009 San Sebastián