RRFM 2009 Transactions - European Nuclear Society

CORROSION BEHAVIOR OF ALUMINIUM ALLOY COUPONS
SUBMERGED IN THE STORAGE POOLS OF SPENT
NUCLEAR FUEL IN CHILE
C. LAMAS 1 , J. KLEIN 2 , H. TORRES 2 , D. CALDERON 2
1
Nuclear Material Department, Advance Materials Section
2
Nuclear Applications Department, Reactors Sub-department
Comisión Chilena de Energía Nuclear, Amunátegui 95, Santiago, Chile
ABSTRACT
Chile has two MTR type research reactors, RECH-1 and RECH-2, and the spent
fuel assemblies of both reactors are being stored in racks placed in the reactor
pool. This paper shows the obtained results of a corrosion surveillance program in
a period of 3 years for racks horizontally. Due to the RECH-1 reactor has two pools
connected by a channel, an additional rack horizontally oriented was submerged
with the purpose to study the effect of flow rate in the corrosion. The
characterization techniques utilized were photography, microscopy and
metallographic analysis. Additionally, some coupons were analyzed by SEM
(Scanning Electron Microscopy) and EDS (Energy Dispersive Spectrometer). From
the results, it concluded that pitting was the most important corrosion mechanism
detected and the aluminum alloy coupons which received a pre-oxidation treatment
shown to be better protected against corrosion. Additionally, the low flow rate of
water in the neighborhood of the spent fuel racks could be an additional factor
contributing with the pit corrosion mechanism due to the presence of sediments.
When aluminum coupons is coming from areas where the flow rate is higher shown
less sediments on the surface and a consequent reduction of pits in quantity and
size.
1. Introduction
Chile has two MTR type research reactors, RECH-1 and RECH-2, and the spent fuel
assemblies of both reactors are being stored in racks placed in the reactor pool. This paper
shows the obtained results of a corrosion surveillance program making use of coupons
submerged in the RECH-1 reactor pool. The program was developed in a period of 3 years
for racks horizontally oriented. Due to the RECH-1 reactor has two pools connected by a
channel, an additional rack horizontally oriented was submerged with the purpose to study
the effect of flow rate in the corrosion. In order to study the effect of sediments in the
corrosion, a sediment collector in each reactor was installed.
2. Experimental Procedure
With the purpose to validate the experimental results, the Corrosion Protocol [1] developed in
the frame of the IAEA Regional Project RLA/4/018: “Management of spent fuel from research
reactors in Latin America” was utilized. Coupons mounted in the racks were made of different
kinds of aluminium alloys and stainless steel 304. The aluminium alloys are representative of
the aluminium used in the MTR fuel assemblies and the stainless steel is representative of
the reactor liner.
The coupons were photographed before the immersion of the racks into the pools. After the
racks were withdrawn and the coupons removed, the following characterization techniques
were utilized: photography, microscopy and metallographic amongst the most important.
Additionally, some coupons were analyzed by SEM (Scanning Electron Microscopy) and
EDS (Energy Dispersive Spectrometer). Data of the water quality of the reactors pool during
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