The IPEN rack

Alloys 1060, 6061 and 6262 are presently being used in IPEN for the manufacture of FAs for the lEA-Rl reactor. The compositions of the alloys are given in Table 6.4. Coupons of the three alloys, 1060 in the processed and scratched condition (to simulate the effect of scratches formed during handling of fuel elements in the reactor coolant), and various combinations of bimetallic couples were mounted in the rack (Fig. 6.2). Four coupons under each set of conditions were exposed. Coupon preparation and pretreatment were as mentioned earlier. This rack was also introduced into the lEA-Rl reactor, close 

Surface features on the facing surfaces of (a) 1060-1060 crevice couple coupons and (b) 1060-SS 304 galvanic couple coupons. 

The observations made from the IPEN rack of coupons after 16 months of exposure to lEA-Rl reactor pool water in the spent fuel section can be summarized as follows. 

The crevice side of the 6061 coupon was much more severely corroded when coupled to SS 304 (compared with 6061-6061 couples). The severe corrosion observed on 6061 coupled to SS 304 was not seen to the same degree on 6061-6061 couples. 

The 1060 surface within the crevice of 1060-SS 304 couples was stained but not pitted. No rust stains were seen on the steel surface within the crevice. 

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The participants were instructed to expose these racks in representative spent nuclear fuel assembly storage basins. They were also encouraged either to add coupons made of site specific alloys to these CRP racks or to fabricate similar racks with site specific alloy coupons. None of the participants added site specific alloy coupons to the racks of Batch I. China, however, prepared and exposed a separate rack with Chinese alloy coupons. This rack was exposed prior to the second RCM. The Chinese rack included coupons of the aluminium alloys 305 and LT24L and of SUS 304-8K the composition of these alloys is given in Table 4.2. A photograph of this rack is shown in Fig. 4.3. Table 4.3 shows the position of these alloy coupons in their additional rack. Brazil manufactured a separate rack (the IPEN rack) of coupons. This included a large number of coupons in different configurations, to allow evaluation of the effect of fuel... 

The IPEN rack exposed aluminium alloys 1060,6061 and 6262, used in the fabrication of fuel assemblies for IPEN s lEA-Rl research reactor. The composition of these alloys is given in Table 4.4. Besides 80 mm diameter coupons of the three alloys, the rack included coupons of 1060 in the processed and scratched condition (to simulate the effect of scratches formed on fuel assemblies during handling in the reactor) and various combinations of galvanic and crevice couples. Table 4.5 lists the sequence of the coupons in the IPEN rack. 

An IPEN rack containing 1060, 6061 and 6262 alloys, used in fuel assembly manufacture, was also immersed in the basin. After 16 months of exposure, it was observed that some pitting had occurred on the uncoupled coupons, mostly on the top surfaces. The aluminium couples were stained inside the crevices but were not pitted. The stainless steel-aluminium galvanic coupons were much more severely corroded. Additional laboratory tests were conducted to determine whether increased levels of silver in the basin water could have increased the corrosion of the aluminium cladding in the IPEN basin. Results indicated no pitting but an increase in darkness of the surface oxide colour with the increase of silver concentration. 

The results obtained from evaluation of the five CRP racks and the IPEN... 

Parallel to this activity, IPEN will analyse the possibility of increasing the number of racks in the lEA-Rl reactor pool and of refurbishing a section of the reactor building in which 50 dry storage horizontal tubes are located (in which three standard spent fuel assemblies per tube can be stored), as discussed in Section 2.1.3.2. 

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