Active coupons experiments

Active Coupon Experiments Coupons (19.8 x 19.8 x 4.00 mm) of Lac du Bonnet granite, obtained from the Cold Spring Quarry near the Whiteshell Nuclear Research Establishment (WNRE), Pinawa, Manitoba, were exposed to granite groun yter ayg briyg ... 

Thin layer activation (TLA) has a long experience in monitoring or measuring wear and erosion. A small quantity of radioisotope tracer is introduced into the metal surface which can be either a coupon or component. Metal loss due to corrosion (provided the corrosion product is non-adherent) can be detected remotely with high sensitivity . 

The importance of the hydrogenase enzyme was also demonstrated in experiments in which mixed cultures of SRB recently isolated from the production water of two pipeline systems in Alberta were circulated through two Robbins Devices (McCoy et al. 1981) at a flow rate of 4Lmin Both loops showed detectable SRB attached to corrosion coupons. One population of the SRB had a high level of hydrogenase activity, which correlated well with the subsequent high corrosion of the metal coupons the other population of SRB had low levels of hydrogenase and low levels of iron loss detected (Bryant et al. 1991). 

Preliminary experiments on coupons which had been plated with a chromium layer and subsequently passivated by hot moist air treatment showed significantly smaller radionuclide deposition when inserted into a PWR steam generator for the duration of a fuel cycle (Asay et al, 1991 b). Other experiments with stainless steel coupons which were exposed over several fuel cycles in the hot as well as in the cold legs of a steam generator channel head showed that chromium-plated coupons exhibited very low levels of activity uptake, as Co and °Co were in all cases lower by more than an order of magnitude than on as-received or on electropolished/passivated coupons. The addition of a passivation step after the chromium-plating treatment had a detrimental effect by increasing the uptake of activity by up to a factor of two (Pick et al., 1992). 

It is also interesting to note that the standard procedure suggests that the scan be initiated by shifting the coupon potential 30 mV active and then scanning in a noble direction at 0.6 V/h. The standard prescribes the scan rate from the cathodic to the anodic side of the corrosion potential but not a time for polarizing the material 30 mV active. This appears contradictory. Scan rate is very important in these experiments. If the sample is immediately driven to a potential 30 mV active with a potentiostatic input, the sample surface can be strongly influenced. In many real-life experiments the procedures described are not adequate. It is... 

Potentiostatic Techniques To determine the critical potential of crevice initiation, coupons in a crevice former device are exposed for a fixed period of time under potentiostatic control and monitoring of the anodic current is used to detect the onset of active corrosion. Several experiments are performed at different potentials and the crevice potential is the threshold potential that corresponds to an infinite initiation time (see Fig. 8 and 9 at the beginning of this chapter). 

The adsorption by ion exchange resins of metallic ions removed by dissolution of magnetite layer of the coupon specimens in the decontamination formulations was studied in the glass loop experiments. Inactive metal ions of iron, nickel and activated corrosion products Co-60, Co-58, Mn-54 and fission products Cs-137, Ce-141, Ce-144, Pr-144 were also effectively removed by the cation exchange resins. Ru-103, Sb-125 were taken up by anion exchange resins. Ru-106, Zr-95 and Nb-95 were taken up by bodi the ion exchange resins. 

Studies of the effectiveness of electropolishing and mechanical polishing in reducing activity uptake have been carried out on the Ringhals 4 reactor in Sweden. Coupons with various surface finishes were attached to the manway insert in the channel head bowl during 1987/88 and 1989/90. The results from the first experiment are summarised in Ref. 4. These experiments have confirmed that... 

The permeation experiments were carried out with pure CO2, CH4, O2 and N2 gases by using a gas permeation system under conditions of constant pressure. Two coupon samples were prepared and tested for each membrane batch. The active area of the coupons was 9.24 cm. The membranes were conditioned for individual feed at 120 psig for a required time to obtain a steady permeation rate. All permeation experiments were carried out at 100 psig. The cell was open to the atmosphere on the permeate side and the flow rate from this side was measured by a bubble flow meter. The permeation experiments were carried out at ambient temperature and the permeation results were corrected to standard temperature and pressure. 

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