Active coupons

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 coupons have been used to continuously monitor corrosion rates in continuous digesters, and to verify the effectiveness of anodic protection systems [180], The surface of a thin layer activation coupon is irradiated to a shallow depth and monitoring is performed with a Geiger counter 6x>m outside the digester wall. Subtracting for effects of half-life decay, the corrosion rate can be estimated from the decreased activity of the coupon. 

Radioactivation Techniques Neutron and thin layer (TLA) activation are non-intrusive techniques ofi ering the prospect of continuous, direct component monitoring, in addition to coupon or probe, monitoring. In principle, localised corrosion can be monitored using a double-layer technique. Process plant applications of the technique have been limited to date. ... 

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 . 

Fincher, D. R., Nestle, A. C. and Marr, J. J., Coupon Corrosion Rates Versus Hydrogen Probe Activity , Materials Performance, 15, 1, 34-40 (1976)... 

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). 

The coupons were contacted with tracer-free groundwater solutions, which were assayed after 28 d to determine the amount of activity that is reversibly bound to the granite under normal groundwater conditions. 

The coupons were gamma counted to determine residual or fixed activity. 

Figure 3. Photograph and autoradiographs of active granite coupon. Dark areas in photograph (A) indicate areas of high mafic mineral content. Light areas in autoradiographs (B), (C) and (D) indicate areas of radionuclide concentration.

Surface activation of BMI coupons was done by rinsing in organic solvents followed by UVOCS activation for 20 minutes. This was essential for good TiC>2 film adhesion. 

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Coupon and autoclave corrosion tests to screen equipment materials for the advanced SI process are being carried out and their experimental data is being continuously logged. The database of merchantable catalysts for a HI decomposition is being constructed through experimental activities. 

Silicon wafer test coupons were designed and fabricated by Case Western Reserve University using 51mm diameter silicon wafers. The wafers were etched with trenches in the size range of 0.5 to 10pm and then covered with an oxide layer. The wafer was diced into three 19 mm x 19 mm square devices. Each trench consisted of a 9 x 9 array of cells. The arrays were located at the center of the 6.35 mm x 6.35 mm active area in the center of each 19 mm square device. Each trench in Device 1 was 5 pm long, 1 pm wide, and 3 pm deep. Device 2 had dimensions 2x that of Device 1, and Device 3 had dimensions 4x that of Device 1. Finally a conductive seed layer of 200 A /1000 A Ti/Cu or Cr/Cu was sputtered on the chip surface. 

Figme 8.15 Trace of basicity and oxygen activity measured on a pre-oxidized 99% Ni coupon with a Na2S04 film at 1173 K in O2—0.1 mol% SO2 gas. The central dashed line in the NiO stable field indicates the minimum in NiO solubility. Numbers in the figme designate the reaction time in hours, except as indicated. (This figme originally appeared in N. Otsuka and R. A., Rapp, J. Electrochem. 

The most actively traded government securities for various maturities are called benchmark issues. Yields on these issues serve as reference interest rates which are used extensively for pricing other securities. Exhibit 1.2 is a Bloomberg screen of the benchmark bonds issued by the government of the Netherlands. European government bonds will be discussed in Chapter 5. As an illustration of a corporate bond. Exhibit 1.3 shows a Bloomberg Security Description screen for 4.875% coupon bond issued by Pirelli SPA that matures on 21 October 2008. 

As we mentioned earlier, it is difficult for credit portfolio managers (where the market is overwhelmingly noncallable) to actively manage convexity of their holdings. However, preferring higher coupon instruments and premium bonds over lower coupon and discount bonds tends to increase the convexity of the portfolio and in turn increases its total return. 

Bond market participants take a keen interest in both the cash and the zero-coupon (spot) yield curves. In markets where an active zero-coupon bond market exists, the spreads between implied and actual zero-coupon yields also receive much artention. 

The individual participants were asked to prepare the corrosion racks and to begin the exposure as soon as possible. Most of the racks were assembled and immersed in fuel storage pools well before the end of 1996. Because of the limited number of racks available, participants were asked to make periodic visual examinations of the coupons to determine whether active corrosion was obvious. If corrosion was visible, the racks were to be removed from the water and the coupons photographed. The racks were then returned to the basin for additional exposure. Water chemistry measurements were made on a periodic basis and monthly visual inspections were performed by most of the participants. 

The pitting rate equation discussed in this chapter, although not accurate, gives a reasonable evaluation of the aggressiveness of the water quahty in fuel storage basins. It has been used to monitor the basin water cleanup activities at SRS, and improvements in water chemistry have been verified by corrosion coupon tests. Additional work is needed to improve this correlation. 

In 1996 the IAEA initiated a CRP on the corrosion of aluminium clad spent research reactor fuels to help evaluate the state of the spent fuel assemblies and to inform pool/basin operators regarding maintenance and housekeeping procedures to extend the lives of the FAs. The main activities of this programme are related to exposing racks of aluminium alloy specimens (coupons) in different spent fuel basins around the world. Five racks were suspended in the 1EA-R1 reactor pool and were subsequently withdrawn after different time spans to evaluate the extent of corrosion of the coupons as a function of alloy composition, crevices, bimetallic effects and water chemistry. During this period the pool water was monitored for pH, conductivity, chloride ion content and radiometry (Table 6.3). The IAEA CRP racks are denoted as racks 1,2A, 2B, 3A and 3B. 

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