[en] Fouling of steam generators has a significant negative impact on the material and thermal performance the steam generators of pressurized water reactors. Corrosion products that originate from various components in the steam cycle of a nuclear power plant get pumped forward with the feed water to steam generators where they deposit on the tube bundle, tube support structure and the tube sheet. Heavy accumulation of deposit within the steam generator has led to some serious operational problems, including loss of thermal performance, under deposit corrosion, steam generator level oscillations, flow accelerated corrosion of carbon steel tube support plates and the failure of steam generator tubes due to high cycle fatigue. This paper will review the factors affecting steam generator fouling, examine the relationship between fouling and degradation of the thermal and material performance of steam generators and investigate the effectiveness of remedial measures to mitigate fouling. (author)

[en] This report tries to bridge the gap between the practical application and the underlying chemistry of sol gel processes as they apply to the production of ceramic nuclear fuel. The relevant principles of colloid chemistry are discussed to provide a suitable background from which to review nearly 25 years of development of sol gel technology in the nuclear industry. The two components of a sol gel process, sol formation and gelation, are discussed separately as well as a process known as gel precipitation that can be used to gel either sols or solutions. A process is identified that appears to be the most suited to the demands of remote fabrication. 40 refs

[en] Fouling remains a potentially serious issue that if left unchecked can lead to degradation of the safety and performance of nuclear steam generators (SGs). It has been demonstrated that the majority of the corrosion product transported with the feed water to the SGs accumulates in the SG on the tube-bundle. By increasing the risk of tube failure and acting as a barrier to heat transfer, deposit on the tube bundle has the potential to impair the ability of the SG to perform its two safety-critical roles: provision of a barrier to the release of radioactivity from the reactor coolant and removal of heat from the primary coolant during power operation and under certain post-accident scenarios. Thus, it is imperative to develop improved ways to mitigate SG fouling for the long-term safe, reliable and economic performance of nuclear power plants (NPPs). This paper provides an overview of our current understanding of the mechanisms by which deposit accumulates on the secondary side of the SG, how this accumulation affects SG performance and how accumulation of deposit can be mitigated using chemical additives to the secondary heat-transport system. The paper concludes with some key questions that remain to be addressed to further advance our knowledge of deposit accumulation and how it can be controlled to maintain safe, economic performance of nuclear SGs. (author)

[en] This book provides coverage of the essential elements of superconductivity theory. It illustrates how principles of superconductivity are applied to electrical devices and circuits

[en] Fouling deposits on steam generator (SG) tubes impede heat transfer and provide an environment for under-deposit corrosion. To better understand the mechanisms of particle deposition on SG tubes, the rate of deposition of magnetite particles onto I-600 has been measured under forced convective and boiling heat transfer conditions in pressurized water. Under forced convective heat transfer, the deposition of magnetite can be described as a two-step process: transport of the particles to the surface followed by attachment to the surface. The deposition rate of magnetite onto I-600 is limited by the rate of attachment for pH ≅ 9 and temperatures between 243 and 293 deg C. Under boiling heat transfer, there is an additional flux of particles to the surface that must be added to the forced convective flux. The magnitude of the enhancement of the deposition rate from boiling appears to be dependent upon pH and is eight times lower in alkaline water for pH 8.5-9.0 than in neutral boiling water at 260 deg C. (author). 13 refs., 2 tabs., 6 figs

[en] The deposition rate of calcium carbonate on a heat-transfer surface has been measured using a calcium-47 radiotracer and compared to the measured rate of thermal fouling. The crystalline phase of calcium carbonate that precipitates depends on the degree of supersaturation at the heat-transfer surface, with aragonite precipitating at higher supersaturations and calcite precipitating at lower supersaturations. Whereas the mass deposition rates were constant with time, the thermal fouling rates decreased throughout the course of each experiment as a result of densification of the deposit. It is proposed that the densification was driven by the temperature gradient across the deposit together with the retrograde solubility of calcium carbonate. The temperature dependence of the deposition rate yielded an activation energy of 79 ± 4 kJ/mol for the precipitation of calcium carbonate on a heat-transfer surface. (author)

[en] A model of particulate fouling has been developed that takes account of the influence of deposit consolidation on the kinetics of the fouling process. Fouling kinetics predicted by the model are linear, falling-rate or asymptotic, depending on the relative magnitudes of the rate constants for deposition, re-entrainment, and consolidation. One of the key predictions of the model is that the steady-state fouling rate is proportional to the ratio Kλ_c/λ, where K, λ_c and λ are the rate constants for deposition, consolidation, and removal, respectively. Tests conducted in a high-temperature recirculating-water loop have demonstrated that chemistry exerts a strong influence on the fouling kinetics of particulate corrosion product under flow-boiling conditions in alkaline water at 270^oC. For example, the fouling rates of lepidocrocite and hematite are 12 and 50 times greater, respectively, than the rate for magnetite. It is argued that the difference can be attributed to the sign of the surface charge that develops on the metal oxide surfaces in the high-temperature coolant, which, in turn, is a function of pH relative to the isoelectric point of the metal oxide. Chemical effects also influence fouling behaviour through the rate of consolidation. For example, when morpholine is used for the alkalizing agent the fouling rate is 3-5 times higher than the case when the pH is controlled using dimethylamine. The difference is attributed to the rate of deposit consolidation, which is 6-20 times greater than the rate of deposit removal for morpholine compared to 0.2-0.3 times the rate of removal for dimethylamine. The results of this investigation, together with the insights provided by the fouling model, are being used to guide the selection of the alkalizing amine to optimize its properties for both corrosion (pH) control and deposit control in the steam generator. (author)

[en] Fouling of tube surfaces in a CANDU steam generator is analyzed using a mathematical model and is shown to account for a major portion of the observed Reactor Inlet Header Temperature (RIHT) rise. First, a detailed heat transfer model is made to account for tube wall temperature at every point along a tube, then the solubility of magnetite is calculated at that wall temperature to check for primary side fouling. Once fouling can occur by magnetite crystal growth on the wall, the rate of fouling is determined by the mass transfer of dissolved iron from the water to the tube surface. The fouling deposit increases heat transfer resistance and thus the heavy water outlet temperature (RIHT) rises. This rise is followed through time and a detailed prediction of deposit weight profiles expected in the tubes is made. The inlet dissolved iron concentration to the boiler is calculated by using a simple flow-assisted corrosion model of outlet feeders. Primary side fouling of the boiler tubes is predicted to be a major contributor to RIHT rise. Coolant pH has a strong effect on flow-assisted corrosion of the outlet feeders and thus on the amount of iron entering the boilers. Deposit weights are predicted accurately for both Gentilly-2 (G-2) and Pickering-1 steam generators using solubility data from Sweeton and Baes at pH 10.3 or 1.4 mg/kg Li. Operation at the low end of the specified pH range seems desirable, e.g. 0.35 mg Li/kg, to reduce the fouling rate of the boiler tubes. Secondary side fouling is predicted to be equally important, but deposit data specific to each plant are needed to assess the precise contribution of this to RIHT rise. A gradual rise in primary side steam quality at the boiler inlet due to RIHT rise will itself generate an RIHT rise simply due to a reduction in boiler area available for sensible heat transfer. Finally, mechanical effects such as divider plate leakage and changes in primary side flow due to pressure tube creep and to increased surface roughness with age, for example, are judged to contribute to one-third of the observed RIHT rise at G-2. 62 refs., 9 figs., 4 tabs

No abstract available

[en] The X-ray detector can be used in radiographic equipment (computer tomographs). It consists of a photoconducting material, such as Ge, CdS, GaAs or HgI. The detector is supplied two electric signals. An output signal is generated by means of a circuit whose intensity is proportional to the incident radiation and whose noise background has been removed. (DG)