[en] The Mark 1 Cryostat requires a cryogenic shroud that must be retracted immediately before firing the NIF laser. This paper evaluates a pneumatic cylinder that has been chosen to open and close the shroud. After a variety of motion control and vacuum compatibility experiments, we concluded that the Bimba feedback control cylinder may be used to retract the shroud with certain modifications to its control system and additional rod seals. The Mark I Cryostat is a system that allows fielding of a wide range of targets on the National Ignition Facility (NIF). The purpose is to have a system with the capability of controlling the target temperature between ∼10 and 300 K. While in the Target Chamber, a shroud must cover the cooled targets. This shroud allows the cold target to be shielded from condensable residual gasses in the target chamber. The removable shroud may be cooled to 80 K to provide a radiant shield for the target from the room temperature target chamber. The shroud must remain over the target until approximately one second before shot time, and then retract on command, without inducing vibration into the target. An actuation system design, which removes the shroud, is constrained by the size limitations of the MK-1, the need to build from low-activation materials, the need to operate in a vacuum, and the need for high reliability. The scheme for retracting the shroud that they investigated was a pressurized air cylinder. The pneumatic cylinder tested in our experiments was built by the Bimba Manufacturing Company. We thought it would be suitable for shroud retraction because its manufacturer claimed that its motion was smooth, highly accurate, controllable and the appropriate size for our needs. The pneumatic cylinder moves a piston by changing the gas pressure in the two sections of the cylinder on either side of the piston. The cylinder also uses the piston as a voltage potentiometer to determine the current position of the piston. This voltage is then output to a controller card, which processes the voltage and compares it to the desired position input by the user. If the piston is not at the input location, the controller card dynamically controls the piston by opening and closing valves to the cylinder, varying pressure on the piston. The piston is connected to a shaft, which through a linkage system, attaches to the removable shroud. This report summarizes our studies of the controllability and vacuum characteristics of the Bimba Pneumatic Cylinder.

[en] We describe some properties of the Laurent polynomial rings in a finite number of indeterminates over a commutative unitary ring. We study some subrings of the Laurent polynomial rings. We finally obtain two cancellation properties. (author)

[en] The concrete is a very durable construction material and his use is based on the principle that concrete is an ideal environment for steel if properly proportioned and placed. In general, reinforced concrete has proved to be successful in terms of both structural performance and durability. However, there are instances of premature failure of reinforced concrete components due to corrosion of the reinforcement. Experience has shown that there are certain portions of exposed concrete structures more vulnerable than others. Methodology for concrete repair it addresses to suggestions of the types of repair methods and materials and a detailed description of the uses, limitations, materials, and procedures for Repair of Concrete. At same the time the methodology presents recommendation on materials, methods of mixing, application, curing and precautions to be exercised during placement. This work presents guidelines for managing reinforced concrete components and specifies the repair strategy with inhibitors incorporating. (authors)

[en] The successive isotope exchange between water-water vapours and hydrogen represents the combination of a distillation process with catalyzed reaction. The two processes are promoted on specific contact elements, which in that case were combined in a mixed packing. The testing of these packings allowed to elaborate an economically optimized packing, which for the catalyzed elements represents a unit per volume of 70%. (Author)

[en] The reliability of all nuclear power plants being dependent on the water chemistry during normal operation, start-ups, shutdown and abnormal operation cases, the water chemistry control is very important. It is necessary mainly to maintain those conditions that should assure minimum materials corrosion and the components reliability in operation. The corrosion may be minimized both by right choice of materials and by narrow chemical control of aqueous environment in contact with metallic materials. Referring to water chemistry management, it found that some amines simultaneously with their action of pH regulating, should have an inhibitor effect on the corrosion behaviour of iron alloys. The alloy studied was the carbon steel SA106 gr.B. The carbon steel samples were submitted to autoclavizings at (260 ± 5)°C and (5.5 ± 0.5) MPa in the three types of solutions having a similar final pH of 9.7, prepared using the following amines: morpholine and cyclohexylamine (AVT), morpholine and triethanolamine (TEA) and respectively morpholine and triethylamine (TREA). After autoclavizings, the filmed samples have been characterized using the gravimetric method, Electrochemical Impedance Spectroscopy (EIS), SEM and metallographic evaluation. On the basis of our experimental results, we concluded that triethanolamine and triethylamine may successfully substitute cyclohexilamine in the chemical treatment of secondary circuit environment. (author).

[en] Concrete is a durable material and its performance as part of the containment function in NPPs has been good. Experience shows that degradation of the reinforced concrete structures caused by the corrosion of the reinforcing steel represents more than 80% of all damages in the world. Corrosion protection may be carried out by the isolation of the concrete reinforcement against aggressive environments through the use of ″corrosion inhibitors″. Migrating corrosion inhibitors are chemical compounds on the amine basis and can protect the reinforcing steel against the corrosion in both oxidation ranges: cathode and anode range. These inhibitors can be applied to existing reinforced concrete structures and will then be carried by water into the proximity of the reinforcing steel. The effectiveness of two inhibitors applied to the mature reinforced concrete was evaluated. The corrosion behaviour of the steel rebar and the inhibiting effects of the amino alcohol chemistry in an aggressive environment were monitored using SEM investigations, gravimetric and electrochemical measurements. (author).

[en] Concrete is a durable material and its performance as part of the containment function in NPPs has been good. However, experience shows that degradation of the reinforced concrete structures caused by the corrosion of the reinforcing steel represents more than 80% of all damages in the world. Much effort has been made to develop a corrosion inhibition process to prolong the life of existing structures and minimize corrosion damages in new structures. Migrating Corrosion Inhibitor technology was developed to protect the embedded steel rebar/concrete structure. These inhibitors can be incorporated as an admixture or can be surface impregnated on existing concrete structures. The effectiveness of two inhibitors (ethanolamine and diethanolamine) mixed in the reinforced concrete was evaluated by gravimetric measurements. The corrosion behavior of the steel rebar and the inhibiting effects of the amino alcohol chemistry in an aggressive environment were monitored using electrochemical measurements and scanning electron microscopy (SEM) investigations. (authors)

[en] Full text: The design in-service life of existing NPPs was often evaluated to 30-40 years, but the present opinion is that the containment buildings may have to ensure safe function for a time span significantly greater than their initial design life. This paper presents some considerations referring to CANDU containment buildings aging providing information on the potential degradation mechanisms for each of the primary materials systems, for identifying the areas where concrete-related structure materials may experience some kinds of degradation. It was performed a study regarding containment degradation (e.g., corrosion of conventional reinforcing steel, pre-stressing steel, etc) and how changing in concrete materials properties may affect the performance of NPP concrete structures. Although the performance of concrete structure has been generally very good, however, there have been incidents related to concrete degradation. Causes of degradation were ascribed to improper materials selection, construction deficiencies or environment effects (e.g., exposure to salt water or high temperature conditions). In this paper it is presented, also, an overview of the various techniques that may be used to detect ageing degradation of concrete containments and the advantages, limitations and primary applications of each method. Traditionally, visual observation has been the common technique used to detect corrosion due to rust induced, which in turn produces the cracking and spalling of cover. These damages are an indication of the corrosive activity developed underneath the cover. Electrochemical techniques are used to detect electrochemical corrosion activity of metallic reinforcement. Many electrochemical techniques are available for monitoring corrosion of steel in concrete structure such as: open circuit potential (OCP) measurement, surface potential (SP) measurements, concrete resistivity measurement, linear polarization resistance (LPR) measurement, etc. Because the containment serves as the ultimate barrier against the release of radioactive materials into the environment, a continuous monitoring and evaluation survey of the containment degradation is necessary. (authors)

[en] Reinforced concrete is the most commonly used construction material all over the word and his uses is based on the principle that concrete is an ideal environment for steel. The concrete is a very durable construction material and his use is based on the fact that concrete is an ideal environment for steel if properly proportioned and placed. The high alkalinity of concrete causes the formation of a saturated hydrated iron oxide passive film on reinforcing steel, which provide good protection against corrosion. However, corrosion of reinforcing steel in concrete has become a major problem in the word and is important to detect her at an early stage. Concrete due to its porous nature has pore solution present in a liquid state. Given the presence of liquid and provided oxygen is present, it is likely that corrosion is possible. Techniques for evaluating the response of reinforced concrete structures to elevated-temperature conditions are presented and studies in which reinforced concrete structural elements were subjected to elevated temperatures are described. Electrochemical techniques i.e., potentiodinamyic polarization and electrochemical impedance (EIS), gravimetric measurements, and SEM investigation were used to assess the effect of elevated temperatures on concrete reinforcement. (authors)

[en] This paper presents a brief overview of steam generator functional parameters of nuclear power plants how use PWR (Pressurized Water Reactor) and PHWR (Pressurized Heavy Water Reactor) reactors, followed by a description of fundamental aspects on steam generator degradation and water chemistry in the secondary side, and also, water chemistry improvement by controlling ph. During operating life, cooling radioactive contamination occurs, but water conditions must be maintained inside specific ranges. Feedwater must be maintained as free from impurities as possible. This requirement involves careful attention to the entire system through which the water flows, either in the form of steam or water, for even though water is used as feedwater be pure at the same time of its entry into the system, it may absorb impurities from the various parts of the installation. Specific attention should be directed to possible points of water leakage from the service water system, as in the main and auxiliary condensers. Feedwater must be treated to maintain the required water conditions. As the concentration of the impurities in deposits increase, the ph can shift locally in these areas to acidic or alkaline conditions, entering in a ph range where initiation of corrosion phenomena cannot be longer excluded. By maintaining of sufficiently reducing conditions, the occurrence of certain corrosion mechanisms will be excluded (like pitting), but certain forms of steam generator tube corrosion may still occur. (authors)