Browsing by Author "Nicholson, FD"
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- ItemHIFAR safety analysis: frequency and offsite consequences of fault sequences initiated by within-plant failures(Australian Atomic Energy Commission, 1986-05) McCulloch, DB; Corran, ER; Petersen, MCE; Nicholson, FD; Innes, RWHIFAR fault sequences, initiated by failures of within-plant equipment and operational procedures, are analysed using probabilistic methods, and their frequencies estimated. Sequence consequences are estimated in terms of potential radiation doses to an individual at 1.6 km radius from the reactor, expressed in terms of emergency reference levels recommended by the National Health and Medical Research Council for consideration of limited evacuation. The results show that the public risk from all such sequences is extremely low.
- ItemMass transfer of corrosion products in high temperature, high pressure water circuits, Part 1 - the CWL-3 mass transfer loop(Australian Atomic Energy Commission, 1975-01) Rodd, JT; Nicholson, FDThe CWL-3 loop is used to study the mass transfer of corrosion products in water at 270ºC for pressures up to 6.9 MPa. Two parallel Zircaloy-2 test sections are heated directly by a low voltage a.c. electrical current to give a heat flux up to 500 W cm-2 and a heat rating up to 1500 W cm-1. Coolant flow rates can be varied up to 0.4 kg cm-2 s-1 with or without boiling. A tracer technique has been developed to monitor continuously the deposition of corrosion products in the test sections during operation of the loop. Magnetite deposits 2.6 nm thick can be readily detected.
- ItemMass transfer of corrosion products in high temperature, high pressure water circuits, part 2 - preliminary experiments(Australian Atomic Energy Commission, 1976-07) Evans, JV; Nicholson, FDThe behaviour of iron oxide crud was studied at 25ºC and over the range 240 to 270ºC in a high pressure water loop. Crud deposition and removal was measured in two parallel, heated Zircaloy-2 tubes using iron-59 as a radioactive tracer. This proved to be a powerful technique capable of detecting crud deposits less than 3 run thick. Rapid deposition of crud was observed following injection into the loop of an iron oxide suspension or a ferric nitrate solution. Crud deposited preferentially on heated surfaces when they were present but not to the exclusion of deposition elsewhere; hot spots on heated surfaces attracted additional deposits. Subcooled boiling appeared to be a more important factor than bulk boiling in the enhancement of crud deposition. The initial rapid deposition of the bulk of the crud throughout the loop was usually followed by a slower transfer of crud from other surfaces to any heated surface present. Unsteady operating conditions, e.g. a change in power, temperature or pH, frequently caused crud bursts, but once steady conditions were re-established the entrained crud was quickly redeposited. The bulk of deposited crud was not readily re-entrained, particularly from heated surfaces, so that crud bursts involved only a fraction of the total crud deposited. Ferric nitrate solutions injected into the loop formed haematite which deposited more slowly and formed more mobile deposits than magnetite which was injected directly into the loop as a slurry. Examination of deposits from both sources showed them to be even and tightly adherent, being removed only with difficulty.
- ItemThe performance of powdered ion-exchange resins(Australian Atomic Energy Commission, 1973-03) Bull, PS; Evans, JV; Nicholson, FDThe coating properties and ion exchange performance of powdered ion-exchange resins were examined in a small test facility. Satisfactory resin coatings were obtained with cation:anion resin ratios in the range 1:1 to 3:1 but use of a 9:1 resin ratio resulted in a high pressure drop across the coating. The 'settled resin volume proved to be a reliable guide to the coating performance of resin slurries. The ion-exchange capacity of the cation resin increased to a small extent with a decrease in sodium concentration in the influent water down to 500 μg ℓ-1. Within the ranges examined, resin ratio, resin loading and flow rate had no significant effect on cation capacity. The effect of exhaustion on the pressure drop characteristics and flocculating properties of various resin ratio's was investigated. The thermal stability of the powdered anion resin was markedly less than that quoted elsewhere for anion bead resin.
- ItemStudy of the variables affecting the corrosion of beryllium in carbon dioxide(Australian Atomic Energy Commission., 1961-12) Draycott, A; Nicholson, FD; Price, GH; Stuart, WIBeryllium is a favoured canning and/or moderating material in the proposed Australian High Temperature Gas Cooled Reactor. With carbon dioxide as the most likely coolant a detailed knowledge of the corrosion of beryllium in this gas is required. Two separate investigations have proceeded simultaneously. First the effect of the following variables was studied; surface preparation of the specimen, temperature (100—725ºC), pressure (0—280 p.s.i.g.), velocity, and impurity content of the gas. The influence of irradiation has not yet been studied. Autoclaves, thermobalances, and dynamic loops were used. The results were statistically analysed and kinetic data obtained. In all cases specimens with etched surfaces yielded approximately 25 — 30 per cent, greater weight gains than specimens with ground or polished surfaces. On extruded material no "breakaway" oxidation was encountered below 650ºC in commercially dry gas (< 20 p.p.m. moisture). The rate of attack was to some extent affected by the pressure of the gas. Breakaway was only observed in one series of specimens at 650ºC. In this particular case the gas pressure was 280 p.s.i.g. However, it seems that surface temperatures of beryllium cans made from extruded material should be maintained below 650ºC in a reactor system using the commercially pure carbon dioxide as coolant. In the second approach a more basic study of the chemistry of the reaction was made as well as a detailed investigation into the variation caused by differences in the composition and fabrication of the metal. Spiral spring balances at atmospheric pressure were used. Extruded material made from beryllium powder oxidized in dry oxygen for a short period of time had greatly enhanced oxidation resistance when exposed to carbon dioxide. Some of the material exposed to wet carbon dioxide at 700ºC and atmospheric pressure did not exhibit "breakaway" oxidation. The weight gains after 1,000 hours exposure under these conditions were never greater than 0.5 mg/cmZ, Some comparisons were made between the reaction rates of beryllium with oxygen and carbon dioxide. In certain circumstances dry oxygen gave breakaway oxidation whereas carbon dioxide did not.