GS plant

The large industrial scale GS plant (lOOkgh-1, 700t year-1, 99.8% D20 product) operated by Ontario Hydro at Bruce Ontario for more than 20 years was... 

We close discussion of the GS process with the comment that it is dangerous. A GS plant requires a very large inventory of highly toxic H2S employed at elevated temperature and pressure in a corrosive environment. The safety of operating personnel and of the population in the area surrounding the plant is a major concern. 

Mass Transport at Very Low Concentrations. Heavy Water Plants. The phenomenon of mass transport at very low concentrations is not unique to the reactor coolant systems. It can occur also in the heavy water production plants. Table III compares iron transport in a reactor primary circuit and a GS plant dehumidifier circuit and illustrates the quantities of iron that can be transported each day. While the concentrations in the reactors are typically two orders of magnitude lower, the flow rates are an order of magnitude higher. The lower concentration in the reactors gives a lower driving force for deposition and the efficiency of deposition is considerably lower. 

The importance of chemistry to the nuclear power industry is now well recognized. Chemical control in water circuits is an accepted part of the operating requirements of nuclear generating stations, as it is for modern fossil-fired stations. While there have been major advances in knowledge of the chemistry of aqueous systems at temperatures above lOQoC, there is still a need for further work. As we improve our understanding of thermodynamics and kinetics of solid-aqueous reactions and the effect of radiation on them, we can expect further advances in controlling radiation fields in reactor circuits and in minimizing iron deposition in GS plants. 

The main drawback of the GS process is the highly corrosive nature of its aqueous solutions. A 400 Mg/yr GS plant requires an inventory of 800 Mg of H2S, which is an extremely toxic, flammable, and corrosive gas with a distinct, disagreeable smell even at low concentrations. Hence, adequate measures must be taken for material selection, fabrication, feed purification, feed and waste discharges in water and the atmosphere, safety of staff, the surrounding population, and environment. ... 

The diameter of the towers of a GS plant, the principal heat exchanger duties, and the heat consumption are determined mainly by the ratio of gas flow rate to product rate, GjPxp. The optimum value of G is, from (13.114),... 

The GS plant for which the most detailed information has been published Is the Savannah River plant of the U.S. AEC. This section summarizes the design and operating characteristics of this plant, which has been in operation since 1955. Section 11.8 describes improvements that du Pont personnel suggested for future GS plants, some of which presumably have been adopted in the newer Canadian plants. 

Figure 13.30 is a flow sheet showing the main process equipment of the Savannah River GS plant and the principal process conditions as given by Bebbington and Thayer [B7]. The plant consists of 24 units of type shown, operated in parallel. Not shown in the figure are the feed-water deaerator, the tower to recover H2S from purge gas, and pumps for liquid. 

Figure 13.30 Flow diagram for unit of Savannah River GS plant. Basis, 1 h. Plant consists of 24 units.

Figure 13.36 Calculated effect of extra feed to hot tower on DjO production rate in GS plant.

The very low D/H natural abundance ratio (0.015%, 150 ppm) is the factor responsible for the high cost of heavy water. Materials balance shows it to be necessary to process a minimum of 8,000 mol feed per mol of product, and even more for reasonable values of tails analysis (for more recent GS plants the feed/product ratio reached nearly 40,000 to 1). At peak, Canadian production is 800 t/year, which means feed quantities approaching 2.4 x 10 t/year. Such amounts demand cheap and easily accessible feed (i.e., water), or alternatively, require D production to be parasitic on some other large industrial process, e.g., NH3 used for fertilizer production or petrochemical processing. However, very often even large-scale industrial facilities are not large enough to be a practical source of deuterium on the scale described above. 

A very large industrial scale GS plant (100 kg/h 99.8% D2O) operated by Ontario Hydro has been described in some detail by Rae (1978). The GS part of the plant consisted of three stages of hot/cold towers with a total enrichment from natural abundance to 20% D2O. Each tower... 

Schematic of dual temperature GS plant. First stage steei...

In the heavy-water plants constmcted at Savannah River and at Dana, these considerations led to designs in which the relatively economical GS process was used to concentrate the deuterium content of natural water to about 15 mol %. Vacuum distillation of water was selected (because there is Httle likelihood of product loss) for the additional concentration of the GS product from 15 to 90% D2O, and an electrolytic process was used to produce the final reactor-grade concentrate of 99.75% D2O. 

J. No lo.gs of es-ie Uial oil of peppermint throngh diffusion in the airaosphcit is occasioned bv thorough dryiug of the plants and prolonged exposure to atmospheric aciiou prior to distillation. (Thio con-clnflioD, however, does not a[i K ar to be quite correct.I... 

Yadav GS, Kathpal TS, Khokar KS. 1988. Residues of endosulfan and monocrotophos in pigeon-pea. Indian Journal of Plant Protection 16 225-230. 

Schlyter F, Birgersson GS (1999) In Hardie J, Minks AK (eds) Pheromones of non-lep-idopteran insects associated with agricultural plants. CABI Publishing, p 113... 

Pullman GS, DeVay JE, Garber RH (1981a) Soil solarization and thermal death a logarithmic relationship between time and temperature for four soilbome plant pathogens. Phytopathology... 

Guide for the Identification and Control of Exothermic Chemical Reactions" (TAA-GS-05 1994). A document in German by the Technischer Ausschuss fur Anlagensicherheit (Technical Committee for Plant Safety) of the Federal Ministry of the Environment, Nature Conservation and Reactor Safety. Addresses safety assessment of reactions during both normal operations and excursions, as well as selection and extent of measures to be adopted. An English translation of this document is provided on the CD-ROM included with this publication. 

Feeny PP (1976) Plant apparency and chemical defense. Res Adv Phytochem 10 1—40 Fraenkel GS (1959) The raison d etre of secondary plant substances. Science 129 1466-1470 Franklin LA, Yakovleva I, Karsten U, Liming K (1999) Synthesis of mycosporine-like amino acids in Chondrus crispus (Florideophyceae) and the consequences for sensitivity to ultraviolet B radiation. J Phycol 35 682-693... 

Grob CS, McKenna DJ, Callaway JC, Brito GS, Neves ES, Oberlaender G, Saide OL, Labigalini E, Tacia C, Miranda CT, Strassman RJ, Boone KB. (1996). Human psychopharmacology of hoasca, a plant hallucinogen used in ritual context in Brazil. J Nerv Ment Dis. 184(2) 86-94. 

Williams PD, Mavituna F (1992) In Fowler MW, Warren GS (eds) Plant biotechnology. Per-gamon, Oxford, p 701... 

FIGURE 12-13 Interaction of Gs with adenylyl cyclase. (PDB ID 1AZS) The soluble catalytic core of the adenylyl cyclase (AC, blue), severed from its membrane anchor, was cocrystallized with G,, (green) to give this crystal structure. The plant terpene forskolin (yellow) is a drug that strongly stimulates the enzyme, and GTP (red) bound to Gsa triggers interaction of Gsa with adenylyl cyclase. 

Rea PA, Li Z-S, Lu Y-P, Drozdowicz YM, Martinoia E. 1998. From vacuolar GS-X pumps to multispecific ABC transporters. Annu Rev Plant Physiol Plant Mol Biol 49 727-760. 

Fig. 1. The nitrate assimilation pathway in higher plants. The pathway of nitrate assimilation in the tobacco leaf is illustrated. In some other species an additional cytosolic GS is found in the leaf. The pathway in plant roots is more poorly documented and more variable GS in roots is mostly cytosolic, and some enzymes such as GOGAT are found as isoforms utilising alternate reducing substrates. T, expected nitrate carrier NR, nitrate reductase NiR, nitrite reductase GS, glutamine synthetase GOGAT, glutamate synthase Fd, ferredoxin Gin, glutamine Glu, glutamate.

Fig. 1. The central importance of the GS/GOGAT pathway in the nitrogen metabolism of higher plants.

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