Simultaneous radiochemical separation of fractions of radioisotopes of primary nuclear reactor coolant water

Discs coated with silver iodide, lanthanum oxalate and calcium-barium sulfate were simultaneously rotated in nuclear reactor coolant water samples for radiochemical separation of iodine isotopes, the group of radioactive rare earth elements and the group of radioactive alkaline earth elements. The reproducibility of the method is discussed.     

Speciation and estimation of radioiodine in reactor coolant water

The species of radioiodine in the primary coolant water of the heavy water moderated, heavy water cooled 100 MW research reactor have been identified. It was observed that IO ₃ ^? was the major species in the reactor coolant during reactor operation and I^? was the major species during shutdown. Organic and elemental forms amount only to less than 2% of total radioiodine. A simple method was developed for the estimation of gross iodine activity in reactor coolant water. The method involves the separation of all inorganic forms of iodine into a photographic film consisting of a thin layer of silver halide. The iodine in the film was estimated by gross counting of the film in a Geiger-Müller counter. Gross iodine activity in the reactor coolant samples estimated by the present method were in agreement with that obtained by direct γ-spectrometry with a Ge detector. It is concluded that the method can be used for the routine estimation of radioiodine in reactor coolant water.¹³³I/¹³¹I and¹³⁵I/¹³¹I ratios in the film were estimated and found to be useful in identifying split rod conditions in the reactor.     

Determination of radioactive cobalt in reactor coolant water by solvent extraction

A rapid extraction separation method is described for the radiochenaical determination of cobalt-58 and cobalt-60 in reactor coolant water. After adjustment of the pH of the sample water to 5.0-5.5, cobalt diethyldithiocarbamate is extracted with benzene. Other nuclides, e.g., manganese-54 and -56, copper-64 and iron-59, which are usually present in reactor coolant water, are also extracted together with cobalt. However, they can be readily removed by washing the extract with mercury(II) chloride solution. The cobalt-58 and -60 activities are measured by gamma counting of an aliquot of the washed extract. Trace amounts of radioactive cobalt in 500 ml of sample water can be quantitatively extracted without the use of carrier. The separation could be finished in 15 min and an average recovery of 99.5 % was obtained, with a relative standard deviation of 1.4% (25 experiments).     

Determination of hydrogen peroxide concentration in THOR coolant during reactor operation

The concentrations of hydrogen peroxide formed in the coolant due to radiolysis were studied during THOR operation at 1 MW. The relation between doses and hydrogen peroxide formation in a neutron-gamma mixed field was investigated. The initial concentration was 2.3×10^–5 g/ml at the beginning of reactor operation, and then it was increased rather rapidly at the first 9 h. The increasing rate was slowed down till the end of 30 h operation. The maximum concentration of hydrogen peroxide was found to be 4.7×10^–5 g/ml, and its decrease followed the exponential curve.     

Filter for the selective removal of tritium from the coolant gas of a high temperature nuclear reactor

A filter for the selective and continuous removal of tritium or deuterium from an inert gas stream is proposed. It is based on the permeation of hydrogen and its isotopes through a highly permeable wall and the removal of for example tritium on the secondary side. The necessary concentration drop to the secondary side is effected by isotope exchange of the tritium atoms on the secondary side with water. The filter concept and the mathematical model, investigations of the influence of various parameters and the selection of the wall material are reported.     

A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N₂H₃ reduces oxygen to O₂ ^– at pH > 7 (k 3·10⁹ dm³· mole^–1·sec^–1), while this reaction does not occur for the protonated form N₂H₄ ⁺ at pH < 7 (k, 5·10⁶ dm³·mole^–1·sec^–1). The rate constants for the disappearance of O₂ ^– have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O^– with N₂H₄ [k=(1.6 ±0.2)·10⁹ dm³·mole^–1·sec^–1] and of O₃with N₂H₄ [k=(1.2 ±0.2)·10⁶ dm³· mole^–1·sec^–1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 341–345, February, 1991.     

Role of excited states in radiolysis of cyclohexane

The mechanism of cyclohexane radiolysis in the condensed phase is discussed with particular attention paid to the cleavage of CC bonds. The contribution of ions and various neutral excitation states to the formation of radiolysis end-products is analysed. As follows from the experimental data shown, short-lived (≈10⁻¹²) superexcited states (S.E.S.) take part in the cyclohexane radiolysis reactions in the liquid phase. The basic process accompanying the decay of S.E.S. molecules is the formation of hydrogen atoms which may acquire excess kinetic energy (“hot atoms”). It is assumed that inspection of hot H atoms along the CC bond constitutes the main source of saturated products formed by cleavage of the cyclohexane ring (C.R.C.P.=cyclohexane ring cleavage products): CH₄, C₂H₆, C₆H₁₄ and so on. In condensed medium, the cleavage of two or more CC bonds in the same molecule, giving rise to unsaturated C.R.C.P. (C₂H₄, C₃H₆, etc.), originates mainly from S.E.S. A smaller amount of unsaturated C.R.C.P. is probably formed via the decay of excited molecular ions. Cleavage of a single CC bond with formation of hexene proceeds effectively from lower excited states which derive particularly from ion-recombination.Experimental data concerning the incidence of polymorphous transformation in cyclohexane on the C.R.C.P. yields are given. A general scheme for cyclohexane radiolysis, based on the cleavage of CH bonds, is postulated.     

Removal of nickel from water and synthetic nuclear power plant coolant water by ion exchange resins

A method for the removal of nickel from waste water by adsorption process on ion exchange resin was studied. The percentage removal of nickel depends upon the contact time, pH and dose of adsorbent. Adsorption of nickel on ion exchange resins obeys Freundlich adsorption isotherm. The applicability of Lagergren kinetic model has also been investigated. In order to understand the adsorption behavior of nickel, a number of batch experiments were conducted at various pH values. The results show that the adsorption is maximum in the pH range 2 to 8. The studies showed that the ion exchange resins IRN77 and SKN1 can be used as an efficient adsorbent material for the removal of Ni(II) from water and coolant water.     

Influence of boric acid on the determination of iron in reactor coolant water by graphite furnace atomic absorption spectrometry

Summary The matric effect of boric acid was investigated in the determination of iron in the primary circuit coolant water of nuclear power plants by furnace atomic absorption spectrometry. The effect of boric acid was of particular interest. The method was applied during refuelling and maintenance periods and the results were used to interpret the chemical changes in the water.

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Einfluß von Borsäure auf die Bestimmung von Eisen in Reaktorkühlwasser durch GF-AAS

     

Role of the low-energy excited states in the radiolysis of aromatic liquids

The contribution of the low-energy excited states to the overall product formation in the radiolysis of simple aromatic liquids--benzene, pyridine, toluene, and aniline--has been examined by comparison of product yields obtained in UV-photolysis and in γ-radiolysis. In photolysis, these electronic excited states were selectively populated using UV-light excitation sources with various energies. Yields of molecular hydrogen and of "dimers" (biphenyl, bibenzyl, dipyridyl for benzene, toluene, pyridine, respectively, and of ammonia and diphenylamine for aniline) have been determined, since they are the most abundant radiolytic products. Negligibly small production of molecular hydrogen in the UV-photolysis of aromatic liquids with excitation to energies of 4.88, 5.41, 5.79, and 6.70 eV and the lack of a scavenger effect suggest that this product originates from short-lived high-energy singlet states. A significant reduction in "dimer" radiation-chemical yields in the presence of scavengers such as anthracene or naphthalene indicates that the triplet excited states are important precursors to these products. The results for toluene and aniline suggest that efficient dissociation from the lowest-energy excited triplet state leads to noticeable "dimer" production. For benzene and pyridine, the lowest-energy triplet excited states are not likely to fragment into radicals because of the relatively large energy gap between the excited state level and corresponding bond dissociation energy. The "dimer" formation in the radiolysis of benzene and pyridine is likely to involve short-lived high-energy triplet states.     

A mass-spectrometric investigation of the radiolysis of methane by reactor radiation

An ‘on-line’ mass spectrometer technique which permits the examination of the effects of radiation at short times has been used to study the radiolysis of methane by reactor radiation. The mass spectrometer used was the AEI MS-10. The experiments were carried out using the UTR-100 reactor at East Kilbride and the results using highly purified methane and methane with radical scavangers are described. With pure methane at 0·25% conversion, G-values of 0·36, 0·24, 0·07 and 0·03 were calculated for C₃H₈, C₄H₁₀, C₅H₁₂ and C₆H₁₄ respectively. No pressure-dependent reactions were observed in the pressure range 50 to 135 torr. The effects of radical scavengers were investigated and irradiation of methane containing 1 to 2% ethylene gave G-values for C₂H₆, C₃H₈, n-C₄H₁₀, iso-C₄H₁₀, C₅H₁₂ plus C₆H₁₄, C₂H₂, C₃H₆, C₄H₈ and C₅H₁₀ of 1·33, 2·02, 2·03, 0·35, 0·34, 0·30, 0·37, 0·90 and 0·31. The effects of adding 1 to 2% propylene and 1 to 2% oxygen were also examined and the results are described in the paper. Experiments with smaller quantities of oxygen emphasize the importance of removing all oxygen from the system before radiolysis begins. The paper then goes on to discuss in some detail the processes involved in the radiolysis of methane and concludes with suggestions for future work.     

Gas phase pulse radiolysis studies of excited states

The results and conclusions of the work of the author and co-workers on excited states proudced by pulse radiolysis of gaseous systems are summarized. Detailed consideration is given to systems containing naphthalene, for which the following subjects are discussed: (1) ionic and non-ionic mechanisms of excited state formation and their relative importance, (2) G-values of excited state formation and (3) energy partitioning in the non-ionic formation of excited states of naphthalene. Rate constants for reactions of excited states of naphthalene are summarized. The use of emission from excited states produced in ion-recombination reactions to determine rate constants for ion-recombination is also discussed.     

Analysis of actinides in the primary coolant of a WWER-440 type reactor

A simple and effective method has been developed for the determination of the transuranium isotopes in primary coolant samples of WWER-440 type reactors. Membrane filters containing undissolved particles from about one liter coolant were destroyed by mineral acids, then americium-curium isotopes and neptunium-plutonium isotopes were coprecipitated sequentially with NdF₃ based on their different redox behavior. Alpha-spectra were determined by silicon semiconductor detectors connected to multichannel analyzers. Activity ratios measured in a reactor unit with a failed fuel element were compared with calculated values of the same type of reactor under similar conditions. Parameters of the defective fuel (burnup, original enrichment) could be estimated.     

A complementary cesium coolant concentration ratio for localizing defective PWR fuel rods during reactor operation

Rough techniques for pinpointing defective fuel pins during actual reactor operation were developed for nuclear power plants. These techniques are based on various fission product concentration ratios. Here, a new cesium concentration ratio,¹³⁴Cs/¹³⁶Cs, was tested in combination with the more usual cesium ratio¹³⁴Cs/¹³⁷Cs. This new cesium ratio confirmed the conclusions drawn from the ratio¹³⁴Cs/¹³⁷Cs and provided some additional information on the location of the defective fuel rods. Application of this second cesium ratio improves the reliability of the rough localization method.     

The yield of solvent excited states in the radiolysis of cyclohexane solutions

It is confirmed by pulse radiolysis that emitting solvent excited states are produced in the radiolysis of n-hexane, methylcyclohexane and cyclohexane. The emission is quenched by benzene and benzene emission appears. Applying stern - volmer kinetics to emissions from solvent, benzene and toluene in cyclohexane a very high energy transfer rate constant, viz., k = 2.8 × 10¹¹M⁻¹ sec⁻¹ is obtained. The yield of the excited state of cyclohexane is not greater than 0.3, and it is concluded that the major part of the excited states of other aromatics produced in cyclohexane solutions comes from ion neutralisation.     

Measurement of <Superscript>90</Superscript>Sr in primary coolant of pressurized water reactor

The present procedure for analysing ⁹⁰Sr combines the use of a non radioactive carrier with high pressure ion chromatography separation, conductivity detection of the carrier and optimized external counting by liquid scintillation. This improvement with respect to traditional methods led to a more rapid and efficient purification stage. The present work proves that activities of ⁹⁰Sr as low as 3 Bq/L can be measured in highly contaminated pressurized water reactor primary coolant matrix without any observed radiochemical interference. The approach shows promise for the analysis of other emitters of low energy radiation, or isotopes subject to high background or matrix effects in a PWR primary coolant.     

Temporal asymmetry of fluctuations in nonequilibrium steady states

Temporal asymmetries of fluctuation paths in nonequilibrium microscopic shearing systems are observed for the first time. Inspired by theories that predict asymmetry of fluctuation paths in stochastic dynamics, we focus on deterministic reversible particle models, which represent a small part of a macroscopic system. We have monitored and measured the asymmetry of the fluctuation paths of various observables as they go away from and towards the mean. The understanding of such asymmetries may scatter light on how irreversibility emerges from the microscopic reversible dynamics and on the behavior of mesoscopic (nanoscale) systems.