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Chemistry at the Whiteshell Laboratories of AECL Research.

One of the most challenging projects underway is the Canadian Nuclear Fuel Waste Management Program

Chemistry is a very important discipline in nuclear research and development, and it features prominently at the Whiteshell Laboratories of AECL Research, located about 100 km northeast of Winnipeg. Established in the mid-1960s with the primary mission to develop an organic-cooled version of the CANDU reactor, Whiteshell Laboratories presently employ about 900 staff, including some 130 chemists and chemical technologists, working on nuclear fuel waste management, reactor safety, reactor development and radiation applications research programs.

The Whiteshell Laboratories are one of the major R&D centres in Manitoba and, indeed, in Western Canada. They are also the base of AECL Research's Chemistry Division, which includes the Analytical Science and Research Chemistry branches, located at the Whiteshell Laboratories, and the General Chemistry and Physical Chemistry branches, located at the Chalk River Laboratories. Thus, on the occasion of the 77th Canadian Society for Chemistry Conference and Exhibition, to be held in Winnipeg this May, we have prepared this brief overview of chemistry programs at the Whiteshell Laboratories.

Underlying and applied chemistry research

This program cultivates expertise in those areas of chemistry underlying AECL's mission and provides chemistry support to the various applied programs. Nuclear waste management and reactor safety are two of the most important issues affecting nuclear power generation today. Thus, much of the chemistry effort at the Whiteshell Laboratories is related to programs in these areas.

Nuclear waste management: A most challenging contribution of chemistry to applied AECL programs is research for the Canadian Nuclear Fuel Waste Management Program. As it is now envisaged [1], used-fuel bundles will be sealed in corrosion-resistant containers, which will be placed in a waste-vault excavated deep underground in stable plutonic rock. The used-fuel containers will be surrounded by a clay-based buffer to minimize groundwater ingress, and the waste vault, once filled with used fuel, will be back-filled and permanently sealed. Chemistry research is contributing information needed to demonstrate the suitability of the U[O.sub.2] waste form and the various engineered barriers, and to predict the long-term behavior of radionuclides in the geosphere after the waste form and the various engineered beers have failed.

In the long term ([greater than]500 years), the used-fuel containers and other engineered barriers are expected to fail and the release of radionuclides contained in the used fuel would depend on the rate of dissolution of the U[O.sub.2] matrix in groundwater. We are carrying out studies to determine U[O.sub.2] dissolution mechanisms as a function of pH, redox potential, temperature, radiation fields, and groundwater anion concentrations.

Thermodynamic data for key radionuclides (U, Pu, Np, Cs, Sr, Tc, I) and groundwater species (Na+, K+, [Mg.sup.2+], Cl-, S[[O.sub.4].sup.2-]) are required in the temperature range 0 [degrees] C to 150 [degrees] C, to determine the chemical forms and solubility data needed to model the transport of radioactive elements from the vault, through the geosphere, to the biosphere, where they will impact on people and their environment.

We are compiling thermodynamic databases of available data and at the same time are carrying out experiments to determine unavailable data (particularly at higher temperatures) and to improve the accuracy of others.

Data for this very important undertaking need to be critically evaluated by experts to ensure that they were obtained using sound measurements, that no calculation errors were made, and to ensure consistency with other data. For this purpose, we are working closely with the scientific community to produce evaluated databases for key radionuclides. The recently completed uranium thermodynamic database is a 700-page volume which consumed several person-years of international effort to prepare [2].

Reactor safety chemistry: A major reason for concern about nuclear power reactor accidents is the radiological impact of radioactive iodine [I.sup.131] and [I.sup.129]. In an accident involving the loss of reactor coolant, such as the Three Mile Island accident in 1979, iodine could be released from overheated fuel into the reactor containment building. Gaseous and other airborne forms of iodine could escape the containment building and, via a number of pathways, reach the human thyroid - a vital organ. Thus, a major portion of our reactor safety chemistry is aimed to develop a model which predicts the behavior of iodine in a reactor accident.

High-temperature (500 [degrees] C to 2000 [degrees] C) experimental studies, as well as thermodynamic calculations, are being carried out to evaluate release of iodine and other fission products (Cs, Ru, Te, etc.) from U[O.sub.2] fuel in an accident. In the case of iodine, we have established that it is released from fuel as CsI, which on contact with water would dissolve and end up in the reactor sump as aqueous iodide, which is involatile and relatively unreactive. However, the iodide can eventually be oxidized to volatile iodine forms, particularly in the presence of ionizing radiation.

We are finding that there are some 150 chemical reactions which can affect the chemistry of iodine in a reactor containment building following an accident. Fortunately, most of these reactions and their rate parameters are known, so the task is primarily one of generating the few fundamental data that are missing, fitting all this chemical knowledge into a kinetic model which predicts the airborne quantity of iodine, and carrying out accident simulation tests to verify the model.

Our work to date shows with a high degree of confidence that in water-cooled power reactors, such as the CANDU, the risk of significant radioactive iodine releases is minimal [3]. This is largely because iodine is released as CsI in the presence of large amounts of steam and water from the reactor cooling system.

Radiation chemistry reactions in the aqueous phase can lead to the formation of volatile forms of iodine ([I.sub.2], HOI, organic iodides); however, such reactions are slow and their contribution can be minimized by maintaining basic pH and reducing conditions.

Underlying chemistry: In this program we cultivate expertise, through long-term research, in areas of chemistry (actinide chemistry, radiation chemistry, surface chemistry, thermodynamics, electrochemistry, etc.) which are important to our business. This program serves as a resource to the more applied programs and also helps us maintain important links with the scientific community.

This program presently includes research on the solid state chemistry of uranium/fission-product mixtures at various temperatures. Research on U[O.sub.2] grain boundary oxidation, on the effect of fission products on fuel oxidation, on the segregation of rare-earth elements in U[O.sub.2] fuel, and on high-temperature thermodynamic data are also carried out under this program.

A program on kinetics and radiation chemistry is currently aimed at obtaining rate constants needed to model iodine chemistry and to understand the interaction of ionizing radiation with matter in general.

More recently, in response to problems with corrosion and crud formation in steam generators of nuclear power reactors, we have initiated a solid state and interfacial chemistry program focusing on crud deposition mechanisms and on the chemical and morphological characterization of such deposits.

Radiation applications research

The use of ionizing radiation for treatment of cancer is a well known medical application credited with saving about half a million person-years of life every year. Our radiation applications research program was established in the mid-1980s to develop new uses for ionizing radiation, and to encourage industrial applications of radiation processing.

Our research in this field revolves mainly around high energy (10 Mev) electron-beam applications using the 1-10/1 electron accelerator, which is a 1-kW prototype of the 50 kW, industrial-scale, IMPELA accelerator, developed by AECL and now marketed by AECL Accelerators. The advantages of radiation processing include formation of novel products with desirable material properties, favourable overall process economics, and often environmental advantages [4].

We are presently studying electron-beam processing of carbon- and aramid-fibre reinforced composites used in a variety of structural applications, primarily by the aerospace industry. These composites are normally produced by thermal curing of epoxies.

We have shown that radiation processing of equivalent acrylated epoxy matrices, at ambient temperature, can be used to produce composites with reduced residual stresses and without any substantial emission of volatile compounds. We have also shown that radiation processing can be employed to produce improved wood-fibre and mineral-powder filled thermoplastics for various applications.

In addition, radiation-induced degradation of materials, as a result of bond scision, can be exploited in the production of pulp and viscose. We have shown that in certain cases, radiation processing of wood chips prior to pulping facilitates the pulping process, resulting in a significant decrease in the overall energy required, without any significant effect on the quality of the pulp.

Very favorable environmental results have also been obtained when radiation processing is used to displace aggressive chemicals used in the production of viscose.

Under this program we are also studying the effects of ionizing radiation on medically important microbes and plastics, for the propose of sterilization of medical supplies; also, following termination of a much larger program on food irradiation for preservation purposes and the elimination of pathogenic bacteria, some effort is dedicated to educational activities on this subject.

Analytical chemistry

Our analytical chemistry program provides analytical chemistry services and carries out the necessary research to meet the demands of a variety of internal and external customers. State-of-the-art facilities and expertise in radio-analytical chemistry, surface chemistry, electrochemistry, chromatography, spectroscopy, mass spectrometry, etc. are maintained by this program.

The Analytical Science Branch laboratories have in place a comprehensive Quality Assurance program and maintain certification by the Canadian Association for Environmental Analytical Laboratories.

The laboratories are a showplace of the degree of sophistication of modern day analytical chemistry and include almost every modern analytical chemistry instrument: scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence, surface ionization mass spectrometry, etc., as well as instruments that are specific to nuclear research, such as alpha-, beta-, and gamma-ray spectrometers, and facilities for handling radioactive samples.

To meet the diverse analytical needs of a nuclear research centre an instrument development program is in place, which is credited with the development of several novel instruments, including an automated hydrogen-in-metals analyzer, an infrared monitor for indoor air quality, a monitor of engine-wear particles in lubricants, and a device used by International Atomic Energy Agency inspectors to monitor storage of used nuclear fuel for Nuclear Non-Proliferation Treaty purposes.

In addition to serving AECL programs, the laboratories are also an important analytical chemistry resource in Western Canada. In this respect, it is interesting to note that in 1978 almost all our facilities were mobilized to analyze the debris from the Russian Cosmos 954 satellite which disintegrated over Canada and had a nuclear power source on board [5]. Over the years the laboratories have been called by many external customers to do various analyses animals, measurement of seabed sand migration using rare-earth traces, and environmental monitoring for a variety of industries.

References

1. "The Disposal of Canada's Nuclear Fuel Waste: The Vault Model for Postclosure Assessment", L.H. Johnson, D.M. Le Neveu, D.W. Shoesmith, D.W. Oscarson, M.N. Gray, R.J. Lemire, and N.C. Garisto, AECL-10714, COG-93-4, (1994).

2. "Chemical Thermodynamics of Uranium", I. Grenthe, J. Fuger, R.J.M. Konings, R.J. Lemire, A.B. Muller, C. Nguyen-Trung Cregu, and H. Wanner, North-Holland, Amsterdam (1992).

3. "The Canadian Programme on Iodine Chemistry in Reactor Safety", R.J. Fluke, G.M. Frescura, N.H. Sagert, K.N. Tennankore and A.C. Vikis, Proc. of the Third CSNI Workshop on Iodine Chemistry in Reactor Safety, JAERI-M, 92-012, Tokai-mura, Japan, 1991.

4. "Advances in Radiation Processing of Polymeric Materials", K. Makuuchi, T. Sasaki, A.C. Vikis, A. Singh, Proc. International Nuclear Congress '93, Toronto, 1993.

5. "Analytical Chemistry on the Trail of Debris from Russian Satellite Cosmos 954", R.B. Stewart and A.G. Wikjord, Chemistry in Canada, 32, 13, May 1980.

R.F. Hamon, MCIC, manager, Analytical Science Branch; W.C.H. Kupferschmidt, MCIC, manager, Research Chemistry Branch; N.H. Sagert, FCIC, senior scientific advisor; A.C. Vikis, FCIC, director, Chemistry Division, AECL Research, Pinawa, MB.
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Title Annotation:chemistry research and development programs
Author:Hamon, R.F.; Kupferschmidt, W.C.H.; Sagert, N.H.; Vikis, A.
Publication:Canadian Chemical News
Date:May 1, 1994
Words:2014
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