Experience with HEU- and LEU-Fuelled SLOWPOKE Reactors.
G. Kennedy.
Nuclear Engineering Institute,
Ecole Polytechnique Montreal, Quebec, Canada

Abstract
Seven SLOWPOKE-2 research reactors, with 93% enriched HEU fuel, were installed in six Canadian cities and in Kingston, Jamaica between 1976 and 1984. In 1985 the first LEU-fuelled SLOWPOKE reactor was commissioned at the Royal Military College of Canada. The HEU-fuelled reactor in Montreal was the first to require refuelling and in 1997 it was converted to the 20% enriched LEU fuel. In this presentation, the refuelling experience and the performance of the two types of reactor cores will be discussed.

For refuelling, the main effort was to convince the licensing authority of the safety of the refuelling procedure and the suitability of all reactor components for long-term operation with the new LEU fuel. The used HEU core was transferred to the bottom of the pool, using a machine designed for the purpose, and then placed in the shipping flask. The installation of the LEU fuel was the same as for a completely new reactor except that the radioactivity of the used beryllium reflector complicated the measurements of neutron fluxes required for commissioning.

After five years of operation with the Zircaloy-clad LEU fuel, no releases of fission products from the fuel to the reactor water have been observed. The operational lifetime of the new core is expected to be 40 years. It has negative reactivity feedback with increasing temperature similar to the HEU core, except at low temperatures, where the temperature coefficient of the LEU core is less negative. This allows it to operate for longer periods at full power, 20 kW, and almost doubles the time between costly reactivity adjustments.

An observation of core water temperatures showed that the LEU core requires 10% more power to produce the same thermal neutron flux. This is attributed to the absorption of neutrons by U-238. For the same reason, the thermal/fast neutron flux ratio in the inner irradiation sites is lower, 4.0, compared to 4.4 with the HEU core. As a result, nuclear interferences are 10% higher in neutron activation analysis with the LEU core.

Enhancement of Miniature Neutron Source Reactor Core Reactivity by Beryllium Shim Plate Addition.
J. Qadir, Masood Iqbal, M. Abdullah, S. Pervez.
Nuclear Engineering Division, Pakistan Institute of Nuclear Science & Technology,
P.O. Nilore, Islamabad, Pakistan.

Abstract
Excess reactivity of Pakistan Research Reactor-2 which is a miniature neutron source reactor, decreased due to fuel burn up and fission products build up after ten years operation. A beryllium shim metal plate of thickness 1.5mm was added into the reflector tray on the top of reactor to compensate these losses.  The control rod was dismantled and withdrawn from the core and the reactor was made sub critical with cadmium shimming. To monitor the neutron population during this experiment, two additional neutron-monitoring channels were installed around the core. This presentation describes procedures, preparation for shimming operations and measurements like excess reactivity, control rods worth, thermal neutron flux, cadmium ratio, after the addition of beryllium reflector. The reactivity of the core was increased from 2.96mk to 3.96mk.

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RA-8 – A Tale of Adaptation.
N. De Lorenzo.
Centro Atómico Bariloche – CNEA
Argentina

Abstract
The RA-8 is a critical assembly able to be operated up to 10 W in steady conditions or 100 W in short transients. Although it was originally designed to define the core neutronic parameters for the CAREM project (a NPP being designed by Argentina), a screening process to identify other applications has been carried out from the very beginning of its design.

This paper summarises the relevant characteristics included in the design to comply with the original purpose and the further modifications included to expand the plant capabilities. In this process, other possible applications with a minimum marginal cost were identified. The following list indicates some of them that are lately explained in the paper:

Validation of Neutronic Calculations: The plant has the capability to measure small reactivities (few tens of pcm) as well as to perform relative and absolute flux mapping. Variable core size and the possibility to simulate local perturbation allows to check the software accuracy in a widely range of conditions.

High energy gamma fields irradiation: Taking advantage of the design, the area above the core can be used to irradiate devices in a high energy gamma field. The characterisation of this field as well as its application in irradiation of components was investigated in detail.

Neutron detectors characterisation: The neutron source used in the plant together with its associated devices allows testing the steady and dynamic responses of neutron detectors. The tests can also be performed under different moderation conditions easily modifiable.

Instrumentation modules development: NIM modules to integrate in safety channels were developed and integrated to the plant instrumentation.

New devices development: New devices (some of them related to Safety Systems) were developed and later approved by the regulatory body.

Training: A wide range of training activities is performed in the facility covering from academic experiments up to on-job activities. The users are also a broad spectrum including reactor operators and IAEA trainees.

Radiation protection services: Air, water and soil sampling and measurements. NORM measurements. Portable monitors checking.

Other applications are performed in order to expand the plant capabilities considering that small benefits compensate the cost involved. This is true since the capital cost was already covered by the project supporting the facility construction.

A Digital Control and Instrumentation System for the SLOWPOKE-2
L. R. Cosby and L.G.I. Bennett.
SLOWPOKE-2 Facility at RMC,
Department of Chemistry and Chemical Engineering, Royal Military College of Canada,
Kingston, Ontario, Canada K7K 7B4

Abstract
The Mk I analogue console was installed with the four original SLOWPOKE-2 reactors in the 1970s and the Mk II console was installed with the reactor at RMC in 1985, at about the same time as at three other installations. A new project to replace analogue console with a digital system was initiated in January 2000. This project is known as the SLOWPOKE Integrated Reactor Control and Instrumentation System (SIRCIS). It is based entirely on Commercial-Off-The-Shelf (COTS) hardware and software development packages. SIRCIS was designed to monitor and display reactor parameters, control the neutron flux better over the total flux range, and archive all pertinent data and status information. A huMan Machine Interface (MMI) was provided to facilitate operator interaction with the system via a Graphical User Interface (GUI). The software was written to Ontario Power Generation and Atomic Energy of Canada Ltd. Software Engineering Standards (OASES), specifically the Category III standard for real-time process computing software. A hardware test rig was used to simulate the reactor and test the software and continues to be used as a test bed for future modification as well as a simulator. With approval from the Canadian Nuclear Safety Commission, SIRCIS was commissioned in Summer 2001, has operated successfully since then, and will be upgraded with a new control rod drive motor in the near future.

Trace Element Analysis using Neutron Activation: Pushing the Limits.
A. Chatt.
SLOWPOKE-2 Facility, Trace Analysis Research Centre, Department of Chemistry
Dalhousie University, Halifax, Nova Scotia, B3H 4J3, Canada

Abstract
Neutron activation analysis (NAA) is well-established analytical technique which is inherently sensitive for many elements. Practical detection limits for a number of elements in real samples can be further improved by following one of several approaches.  Since the neutron flux of the SLOWPOKE-2 reactors is lower than other research reactors (such as TRIGA) by an order of magnitude or so at normal operating power levels, innovative ways are needed to enhance the activity of interest and/or to suppress interfering activities.  We have developed several instrumental NAA (INAA), preconcentration NAA (PNAA) and radiochemical NAA (RNAA) methods for "pushing the limits" of a number of elements.

 In order to improve the detection limits in reactor flux INAA, we first thought of using short-lived nuclides which require shorter irradiation times to reach saturation activities. Using the conventional one-shot INAA approach, we found that about 20 elements can be determined with better limits via their short-lived nuclides compared to their longer-lived counterparts.  Then we developed cyclic INAA (CINAA) and pseudo-cyclic INAA (PCINAA) methods where irradiation-decay-counting cycles are repeated for an optimum number of cycles to achieve better detection limits. We originally developed these INAA methods using conventional gamma-ray spectroscopy. Then we improved the limits further by using anti-coincidence gamma-ray spectroscopy. In almost all cases the detection limits improved for short-lived nuclides using anti-coincidence gamma-ray spectroscopy.  The extent of improvement depended on the photopeak, dead time, position of the annulus and counting geometry among several other factors.  We have developed INAA methods using epi-thermal neutrons in conjunction with conventional and anti-coincidence gamma-ray spectroscopy, and found that the limits for a number of elements can be significantly improved in several types of sample matrix.  We have also developed PNAA and RNAA methods for lowering detection limits of elements which produce short-, medium- and long-lived neutron activation products. It is now possible to measure sub-ppb levels of many elements with high precision and accuracy.

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The Miniature Neutron Source Reactor and Application on Epithermal Neutron Activation Analysis.
Zhang Yongbao, Wang Ke, Hou Xiaolin
P.O.Box 275-75, Beijing, China, 102413

Abstract
This report describes miniature neutron source reactor and the laboratory work on epithermal neutron activation analysis in it. The cadmium and boron ratios from 44 elements, totally 66 nuclides, are determined in the inner and outer irradiation sites. The α, f and Φ_th values are measured using the bare triple-monitor method. The application of ENAA in biological, Environmental, geological and industrial fields are discussed.

Nuclear Analytical Methods at ICENS Part 2: Application of NAA to Environmental Geochemistry, Agriculture and Health.
M. Vutchkov, C. Grant, G. Lalor and J. Preston
International Centre for Environmental and Nuclear Sciences
University of the West Indies,
Mona, Jamaica

Abstract
Neutron Activation Analysis is the primary analytical technique at ICENS applied to environmental geochemistry, agriculture and health related studies in Jamaica. Instrumental and pre-concentration NAA procedures have been used for determination of minor and trace concentrations of up to 60 elements in various matrices, such as soil, plants, animal and human tissues. Agricultural soils and plants were irradiated simultaneously using in-core and in-pool irradiation schemes. Detection limits obtained by in-pool irradiation of geological samples are adequate for most elements in Jamaican soils. X-ray Fluorescence techniques has been used to extend the analytical range for elements exhibiting poor sensitivities by NAA, such as Si, P, K, Ca, K, Ni, Cu, Ba, Ni, Rb, Pb, etc. These combined in-core, in-pool NAA and XRF procedures have resulted in more than 30% increase in reactor flux usage.

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