Mushtaq Ahmad Isotope Production Division Pakistan Institute of Nuclear Science and Technology (PINSTECH) Islamabad, PAKISTAN

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1 Mushtaq Ahmad Isotope Production Division Pakistan Institute of Nuclear Science and Technology (PINSTECH) Islamabad, PAKISTAN Abstrct Both reactors (Pakistan Research Reactor 1 and Pakistan Research Reactor-2) at PINSTECH have been used for human resource development, radioisotope production and neutron activation analysis. Beam work usually includes using neutron beams outside of the PARR-1 for a variety of analytical purposes. Facility for neutron radiography, prompt gamma neutron activation analysis, neutron scattering for material analysis have been functioning. Improvements in the instrumentation and control system of PARR-1 are continuously being made to enhance the safety and availability of the system. 1. Introduction Pakistan Institute of Nuclear Science and Technology (PINSTECH) Islamabad is operating two research reactors (PARR-1 and 2) to provide services to the users for the production of radioisotopes and for neutron irradiation. Salient features of both reactors are presented in Table 1 and 2. Since initial criticality, PARR-1 has rendered invaluable service in the training of manpower, production of radioisotopes and as a source of neutrons for basic and applied research. To reduce nuclear proliferation concerns it became essential that its core be converted for operation with low enriched uranium (< 20% 235 U) fuel. The PARR-1 is a swimming pool type research reactor originally designed for a thermal power of 5 MW. Its core has been redesigned to operate with LEU fuel at a power level of 9 MW in 1992 and 10 MW in Pakistan Research Reactor-2 (PARR-2) is a 30 kw tank-in-pool type research facility. It uses Highly Enriched Uranium (HEU) as its fuel, light water as moderator and metallic beryllium as reflector. Fission heat generated in the core is removed through natural convection. The reactor core is enclosed in an aluminum vessel suspended in an underground pool. Long-term reactivity compensation is achieved by increasing the thickness of top beryllium reflector. Reactor has ten irradiation sites, five of which are located inside the beryllium reflector while the rest surround the reflector. The thermal neutron fluxes in these sites are and 5 x n/cm 2 -s, respectively. These irradiation sites are accessed through pneumatic sample transfer tubes. Table. 1 Pakistan Research Reactor-1 (PARR-1) General Data Owner: Pakistan Atomic Energy Commission Operator: Pakistan Institute of Nuclear Science and Technology Islamabad Address: P.O. Nilore, Islamabad Construction date: Criticality date: Initial cost: 6.6 M US$

2 Annual cost: 0.5 M US$ Total staff: 30 Operator: 13 Technical Data Reactor type: Pool Thermal power, steady, kw: 10, Max flux SS, thermal, n/cm 2 -s: 1.5 x10 14 Max flux SS, fast, n/cm 2 -s: 6.0 x10 13 Moderator and coolant: Light water Reflector: Graphite, water Control rod material: Ag, In, Cd Criticality with LEU: Oct 1991 Power increase; 9 MW in May 1992 Power increase; 10 MW in Feb 1998 Experimental Data Horizontal channels: 7 Horizontal max flux n/cm 2 -s: 4.7 x10 13 Horizontal use: Basic research Vertical use: Neutron activation analysis Core irradiation facilities: 2 Core max flux n/cm 2 -s: 1.5 x10 14 Reflector irradiation facilities: 3 Fuel Data Min critical mass, kg U-235: 4.42 Normal core loading, kg U-235: 6.59 Fuel material: U 3 Si 2 -Al Enrichment min%: Enrichment max%: Origin of fissile material: USA, China Utilization Basic/applied research: Neutron diffraction, n,γ reaction, NAA, Radioisotopes Isotope production: I-131, P-32, Br-82 etc., Neutron scattering: Two Diffractometers Neutron radiography: Yes Nuclear chemistry: Neutron activation analysis Training: Reactor supervisors, operators, students

3 Table. 2 Pakistan Research Reactor-2 (PARR-2) General Data Owner: Pakistan Atomic Energy Commission Operator: Pakistan Institute of Nuclear Science and Technology Islamabad Address: P.O. Nilore, Islamabad Construction date: Criticality date: Initial cost: 2 M US$ Annual cost: 70 k US$ Total staff: 10 Operator: 7 Technical Data Reactor type: MNSR (Miniature Neutron Source Reactor) Thermal power, steady, kw: Max flux SS, thermal, n/cm 2 -s: 1.0 x10 12 Max flux SS, fast, n/cm 2 -s: 3.2 x10 11 Moderator and coolant: Light water Reflector: Beryllium, water Control rod material: Cd Experimental Data Vertical channels: 10 Vertical max flux n/cm 2 -s: 1 x10 12 Reflector irradiation facilities: 10 Small irradiation sites: 8 x 7 cm 3 Large irradiation sites: 2 x 25 cm 3 Fuel Data Min critical mass, kg U-235: 0.98 Normal core loading, kg U-235: 1.00 Fuel material: Uranium-Aluminum alloy (UAl 4 -Al) Enrichment min%: Enrichment max%: Origin of fissile material: China Utilization Basic/applied research: NAA, Radioisotopes Isotope production: Short lived Nuclear chemistry: Neutron activation analysis Training: Reactor supervisors, operators, students

4 2. Experimental Facilities and Usage Pakistan Research Reactor-1 (PARR-1) is equipped with a number of experimental facilities (Fig. 1). i) Six radial beam tubes and one tangential through tube ii) Core side irradiation facility iii) Thermal column iv) Three pneumatic rabbit stations v) Dry gamma irradiation cell vi) Hot cell vii) Bulk irradiation area 2.1 Beam Tubes Six radial beam tubes and one tangential through tube are installed in the stall end of the reactor pool. Three of the radial tubes are of 165 mm φ and the other three 220 mm φ. The diameter of the tangential through tube is 132 mm. Each tube assembly consists of an embedded stainless steel liner, a retractable stepped aluminum tube, a set of aluminum canned baryte concrete and lead plugs and a gasket seal installed on the outer face. Each beam tube has the provision for flooding with demineralized water (which can also be circulated to prevent stagnation and avoid buildup of radioactivity) and exhaust air through stack. The tangential through tube is placed along one face of the reactor core and runs through the concrete pool walls from one side to other. It has the same structure at both ends as a beam tube and possesses the same design features of shielding, flooding with demineralized water and gasket seals at the outer face.

5 The radial beam tubes terminate at about 7 mm from the core but the through tube is located at a greater distance. Neutron flux in the beam tubes depends upon their location and core arrangement. For the first high power core average thermal neutron flux at the innermost end of the flooded beam tube varies from 3.8 x (for 6) to about 1.1 x for beam tubes 2 and 5. Different experiments such as neutron diffraction, (n, γ) reaction and neutron radiography have been installed on these beam tubes. 2.2 Core irradiation facilities Flux traps have been provided for incore irradiation of samples. In the first high power core the unperturbed neutron flux in the flux traps varies from 3.5 x to about 2 x with an average of about 1.3 x In the equilibrium core, average thermal neutron flux of the order of 6 x and 1.6 x n/cm-s is expected at locations F-4 and C-7, respectively. In addition, the area outside the graphite reflector can be utilized for core side irradiation. 2.3 Thermal column A graphite thermal column is provided for experiments requiring thermal neutrons. It is an assembly of graphite stacked in aluminum chamber 1.22 m 2 extending towards horizontally from the inside wall of the stall pool. The thermal column is extended to the reactor core face with the help of an extension assembly mounted on the support frame bolted to the pool floor mounting pads. The Extension is an aluminum canned graphite assembly provided with a thick lead gamma shield. At the outer face of the thermal column an experimental space about 0.59 m long is available. The end of the thermal column is closed and shielded by a steel frame 1.68 m x 1.53 m and 1.53 m thick concrete door having four access holes of 150 mm diameter. When not in use, these holes are closed with concrete filled aluminum plugs for shielding. The concrete door can be moved out on steel rails embedded in the floor. Neutron activation experiments can be installed at the thermal column face. Experiments can also be installed in the experimental holes up to a depth of 1.5 m. These holes are created by removing two graphite blocks of 100 x 100 x 600 mm and 100 x 100 x 900 mm. 2.4 Pneumatic rabbit system Three independent pneumatic tubes, 57 mm φ are provided to deliver sample capsules called rabbits into the high neutron flux areas around the core. A constant exhaust system, vented to the stack, allows the rabbits to be inserted or removed while the reactor is in operation. The irradiation time is controlled manually or by an automatic timer. Two pneumatic tubes terminate in the Chemical and Isotope Laboratory at the beam port floor while the third terminates in the hot cell. The rabbit travel speed to and from the reactor is 10 to 13 m/s depending up on the weight of the rabbit. The maximum weight of the sample including the rabbit is limited to 400 g. The thermal neutron flux varies with core configuration and control rod position. In the first high power core it is of the order of 4.5 x for RS-1 and RS-3 and 2.4 x for RS-2.

6 2.5 Dry gamma irradiation facility The dry gamma irradiation facility, located on the beam port floor, is a 1.82 m x 2.64 m and 2.14 m high concrete shielded room attached to the open end of the pool (Fig. 2). Irradiated fuel elements, which act as gamma radiation source can be inserted into a holder located in the open pool in front of the window. Up to eight fuel elements can be arranged in a row in front of the aluminum window. After completion of the exposure, the fuel elements are removed to the storage racks for taking out the irradiated targets. Degradation of various organic pollutants using this facility has been investigated. Dose intensity of fuel elements across an aluminum window was calibrated inside gamma cell using Teletector probe, FAG, Germany and it was 250 Grey per hour. 2.6 Hot cell Hot cell is a 1.82 x 2.64 m and 3.75 m high-shielded room adjacent to the open end of reactor pool located at the intermediate floor level directly over the gamma cell (Fig. 2). This room is equipped with master slave manipulators; a one tone overhead crane and a 0.61 m 2 transfer port assembly, which connects hot cell to the open pool. The crane, master slave manipulators and the transfer port are operated from outside the hot cell. A radiation resistant oil filled shielding glass window provides visibility in the hot cell. The walls of the hot cell are made of about one meter thick heavy density concrete and permit handling of about 1000 curies MeV radioactivity. The inside of the cell has steel lining and is coated with a special paint to permit easy decontamination. Entrance of the cell is provided through a 10 ton concrete filled steel door supported on precision hinges. Isotope storage liners with plugs are provided in the shielding wall.

7 2.7 Bulk irradiation area The open pool, which has an area of 35 m 2, can be used for bulk irradiation studies. The reactor can be operated in this area up to full power and large space available around the reactor can be utilized for experiments. 2.8 Experimental services Service piping system is provided with taps in a covered trench around the reactor face at the beam port floor to supply cold water, demineralized water, compressed air, gas and drainage connections for use in the beam tubes and the through tube. Plugged connections are provided to allow circulation loops to be set-up for the introduction of special fluids. The pressure of liquid and gas supplied to the beam tubes should, however, be limited to 1 kg/cm 2 to prevent liquids from being forced out into the ventilation system. Electrical power at 230 V single phase and 400 V three phase is available in the reactor hall. Provision is also made for interlocking the experimental equipment with the reactor scram system. 3. Radioisotope Production Facilities Production of radioisotopes started since Pakistan Research Reactor-1 went critical in December Pakistan Atomic Energy commission is helping government in health sector by operating 13 Nuclear Medical Centers in Pakistan, while a few more are expected functioning shortly. In these medical centers more than patients are treated every year. For many years Isotope Production Laboratories are meeting all the demands of Sodium Iodide ( 131 I), Phosphorus-32 ( 32 P) and cold kits for 99m Tc radiopharmaceuticals for these centers. Sterile PAKGEN 99m Tc are also being fabricated weekly in a 99 Mo loading clean room facility created under an IAEA Technical Cooperation Project. Now a days PINSTECH is also providing its products to various private and government hospitals, treating patient with nuclear medicine. The number of such hospitals are ~ 20. With the constant support of government PINSTECH has upgraded its production and quality control installations with technologically advanced equipments, aiming towards maximum automation and standardization, while strictly following the methodologies of Good Manufacturing Practices (GMP) and protocols of International Atomic Energy Agency (IAEA), Vienna. The main goal of Isotope Production Division at PINSTECH is to maintain uninterrupted supply of radioisotopes/radiopharmaceuticals and in-vivo kits for 99m Tc radiopharmaceuticals to their users. Radioisotopes find applications in various fields such as nuclear medicine, diagnosis and cure of disease, hydrology, sedimentology, agriculture and industry. Large amounts of Sodium-24, Bromine-82, Chromium-51, molybdenum- 99, Cesium-134, Lanthanum-140 etc., were prepared for such applications. Various facilities available for radioisotope processing are as follows; 1. IODINE-131 Production Cell (Wet Distillation Technique). Maximum capacity per batch 10 Ci/370 GBq. 2. Iodine-131 Production Cell (Dry Distillation Technique). Maximum capacity per batch 10 Ci/370 GBq.

8 3. Phosphorus-32 Production Cell (Dry Distillation Technique). Maximum capacity per batch 10 Ci/370 GBq. 4. Sulpher-35 Production Glove Box 5. Molybdenum-99 Loading Facility for preparation of 99m Tc generators 6. Hot Cell with Master Slave Manipulators 7. Fume Hoods and Glove Boxes (for small scale production of different radionuclides and R&D work) 8. Workshop for target preparation and sealed source fabrication 9. Laboratories for determination of radionuclidic, radiochemical and biological purity 3.1 Production of Iodine Wet Distillation The neutron irradiated tellurium is dissolved in an oxidizing medium (chromic and sulphuric acid) converting tellurium to telluric acid wherein the elemental iodine is released and converted to iodic acid (HIO 3 ). This is reduced with oxalic acid releasing elemental iodine vapor, (distilled at 140 o C) which is collected in alkaline scrubbers as sodium iodide in sodium sulphate/sodium bisulphate/ NaOH solution. Flow sheet diagram is shown in Fig. 3.

9 3.1.2 Dry Distillation The irradiated tellurium dioxide is heated at a temperature ~700 o C under vacuum. The 131 I released from the matrix of the target as vapor is then trapped in carbonate/bicarbonate buffer (Fig. 4). Weekly demand of Iodine-131 in Pakistan is 3-5 Ci. Iodine-131 labeled MIBG (20-30 mci) by isotope exchange method is also prepared for diagnostic applications. To minimize the radiation exposure of paramedical staff facility for preparation of Iodine- 131 capsules for diagnosis and therapy are underway. 3.2 Production of Phosphorus-32 Neutron irradiated Sulfur is distilled at 450 o C in a quartz furnace. Residual 32 P is dissolved in dilute HCl and H 2 O 2 and finally purified by passing through cation exchange column. The product obtained is H 3 PO 4. Yearly demand of 32 P is 0.5 Ci. Flow sheet diagram of process is shown in Fig. 5. Small-scale production of 32 P is obtained by extraction in boiling water from neutron irradiated sulfur and purified by passing through cation exchange column.

10 3.3 Molybdenum-99 Loading Facility Under IAEA Technical Co-operation Project PAK/4/40, Institute of Isotopes Co. Ltd, Budapest, Hungary provided the Molybdenum-99 Loading Facility for the manufacturing of fission molybdenum-99 based alumina column chromatography 99m Tc generators in a clean room environment. The laboratory is divided into dress change rooms, preparatory room, generator loading room, test elution room and packaging room. The generator loading room is provided with two hot cells, air locks and two laminar air flow. The door of each change area are interlocked to maintain air pressure differential. Because of the importance of 99m Tc generator in nuclear medicine, clean system is provided during active operation to get the product free from bacteria and pyrogens. This is achieved by installing HVAC system, which provides clean airs to the various premises of facility through HEPA filters. The unit ensures the following values in clean room. Temperature: 22 ± 2 o C Humidity: 50 ± 5 % Relative pressure: minimum over pressure of 15 Pa (1.5 mm w.g) with respect to adjoining room with higher contamination. Number of air cycles: 50/h Air velocity: ~0.5 m/s Fresh air: 20 %

11 Hot cells are installed in clean room facility of class 10,000 to meet GMP regulation during 99m Tc generator production. In order to contain radioactive particles in the cells, negative air pressure is provided which is connected to the main negative pressure line installed in the building. Arrangement of loading PAKGEN generator is shown in Fig PAKGEN 99m Tc Generator PAKGEN 99m Tc generator manufactured at PINSTECH consists of a chromatographic separation system and an appropriate elution device (two vial system, saline eluent vial and evacuated 99m Tc collection vial. The chromatographic separation system comprises a glass column packed with aluminum oxide, onto which the highly purified fission 99 Mo is adsorbed in the form of molybdate. The generator column is sealed to each end with a rubber plug with the help of aluminum cap. Specially designed, sterilized stainless steel needles are connected to the column for passage of saline solution. Sterile filtered air is introduced to the system during the elution in order to keep the column in a dry state between elutions and thus maintains high yields of 99m Tc. A minimum of 40 mm lead surrounding the column provides sufficient radiation protection. PAKGEN is eluted by using 30 ml sterilized evacuated vials and the elution volume is 5 ml, 10 ml or 15 ml. The eluent (0.9 % NaCl) does not contain any additives; such as oxidizing agent that could adversely effect kit labeling. The activity sizes of PAKGEN generators are 100 to 700 Ci of 99 Mo at reference day.

12 3.5 Molybdenum-99 The molybdenum-99 is shipped in amount of 10 Ci (reference date) in a plastic bottle shielded by depleted uranium. The uranium shielding is placed in a steel barrel during shipment (89 kg Type B (U) container). Values of radionuclidic purity are guaranteed by 99 Mo bulk supplier (AEC South Africa). Highly purified fission product 99 Mo is supplied as mentioned in British/European Pharmacopoeia. The 99 Mo is shipped as 5-10 ml solution of 0.2 M NaOH containing NaOCl as oxidizing agent. After two successful clinical trials regarding the performance of PAKGEN 99m Tc generators carried out at different nuclear medical centers in Pakistan, fortnightly supply of PAKGEN generators were started. For the last one-year generators are weekly manufactured in this laboratory to meet the demands of Atomic Energy Medical Centers and few private/government hospitals. At the moment 10 Curies (at reference date) of Molybdenum-99 ( for conversion to Technetium-99m generators) is being imported from South Africa in Pakistan. Some problems faced by PINSTECH with imports of fission Molybdenum-99 i) Uncertainty of arrival of bulk 99 Mo ii) Custom clearance at air port iii) Return of depleted uranium container iv) Activity variation v) Steel container of 99 Mo plastic bottle vi) Size of 99 Mo plastic bottle vii) Long Holidays in Pakistan are different from Supplier To overcome the problems associated with the import of these generators/ 99 Mo, such as availability of hard currency, increase in the price of Molybdenum-99, import policies, delay and changes in supply schedule, etc. the indigenous production of Molybdenum-99 in the country was approved by Ministry of Science and Technology of Pakistan. Research and Development Program for production of 99 Mo/ 99m Tc generators Work on all the three options are underway at PINSTECH i) Fission Molybdenum-99 ii) (n,γ) molybdenum-99 for gel generators iii) (n,γ) molybdenum-99 for inorganic polymer adsorbent The present day industrial scale production of 99 Mo is fission based and involves neutron irradiation of highly enriched uranium (>20% 235 U) containing targets in a reactor. Elaborate processing precautions are required to avoid fission product or transuranic contamination of 99 Mo. Problems related to waste disposal are complicated. To reduce nuclear proliferation concerns low enriched uranium (< 20% 235 U) targets for neutron irradiation and separation of 99 Mo will be developed. Demand of Iodine-131 in Pakistan is increasing day-by-day, since large amount of Iodine-131 is produced during fission process, extraction of fission Iodine-131 may solve this problem.

13 Preformed gels of Ti, Zr and Zn molybdate were irradiated in reactor. After irradiation the gels were not stable. The yield of 99m Tc was low and breakthrough of 99 Mo was high. For local/city supply of 99m Tc Jumbo generator of zirconium molybdate is a good choice. Different concentrating system for 99m Tc/ 188 Re has been developed which may be utilized for preparation of highly concentrated solution of 99m Tc for kit labeling. To avoid difficulties faced in the preparation of gel generators synthesis of inorganic polymers, (poly zirconyl chloride (PZC) etc.) which have extraordinarily higher adsorbability of Mo than alumina will be performed. Loading capacity of Mo and separation of 99m Tc from adsorbed 99 Mo from substrate will be studied. Fabrication of hot cells facility for preparation of therapeutic doses of 153 Sm-EDTMP and 131 I-MIBG has also been planned. 3.6 Quality Control Radionuclidic quality control laboratory is equipped with, HpGe detector coupled with Canberra 85, multichannel analyzer, Alpha and Beta counters, dose calibrators and gross gamma counters. Radiochemical quality control laboratory is equipped with, 2π scanner, HPLC, electrophoresis, gamma counter, spectrophotometer, ph meter, radiochromatographic apparatus. Biological quality control laboratory has laminar flow, incubators, oven, biodistribution, sterility, pyrogenicity testing facility. 4. Neutron Radiography Neutron radiography as a non destructive testing technique has played a prominent role in the development of fuel for research and power reactor; studying of dimensional changes due to irradiation; inspection of corrosion in airframe structures and propeller blades; detection of light components and materials in explosives and investigation of transport of water into building materials etc. A neutron radiography facility by extracting a beam of thermal neutrons through a radial beam transport around the PARR-1 has been established. Graphite block of 30 cm thickness and bismuth block of 25 cm thickness has been used to boost up thermal neutron flux level and filter out high energy gamma radiation from the beam respectively. Thermal neutron flux level of the order of 1.06 x 10 6 n/cm 2 -s and a neutron flux to gamma ray dose ratio of the order of 10 5 n/cm 2 /mr have been measured at the object position which make the facility useful for investigation of material characteristics and properties applying direct neutron radiography method. The facility has been subjected to modifications and changes in order to enhance thermal neutron flux level and reduce the exposure time for better image quality at the object position. Visibility of holes under the lead and acrylic step wedges categorize the facility for direct applications Neutron cross-sections of different metallic as well as composite materials have been determined by applying neutron radiographic technique. The use of neutron radiography as a complimentary technique to ensure the quality of nuclear fuel in addition to other applications like detection of light components in explosives and pyrotechnic devices is investigated. Detection of corrosion in aluminum joint deformation in aeronautical components and honeycomb structures is also evaluated. Layout of neutron radiography facility around PARR-1 is shown in Fig. 7.

14 5. Neutron Scattering Neutron diffraction techniques are widely used in the study of condensed matter. The application ranges from solid state physics, chemistry, crystallography, and material sciences to biology and cover both fundamental and applied research. Neutron scattering is significant because it provides information that often cannot be obtained using other techniques, such as optical spectroscopy, electron microscopy and X-ray diffraction. The technological advances in miniaturization of electronics, advent of personal computers, and sophisticated detectors, have led to the development of new strategies in neutron diffraction. In addition the distinct technological advances like focusing monochromators, multi counter assemblies and position sensitive detectors are ensuing in rapid data acquisition for small samples, real time measurements, and online data analysis. At PINSTECH, the neutron diffraction programme is centered around a triple axis neutron spectrometer, installed in the early seventies. Over the years, it has been used for the structural studies of cellulose, order disorder transitions in iron based alloys and superionic conductors, determination of thermal parameters of materials, lattice dynamics of mixed alkali halides and copper nickel alloys as well as texture studies of copper and aluminum. Up gradation of neutron spectrometer has been achieved by developing a multi-counter assembly to replace the single BF 3 detector and replacement of older data acquisition and spectrometer control system with PC based system for automated operation. Layout of the neutron diffractometer with multicounter assembly installed at PARR-1 is shown in Fig. 8.

15 6. Prompt Gamma Neutron Activation analysis The experimental prompt gamma neutron activation analysis, which was indigenously designed, fabricated and installed at the tangential through tube of PARR-1, is shown in Fig. 9. It consists of a collimator, a shutter, n-γ shielding arrangement, target assembly, a beam catcher and a gamma-ray detection system. The collimator is mainly an arrangement of lead and borated wax canned in aluminum cylinders extending from the reactor core to the externally placed beam catcher. A reactor grade graphite solid cylinder is used as a reflector, which directs the core neutrons into the collimator. The collimated neutrons on their flight path are allowed to pass through a bismuth crystal (φ = 10 cm, L = 5 cm) to reduce the fission gamma rays, epithermal and fast neutrons. The diameter of the final collimated neutron beam at the target position as measured by using solid state nuclear track detectors is 3 cm. Beam shutter and a heavy n,γ shielding (of lead and wax) is arranged soon after the reactor s biological shield wall to control the neutron beam and radiation safety to the working personnel. Finally the extracted neutron beam is dumped into the beam catcher. Perspex rectangular target holder assembly capable of accommodating pellets, powders, liquid and solid samples is positioned in the beam paths between the n-γ shielding and the beam catcher. The target holder is surrounded with 6 Li 2 CO 3 jacket to capture the neutrons sneaking from the beam to the detector. Prompt gamma rays originating from samples as a result of thermal neutron capture are measured with a 172 cm 3 high purity gamma ray detector located at 30 cm from the beam center. The detector is coupled with 4096-channel computer controlled pulse height analyzer for data acquisition. A gamma collimator between target assembly and the detector helps to

16 eliminate the gamma rays arising out of the neutron collimator and the neutron catcher which ensures the better condition for the detection of sample gamma rays. A 6 Li 2 CO 3 plug (φ = 8.5 cm, L = 10 cm) was fixed in the gamma collimator to protect the detector from neutron radiation damage. Multichannel analyzer was calibrated in the range of 5-9 MeV. (i.e., the region of interest) for the identification of elemental prompt gamma rays. Several important elements such as those with very high capture cross-sections (B, Cd etc.), pureβ-emitters (S, P etc.) or those changing into stable nuclides after thermal neutron irradiation are analyzed with this technique. Some material which may decompose or explode, physically too large or radiation damage, heating and residual activity are undesirable can also be accommodated with PGNAA. 7. Improvements in PARR-1 Instrumentation and Control System after Renovation The instrumentation and control system of PARR-1 was renovated in 1986 and the system was almost completely replaced for operation at 5 MW. The system was further upgraded during the upgradation in 1991 for operation at 9 MW with LEU fuel. After the upgradation, improvement of the system is continuously being made to enhance the safety and availability of the system. A comparison of the performance of new system with the old system shows that the frequency of unscheduled shutdown of PARR-1 has been reduced from a minimum of 30% with the old system to less than 2% with the new system. The old instrumentation on the reactor was of electron tube-base design, which was commissioned in 1965 and may have been designed several years earlier. At the time of first renovation in 1986 the system was about 20 years old, which had several operational problems due to obsolescence and aging of old electronics, particularly nonavailability of replacement parts and high failure rate. The nuclear instrumentation was

17 developed with imported channels from H & B; the NIM modules were replaced with the locally developed euro-card type nuclear channels. Some new systems have also been incorporated with the I&C systems and some channels have been improved to enhance the safety and availability of the upgraded reactor. This includes the installation of Emergency Core cooling System, Battery Backup System, a new annunciating panel and thermal power-monitoring channel. The N-16 channels and process channels have also been improved. Some process instruments, area radiation monitors, chart recorders and indicators are also being changed.