Renovation of the pneumatic transfer system of the Dalat Nuclear Research Reactor

Full text: The Dalat Nuclear Research Reactor (DNRR) was reconstructed during 1982 - 1984 period from the previous 250 kW TRIGA MARK II reactor installed in 1963. The reconstruction had been completed at the end of 1983. The reactor core, the control and instrumentation system, the primary and secondary cooling systems as well as other associated systems were newly designed and installed. The PTS was improved for two irradiation channels in reactor. The first channel, namely 13-2 channel is received a neutron flux about 1012 n cm-2 s-1 at the irradiation site and the second channel, namely thermal channel is received a neutron flux about 1010 n cm-2 s-1 at the irradiation site. The renovated reactor reached its criticality in November 1983 and obtained its nominal power of 500 kW in March 1984. Since then DNRR has been operated safely. It is mainly used for research, radioisotope production, neutron activation analysis and training. Since its improving from the previous system, the Pneumatic Transfer System (PTS) of the Dalat Nuclear Research Reactor (DNRR) has been playing an important role in the field of Instrumental Neutron Activation Analysis (INAA). However due to using discrete and low-level integrated electronic components, the system's technology was somewhat obsolete. After ten years of operation, the system's reliability was degraded because of ageing effects on equipment and electronic components. Furthermore, this system is unable to perform the cyclic INAA (CINAA) technique. Renovation of the PTS is imperative not only for increasing its reliability but also for expansion in functioning and convenience in operating. Following this spirit, the PTS has been renovated in the framework of the Vietnam Atomic Energy Committee (VAEC) Project, named 'Renovation of the Pneumatic Transfer System of the Dalat Nuclear Research Reactor'. Renovation and modernization tasks were implemented from March 2000 to February 2002. The main results are redesign and construction of the PTS's control system which based-on PC and construction of the measurement system on the spot based on gamma-ray spectrum system using semiconductor detector Ge for research on the CINAA technique with short-lived radioisotopes. The Main technological specifications of the renovated PTS are: (1) Simple and safety in operation with two mode: Manually and automatically (2) The length of the rabbit pipelines from the measuring - taking specimen capsule box to the irradiation site are about 15m with the 13-2 channel and 4m with the thermal channel. (3) The transfer time of rabbit from the specimen capsule loading box to the irradiation site and return is 2s - 2.2s with the 13-2 channel and 1s - 1.1s with the thermal channel. (4) The system enables the user to irradiate rabbits one by one continuously with predetermined length of irradiation times for every one of them. (5) Permitting to irradiate a rabbit with cycle of irradiation - measuring - irradiation with a predetermined number of cycles. (6) The process of irradiation - transfer - measuring - taking with one or more of irradiation capsules is carried out automatically. (7) The distance between detector block and measurement site, which contained irradiated capsule, enables to chance from 2cm to 20cm on the horizontal direction by a 'rail-car' with the moving speed is 2.8cm/min. This 'rail-car' is controlled by the user from control cabin. (8) The software program of the RPTS was written in Turbo C and Assembler languages. It is user-friendly and the most of information on the PTS such as transfer time, irradiation time, measurement time, number of cycles, position of rabbit, etc., are displayed on the screen under digital or graphic type and saved in hard disk for the task of operation management. (9) The control and measurement center is installed in a cabin which is located in the reactor hall. The renovation and modernization of the PTS were carried out by staff members of the Nuclear Research Institute. The RPTS was checked, commissioned by the VAEC and put into operation since February 2002. Until now, the system is working with high reliability, convenience for users and easy for repairing and maintenance works. In the implement process, a lot of technological problems such as how to detect exactly rabbit's position before into or out from the core and measuring-taking box, how to design and construction of the rabbit pipeline with short length and suitable style for rabbit's moving smoothly, how to brake softly the irradiation capsule in to measurement site, etc. are solved strictly. The radiation background in the measuring-taking box is increased by the radiation dusts discharged from the rabbit pipeline during operation process. In order to reduce their influence, the rabbit pipeline must be cleaned in periodic. (author)