Performance Evaluation of Converted and Upgraded PARR-1

Pakistan Research Reactor-1 (PARR-1), a swimming pool MTR type research reactor which attained full power of 5 MW in June, 1966, with 93% high enriched uranium (HEU) fuel was converted to <20% Low Enriched Uranium (LEU) fuel in October, 1991. The reactor power was also upgraded from 5 MW to 9 MW and then to 10 MW. Different critical and full power operational core configurations were assembled with the new fuel. The final equilibrium core was assembled with 27 standard fuel elements (SFE) and five control fuel elements (CFE) having a central flux trap facility for high neutron flux. Detailed neutronics and thermal-hydraulic design calculations were made for the core conversion programme. After achieving the initial criticality several critical and power experiments were performed on the new core for the verification of design data and to determine the nuclear performance of the reactor. A comparison of the measured and the calculated results was also made. The results of the characteristics tests indicate that the performance of the new reactor is within the design limits. In flux trap thermal neutron flux is about 2x10 n.cm. s which is five times higher than the average neutron flux of the core. seven standard and two control fuel elements have achieved designed burnup of 35%. Their physical inspection predicts excellent condition. INTRODUCTION PARR-1, a swimming pool, MTR type reactor attained full power of 5 MW on June 22, 1966 with 93% Highly Enriched Uranium (HEU) fuel. The reactor is cooled and moderated by Light water. Light water and graphite act as the reflector. Since its commissioning, PARR-1 has been mainly utilized for studies in solid state physics and neutron diffraction, nuclear structures, fission physics, Neutron Activation Analysis (NAA) radioisotope production and training of scientists, engineers and technicians. The reactor was operated with HEU fuel for about 30,000 hours and produced about 93,000 MWh energy. The reactor was shutdown in 1990 for core conversion to commercially available LEU fuel. During the process of core conversion the reactor power was also upgraded to 10MW to meet the demand of higher neutron flux and to compensate the penalty in neutron flux due to conversion from HEU to LEU fuel. Most of the reactor systems including primary and secondary heat transport system, were renovated and several additional systems were installed. IAEA also provided technical assistance for the completion of this project. PARR-1 went critical with 20% LEU fuel on October, 31, 1991 and attained the upgraded power level of 9 MW on May 7, 1992. The reactor power was raised to 10 MW in 1998 after enhancing the primary flow rate. Following is a list of major achievements in the core conversion and power upgradation programme of PARR-1. i) Detailed reactor design calculations for core neutronics, thermal hydraulics and accident analysis were completed. ii) Final safety analysis report was prepared. iii) A storage bay was constructed for the irradiated fuel/active components. The reactor was partially decommissioned and the active core components were transferred to the storage bay in February 1991. iv) A fuel transfer cask was designed and fabricated for the transfer of HEU fuel. v) Stainless steel lining of the reactor pool and holdup tank was completed in September 1991. vi) Extensive building repairs were done vii) Heat transport system was modified and upgraded in September 1991. New HVAC system was also installed. viii) A laboratory for reactor startup studies and critical, low power and full power tests, was established in September 1991. ix) The new LEU core was made critical in October 1991. Several critical core configurations were made for experimental measurements. ix) The first operational core was assembled in January, 1992 and low power tests were started. xi) Based on the results of critical and low power experiments the reactor power was raised in steps to 9 MW in May 1992. xii) Emergency core cooling system (ECCS) was installed in March, 1992. xiii) The reactor power was raised to 10 MW in 1998. xiv) The reactor is operating routinely satisfactorily since July, 1992. REACTOR PHYSICS CALCULATIONS Detailed neutronic calculations were made using different fuel types, uranium loadings and fuel burnups. Initially, U3O8Al fuel was considered with the uranium density of 3.1 g/cm corresponding to 270 g of U-235 per fuel element. However, to achieve a design burnup of the fuel of 35% it was necessary to increase the uranium loading to about 3.3 g/cm which could be obtained in silicide fuel. Based on these considerations the LEU fuel selected was 20% enriched U3Si2-Al. The design data of the LEU fuel is given below. Fuel material U3Si2-Al Fuel Enrichment (% by weight) 19.99 U-235