Thermal power calibrations of the IPR-R1 TRIGA reactor by the calorimetric and the heat balance methods Amir Zacarias Mesquita * , Hugo Cesar Rezende, Rose Mary Gomes do Prado Souza Nuclear Technology Development Center e CDTN, Campus da UFMG e Pampulha, P.O. Box 941, 30.123-970 Belo Horizonte, MG, Brazil article info Article history: Received 21 May 2010 Accepted 1 August 2011 Keywords: TRIGA research reactor Thermal power Calorimetric Heat balance abstract Since the first nuclear reactor was built, a number of methodological variations have been evolved for the calibration of the reactor thermal power. Power monitoring of reactors is done by means of neutronic instruments, but its calibration is always done by thermal procedures. The purpose of this paper is to present the results of the thermal power calibration carried out on March 5th, 2009 in the IPR-R TRIGA reactor. It was used two procedures: the calorimetric and heat balance methods. The calorimetric procedure was done with the reactor operating at a constant power, with primary cooling system switched off. The rate of temperature rise of the water was recorded. The reactor power is calculated as a function of the temperature-rise rate and the system heat capacity constant. The heat balance procedure consists in the steady-state energy balance of the primary cooling loop of the reactor. For this balance, the inlet and outlet temperatures and the water flow in the primary cooling loop were measured. The heat transferred through the primary loop was added to the heat leakage from the reactor pool. The calorimetric method calibration presented a large uncertainty. The main source of error was the determination of the heat content of the system, due to a large uncertainty in the volume of the water in the system and a lack of homogenization of the water temperature. The heat balance calibration in the primary loop is the standard procedure for calibrating the power of the IPR-R1 TRIGA nuclear reactor. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The IPR-R1 TRIGA Mark I nuclear research reactor at the Nuclear Technology Development Center e CDTN (Belo Horizonte) is an open pool type reactor. It was designed for research, training and radioisotope production. The fuel elements in the reactor core are cooled by water natural circulation. The heat removal capability of this process is great enough for safety reasons at the current maximum 250 kW power level configuration. However, a heat removal system is provided for removing heat from the reactor pool water. The water is pumped through a heat exchanger, where the heat is transferred from the primary to the secondary loop. The secondary loop water is cooled in an external cooling tower. TRIGA reactors are the most widely used research reactor in the world. There is an installed base of over sixty-five facilities in twenty-four countries on five continents. General Atomics (GA), the supplier of TRIGA research reactors, continues to design and install TRIGA reactors around the world, and has built TRIGA reactors in a variety of configurations and capabilities, with steady state thermal power levels ranging from 100 kW to 16 MW. The TRIGA reactors are used in many diverse applications, including produc- tion of radioisotopes for medicine and industry, treatment of tumors, nondestructive testing, basic research on the properties of matter, and for education and training. The TRIGA reactor is the only nuclear reactor in this category that offers true “inherent safety”, rather than relying on “engineered safety”. It is possible due to the unique properties of GA’s uraniumezirconium hydride fuel, which provides unrivaled safety characteristics, which also permit flexibility in sitting, with minimal environmental effects (General Atomics, 2009). The IPR-R1 TRIGA reactor at CDTN has started up on November 11th,1960. At that time the maximum thermal power was 30 kW. The actual forced cooling system was built in the 70th and the power was upgraded to 100 kW. Recently the power was upgraded again to 250 kW at steady state. Before the first startup of the reactor the pool water was heated by calibrated electrical heaters, with a known power, immersed into the core. This will result in a water temperature increase in a certain time interval which can be measured very accurately by thermometers. The reactor was then operated to give the same rate of water temperature rise, with the forced cooling system shut down. Thus the thermal power of the operating reactor could be easily calculated. This method was used by General Atomics (GA) in the startup of several facilities. * Corresponding author. Tel.: þ55 31 3069 3232; fax: þ55 31 3069 3411. E-mail address: amir@cdtn.br (A. Z. Mesquita). Contents lists available at ScienceDirect Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene 0149-1970/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.pnucene.2011.08.003 Progress in Nuclear Energy 53 (2011) 1197e1203