Development and validation of operational reactor physics code “ORPAC” for research reactors at Trombay

An interactive code system ORPAC has been developed to perform calculations related to operational reactor physics jobs of research reactors. The code is aimed at providing a handy tool for radioactivity estimation, safety analysis related with isotope irradiations and post irradiation handling, xenon transients, etc. Initially the code was developed to cater the operational needs for Dhruva and hitherto operating CIRUS reactor. With the commissioning of 2 MW Apsara-U reactor, it was necessary to enhance its features for extending its support for the newly commissioned reactor. The code ORPAC is upgraded to solve generalized Bateman equations for neutron transmutation reactions e.g. (n, γ), (n,p), (n,α), (n,2n), etc. The code is designed to provide users to select cross-section data library from drop down list for appropriate spectrum of irradiation position in the concerned reactor. Spectrum averaged cross-section library has been generated using PREPRO-19 and ENDF/B-VIII library for Apsara-U and Dhruva reactors. 69- group structure from WIMSD is used to generate effective one-group cross section of isotopes using neutron spectrum of given irradiation position. Estimation of xenon transients, reactivity load of isotope samples, nuclear heating, dose rate, and shielding thickness of lead cask for transportation of radioisotope has also been included through different modules. This software can be used for any research reactor by incorporating its neutron spectrum and corresponding one-group cross-section library. It has improved and generalized methodology, updated data library, increased usage options, inclusion of more facilities and better graphical user interface as compared to its predecessor. In this paper, radioactivity in fuel as well as target materials for radioisotope production are discussed in detail and validated with measurements and standard code ORIGEN.