NORM detection challenges in the Gas industry: 3D simulation of Pb-210 presence in Gas field pipework

Abstract

Present interest concerns 3D simulations of the presence of naturally occurring radioactive material (NORM) internal to gas-field pipework. The particular aim is to develop capability for examining ²¹⁰Pb NORM in tubulars, valves, other such component parts, separators and storage vessels. To-date the major emphasis of related studies has been on developing best practice for protection of workers dealing with the build-up of NORM-affected facilities, including attachments to inner surfaces of gas piping. Nonetheless, to-date identification and potential environmental impact of thin (few millimetre thick and less) deposits in gas lines has remained challenging. Given an increasing trend in decommissioning activities, in part with industry setting targets for carbon reduction, validation of NORM removal towards obtaining NORM-free piping is a matter of particular interest. Efficacious techniques for removal of internal surface NORM contamination can be expected to increase prospects for reuse and repurposing of NORM-free steel, important in seeking to reduce new steel production and hence reduction of carbon load to the environment. To-date, surveys of the presence of NORM have been dominated by hand-held survey meters, sensing gamma emissions transmitted through affected pipework. To a lesser extent this has been supported by workover samples collections and gamma spectroscopy, examples of which have been covered elsewhere. Herein, the focus is on simulations of the presence of ²¹⁰Pb and its progeny, with use made of the TOPAS Monte Carlo code to model the 3D distribution of the electron-, photon- and alpha fluence in- and around small sections of ²¹⁰Pb depositions in carbon-steel gas pipes, limited in extent for practical purpose to 10 cm simulated length. Results support the conventional understanding of the low likelihood of sensing the presence of ²¹⁰Pb via measurements conducted externally to affected pipes, also highlighting the geometric basis for the propensity for NORM accumulation around pipework bends. Present simulations are intended to help inform development of appropriate detector technology and their use in internal surveys, the various distributions pointing to progressive reduction in detection capability as a function of separation of a sensor from pipe surfaces, radically so for alpha activity as expected. Given the presently assumed conditions, beta particle emission is seen to offer the greatest potential for effective detection. Safe, real-time means for internal surfaces radiometry, are currently under development, doped glass fibres for instance allowing access to pipes of restricted dimensions, including around curvatures. Beta- and gamma-emission detection are the favoured options, with efforts aimed at sensing alpha-particle decay of ²¹⁰Po pending characterization of thin sensor coatings.