Predisposal management of legacy radioactive materials at the PRR-1 storage facility

Abstract

This paper describes the predisposal management of legacy neutron sources (LNS) and activated materials previously stored at the Philippine Research Reactor-1 (PRR-1) facility. The materials of interest included two disused ²⁵²Cf neutron sources and one neutron-activated item, confirmed by the presence of ⁶⁰Co gamma emissions. All of these items had been submerged in the reactor's spent fuel storage tank for over 30 years, with limited historical documentation. Comprehensive characterization using gamma spectrometry enabled the identification and classification of these materials, providing critical data for planning the safe recovery and predisposal process. The operations involved recovering and dismantling of the source rods, extraction of the neutron sources, contamination assessment, and subsequent encapsulation within a 200-liter shielded drum for interim storage. The entire procedure was executed in accordance with the facility's radiation protection program and instructions on management of radioactive waste, which are anchored to national regulatory requirements under the Code of PNRI Regulations (CPR). Surface dose rates of the storage drum were measured at 7.5 μSv/h for neutron radiation and 15.6 μSv/h for gamma radiation – both significantly below the regulatory transport limit of 2 mSv/h. Personnel doses recorded during the operation remained within occupational exposure limits, and contamination levels, verified through swipe sampling before and after the activity, were within acceptable thresholds. The successful implementation of this predisposal activity mitigates potential radiological risks and contributes to the continued safe and compliant operation of the PRR-1 facility.