Evaluation of the Philippine Research Reactor-1 Structures

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Introduction

The Philippine Research Reactor-1 (PRR-1) facility is a science and technology infrastructure with a rich history as the first and, thus far, the only nuclear facility that has operated in the country [1]. In support of the planned reoperation of the facility with the Subcritical Assembly for Training, Education, and Research (SATER), the evaluation of PRR-1 structures was contracted out by the facility operators. Considering that the PRR-1 structures are more than 60 years old, the evaluation aims to ascertain the structural integrity of the facility for SATER. This work presents an overview of the structural evaluation that was conducted by an external contractor, AMH Phils for the following PRR-1 structures: reactor dome, reactor pool, and fuel storage tank. Key results of the seismic hazard assessment and geotechnical investigation are presented as well as the main findings on the evaluated structures.

Materials and Methods

The assessment of PRR-1 structures followed the workflow diagram in Fig. 1. All components were modelled based on facility drawings using finite element analysis (FEA) with an elastic approach. Analysis were performed using STAAD.Pro CONNECT Edition by Bentley Systems.

Results and Discussion

Geotechnical investigations show that the subsoil condition in the PRR-1 building site has a bearing capacity of 900 kPa assuming an isolated foundation system with depth of 1.5 m and width of at least 1 m. Meanwhile, the probabilistic seismic hazard analysis for the site that was performed for return periods of 475, 1,000, 2,475, and 4,975 years with 5% and 2% damping ratios, resulted in response spectra that peaked at a period of 0.10 sec, indicating that resonance may occur for very rigid structures. Based on the most critical combination of dead loads, live loads, fluid loads (as applicable), and seismic loads, the maximum principal stresses were determined for the evaluated structures. As shown in Fig. 2, the resulting stresses and demand-to-capacity ratio, only one segment in the reactor building exceeded the allowable tensile capacity by 1% margin, and most of the existing wall and dome reinforcement are sufficient. In the reactor pool, the ratio for tensile stresses exceeded 1.0 throughout the elevation of the structure, while in the tank, a maximum compressive principal stress of 14.30 MPa is developed under the seismic load combination.

Conclusions

The existing PRR-1 structures were evaluated with seismic hazards and geotechnical data duly considered. Results demonstrate that the PRR-1 structures are suitable for operating SATER as a Hazard Category 4 facility. Nevertheless, the recommended retrofitting based on evaluation results will be implemented to meet the life-safety performance objective.