Keywords: reactor pool working platform, guide tubes, refuelling cover, research reactor, response spectrum analysis, structural integrity, hydrodynamic mass effect.

The objective of the study, presented in this paper, is to design the reactor pool working platform (RPWP) including the guide tubes and refuelling cover, and to evaluate the structural integrity of those during and after the seismic events. They are installed in the reactor pool of a research reactor. The main function of the RPWP covers the reactor pool, supports the guide tubes and a refuelling cover, provides a working place near the reactor, and suppresses the rise of flow induced by the primary cooling system. The guide tubes provide the ways to have the radioisotopes irradiated. The refuelling cover protects the reactor structure assembly and supports some guide tubes. The design of the RPWP, guide tubes and refuelling cover has been performed according to the guideline of AISC N690 code [1] and US NRC Regulatory Guides. Those are classified as non nuclear safety (NNS) and seismic category II structures.

The three-dimensional finite element model of the RPWP, refuelling cover and guide tubes is developed by utilizing the MIDAS program. For modelling of the structure of the RPWP, refuelling cover and guide tubes, beam elements which have a total of six translational and rotational degrees of freedom along each coordinate system are used. The weights of the structural members, dead load and part of the live load are considered as distributed masses. In addition, because they are submerged in and influenced by water, the hydrodynamic mass effect is taken to account [2]. These are considered as the point masses in the finite element model.

In order to investigate the dynamic characteristics of the RPWP, refuelling cover and guide tubes, modal analysis of the finite element model developed is performed. To evaluate the structural integrity of the RPWP including the guide tubes and refuelling cover, the response spectrum method has been applied under the seismic loads of SSE (safe shutdown earthquake). The possibility of impact between the top of the reactor structure assembly and the bottom of the refuelling cover is investigated. The analysis results show that the maximum stress values of the RPWP, guide tubes and refuelling cover when subject to the seismic loads are within the specified code limits. It is also confirmed that the impact does not take place under the SSE event. Therefore, any damage to the structural integrity is not expected when the RPWP, guide tubes and refuelling cover are installed and utilized over the reactor pool.

1

ANSI/AISC N690, "Specification for Design, Fabrication, and Erection of Steel Safety-Related Structures for Nuclear Facilities", American Institute of Steel Construction, 1994.

2

R.D. Blevins, "Formulas for Natural Frequency and Mode Shapes", Van Nostrand Reinhold, New York, 1979.

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