《A Measurement of a Control Rod Drop Using an LVDT》.pdf

A Measurement of a Control Rod Drop Using an LVDT ∗ Myoung-Hwan Choi , Ji-Ho Kim, Hyung Huh, Je-Yong Yu, Dong-Seong Sohn Korea Atomic Energy Research Institute, 1045 Daedeokdaro, Yuseong, Daejeon, 305-353, Korea ABSTRACT A control element drive mechanism is a reactor regulating system, which is to insert, withdraw, or maintain a control rod containing neutron-absorbing material within a reactor core to control the reactivity of the reactor. The ball-screw type CEDM for the small and medium research reactor has a spring-hydraulic damper to reduce the impact force due to the free drop of the CEDM. This paper describes the experimental results to obtain the drop characteristics of the CEDM. The tests are performed by using a full-scale structure except the control element assembly, and a drop time and displacement after an impact are measured by using an LVDT. The influences of the rod weight and the drop height on the drop behavior are also estimated on the basis of test results. In case of the longest stroke, the drop time of the control rod is within 4.5 seconds to meet the design requirement. The behavior after the impact shows a general damping motion of the spring-damper system, and the maximum displacement is measured as 15.6 mm. Keywords; CEDM, LVDT, damping system, drop test, impact, displacement 1. INTRODUCTION A control element drive mechanism (CEDM) in the nuclear power plant is an important device to control the reactor power by adjusting its position in the core during normal operation, and to shut down chain reactions by quickly inserting a neutron absorber into the core under a scram condition. CEDMs of various types with a driving mechanism have been developed for application in