Numerical and experimental study of hydraulic dashpot used in the shut-off rod drive mechanism of a nuclear reactor

• Hydraulic dashpot performance is studied numerically as well as experimentally.
• Instantaneous pressure built-up in the dashpot is mainly contributing for damping of freely falling shut-off rod at the end of its travel.
• At elevated temperature, dashpot pressure does not reduce in proportion to the reduction in viscosity.
• ‘C’ grove in the dashpot shaft flattens the pressure peak and shifts it toward the end of operation.

Hydraulic dashpot design for shut-off rod drive mechanism application in a nuclear reactor has been analyzed both numerically and experimentally in this paper. Finite element commercial code COMSOL Multiphysics 4.3 has been used for numerical analysis. Experimental validation has been done at two different cases. Experimental test set-ups and hydraulic dashpot constructions have been described in detail. Various combinations of dashpot oil viscosity and clearance thickness have been analyzed. Important experimental results are also presented and discussed. Pressure distributions in the dashpot chambers obtained from COMSOL are given for both the set-ups. Numerical and experimental results are compared. Dashpot designs have been qualified after detailed analysis and testing on full-scale test stations simulating actual reactor conditions (except radiation).