A Review of Vortex Amplifier Design in the Context of Sellafield Nuclear Operations

Abstract

Vortex amplifiers have for over 30 years been used to ensure containment of glove-box ventilation in the event of a barrier breach, the most likely such breach being damage to the glove itself. Containment is achieved using fluidic principles to control the glove-box depression and ventilation rate under both normal and emergency conditions; in the event of such a breach vortex amplifiers can switch quickly between these two states without recourse to electrical, pneumatic or manual intervention. This paper begins by summarising the developments in vortex amplifier design used at the Sellafield site by successive companies engaged in fuel technology, reprocessing and decommissioning (British Nuclear Fuels PLC (BNFL), BNFL Engineering Limited, British Nuclear Group and Sellafield Limited). The main reasons for design changes have been practical issues of set-up, cleaning, filter and waste minimisation, and space limitations. The development culminates in the use of a smaller version of the vortex amplifier (VXA) which is a nearly exact geometrical scaling of its predecessor and which has been standard design for over a decade. Initial use of this device, the mini–VXA, led to a substantial increase in the amount of inert gas needed to maintain the required oxygen-depletion conditions within the glove-box, implying some escape of oxygen into the glove-box. The use of the mini–VXA introduced practical issues relating to (i) its control characteristics and (ii) the reverse flow of air in the supply port. Comparison with the published design specification demonstrates that the geometrical scaling process has led to a slightly hysteric characteristic. Tests conducted by the authors indicate (i) that the origin of the escaping oxygen is the control air feeding back through the supply ports and (ii) that a prototype chamber and orifice plate arrangement between the glove-box and mini–VXA significantly reduces the inert gas demand in normal usage. This prototype arrangement introduced problems in maintaining a clean environment in the chamber, so the chamber and orifice was substituted by a detachable cowl that enabled the mini–VXA to be located within the glove-box and provided access for cleaning.