A Recommended Design Approach for Breeder Reactor Cover Gas Seals

Abstract

Technological progress requires that lessons learned in initial design efforts be incorporated into the following design effort. One area where improvement can be made is in the design of elastomer seals for containment of breeder reactor cover gases. Liquid metal fast breeder reactor (LMFBR) vessels, unlike PWR’s, operate at a very low pressure. The reactor cover gas may be maintained at a pressure of less than 1 psia. This low pressure level and moderate temperatures of the vessel head-mounted refueling and monitoring equipment permit the use of elastomer seals in this equipment to contain the cover gas. Existing seal designs are based on a conservative design philosophy which was established in the late 1960’s when the FFTF project was in its formative stages. The information gained in the design and development of LMFBR seals during the past decade indicates that some changes in the approach to seal design could result in improved seals and reduced downtime for seal maintenance. This document presents the design approach currently used for cover gas seals, and points out how improvements can be made based on today’s knowledge of breeder reactors and elastomer seals. A suggested new seal design concept is presented which may better meet the LMFBR commercial program needs. The basic assumption used to design cover gas seals conservatively states that elastomer seals, even when new, can leak, and primary consideration must be given to preventing the outflow of radioactive cover gas. The suggested new design concept acknowledges that elastomer seals are effective, and the primary consideration should be one of controlling the gases which permeate through the elastomer seal material. Finally, information which was obtained from the cover gas seal development program for FFTF, which is of value to all LMFBR equipment designers, is summarized.