Pickering NGS B Calandria Inlet Line Failures and Repairs

Abstract

In September 1986 it was found that unit 6 moderator was being slowly downgraded. By using tritium as a tracer and by manipulating system pressures to reverse the leak direction, it was identified that the leak was at an interface of the moderator and shield cooling system. The precise site of the leak was located using a remote viewing submarine. The leak was on the west calandria inlet Line at a shield tank penetration. Alternate draining of the moderator, then the shield tank, was necessary to repair the line. The east calandria inlet line was also found to be cracked although not leaking. This was repaired. The cause of failure was high cycle fatique at a poor weld. A similar failure occured on unit 5 and this was also repaired.