Description Components Safety Radiological Safety Construction, Commissioning & Operation Summary Reactor Vessel Internal Inspection History of FBTR

Visual Inspection of Reactor Vessel and Internals

The technical specification for FBTR operation stipulates visual inspection of reactor vessel internals periodically to assess the extent of sodium oxide deposition on the vessel walls, ascertain non-plugging of small pipes (like siphon break, argon, sodium purification return, emergency injection, overflow pipes) and general examination of vessel and internals for any abnormalities. Visual inspection, the first and oldest NDT method, was effectively utilised with the help of various visual aids for the inspection to assess the condition of the Reactor Vessel internals and Liquid metal seal (LMS) inspection.

Reactor vessel internal examination has been carried out six times so far with the help of periscope and projector (developed by DRHR, BARC) installed in the experimental canals. For this examination reactor vessel sodium is partially drained.

The small pipes were found clear and non-plugged. Sodium deposits were seen at a few spots. Siphon break pipe, provided to prevent automatic draining of sodium from reactor vessel in the event of any rupture in the primary sodium piping, was checked for non-plugging. This was checked by establishing flow through the pipe after partially draining sodium in the reactor vessel below the bottom level of siphon break pipe and running one primary pump. Clear sodium flow was observed. In case of sodium leak from reactor vessel, sodium will be injected from flooding circuit through emergency injection pipe into reactor vessel to keep the core completely submerged and avoid overheating of the core. Non-plugging of this pipe was checked by establishing sodium flow from flooding tank to reactor vessel. The sodium column flowing down this pipe was seen with the help of periscope. The Argon pipe opening was clear with no plugging. Overflow pipe, Sodium purification return pipe were seen to be in good condition.

The sodium inside the reactor is so pure that it acts as a mirror. This reflective property of sodium was put to use for viewing the lower surfaces of the rotating plugs.In the partial drained condition with both the primary pumps switched off, the free level of sodium was clear, shining and looking like a mirror.  Reflection of pipes, level probes, plug bottom surfaces were seen very clearly.

The new periscope was designed and developed by DRHR and Spectroscopy Division of BARC and supplied to FBTR.The vital reactor vessel internal inspection carried out with new periscope in Aug 2005 was satisfactory. The images were comparatively sharper and the resolution was excellent for our purpose.