FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

ABSTRACT
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WET CHANNEL INSPECTION SYSTEMS FOR CANDU NUCLEAR REACTORS,..
CIGAR AND CIGARette
M.V.C. l\olzi>, M.P. Volbzy and K.S. Uakil
Ontaftlo Hydto, To Konto, Ontario, Canada
This paper describes and compares the operation of the CIGAR and CIGARette wet
channel inspection systems that have been developed by Ontario Hydro for CANDU
nuclear reactor pressure tubes. Initially, the highly sophisticated,
automated CIGAR (£hannel inspection and Gauging Apparatus for Reactors) is
described. When the hydride blistering problem was discovered in Pickering
NGS Units 1 and 2 in late 1983, CIGAR was not operational, so a less
automated, slower system called CIGARette was rapidly designed and built. The
operation and some problems experienced with CIGARette are also described.
1. INTRODDCTIOH
Pressure tubes in CANDU nuclear reactors contain the bundles of natural
uranium fuel and act as a pressure boundary (see figure 1). There are several
hundred pressure tubes per reactor, mostly made of Zr-2.5%Nb, and these are
surrounded by a calandria tube containing dry gas between the two tubes.
Pressure tubes are 103 mm inside diameter, 4.0-4.5 mm wall thickness and
about 6m long. The pressure tube and calandria tube are separated by garter
spring spacers, from two to four per pressure tube, depending on the unit.
There are two general reasons for inspecting pressure tubes - regulatory and
economic. So far the mandatory regulatory requirements have been less
demanding than special requirements, only requiring gauging of a few pressure
tubes per year/1/. The economic reasons vary from wanting information on
pressure tube behaviour, to predicting and correcting pressure tube problems,
to major, well-publicized outage problems. The latter include the rolled joint
delayed hydride cracking in Pickering units 3 and 4 in 1973-74/2/, and the
more recent hydride blistering problem in Pickering units 1 and 2, which was
the impetus for this paper.
There are two general approaches to inspecting pressure tubes, namely 'dry'
and 'wet' channel systems, and Table 1 gives a sample list of both types. Dry
channel systems require pressure tubes to be defuelled, isolated, drained and
opened, so they require more time and man-rem than wet systems. Also
ultrasonic volumetric inspection is difficult to perform in a dry channel. Wet
channel inspections are performed in a defuelled channel still connected to
the primary coolant circuit. Channels can he defuelled on-line beforehand to
save time and costs with either approach.