Failed Fuel Location System
The Project
CANDU reactors are equipped with a Failed Fuel Location System that is designed to detect fuel failures, and to determine in which channel of the heat transport loop the fuel has failed. In order to test the heat transport system for evidence of a fuel failure, D2O from the system must be selectively channeled past neutron detectors which record the neutron fields for evidence of fuel failure. The system required involves both remote handling equipment and pressure boundary tank system.
The Solution
D20 samples from each reactor channel are sequentially monitored to detect a comparatively high level of delayed neutron activity. A high activity indicates that the integrity of a bundle may have been compromised and that fission products are entering the primary heat transport system.
In order to monitor the samples, an automatically controlled, rail mounted, overhead crane, traverses above a series of dry wells mounted in a large D20 moderator tank. There are 102 wells laid out on a 6 x 17 pattern. Each well contains two sample coils, one above the other, and each sample coil receives coolant directly from a specific reactor channel.
In operation, the overhead crane makes an automatic sweep above the dry wells, stopping at specific rows in accordance with a predetermined sample program. The crane then lowers neutron detectors, six at a time, into a designated row of six dry wells. The detectors are lowered to a specific depth, to sample either the upper or lower coils, as required. All radiation data is then sampled for alarm status and archived for future analysis.
Project Responsibility Highlights
- Detailed design based on AECL specifications and concept drawings
- Stress intensity (per ASME Sec. III, Class 1) for headers and tees, considering multiple loading conditions (pressure, thermal transient, seismic).
- Stress analysis (by finite element method) of moderator tank under operating and seismic loadings, including the sloshing effects of the contained water.
- Seismic qualification (by shaker table testing) of sample coil assembly.
- Registration with the requlatory authority
- Manufacture, assembly and testing of overhead crane, sample coil assemblies, moderator tank, carriage, and headers.
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