Project Overview

During operation, the pressure tubes (PT) of CANDU reactors are known to absorb deuterium. Over time, the accumulation of deuterium can threaten PT integrity. Specifically, a high PT deuterium concentration increases the risk of Delayed Hydride Cracking initiation from severe flaws, which reduces the PT fracture toughness and can result in the formation of hydride blisters. Therefore, the monitoring of deuterium uptake in PTs is important for the continued operation of ageing CANDU reactors.

Monitoring of the deuterium requires that samples are taken from the tubes at key locations using a custom designed tool known as a the Circumferential Wet Scrape Tool or CWEST*. This tool interfaces with the Rapid Delivery Machine (RDM) to collect samples from fuel channels under shutdown conditions. The samples are then transferred from the tool to a flask by means of a retrieval system, so that they can be taken for deuterium content analysis.

With some challenges to the historic tools Ontario Power Generation required an improved design and the supply of new tools.

How We Helped

The historic CWEST* systems deployed at Pickering and Bruce Power were used as the baseline systems to generate the new design for Darlington Nuclear Generating Station (DNGS).

The primary aspects of the design included updates to the control system to integrate with the station interfaces at DNGS, the RDM interface, and to consolidate the hardware in the Pickering CWEST* SCADA rack (PLC, HMI computer, etc) into the vault cart.

The key design activities Included:

  • Designing new interface cables and off-reactor test equipment
  • Re-designing the vault cart and hydraulic cart
  • Preparing a new suite of design documents generated to meet the design requirements
  • Flaw assessments, design calculations, technical memos, Etc.
  • Procuring all parts to build new equipment and retrofit the Pickering carts
  • Constructing cables and junction boxes and retrofitting the electrical cabinets on the vault cart and hydraulic cart
  • Developed new software and testing it

The benefits of the new system include;

  • Reduction in dose to staff for scrape campaigns
  • Reduction in outage critical path durations
  • Increased scope capabilities compared to legacy non-machine delivered scrape tooling

*CWEST not available for sale outside of Canada until after November 30, 2027.