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Detailed Radionuclide Inventory of a Nuclear Station’s Steam Generators

Radionuclide inventories of in-service and out-of-service steam generators were developed using in-situ gamma spectrometry and characterization of archived tube sections.

​The scope of the refurbishment activities at the client’s station included the replacement of all existing steam generators.  Those from the first 2 units were removed and placed into interim storage at a nuclear waste management facility.

The client has contracted with a qualified international supplier for the final disposal of the steam generators.   The units will undergo metal recycling via melting, and the active tube bundle from each steam generator will be segmented and returned for storage at the local facility.

Shipment of the discarded steam generators requires an assessment of their radionuclide inventory.  Radionuclides of particular interest include the gamma emitters Co-60 and Cs-137; the alpha emitters Pu-238, Pu-239, Pu-240, Am-241, Cm-244; the beta emitters H-3, C-14, Ni-63, Sr-90, Pu-241, Tc-99, I-129; and the X-ray emitter Fe-55.  These radionuclides are confined principally to the oxide layer present on tube internals as well as on other primary side surfaces.

Kinectrics was contracted to develop the radionuclide inventory data for all steam generators.  Data for both in-service steam generators and those in storage was developed as follows:

  • Previously removed tube sections from various steam generators were radiochemically characterized.  Scaling factors using the detailed alpha and beta activity data obtained were derived for application to the entire steam generator.
  • In situ gamma spectrometry and dose rate surveys were performed on various steam generators.   Measurements were made using a hyperpure germanium detector and a miniature cadmium zinc telluride (CZT) detector inserted into a tube through the tubesheet.
  • A detailed assessment was conducted to obtain the overall tritium inventory.  A combination of approaches, including estimations based on permeability of tritium through metals, was employed.
  • Measured tube gamma activity data was used to perform dose rate assessments.
The data developed was presented to the regulator to obtain approval for the first planned shipment.