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Study of the Impact of Stellite Material on PWR Co-60 Contamination

[+] Author Affiliations
Liying Zhang, Yaxiao Wang, Xiaoxia Wang, Aijun Mi, Yawei Mao

China Nuclear Power Engineering Co., LTD., Beijing, China

Bo Gao

Fujian Fuqing Nuclear Power Co., Ltd, Sanshan Town, China

Paper No. ICONE25-67859, pp. V007T10A041; 5 pages
doi:10.1115/ICONE25-67859
From:
  • 2017 25th International Conference on Nuclear Engineering
  • Volume 7: Fuel Cycle, Decontamination and Decommissioning, Radiation Protection, Shielding, and Waste Management; Mitigation Strategies for Beyond Design Basis Events
  • Shanghai, China, July 2–6, 2017
  • Conference Sponsors: Nuclear Engineering Division
  • ISBN: 978-0-7918-5785-4
  • Copyright © 2017 by ASME

abstract

According with the requirements of HAF-102[1], the purpose of radiation protection optimization is to achieve occupational exposures as low as reasonably achievable (ALARA). More than 80% of the collective exposure doses are received during the outage for PWRs. Activated corrosion products, especially Co-60, deposited on the surface of reactor coolant system are the main causes of these doses. Co-60 is the principle contributor to out-of-core radiation fields in PWRs, which is a high energy gamma emitter with a 5.3 year half-life period. The contamination by Co-60 plates out in plant piping systems and produces long term high radiation areas in the plant. Stellite, a hard facing alloy trade, which has high Co-59 content (approximately 60%), is identified as one of the most important source of Co-60 in reactors, whereas the contribution of Stellite to cobalt are always not paid enough attention to. Cobalt is released through ware and corrosion of Stellite. When cobalt is released in systems with a flow path to the reactor, it can become activated by neutron to Co-60.

This paper analyzes the Stellite material release into the primary coolant. Based on the above considerations, the impact of Stellite replacement on plant contamination by Co-60 is calculated and analyzed with the use of activated corrosion product source term calculation program. The primary conclusions are as follows: (1) Reducing the quantity of Stellite material used during the design and building of PWRs can significantly reduce the Co-60 deposition on primary circuit. (2) The replacement of Stellite material has a positive impact on PWR contamination by Co-60, but the outcome is not so significant. Based on the above analysis, recommendations are made. Stellite material replacement project can be used for the operating reactors to reduce the Co-60 contamination. But for the design and building of new reactors, reduction of the use of Stellite material is the best choice.

Copyright © 2017 by ASME

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