Corrosion Science and Technology

The Corrosion Science Society of Korea (한국부식방식학회)
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Analysis of CRUD Flake Applied to Abnormal High Beam Current by Shielded-EPMA

  • Jung, Y.H. (Korea Atomic Energy Research Institute) ;
  • Baik, S.J. (Korea Atomic Energy Research Institute) ;
  • Ahn, S.B. (Korea Atomic Energy Research Institute)
  • Received : 2018.10.18
  • Accepted : 2018.12.03
  • Published : 2018.12.31
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Abstract

CRUD specimens, scraped from twice-burned fuel cladding in the Korean Nuclear Power Plant, were analyzed using Shielded-EPMA. The principal elements of the CRUD were identified as Ni and Fe, at an approximate ratio of 1.3 Ni/Fe. To investigate the morphology and composition of the pure metallic materials in the CRUD, coolant impurities must be removed. This can be accomplished by increasing the EPMA current to an abnormally high intensity until the impurities are melted. Normally, EPMA applications are performed at conditions of 20 kV voltage and 20 nA current. But in our study, the applied current was increased up to 1200 nA, over time increments ranging from 5 to 30 seconds. This technique was performed by opening an adjustable aperture for the gun alignment. Results showed impurities contained in the CRUD material disappeared and pure metal materials, e.g., Ni and Fe, remained. This method presents an innovative way to analyze CRUD.

Keywords

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Fig. 1 The scraper structure and working in the KNPP poolside.

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Fig. 2 Trail covered with pine leaves(a), CRUD collection filter(b) and optical photograph(c) (x350).

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Fig. 3 SEM and x-ray map of a CRUD flake. Applied to normal beam current injection.

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Fig. 4 Before abnormal high beam current injection (Beam condition: 20 kV, 20 nA).

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Fig. 5 EPMA monitor(a), Burning spot on monitor(b), CRUD flake before and after burning (c, d) and Close-up image of after burning CRUD (e, f). (Beam conditions: 20 kV, 1200 nA, Beam exposure time: 5 sec)

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Fig. 6 After burn, remained metallic CRUD precipitate no1~no 3 analyses (SEM x10,000).

Table 1. Chemical composition of CRUD flakes at area measured by EPMA normal analysis (at%)

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Table 2 CRUD Mass by ICP-MES Analysis, μg/filter (Oxygen Not Included)

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Table 3 After burning, remained metallic quantitative analyses. (Beam conditions: 20 kV, 20 nA)

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