Environmental Testing of a B4C-Ni Prototype Control Rod

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Summary: A prototype control rod containing absorber plates made from an electro- deposited dispersion of boron carbide in nickel was tested in the VBWR. It was exposed to the reactor environment of 545 degree F boiling water and thermal neutron fluxes (perturbed) which ranged from 0.6 to 1.1 x 10/sup 13/ nv for 2236 hours over a period of six months. The maximum B/sup 10/ burnup achieved during the test period was 1.8 percent. After irradiation, the rod was examined. The results of the examination are summarized below: (1) The B/sub 4/C-- Ni plate assembly did not undergo significant dimensional … continued below

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36 pages ; illustrations.

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Megerth, F. H. & Zimmerman, D. L. October 15, 1963.

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Summary: A prototype control rod containing absorber plates made from an electro- deposited dispersion of boron carbide in nickel was tested in the VBWR. It was exposed to the reactor environment of 545 degree F boiling water and thermal neutron fluxes (perturbed) which ranged from 0.6 to 1.1 x 10/sup 13/ nv for 2236 hours over a period of six months. The maximum B/sup 10/ burnup achieved during the test period was 1.8 percent. After irradiation, the rod was examined. The results of the examination are summarized below: (1) The B/sub 4/C-- Ni plate assembly did not undergo significant dimensional changes during irradiation. (2) Numerous blisters developed on both the outer and inner surfaces of three of the four plates. Blistering was more severe on the outer surface than on the inner, and was most severe in a large region located in the lower half of plate 4. Metallographic examination revealed that the blisters were located only in the 2- mil protective nickel overlay covering the B/sub 4/C-- Ni dispersion. It was concluded that they formed from the buildup of gas pressure at the Ni: Ni-- B/sub 4/C interfaces, rather than from corrosion attack. Helium from the B/sup 10/(n alpha )Li/sup 7/ reaction probably contributed to this pressure. However it is conjectured that the major gas was very likely hydrogen, possibly generated and dissolved in the nickel during electroplating and then released to defects at the Ni: Ni--B/sub 4/C interface during reactor exposure. The variation in the degree of blistering among the four plates of the prototype indicated that the blistering was related to variations in the fabrication process. Failure of the nickel overlay was not observed in any of the blisters examined metallographically, and the underlying B/sub 4/C-- Ni appeared to be in good condition. (3) Evidence of corrosion attack of the B/sub 4/C was observed in the form of white deposits on both the inner and outer surfaces of the plates. On the outer plates these deposits were concentrated primarily near regions where the B/sub 4/C--Ni layer was unprotected by the nickel coat, namely, screw hole locations. Metallographic examination revealed definite evidence of corrosion attack in the unprotected screw hole surfaces. (4) The deposition of white corrosion products was more extensive on the inner plate surfaces than on the outer surfaces. Corrosion attack of the nickel coat on an inner surface was observed in a region of close contact between the absorber plate and stainless steel support frame. Metallographic examination revealed that this attack was localized and extended through a maximum of 50% of the nickel coat thickness. Corrosion test coupons fabricated from plate material similar to that used in the control rod were also irradiated in the VBWR. Because of their location in a higher neutron flux region and longer exposure period (5000 hours) they reached a B/sup 10/ burnup of 12.2%. Post-irradiation examination of these specimens revealed no evidence of blistering in the nickel coat. The edges of the B/sub 4/ C-- Ni layers unprotected by the nickel coat suffered severe corrosion attack, and thickness increases up to 6% were detected. The corrosion attack and swelling were much more severe than that observed in an earlier group of specimens irradiated to 3% burnup. Direct visual examination revealed no attack of the nickel coat; however, metallographic examination revealed attack which penetrated up to two-thirds of the nickel's thickness.

Physical Description

36 pages ; illustrations.

Notes

Digitized from microopaque cards.

U.S. Atomic Energy Commission Contract AT(04-3)-189 Project Agreement 4.

Includes bibliographic references (page 4-28).

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  • Report No.: GEAP-4296
  • Grant Number: AT(04-3)-189 PA 4
  • SuDoc Number: Y 3.At 7:22/GEAP-4296
  • Accession or Local Control No: metadc1201362
  • Archival Resource Key: ark:/67531/metadc1201362

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Creation Date

  • October 15, 1963

Added to The UNT Digital Library

  • Aug. 15, 2019, 10:26 p.m.

Description Last Updated

  • May 26, 2021, 11:36 a.m.

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Megerth, F. H. & Zimmerman, D. L. Environmental Testing of a B4C-Ni Prototype Control Rod, report, October 15, 1963; San Jose, California.. (https://digital.library.unt.edu/ark:/67531/metadc1201362/: accessed June 21, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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