EFFECT OF NEUTRON EXPOSURE (nvt)

Tests were conducted at the General Electric Test Reactor (GETR) to determine the effects of nvt on the pulse height spectrum of an in-core detector. Detector assembly No. 2 was used for these tests. During the data-taking periods before and after high flux irradiation, the detector

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assembly was in a neutron flux of approximately 8 x 10 nv and a gamma flux of 4. 3 x 10 R/h.

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The peak flux during irradiation was about 8 x 10 nv. The detector assembly was in this flux

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for a period of 29 days, which resulted in an integrated exposure of 2 x 10 nvt. Compared in Figures 4-11 and 4-12 are the pulse height spectrums before and after the irradiation period.

No conclusions regarding changes in sensitivity can be drawn from this data since the exact values of neutron and gamma fluxes were not known. However, it appears that the high integrated flux had little effect on the pulse height spectrum.

POLARIZING POTENTIAL = 400V TEMPERATURE s 75°F COUNTING TIME = 10 MINUTES

 

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Figure 4-11. Neutron Differential Pulse Height Spectrum Before High nvt Exposure

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Figare 4-12. Neutron Differential Pulse Height Spectrum After Exposure to 2 x 10 ‘nvt

 

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The irradiation did cause a change in breakdown voltage from 850 V to about 400 V, but since a short portion of the in-core cable was also in the high flux region during the tests it is difficult to state accurately whether or not the breakdown actually occurred in the chamber or in the cable of the in-core detector assembly. .

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SECTION V