Gamma scanning the primary circuit of the Peach Bottom HTGR

Conference · Sun Oct 31 04:00:00 EST 1976

OSTI ID:7231336

Hanson, D L; Baldwin, N L; Selph, W E

The plateout distribution of gamma-emitting nuclides in the primary circuit of the Peach Bottom HTGR at end-of-life has been determined by in situ gamma scanning. The specific activity was mapped by scanning the accessible ducting at 12 locations with a Ge(Li) detector and by axially traversing 79 steam generator tubes with travelling CdTe detectors from the water side. Following destructive removal of trepan samples, a travelling intrinsic germanium detector was inserted sequentially into two vertical ducts and the plateout mapped along 6-m runs of ducting. Calibration measurements on mockups allowed reduction of the spectra to specific activity. The measured plateout profiles were in excellent agreement with those predicted with the PAD code. The dominant gamma emitters were Cs-137 and Cs-134; their relative distributions were similar. Little local structure to the plateout in the ducts was observed, only a gradual decrease in specific activity in the direction of coolant flow. In the steam generator, a significant entrance effect was observed in the superheater section; the activity was highest where the inlet jet impinged and lowest at the ends of the bundle despite the presence of a flow baffle. The effect damped out with penetration into the bundle, and the axial profile was uniform at the economizer exit. When the axial profiles are averaged, the specific activity decreased monotonically across the tube bundle. Cesium deposition throughout the circuit was apparently mass transfer controlled with the exception of the hot duct where the accumulation was limited by the high temperatures. The superheater entrance effect probably resulted from the maldistribution of coolant flow. The profiles suggest that cesium was transported primarily in atomic form despite the presence of carbonaceous dust. Finally, the measured plateout distribution verifies the reference methodology used to make such predictions for large HTGR design.

• Research Organization: General Atomic Co., San Diego, CA (USA)
• OSTI ID: 7231336
• Report Number(s): GA-A-14161; CONF-761103-18
• Country of Publication: United States
• Language: English

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21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
210300* -- Power Reactors
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Graphite Moderated
ALKALI METAL ISOTOPES
BETA DECAY RADIOISOTOPES
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CESIUM 134
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COOLING SYSTEMS
DEPOSITION
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GAS COOLED REACTORS
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HOURS LIVING RADIOISOTOPES
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INTERNAL CONVERSION RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
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PEACH BOTTOM-1 REACTOR
POWER REACTORS
PRIMARY COOLANT CIRCUITS
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