Nuclear Power Plant I

Type of neutron detector Fission counter

Type of signal cable Single and double shielded coaxial

Location of pulse preamplifier At top of detector instrument well

Location of pulse amplifier In amplifier cabinet at control room

Distance between pulse amplifier and preamplifier 90 ft

Distance between neutron detector and preamplifier 24 ft

Method of grounding Multiple-point grounding system Both the preamplifier and the amplifier are grounded to the building ground at the point of their installation The signal-cable shield is grounded at the preamplifier and the amplifier The neutron detector is grounded through the signal-cable shield back at the preamplifier

Operating problems and modifications During the initial installation period and preoperational testing of the neutron-monitoring system, noise in the start-up channels was prohibitive Noise was reduced by replacing the RG-8/U single shield coaxial cable with RG-71/U double-shield coaxial cable Other noise problems caused by the operation of relays, motor starters, and switches were eliminated at the source xhe switches and motor starters for the fission-chamber carts were a source of noise causing large transients in the start-up channels Some problems were eliminated by installing filter capacitors across switches

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