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Daya Bay RPC Gas Safety System - Gas Cabinet Test Report

Changguo Lu, Kirk McDonald

Princeton University

(October 11, 2009)

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Isobutane Gas Cabinet

The Uniform Fire Code requires 150-200 linear ft/min of air through the window opening.

Fresh air in

ventilation duct

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Test Setup

Fan to suck the air out

6” ID PVC pipe, 5’ long

Pitot tube, high pressure port

Pitot tube, low pressure port

Digihelic pressure gauge

The air flow velocity in the gas exhaust pipe is measured by a Pitot tube, and readout by a Digihelic differential pressure controller.

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Air Velocity Sensor and Controller

A Dwyer model 160-8 Pitot tube is used in our system. Pt is the total pressure, Ps is the static pressure. Notice the sensing holes for these two pressures. The Digihelic shown on the left can measure the pressure difference between Pt and Ps, this is Pv, the air velocity pressure.

Working principle: Pitot tube to measure the air velocity.

Dwyer model Digihelic DH002 differential pressure controller

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Converting curve between pressure and air velocity

The red line region is the required air velocity range in the 6” exhaust pipe.

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Test results

A 4W fan is used in this test. The reading on Digihelic gage fluctuated between 0.064” and 0.088” water; the average differential pressure was ~ 0.07” water, which fell into the red line region mentioned in previous slide.

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Isobutane sensor (HAD)

Inside of the gas cabinet one RKI LEL sensor/transmitter (model #65-2400RK) is installed near the bottom of the cabinet. It is used to detect the leakage of Isobutane. The full range is 100% of LEL (Low Explosive Limit) Isobutane in air. When the detected Isobutane level is above 10% of the LEL, the alarm LED on the gas status crate will turn on, it also shuts off the solenoid valve on the isobutane cylinder switchover panel.

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Calibration of HAD sensor

The output of the HAD sensor is 4–20 mA corresponding to the LEL from 0% to 100%. We use a Simpson controller to monitor this signal, and to convert it to 0 – 5V DC voltage signal which is sent to slow-control system.

A calibration gas cylinder with 34L 50% of LEL Isobutane/air is used to calibrate this HAD sensor (the calibration kit is RKI model #81-F016RK). For this, we attached a calibration cup to the HAD sensor, connected a gas tube to the calibration gas cylinder, opened the valve, and the HAD sensor/transmitter output was 12 mA DC current, which corresponds to 50% LEL.

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Explosion proof digital scale

The scale used inside of the gas cabinet is an explosion proof scale. There is no electric parts used in the scale platform, which is inside of the gas cabinet. Its digital readout is mounted outside of the gas cabinet.