TA - Model HWLD-77 -Heavy Water Leak Detector

• Model -77 - Heavy Water Leak Detector
• Low level real time tritium-in-water monitor
• Sensitivity of 1.0 kBq per liter in 3 minutes
• 3.7kBq/L detectable in 20 Seconds

HWLD Monitors – Recent improvements and upgrades

• Full on-board computing system for data analysis.
• New Microflow system has 3 major benefits
• Factor of 10 less use of scintillation fluor
• Allows long sample counting for outstanding low end sensitivity.
• While still maintaining constant flow resulting in zero dead time, so even short-duration, high-concentration tritium spikes will still be detected.
• Statistical significance lamp lets user know if measurement level exceeds MDA levels.
• All data is automatically logged and archived allowing later study.
• Full ethernet compatibility and SCADA ready communications.

This monitor was originally designed for real time low-level detection of tritium in water in the industrial environment of nuclear power plants and has now been updated and adapted for environmental and scientific applications.

Low MDA, reliability, ruggedness and simplicity of operation is what sets this monitor apart from less durable laboratory type of the equipment.

The primary purpose of the Model 1925 was to detect the leak of heavy water in nuclear power plants that utilize CANDU reactors; however, the MODEL – 77 has been redesigned, upgraded and is used for other purposes such as monitoring changes in tritium content of ground water, rivers, lakes or ocean currents.

Low Minimum Detectable Activity (MDA)
The unit detects tritium decay with Photo Multiplier Tubes (PMT) working in coincidence mode. Use of highly effective PMTs, specially designed sampling cell to minimize cosmic radiation and Cherenkov effects and 1" lead shielding provide for low background noise of only One Count Per Second and sample counting efficiency of 40%.

Fast Response Time
The response time from the moment when sample enters the system to the moment the unit starts to respond is less than 20 seconds and in 3.0 minutes the full value of tritium concentration in the sample is displayed on the screen. New Microdrive sampling system and advanced data analysis allow detection to lower limits from 20 seconds to 30 days period.

Remote Monitoring and Alarming
The instrument is equipped with USB, Ethernet and 4-20mA output for remote monitoring as well as with 2 alarm outputs and malfunction outputs in the form of dry, fail-safe, relay contacts. Alarms are user adjustable. Malfunction alarms activate in case of the electronics and/or mechanical failures in the system.

Data Recording
The instrument is equipped with Serial Data Recorder that utilizes Microdrive card to store up to five years worth of readings in daily files. This information is in text format that is easily extractable to Excel for analysis and graphic presentation.

Pressure Regulating Equipment
In applications where sample inlet line is under pressure as when measuring H-3 in drinking water pressure of input sample streams can be up to 15psi. This pressure is immediately reduced to 2- 3psi via Pressure Regulating Valves (PRV). Each PRV is associated with Pressure Relieve Valve set to open at 14.5psi, therefore, the pressure in the system can never be more than 14.5psi, which makes it safe to handle. This also makes the instrument a Class 6 Nuclear Device.

Fully Integrated Package
Model -77 is a completely self-contained instrument for real time observation of tritium concentration in water. The instrument is mounted inside of the 7` tall steel enclosure with reinforced anchoring feet and locked access. Liquid scintillator is connected to the unit externally and it is stored inside of the polyurethane drum of 65 gallons. Currently this quantity of liquid scintillator is sufficient for 2 years of continuous, 24/7 operation.

The main subassemblies are:

1. Sample water input lines
2. External cooling loop input/output lines
3. Internal cooling loop complete with chiller, chiller pump and plumbing
4. Water purification system and micron filter
5. Sample water pump
6. Detection module
7. Data acquisition and analysis electronics module
8. System control module
9. Waste water output line, RV output line and sample bypass output lines.

Cooling System
In order to have maximum efficiency of the photo-multiplier tubes and the liquid scintillator, solution that is tested inside of the sample cell is kept between 12°C and 20°C. This is achieved by internal cooling loop system, which is a closed loop cooling system with its own pump and chiller unit. If the unit operates in extreme temperatures (more than 45°C) external cooling loop is provided, where user can provide chilled water from its own source.

PLC Control
Sampling of input lines and control of alarms and pumps is done by PLC unit placed inside of the System Control Module. There is an alarm provided in case of PLC failure as well as manual override so that the operation can be continued manually until PLC is replaced. Manual operation is a backup sys-tem; the unit normally operates in automatic mode.

Routine Maintenance
Scheduled maintenance of consumables is required. Liquid scintillator needs to be replenished every 2 years and sample water filters need to be re-placed. Also, periodic check of the efficiency and background is recommended if there is a possibility of increased background contamination and due to standard lifecycle of electronics components.

Annual Inspection and Service
It is recommended that the instrument be inspected and serviced on an annual basis to ensure continuing trouble free operation. All components of the instrument should be inspected and instrument re-calibrated.

Repair
Equipment failures of a minor nature can be repaired under local supervision by the operator of the equipment. When necessary, the manufacturer (Overhoff Technology Corporation (OTC)) can dispatch service personnel for quick remediate action.

Documentation
All OTC equipment is accompanied by complete documentation, which includes the following:
1. User and Maintenance Manual that contains:

• a. Theory of operation
• b. Installation instructions
• c. Operation instructions
• d. Calibration procedure
• e. Suggested maintenance
• f. Repair instructions
• g. Drawings, diagrams and schematics

Factory training will be provided by the manufacturer, free of charge. Assistance with commissioning is also available by the manufacturer (OTC) on-site for a reasonable fee.

Electronics and Measurement:

• Measurement Range: 0 -- 130kBq/L
• Sensitivity: See Chart
• Detectable Limit: 20Bq/L (in 7 days) at confidence level of 95%
• Display: 7” Color LCD monitor
• Response Rate: 20 seconds beginning of the response,
• 3.0 minutes full value displayed
• Measurement Method: Liquid Scintillation Counting
• Detector: Dual PMT coincidence counter surrounded by multi-element shielding
• Signal Processing: Electronic signal processing of coincident pulses for tritium specific wave shapes (height and duration)
• Measurement Alarm
• Set Point: Can be manually adjusted
• Data Recording: Serial Data Recorded with Microdrive card

Sampling System:

• Sampling/Mixing System: Dual head, single shaft low flow rate pump providing flow of sample and liquid scintillator.
• Mixing is done at the T-joint and at the entrance on the sample cell.
• Sample Cell: Waste:Stainless steel cell, volume 5cc with fused silica windows and Viton O-rings for sealing.
• Management: Waste water output lines with Swagelok® fittings are pro-vided, user to provide waste collection system. Nominal 80 gallons/year.

Environmental:

• Temperature: Oo C to 50o C
• Humidity: 0 to 95 % R. H.
• Seismic: Withstands modest shock
• General: Equipment to be sheltered from exposure to raw elements.
• Electrical: Power 110/230VAC, 5A main power, +24VDC for 4-20mA and connections for the remote alarms and monitoring
• Mechanical: Self contained, mounted on a steel frame with lifting eyes for easy transport.
• Dimensions: 31.5in x 23.6in x 84.0in (800mm x 600mm x 2133mm)
• Weight: 1100 lb (~500 kg)