Overhoff TRIATHALON-H3 Manuale utente

TRITIUM MONITOR

TRIATHALON-H3

with optional Totalizer

OPERATION AND MAINTENANCE MANUAL

Revision 0

DATE: 20-Aug-2014

Generic Version

OVERHOFF TECHNOLOGY CORPORATION

1160 US ROUTE 50, MILFORD, OHIO, USA

TABLE OF CONTENTS

Section I. Introduction Page

1 General Description 2

2 Physical Description 2

3 Features 3

4 Performance Specifications 4

5 Principle of Ion Chamber Measurments 6

Figure – Front View 9

Figure – Block Diagram 10

Figure – Customer Connections 11

Section II. Installation

1 General 12

Figure – Installation Diagram 13

2 Equipment Checklist 14

3 Storing, Handling, Unpacking 14

4 Assembly 15

5 Maintenance 16

Section III. Drawings and Schematics 17

Enclosure General Layout, Exterior 18

Enclosure General Layout, Interior 19

Pneumatic Diagram 20

Section IV. Operation 21

1 Startup 22

2 Shutdown 22

3 Main Screen 23

4 About Screen 25

5 Setup Screen 26

6 Datalogging 32

7 Software Upgrade Procedure 33

8 Network Addressing 34

9 4-20 mA Connection (optional) 34

1.0. GENERAL DESCRIPTION

This tritium monitor consists of dual 2-liter ionization chambers with an integral

electrometer coupled to the electronic circuits for display and control inside one fiberglass

reinforced plastic molded enclosure suitable for wall mounting.

One ionization chamber, referred to as the measurement or upstream chamber,

measures in a positive manner. The second ionization chamber, referred to as the

compensation or downstream chamber, is identically constructed but subtracts from the

measurement of the upstream chamber. This is how dual chambers serve to cancel the

effects of external gamma fields and provide differential measurements.

Ionization chambers respond not only to the airborne radioisotope, which circulates

through the ionization chamber, but also respond to the presence of external high-energy

radiation capable of ionizing the air inside. Therefore, ionization chambers will respond

to X-rays and gamma radiation as well. Additional gamma radiation suppression can be

accomplished by using lead shielding. The electrometer serves to transform this current

into a form and magnitude suitable for display, alarm, and external uses, as the ionization

current itself is very weak.

The monitor contains all signal processing, alarm and external interface circuits, read out,

and all required power supplies. The signal processing circuits serve to reject unwanted

signals and to translate the electrometer signal voltage into a form and magnitude

suitable for display, alarm and external uses as well.

The alarm circuits provide a visual signal and relay outputs for remote connection to

denote that a preset level of measurement has been exceeded or certain malfunctions.

2.0. PHYSICAL DESCRIPTION

The Model Triathalon-H3 is a single range, ionization chamber monitor for the measurement

of tritium in a NEMA 4X enclosure suitable for permanent installation and for continuous duty.

The enclosure has a hinged door with a polycarbonate window. Behind the hinged door is a

front panel that is hinged so that it can be opened for servicing the various components

inside. The sample inlet and exhaust fittings are located on the left side of the enclosure.

Fittings for Tritium and Total Tritium measurement are located on the right side of the

enclosure. Wiring conduit connections are provided on the bottom of the enclosure and

consist of AC power conduit and control wiring conduit.

The following are located on the front panel:

Fuse holder, main power switch, ‘ON’ and ‘OFF’ indicators.

An LCD color touch screen serves the majority of control and display functions. These

include the tritium measurement, alarm set points and indication.

A 0-10 LPM adjustable flowmeter to indicate and control the sample flow.

The following are attached to the enclosure subpanel inside the enclosure:

Dual 2 liter ionization chamber;

Sample pump, differential pressure switch used for sensing a low flow condition, and all

DIN rail mounted electrical connections.

The following are located on the outer left side of the enclosure:

Stainless steel tubing connections for sample inlet and exhaust

HEPA filter for downstream sample stream.

The following are located on the outer right side of the enclosure:

Hose connections for a desiccant column used for noble gas compensation mode

HEPA filter for downstream sample stream.

3.0. FEATURES

While the basic purpose of the Overhoff Model Tiathalon-H3 tritium monitor is to measure

the presence and level of tritium (HTO and HTO+HT), this particular instrument,

described herein, has these special features.

1. Tritium Monitoring measurement range over four plus decades, using dual ionization

chambers with a nominal volumes of 2 liters each.

2. One ionization chamber (measurement or upstream) serves to collect the current

produced as tritium decays radioactively. The second ionization chamber

(downstream or compensation) is identically constructed, but subtracts from the

measurement of the upstream chamber. Overhoff tritium monitors are equipped with

special circuitry to identify and reject ionization currents that are produced by

decaying radon, or other airborne alpha emitting radioisotopes.

3. There is an internal pump system for sample transport through the ionization

chamber.

4. The Model Tiathalon-H3 consisting of the tritium monitor and the pump system as

described above provides all data and performs all local control functions.

4.0. PERFORMANCE SPECIFICATIONS

The following specifications will apply when this is used for the measurement of tritium:

4.1. MEASUREMENT

Range 1 – 19999 μCi/m3

Display LCD color touch screen

Accuracy ±5 % of reading, ±L.S.D., whichever is greater

Stability and Drift ±1μCi/m3long term (thirty days), ambient temperature conditions

Noise ±1μCi/m3, 1 sigma, with alpha suppression in use

Response Rate two linear electronic time constants

approximately 20 seconds for signals up to about 80 μCi/m3

approximately 3 seconds for signals above 80 μCi/m3

Gamma A second ionization chamber of equal volume, mounted on the

Compensation same axis, serves to cancel effects of external gamma fields

Offset Compensation: Manual compensation control provided to offset the effects of

gamma radiation and/or tritium build-up

Over Range Indication The LCD screen will flash when the measurement has exceeded

19999 μCi/m3

Warm Up Time: less than five minutes

4.2. ALARM SYSTEMS

Tritium Level There are two Tritium Level Alarms, the indicator on the LCD is

normally green and the message displayed is “Tritium Level OK”.

Alert Level Tritium Alert Level Alarm preset from 1 – 1000 μCi/m3. Upon a

Tritium Level Alarm the indicator on the LCD will turn yellow and

display “ALERT LEVEL ALARM”.

High Level Tritium Level Alarm preset from 10 – 10000 μCi/m3. Upon a

Tritium Level Alarm the indicator on the LCD will turn red and

display “HIGH TRITIUM LEVEL”.

Mode Default mode for level alarms is non-latching, Enter SET-UP to

select either latching or non-latching modes.

Malfunction Two conditions initiate a MALFUNCTION ALARM

1. Power Supply Fault; Upon any failure of the low voltage power

supplies, the LCD will turn red and display “POWER SUPPLY

FAULT LV. Upon any failure of the high voltage bias supplies,

the LCD will turn red and display “POWER SUPPLY FAULT HV.

2. Sample flow; upon a low flow condition, the LCD will turn red

and display “LOW FLOW”.

Relay closure Relays for all alarms operate in the failsafe mode

4.3. IONIZATION CHAMBER

VOLUME measuring: 1,600 cm3

total wetted: 2,000 cm3

ELECTRODES Solid wall on both sides

GASKETS silicone rubber

PRESSURE 0.1 to 2 atmospheres

PORTS 3/16’’ I.D. Vinyl Tubing

MATERIALS OF all wetted surfaces, stainless steel

CONSTRUCTION

4.4. EXTERNAL SAMPLE 3/8’’ O.D. Stainless Steel Swagelok Fittings

CONNECTIONS

4.5. FLOWMETER 0-10 LPM adjustable rotameter

4.6. DUST AND high efficiency 99.99% at 0.1 microns cartridge type

ELECTROSTATIC Solberg Manufacturing Product No. HE04

FILTER

4.7. PUMP long life continuous duty linear motor driven diaphragm

type, Medo Model VCO201E1

4.8. ENVIRONMENTAL storage: -30°C to +50°C

TEMPERATURE operating: 5°C to +50°C

HUMIDITY 0 to 95 % R.H.

4.9. REMOTE INTERFACE refer to Figure 3, Customer Connections

SCREW TERMINALS high and low analog outputs

CONNECTIONS alarm relay outputs

4.10. POWER 115 VAC, 50/60 Hz, 5A, single phase

4.11. PHYSICAL

ENCLOSURE Molded fiberglass with polycarbonate window on a

hinged door. Color: light gray, NEMA 4X, IP66

DIMENSIONS 16.2’’ Wide x 20.3’’ High x 9.19’’ deep

[41.2cm Wide x 51.5cm High x 23.4cm deep]

WEIGHT 43 lbs [19.6 kg]

5.0. PRINCIPLE OF IONIZATION CHAMBER MEASUREMENTS

A tritium monitor is an instrument using flow through ionization chambers designed to

determine the presence and level of radioactive gas (tritium) in air or other gas streams.

These monitors may be used to detect radioactive gases in many applications like:

room air

stacks, hoods, or other effluent passages

process piping

glove boxes, and similar

These monitors are generally calibrated in terms of (micro) Curies per cubic meter though

other units can be used as requested (Bequerel, pCi/cm3, etc.).

The principle of measurement is based on collecting the current that is generated by the

radioactive decay (of tritium) inside an ionization chamber. The ionization current is

proportional to the total activity of the radionuclide (tritium) being detected.

A tritium monitor consists of the following parts:

1. An ionization chamber to collect the ionization current.

2. A sampling system to circulate the sample (air) through the ionization chamber.

3. An electrometer to amplify the very weak ionization current.

4. All other associated electronics to process and display the signal.

Ionization chambers respond not only to the airborne radioisotope, which circulates

through the ionization chamber, but also respond to the presence of external high energy

radiation capable of ionizing the air inside. Therefore, ionization chambers will respond

to X-rays and gamma radiation as well.

To overcome this effect, Overhoff Technology Corporation (Overhoff) tritium monitors are

sometimes supplied with compensating ionization chambers. Here a second ionization

chamber is used to cancel the effects of external radiation. Overhoff tritium monitors are

equipped with special circuitry to identify and reject ionization currents that are produced

by decaying radon, or other airborne alpha emitting radioisotopes.

5.1. CONTAMINATION, PLATE OUT OF HTO

When measuring significant levels of tritium for any but very short periods of time, the

walls of the ionization chambers will become coated with a thin layer of tritium oxide.

This leads to a background signal, where value may vary with time and is larger than the

minimum desired signal level.

5.2. DUST FILTERS

Dust filters must always be included in the sample flow stream upstream of the ionization

chamber. Accretion of dust, in even the slightest amount, results in erratic and noisy

instrument behavior. If accumulation of dust and dirt in the ionization chamber is allowed

to continue, the chamber will ultimately have to be disassembled and cleaned out. An

arcing due to dirt build up can also destroy the sensitive electrometer circuit.

5.3. RESPONSE OF IONIZATION CHAMBERS TO RADIATION

The current generated in an ionization chamber is the result of collecting electrons

generated from ionization of gas caused by occurrence of a nuclear event in the gas

inside.

The number of ions (magnitude of the current) is influenced by numerous factors like

energy, physical nature and particle range. As a good rule of thumb for beta particles in

air, one secondary electron (and one positive ion) is formed for every 34 electron volts of

energy lost by the primary beta particle as it travels its path.

The Curie is defined as 3.71 x 1010 nuclear decay events per second. The mean energy

of tritium decay is 5.69 kev. Therefore it is calculated that 1 Curie of tritium produces an

ion current very close to

1 x 10-6 amperes.

A concentration of 1 μCi/m3of tritium in a chamber of a volume of 1 liter will thus produce

a current of

1 x 10-15 amperes.

It must be remembered that the ionization chamber responds to the quantity of tritium

present inside. This is to say that effects due to temperature and pressure may,

depending upon the circumstances of measurement, need to be accounted for. Even if a

sample of gas is known to contain tritium at a certain concentration, i.e., parts per million

or other, it must be remembered that the activity, i.e., amount per unit volume, is

nevertheless dependent upon temperature and pressure. The ionization chamber only

responds to the quantity of radioactivity inside.

Ionization chambers also exhibit several other peculiarities. The wall effect can be a

problem if the track length of the decaying particle is appreciable when compared to the

dimensions of the chamber.

For ionization chambers with small linear dimension, and if the track of ionized particles is

comparatively long (the mean free path), an appreciable part of the energy of the primary

particle is simply dissipated in the wall of the ionization chamber. This effect increases

as the chamber dimensions shrink, and decreases as the chamber dimensions increase.

In air, atmospheric pressure, the maximum mean free path of a tritium beta particle is of

the order of five millimeters, and for chambers with linear dimensions of ten centimeters

or greater this “wall” effect becomes negligible.

At high concentrations, another effect takes place.

When the ion population density is high, some of these positive and negative ions will

recombine and are lost to the measurement electrode.

This is known as saturation or as stagnation since the effect is more pronounced in

corners of the ionization chamber where the potential field gradient is low. Increasing the

ionization chamber voltage can reduce the effect.

For measurements of tritium at very high concentrations, such as are required when

working with pure T2, special chamber geometry is employed. Long slender ionization

chambers, with relatively large internal ion collecting electrodes and short spacing

between the chamber elements will enhance field gradients. With even moderate

polarization potentials of 100 V or so, such chamber geometry shows linear response

even to pure tritium streams.

5.4. DISCRIMINATION AGAINST ALPHA PULSES

Since the energy of an alpha decay is at least 10,000 times more active than that of a

tritium beta event, suppression of alpha pulses needed in order to distinguish the

presence of tritium at low levels. Stable and accurate measurements of tritium for values

below 50 μCi/m3can only be obtained with means to suppress response to alpha decay.

Alpha decay events, as detected in an ionization chamber, are not instantaneous. The

special circuitry, which recognizes the alpha pulses, requires some amount of time to

suppress the event. During pulse suppression, the instrument analog circuitry is placed

in a “holding” mode; response is frozen during the interval associated with the alpha

event. The holding intervals occur at random, but effectively add to the apparent time

constant of the electronics. The instrument response becomes slower with increasing

radon or gamma noise background. For large background the instrument will even

freeze completely, the alpha pulse light will be permanently illuminated.

5.5. TECHNICAL SPECIFICATIONS

The proposed instrument will be designed and constructed for your particular application.

It will be built and tested to these specifications.

Circuit diagrams and interconnections between parts of the monitor, as well as those

leading to user selected remote devices or interfaces, will be provided with the

maintenance manual.

Consult the factory for further information, or for application engineering at

1160 US Route 50, P.O. Box 182

Milford, OH 45150-9705, USA

Telephone (513) 248-2400

Facsimile (513) 248-2402

Email: [email protected]

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