ML19224B190
| ML19224B190 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 02/25/1977 |
| From: | Metropolitan Edison Co |
| To: | Mullinix W NRC/IE |
| References | |
| 1708, TM-0115, TM-115, NUDOCS 7906140191 | |
| Download: ML19224B190 (5) | |
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DfI DOCUMENTS DOCUMENT NO:
COPY MADE ON OF DOCUMENT PROVIDED BY l
U i METROPOLITAN EDISON COMPA1W.
Wilda R. Mullinix, NRC T
790614019; I91 146
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Revision 2
s 1708 2
THP.EE f.11LE ISLAND NUCLE AR STATION STATION HEALTH PHYSICS PROCEDURE 1708
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PLATEAU DETERMINATION FOR-PCC-llT Table of Effective Pages Pace Date Revision.
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1708 Revision 2 02/25/77 THREE MILE ISLAND NUCLEAR STATION STATION HEALTH PHYSICS PROCEDURE d1708 Background Determination for Packard TRI - CARB 1.0 PURPOSE The purpose of this procedure is to list the steps taken to determine the operating voltage plateau for the PCC - llT, gas flow proportional counter.
The operating voltage for the proportional counter is determined from the voltage plateau.
2.0 DISCUSSION The internal proportional counter voltage curve is characterized by two plateaus. At the lower voltage plateau the instrument is responsive to alpha particle ionization. At the second plateau (higher voltage) the scaler counts pulses from both Alpha and Beta particles. A plateau determination normally is required at initial startup, after maintenance and when operating characteristics indicate.
NOTE:
Of) NOT exceed 2000 V at any time.
3.0 REFERENCES
3.1 PCC - IIT Tech Manual 3.2 ORTEC Manuals for the following instruments.
1.
Model 456 - High voltage supply 2.
Model 451 - Amplifier 3.
Model 719 - Timer 4.
Model 770 - Counter 4.0 EQUIPMENT I
4.1 Proportional Counter Converter Model PCC - IIT 4.2 Model 456 High Voltage Supply 4.3 Model 451 Spectroscopy Amplifier 4.4 Model 719 Timer f9l Jfg 1.0
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09/17/75 1768 Revision 1 4.5 Model 770 Counter 4.6 Alpha and Beta Standard Sources 4.7 90% Argon,10% Methane Counting Gas 5.3 OPERATIflG IflSTRUCTI0t1S - ALPHA NOTE:
Fully open the gas supply valve located on the wall behind the instrument.
Check for flow in the bubbler window.
If none is apparent, the gas cylinder may require replacement.
This instrument is used for Alpha and Beta counting, therefore, an efficiency for each plateau must be determined.
5.1 ALPHA PLATEAU 5.1.1 Turn ORTEC cabinet power supply on.
5.1.2 Turn on high voltage power supply.
5.1.3 Insure spectroscopy amplifier fine gain is at 5.80 and cour e gain is set at 5.
5.1.4 Insure that discriminator on 770 counter is set at 1.
5.1.5 Turn detector toggle switch to Oti.
Set timer to one (1) minute count as follows.
5.1.6 Insure Preset is set to one (1).
Insure Multiplier is set to 100.
Insure Time base is set to 0.01 min.
5.1.7 Depress RESET button on counter.
5.1.8 Turn drawer latch to left and pull out.
Insert Alpha Source in the planchet holder vith activity side up, in the appropriate counting geometry, close and latch drawer. Push Purge button.
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Purge light will light.
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i 5.1.9 After purge light goes off, Depress start button on timer, the interval light should light.
Completion of counting is indicated by the interval light going out.
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09/17/75 170S Revision 1 5.1.10 Start at about 800 volts and increase voltage until scaler begins to record counts.
5.1.11 Round off this voltage to the nearest 50 volts and record as the starting voltage.
5.1.12 Depress RESET and START buttons and take a one (1) minute count at this voltage and at 50 volt increments.
5.1.13 Prepare a sheet of semi-log graph paper by labeling the X axis (horizontal) in voltage increments and Y axis (vertical) in counts per minute increments.
5.1.14 Record and graph voltage and corresponding counts per minute at each increment before proceeding to next step.
5.1.15 The end of the ALPHA Plateau is indicated by a sharp rise in counts per minute for a normal voltage increase.
5.1.16 Replace the ALPHA source with a BETA Standard source and resume with step 5.1.7.
5.1.17 Determine the operating voltage setpoints from each plateau according to section 6 and record on the plateau curve, and the instrument for ALPHA and BETA determinations.
Put the Plateau curve in the Plateau Curve Log book.
6.0 OPERATING VOLTAGE SELECTION 6.1 Select from the Count Rate versus Voltage Curve the approximate beginning and ending point of the plateau (flat portion of the curve).
6.2 Take one third of the difference between voltages of Step 6.1 and add to the beginning voltage.
Round this figure to the nearest t
50 volts. Use this value as the operating voltage set point until another plateau detennination indicates a different voltage is best for optimum operation.
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