ML19224B393

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Health Physics Procedure 1753,Revision 1:operation & Calibr of PNR-4 Neutron Rem Counter
ML19224B393
Person / Time
Site: Crane Constellation icon.png
Issue date: 02/11/1977
From:
Metropolitan Edison Co
To: Mullinix W
NRC/IE
References
1753, TM-0131, TM-131, NUDOCS 7906150048
Download: ML19224B393 (11)
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DOCUMENT NO:

COPY MADE ON OF DOCUMENT PROVIDED BY

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METROPOLITAN EDISON COMPANY.

Wilda R. Mullinix, NRC

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02/11/77 THREE MILE ISLAND NUCLE AR STATION STATION HEALTH PHYSICS PROCEDURE 1753 OPERAT10!1 Af1D CAllBRAT10f1 0F PfiR-4 fiEUTR0fi REfi COU'JTER Table of Effective Pages Pace Date Revision Pag Date R evision Page Date_

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1753 Revision 1 02/11/77 T:iREE MILE ISLAND fiUCLEAR STATION STATION HEALTH PHYSICS PROCEDURE

~ Operation and Calibration of PNR-4 Neutron Rem Counter 1.0 PURPOSE

.4 The purpose of this procedure is to explain in deta!' the operation and calibration of the PNR-4 fieutron Rem Counter.

2.0 DISCUSSION 2.1 The PNR-4 Neutron Rem L ;unter is a portable, battery operated instrument for thc detection and measurement of the dose rate from the neutron rediation.

The instrument detector is a nine (9) inch tube in diameter, cadmium loaded, polyethylene sphere with a BF3 the center.

This detector has been shown to have a response which closely follows the theoretical dose from neutrons over the energy range of 0.025eV (thermal) to about 10 meV.

The BF u e allows 3

excellent gamma rejection.

2.2 The dose rate is read out by the Eberline Lin-Log presentation, which eliminates scale switching and multiplying factors, yet retains linear increments within each decade.

Four decades are covered using two meter movements to yield a scale length of about 1.5 inches per decade, which gives maximum readibility and ease of i

I interpretation.

Full scale readings of the four decades are 5, 50, 500 and 5,000 m rem /hr respectively.

The counter may be detached from the detector for remote mo'itoring or ease of carrying.

The counter electronics are mounted on three plug-in etched circuit boards for ease of maintenance.

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1753 Revision 1 02/11/77

3.0 REFERENCES

3.1 Eberline PNR-4 Neutron Rem Counter Tech Manual.

I 4.0 EQUIPMENT 4.1 Eberline PNR-4 Neutron Rem Counter.

,4 4.2 AmBe neutron source.

4.3 Eberline MP-1 Mini-Oulser.

' 4.4 Gamma source.

4.5 Electrostatic Voltmeter, 0-34V range.

5.0 OPERATING INSTRUCTIONS 5.1 External Controls and connectors (see Figure 1753-2).

5.1.1 Three position switch turns instrument to 0FF, ON or BATTERY check position.

A spring returns switch from BATTERY check position to the ON position.

5.1.2 "High Voltage Adjust" controls magnitude of high voltage applied to the detector.

Clockwise rotation increases voltage.

There are radial marks around control for reference.

5.1.3 A phone connection for headset, speaker or external scaler is provided.

5.1.4 A connector for a detector also is provided.

5.2 INTERNAL CONTROLS 5.2.1 Calbration controls; there are four controls to adjust meter reading to agree with neutron dose rate at the detector.

5.2.2 Sensitivity control; A 20 turn control adjusts the input sensitivity.

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1753 2/8/'/4 Revision 0 5.3 USING THE INSTRUMENT 5.3.1 Turn the switch to the battery check position. The left pointer (black) should read in the green area of the meter dial.

Release the switch and it will return to the ON positpon If the pointer reads below the green area of the meter dial, replace the batteries as described in Section IV. A.2 of the PNR-4 Tech Manual.

5.3.2 Reading the Lin-Log presentation is quite case.

Read the pointer that is on scale. The black pointer is read up to 50 mrem /hr. Above this value it disappears from view and the red pointer is read.

Tne fluctuation of the pointer is normal and is caused by the random nature of radioactive emission.

Watch the pointer long enough to obtain the average reading.

5.4 CALIBRATION 5.4.1 To completely set-up and calibrate the PNR-4, three steps are required plus an additional verification check with a neutron source.

5.4.2 Input Sensitivity: Remove the PNR-4 from its case and connect the MP-1 output to the spring connector.

(Junction of R8 & C2).

5.4.2.1 Set MP-1 CPM at 20K (20x1K) Counts per minute and Amplitude the 3 millivolt (mV) range.

5.4.2.2 Slowly turn the Amplitude Fine control upward until the PNR-4 meter responds and settles at a reading.

(Reading should be 400 mrem /hr., but this is not critical at this point).

5.4.2.3 Adjust the Amplitude Fine control down~ ward until the PNR-4 meter reads 1/2 of that reading above.

The MP-1 amplitude meter should read 2.0 + 0.5 m volts.

If outside of these limits, the sensitivity must be adjusted.

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1753 Revision 1 02/11/77 5.4.2.3.1 Adjust MP-1 Amplitude Fine Control for 2.0 m Volts and adjust the sensitivity (located on the AMP-DISC-BIflARY card, see Figure 2-2 in Tech Manual) for a PNR-4 meter readirig of approximately 1/2 of that reading obtained in 5.4.2.2 above.

J 5.4.3 Meter Calibration:

Connections same as 5.4.2 above.

Set MP-1 Amplitude at 3 mill 1 volts.

5.4.3.1 Turn R3 and R5 (located oi PNR-4 chassis; see Figure 2-1 and 2-2 in Tech Manual) maximum clockwise.

5.4.3.2 Set MP-1 at 200 CPM (20x10) and adjust R2 for a PNR-4 meter reading of 4 mrem /hr.

5.4.3.3 Set MP-1 at 2K CPM (20x100) and adjust R3 and PNR-4 meter reading of 40 mrem /hr.

5.4.3.4 Set MP-1 at 20K (20x1K) and adjust R4 for a PflR-4 meter reading of 400 mrem /hr.

5.4.3.5 Set MP-1 at 200K CPM (20x10K) and adjust R5 for a PNR-4 meter reading of 4K mPsem/hr.

I 5.4.3.6 Disconnect MP-1 and replace PNR-4 in its case.

I 5.4.4 High Voltage 60 5.4.4.1 Expose the detector assembly to a gama field (either Co or 17 Cs) of approximately 10 R/hr and adjust the HV ADJUST control until the meter reads approximately 1 mrem /hr.

NOTE:

The high voltage is slow coming down.

If a downward adjustment was made, turn the instrument off for about 1 minute, then back on and verify setting.

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1753 Revision 1 02/11/77 5.4.4.2 Remove the instrument from its case and measure the high voltage on the spring connector with an electrostatic voltmeter.

Adjust the HV ADJUST control for a high voltage 50 volts less than that measured.

Turn the instrument off until the voltage

.4 drops significantly, then back on and verify setting.

5.4.5 Neatron Test:

Expose the detector assembly to a known fast neutron field and read the meter.

The reading should agree with the field within n + 20%.

5.4.6 cal.IBRATION WITH THE NEUTRON SOURCE 5.4.6.1 A Ambe neutron source will be used to calibrate the PNR-4 neutron Rem counter.

5.4.6.2 The Ambe source will be set on a table surrounded by poly bricks for shielidng per HPP-1633.

5.4.6.3 There are graduated marks on the entire length of the calibration tables to measure the distance from the source to the instrument.

These graduated marks are in centimeters.

5.4.6.4 The PNR-4 neutron Rem counter has four decades and should be calibrated on all four decades.

5.4.7 To calibrate with the neutron source follow the procedure ~

below.

5.4.7.1 Turn R3 and R5 maximum clockwise.

S.4.7.2 Place instrument in 4 mrem /hr field and adjust R2 to ebtain a 4 mrem /hr reading.

5.4.7.3 Place instrument in 40 mrem /hr field and adjust R3 to obtain a 40 mrem /hr reading.

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02/11/77 Place instrument in 400 m/ Rem /hr field and adjust R4 to obtain 5.4.7.5 a for 400 mrem /hr reading.

Place instrument in 4000 mrem /hr field and adjust R5 to obtain 5.4.7.6 4

a 4000 mrem /hr reading.

The formula to calculate the strength of the AmBe source at 5.4.8 varying distances from the source to the instrument is as follows:

p_xJQj,=N/CM/SEC 4n d 9

_N /_C_M.~_/.S E Cx 2.5 = mrem /hr 7

55N/CM /SEC c = neutron flux of AmBe source 1.21x10 N/SEC/Ci Ci = number of curies AmBe source containas 4.59 curies 4 = constant n = 3.1416 d = distance from scurce to instrument in centimeters, squared.

55 - average N/CM /SEC of fast neutrons being emitted from AmBe source 2.5 = average dose equivalent in mrem /hr.

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1753 Revision 1 02/11/77 Example:

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(4)(3.1416)(10) 8 2

5_._S 5_3 9_x 0 = 4.42x10 N/CM /SEC 1.26x10 4.42x10 _N/CM /SEC x 2.5 = 2008.9 mrem /hr 55 N/CM /SEC 5.4.8.1 The formula used to calculate the distance to place the instrument from the source, if the dose rate is know, is:

mrem /hr x 55 N/CM /SEC = N/CM /SEC 2.5 c_x Ci

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(N/CM /SEC)

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) (N/CM /SEC)

Example:

4 mrem /hr x 55 N/CM /SEC = 88 N/CM /SEC 2 5 mrem /lir.

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(4)(3.1416)(88 N/CM /SEC 7

5.55x10 = 224.1 CM I

1.11x10 5.4.9 Using the formula given in 5.4.8.1 the distances for the three remaining decades are:

70.9 Cf1 for 40 Mrem /hr.

22.4 CM for 400 Mrem /hr.

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1753 2/8/74 Revision 0

  • 7.1 CM for 4000 Mrem /hr.
  • The distance from the detector tube to the outside of the sphere is 11.43 CM so the contact reading should be 1537.7 mrem /hr.

,4 5.4.10 Calibration adjustments are as follows:

(refer to Figure 1753-1).

5.4.11 Section 1 and 2 of the driver combine to deflect meter one, and Section 3 and 4 to deflect meter two.

The calibration 6

controls adjust this combination for the proper meter reading Vs input count rate.

Each pair of sections and meter is completely independent of the other.

5.4.12 The first control (R2 and R4 respectively) adjusts the slope of the meter current Vs frequency line for both sections.

The second control (R3 and R5 respectively) adjusts the point where the lower frequency sections saturates.

This saturation forms a stable base upon which higher frequency section operates.

5.4.13 Record on form 1749-1 each calibration and attach calibration sticker with date and intiials.

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