ML20054H166

Forwards Addl Info Re RCPB Leakage Detector,Per 820317 Request & LACBWR Primary Piping & Reactor Vessel Leak Detection Sys Performance

ML20054H166
Person / Time
Site:	La Crosse File:Dairyland Power Cooperative icon.png
Issue date:	06/14/1982
From:	Linder F DAIRYLAND POWER COOPERATIVE
To:	Crutchfield D Office of Nuclear Reactor Regulation
Shared Package
ML20042C714	List: ML20042C712 ML20054H166
References
TASK-05-05, TASK-5-5, TASK-RR LAC-8346, NUDOCS 8206230058
Download: ML20054H166 (18)

Text

,- -

DlDA/RYLAND h

[k COOPERAT/VE

• PO BOX 817

• 261s EAST AV SOUTH

• LA CROSSE. WISCONSIN 54601 (608) 788 4 000 June 14, 1982 In reply, please refer to LAC-8346 DOCKET N0. 50-409 Director of Nuclear Reactor Regulation ATTN: Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch #5 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.

20555

SUBJECT:

DA!RYLAND POWER COOPERATIVE LA CROSSE BOILING WATER REACTOR (LACBWR)

PROVISIONAL OPERATING LICENSE N0. DPR-45 SEP TOPIC V-5, REACTOR COOLANT PRESSURE BOUNDARY LEAKAGE DETECTION

REFERENCE:

(1) NRC Letter, Crutchfield to Linder, dated March 17, 1982 Gentlemen:

Reference (1) requested LACBWR to supply certain infonnation that was missing in the evaluation of subject. Also to inform you within 30 days if LACBWR, as built, differs fran that assumed in the evaluation.

Enclosed is the missing information and certain other information describing LACBWR as-built condition.

Also enclosed, for your information, is Technical Report DPC-851-21, "LACBWR Primary Piping and Reactor Vessel Leak Detection System Performance."

Very truly yours, DAIRYLAND POWER COOPERATIVE AM

< kcn Frank Linder General Manager FL: HAT:eme O

Enclosures cc:

J. G. Keppler, Regional Administrator, NRC Region Ill NRC Resident inspector

' 8206230050 820614 PDR ADOCK 05000409 P

PDR WP-1

-.~

LA CROSSE BOILING WATER REACTOR SYSTEMATIC EVALUATION PROGRAM SAFETY EVALUATION REPORT TOPIC V-5 REACTOR COOLANT PRESSURE BOUNDARY LEAKAGE DETECTOR The following is additional information addressing the individual concerns of Reference 1.

Based on your review of Topic V-5, you have determined:

(1) The systema employed for the detection of leakage from the reactor coolant pressure boundary to the containment do not meet the recommendations of Regulatory Guide 1.45.

Specifically, all of the recommended types of detection systems are not employed and for those systema employed, the ayatem eensitivity, selenic qualification, indication and testing specificatione do not meet the recommendations of the Guide.

All leakage in the form of water in the containment is collected in a single retention tank, also, all the water from air conditioning units drains, surge tank overflows, pump shaf t seals, FESW over flow, systems drainage, and any water used in decontamination of floors, pipe surfaces and components goes to tnis same retention tank.

The accumulation of water in the retention tank is recorded every four hours and the leakage rate to containment is calculated at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Generally, the total accumulation of water in containment is at a rate less l

than the Technical Specification limit of unidentified leakage.

If the total leak rate to retention tank approaches the unidentified leakage rate limit, then known (identified) sources of water are measured and a search for unidentified leakage is initiated.

This method of collecting leakage, calculating leak rate and, if necessary, measuring identified leak sources is in accordance with the first method recommended by Regulatory Guide 1.45.

The second type of leak detection recommended by Regulatory Guide 1.45 is Airborne Particulate Radioactivity Monitoring. LACBWR has an airborne particulate monitor in operation on the air exhausted from the lower reactor cavity for 20 out of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> a day.

It is used on the upper reactor cavity for the other four hours. Another airborne particulate monitor is continuously in operation on the air exhausted from the two forced circulation pump cubicles. The exhaust air from the reciruclation pump cubicles is routed through HEPA filters, and is exhausted from the Containment Building. Each of these monitors output is displayed on a strip chart recorder in the control room. Activity is logged every hour and a rate of activity increase is determined at that time.

If the activity has inexplicably increased on either monitor, then the leak rate is calculated, and in any case, at least once a day.

WP-1 1

One of the third types of leak detection recommended by Regulatory Guide 1.45 is Airborne Gaseous Radioactivity Monitoring. Neither the Reactor Cavity Monitor, nor the FCP cubicle monitor have gaseous activity monitoring capability, but there is a third monitor that measures both the particulate and gaseous radioactivity in the ventilation airflow that exits the Containment Building. The monitor samples the ventilation exhaust airflow f ran the containment downstream of a set of absolute filters, therefore, the particulate activity at this monitor is non-conservative in leak rate CdlCulations. The gaseous activity measured by this monitor is unaffected by the liEPA filters and can be used in containment leak rate calculations.

In addition to the airborne activity monitor there is a dew-point monitor on the airflow from the lower reactor vessel cavity that indicates on a strip chart in the control room.

The lower reactor vessel cavity is a closed volume into which dry air, at a fixed flow rate and of non-detectable radioactivity is supplied at a positive pressure. The airflow which exits through the airborne particulate radioactivity monitor discussed above also is monitored by the dew-point detector. Changes in the exit dew-point are used in calculating leakage rates of moisture into the reactor vessel cavity from reactor coolant pressure boundary and/or feedwater piping.

Leak rates from a dew-point monitor located in the airflow from the upper reactor vessel cavity is also done in the same manner, except that the upper cavity is not a closed volume and does not have dry air supplied to it.

A dew-point monitor also is located in the air stream from the FCP cubicles and based on the air flow rates from containment, a leakage rate is calculated.

Once per day, an overall leak rate to containment atmosphere is calculated by means of a high volume air sampler, utilizing the latest primary water as the source of specific activity.

Once a week, an overall leakage rate to containment atmosphere is determined based on a Tritium arealyses balance.

Systems Sensitivity Retention tank level is calculated by:

(A ft) 500 gal /ft Leak rate (gpm)

=

1440 minutes / day or

.347 (a ft)

Leak rate (gpm)

=

The tank level is read from a levelometer with an accuracy of + 1/8 inch on the air tubing and the instrument mechanism has an accuracy of + 2%. The response time of the instrument is practically instantaneous, but is irrelevant, because the reading is taken every four hours.

WP-1 1

Each of the airborne particulate monitors of the air from the reactor cavity and FCP cubicles consists of a Nuclear Measurements Corp., Model LCRM-2M, with a Model N120NBGM tube with a 2 inch diameter eno window detector, monitoring a 2 inch diameter fixed filter.

Information on the sensitivity and response time of the airborne particulate and gaseous monitor on the containment ventilation exhaust airflow is enclosed. The monitoring system consists of the following Tracerlab equipment: two MD-4B beta scintillation detector assemblies for particulate monitoring, one with a range of 6 x 10-6 to 6 x 10-3 pc/cc for measuring immediate particulate activity, and the other beta detector has a range of 6 x 10-9 to 6 x 10-4 pc/cc for measuring delayed particulate activity; a Model MA-1A(V) filter-type transport mechanism, used along with the beta detectors for particulate monitoring; one MG-1A gas sampler (scintillation-type, gamma) and MD-5B gamma scintillation detector assembly for gaseous monitoring, with a range of 6 x 10-3 to 6 x 00 pc/cc; a local flow switch that actuates a visual alann for low flow; a local control panel and cabinet assembly; and three remote RM-20B transistor precision log ratemeters (with RM-408) power supplies in the main control room, with adjustable level trip settings to actuate visual and audible alarms and with outputs to drive a strip chart recorder.

The monitoring detectors are in a sampling line at the inlet end of the containment building exhaust duct, immediately downstream of the HEPA filters.

The dew-point system consists of 6 detectors located as follows:

1.

Upper reactor cavity vent line 2.

Lower reactor cavity vent line 3.

Reference - Containment Building Mezzanine 4.

Containment Building Ventilation Exhaust 5.

Containment Building Sub-basement inlet to FCP cubicles.

6.

Air conditioner discharge duct.

The leak detection sensitivity of a detector is calculated as follows:

Dry air is continuously supplied to the lower reactor cavity.

Approximately 5.5 cfm of air is discharged from the lower reactor cavity to the activity monitor.

If we assume the difference between the dew points of the dry air and effluent air is 10* F. at a dry bulb temperature of 70 F., then:

3 (77.6 - 53.6) grains / pound 3(.075 pounds /ft )

Leak

=

Rate

(.0648 grams / grain) (5.5 ft / min.)

(24) (.075) (.0648) (5.5)

Leak

.64 cc/ min.

=

=

Rate WP-1 The stability of the Foxboro dew point sensor has been proven out by experience through periodic calibrations and years of field experience at similar installations. The sensitivity of the Instrumentation (sensor +

recorder) is l' F. and the sensor response time is about 50 seconds for a 10' F. step change in dew point.

Seismic Qualification None of the leak detection equipment nor its installation is specifically qualified to any seismic criteria.

Indications The sump (retention tank) level alarms, both visually and audibly, in the control room.

All of the radiation monitors have continuous indication by virture of a recorder in the conwel room.

Additionally, the containment building particulate and gaseous radioactivity is continuously indicated on a meter in the control room. Also, this monitor will alarm, both visually and audibly, in the control room on high activity, and circuit failure, including low airflow through the monitor.

The humidity measurement system indicates in the control room continuously on a strip chart recorder.

Testing and Calibration All the radioactivity monitors are tested bi-weekly, with the plant operating or shutdown. Calibration of each of the monitors is performed regularly whether the plant is operating or shutdown.

The humidity detectors are cross-calibrated regularly, with a psychrometer, whether the plant is operating or not.

(2) Proclaions are mde to monitor reactor coolant in-leakage to those ayatema listed in Table 2.

Houever, from the reciev of the referenced information it is not clear that this table includes att systems which interface with the reactor coolant pressure boundary.

WP-1 REACTOR COOLANT PRESSURE BOUNDARY LEMKMGE 10B1ECYYLDM b5VDhV45 Regulatory Guide 1.45 Requirements TABLE 2:

Plant: LA CROSSE Testable '

Intersystem Leakage Methods to Time Reg'd Earthquake For Control Room Document-During Systems which Measure RCPB Leak Rate to Achieve Which Function Indication for ation Normal Interface with/RCPB In-Leakage Sensitivity Sensitivity Is Assured Alarms & Indicators Reference Operation Component Cooling

1. Radiation Detects Dependent None

1. Indicator O&M Manual Yes Water System Monitor concentra-on

2. Recorder tions of Leak

3. High Alarm SAR 1 x 10-6 c/cc Rate (audible & visual) Sec. 8.8.1 p

y emitters >

1 MEV

2. Surge Total None SAR Yes Tank leakage Level

> 50 gals.

Liquid Waste and Radiation Components, equipment, indications, sensitivity Yes Service Water System Monitor identical to CCW System Monitors above.

(Note 1)

Plant Radiation Components, equipment, indications, sensitivity Yes Circulating Monitors identical to CCW System monitor above.

Water Discharge NOTE 1: This monitor is capable of being valved into either the radioactive liquid waste discharge line, or the service water fran tre CCW heat exhcangers. Because the service water joins the plant circulating water discharge, ahead of the Plant Circulating Water Discharge radiation monitor, the Liquid Waste and Service Water System monitor is very seldom in service on the Service Water System.

WP-1

-5

I i

(3) Informatin~. :::.:erning the use of reactor coolant inventory balances,

}

for RCPB teakago detection as indicated in Table 3, is incomplete, l

therefors, its ccttribution to overall detection system effectivenese cannot be dete:minsi.

During operation of LACBWR, a boiling water reactor, the reactor coolant inventory is maintained around a nominal level in the main turbine condenser i

hotwell, by automatic make-up fran, or automatic rejection of water to the i

condensate storage tank.

j The condensate storage tank has a nominal 11,000 gallons of water. Tank level j

and high and low levels alarms are indicated in the Control Room. Therefore, 1

gross RCS water inventory is capable of being determined. The addition of l

water to the condensate storage tank, and therefore to the RCS, is by manual means.

i Also during operation, one of the retention tanks in containment is used to collect all of the water that accumulates inside containment. This includes

]

water from the air conditioners, water used in cleaning and/or decontaminating j

equipment, floors, and other surfaces in the containment building, as well as RCS leakage and leakage from other water sources. Therefore, a RCS water o

)

inventory balance is most difficult to obtain and is therefore not very useful in detecting RCS leakage.

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WP-1 i l

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,..,.. -, _ -. -, - - _ - ~

1 Mr. Dennis M. Crutchfield, Chief June 14, 1982 U. S. Nuclear Regulatory Commission Distribution of LAC-8346 A-11 S-23 T-51 Rdg SEP NB TL SRC Treninel Shimshak Parkyn Towsley Rybarik Brimer Nowicki Boyd/Kel1ey Goodman /Polsean SS WP-1

1005 MAP-1B CONTINUOUS AIR PARTICULATE MONITOR MAP-IB/MGP-lA (or2) COMBINATION GAS AND AIR PARTICULATE MONITOR I.

SYSTEM GENERAL DESCRIPTION The Tracerlab MAP-1B Monitor is a complete system for continu-ous measurement of the radioactivity of airborne particulates. Radio-isotopes present in the air as particulates or adhering to dust particles are concentrated by drawing a large colume of air through an efficient moving filter. A radiation detector views the collected particulates at the deposition area and presents an electrical signal to circuitry that averages the detector output pulse rate. This average rate is displayed on a meter, and, in the standard system, on a recorder chart. By mathe-matical manipulation of the system parameters, the concentration of ra-dioactive particulates in c/cc of air can be closely computed.

~

The model designation MAP-1B/MGP-1 A (or 2) indicates that a l

gas monitor is included and that such a system measures both particu-late and gaseous radioactivity. For a list of the equipment s upplied in your system, refer to the Component List.

1 II.

SYSTEM SPECIFICATIONS A.

Sensitivity i

The sensitivity of the system is the minimum detectable con-centration of a praticular radioisotope in the air. The following tables give this corcentration in microcuries (. c) per cc of air for various detectors to give a net count rate equal to the detector background count L,

rate. (1 c = 2. 2 x 106 disintegrations per minute. ) The figures in

[J' apply only in the absence of other interfering activity such Tables I and II as the naturally occurring radon-thoron daughters (see Section IV).

When j

other activity is present, the isotope one wishes to measure must cause a counting rate over and above that caused by the other activity.

B.

System Response 1.

Air Particulate Monitor ll 3

The high sensitivity of the MAP-1B is obtained by main-taining a high flow rate of air through a slowly moving filter. (A detailed 1

4 N

E E

E E

E E

E Energy and Type Min. Detect.

Detector Activity Half-Life in MEV Conc.

c/cc B ackground Net Signal l 3

O. 76g/,'

0,15

2. 5 x 10 25 cpm 25 cpm i

MD-I B C

5500y 204

1. O x 10-T1

3. 5y l

4 mg/cm Sr 22-Y 20y O. 54 /,, 2. 2/ _

3. 0 x 10_12 2

90 90

1. O x 10_3 3 B e t a - G amma Na 2,6y

0. 54/#,

1,28

, 0. 61[y,

13 l3y0

8. id O.36

1. 0 x 10 GM I

-12 l

Co 5.3y

0. 3

,1. 3 y,~1.17 8. 0 x 10 y37

-12 l

Ce 3.3y O. 5

',1. l #

4. 2 x 10 147

-11 f

Pm 2.6y 0, 22j -

f. 5 x 10 t

MD-3B l

Alpha Scintillation Po 138d

5. 3 J.

I x 10-12 3 cpm 4 cpm 0

MD-4B C

5500y O.15g~'

1 x 10-20 cpm 20 cpm Beta Scintillation Tl 3.5y 0.76 /

5 x 10~ 2 204

[,

60 y, 1. 3 y/'

7 x 10 fI 250 cpm 200 cpm MD-5B Co 5.3y 1.1 y

I331

8. ld O.36 7, 0.61 9 x 10~

Gamma Scintillation 131

'e l'

% c h e<c k c ou t c t rec >mmended for I (5 pc)

Mamsured at air flev rate of 10 scim, for otherwir c ancontaminated filters.

SENSITIVITIES OF TRACERLAB MA-IB FILTER TAPE TRANSPORT MECHANISM E

TABLE I

E Lj,E E Y E E

l Energy and Type (MEV)

Minimum Detect. Conc, pc/cc

. Activity Gammas Betas Half-Life MG-1 A*

MG - 2*

• I9 O

1. 3(65%)

4.5(30%)

34 a conds 7 x 10-7 5 x 10'7

c. 2(96%)

2.9(76%)

1 0.1(4%)

I 0

A

1. 37(100fi) 1.24(1905) 110 vnduatee

4. 25 x 10' 1x W l

^

4

4. 54(0. 35 % )

8.49(100%)

%4 yeaurs 3.5 x Wf am.Se' i

1 6.36(87%4 0.41(SPJr)

A.3 days

.Z.? x lo-2 gle'6 51 O. 6 589 %)

• -? %I.

=

= = -.

=-

82 3x 10 Br ydecay 9.46(2005) 36 honra meheme in hubt

-6

-6 Xe*

4,04(100%)

0.34(100%)

5.3 days 4 x 10

3. 5 x 10

• WE TracerIr5 MD-5B Scireiitarnam Detector (250 cpenbackground, 3" lead shielding).

• eWith Tracerlah MD-11BLarge Area Beta-Gamma Detector (259 cpm background, 2" lead shielding).

SENSETIVITIES OF TRACERLAB MG-1A AND MG-2 GAS SAMPLERS FOR MET SGNAL EQtIAT.TO BACKGROUND T A B 1 E II A

1008 l

description of the tape transport mechanism is given in Section VI, A)

Although the particulates are deposited immediately in front of the ra-diation detector, a finite time is required to reach counting rate equilib-rium, dependent upon the transit time of the filter past the sampling ap-erture. The response of the system as a function of time is a second f

order equation, the solution of which is plotted in Figure 1.

]

The time required to reach equilibrium is two hours; however, this should not imply that there is a delay of two hours before i

an increase in activity will be indicated. An example in Section V illus-trates how the information from Figure 1 can be applied.

2.

Gas hionitors - hiG-1 A, hiG-2 m

I

_,J By virtue of the 10 cfm sample air flow rate, the sample l

volume in the gas monitors is changed in less than two seconds. The I

ratemeter, on the other hand, will usually be set with its time constant in the region of 10 to 40 seconds. Therefore, the response is predomi-nantly a function of the ratemeter time constant which has the typical ex-iQ ponential-form of 1 - e t/RC. In one time constant (t = RC) the rate-meter output has reached about 63 percent of the equilibrium output and t

M in five time constants (t = 5 RC), the output has reached over 99 percent of the eqitilibrium putput.

Refer to RATEhiETER for characteristics of the partic-l ular ratemeter supplied with your system.

U]

C.

Temperature Limits 1.

Environmental Temperature Limits The maximum environmental temperature is limited j

by the particular detector (s) supplied. If the Geiger-hiueller detector (Tracerlab hiD-IB) is used, the maximum environmental temperature is 100 F.

If a scintillation detector is used (Tracerlab hiD-3B, Af D-4B or hiD-5B) the maximum environmental temperature is 1600 F.

If the g

hiG-2 is included in a combination air particulate - gas monitoring sys-tem, it will incorporate a large area Geiger-hiueller type detector

^^~~

(Tracerlab hiD-11B). The environmental temperature limit for this de-tector is 200 F.

The maximum allowable temperature will be deter-mined by the detector having the lowest limit.

s 2.

Ventilation Requirements e

4

_.J Normally, no special provision for ventilation is re-f quired for the KIAP-1B system since the open design of the enclosure Lq J

J J 15

p 1017 l'

ratemeter on a long-time constant, check the detector background in your For abnormal background, refer to tne section on troubleshooting, area.

Sec: ion VIII.

2.

Contribution from Check Source Determine the equilibrium counting rate from the check Observe the same con-source by turning the check source control switch on.

ditions as the above paragraph. The check source is not intended as a calibra-tion standard but rather as a check of the operation of the detector and circuitry.

For troubleshooting, see Section VIII.

V.

SYSTEM OF OPERATING PROCEDURE A.

Interpretation of Data 1.

Natural Activity Contribution The natural activity contribution to the counting rate is tht' These result of the collection of naturally-occurring radioactive particulates.

particulates are daughters of radon and thoron gases which result from decay The concentration of of uranium and thorium deposits in the earth's crust.

these particulates depends on locale and meteorological conditions and will usually be within the range from 10-9 o 10-11 c/cc. The uncertainty of the t

contribution by this natural activity can be reduced by noting the activity level Weather accompanying high in the locale and how it fluctuates with weather.

natural activity background is typically characterized by poor visibility, high humidity and warm temperatures while clean air is characteristic for its low Past experience is that the con-concentration of radon and thoron daughters.

tribution from natural activity may range from 250 to 3000 cpm with the MD-These limits may be used in the absence of other data.

1B as the detector.

The increase in gamma contribution (MD-5B, 300 key In one year of testing it was noted that threshold) is typically 200 to 400 cpm.

natural gamma activity above 100 Kev (INTEGRAL) varied over a range of 2:1 but never gave net readings over 450 cpm.

2.

Calculation of Specific Radioactivity When a gas monitor is used in series with a particulate monitor and each indicates a specific activity, the contamination in the incom-ing sample is the sum of the two computed results. The gas monitor sees only gaseous activity since the particulates are collected at the filter while the par-ticulate monitor is relatively insensitive to gaseous activity if the FP-1 paper is used.

The CFP-1 paper is capable of adsorbing certain gases and produces count rates slightly higher than the FP-1 paper under certain con-ditio ns. I

1018 A computation may be made for isotopes other than those listed in Tables I and II by choosing a sensitivity for a listed iso-tope having radiation energies similar to the contaminant in question.

l Application of the data in Tables I and II becomes invalid if the contami-nant is of short half-life relative to the instrument response. For short half-life isotopes, the computed activity from the instrument reading is lower than the actual activity of the sampled air.

The following formulae and example will serve as a guide when calculating the specific activity in the sample air.

The fol-lowing information should first be obtained from the chart record:

Gross count rate:

N 8

Background count rate:

Nb (detector background plus natural activity contribution)

Contaminant collection time:

t (if less than two hours) c Using te, obtain the percent equilibrium s from Fig-ure 1.

Determine contaminant equilibrium counting rate, Nc Ne =

8-E From Table I, select the isotope with an energy similar to the suspected contaminant and determine the concentration in microcuries per cc to equal detector background:

A c/cc G cpm Applying a flow rate correction if necessary, determine contaminant concentration:

c 10 cfm A pc/cc Concentration x

x pc cc actual flow Gcpm For example, suppose the MAP-1.B system was monitoring a potential hazard from Sr90 + y90 Previous data showed the background count rate to be about 500 cpm and the alarm level was set at 1000 cpm and q

an alarm condition occurred with the flow rate at 9 cim. Inspection of the chart record showed the build up from 500 to 1000 cpm required 16 minute s.

l M II

1019 I

From Figure 1,16 minutes corresponds to 25% of the equilibrium count rate. Contaminant equilibrium count rate would then be b

1000 - 500 N, =

2000 cpm l

=

,25 From Table I, (at 10 cim) 3 x 10-12 c/cc Sr90, 790 yields 25 cpm net. Contaminant concentration would then be 10 cfm x 10 c/cc

2. 66 x 10-10 e

x 2000 cpm x

=

9 cim 25 cpm cc If gaseous activity is also measured, its contribution may be taken di-rectly from Table II with no correction for flow rate or response time.

B.

Routine System Checks 1.

Detector Background Detector background determinations taken at regular intervals establish a zero base from which to make computations re-garding the specific activity level being measured. The procedure is simply to remove the influence of any recently collected dust by oper-ating the filter drive at its " Fast Advance" speed for 10 or 20 seconds and then noting the counting rate from the detector. After advancing the filter, turn the pump off while making the measurement to avoid collecting radioactive particulates.

If the system has a gas monitor, background should be taken after purging with clean air. If contamination of the sample chamber is suspected, use the-following cleaning procedures:

a.

MG-1A System: Remove the interconnecting hoses and flush the chamber with water or acid.

b.

MG-2 System: Replace the plastic sleeve on the detector. Flush the chamber with water or acid.

For further detail, see SAMP1ER.

2.

Check Source A routine for employing the check sources will, with little effort, confirm that the system components are in order. Again, _ _ _ _ _ _ _ _ _.

1026 l'

H.

Gas Monitor j

The main element in the gas monitoris the sampler which includes the shielded gas flow cell and the radiation detector. The gas monitor measures the radioactivity of the sampler after it passes through the filter tape. The gas monitor enables detection of gaseous radio-isotopes such as A-41, Kr-85, I-131 and Xe-133. Details of the gas sampler are described in SAhiPLER.

l I.

Detector Background When the filter paper is either perfectly clean or entirely 4

removed and the detector is properly located in the shield, the count-ing rate obtained is termed " detector background". It is caused by cosmic rays, ambient gamma flux, and radiations from minute im-purities in materials of construction. Detector background is normally:

Dete ctor

Background

AfA-1B hiG-1 A hiG-2 hiD-1 B 20 cpm AfD-3B 3 cpm hiD-4B 20 cpm hiD-5B 150 cpm 50 cpm hiD-1 IB 260 cpm l

Tests of the MAP-IB in a high gamma field show the sen-sitivity of the AID-1B detector to be approximately 100 cpm /mr per hour (flux from Ra-226 daughters). The hiD-4B sensitivity is of compar-able magnitude. The Af D-5B, because of its higher gamma efficiency, will have a sensitivity to ambient gamma flux one to two orders of magnitude higher (e. g., 1000 to 10,000 cpm /mr per hour).

The magnitude of detector background in the presence of an ambient gamma flux will be dependent upon the orientation of the A1AP-1B to the gamma source, due to unequal directional shiciding. The back of the detector is least protected. Thus, it is desirable to orient the system to minimize background contributions from local gamma sources. The directional characteristics are shown in Figure for the hiD-5B detector.

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Response of MAP-lB To Step g

increase. in 12 Concentration s

Percent Ec;uilibnu m vs Time.

f V VS 2.-18 -6+

SMS 4-4-(ol fFlxED FILTER MOVING FILTER l00

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T RACERLAB-WEST

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RICHMOND CALIF 20 vo a

s Ion m m i m m /

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Ou O

20 40 60 BO 100 120 14 0 160 TIME - MINUTES A = MEASURED