ML20042F106
| ML20042F106 | |
| Person / Time | |
|---|---|
| Site: | Reed College |
| Issue date: | 04/16/1990 |
| From: | Ruby R REED COLLEGE, PORTLAND, OR |
| To: | Scarano R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 9005070226 | |
| Download: ML20042F106 (19) | |
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REED COLLEGE 'Pordand, Oregon 97202 8199 :
< ,M.IVED !
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Ross A Scarano, T 'ector ,
Division of Radiatior Safety and Safeguards '
O. S. Nuclear Regult. iry Commission, Region V t l 1450 Maria Lane, Su, e 210 l - Walnut Creek, Califort la P4596 !
l Re: Docket 50 288, License R112
Dear Mr. Scarano:
l This letter is 1.n reply to your letter inquiring about our Gaseous Stack Monitor i (GSM) calibration. When I joined the Facility in September of 1987, I found that we i had a strong recommendation from Inspector Michael Cillis that essentially all of our i documentation was in need of rewriting, and that the exhaust air sampling system was '
in need of considerable overhaul. As of now, all of the essential documentation has been '
rewritten, including 15 of our 33 Standard Operating Procedures, in addition,5 more !
SOP's are currently before the Radiation Safety Committee (RSC). Certainly, this is not .
l a record of disregarding Procedures in the broad sense. 3 During 1988 and 1989, an overhaul of the exhaust alt sampling system was uncertaken, and a draft of a new SOP for calibrating the GSM was worked on. The new SOP was much more detailed than the current SOP, which dates from May of 1981.
When all of the hoses were replaced, and other leaks were sealed, we began to see, for the. 1 first time, actual indication of argon 41 production from reactor operation at or near to full power. Heretofore, we have been estimating our argon 41 production by extrapolating data from measured output at OSU, but starting in 1990, our Annual Report will reflect a value which was measured here, in early 1990, we performed a calibration of the GSM in the traditional manner in which it has been done here and at other TRIGA reactors. Following the calibration, in applying the argon-based criterion in the SOP for determining the failsafe sctpoint, we found that with our much more sensitive GSM, the predicted setpoint would fall well L
within the range corresponding to normal operation. Obviously, the setpoint criterion had never before mattered, in the era in which no evidence of argon-41 ever appeared, but now a realistic criterion was essential. At that point, I regarded the situation as "
corresponding to operation with an entirely new GSM, for which the old fallsafe setpoint criterion was inappropriate. I, therefore, authorized interim fallsafe and alarm i
setpoints to be employed, based on a criterion used at other TRIGAs, to remain in place l until the Radiation Safety Committee could meet and approve of a new SOP At the time, it was also necessary to consider whether the increased sensitivity could be indicative, instead, of an actual radiation release. This prospect was rejected for 2 reasons: The increase in sensitivity was concurrent with the elimination of leaks in the exhaust air sampling system; and 2 independent monitors which sample air in the reactor bay, 4 evidenced no comparable increase in readings.
pr$8sse 888%r 3203 Southeast Woodstock floulevard' Portland. oregon 97202 8199 h[U Telephone rsos) 172 1112 ~
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j The Radiation Safety Committee met on March 8th and again on March 22nd, with i the new GSM SOP on the agenda both times. The Committee agreed that the old criterion i for determining the failsafe and alarm setpoints was in need of modification, but i the members were unsure whether, according to the provisions of 10CFR20, the ,
criterion in the new SOP would require a license amendment. They requested that i ,
investigate this question with the NRC, and on March 26th, I phoned Ted Michaels ar.d started discussions on this point, which were resumed on April 4th. The Committee also noted the old criterion was based on allowing 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of operation per week at the fallsafe setpoint, and that the interim set points were a factor of 3 higher than the old criterion called for. They then approved continued operation with the interim setpoints, provided that the maximum number of weekly hours of operation at the fallsafe setpoint would be reduced from 4 to 1. Accordingfy, on March 26th, I issued a Notice to
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Operators in-orporating the Committee's recommendation. Mr. Michaels and his ~
, consultants Sve since advised that the set point criterion in the new SOP can be ,
l justified thrc. sob a 10CFR50.59 analysis, and such has been prepared for approval by the RSC along with the new SOP.
The RSC will meet in about 2 weeks to consider the situation further.
l Meanwhile, I am enclosing the current SOP, a draft of the new SOP, and a draft of the l
10CFR50.59 analysis for your inspection. I can assure you that SOPS are seriously regarded here, and I am most interested in what my critic has had to say in this regard.
l Under 10CFR19.16, we are entitled to a copy of the complaint, and I would be Orateful
- i for same.
l Sincerely, Lawrence Rub s Professor Reactor Director -
enc: Current SOP 31
, Draft New SOP 31 Draft 100FR50.59 Analysis cc: Douglas Bennett, Provost /w.o. enc.
David Dalton, RSC Chmn/w.o. enc.
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~ GASEOUS STACK MONITOR: sop 31 I
i Note: Because of the complex nature of this SOP, the large number of rather complex equations and the use of Greek symbols, a much more detailed SOP exists in the Gaseous Stack Monitor Book !
in the console room of RRF. The copy which you are now reading ;
is not intended for the actual calibration, but rather only for a j qualitative understanding of how the process is accomplished. l 31.1 PURPOSE The gaseous stack monitor directly measures the concentra- !
tion of radioactive gasses released to the environment through the air ventilation system. This is accomplished by a snell (7 ;
cfm) sample of gas being removed by a pump from the top of the '
ventilation stack. Following the pump, the gaseous sample is passed through a 755 m1 lead-lined container in which is placed a l thin-walled aluminum GM detector. The activity detected by the ,
the GM tube is transmitted down~to a rate meter pieced in the console room. .
Because Ar-41 is the major isotope released during a reac-tor run, it is the nuclide used for calibration. The calibration
( procedure consists of irradiating a known quantity of Ar gas, using a Au wire to simultaneously determine the flux and calcula-ted the quantity of Ar-41 generated. This Ar-41 is then injected into the cavity surrounding the GM counter and the ratio of the concentration of activity to the epm is calculated; this ratio hss units of microcuries per ml per epm. Knowing this calibration factor, the alarm and failsafe points can be set.
31.2 FREQUENCY The Ar-41 approach to c'alibration must be done a t least once every year. A far less complicated (and faster) method using an external non- gaseous source may be used otherwise. It is described in paragraph 31.10. '
31.3 EQUIPMENT External source such as the 2 mg Ra-226 cource A voltmeter Ar gas and regulator 2 dram polyvlal 2 hypodermic syringes A water bath 31.4 PERSONNEL A RO to irradiate the Ar and several assistants. Normally the gaseous calibration method requires the better part of 2
! days.
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4 GASEOUS STACK MONITOR: sop 31 31.6 PREb!MINARY ACTIONS Before the calibration is started, a plateau curve must be taken on the monitor probe. This is accomplished by placing a source near the probe and then plotting the observed counts per minute as a function of the high voltage applied to the detec-tor. The exact details of how to take a plateau curve on a GM counter is described in the SOP for the CAM. The high voltage is monitored by the purple test point on the left front of the pc-board and the HV is changed by the small trimpot located in the f r ont. middle of the pc-board. Be sure that neither the adjusting screwdriver not the HV probe accidently touch ground for this will burn out the low current HV power supply.
31.6 CALIBRATION PROCEDURE USING Ar-41 A 2 dram polyvial is filled with Ar gas by displacement of water. After filling the vial or vials are sealed and a known quantity of gold wire is scotch-taped to the vial. The vial is irradiated in the Lacy Susan; typical irradiation times of 5 minutes at 150 watts are used. The time of the end -of bombard-ment (E0B) is noted. The hoses to the lead chamber of the gaseous stack monitor are removed; one port into the chamber is tightly sealed with a rubber stopper, the other port is sealed
- \ with a one-hole rubber stopper containing a rubber septum to per-mit insection of the Ar. The irradiated Ar gas is removed from the polyvial by the simultaneous puncture of two hypodermic needles; one hypodermic slowly removes 5.0 ml of gas while the other displaces it with 5 ml of water. The 5.0 ml of gas are then in$ected into the counting chamber of the stack monitor.
Af ter waiting several hours f or the Ar-41 to decay the count rate data is transferred to semi-log paper and the count rate at E0B is determined assuming a half-life of 110 minutes.
The neutron flux during the irradiation is determined by counting the Au-198 410 Kev gamma-ray on shelf 8 of the Reed GeLi. The activity is extrapolated back to the end of bombard-ment and then converted to the disintegration r.3 t c using the counting efficiency for peak area. By knowing the disintegration rate, the number cf Au-197 atoms irradiated, the ( n, ga mma ) cross section and the length of the irradiation, the neutron flux is easily calculated.
The exact quantity of Ar-41 activity is calculated from the above calculated neutron flux, the known number of Ar - 4 0 atoms present during the irradiation, the (n, gamma) cross section on Ar-40, the length of irradiation and the Ar-41 half-life. The ,
number of Ar-40 atoms are calculated assuming an ideal gas and correcting for water vapor pressure and the isotopic abundance of AI-40. The unit of Ar-41 activity should be in micro-curies (-3.7 x E'4 dps equals 1.0 microcuries).
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_GASEQUS STACK MONITOR: sop 31 The failsafe and alarm set points are calculated by first determining F, which is the ratio of micro-curies to cpm at E0B and dividing by the volume of the count chamber. This has units of microcuries per _ ml per epm; multiplication of this factor by
- the epm on the detector will give the micro-curies per m1 being ,
released at the stack.
31.7 ADJUSTME!!TS Setting the Fail-safe point: It has been agreed that .t he fail-safe point will represent a release indication for Ar-41 -
such that if the reactor facility operates with the gaseous stack ,
monitor just at the fail-safe point for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> every week durLng :
the year, then this will represent the maximum allowed release ,
set by the State. The fall-safe point is set by dividing the Mpc set by the State by the ftaction of time which 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> per week represents (4/168); this will be the MpC during the 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> inter-val. This is then divided by the factor F and.the nor mal back- i ground count rate added by achieve the fail- safe set point.
Setting the alarm-set point: The philosophy for esta- ,
blishing the the alarm set point is to base it on the release of a fission product. It will be assumed that the Icvels of gaseous t fission product activity are just enough to go just to the alarm set point, but not to exceed it and thus trip the isolation cy- '
ele. It is assumed for purposes of this calculation that the Reactor Facility could be in such a situation for 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> per '
year. The maximum permissible release of noble gas fission pro-l ducts if for Kr-07 and 88. It is assumed that all of the bromine and lodine fission products are dissolved in the water and ;will not be released to the environment. By dividing the maximum per- ;
missible release concentration by the fraction of the year which is represented by 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br />, the relense rate during the 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> is determined; this is then divided by the factor P to establish the alarm set point to which normal background must be added.
31.0 CLEAN Up After completing the calibration, be sure to replace all of the equipment into the box for future use. The gaseous coun-ting chamber in the loft should be reassembled and it Ghould be verified that the counter seems to be working properly.
31.9 LOGGING IN The complete set of data should be placed in the gaseous stack monitor booP, with the exception of the actual graph as recorded on the strip chart recorder. A brief note should be made in the main log book noting when the calibration is first started and when the detector is considered back in service. A note must be placed on the strip chart recorder indicating the reason for the non-background traces which occur during the calibration.
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GASEOUS STACK MONITOR: sop 31 31.10 A FAS7ER AND SIMPLER WAY OF CALIBRATION The method described above must be accomplished at least once every year. More frequently it in easier to do a calibra-tion whleh involves placing the 2 mg Ra-226 source exactly 1.0 meters f r om the end of the probe. The central axis of the detec-tor is placed parallel to'and in the same plane as the radiation field. The count rate 10 determined with the cource in this con-figuration. Calculation of the factor F with units of microcu-rien per ml per epm is then made by multiplying the source count rate by 5.0 E ~12. Then the fall safe and alarm set points can be adjur.ted as outlined in 31.7.
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.' 1 RRF FACILITY DOCUMENT 10CFR50.59 REVIEW t
,Hle:
Summary of Pronomad Chance:
The SAR1predicted an argon-41 concentration of 1.46 X 10-6 pCL/ml in air exhausted from the stack at full power. This is 36.5 times unrestricted MPC. To stay within MPC, and operating limit of 1/42 of a week, i.e. 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, was imposed in the original SOP 31, last revised 2 on May 14,1981. The new3 SOP permits the telease of 11.6 times MPC, avera0ed over a year, based on a calculation which shows that the -
maxlmum dose to a person in an unrestricted area, next to the exhaust stack, would not exceed 500 mrom if dispersion and radioactive decay of the argon-41 are taken into account. Experimental measurement of the argon 41 release, based on the calibration of the stack-Oas monitor with a known quantity of argon 41, predicts an upper limit to the release, l.e. assuming that all of the lar0est ever observed sl9nalis from argon 41, of 4.38 X 10 6 pCl/mt, i.e.110 times MPC at full power. This implies operation could be undertaken for 1/10 of a week, i.e.16.8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> without exceeding the 11.6.MPC limit. The .
criterion adopted in our new3 SOP is to base the alarm set point on a maximum of 12 full-power hours per week. Thus, the annual dose restrictions of 10CFR20 are conservatively observed.
I IInt of Soecifle Sections of Facility Documents Related to the Pronomad Chanoa:
- 1. Reed Reactor SAR, April 15,1967, Appendix D.
- 2. SOP-31: Calibration of the Gaseous Stack Monitor, May 1981 Revision.
- 3. SOP 31: Calibration of the Gaseous Stack Monitor, April 1990 Revision.
Determination of Anotienhility of 10CFR50 59 to Pronomad Chanos:
Part 1: Does the Proposed change involve a change in the t icense including the incorporated Technical Specifications? Yes/No Part 2: Does the proposed change constitute an unreviewed safety question; specifically, -
a) Does the change increase the probab!:lt occurrence or consequences of an accident or malfunction of equipment important to safety? Ye .
b) Does the change teate the possibilityi n accident or malfunction of a different type than evaluated previously? Y c) Does the chan specifications? Yes@ ge reduce the margin of safety as defined in the basis for any t
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o Approved by Q- } ._
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. . 6 M REED I Calibration of the C O C REACTOR !'
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Gaseous Stack Monitor FACILITY c gecaw: 4/90 i Standard Operating Procedure 31.1 Scope:
t This procedure describes the actions to be taken for calibrating the gaseous stack
. monitor (GSM), which directly measures the concentration of radioactive gases released to the environment through the alr ventilation system.
{ 31.2 Schedule: ;
The GSM shall be calibrated once every six months and at intervals not to exceed ;
seven and a half months.
31.3 Personnel Requirements: '
Any individual designated by the Reactor Suprvisor the Director may calibrate the GSM, though a licensed operator is required for the irradiation of the gold and argon l samples. An individual trained in the use of the gamma spectrometer will be needed to
- measure the activity of the gold foil.
31.4 Prerequisites:
31.4.1 The following equipment should be available: i I digital thermometer I small portable source sitch as a beta check source I
argon gas ;
gold foil i
two 2 dram polyvials 2 hypodermic s> Tinges 2 rubber stoppers, one with a hole containing a rubber septum l a water bath ,
a complete and signed irradiation request form for irradiating argon and gold l airflow transfer standard 7 transfer standard calibration curve in Stack Log l
duct tape l
insulated screwdriver suitable for adjusting the HV '
l l 31.4.2 A start up shall be completed.
31.4.3 Proper security procedures shall be followed when entering the loft.
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j 31.4.4 Since this procedure requises the removal of the GSM from service for a '
period of several hours, it should be scheduled for a time when no reactor operation :
is anticipated.
31.5 Precautions:
31.5.1 The procedure for transferring the Ar gas from the polyvial to the syringe !
can be difficult if unfamiliar. Practice beforehand using an att filled vial. Two polyvials are qwed so that if there are any probierns with transferring the first Ar
, sample, another is ready for irradiation. '
31.5.2 Care should be taken when performing the high voltage plateau to avoid
, electric shock.
31.6 Order: '
Data analysis may be performed at any time during the procedure. The calibration steps shall be performed in the order outlined. ,
31.7 Procedure:
- Record all data and calculations on a GSM Calibration Data Sheet (see Appendix 31.A).
31.7.0 Measuring the airflow 31.7,0.1 Note in the Main Log that the GSM will be out of service.
31.7,0.2 With proper security precautions, enter the loft.
4 31.7,0.3 Shut off the motor producing airflow to the stack monitors, and -
insert the airflow transfer standard in series with the loft flowmeter, and . -
next to it. 'Use duct tape to seal the connection. Make sure that the transfer-standard flowmeteris vertical. Restart the motor. Record in Appendix A, the readings for the loft flowmeter and for the transfer standard flowmeter.
Tum off the motor and remove the transfer standard from the stack monitor i flow circuit. Leave the motor off.
31.7,0.4 Insert the transfer standard into the system at the inlet from the
! stack. Again, make sure that the transfer standard incteris vertical, and use duct tape to seal the connection. Start the pump motor and record the reading on the transfer standard. If the reading differ., by more than 20%
i from tae reading observed in 31.7.0.3, there may be a leak in the system.
Stop and inform the Reactw Supervisor or the Director. Otherwise, turn off >
! the motor and remove the the transfer standard from the system.
31.7,0.5 Using the latest transfer-standard calibration curve in the Stack Irg, and the data in Appendix A, calculate the stack airflow reading which ~
corresponds to a true value of 6.0 cfm. Set the airflow reading to this value, and record it in Appendix A. Graph your data if necessary.
31.7.1 2eroing the meters:
31.7.1.1 Tum off the high voltage by unplugging the GSM.
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31.7.1.2 Let both meter needles settle to their lowest points.
31.7.1.3 Using the insulated screwdriver, turn the small screw on the front of the meter so that the needle now rests at zero.
31.7.1.4 Adjust the chart meter zeroing using the zero adjustment, which is underneath the take up roll in the chart paper box.
31.7.2 High Voltsce Platenu*
31.7.2.1 Note in the Main Log that the GSM will be out of service, ifit has not already been so noted.
31.7.2.2 Remove the GSM probe from the shielding chamber up in the loft. Place the probe on the floor, being careful not to cause any damage.
Plug in the GSM.
31.7.2.3 Place the small beta check souxe near the probe tip, close enough to register 5000 cpm on the GSM meter.
31.7.2.4 WARNING. HV can be dangerous; see Precautions section 31.5.
Using the insulated screwdriver, adjust the high voltage by turning the small trimpot in the front middle of the IC board. Stan with the voltage tumed all l'
the way down (clockwise). Turn the trimpot counterclockwise by one division marked off on the trimpot. Record the epm reading. Repeat this at step increments of of one division, waiting a few minutes to allow the .
reading to settle down. With each voltage increment, record the corresponding meter epm reading.
l 31.7.2.5 Plot the data on a EDE versus divisions graph. ;
31.7.2.6 Set the GSM high voltage to a voltage level that lies in the plateau i region, somewhere between the midpoint and 1/3 of the way along the i plateau from the lower edge, Unplug the GSM.
31.7.2.7 Put the GSM probe back into the shielding. Tum on the airflow motor and plug in the GSM. Note in the Main leg that the GSM has been returned to service and make a note on the GSM chan paper explaining the reasons for the higher than background readings, .
31.7.3 Calibration Procedure 31.7.3.1 Fill each 2-dram polyvial with argon gas by displacement of water. Make sure that the argon lines are adequately flushed before the sample is collected, in order to prevent the irradiation of air instead of argon. Heat seal and number each polyvial. l 31.7.3.2 Record the temperature in the room where the argon is collected. . >
Use the digital thermometer, i 31.7.3.3 Record the atmospheric pressure from the barometerin Room 7.
j 31.7.3.4 Determine the pressure of the argon gas. This will be the 3
difference between the atmospheric pressure read from the barometer and DRAFT of 4/11/90
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O the vapor pressure of water at the room temperature. The vapor pressure of ;
water can be found in Appendix A orin any CRC Handbook, indexed .
under vapor pressure aqueous vapor, over unter below 100*C .
31.7.3.5 Weigh out two pieces of gold foil, about 0.03 grams each. Insert each into a polyethylene envelope, and write the foil mass onto the latter. '
Tape one of the envelopes to the outside of each polyvial.
31.7.3.6 Bring the reactor to constant power at 150 watts. Irradiate one of I the polyvials for five minutes in the rabbit system or 10 minutes in the I.azy Susan. Record the console clock time at end of bombardment (EOB). i 31.7.3.7 Scram the reactor. Turn off the stack monitor pump in the loft. l Note in the Main Log that the GSM will be out of service. '
31.7.3.8 Remove the hoses from the lead chamber. Seal one port into the ;
chamber using a rubber stopper. Seal the other port using a one holed ;
rubber stopper with a rubber septum.
31.7.3.9 Take the irradiated argon filled polyvial up to the loft. Remove the irradiated Ar-41 gas by puncturing the polyvial with two hypodermic -
needles: in one endof the polyvial insert tie needle of an empty syringe, while in the other end, insert the needle of a water filled syringe.
Simultaneoasly withdraw 5.0 ml of Ar-41 gas from the polyvial and inject 5.0 ml of water to replace it.
31.7.3.10 Inject the 5.0 ml. of Ar-41 gas through the rubber septum stopper into the GSM counting chamber. If there are any problems at this step or in the previous step, the chamber must be purged of any Ar-41 that might have been injected and reassembled, the GSM returned to service, the reactor restarted and the second vial irradiated.
31.7.3.11 After waiting several hours for the Ar-41 to decay, examine the semi log chart recorder paper. Detennine the count rate at end of bombardment for the GSM probe, in cpm.
31.7.3.12 Remove the rubber stoppers from the stack chamber. Replace the hoses, making certain they are tightly fastened. Turn the stack sampling pump back on, and note in the Main leg that the GSM is back in service.
31.7.3.13 Count the activity "A" of the gold foil in the gamma .
spectrometer.
31.7.3.14 Return all equipment to where it was found. The gold foil ;
should be stored in the salc.
31.7.4 Data Analysis 31.7.4.1 Determine the activity of the Au-198 at time of EOB using:
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given knowledge of the gamma count on the Au 198 activity (corrected for detector efficiency), the decay constant for Au 198, and the time interval between EOB and counting, t
31.7.4.2 Having determined the activity of the gold foil in dps at end of bombardment (EOB), calculate the neutron flux during the irradiation:
(31.2)
$ = NO(1-c*) i 31.7.4.3 Use this to calculate the exact quantity of Ar-41 activity present at end of bombardment: ,
1 AAr' = NAr h O(1-e*M) (31.3) [
Assume an ideal gas, correcting for both the water vaimr pressure (as per 31.7.4.5) and the isotopic abundance of the Ar-40. Tae unit of Ar-41 activity, AAr in microcuries,is computed from AAr'in dps.
31.7.4.4 Determine F, the ratio of microcuries to epm for the GSM probe ,
3 divided by V, the volume for the GSM chamber (755ml).
i F=^ (31.4)
Multiplyi,ng this constant by the epm reading on the monitor will give the microcunes per ml being released by the stack. '
31.7.4.5 The failsafe and alarm set mints are determined by the. maximum permissible sclease of argon-41. It us calculated that a continuous release of 11.6 MPC, where MPC is given in 10CFR20 App. B, will provide no more than a whole-body dose of 500 mrem to a person standing near the exhaust stack in an unrestricted area. The calculation is shown in Appendix B,in
' which both dispersion and radioactive decay are considered. To take advantage of yearly averaging, it is further assumed that the reactor operates at or near full power for up to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> per 168-hour week. Then, the j
alarm set point is calculated asAlarm set point (cpm) = Background (cpm) +
I (11.6 MPC/F)(168/12) 4 The failsafe set point is set approximately at a 20% lower net count, i.e.
Failsafe set point (cpm) = .8(alarm set point-background) + background 31.7.5 Set the failsafe and alarm set point using the beta check source and i
by proceeding to remove the GM tube from its shield as per the procedure in 31.7.2.1 and 31.7.2.2. *Ihen, use the trip set dials inside the GSM ratemeter box to set the trips. Next, unplug the GSM and retum the GM tube to its shield. Finally, plug in the GSM and note in the Main Log that it is back in service. ,
31.7.6 Start the stackgas pump. Reset isolation.
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31.7.7 Update both the calibration sticker and the alarm set point sticker on
, the GSM ratemeter box. ,
31.8 Logging Requirements: ,
Throughout the calibration procedure, any changes in the status of the GSM shall ,
be recorded in the Main Log. Record on the GSM chart aper that the non normal readings
- are due to the calibration of the monitor. All calibration c! in the Stack ata shall be stored Monitor Book.
31.9 Specialt None.
31.10 Acceptance Crlierla:
This procedure is complete when the Reactor Supervisor has reviewed and signed the GSM Calibration Data Sheet and the individual responsible for completing the GSM calibration has signed and dated the appropriate line of the Semi annual Checklist.
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Appendix At Gaseous Stack Monitor Calibration Data Sheet Data from high volatge plateau on the GSM probe: Date / /
i divietnn enunt epm 1
2 3
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6 7
8 9
Pwater vapor DC atm DC atm division 18 0.0201 25 0.0309 19 0.0214 26 0.0328 20 0.0228 27 0.0348 liigh Voltage set at:
21 0.0242 28 0 0369
_ divisions 22 0.0258 29 0.0391 23 0.0274 30 0.0414
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24 0.0291 31 0.0438 Data collection:
i 1.3 Temperature in room where vials filled with argon: T- *C + 273 = 'K Pressure of the argon gas in the polyvials.
1.4 Atmospheric pressure from barometer in Rm.7 : P= "Hg Convert to atmospheri: units: Patm - P x 0.033 atm/"Hg - atm Pressure of water vapor at room temperature T(see 1.3):
Pwater vapor - atm L
1.5 Pressure of argon gas:
par - Patm. Pwater vapor = atm i 1.6 Mass of gold wire:
Vial #1: g.
' Vial #2: g.
l.7 Console clock time at EOB:
- 1.11 Count rate at EOB from OSM chart paper (extrapolated)
- C= cpm 1.12 OSM background count rate before injection of argon: Bkgd = cpm 1.13 OSM hoses reconnected: OSM on: Main leg updatei 1.14 Data fmm the gamma spectrometer for activity of the Au foil (from the vial used):
Detector Efficiency (Eff) =
(see current calibration chart for shelf used)
Counts: in minutes. Start time Data Analysis:
2.1.a Calculate the activity of the Au foil (f'om the vial used) from the gamma spectrometer :
l ,
DRAFT of 4/11/90
< 1 e, , . .
Detector Efficiency (Eff) . E ds P
dps min x 6 Eff =
2.1.b Activity of onid fail at time of EOB? i L
^EOB* ,,x3g where A = nctivity of goL foil measured on the GeLi - dps
- A = decay constant for gold - 1,79 x 104 nun 1 At = time elapsed between gamma count (midpoint) and time of EOB- - min '
= dps 2.2 Neutron nun durine irradiarinn-AEOB No(1-e AI) 3 where o = neutron capture x-section for gold . 9.88 x 10-23 cm2 A - decay constant for gold - 1,79 x 10 4 min I t - irradiation time - 5 min
" ^
N - number of atoms of gold = ,, ,'g ,, , N, where atomic mass of Au = 196.97 g/mol >
mass of Au foil = g Na - 6.02 x 1023 atoms /mol
= atoms
= neutrons / cm2 .3,c l
DRAFT of 4/11/90 .
.,s.
2.3a Numhet of Ar-40 msnme in SM NAr - N, n (%Ar40 x .01) where N, - 6.02 x 1023 atoms /mol
%Ar 40 - abundance percentage of Ar40 - 99.6%
"" PArV RT where T - temperature in room where argon gas collected
'K (see 1.3) par - Pressure of argon gas at collection (rice 1.5)
- atm V -volumeof argoninjectedintochamber 5.0 ml. - 0.005 i
'I" R - gas constant - 8.2 x 10 2 mol 'K
- nel
- atoms -
2.3b Activity of Ar-41 at time of EOB:
AA/ - N A r h 0(1 c'A')
whee NAr - number of atoms of.Ar 40(see 2.3a)
= atoms
$ = Ilux (see 2 2) - neutrons /cm2 .3,e a - neutron capture cross t.ection for Ar40 - 6.5 x 10-25 cm2 A = decay constant for Ar4 0 - 6.31 x 10 3 min't !
t - Irradiation time - $ min
- dps I
2.3c Convert Ar-41 activity from dos to ucuries-A/A
^^# " 3.7 x 104
{
i DRAFTof 4/11/90 i
2.4 Determine F:
p . ^Ar..l.
'CV where AAr - argon activity - ticuries C - activity as measured by the GSM = cpm V . volume of the GSM chamber - 75$ ml
= uCi/ cpm ml 2 $ Calculate the new alarm set anint' Alarm set point - Background + (11.6 MPC/F)(168/12) where MPC = 4 x 10-8 4Ci/mi for Ar 41 Background - background rading on GSM o a epm a epm 2.6 Cniculate the new faitenfe set nnint-Failsafe set point - 0.8(Atarm set point-Background) + Background where Background - background reading on OSM
= cpm
= _Spm 3.0 Failsafe set at:
cpm Alarm set at:
cpm 4.0 Isolation reset:
l Failsafe and alarm set point sticker updated:
l i
l i
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l DRAITof 4/11/90 l
SOP 31 Appendix B
,' ,' . . . Still Air Correction Factor This calculation determines the dose rate to a pmm itanding in an unrestricted area next ;
to the stack, at a time when argon-41 has been released for a period long compared to the half life. Both dispenion in still atr and radioactive decay are considered. It is assumed that gas from the stack spreads out in a hemispherical cloud, pushing away the existing air before it, i i
D = dose rate to non in unrestricted area next to stack !
V = Volume of e haust air from stack !
Q = airflow from stack = 1330 cfm = 6.277 X 105 ml/s u(r) = radial expansion velocity of gas from stack (cm/s)
X(r) = gas concentration at r (pCi/ml) ;
F(n) = gamma function of n, with recunion relation f(n)=[F(n+1)]/n
- c = Flux to-dose-rate convenion factor for argon 41 gamma rays I kit = decay constant for argon-41 = 1.05 X 10-4s 1 !
441 = air atten, constant for argon-41 gammas = 0.68 X 10 d em'I Continuity determines the exhaust velocity u(r), and requires that dV/dt = 2xr2 dr/dt, i.e. Q = 2xr2u.
Because of radioactive decay X(r) = X(o)c 4tt, where - -
2xr2dr = c 2# I e 41( c-pr dr D = c' o 4xr2 'o
'r dr' 2x where t = ' o u(r') " M(4')3 '3" @2x D=c 4 , "o e A(4')3 e-( r) d( r), where A = 2xLiI 3Qp3 = 1113 DMPC = C .
e-( r) d(pt) = c D Xo 3
DMPC , XMPC ' o eIll32 5 dx
{ Note: , ", e AAP dx = T(1/p)}
fpy D '"
Xo 33,3 F(1/3) F(4/3) 1
3 <
E < XMPC ' o 3(1113)l/3 < 1/3 3(1113)l/3 D Xo (0.8934) Xo 1 E <XMPC 10.36 <XMPC U Thus, ; release of Xo =11.6 XMpc at the stack, continuously, will produce a dose rate less than DMPC, i.e. less than 500 mrem /yr.
- e -
.s.*
o .
J OSM AIRFIOWMEASURMENTS Transfer Standarti at inlet front the Stad GSM (cfm) Trnncfer St'd (cfm) True (cfm) 3.5 4.5 5.0 I 5.5 I 6.0 _
r Transfer Standard before Pump '
GSM (cfm) Transfer St'd (cfm) True (cfm) 3.5 '
4.0 4.5 5.0 5.5 '
6.0
% difference in transfer 4tanderd readings is less than 20%
Airflow at inlet from the stack set to 6.0 cfm "True" Corresponding GSM flow meter reading cfm Calibration sticker updated:
Date completed By signature Date reviewed By supervisor review signature DRAFT of 4/11/90