ML12060A344

University of Maryland - Response to NRC Request for Additional Information Regarding the License Renewal for the Maryland University Training Reactor

ML12060A344
Person / Time
Site:	University of Maryland
Issue date:	02/09/2012
From:	Al-Sheikhly M Univ of Maryland
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME1592
Download: ML12060A344 (26)

Text

UNIVERSITY OF MARYLAND GLENN L. MARTIN INSTITUTE OF TECHNOLOGY February 9, 2012 A. JAMES CLARK SCHOOL OF ENGINEERING Department of Materials Science and Engineering Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555-0001 Building 090 College Park, Maryland 20742-2115 301.405.5207 TEL 301.314.2029 FAX www.rnse.umd.edu

Reference:

UNIVERSITY OF MARYLAND, REQUEST FOR ADDITIONAL INFORMATION REGARDING THE LICENSE RENEWAL FOR THE MARYLAND UNIVERSITY TRAINING REACTOR ("MUTR") (TAC NO. ME1592), Docket No. 50-166, License No. R-70 The University of Maryland hereby submits the Ar-41 Measurements and Report in response to NRC Requests for Additional Information issued on April 6, 2010 and, by letter, on September 8, 2011 and February 18.

The document submitted today supplements the University's May 12, 2000, application for renewal of the license identified above as supplemented in response to Requests for Additional Information by letters dated June 7, 2004; August 4, 2004; September 17, 2004; and October 7, 2004; April 18, 2005, April 25, 2006 (two letters); August 28, 2006 (two letters); November 9, 2006 and December 18, 2006; May 27, 2010; August 27, 2010; September 22, 2010 and December 14, 2010; January 31, 2011; February 2, 2011; March 17, 2011; May 2, 2011, July 5, 2011, July 29, 2011; September 26, 2011; September 28, 2011; October 12, 2011, and January 31, 2012.

Please write or email me at: Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742-2115 or email Materials Science and Engineering, University of Maryland, College Park, MD 20742-2115 or mohamad@umd.edu if you have questions about this submission.

Please copy Prof. Robert Briber on any such correspondence:

Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742-2115; rbriber@umd.edu.

I declare under penalty of perjury that the foregoing is true and correct.

Sincerely, AWV44 Mohamad AI-Sheikhly Professor and Director Maryland University Training Reactor cc:

Robert Briber (By e-mail)

IJ1o

Ar-41 Occupational and Public Dose Assessment at the MUTR This section deals with the assessment of radiation dose contributions due to Argon-41 gas generated from operation of the Maryland University Training Reactor (MUTR). The MUTR is housed at the Chemical and Nuclear Engineering Building on the University of Maryland College Park Campus. The MUTR is used for the training of Nuclear Engineering students and for research purposes.

Radiation Protection Federal guidelines demand that "A sustained effort should be made to ensure that collective doses, as well as annual, committed, and cumulative lifetime individual doses, are maintained ALARA (As Low As Reasonably Achievable)." In working toward this goal, several conditions needed to be taken into account. Firstly, the dose levels of Argon-41 achievable in areas immediately adjacent to the MUTR accessible by the general public were to be kept below limits as outlined in Federal regulation 10 CFR 20.

Secondly, total dose contribution of Argon-41 for radiation workers in the MUTR facility must not only be kept below the limits specified in 10 CFR 20, but also ALARA. Thirdly, actions taken to comply with the first two tenets must not cause excess wear or damage to operation controls or components of the MUTR or induce excessively adverse working conditions for radiation workers at the MUTR.

To ensure safe and productive use of the MUTR, all activities taken there are conducted in strict accordance with federal and state safety regulations. Operation at the MUTR shall be carried out in ways designed to minimize unnecessary radiation dose to radiation workers and to members of the general public. These doses shall be maintained ALARA.

Sources of Argon-41 Argon-41 is generated during use of the MUTR. Most stems from the activation of dissolved air in the reactor water, though some trace contributions may come from neutron beam activation of air trapped in the thermal column or beam ports. As the reactor water warms, it loses its ability to hold air and it percolates through the reactor pool surface. Assays of Argon-41 levels within the MUTR have been performed to determine concentration and public dose due to normal reactor operations.

Occupational Dose to Argon-41 from Normal Reactor Operations The dose risk for those occupationally exposed to Argon-41 is determined by calculating its concentration in air in terms of activity per unit volume. This is compared to the Derived Air Concentration (DAC),

which is the threshold whereupon a radiation worker over the course of a standard "work-year" would receive a dose equivalent to their annual limit of 5 rem per year for whole body dose. The DAC for Argon-41 is 3.0 x 10-6 uCi/ml.

An accurate measure of Argon-41 levels at the MUTR was necessary to evaluate actions to mitigate potential doses. Two techniques were chosen to obtain this data. The first involved using an unshielded radiation measuring probe, a High Purity Germanium (HPGe) detector, to directly measure gamma emissions from Argon-41 and track its increase in concentration until equilibrium was obtained. This data provided the time required to reach maximum Argon-41 concentration, as shown in Figure 1.

Figure 1 Argon-41 levels at maximum power from time zero to 300 minutes MUTR Control Room Spectra 60000 S.

.Post Shutdown 4 2 Minutes

-250 kW + 299 Minutes 250 kW + 276 Minutes

-*-250 kW + 252 Minutes S---250 kW + 228 Minutes 250 kW + 204 Minutes

-250 kW + 182 Minutes 30000 250 kW + 158 Minutes 250 kW + 136 Minutes

_:250kw.- 114 MinuteS

-250kW.

92 Minutes

-*.250 kW + 69 Minutes

-*-250kW+ 47 Minutes

-o-250 kW + 25 Minutes 4--1-250 kW + 0 Minutes 100 1250 1260 1270 1280 1290 1300 1310 1320 1330 1340 1350

.Channel The results indicated a time of between 3 V/2 and 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to reach equilibrium of Argon-41 within the MUTR facility. These results were projected in a graph versus time, as shown in Figure 2. The sample counts taken from 180 minutes to shutdown were averaged to determine an equilibrium value. From this projection, Argon-41 increased approximately 0.56% of the averaged equilibrium rate per minute from Time Zero.

Figure 2 Argon-41 levels versus time 45000 40000 35000 30000 25000 20000 15000 10000 5000 0

50

-2 25

-3 50 100 150 200 250 300 350

The second technique took air samples from various locations within the MUTR facility and measured activities of Argon-41.

Concentrations in various zones within the MUTR and in areas adjacent to it could then be determined.

All measurements in these assays were taken with the MUTR at its maximum power (250 kW) and air samples were taken with Argon-41 levels at equilibrium. In actuality, the MUTR could not be operated at maximum power for the duration of one "work-year" (2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />) in the course of a calendar year. These conditions were chosen for the evaluation, however, to provide a safety margin as it represented "worst-case" conditions.

Air samples were taken from four zones within the MUTR facility as indicated in Figure 3.

All the samples were taken at breathing level, defined as 1 meter above the floor for sitting position, and 1.5 meters for standing positions. Position A took samples at the reactor pool edge at a height of 1.5 meters.

Position B took samples 1 meter back from the reactor control console at a height of I meter. Position C took samples at 2 meters back from thermal column at a height of 1.5 meters. Position D took samples at 1 meter from balcony edge at a height of 1.5 meters.

I liter Marinelli beakers evacuated under vacuum were used to take the air samples. Measurements of the Marinelli beakers after evacuation indicated a pressure of approximately 150 Torr, a level comparable to the rating of the vacuum pump used (Little Giant model 13154). This translates to approximately 20% of the original volume of air held within the beaker. To account for the difference from ideal vacuum, the Marinelli beakers were evacuated in the sample zone within the MUTR. Each Marinelli beaker was then evacuated three times (opening on-site in between each evacuation) to reduce the amount of original ambient air within the beaker to less than 1% of the sample volume. Three samples were taken at each location and the sample closest to the median was used for activity calculations. This would eliminate the effect of outliers possibly caused by loss of vacuum of the Marinelli beakers or anomalous plumes of Argon-4 1.

Figure 3 Argon-41 sampling locations 230ME B

A 1308A D

2308W

To account for deviations from Normal Temperature and Pressure (NTP - 200 C and 760 Torr),

measurements of ambient temperatures and pressures were taken with each sample. With this data, an Effective Volume of air contained within the Marinelli beaker was calculated. Effective volume was determined from the Ideal Gas Law. With PV=nRT as our sample of gas and P'V'=nRT' as a sample of gas at NTP, we can calculate the following:

nRT V =P nRT V

p V'

nRT' nRT v=

PP nRT' P/

nRT' P/

nRT P

-n--R--'

p, As V' = 1 liter T

T' TP' PT' Efficiency calibration carried out using an air equivalent standard (Eckhart and Ziegler Standard 81144A-577), as shown in Figure 4. The efficiency for Argon-41(which has a gamma emission energy of 1293 keV) was determined by calculating the slope between Co-60 energies (1173 keV and 1332 keV). For the measurements taken in this assay, the fractional efficiency for Argon-41 was calculated to be 6.61 x 10-3.

Figure 4 - Efficiencies of radionuclides contained in Eckhart and Ziegler Standard 81144A-577 w~o E -oi...

w~oE-o3 0

t

+

500 loco Energy (keV) t500 2000 Activity was determined by first decay correcting the total counts back to the time of sampling. The decay-corrected counts were then divided by the detector efficiency to get the total counts over the counting period.

The counts were divided by the total time in seconds to determine decays per second (Bq) and then converted to jtCi. The equation is as follows:

Activity = (Counts/1200 )/(37000dps/([tCi))

The final concentration is a ratio of the Activity to the Effective Volume in milliliters.

The results of the assays of the MUTR at maximum power and Argon-41 levels at equilibrium are shown in Tables I and 2.

Table 1 Argon-41 count levels with relevant sample data at time of acquisition with calculation values highlighted.

Location Time of Transit Time of Air Humidity Pressure Water Counts Sample time (s)

Acquisition Temp

(%)

(in)

Temp Console I

2 12:51 159 12:53 75 24 30.16 39.1 1330 3

13:13 152 13:15 75 25 30.15 38 1150 Bridge 1

-7 2

13:59 138 14:02 78 25 30.11 36.3 1132 3

14:21 158 14:24 78 25 30.10 35.6 1205 Experiment 1

14:45 120 14:47 69 28 30.09 35.1 2643 Floor 2

3 15:31 125 15:33 65 33 30.08 34.3 3794 Balcony' 1

15:52 129 15:54 75 30 30.07 33.8 961 2

16:14 250 16:18 75 30 30.07 33.8 964 1 As only two samples could be obtained prior to reactor shutdown, their results were averaged for the sake of calculation.

Table 2 Argon-41 concentrations at equilibrium expressed as activity/volume and in percentage of DAC in the occupationally exposed area of the MUTR at maximum power Sample Location Air Temp (C)

Air Press (TORR)

Effective Volume (I)

Console 23.3 766.1 1.16 Bridge 25.6 765.3 1.27 Exp. Floor 1 8.9 764 0.94 Balcony2 23.9 763.8 1.19 12:30 12:32 1296 1312.5 13:36 13:38 1134 1148.4 15:08 15:10 2848 2884.2 15:52 15:54 963 975.3 0.0045 3.87E-06 129.0 0.0039 3.08E-06 102.6 0.0098 1.05E-05 348.5 0.0033 2.79E-06 93.2 Since the MUTR takes between 3 1/22 and 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> for Argon-41 to reach equilibrium values, the calculated concentrations of Argon-41 do not represent a proper way to compare to the DAC. To account for lower concentration of Argon-41 over the time interval between Time Zero and equilibrium, an Effective Concentration was determined by 1) assuming a linear increase in concentration until equilibrium; 2) obtaining the equilibrium level from an average of counts taken between 180 to 299 minutes; and 3) using 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> as the time to reach average equilibrium. With a linear concentration increase inArgon-41 concentration, the effective concentration would be 0.75 of the average equilibrium, assuming 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> operation of the MUTR. The results are shown in Table 3.

Table 3 Effective Concentration of Argon-41 levels over 8-hour operation of the MUTR at maximum power Exp. Floor I

0.0098 1.05E-05 I

7.84E-06 I

261.4 Balcony 0.0033 2.79E-06 2.1OE-06 69.9

Even adjusted as Effective Concentration, the assays of Argon-41 still yield two zones near or above the DAC. One possible action to minimize levels of Argon-41 would be to run the ventilation fans within the MUTR during all hours of operation. While this would definitely minimize public and radiation worker dose contributions from Argon-41, it would have several negative effects on the MUTR facility and its operation. During the winter months, outside air would cause a severe drop in temperature, as the air is not conditioned, and this would likely affect safe operator and worker performance. High humidity, especially in the summer months, would eventually corrode and degrade control components such as relays. For this reason, constant operation of the fans was not considered a viable action. Instead, intermittent use of the fans during MUTR operation was chosen as the technique best suited to meet the required conditions. At 50% of the maximum concentration of Argon-41, the fans were operated for ten and fifteen minutes intervals (allowing for a complete change of the volume of air in the MUTR). In this way Argon-41 's dose contributions would be mitigated, as dictated by the ALARA principle, while not affecting the safe operation of the MUTR through excess wear. This was tested in the experiment shown below.

The first trials tested 10 minute runs of the ventilation fans approximately every two hours. Assays were conducted using both an open HPGe probe at the Console and evacuated Marinelli beaker samples at the Experiment Floor. The HPGe probe logged data every 20 minutes and the Marinelli samples were taken at points prior to and after fan operation. These tests indicated the technique would result in an effective concentration of 50 to 55% of the average equilibrium, assuming an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> operation of the MUTR at full power (See Figure 5).

Figure 5 Chart of effects of 10 minute ventilation fan operation on Argon 41 concentration, expressed as percentage of the DAC 120%

Fan Effects on Argon 41 Concentration in Control Room. Normalized to mO:oo U 0:23 100%

0:43

• 1:07 0 1:30 80%

0 1:52 N 2:24 60%

12:46

'00%

03:10 a 3:32 40%

3:57 m 4:28 N 4:50 20%

0 5:11 1 5:44 0%

166:06 Time (HH:MM)

Considering the concentration of Argon-41 found on the Experiment Floor, the next trial increased the length of fan operation to 15 minutes. Evacuated Marinelli beakers were used to assay Argon-41 concentration at the Console. Two samples were taken for each fan run, one prior and one after, to calculate the drop in Argon-41 concentration. For these tests, movement to and from the MUTR was restricted as much as possible and the door from the Console to the Bridge was shut. This resulted in higher concentrations of Argon-41 than would be found under normal conditions, but would give the clearest indication of the ventilation fan performance. The results of the tests are shown in Table 4.

Table 4 Argon-41 reductions in concentration with ventilation fan operation expressed as activity/volume and in percentage of DAC in the occupationally exposed area of the MUTR at maximum power Sample Location Air Temp (C)

Air Press (TORR)

Adjusted Volume (1)

Console pre 1 22.2 771.9 1.09 Console post 1 18.8 771.9 0.93 Console pre 2 20 771.9 0.98 Console post 2 20 771.4 0.99 Console pre 3 21.7 769.9 1.07 Console post 3 20 769.9 0.99 10:45 10:48 1093 1106.91 11:16 11:17 339 343.31 1:04 1:06 1575 1595.04 1:34 1:36 395 400.03 3:22 3:23 1793 1815.81 3:49 3:51 315 319.01 1106.91 0.0035 3.16E-06 105.32 343.31 0.0011 1.16E-06 38.57 0.69 1595.04 0.005 5.05E-06 168.45 400.03 0.0012 1.27E-06 42.22 0.75 1815.81 0.0057 5.29E-06 176.29 319.01 0.0001 1.01E-06 33.6 0.82 Argon-41 concentrations averaged drops of 75% after ventilation fan runs of 15 minutes. We can project this pattern of reduction onto the equilibrium levels of Argon-41 obtained under normal conditions at maximum power. Conducting 15 minute fan runs every two hours results in the reductions in Argon-41 concentrations in the following tables and graphs.

Table 6 Reduction in Argon-41 concentration at MUTR Bridge expressed as percentage of DAC with reactor power at 250kW 0

0 2

52.5 2.42 16.3 4.42 68.8 4.84 17.2 6.84 69.7 7.26 12.3

%of DAC 80 60 40 *

%of DAC 20 0

0 2

2.42 4.42 4.84 6.84 7.26 Average % of DAC 33.8 Table 7 Reduction in Argon-41 concentration at MUTR Console expressed as percentage of DAC with reactor power at 250kW 0

0 2

65 2.42 20.2 4.42 85.2 4.84 21.3 6.84 86.3 7.26 15.2

%of DAC 1001 90 70 40 30 20 10 0

0 2

2.42 4.42 4.84 6.84 7.26 Average % of DAC 41.9 Table 8 Reduction in Argon-41 concentration at MUTR Balcony expressed as percentage of DAC with reactor power at 250kW U

U 2

46.6 2.42 14.4 4.42 61.0 4.84 15.3 6.84 61.9 7.26 10.9 Average % of DAC 30.0

%of DAC 70 60 50 40 30 -

• %of DAC 20 10 0

0 2

2.42 4.42 4.84 6.84 7.26

Table 9 Reduction in Argon-41 concentration at MUTR Experiment Floor expressed as percentage of DAC with reactor power at 250kW

%of DAC U

U 250 2

175 2.42 54.3 4.42 229.3 4.84 57.3 6.84 232.3 7.26 40.9 o AC A

200 150-100 -

50-

• %of DAC Average % of DAC 112.7 U

1 1

0 2

2.42 4.42 4.84 6.84 7.26 Using ventilation fan runs at two hour intervals result in overall Argon-41 concentrations well below the DAC except in the case of the Experiment Floor, which remains at an estimated 112.7% of the DAC.

Estimated Annual Dose to Uncontrolled Areas due to Argon-41 Production from the MUTR The dose risk for members of the general public in uncontrolled areas due to Argon-41 is conducted using two modeling software packages: the Environmental Protection Agency program COMPLY, and HotSpot (Version 2.07.1). To model the dose to the general public outside the Chemical and Nuclear Engineering Building, which houses the MUTR, both programs are used.

Both models take into consideration factors such as release height and wind speed. HotSpot uses a more detailed model to calculate the Total Effective Dose Equivalent (TEDE) to a receptor. For the total activity, the average concentration of Argon-41 generated by the MUTR at maximum power at equilibrium, 5.82 xl0-6 gCi/ml, was multiplied by the total volume of the facility. With ventilation fans running every 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> during operation, 4 "flushes" of 75% of the total Argon-41 activity would occur each operating day. Projected over 250 operating days per year, this calculates to 1.7 Curies per Year released.

The HotSpot program projection can be found in Attachment A. According to HotSpot, the maximum possible dose received by a member of the general public would be 1.81 mrem.

The factors were then entered into the COMPLY program as a confirmation model. The report can be found in Attachment B. The maximum potential dose according to the COMPLY model projects to 5.1 mrem per year.

To account for seepage of Argon-41 at ground level, HotSpot was used to model leakage. A leakage rate of 5% of the previously calculated total activity at the surface was used to calculate potential dose. As a point of comparison the leakage model was calculated manually. The calculation assumed no ventilation fans run during the operation, the most conservative model. One calculates the Deep Dose Equivalent (DDE) to members of the public at a given distance downwind from the facility by the following equation:

DDE thy or DDEwb =

ji [(X/Q) DCFext Ai Xv [exp{-Xti,-exp{-)it 2}])/()1 )]

Where:

Parameters used to calculated Dose Room Ventilation exhaust rate Room Leakage rate Reactor Room Volume 2.83 0.00236 1700 m3/s m3/s m3 Variables in the Dose Equation X/Q

DCFex, Ai xv ti t2 Atmospheric dispersion coefficient in s/m 3 External Dose Conversion Factors mrem m3 uCi-' s' Released Activity per isotope I in uCi Ventilation Constant (leakage rate/reactor volume) I/s time plume arrives at receptor point s 5 s time plume has passed receptor point s 28800 s radioactive decay constant in 1/s Note: only one set oftl and t2 values are used as the change in arrival and passage does not change the TEDE values with any significance between 100 and 300 m.

The results of this calculation are shown in Table 10.

Table 10 Argon-41 Leakage Dose rate per day in mrem/day DDE Public Ground Level Release (Leakage Case)

Isotope X/Q (10)

X/Q X/Q X/Q (300)

BR DCFX Ai [uCil I*

Ar-41 6.OOE-02 2.41E-02 6.63E-2.61E-03 3.30E-2.41E-3.95E+03 1.052E-03 04 04 04 ti exp{-

?Rt1) t2 exp{-

DDE(IOm)

DDE (lOOm)

DDE (200m)

DDE (300m) 0 1.OOE+0T 2.88E+04 4.83E-02 7.11E-03 I 2.86E-1 7.86E-3.09E-04 03 04 Total dose to public over 50 weeks/yr at 8hr/d 1L178 rnrm Ai is 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> activity tI is 0 time t2 is 8hrs

Figure 6 Forecasted Exponential Trend Line Analysis of the X/Q Values for 100 to 300 meters Leakage forecast of 10 meter x/Q [s/m3]

0.08l-0.07 0.06 0.05 0.04

-X]Q [s/m3]

0.03

-Expon.

(X/Q [s/m3 y =

.069e-0011X 0.02 R'

0.9914 0.01 0

0 s0 100 150 200 250 300 350 distance along centerline Ground Level Release (H =0) Centerline X/Q [s/m 3] = [1/lOyazn]

X(xO) [m]

A B

C E

F 100 4.02E-04 9.95E-04 1.59E-03 1.75E-02 2.41E-02 200 1.18E-04 2.65E-04 4.72E-04 4.25E-03 6.63E-03 300 4.14E-05 1.14E-04 2.02E-04 1.88E-03 2.61E-03 X(X,O) [M] x/Q [s/m3]

300 2.61E-03 200 6.63E-03 100 2.41E-02 10 6.00E-02 The HotSpot leakage model projection can be found in Attachment C. The maximum potential dose to a member of the general public according to the HotSpot model is 4.39 mrem.

Conclusion In uncontrolled areas, the potential public dose due to Argon-41 is well within the limits specified in 10 CFR 20. The potential occupational dose contribution due to Argon-41 is also well within regulatory limits when the ventilation fans are operated at 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> intervals for a minimum of 15 minutes at all locations within the MUTR except the Experiment Floor. In order to maintain the occupational dose of all workers around the MUTR, the following additional precautions will be taken.

EXPERIMENT FLOOR KILOWATT HOUR RESTRICTION The DAC of 3.0 x 10,6 ptCi per ml is based on a work year of 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />. Access to the Experiment Floor of the MUTR shall have an annual cap of the equivalent of 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> at full power. After reaching this threshold, personnel shall be restricted from accessing the Experiment Floor during reactor operation.

Logs of total kilowatt hours of operation are maintained at the MUTR. With such a cap in place, all of the zones within the MUTR will have effective Argon-41 concentrations below the DAC (projected over the course of the calendar year).

ALARA PROGRAM All radiation workers at the MUTR are issued dosimetry sensitive to beta, gamma and neutron radiation on a bimonthly basis. The ALARA program triggers an investigation whenever a radiation worker receives a dose of 10% of the bimonthly limit (approximately 80 mrem). The investigation will take into account worker technique and evaluate possible changes in potential dose. This assures workers at the MUTR that not only will their occupational dose be within regulatory limits, but will be maintained ALARA.

The MUTR will continue to evaluate performance on an ongoing basis and strive to optimize all techniques to reduce the level of exposure due to Argon-41.

In this way, we can assure that both workers within the MUTR and the general public that safety is a top concern at the University of Maryland.

Attachment A - Annual Release of Ar-41 from MUTR Effluent Assessment From HotSpot

Annual Release of Ar-41 from MUTR HotSpot Version 2.07.1 General Plume Feb 03, 2012 03:33 PM Source Material

Ar-41 1.0961 E+02 m Material-at-Risk (MAR) : 7.4200E+00 Ci Damage Ratio (DR) :1.000 Airborne Fraction (ARF) :1.000 Respirable Fraction (RF) :1.000 Leakpath Factor (LPF) :1.000 Respirable Source Term

7.42E+00 Ci Non-respirable Source Term : 0.OOE+00 Ci Effective Release Height : 7.25 m Wind Speed (h=10 m)

2.00 m/s Distance Coordinates

All distances are on the Plume Centerline Wind Speed (h=H-eff)

1.68 m/s Stability Class

F Respirable Dep. Vel.

0.00 cm/s Non-respirable Dep. Vel.

8.00 cm/s Receptor Height

1.5 m Inversion Layer Height

None Sample Time

• 10.000 min Breathing Rate

3.33E-04 m3/sec Maximum Dose Distance

0.32 km MAXIMUM TEDE

1.81E-03 rem Inner Contour Dose

1.0 rem Middle Contour Dose

0.500 rem Outer Contour Dose

0.100 rem

Exceeds Inner Dose Out To : Not Exceeded Exceeds Middle Dose Out To: Not Exceeded Exceeds Outer Dose Out To : Not Exceeded FGR-l I Dose Conversion Data - Total Effective Dose Equivalent (TEDE)

Include Plume Passage Inhalation and Submersion Include Resuspension (Resuspension Factor: Constant Value) I.OOE-05 1/meter Exposure Window:(Start: 0.00 years; Duration: 1.00 years) [100% stay time].

Initial Deposition and Dose Rate shown Ground Roughness Correction Factor: 1.000 RESPIRABLE DISTANCE T E D E TIME-INTEGRATED ARRIVAL TIME AIR CONCENTRATION km (rem)

(Ci-sec)/m3 (hour:min) 0.010 0.100 0.200 0.300 0.400 0.500 0.OE+00 2.9E-05 1.2E-03 1.8E-03 1.7E-03 1.4E-03 0.OE+00 1.2E-04 5.2E-03 7.5E-03 7.OE-03 5.9E-03

<00:01

<00:01 00:01 00:02 00:03 00:04

Attachment B - Annual Release of Ar-41 from MUTR Effluent Assessment From COMPLY

40 CFR Part 61 National Emission Standards for Hazardous Air Pollutants REPORT ON COMPLIANCE WITH THE CLEAN AIR ACT LIMITS FOR RADIONUCLIDE EMISSIONS FROM THE COMPLY CODE, VERSION 1.4 Prepared by:

University of Maryland MUTR Building 090 Mary Dorman 301-314-8336 Prepared for:

U.S. Environmental Protection Agency Office of Radiation Programs Washington, D.C. 20460 Ar-41 release from MUTR SCREENING LEVEL 2 DATA ENTERED:

RELEASE RATES FOR STACK 1.

Release Rate Nuclide (curies/YEAR)

AR-41 3.710E+00 RELEASE RATES FOR STACK 2.

Release Rate Nuclide (curies/YEAR)

AR-41 3.710E+00 SITE DATA FOR STACK 1.

Release height 7 meters.

Building height 11 meters.

The source and receptor are not on the same building.

Distance from the source to the receptor is 10 meters.

Building width 14 meters.

SITE DATA FOR STACK 2.

Release height 7 meters.

Building height 11 meters.

The source and receptor are not on the same building.

Distance from the source to the receptor is 10 meters.

Building width 14 meters.

Default mean wind speed used (2.0 m/sec).

NOTES:

Input parameters outside the "normal" range:

None.

RESULTS:

Effective dose equivalent:

5.1 mrem/yr.

• • • Comply at level 2.

This facility is in COMPLIANCE.

It may or may not be EXEMPT from reporting to the EPA.

You may contact your regional EPA office for more information.

• • • • • • • • • • END OF COMPLIANCE REPORT

• Attachment C - Leakage Dose from MUTR for Argon-41 Effluent Assessment From HotSpot

Annual Leakage Dose from MUTR for Ar-41 HotSpot Version 2.07.1 General Plume Feb 03, 2012 03:31 PM Source Material

Ar-41 1.0961 E+02 m Material-at-Risk (MAR) :3.7100E-01 Ci Damage Ratio (DR) : 1.000 Airborne Fraction (ARF) : 1.000 Respirable Fraction (RF) :1.000 Leakpath Factor (LPF) :1.000 Respirable Source Term

3.71E-01 Ci Non-respirable Source Term : 0.OOE+00 Ci Effective Release Height : 0.00 m Wind Speed (h=10 m)

2.00 m/s Distance Coordinates

All distances are on the Plume Centerline Wind Speed (h=H-eff)

0.83 m/s Stability Class

F Respirable Dep. Vel.

0.00 cm/s Non-respirable Dep. Vel. : 8.00 cm/s Receptor Height

1.5 m Inversion Layer Height

None Sample Time

10.000 min Breathing Rate

3.33E-04 m3/sec Maximum Dose Distance

0.067 km MAXIMUM TEDE

4.39E-03 rem Inner Contour Dose

1.0 rem Middle Contour Dose

0.500 rem Outer Contour Dose

0.100 rem Exceeds Inner Dose Out To : Not Exceeded Exceeds Middle Dose Out To : Not Exceeded Exceeds Outer Dose Out To : Not Exceeded FGR-11 Dose Conversion Data - Total Effective Dose Equivalent (TEDE)

Include Plume Passage Inhalation and Submersion Include Resuspension (Resuspension Factor : Constant Value) 1.00E-05 I/meter Exposure Window:(Start: 0.00 years; Duration: 1.00 years) [100% stay time].

Initial Deposition and Dose Rate shown Ground Roughness Correction Factor: 1.000 RESPIRABLE DISTANCE T E D E TIME-INTEGRATED ARRIVAL TIME AIR CONCENTRATION km (rem)

(Ci-sec)/m3 (hour:min) 0.010 0.OE+00 1.4E-19

<00:01 0.100 3.4E-03 1.4E-02 00:02 0.200 1.2E-03 5.2E-03 00:04 0.300 6.OE-04 2.5E-03 00:06 0.400 3.5E-04 1.5E-03 00:08 0.500 2.3E-04 9.7E-04 00:10

Response to Request for Additional Information Regarding Occupational and Public Doses During Normal Operation Due to Ar-41 Occupational Dose Mr. Edward Case of the Radiation Safety Office conducted a series of measurements to determine Ar-41 concentrations inside the reactor building with the reactor operating at full power (250 kW) for two different scenarios: (1) no operation of the ventilation system fans, and (2) intermittent fan operation. Measurements were taken at four locations: reactor bridge, control room, balcony, and experimental floor. At steady state Ar concentrations (reached approximately four hours after startup and power ascension to 250 kW) and 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> of reactor operation in a year, the DAC is exceeded in the control room (-129%) and experimental floor (-350%). If the time to reach equilibrium Ar is taken into account, these values reduce to

-97% and -260% respectively. Bridge and balcony data were not evaluated, since personnel will not be in either of these areas for any extended periods of time.

From these results, it was clear that Ar concentration, especially on the experimental floor, needed to be reduced. Therefore, the decision was made to operate the ventilation fans intermittently. Measurements taken for 15 minute fan operation every 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of reactor operation showed significant effects. The control room concentration is reduced to - 42% of DAC (assuming 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> of operation at full power) and -112% of DAC for the experimental floor.

Therefore, a decision was made to require intermittent fan operations - 15 minutes every two hours of reactor operation. This will require a change to the current technical specifications Section 3.5 and 4.5. The proposed TS changes are attached.

Additionally, it was decided to restrict personnel access to the experimental floor if the equivalent of 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> of operation at full power (3.75xl 0A5 kW-hr) is reached in a calendar year. Logs of kW-hr are currently maintained, so a new operating procedure will be written which incorporates this limitation. In this manner, it is ensured that the maximum dose that a person could get on the experimental floor, assuming he/she was there for the maximum allowable kW-hr is approximately 80% of the DAC.

It must be recognized that the measurements and analysis have determined the worst-case occupational exposure from Ar-41 utilizing an operating time of 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />. Realistically, the MUTR is not capable of operating for this period of time due its inherent design. Although the University is not taking credit for this fact in its calculations, it must be acknowledged that in reality, the potential occupational dose to workers from Ar-41 at the MUTR, would be much lower than presented.

That being said, the ALARA program at the University of Maryland closely monitors occupational doses of the individual. There are varieties of radiation sources a worker can be exposed to, not only Ar-41. The University's ALARA program requires an investigation of any radiation worker receiving a dose equivalent of 10% of the annual occupational limit (80 mrem, DDE for bi-monthly monitored individuals.). The investigation will entail an evaluation of the

worker's behavior in and around the MUTR and their techniques surrounding any experiments.

Any necessary actions required to limit excessive radiation dose will be prescribed according to the ALARA principle. Notwithstanding, the restrictions cited above, recognizing what we've determined about how Ar-41 behaves in the reactor bay, ALARA dictates that worker time is minimize on the reactor floor at all times.

As stated above, access to the MUTR experiment floor will be restricted whenever the reactor achieves a total equivalent of 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> at full power (3.75x 105 kW-hr, in which the level of Argon-41 reaches approximately 80% of the DAC over the calendar year), regardless of the total dose received by personnel. This will provide an additional safety precaution toward keeping radiation worker dose ALARA around the MUTR.

Public Dose COMPLY and HotSpot were used to determine public dose outside of the reactor building, assuming 5% leakage from the facility. Results show that doses are well within the limits of I OCFR20.

Mr. Case's report, which details his experimental measurements and analysis for the occupational dose, and the results of the COMPLY and HotSpot calculations, is attached.

Response to NRC Request for Additional Information Regarding Occupational and Public Doses During Normal Operation Due to Ar Technical Specification Revisions (Revisions are highlighted in red)

(Note that this revision also includes changes made to Sections 3.5 and 4.5 in response to the Request for Additional Information regarding the Maximum Hypothetical Accident.)

Section 3.5 VENTILATION SYSTEMS Applicability These specifications apply to the ventilation systems for the reactor building.

Objective The objective of these specifications is to ensure that air exchanges between the reactor confinement building and the environment do not impact negatively on the general public.

Specifications

1.

Air within the reactor building shall not be exchanged with other occupied spaces in the building.

2.

All locations where ventilation systems exchange air with the environment shall have failsafe closure mechanisms.

3.

Except during non-routine fuel movement operations, forced air ventilation to the outside shall automatically secure without operator intervention in such case that the radiation levels exceed a preset level as defined in facility procedures. The setpoints are: 50 mR/hr (bridge monitor), 10 mR/hr (exhaust monitor).

4.

During non-routine fuel movement operations, the ventilation system shall be operating.

5.

The ventilation system shall be operated for a period of 15 minutes every two hours of reactor operation.

Bases

1.

This specification ensures that radioactive releases inside the reactor building will not be transported to the remainder of the building.

2.

This specification ensures that the reactor building can always be isolated from the environment.

3.

This specification ensures that in the event high radiation levels are detected, radioactive release will be minimized by stopping forced flow to the outside environment except during non-routine fuel movement operations.

4.

This specification ensures that in the event that a fuel bundle is damaged when out of the reactor pool, the subsequent radioactive release will be diluted and dispersed in the outside environment.

5.

This specification ensures that the concentration of Ar-41 does not reach levels which would exceed the maximum allowable by periodically purging of the reactor building to the outside environment.

Section 4.5 VENTILATION SYSTEMS Applicability This specification applies to the reactor ventilation system.

Objective The objective is to assure that provisions are made to restrict the amount of radioactivity released to the environment.

Specifications The operability of and the ability to secure the ventilation system shall be verified before the first reactor operation of the day.

Bases The facility is designed such that in the event that if excessive airborne radioactivity is detected during normal operations, the ventilation system shall be shutdown to minimize transport of airborne materials.

Requiring that the ventilation system be operating during non-routine fuel movement operations ensures that requirements of 10 CFR Part 20 for personnel outside of the reactor building are met. Analysis indicates that in the event of a major fuel element failure reactor building personnel would have sufficient time to evacuate the facility before the maximum permissible dose (10 CFR Part 20) is exceeded.

Requiring intermittent ventilation system operation during reactor operation ensures that requirements of 10 CFR Part 20 for reactor personnel are satisified.