ML13305A128

Proposed Technical Specification Modification

ML13305A128
Person / Time
Site:	Washington State University
Issue date:	10/08/2013
From:	Wall D Washington State Univ
To:	Wall D Document Control Desk, Office of Nuclear Reactor Regulation
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Download: ML13305A128 (36)

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WASHINGTON STATE1 UNIVERSITY Nuclear Radiation CenterDate: October 8, 2013To: Document Control DeskFrom: Donald Wall, Ph.D.DirectorRe: Proposed Technical Specification Modification The purpose of this letter is to request an amendment to the Technical Specifications for facilityLicense R-76, Docket number 50-27. Specifically, this request proposes to modify the range ofallowed ventilation system flow rates. The document which is included with this letter providesa complete data analysis to show the impact of ventilation system flow rates on whole body andthyroid doses for reactor personnel within the reactor pool room and for offsite individuals.

Theproposed modification to the Technical Specifications will allow greater operational flexibility within the range of proposed ventilation system flow rates while also remaining well below thedose limits for personnel and the public.I declare under penalty of perjury that the foregoing is true to the best of my knowledge.

Respectfully Submitted Donald WallP.O. Box641300,

Pullman, WA 99164-1300 509-335-8641

• Fax: 509-335-4433

-www.wsu.edu/nrc

?ýt2'0 Analysis of the Influence of Ventilation System Flow Rates on Radiation DosesFollowing a Maximum Hypothetical Accident1.0 Introduction The purpose of this letter is to provide an analysis of doses to individuals in the reactor poolroom and to members of the public who could be off-site during the course of a MaximumHypothetical Accident (MI-A). The type of releases arising from an MHA considered in thisletter are elevated releases through the Dodgen Research Facility exhaust stack. The currentTechnical Specifications prescribe specific ventilation system flow rates. The present analysiswill show that the ventilation system flow rates that are prescribed in the Technical Specifications are much greater than necessary to provide adequate protection for facilitypersonnel and members of the public. WSU therefore proposes to modify the Technical Specifications 3.4(1)(a) and 3.4(1)(b) to allow a range of acceptable ventilation system flowrates.Technical Specifications 3.4(1)(a) and 3.4(1)(b) were added after discussions with the U.S. NRCat the time of the renewal of facility license R-76. The requirement was added on the basis of theMHA analysis that was presented in Appendix MHA in a letter to the U.S. NRC dated June 13,2008 (ML0832380265).

The MHA analysis presented doses and dose rates uinder variousscenarios, but did not present results as a function of ventilation system flow rate. The presentanalysis expands the examination of the release scenarios by presenting the dose rates and dosesas functions of ventilation system flow rates for personnel in the reactor pool room, and for amaximally exposed member of the public external to the facility.

The current Technical Specification for exhaust system flow rates is listed below, followed bythe proposed modification.

2.0 The WSU Technical Specifications Section 3.4.(1).3.4 Ventilation SystemSpecifications:

(1) The reactor shall not be operated unless the facility ventilation system is operable andoperating, except for periods of time not to exceed 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to permit repair or testing ofthe ventilation system. The ventilation system is operable when flow rates, dampers andfans are functioning normally.

The normal, dilute and isolation modes shall be operablefor the ventilation system to be considered operable.

Page 1 of 35

a. The exhaust flow rate of the ventilation system in the normal mode, from thereactor pool room, shall be not less than 4000 cfm.b. The exhaust flow rate of the ventilation system in dilute mode, from the reactorpool room, shall be 300 cfm.3.0 Proposed Modification to Technical Specification Section 3.4.(1)WSU proposes to change the text of section 3.4(1) of the Technical Specifications to thefollowing (the proposed change is marked with a change bar):3.4 Ventilation.

SystemSpecifications:

(1) The reactor shall not be operated unless the facility ventilation system is operable andoperating, except for periods of time not to exceed 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to permit repair or testing ofthe ventilation system. The ventilation system is operable when flow rates, dampers andfans are functioning normally.

The normal, dilute and isolation modes shall be operablefor the ventilation system to be considered operable.

a. The exhaust flow rate of the ventilation system in the normal mode, from the reactorpool room, shall be not less than 1000 cfm.b. The exhaust flow rate of the ventilation system in dilute mode, from the reactor poolroom, shall be not less than 100 cfim.c. The flow rate from the fresh air makeup supply to the exhaust from the reactor poolroom, when in the dilute mode, shall be at least 4 times greater than the pool roomexhaust flow rate.4.0 Comparison to Other Research Reactor Facilities Page 2 of 35 The Technical Specifications of some other research reactor facilities were surveyed for thepurpose of determining a general practice of including ventilation system requirements in theLimiting Conditions of Operation.

The following facilities were surveyed:

Facility Facility ADAMS Ventilation System FlowLicense Accession Rate Specification Number Number (a)Texas A & M University R-83 ML121 IOA1 16 NoOregon State University R-106 ML052290051 NoDow Chemical Company R-108 ML 110490391 NoKansas State University R-88 ML080580275 NoReed College R-112 ML120530021 NoUnited States Geological R-1 13 ML092120136 NoSurveyUniversity of California-R-1 16 MLI2087A215 YesIrvineUniversity of Maryland R-70 MLI 1124A124 NoUniversity of Utah R-126 ML1 12500333 NoUniversity of Wisconsin R-74 ML 110340310 Yes(a) The ADAMS Accession Number indicates the source document for the Technical Specifications Texas A & M University, Oregon State University, Dow Chemical

Company, Kansas StateUniversity, Reed College, United States Geological Survey, University of Maryland andUniversity of Utah do not have a Technical Specification which stipulates a specific ventilation system flow rate.The University of California-Irvine TS 3.5.1(a)(2) states the reactor shall not be operated unlessthe ventilation system is operating, as indicated by: "a minimum total exhaust flow rate from thereactor area of 4000 cfm is present."

The Basis for the TS indicates that the flow raterequirement arises from air effluent releases ofAr-41.

No mention is made of MHA influence upon ventilation system flow rate requirements.

Page 3 of 35 The University of Wisconsin Technical Specification 3.5 stipulates an exhaust system flow rateof at least 9600 scfin. The Basis indicates that the flow rate requirement arises from air effluentreleases of Ar-41. No mention is made of MHA influence upon ventilation system flow raterequirements.

Page 4 of 35 5.0 Analysis of the Impact of Flow Rate upon DoseThe quantity of volatile radionuclides that could be released following an MHA (cladding'failure in air of a single TRIGA fuel rod) have been previously determined and documented.

Ananalysis was presented in the June 13, 2008 letter (ML0832380265) and again in a lettersubmitted to the U.S. NRC on July 18, 2011. The July 18, 2011 letter describes the dose to amember of the public at the nearest occupied residence due to a ground release when theventilation system is in the isolate mode.In the present analysis it is assumed that a member of the public remains off-site during theamount of time that is required to release 99.9% of the airborne radionuclide inventory from thereactor facility.

The dose to a maximally exposed individual, given as the product of the time-integrated concentration and the dose conversion factor, may be used as an upper limiting valuewhen the individual is exposed for the entire duration of the release.Table I provides the radionuclide inventory released into the pool room, (as calculated byGeneral Atomics and documented in the June 13, 2008 letter to the U.S. NRC) following failureof the fuel cladding of a single TRIGA fuel rod in air.Table I. Volatile Fission Products and Quantities ActivityIsotope released (gCi)Br-82 26Br-83 3300Br-84 6400Br-85 75001-131 17,8001-132 26,8001-133 41,3001-134 47,6001-135 38,700Kr-83m 3300Kr-85m 7500Kr-85 500Kr-87 15,300Kr-88 21,700Xe-131m 200Xe-133m 1200Xe133 40,300Xe-135m 7200Xe-135 27,500Xe-138 39,100The volume of the WSU reactor pool room used in these calculations is I x 109 mL. The amountof time that is required for 99.9% release from the pool room is illustrated in Figure 1.Page 5 of 35 160,000140,000 --120,000100,000 .. **--.**....

---o 80,000E60,000 -- --- ... ...........

40,0002 0 ,0 0 0 .--- .... .....................

..... ..............

... ..................................................

20,000 ----0 1000 2000 3000 4000 5000flow rate (cfm)Figure 1. The figure illustrates the amount of time, as a function of ventilation system exhaustrate, that is required for 99.9% turnover of the air in the pool room.The ventilation system design flow rates when in the normal mode are 4250 cfin input and 4500cfm exhaust, as described in the WSU Safety Analysis Report of 2002. The air exhaust exits thereactor building through an elevated exhaust stack and is swept away by air movement which isconservatively set at 1 m/s in the present analysis.

In the cases of offsite exposure the assumption is made that the member of the public is notevacuated and remains exposed to the plume during the entire time of passage of the plume. Theamount of time for plume passage depends upon the ventilation system flow rate, as illustrated inFigure 1.Page 6 of 35 The dose depends upon the product of the dilution factor, dose conversion factor, airborneradionuclide concentration, time of exposure and ventilation system flow rates. The dilutionfactor only applies when the ventilation system is in the dilute mode-no dilution factor applieswhen the ventilation system is in the normal mode.The present analysis assumes a complete release of volatile fission products, including iodine.The present analysis also assumes that a member of the public is exposed to the plume formed bythe exhaust gas effluent for the entire time that it is required for 99.9% turnover of air in the poolroom. Thus, no credit is taken for a limited time of exposure that would result if an evacuation of the vicinity of the facility were conducted.

As a result, these two assumptions set a boundingcondition for the upper limit of exposure under a worst-case scenario.

Table II provides dose conversion factors for thyroid and whole body exposure.

The values aretaken from "Manual of Protective Action Guides and Protective Actions for Nuclear Incidents",

U.S. Environmental Protection Agency, EPA-400-R-92-001.

Page 7 of 35 Table II Dose Conversion Factors for Whole Body and Thyroid ExposureWhole Body Dose Thyroid DoseConversion Factors Conversion Factorsradionuclide

[rem/([tCi-cm-3hrl)]

[rem/(ýtCi.cm 3.h'r-)]Br-82 1250Br-83 83Br-84 125Br-85 1151-131 220 1.3 x 1061-132 1400 7.7 x 1O31-133 350 2.2 x 10'1-134 1600 1.3 x 1031-135 950 3.8 x 104Kr-83m 100Kr-85m 93Kr-85 1.3Kr-87 510Kr-88 1300Kr-89 1200Xe-131m 4.9Xe-133m 17Xe-133 140Xe-135m 250Xe-135 140Xe-137 110Xe-138 7105.1 Dose calculations for personnel dose for 5 minute exposure in the pool roomThe time integrated concentration (TIC) for personnel exposure in the reactor pool wascalculated for an exposure time of 5 minutes according to the following equation:

TIC(300s)=

A [1 -e-(v+oDK)3°os]

V(Xv +X DK)Where TIC is the time integrated concentration for either thyroid or whole body dose, A is theactivity in tCi, V is the pool room volume in cm3, kv is the pool room ventilation rate in s-1, ),DKis the radioactive decay rate constant.

For example the TIC for a 300 second pool room exposureto 82Br with the ventilation system flow rate of 300 cfm is calculated as follows:Page 8 of 35 TIC(30s) TIC(300s)

= I- X- 1[ l,3(1 2 ý~1 --e- (1.4210-4.-'*5.4 id0-6s-$O00s lx 109cm3(.42x s' +5.45 x 106s -)=7.63 x 10' iCi .s-cm-3where the ventilation flow rate constant,

,v is given by the flow rate, 141,584 cm3/s (300 cfm inthe present example) divided by the pool room volume in cm3, kDK is the radioactive decay rateconstant for 82Br.The dose to an exposed individual in the reactor pool room is given byDose (mrem) = TIC([tCi's'cm-

3) x DCF(rem/ýtCi-s.cm-

3) X [1000(inrem/rem)/3600(s/hr)]

Continuing with the example of 82Br in the reactor pool room:Dose(mrem)

= (7.63 x 10-6 ýtCi s. cm3) x (1250 rem/pCi, s cm3) x [(1000 mrem)/(rem/3600 s/hr)]=2.65 x 10-3 mremDoses to personnel in the pool room were calculated in the same manner for a variety of exhaustrates from the pool room. Doses to personnel in the pool room are dependent upon theventilation system exhaust rate but are independent of the ventilation system mode, thus plots ofpersonnel doses are presented as functions of exhaust flow rate only. The doses for eachindividual radionuclide are plotted in Figures 2 through 5. Figure 6 provides the total dose as asum of the contributions from each radionuclide in Figures 2 -5.Page 9 of 35 0.070 -0.060 -" " -....,0.050 -' 0.04020.0300.020- -----0.0100.000 ....0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 2. Whole body doses arising from exposure to Br-82 (e), Br-83 (m), Br-84 (A), Br-85(*) in the reactor pool room for 300 seconds as a function of pool room exhaust flow rate. Thedoses are not dependent on the ventilation system mode.Page 10 of 35 7.06.05.0"4.0S3.02.01.00.0 ...0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 3. Whole body doses arising from exposure to 1-131 (e), 1-132 (n), 1-133 (A), 1-134 (u),1-135 (o) for 300 seconds in the reactor pool room. The doses are not dependent on theventilation system mode.Page 11 of 35 3.53.0 --'--2.5 -.E2.0E1.51.00.50. 0 i C CCZ0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 4. Whole body doses arising from exposure to Kr-83m (o), Kr-85m (0), Kr-85 (0). Kr-87(A), Kr-88 (m), Kr-89 (e) for 300 seconds in the reactor pool room. The doses are notdependent on the ventilation system mode.Page 12 of 35 2.52.0U1.5E1.00.54AA-AAA A A A A A A A A A A A0.0 1 13 0 -8 S--- 13 00 a a a a a a0 1000 2000 3000 4000Exhaust Flow Rate (cfin)Figure5.

Whole body doses arising from exposure to Xe-131m (o), Xe-133m (n), Xe-133 (0),Xe-135m (A), Xe-135 (m), Xe-137 (9), Xe-138 (*) for 300 seconds in the reactor pool room.The doses are not dependent on the ventilation system mode. Xe-131m and Xe-133m both lie onthe baseline.

Page 13 of 35 2520,-,15EE1001000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 6. Whole body dose for a 300 second exposure in the pool room, sumnmed for allcontributing radionuclides.

The dose is not dependent on the ventilation systemn mode ofoperation.

Page 14 of 35 5.2 Dose calculations for a member of the public for a 99.9% turnover of the pool roomairThe Time Integrated Concentration at the site boundary is given by:TI~) x DF [ IvxKt].TIC(s)=

V(kv + kDK)Where TIC is the time integrated concentration for either thyroid or whole body dose, is aparameter that describes the initial dimensions of the plume, A is the activity in ltCi, DF is thedilution factor that arises from the mixing of pool room exhaust air with fresh outside air whenthe ventilation system is in the dilute mode, V is the pool room volume in cm3, kv is the poolroom ventilation rate for a particular ventilation system flow rate, kDK is the radioactive decayrate constant.

The unitless dilution factor is:DF = CFMex"aust CFMoxl ....t + CFMUflshWhere CFMe,,haust is the flow rate out of the pool room, and CFMfresh is the flow rate of freshoutside air that is used to dilute the pool room air before release through the exhaust stack.The -Qterm is defined as:Where u is the windspeed in rn/s, and ay and cz are the initial dimensions of the plume, given byW b = 17.07 =4.3 4.3andH b 8.53_r _ --3.972.15 2.15Page 15 of 35 Wb is the width of the building in meters (17.07 m) and Hb is the height of the building in meters(8.53 m). Using a conservative wind speed of 1 m/s the 2K value for the nearest member ofthe public is:_ _ _ _ .0 2 0 2 s/n ,3The X/Q value acts as a dilution factor for plume dispersion, and is valid as long as the effluentrelease rate is enough lower than the air movement rate such that the effluent disperses within theair volume created within the lee of the building without significant displacement of the air.Consequently, the X/Q value is normalized and may be treated as a unitless dilution factor.The TIC for an offsite exposure to 82Br with 99.9% air turnover from the pool room with theventilation system flow rate of 300 cfin and a fresh air addition rate of 1700 cfin is calculated asfollows(0.0202) x 26 gCi x 300 cfin/(300 cfin +11700 cfm) -( 421"+5.45'10-I48 7891]XTIC- [1- e-('sx' cnm3/,m31 X 109 C1,3 x(I1.42 x 10-4S- + 5.45 x 10-6S-1)=0.54 gCi. s. m3The time integrated whole body dose rate, or dose, to an offsite individual exposed to 12Br for48,789 seconds, or approximately 13.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> that is required for 99.9% turnover of pool room airat 300 cfm flow rate is given byDose(mrem)

= TIC(ltCi

.s- m"3) x DCF(rem cm3" hlr -LtCi-')

x (I 000mrem / rem) x......(3600s / hr) X (10-6 m3 / cm3)Dose = (0.54 tCi

• s. in-3) x (1250 rem" cm3 .hr- _tCi-) x (1000 nurem/rem) x (3600 s/hr) x (10-6 n3/cm131)=1.86 x 10-4 nremDoses to an exposed individual offsite were calculated for dilute mode for a variety of exhaustrates from the pool room, assuming a constant fresh air addition rate in dilute mode of 1700 cfm.Doses were also calculated for an exposed offsite individual with the ventilation system innormal mode. The only difference is that a dilution factor is used for the dilute modecalculations, whereas no dilution factor is used for the normal mode calculations.

Since aconstant 1700 cfin flow rate is assumed for the fresh air addition rate when in dilution mode, it isapparent that the dilution factor depends upon the pool room exhaust rate. The normal modedoses do not include a dilution factor at all; it may be concluded that all flow rates for both poolPage 16 of 35 room exhaust and fresh air makeup are bounded by doses arising from normal mode for normalflow rates that are equal to dilute mode pool room exhaust rates. The doses to an offsiteindividual arising from each individual radionuclide, with the ventilation system in dilute mode,are presented in Figures 8 -10. Figure 11 provides the total dose as a sum of the contributions from each radionuclide in Figures 8 -10. The doses to an offsite individual arising from eachradionuclide, with the ventilation system in normal mode, are presented in Figures 12 -15.Figure 16 provides the total dose as a sum of the contributions from each radionuclide in Figures12- 15.0.00250.0020,-,0.0015 E0.00100.00050.0000010002000300040005000Exhaust Flow Rate (cfm)Figure 7. Whole body doses as a function of pool room exhaust flow rate arising from offsiteexposure to Br-82 (o), Br-83 (a), Br-84 (0), Br-85 (A) with the ventilation system in dilutemode.Page 17 of 35 0.250.20 -,0.15EE00.100.050.000 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 8. Whole body doses as a function of pool room exhaust flow rate arising from offsiteexposure to 1-131 (e), 1-132 (o), 1-133 (0), 1-134 (A), 1-135 (m) with the ventilation system indilute mode.Page 18 of 35 0.140.120.10E 0.08o 0.060.040.020.00 -- -- --------0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 9. Whole body doses arising from offsite exposure to Kr-83m (0), Kr-85m (M), Kr-85(A), Kr-87 (0), Kr-88 (o), Kr-89 (o) with the ventilation system in dilute mode.Page 19 of 35 0.060.050.04EE0.03U00.020.010.000 1000 2000 3000 4000Exhaust Flow Rate (cfm)Figure 10. Whole body doses arising from offsite exposure to Xe-131m (o), Xe-133m (in), Xe-133 (o), Xe-135m (A), Xe-135 (o), Xe-137 (o) and Xe-138 (0) with the ventilation system indilute mode.Page 20 of 35 1.00.90.80.7_-.0.6EE 0.50.40.30.20.10.0 ....0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 11. Whole body dose for an offsite exposure, with the ventilation system in dilute,summed for all contributing radionuclides.

Page 21 of 35 0.0140.0120.010E 0.008ES0.0060.0040.0020.0000 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 12. Whole body doses arising from offsite exposure to Br-82 (0), Br-83 (.), Br-84 (A)and Br-85 (*) with the ventilation system in normal mode.Page 22 of 35 3.02.52.0 -EE 1.5Vl)1.00.50 1000 2000 3000 4000 5000Exhaust Flow Rate (cfi-n)Figure 13. Whole body doses arising from offsite exposure 1-131 (e), 1-132 (i), 1-133 (A),1-134 (o) and 1-135 (0) with the ventilation system in normal mode.Page 23 of 35 1.61.41.2 -1.0 -EE0.80.60.40.20.0 , , , f"0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 14. Whole body doses arising from offsite exposure Kr-83rn (9), Kr-85m (-), Kr-85 (A),Kr-87 (o), Kr-88 (o) and Kr-89 (0) with the ventilation system in normal mode.Page 24 of 35 0.70.6 -0.5 -E 0.4Eo0.30.2 -0.10.00 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 15. Whole body doses arising from offsite exposure to Xe-131mn (e), Xe-133m (w),Xe-133 (o), Xe-135m (A), Xe-135 (o), Xe-137 (*) and Xe-138 (0) with the ventilation systemin normal mode.Page 25 of 35 12108EE6U4200 1000 2000 3000 4000 5000Exhaust Flow Rate (cfiui)Figure 16. Whole body dose for offsite exposure, with the ventilation systemn in normal, sumnmedfor all contributing radionuclides.

Page 26 of 35 5.3 Thyroid dosesThe equations that are used to calculate thyroid doses are nearly the same as for whole bodydoses, with the only changes being that only the isotopes of iodine are considered, and the doseconversion factors for radioiodine imparted doses are different than for whole body doses. Thethyroid doses for each isotope of iodine for a 300 second exposure in the pool room arepresented in Figure 17, and Figure 18 illustrates the sum of the contribution of each radionuclide to the total thyroid dose for an individual in the pool room. Figure 19 shows the contribution ofeach isotope of iodine to offsite exposure, with the ventilation system in dilute mode. The sumof the contribution of each isotope to the total thyroid dose to an offsite individual, with theventilation system in dilute mode is illustrated in Figure 20. Figure 21 shows the contribution ofeach isotope of iodine to offsite exposure, with the ventilation system in normal mode. The sumof the contribution of each isotope to the total thyroid dose to an offsite individual, with theventilation system in normal mode is illustrated in Figure 22.250020001500EEEQ)1000500------. -------0010002000300040005000Exhaust Flow Rate (cfm)Figure 17. Thyroid doses arising for a 300 second pool room exposure to 1-131 (o), 1-132 (u), I-133 (A), 1-134 (*), 1-135 (9). The doses are not dependent on the ventilation system mode.Page 27 of 35 300025002000,-150010005000 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 18. Thyroid dose for a 300 second exposure in the pool room, summed for allcontributing iodine radionuclides.

The dose is not dependent on the ventilation system mode ofoperation.

Page 28 of 35 160140120100E80604020 -20o A , , -" --" --*-0 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 19. Thyroid doses arising from offsite exposure to 1-131 (o), 1-132 (mn), 1-133 (A), 1-134(*), 1-135 (*) with the ventilation system in dilute mode.Page 29 of 35 250200,150100500 1000 2000 3000 4000 5000Exhaust Flow Rate (cfm)Figure 20. Thyroid dose for an offsite exposure, with the ventilation system in dilute, summedfor all contributing iodine radionuclides.

Page 30 of 35 30002500 -2000E5-IE1500U100050000 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 21. Thyroid doses arising from offsite exposure to 1-131 (o), 1-132 (i), 1-133 (A), 1-134(e), 1-135 (,) with the ventilation system in normal mode.Page 31 of 35 4000350030002500E%20001500 -100050000 1000 2000 3000 4000 5000Exhaust Flow Rate (cfin)Figure 22. Thyroid dose for an offsite exposure, with the ventilation system in normal mode,summed for all contributing iodine radionuclides.

Page 32 of 35

6.0 Discussion

Whole body doses imparted by individual radionuclides are plotted for a 300 second exposure inthe pool room, and offsite exposure with the ventilation system in either dilute or normal mode.Plotting the doses individually provides insight into the relative contribution to the total dosecontribution by each radioactive isotope.The individually plotted doses as functions of exhaust system flow rates show different types ofdependencies on flow rate. Dose dependence upon exhaust flow rate is more apparent for offsiteexposure than pool room exposure because the doses depend upon radionuclide inventory

release, dose conversion factors and radionuclide half-life.

Most dose curves for personnel within the pool room show only a slight curvature in the dependencies as functions of exhaustrate due to the short exposure time-there is not sufficient pool room air turnover, even at thehighest flow rates, to cause a significant deviation from linearity for the short exposure time.Much longer exposure times are used for an offsite individual due to the assumption that theperson remains at the offsite location for the amount of time that is necessary to achieve 99.9%turnover of the pool room air. Consequently, the offsite doses exhibit a greater dependency uponthe half-lives of the radionuclides.

The doses that are calculated for the dilute mode differ from the doses in normal mode for thesame pool room exhaust flow rates. This is because an assumption is made that the fan whichsupplies fresh outside air as diluent is providing air at a constant rate of 1700 cfin, thus requiring the incorporation of a dilution factor which is also dependent upon pool room exhaust flow rate,i.e. the magnitude of the dilution factor decreases as pool room exhaust flow rates increase.

It was chosen to carry out the calculations over a pool room exhaust flow rate range of 100 -4600 cfm. The lower limit, 100 cfm was chosen because it would balance the estimated leak ratefrom the pool room when the ventilation system is in the ISOLATE mode. An exhaust rate of100 cfm would prevent a ground release, and remove pool room air from the building via theventilation exhaust stack. An upper limit of 4600 cfm was chosen to bracket the upper range ofthe ventilation system design of 4500 cfm exhaust flow rate and the 4000 cfm Technical Specification limit. In all cases, doses to both personnel and offsite individuals decrease withincreasing flow rates beyond 4000 cfin, making the 4600 cfin rate a conservative Lipper limit forthe calculations.

The doses summed across all radionuclides generate the criteria by which it is possible to defineacceptable exhaust flow rates. NUREG-1537 stipulates dose limits of 5 rem whole body and 30rem thyroid dose for research reactors licensed before January 1, 1994.Figure 6 illustrates the whole body dose for a 300 second exposure of personnel within the poolroom. Personnel exposure within the pool room is independent of ventilation system operational mode, but depends only upon pool room exhaust flow rate. Figure 6 shows that the maximumdose of 22 mrem occurs at the minimum flow rate of 100 cfm, and decreases as exhaust flow ratePage 33 of 35 increases.

A 22 mrem dose is well below the 5000 mrem whole body dose limit. As a result,there is no possible exhaust flow rate in excess of 100 cfm that would cause the dose to exceedthe whole body dose limit for personnel in the pool room.Figure 18 shows that the maximum thyroid dose occurs at an exhaust flow rate of 100 cfm for a300 second exposure within the pool room. The thyroid dose at 100 cfm exhaust flow rate is2808 mrem, which is much less than the 30,000 mrem limit of NUREG 1537. Consequently, there is no possible exhaust flow rate greater than 100 cfirn that would cause the dose to exceedthe thyroid dose limit for personnel in the pool room.Figure 11 illustrates the whole body dose for an offsite exposure, summed across all of the Br, I,Kr and Xe isotopes that are released.

The figure shows a maximum whole body dose of 0.90mrem at about 600 cfm. Flow rates that are lower than 600 cfm provide more time for short-lived radionuclides to decay, thus decreasing the dose, and at flow rates greater than 600 cfm theexposure time becomes increasingly important because the time of exposure decreases as flowrate increases.

A dilution factor of 0.26 is used for the 600 cfin calculation

((600 + 1700)/2300

=0.26). The 0.90 mrem whole body dose is less than the 500 mrem whole body dose limitprovided by NUREG-1537.

It is not necessary to also carry out the calculations with variedfresh air makeup flow rates other than 1700 cfm because the worst-case scenario for any offsitewhole body dose is given by doses arising from releases when the ventilation system is in thenormal mode, which does not include a dilution factor, provided that compliance is alsomaintained at all possible flow rates when in the normal mode (see below).Figure 20 shows the thyroid dose for an offsite exposure with the ventilation system in dilutemode. The maximum dose of 207 mrem occurs at a flow rate of 100 cfmn. At 100 cfin exhaustrate the dilution factor is 100/1800

= 0.056, which steadily decreases as pool room exhaust flowrate increases, as long as the fresh makeup air flow rate is maintained at 1700 cfin. Any makeupair flow rate in excess of 1700 cfin will decrease the dilution factor, thereby decreasing the dose.As a result, any pool room exhaust flow rate is acceptable as long as the makeup air flow rate isat least 1700 cfm. The worst case scenario occurs when the makeup air flow rate decreases to 0cfm, in which case, the dilute mode doses would be identical to normal mode doses for the samepool room exhaust rates. However, even a minimal amount of makeup flow has a substantial impact upon offsite doses. For example, a makeup flow rate of 0 cfm with the pool roomexhaust flow rate at 100 cfm would lead to an offsite thyroid dose of 3718 torerm, which isidentical to a 100 cfm pool room exhaust flow rate in normal mode. However, when in dilutemode, and a 100 cfm pool room exhaust flow rate, a makeup air flow rate of only 50 cfm willlower the thyroid dose for an offsite person to 2479 mrem. Setting an administrative limit for anoffsite person thyroid dose of one-fourth the NUREG-1537 limit, or 750 mrem, provides limitingvalues for the allowed flow rates for both pool room exhaust and makeup air flow rate, i.e. aminimum of 100 cfm for pool room exhaust and a minimum of 395 cfm for makeup fresh air.Any combination of pool room exhaust and makeup fresh air flow rates will lead to an offsitePage 34 of 35 thyroid dose of 750 mrem or less, as long as the pool room exhaust rate is at least 100 cfm andthe makeup fresh air flow rate is at least 395 cfm. This letter proposesApplying the same criterion, (i.e. 750 mrem maximum thyroid dose for an offsite individual) tosetting the boundary condition for pool room exhaust flow rate when in normal mode, it becomespossible to set a minimum flow rate, which must be higher than the pool room exhaust flow ratein dilute mode because no dilution is available in normal mode. The pool room exhaust flow ratewhich yields a 750 mrem offsite thyroid dose is 528 cfm. Consequently, any pool room exhaustflow rate greater than 528 cfm will lead to an offsite thyroid dose less than 750 mrem. Aconservative pool room exhaust flow rate of 1000 cfm would lead to a dose of 399 mrem.7.0 Comparison with the Technical Specifications of Other Licensed Facilities The table in section 4.0 provides a summary of the ventilation system specifications at 10 otherlicensed facilities.

There are only 2 facilities, the University of California-Irvine, and theUniversity of Wisconsin, which stipulate specific flow rate requirements.

In both cases therequirements are put in place to account for Ar-41 releases.

None of the 10 listed facilities has aventilation system flow rate requirement which is based upon MHA releases.

8.0 SummaryNone of the 10 other facilities which have been surveyed (see Section 2.0) have ventilation system flow rate requirements based upon MHA analysis.

This document shows that there is awide variety of exhaust system flow rates that provide acceptable protection to the facilitypersonnel and to members of the public. Consequently, WSU proposes to modify Technical Specifications 3.4(1)(a) and 3.4(1)(b) to allow a range of acceptable exhaust system flow rates.The requested modification is provided in Section 3.0 of this document.

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