ML20247L997

Radioiodine & Particle Transmission Through Selected Sampling Lines at Seabrook Station, Revised Final Rept

ML20247L997
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Site:	Seabrook
Issue date:	05/31/1989
From:	SCIENCE APPLICATIONS INTERNATIONAL CORP. (FORMERLY
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ML20247L989	List: ML20247L986 ML20247L997
References
SAIC-89-1422, NUDOCS 8906020323
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SAIC-89/1422 l-RADIOI0 DINE AND PARTICLE TRANSMISSION THROUGH SELECTED SAMPLING LINES AT SEABROOK STATION Prepared by utility Services Dopartment Science Applications International Corporation Rockville, Maryland 20850 1

Prepared for New Hampshire Yankee Route 1, Seabrook Station Seaorook, New Hampshire 03874 <

Revised Final Report May 1989 l

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SUMMARY

This revised report contains the results of measurements and calculations performed by Science Applications International Corporation (SAIC) to estimate radioiodine and particle transmission through selected sampling lines and to study the transport of a gaseous tracer from a reactor coolant pump cubicle to the Reactor Coolant Pressure Boundary Monitor. The sampling lines evaluated were those for the Auxiliary and Service Building I Exhaust Monitor (ASBEM), the stack Wide Range Gas Monitor (WRGM), both the low-range and the modified high-range sections (designated WRGM-LR and WRGM-HR*), the' Gland Steam Condenser Exhaust Monitor (GSCEM), and the Reactor Coolant Pressure Boundary Monitor (RCPBM).

l The Radiciodine Line loss Test Facility in SAIC's Rockville Laboratory was used to measure the transmission of elemental iodine (1 2) through replicas of two of the sampling lines. Elemental iodine is the most reactive of the gaseous radioiodine species found in reactor effluents. It deposits on surfaces and may later be resuspended or bound to the surface. Trans-mission of 131I2 through the lines was measured and the data were analyzed to determine average deposition velocities for 12 in the lines. Measurements  !

of the subsequent resuspension of deposited radiciodine were made. The data l were analyzed to determine the average resuspension rate constant and the best estimate of the fixation rate constant. The experimental values of the deposition velocity, and of the resuspension and fixation rate constants are used in SAIC's model of iodine transport to estimate the transmission factor for the depositing species (TF d) under a wide range of conditions. The TFd is the ratio of the 131 I2 concentration at the line outlet to that at the inlet. When a mixture of iodine species is present, the transmission for total gaseous iodine (TF g ) is similarly defined.

Estimates of the deposition, fixation, and resuspension parameters obtained from measurements made as part of this and previous studies were used to estimate transmission factors for the five lines. Expected iodine

. species distributions in the air being monitored were also considered in preparing recommendations for the most appropriate transmission factors.

These are presented for each of the lines under consideration. Recommended i

- _ _ _ _ _ - _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ i

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. transmission factors for three of the lines are shown in the following table.

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For the ABSEM and GSCEM lines, there is little variation of TFg with time after a concentration increase. However, the value of TF for g the WRGM-LR line would be expected to increase to 0.9 at equilibrium. The recommended Expected Transmission Factor line for Gaseous Radioiodine (TFg l ASBEM 0.96 WRGM-LR 0.8 GSCEM 0.95 TFg for the WRGM-LR line reflects the average radiciodine species distri-bution observed in the plant vents.of operating PWRs. No comparable data are, available for iodine species in the exhausts that would be carried through the ASBEM and GSCEM lines during normal' operations.

The value of TFg for the RCPBM line is expected to change with time because of changes in the iodice species distribution in containment. The  ;

following table gives recommended values for that line for selected times after a large increase in 131I concentration.

Expected Transmission Factor for Gaseous Iodine (TFg l Line Z_h 5h 20_h Eq_ h 200 h RCPBM 0.7 0.8 0.8 0.9 1 ii c = _ __ _ _-

. o The principal reason for revising this report was to reassess the post-accident transmission factors for the WRGM. Since the original report was -

prepared, the post-accident s%pling arrangement was changed to assure more reliable samples. An isokinetic nozzle has been installed in the WRGM-LR line near the high range sample skid, so the ' post-accident sample would travel only a short distance in a small diameter line with a low flow rate.

The majority of the sample flowing through the WRGM-LR line will simply be diverted back into the Plant Vent. This sequence of two lines is termed the WRGM-HR* line. Because it cannot be assured that the bulk of the radioiodine will not' be present as I2 during the early stages' of the accident, the .

estimated transmission factor for the WRGM-HR* line is based upon results for that species. The recommended initial TFd for the WRGM-HR* line is 0.4. The TFd is estimated to increase to 0.7 at equilibrium. To achieve the initial TFd for the first post-accident sample, it is recommended that contaminated air from the Plant Vent be drawn through the high flow rate section (and diverted directly back to the Plant Vent) for a minimum of 20 minutes prior to extraction of sample. Continued operation of the high flow rate section will result in increased transmission factors for subsequent samples.

Transmission factors for particles through the sampling lines were computed using the DUCT code developed by SAIC. The code calculations are based upon empirical measurements of particle deposition in vertical and horizontal tubes and of particle impaction in bends. Results, expressed as particle transmission factors (TFp ), were obtained for six particle diameters and five particle densities.

There is unfortunately not a collection of data that defines the aero-  !

dynamic size distribution for radioactive particles in PWR effluent air streams and containments. The following aerosol transmission factors are estimates. In making these estimates, it was assumed that the radioactive particles will be in the normal density range of 1--3 g/cm3 and that only a small fraction of the activity will be associated with particles having diameters greater than 5 pm. The first four estimates in the table are believed to be conservative, i.g., to result in overestimates of the losses.

Because the filters in the containment air recirculation systems will remove iii

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Estimated Transmission 1 Line Factor (TFa I f

ASBEM 0.9 WRGM-LR 0.8 q WRGM-HR* 0.7" L GSCEM- 0.9 RCPBM 1 particles with diameters greater than 1/Im, the remaining aerosol will be transferred through the line with minimal losses.

When particle size data are avilable, these recommended values should be modified accordingly. It is particularly important that the aerodynamic size distribution for plant vent be determined, as that is expected to be the principal discharge point for radioactive particles.

Measurements of the transport of helium (He), a gaseous tracer, from the B Reactor Coolant Pump (RCP-B) cubicle to the Reactor Coolant Pressure Boundary Monitor were made with two different containment fan alignments.

The RCP-B cubicle is a likely point of coolant leakage and is located diametrically opposite the inlet to the monitoring line, about 150 feet-away.

In both tests, the initial detection of He at the monitor occurred in less l

than 5 minutes. The time required for the He concentration to double was 15 minutes in the first test and about 25 minutes in the second test. Both tests showed the prompt detection of the tracer and a continuous increase in He concentration at the monitor during the test.

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SUMMARY

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-1. INTRODUCTION ...........c.

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- 2; EVALUATION OF RADIOI0 DINE DEPOSITION AND RESUSPENSION . . . . 3 2.1L EXPERIMENTAL METHODS . . . ... . . . . . . . ... . . . .. 4 ,

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2.2 -MODEL OF_RADIOI0 DINE BEHAVIOR . . . .. . . . . . . . . 6 2.3. MEASUREMENT RESULTS . . ....... . .......... -9

3. APPLICATION.0F RADICIODINE MEASUREMENT RESULTS ... . . . . . 17 n

4. ' CALCULATIONS OFLPARTICLE TRANSMISSION . . . . . . . . . . . . .

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5.- HELIUM TRACER MEASUREMENTS . . . . . . . . . . . . . . . . 33 5.1 HELIUM MEASUREMENT TECHNIQUES . . . . . . . . . . . . . 33-5.2 HELIUM RELEASE TEST RESULTS .............. 34 6

5.3 CONCLUSION

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6. REFERENCES ......................... 39

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.- 1. INTRODUCTION This revised report contains the results_ of measurements and calculations performed to determine appropriate transmission factors for radiciodine and. particles- through selected sampling lines at Seabrook Station. The lines evaluated were those transporting samples to: the Administration and Service Building' Exhaust Monitor (ASBEM), the Wide Range Gas Monitor (WRGM) for stack effluents (Low Range (LR) and modified High Range (HR*) lines), the Gland Steam Condenser Exhaust Monitor (GSCEM), and the Reactor Cooolant Pressure Boundary Monitor (RCPBM). Important charac-l teristics of the five. lines are given in Table 1. All five lines are made of Type 316 stainless steel.

Table 1. CHARACTERISTICS OF SELECTED SEABROOK SAMPLING LINES Inside Sampling Sampling Line Approximate Diameter Flow Rate for Lenath (cm) (cm) (cm3 /s)

Admin. & Serv. Bldg.

Exhaust Monitor 1090 2.21 1420 Stack, WRGM-LR 3710 1.57 788 Stack,.WRGM-HR*

High Flow Rate Sec. 3710 1.57 788 Low Flow Rate Sec. 188 0.213 28.3 Gland Steam Condenser Exhaust Monitor 500 0.940 472 Reactor Coolant Pressure.

Boundary Monitor 830 1.57 1180 The first three lines operate at about 430C with about 50% relative humidity. The GSCEM Line is expected to operate at a rather high temperature, about 580C, with a relative humidity of 90 to 95 percent.

The RCPBM Line will operate under ambient conditions for that building, about 490C and about 90 percent relative humidity.

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- Parts of the WRGM Lines are outside and these lines are heat traced.

The modified WRGM-HR*:line consists of two sections. The high flow rate section is the WRGM-LR line. The new low flow rate section is a short line from an isokinetic probe in the WRGM-LR line to the high range monitoring equipment.

l-Measurements.of radiciodine deposition on and resuspension from l interior surfaces of replicas of two Seabrook lines were performed by L Science Applications International Corporation (SAIC) in the Rockville Line 1

!' Loss Measurement Facility. The physical and operating characteristics of

'the WRGM-LR Line and.the GSCEM Line were replicated experimentally. The experimental testing methods are described in Section 2.1. The radiciodine deposition and resuspension model developed by SAIC for the evaluation of line. loss data is presented in Section 2.2. The model was used to evaluate -

the experimental data and to compute equilibrium and transient transmission factors. The measurements results and the evaluation of the deposition and resuspension parameters are given in Section 2.3.

Section 3 discusses the application of the results of line loss measurements and calculations made using the model with parameters derived from measurements. In Section 4, the results of calculations of the transmission of particles through all five lines are presented.

Section 5 contains the results of helium (He) tracer measurements to determine the transport time from probable containment leakage points to the inlet to the containment air sampling line. References are listed in 'he t last section.

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2. EVALUATION OF RADIOI0 DINE DEPOSITION AND RESUSPENSION Transmission of radiciodine through sampling lines depends upon the characteristics of the line and the radioiodine species present. Refer-ence 1 summarizes available measurement data on the distribution of radioiodine (131 1) species in pressurized water reactor (PWR) effluents.

Most of the measurement results on which the mean values for PWRs are based are given in References 2 and 3. Table 2 shows the average radiciodine species distributions that have been measured in PWRs. These species distribution data were obtained during normal operations.

Table 2. AVERAGE RADIOI0 DINE (131 1 ) SPECIES DISTRIBUTION IN PWR EFFLUENT DURING NORMAL OPERATIONS Soecies Percent of Total Radiciodine Associated 2 with Particulate Elemental Iodine (I2 ) 27 Hypoiodous Acid (H0I) 40 Organic Iodides 31 i Elemental iodine gas (I2 ) is the most reactive of the observed species and is the most likely to deposit in sampling lines. The deposi-tion velocity (V ,d cm/s) is the pr.rameter often used to characterize the air-to-surface transfer process. The deposition velocity of H0I is estimated to be <5% of that for I2 . Deposition velocities of organic iodides, such as methyl iodide (CH3 I), are even smaller, -0.1% of the deposition velocity of elemental iodine.4,5 Thus, most losses of radio-iodine in sampling lines will be due to deposition of 1. 2 The amount of deposition of elemental iodine that occurs depends upon the design and l operation of the sampling line. Resuspension of deposited activity also depends upon the operating characteristics of the sampling system.

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-' The iodine species distributions shown in Table 2 are not common to all PWR sampling situations. The species distributions in containment buildings have been found to change with time.3 Measurements in Gland Steam Condenser Exhaust lines have not been reported. The distribution of. iodine species in the exhaust from the Administration and Service Buildings is similarly uncertain; however, this discharge path is not expected to carry large concentrations of 131I , j

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I The longest line, that for the low range of the Plant Stack WRGM, and the high temperature, high relative humidity line for the condenser exhaust monitor were selected for evaluation in the laboratory. To evaluate radio-iodine deposition and resuspension, replicas of the two lines, described in Table 1, were tested in SAIC's Line loss Measurement Facility in Rockville.

The following subsection describes the facility and the tests conducted. A model of radiciodine deposition and resuspension is discussed in Section 2.2  !

to provide the framework for data interpretation and analysis. The results of the measurements are presented in Section 2.3.

2.1 EXPERIMENTAL METHODS Figure 1 is a schematic diagram of the line loss testing apparatus.

The line was coiled in an isothermal enclosure operated at the desired t temperature and elemental iodine was injected into the line. During the injection period, radioiodine concentrations and species distributions were measured using SAIC radioiodine species samplers. Sampler design and operating characteristics are discussed in References 6 and 7. Following the injection period, the mixing chamber was isolated and the sampling line l

was purged with filtered laboratory air to measure resuspension of deposited radiciodine.

i 131 All sampling cartridges were counted for 1 using a Ge(Li) spectro- ,

meter whose calibration is traceable to the National Bureau of Standards.

Counting results were corrected for decay from the end of the sampling period to the time of analysis. Radioiodine air concentration results were also corrected for radioactive decay during sampling. This latter decay 131 correction assumes that the concentration of 1 in the air stream was constant during the sampling period.

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1 Elemental iodine (1 )2 was generated using the Dushman reaction: I 10 (1) 3 + 5 F + 6H % 3I2 + 3H 2 O l '

A reaction vessel (2-neck boiling flask) containing 20% sulfuric acid and potassium iodate was simultaneously heated, stirred, and purged with a flow of helium. The production rate of elemental radioiodine was controlled by j using a peristaltic pump to inject radioactive sodium iodide solution into the reaction mixture. This method allows an almost constant production rate over the time of the iodine injection.

2.2 MODEL OF RADI0 IODINE BEHAVIOR Prior to discussing the measurement results, it is useful to describe the conceptual model of radiciodine behavior in sampling lines and to define the parameters being measured. Previous studies2 ,6 of the behavior of airborne radioiodine in building ventilation exhaust and in discharge lines have shown that:

o decay of the short-lived isotopes exceeds that expected based on air transit times, implying a physical retention mechanism o chemical species changes occur that shift the activity balance from ,

I reactive (depositing) to nonreactive forms.

0 A simple two-compartment model was developed that incorporated the most probable mechanisms that account for the observed species changes and depletion of short-lived radioiodines. The mechanisms are deposition of reactive species on surfaces, species transformations on the surfaces, and resuspension of deposited radioiodine. The deposition and resuspension phenomena were also observed in laboratory studies of radioiodine behavior.7 Although they have been observed frequently, the species transformation processes are not well understood.

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i The original mod'e1 6 assumed that the total air volume and the interior surface of.the.line. could each be treated as a single compartment. For long sampling lines, that assumption is frequently not valid. A sampling line is now modeled as a sequence of segments in which the air concentration is approximately constant. The deposition and resuspension model is applied to each segment.of the line. A typical application involves 20 line segments.

Figure 2 illustrates an improved model of radioiodine transmission that has. been found to be more representative of laboratory measurements of radiciodine behavior in sampling lines. Only one of the line segments is shown explicitly. The airborne activity leaving one line segment becomes the input for the next segment. Radioiodine species transformations are believed to take place on the interior surfaces of the line, but.the chemical transformations are not considered in detail in the model. Some of the chemical changes' lead to resuspension of various species; others are involved in the fixation process.

The differential equations used to describe the transport of activity in a line segment as a function of time (t, s) are given below:

dq a =

I+rq ~s (Av + 3 + A) 9 a (2) dt dq

" 0ga ~ (r + + )Q s (3) dt dq p 49s ~ A4 f )

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where 1 q is the activity (pCi) of the. airborne radioiodine in the segment '

a I is the rate (#Ci/s) at which activity enters the line ,

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Deposition Resuspension Deposition Resuspension RADIOlODINE HADl010 DINE RESUSPENDABLE RESUSPENDABLE FROM SURFACES FROM SURFACES l

Iixation fixation I

RADl010 DINE FIXED RADl010 DINE FIXED ON SURFACES ON SURFACES l

Figure 2. Model of Radiciodine Behavior in Sampling Lines (two line segments shown) 8

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q s is the activity (yCi) of radiciodine on surfaces of the line segment that is available for resuspension r .is the resuspension rate constant.(s-I)

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is the exh'aust' rate constant (s-I); it is the ratio of the 3 3 exhaust flow rate (Q, em /s) to the volume sV cm ) of the line segment 6 is the deposition rate constant (s"I); it is the product of.the

> ' deposition velocity (V d, cm/s) and the surface-to-volume ratio (A/V,cm-1) for the line A is the. radiological decay rate constant (s-I)-

d' is the rate constant (s-1) for the' fixation process qr is the activity (yCi) of radiciodine fixed on the line segment surface.

To apply the model given above, the values of the parameters r, Ay , 6, and p must be known. Using _the data in Table 1, the. values of (A/V) and Ay

~for the sampling. lines are readily computed. The deposition, resuspension, and fixation parameters (Vd , r, and () are best estimated from experimental data for replicas of sampling lines.

The experimental measurements of deposition and resuspension made using replicas of the two Seabrook lines are discussed in the next section.

The'parametem needed to apply the 20-segment model to the two lines were derived from iaboratory measurements. The derived parameters are only

. applicable to the 20-segment model discussed above. Their use in a dif-ferent kind of model is not appropriate and would yield invalid predictions of radiciodine transmission.

2.3 MEASUREMENT RESULTS Measurements of the radiciodine deposition and resuspension in the two sampling lines are presented below. Deposition measurements are presented first. Subsection 2.3.2 contains the data from the measurements of resuspension of radioiodine.

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2.3.1 Deoosition Measurements

.The results of radiciodine concentration measurements during radio-iodine -injection are given in Table 3. The two-sigma fractional counting uncertainty for each concentration measurement is shown in parentheses, The radioiodine species distributions were measured during the injection period for the WRGM-LR line. It was estimated that about 94 percent of 131 the injected 1 was present as 12 . Approximately 3.9 percent was estimated to be present as HOI. Less than 1 percent of the activity was collected on the particulate filter; part or all of that activity was probably 12 that adhered to the filter. The less reactive organic iodides accounted for about 2.4 percent of the total. These species fractions are generally consistent with those made previously in the test facility, ,

although the amount of HOI is somewhat larger than normally observed.

-Species measurements were not made during the test of the GSCEM Line because the operating temperature was higher than the acceptable range for the radiciodine. species sampler.

Table 3. MEASURED RADI0 IODINE CONCENTRATIONS DURING THE INJECTION PERIOD Average Measured a

Line Sampling Concentrat{gn Transmission Designation Point (uCi/cm ) 31 1 3 Factor (4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />)

WRGM-LR Inlet 1.19x10-6 (0.4%) 0.086 Outlet 1.02x10-7 (1.0%)

GSCEM Inlet 8.07x10-6 (1.3%) 0.95 Outlet 7.63x10'O (2.2%)

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a. Two-sigma fractional counting uncertainties are given in parentheses.

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.o The measured transmission factors during the 4-hour injection periods (TF(4hr))wereabout0.09and0.95fortheWRGM-LRLineandGSCEMLine, d

respectively. Transmission of 12 through the WRGM-LR Line was less than expected.- The expectation of a-higher TF was based upon experience with lines of similar diameters and flow regiemes. Although the Reynolds. numbers for the.other lines were slightly different, review of the current experi-mental data base indicates that this result is at the extreme of the range.

The measured.131 I concentrations were used to compute the average D deposition velocity for 1 2in each line section. It is assumed that the fractional. loss due to deposition is the same'in each of 20 segments and that resuspension'can be ignored during the 4-hour injection period. If C s and C* are the 131 1 concentrations (yCi/cm 3 ) at the inlet and outlet of the segment,'respectively, that assumption means (C*s/Cs ) is the same for each segment and that (C*s/Cs ) - TFd (4 hr). Under the assumed conditions, Equation (2) is simplified and its solution can be manipulated to yield an expression for the deposition velocity in~the line. The average deposition veloc.ity was computed using Equation (5) for a 20-segment line.

Q (1 - C*/Cs )

V d" '(5)

A s (C*s/C s )

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d is the average deposition velocity (cm/s) of 1 2 in any segment of f the line 3

Q is the exhaust flow rate (cm /s) for the line (and for each segment)  !

A s

is the interior surface area (cm 2) of the line segment.

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.The estimated average deposition velocity for the WRGM-LR line was 0.11 cm/s, an extreme value. For GSCEM Line, the average deposition j velocity was estimated to be 0.018 cm/s. A note of caution is appropriate here. These estimated values of Vd are appropriate only for 20-segment models of the two lines; their use in other different models will not yield valid predictions.

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fi 2.3.2 Resuspension Measurements Following the period of deposition during radioiodine injection, ,

131 filtered laboratory air, containing no 1, was drawn through each line at the normal sampling rate. The line outlet concentration was monitored to l determine the 131 1 activity resuspended from the interior surfaces.

Table 4 contains the results of measurements of 131 1 resuspended from the wall of the WRGM-LR Line during a 22-day period following deposition of 131 I in the line. The concentrations of resuspended 131 1 decrease mono-tonica11y with time. 'Radioiodine species measurements were made during the first five periods. The average elemental iodine fraction was about 81%.  ;

Slightly more than 5% of the 1311 was on the particulate filter and, as noted, part or all of this activity may have been 1 2that adhered to the. )

filter. The total of the two less reactive species averaged a little more ,

131 than 13% of the total resuspended 1 activity.

The concentration data shown in Table 4 were used to estimate the resuspension rate constant (r) for each sampling period and the fixation  ;

rate constant (d). The first step in this process is to determine provisional values of the resuspension rate constant under the assumption that p = 0. The procedure that was used is described below.

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The surface activity at the start of the resuspension period (qso,pCi) was estimated using the measurements during radiciodine injection, using Equation (6):

q -

AC Q t g (6) l so t where AC is the concentration difference between the inlet and outlet of the line and tg is the duration of the injection period. For a period of no radioiodine input and approximately constant air concentration, Equation (2) i can be rearranged to yield an expression for the average resuspension rate i constant r. The equation is l l

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Table 4. ' MEASURED" CONCENTRATIONS OF 131I DUE TO RESUSPENSION .

IN.THE WRGM-LR LINE Average Duration Concentrat{gg"1 Period (minutes) fuCi/cm3 ) 32 1 1440 4.19x10-10 (0.7%) ,

2 1560 8.73x10-Il (4.7%)

l 3 3810 2.03x10-Il (1.6%).

4 4320 5.09x10-12 (4.9%)

5. 5880 1.90x10-12 (15%)

6 5830 1.42x10-12 (3.7%)

7 4490 7.08x10-13 (3.7%).

8 11280 2.64x10-13 (6.8%)

9 5610 2.10x10-13.(6.5%)

a. Two-sigma fractional counting uncertainties are given in parentheses.

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r

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'A s where C.is the average concentration (yci/cm3 ) of I3I I. For the conditions stated above (I - 0 and qa ; constant), Equation (3) yields the following expression for the surface activity as a function of time:

q (t) =

t a (1-e~"s ). , q,9 g -e s t (8) s s i where a = r + A + d is the total removal rate constant describing loss 3

of resuspendable 131.I from the surface. The average surface concentration during a sampling period (ts , s) under the stated conditions is given by Equation -(9):

4 09 a ~ t A t

, a, (1-e "s s) , so (1-e~"s s) g s a s

t s *s t s The mean surface activity during a period determines the computed values of the resuspension rate constant and is, in turn, affected by it.

Equation (6) was used to calculate q so f r the first measurement period.

Equations (7) and (9) were used iteratively to compute self-consistent values of the resuspension rate constant and surface activity for the first measurement period. Then Equation (8) was used to compute the surface activity that would be present at the beginning of the second measurement period. The calculations using Equations (7), (9), and (8) were then performed for each subsequent resuspension measurement period. The value of used in the calculations for each line section was based on the deposition velocity estimated using the measurements discussed in Section 2.3.1.

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The calculated provisional resuspension rate constants are shown in Table 5. The values decreased substantially with time. The rate of I decrease was used to find an initial estimate of the fixation parameter p.

Calculations of resuspension rate constants were then performed in the manner described above for a range of values of p. The range and vari-ability of the computed resuspension rate constants was examined for each set of values corresponding to a particular p. The best-fit value of p was

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determined by finding that value which minimized the variation in computed i values of r.

Table 5. PROVISIONAL AND FINAL RESUSPENSION RATE CONSTANTS DERIVED FOR SEABROOK WRGM-LR LINE Average Resuspension Rate Constant Final Period Provisional (6 - 0) (6 = 2.1x10-6 s-1) 1 3.2x10-8 3.4x10-8 2 7.2x10-9 9.5x10-9 3 2.0x10-9 3.6x100 4 6.3x10-10 1.9x10-9 l 5 3.2x10-10 1.8x10-9 6 3.4x10-10 4.0x10-9 7 2.3x10-10 5.3x10-9 8 1.4x10-10 7,4x10-9 9 1.8x10-10 3.4x10-8 The final resuspension rate constants for the WRGM-LR Line are shown in Table 5. It was found that 2.1x10-6 3 -1 was the best value for the fixation rate constant 4 The mean value of the resuspension rate constant

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( standard deviation of the mean) was 1.1 0.5x10-8 s . The reason for the very low resuspension rate constant for the WRGM-LR Line is not clear; it is also at the extreme of the range for comparable lines.

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l

'l j

The range of the set of final values of r is about a factor of 19, j compared with a value of about 75 when the fixation process was not included in the model (provisional values'in Table 5). Although substantial effort was required to determine the fixation parameter and corresponding resuspen- )

sion rate constants, the results in Table 5 indicate that it is worthwhile  ;

and that the latest revised model (Figure 2) is an improvement.

The procedure described above was applied to the resuspension data for j the GSCEM Line. The fixation rate constant for that line was ' estimated to -l be 4x10-6 s-1 The mean resuspension rate for that line was also higher, j 5x10-7 s~l. Application of the results of these measurements is discussed l in the following section. It should be noted that the deposition, resuspension, and fixation rate parameters in this section are appropriate only for the 20-segment model used to derive them from the measurement results.

-1 I

l 16

c.

. 3. APPLICATION OF RADI0 IODINE MEASUREMENT RESULTS The' deposition and resuspension parameters derived from experimental measurements are used in calculations of transmission of 12 through the sampling lines. The results are expressed in terms of the transmission factor (TFd), defined to be the ratio of the concentration of'131 I2 at the y outlet of the line to the concentration entering the line. The lower the I TFd , the greater the loss of 131 12 due to deposition in the line. The 20-segment model was used to calculate equilibrium transmission factors and to estimate radioiodine behavior during departures from equilibrium conditions.

These calculations are discussed below.

4 The deposition velocities and resuspension rate constants for the-lines were measured at the nominal line operating temperatures. There.is evidence that both parameters depend upon temperature; however, the data are limited in scope and, for deposition velocity, rather variable. Small changes

( 10 C) in the line operating temperature are not expected to have an important effect upon either the deposition velocity or resuspension rate )

constant. Temperature variations of this magnitude are not expected to  !

affect the TF , so long as condensation of water vapor does not occur.

d Observed differences in laboratory transmission factor measurements at the .same temperature indicate the overall variability of the process. Dup-licate tests with a single line yielded transmission factors of 0.48 and

.0.62. Tests of four lines of the same diameter and flow rate, but differing lengths, yielded transmission factors ranging from 0.45 to 0.72. When the results are normalized to a common length, the variation in transmission factors for the four lines was 0.55--0.61. These previous observations of variability are probably representative for the GSCEM line. However, as the measured TF decreases, the variability between tests is expected to increase.

A case in point is the test result for the WRGM-LR line presented in Section 2. As indicated, the data were surprising. The test conditions and data were examined, but no basis was found for invalidating the result.

17

Examination of other testing results shows the measured transmission factor j and resuspension rate constant to be at the extreme of the range of results for comparable lines. The parameters derived from measurements of the mock-ups for the WRGM-LR Line (Line A) and three comparable lines are shown in Table 6. The ratio (Q/d) is proportional to the Reynolds number and is Table 6. PARAMETERS FOR SEABROOK WRGM-LR AND COMPARABLE LINES l

Transmission Vd (cm/s) Rate Constants Coefficient for WRGM-LR Resuspe sion Fixati n line (Qfd)

(cm /s_1 (B. 1/m) Line r (s 1 .A (s- )

A 500 -0.0662 0.11 1.1x10-8 2.1x10-6 ,

B 496 -0.0112 0.018 3.9x10-6 3.4x10-7 C 472 -0.00632 0.010 6.9x10-6 1.6x10-6 D 496 -0.0111 0.018 4.5x10-6 4.8x10-7 MEAN 0.039 3.8x10-6 1.1x10-6 i

indicative of the flow regieme which controls air-to-surface transport in the line. As the second column shows, the flow regiemes for the other three lines (B, C, and D) hre quite similar to that for the WRGM-LR Line. All four lines were made of stainless steel and were tested in the same way (as described in Section 2.1). No consistent differences in test results have been observed for lines made of Type 304 or Type 316 stainless steel. The l

transmission parameter per unit length ($, m-1) is shown in the third column and shows Lines A and C are at the extremes of the distribution. The fourth column shows estimates of the deposition velocity (V ,dcm/s) for the WRGM-LR ,

Line derived from the four values of A. The last two columns show the resuspension and fixation rate constants for the four sets of measurements.

The measured resuspension rate constants are again bounded by the results 18

.I p' 4 .

for Lines A and C. The range of the fixation rate constants is smaller.

The mean values of dV , r, and p are shown at the bottom of the table. They are better estimates of the true parameters for the group of lines than any of the individual results.

It could be argued that the niedian deposition velocity (0.024 cm/s) would be more appropriate than the mean because the distribution appears to j be skewed. Three of the four values of Vd are less than the mean value of 0.039 cm/s. However it is not clear that the distribution is log-normal, so the more cautious approach of using the mean value was followed. The mean values for all three parameters are used below in developing best estimates  ;

of the transmission factors for the WRGM-LR and WRGM-HR* sampling lines. As  ;

a check on this approach, a random number generator was used to sample the distribution of deposition velocities and the results of calculations using those values are also presented (page 22).

During a period of constant elemental iodine input to the sampling line, the surface activity in each segment will gradually increase to an equilibrium value. The equilibrium is reached when deposition of elemental iodine onto surfaces in the segment is balanced by resuspension of 13I 1 from those surfaces. Calculations of the balance in each line segment and of the net transmission of activity under those conditions were made using the 20-segment model and the values of dV , r, and p derived from the laboratory measurements. The parameters used in the calculations are given in Table 7.

The equilibrium transmission factor for the depositing species (TFde) is defined as the ratio of the 131 1 activity leaving the line to that entering the line (I, pCi/s), when equilibrium has been reached. The equation is:

TF de A9v ae(20)/I (10) 131 where gae(20) is the equilibrium 1 activity in the last (20th) line segment and A y is the previously defined exhaust rate constant. The 19 l

v -

c l .;,; ~ . ,

I'

. Table 7. PARAMETERS USED IN CALCULATIONS OF RADIOI0 DINE TRANSMISSION THROUGH SEABROOK LINES.

Parameters for Radioiodine Transmission Model Line Designation yd (cm/s) d'(s-1) r (s-1)

ASBEMa 0.012 8.0x10-7 5.6x10-6 WRGM-LRa,b .0.039 1.1x10-6 3.8x10-6 WRGM-HR*

High Flow Rgte Section a ,o 0.039 1.1x10-6 3.8x10-6 Low Flow Rate Sectiona - 0.043 8.5x10-6 1.1x10-7 GSCEMb= 0.018 4.0x10-6 5.0x10-7 RCPBMa 0.039 3.1x10 3.3x10-6

.a. Parameters determined from laboratory measurements of similar lines.

b. Parameters determined from laboratory measurements of replica.

. calculated values of TFde are shown at the bottom of Table 8. The result for the WRGM-HR* line reflects transmission losses in both the high and low flow rate sections of the line. For two lines in sequence, as those are, the transmission factor for the complete flow path is the product of the two individual TFs. Although little is known about the radioiodine species that would be expected following a " typical" accident, the equilibrium transmission factor for 1 2 (TFd e) provides a lower bound for the long-term average transmission factor.

20 M l-_-____________ _ _ _ . _ . . . _ _ _ _ . _

Table 8. TIME DEPENDENCE OF TRANSMISSION FACTORS FOR 131 1

-FOLLOWING A LARGE INCREASE IN EFFLUENT CONCENTRATION Transmission Factor for 131 12 (TFd )  ;

e . 1 Time (hours) ASBEM WRGM-LR WRGM-HR* GSCEM RCPBM After Event Line_ Line line line Line 2 0.96 0.42 0.41 0.95 0.88 ,

5 0.96 0.44 0.43 0.95 0.88 20 0.98 0.50 0.49 0.95 0.89 50 0.98 0.59 0.58 0.95 0.91 200 0.99 0.72 0.71 0.96 0.93  ;

i Equilibrium 0.99 0.72 0.71 0.96 0.93 j Value (TFde) 4 l

l The ASBEM line which is relatively short and is operated at a high flow rate is estimated to have a TFd e of 0.99. The values for the GSCEM and RCPBM lines are similarly high. The results for the WRGM-HR* line is nearly the same as the estimated TFde for the WRGM-LR line indicating only minor losses in the new short low flow rate section.

1 If the input of depositing species to the sampling line increases from IA (gCi/s) to IB (pci/s), .it will take time for the line to reach a new equilibrium distribution of airborne and surface activity. The deviation would be greatest following an extended shutdown or if IB >> AI . The 20-segment model was used to predict the rate of approach to equilibrium.

Table 8 also contains the computed values of the transmission factor for depositing species as a function of time for the five lines. Little change is seen with time for three of the five lines because the initial trans-mission factors are so high that a large change is not possible. For the 21 l

v.. > ,

WRGM-LR and WRGM-HR* lines, the equilibrium transmission factors are about l'.7 times the initial values.

The results in Table 8 show that the overall TFd for the WRGM-HR* line '

is controlled by the long, high flow rate section, the WRGM-LR line. To )

collect highly contaminated samples soon after an accident, the flow through that section would be diverted directly back to the Plant Vent rather than passing through filters on the low range WRGM skid. The isokinetic sample extraction nozzle would be used to withdraw a small aliquot of the air ,

sample stream. The radiciodine species in the Plant Vent soon after an accident could be predominantly elemental iodine. To assure that an initial TFd of 0.4 is achieved, it is recommended that the WRGM diversion pump be ,

operated for a minimum of 20 minutes prior to collection of the first i sample.

1 Alternative calculations of the initial TFd for the WRGM-LR line were ,

performed using the distribution of deposition velocities in Table 6. As  !

noted there, three of the four values were less than the mean. It was assumed.that the results for Lines C and A represent the 5th and 95th percentile values of the distribution. A random number generator was used.

to select 200 random values from the distribution of Vd and those were used to compute initial transmission factors for the line. The mean of the 200 g values of TFd (2 h) was 0.54. The fraction lost _ (1 - TFd) appears to be log-normally distributed with a median value of 0.40 and a geometric standard deviation of aboout 1.5; the median TFd was 0.6. These results, which are not strongly dependent upon the choices cf r and p, confirm that

( the choice of the mean deposition velocity yields a cautious estimate of the initial TFd for the lines in Table 6.

For normal operation of the WRGM-LR Line, the equilibrium transmission factor for total gaseous radioiodine (TFg ) will be almost certainly higher than that quoted above for I 2. As Table 2 shows, elemental iodine accounts for only 27 percent of the 131 1 in typical PWR effluents. Because the deposition velocities of HOI and organic iodides are small, the trans-mission factors for these species are approximately one. At any time, 22

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ __ a

i the fractional transmission of the gaseous radioiodine (TFg) is approximated by:

. q TF g

=

TFd xFe+Fh+F o (11)  !

4 where F e is the fraction of the gaseous radiciodine that is in elemental form, F

h is the fraction of the gaseous radiciodine present as H01, F

o is the fraction of the gaseous radioiodine that is in organic form, and the other quantities-were defined above. The average values of the fractions'F , F , and F based upon previous PWR measurements are calcu-o h o lable using the data in Table 2 and are 0.27, 0.41, and 0.32, respectively (for normal operations).

If the average PWR effluent species distributions apply to the Seabrook Station effluents, then during normal operations, the value of TF e g would be expected to be about 0.93 for the WRGM-LR Line. Soon after a sharp increase in activity with no change in species, TFg is estimated to.be 0.84 for the WRGM-LR line. Of . course, the value of TFg e at any time depends upon the actual distribution of radioiodine species. Better estimates can be made when a representative species distribution in the Seabrook stack effluent  !

stream can be measured.

l The overall radiciodine transmission factor must also reflect the transmission' factor for the particulate fraction (TF ) which a depends upon the size distribution of the radioiodine activity. The overall transmission factor for radioiodine is:

L TF; -

Fp x TF, + TF g x (1 - Fp )

(12) where F p is the fraction of the total radiciodine activity in particulate form. Previous measurements at PWRs indicate that pF is 0.02. Values of transmission factors for various particle sizes and densities are given in Section 4.

f 23 l

_ _ _ --_ _ _ __ ___ _ ___ _ _ _ _ _- _ - - _ - _ .)

At times greater than a few hours after an accident, the transmission factor for total gaseous I3I I (TF g) in the RCPBM Line would almost certainly exceed the corresponding value of TFd given in Table 8. As time passes, the fraction of the airborne radiciodine that is elemental would be reduced and the concentrations of less reactive forms would increase. There are a few measurements of radioiodine species in PWR containment buildings that  ;

indicate this change. The first measurements of radiciodine species in l j

the TMI-2 containment were not made until about 3 months had elapsed.8 9

The initial measurements of 131 1 and subsequent measurements of 1291 showed that the elemental iodine fraction was less than 0.1 at long times after the accident.

Measurements of species changes in the containments of PWRs during  !

normal operation may indicate the rate at which post-accident species changes would occur. Table 9 contains estimates of Fe based upon measure-ments during normal operations in PWR containments.3 These estimates were used to project values of TF for g the Seabrook RCPBM line.

If the input of I 2

into a line decreases sharply from IAto I C

(#Ci/s), with IA " I , then C the measured outlet concentration can exceed the inlet concentration. This may occur due to resuspension of radiciodine previously deposited on surfaces of the line. The largest effect would be observed if the line had reached equilibrium with the initial input rate before the decrease occurred.

The 20-segment model described above was used to estimate the magnitude of this effect. The results showed that even following equilibration of these sampling lines with pure 1,2 the effect on a 24-hour air sample would be an overestimation of the 131 I release by less than 5% of the equilibrium release rate.

l l

24

q

]

i l

Table 9. ESTIMATED TIME DEPENDENCE OF ELEMENTAL I0 DINE FRACTION AND PROJECTED GASE0US IODINE TRANSMISSION FACTOR (TFg ) FOR RCPBM LINE Estimated Projected Time Elemental Iodine Transmission factor (hours) Fraction (Fe la (TFg) for RCPBM Line 2 1 0.7  !

6 0.9 0.8 20 0.8' O.8 50 0.6 0.9 200 0.1 1 l

a. Derived from best fit curve through data for PWR containments durina normal operations,

b. Projection assumes that observed changes in Fe with time also apply to p_ost-accident conditions.

i 25 u_ _ _____- _ _ . _

l 4.0 CALCULATIONS OF PARTICLE TRANSMISSION The fractional transmission of particles through sampling lines depends upon the characteristics of the particles and upon the characteristics of the sampling line. The most important particle characteristics are the diameter and density. This section contains results of calculations of

' transmission factors for the Seabrook lines described in Table 1 for a range of particle sizes and densities. -

The aerosol transmission calculations were performed using the DUCT computer code developed by SAIC. The computer code is based on empirical  !

relationships for various depletion mechanisms. The calculations consider Brownian and turbulent diffusion, sedimentation, and impaction of aerosol particles in the sampling line.

For each line segment, the DUCT code computes the fraction of particles of the specified diameter and density that: (a) are deposited in a given section of line and (b) are lost by impaction in bends in the line. The fraction deposited (F, dimensionless) is given 10 by F- 1 - exp (-4 V dL/hu) (13) where V d is the deposition velocity (cm/s) of the particles L is the length (cm) of the line segment h is the diameter (cm) of the line u is the mean fluid velocity (cm/s) in the line, f Separate calculations are performed for horizontal and vertical line L segments. Slant sections are treated as horizontal, which generally over-estimates the losses in the slanted line segments.

l For horizontal lines, the deposition velocity is computed using the relationships of Matsui gt _a_1.11 and Yoshioka et al.12 When gravitational f settling contributes to the deposition velocity, that contribution is 26 l

t

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - . _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - . _ _ _ _ _ _ _.____.._________-.a

jI i ^ .g'. _

.- .. estimated.using. Stokes's Law. For vertical line segments, the relationships developed by Beal.13 are employed to compute V

• d The overall transmission factor for a line reflects deposition in both the horizontal and vertical. sections. The transmission factor for particles Lthrough the line, TF p, is comptited using

.TF p

=

(1-Fg ) (1-Fy)- (14) where FH .is the fraction of particles deposited in the horizontal sections and bends Fy is the fraction of particles deposited in the vertical sections and bends.

Results of the~ calculations of particle transmission thrcugh the two lines are presented in Table 10 for six particle diameters in the range

. 0.1 ym to 5 ym. Results.are given for five particle densities, ranging from 1 to 10 g/cm3 . The results given for the WRGM-HR* line reflect losses in 'both .the high and low flow rate sections of the line. For two lines in sequence,- as- those are, the transmission factor for the entire flow path is the product of the TFs for the two components.

The results for the Auxiliary and Service Building Exhaust Monitor (ASBEM) Line indicate the TF p is 0.5 or greater for the entire spectrum of particle sizes and densities examined. For the normal range of particle densities, 1--3 g/cm3 , the values of TFp are -0.8 or greater, even for a particle diameter of 5 gm.

The values of TFp for the two WRGM lines decline rapidly for particle diameters greater than 1 ym. At Seabrook, all of the post-accident effluent discharges pass through HEpA filters prior to monitoring and release to the environment. The particles most likely to penetrate such filtration systems l,

are small (-0.3 ym). The results in Table 10 show that transmission losses for 0.3-ym particles in the WRGM-HR* line combination will be 2% or less for any of the densities considered. Most of the air monitored by the WRGM-LR l

27 E_-_---------------

o ,

. ;Wq, ,

4

.. 2 ..

Table 10. .. COMPUTED. TRANSMISSION FACTORS FOR PARTICLES FOR SEABR00K STATION SAMPLING LINES TRANSMISSION FACTOR (TFp ) F0Pc h SPECIFIED FARTICLE DIAMETER AND: DENSITY ,

Particle Density fo/cm 3)

Particle Diameter-(um)- 1,0 2A, 3_a_ }_JL 10 Results for ASBEM Line -

0.1 .1.0' 1.0 1.0 1.0 1.0 d

0.3 1.0 1.0 1.0 1.0 1.0 0.5 1.0 1.0 1.0 0.99 0.99 1.0 0.99 0.99 0.99 '0.98 0.96 3.0; 0.95 0.93 0.91 0.87 0.75 5.0 0:87 0.84' O.78 0.70 0.50 Results for WRGM-LR Line 0.1- 0.99 > 0.99 0.99 0.99 0.99 0.3 0.99 H0.99 0./ 0.99 0.98 0.5 0.99 0.99 0.99 0.98 0.97 1.0 0.98 0.98 0.97 0.95 0.87 3.0 0.87 0.83 0.76 0.62 0.23 5.0 0.65 0.51 0.31 0.14 a l

l

a. ~ Calculated transmission factor was <10-2 ,

i 28

___-_-_--__-________--__---_-________-____a

. e .. .

Table 10 (Continued):

COMPUTED TRANSMISSION FACTORS FOR PARTICLES FOR SEABROOK STATION SAMPLING LINES TRANSMISSION FACTOR (TFp ) FOR SPECIFIED PARTICLE DIAMETER AND DENSITY 1

3 Particle Density (a/cm )

Particle Diameter (um) 0 L_0_ 2.0 3.0 5.0 10 Results for WRGM-HR* Line 0.1 0.99 0.99 0.99 0.99 0.99 0.3 0.99 0.99 0.99 0.99 0.98 0.5 0.99 0.99 0.98 0.98 0.95 1.0 0.97 0.97 0.92 0.83 0.54 3.0 0.41 0.27 0.11 0.013 a 5.0 0.023 a a a a Results for GSCEM Line 0.1 1.0 1.0 1.0 1.0 1.0 0.3 1.0 1.0 1.0 1.0 1.0 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.99 0.99 3.0 0.98 0.97 0.94 0.89 0.59 5.0 0.90 0.84 0.69 0.41 a

-2

a. Calculated transmission factor was <10 ,

29

p .. y . .. - . .

@m,

.- . ~ .. .-

q ...

I5 s L,

Tabis 10-(Continued):

. COMPUTED TRANSMISSION FACTORS FOR PARTICLES 4 l- FOR SEABROOK STATION SAMPLING LINES

. TRANSMISSION FACTOR (TFp ) FOR SPECIFIED PARTICLE DIAMETER AND DENSITY ~

L Particle' Density (a/cm 3).

>< Particle Diameter (um) R R R 5.0 ._}.0_.

L' Results'for RCPBM line 0.1 1.0 1.0 1.0 1.0 1.0 0.3 1.0 1.0 1.0 1.0 1.0 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.99 0.99 0.99 0.97

. 3. 0 - 0.96 0.95 0.90 0.80 0.97

-5.0 0.82 0.73 0.56 0.34 a-

a. Calculated transmission factor was <10-2 ,

l 4

i L ,

1 4

30 g

. , e .1 ,

n . . .

system has also passed through HEPA filters. However, the radwaste building 1 effluent will not have' been filtered. The contribution of the radwaste building to the total particulate radionuclides discharge varied at plants studied previously.2,3 As a result, it is not possible to predict with confidence what the particle size distribution in the normal effluent stream will be.

Results for the Gland Steam Condenser Exhaust Monitor Line indicate transmission factors of about 0.7 or greater for particles of normal density with diameters between 0.1 and 5 #m. No data are available on particle size distributions in gland steam exhaust lines, although both the number of particles and their diameter would be expected to be small.

1 3  !

The' transmission of particles with densities between 1 and 3 g/cm

.through.the RCPBM Line is expected to be greater than 0.5 for all diameters considered. Because many of the particulate radionuclides in the contain- i ment air will be the daughters of noble gas radionuclides, it is reasonable

?

to expect that the median diameter would be small, probably less than 1 Am.

Data on the efficiency of the roughing filters in the containment air

• handling system indicate that particles with diameters of 1 ym or greater will be effectively removed after a few air turnovers.

As the results in Table 10 show, the transmission factor for particulate material through a sampling line can vary over a wide range, depending upon

'the size and density of the airborne particles. The aerosol being sampled  ;

will frequently consist of a variety of particles of differing sizes. For that reason, many calculations of transmission factors for specific particle sizes and densities were performed. The following paragraphs deal with the use of the computed values of transmission factors for specific particles (TFp ) to determine the transmission factor for the aerosol of interest (TF,).

The transmission factor for a mixture of particles can be computed using: 1

= (15)

TF, lE(TFp )4 x RF j 31

_ _ - - - _ - - __________o

'. s ;.;,

y. - *; e where TF is the transmission factor for the aerosol, th size (Th)$p is the transmission factor for particles.in the i L range, and RF is the fraction of the aerosol radioactivity associated with 9

particles in the i th sizerange(IRF4 = 1).

.The size ranges to be used in the calculations will be determined by the impactor used for the measurements and its operating characteristics.

Some units divide the aerosol into six fractions; others employ additional (or fewer) stages and provide a more (or less) detailed breakdown of par-ticle sizes. Table 10 contains values of TF p for a specific set of particle sizes. Calculated transmission factors for other particle sizes can be provided to match the radioactive particle size. distribution determined by different impactor designs.

For some situations there will be no measurement data that define the radioactivity distribution versus particle size; post-accident aerosols are in this. category and are perhaps the most difficult to characterize. In the absence of measurements of the fractionation of radioactivity among the various particle sizes in the ambient aerosol, a reasoned analysis must be used to estimate TFa -

i 9

32 1

3 ,#;,. ,,

n. ,

a 5.0 HELIUM TRACER MEASUREMENTS The monitor used to detect leakage from the Reactor Coolant Pressure Boundary (RCPB) at Seabrook is designated RM-6526. The monitor, located in the basement of the Primary Auxiliary Building, draws air from the con-tainment through a short line (see Table 1). A tracer gas, helium (He), i was used to evaluate the transport of airborne material in the containment from potential coolant leakage points to the monitor. The transit time for radionuclides released via coolant leakage is an important parameter in determining _the response time for the monitor.

The experimental techniques and measurement results are discussed in the'two subsections which follow. Conclusions reached from the testing are given in Subsection 5.3.

5.1 HELIUM MEASUREMENT TECHNIQUES Helium was released at a controlled rate into the B Reactor Coolant Pump (RCP-B) cubicle. The RCP-B cubicle is located on the opposite side of the containment building from the inlet to the sampling line for the RM-6526 monitor. This release location was selected because it is both a credible coolant leakage point and is also about as far away from the sampling line as a release point could be. The He release rate was monitored with a mass flowmeter calibrated for helium flow rates in the range from zero to 4720 cm3 /s.

The He concentration at the RM-6526 skid was measured using a calibrated helium monitor. The monitor is a mass spectrometer tuned specifically to measure helium (4He). Calibration was accomplished using bottled standards containing He concentrations of 20, 70, and 100 parts per million (ppm, by volume). The natural background concentration of 4He in the air averages about 4 ppm and provides a fourth concentration level. The monitor was calibrated using the bottled standards before and after the testing.

Table 11 contains the calibration results. The He monitor scale readings were consistent and corresponded closely to the injected He concentrations (ppm).

33

- _ _ _ - - -__-__-________-_____a

. s. . ' .

]

, g ,, g  ;

+

, }

Table 11. HELIVM MONITOR CALIBRATION RESULTS O

Helium Monitor Scale Readino

. Input Helium Before After Concentration (com) Testina .Testina

,, 20 19.2 20.0 70 69.7 70.8

'100 100 96.8

, The He monitor was connected to the RCPB Monitor at the RM-6526 sampl-L ing skid by replacing the sample bomb with appropriate tubing and fittings for the He monitor. The RCPB Monitor was operated at the normal flow rate o'f 1180 cm 3 /s and the valves 'were aligned to route'the airflow tt. rough the tubing containing the tap for the He. monitor.

5.2 HELIUM RELEASE TEST RESULTS i

Two. tests were conducted. During the first test, helium gas was released at the rate of 425 cm3/s into the RCP-B cubicle. During that release, five of the six containment air handling fans were on; fan CAH-FN-1E was off. Helium was detected at the monitoring location, by visual observation of the meter on the He monitor, about 5 minutes after the start of the release. The concentration at the monitor was 1 ppm above the background and registered on the strip chart recorder after approximately 11 minutes. Figure 3 shows the time history of the net helium concentration measured during the first He release test. Although measure-ement data were recorded continuously throughout the test, only periodic concentraiton values are shown in the plot. After 16 minutes, the measured 34

, 7 2 , ,1., <

]

c: 1, b

. oc

.4

,, I

]

c , l 4

1

-l n;

, i L

]:l t

p.

.SEABROOK TEST #1

.40

-30 ..

. Net [He] 20 *

(ppm) 10 .

0.-.-.

0 20 40 60 80 100 Time (min) After Start Figure 3. Net Helium Concentrations (ppm)

Measured During Test #1 55

-_:- . _ =-_. -_ - _ _ _ - - _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

J ru ..

concentration 'was about twice the natural background level. The concentra- j tion continued to' increase and was 32 ppm above background at the end of the f 60-minute release period. Measurements in the first test were continued for j l

96 minutes, at' which time -the net He concentration'was 38 ppm, slightly below 1

the maximum of 40 ppm that had been measured between 87 and 90 minutes. 1

'Because the inlet to the sampling line 'for the air monitor is located against the wall of the containment, it was anticipated that the time required for transport of released material would be relatively long. The rapidity with which the monitor detected the He release was a surprising  !

result.1It appeared possible that the fan alignment could be responsible for the prompt transport of He to the monitor. To test this hypothesis, fan CAH-FN-1B was turned off and fan CAH-FN-1E was started prior to the second test.

The second release of He gas was also into the RCP-B cubicle, but at the higher rate of 1510 cm3 /s. The existing He concentration in the containment, due to the first test release and natural background,. was 43 ppm. Figure 4 shows the change in measured net He concentration with time during Test #2. Again only concentrations measured at specific times are shown, although a continuous record was made during the test. Between 3 and 4 minutes after the start of the release, the He concentration had increased by 1 ppm on the strip chart recorder. After 12 minutes, the He concentration was 15 ppm above the pretest value of 43 ppm. The net con-centration had increased to 32 ppm after 18 minutes. The total concentration exceeded the upper limit of the scale (100 ppm) after 29 minutes. At that time, the net He concentration from the second release was 57 ppm. The  !

test was terminated at that time because the He monitor was off-scale. I

5.3 CONCLUSION

S Transport of the helium tracer from the RCP-B cubicle to the inlet to the RCPB Monitor (RM-6526) was rapid; initial detection of He occurred in less than 5 minutes in both tests. The time required for the He concen-tration to reach twice the natural background level was about 16 minutes in the first test. In the second test, the ratio of the release rate to 36

_ _. _ _ _ _____-_____-___________D

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60 50 40

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Time (min)' After Start Figure 4. Net Helium Concentrations (ppm)

Measured During Test #2

( 37

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~.N- .- . - . _ _ - - . _ , - - . . - _ _ -- - - - - - _ _ _ _ . - . - - - _ _ - - _w._-_-_._..____ _ _ . - - - - _ - _ . - - - - - - - - _ - - - - - - _ _ _ - - _ . -

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$, ' the pre-test background concentration was lower 'and the time required for

- :the'He concentration:to reach two times'the pre-test background was about E  : 25 minutes'.--: Both tests showed that transport of tracer gas from'a distant coolant leakage point occurred quickly and that the concentrationsTincrea' sed steadily during the period of release.

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, 6. REFERENCES

1. J. H. Keller, L. G. Hoffman, and P. G. Voillequs, Wet Deposition Processes for Radioiodines, NRC Report NUREG/CR-2438 (August 1982).

C. A. Pelletier, J. E. Cline, E. D. Barefoot, R. T. Hemphill, 2.

P. G. Voillequs, and W. A. Emel, Sources of Radiciodine at Pressurized Water Reactors, EPRI Report NP-939 (November 1978).

3. J. W. Mandler, B. G. Motes, C. A. Pelletier, A. C. Stalker, T. E. Cox, P. G. Voillequd, S. T. Croney, D. W. Akers, C. V. McIsaac, N. K. Bihl, G. A. Soli, S. W. Duce, J. K. Hartwell, J. W. Tkachyk, and L. S. Loret, In-Plant Source Term Measurements at Four PWRs, NRC Report NUREG/CR-1992 (August 1981).

4. M. J. Kabat, Deposition of Airborne Radioiodine Species on Surfaces of Metal and Plastics, in Proceedings of the 17th DOE Air Cleanino Conference, DOE Report CONF-820833 (February 1983).

131

5. P. G. Voillequ6 and J. H. Keller, Air-to-Vegetation Transport of I as Hypoiodous Acid (H01), Health Phys., M , 91 (1981).

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7. R. T. Hemphill and C. A. Pelletier, Surface Effects in the Transport of i

Airborne Radiciodine at licht Water Nuclear Power Plants, EPR1 Report l

NP-876 (September 1978).

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I

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I Containment Atmosohere Durina and After the Ventina, DOE Report l GEND 009 (April 1981) l 10. A. K. Postma and L. C. Schwendiman, Turbulent Deposition in Sampling Lines, in Proceedings of the AEC Air Cleanino Conference, AEC Report TID-7627 (1961).

i 11. H. Matsui, Y. Yashida, M. Murata, and T. 0hata, Measurement of Deposi-I tion Fraction of Aerosol Particles in a Horizontal Straight Metal Pipe, J. Nucl. Sci. Tech., 11, 300 (1974).

I 12. N. Yoshioka, C. Kanoaka, and H. Emi, Kaaaku Buturi, f, 89 (1971) (in Japanese).

13. S. K. Beal, Deposition of Particles in Turbulent Flow on Channel or Pipe  :

Walls, Nucl . Sci . Enar. , @ (1970) .

39