ML20214L947

Analysis of Dose Rate Under TMI-2 Reactor Vessel

ML20214L947
Person / Time
Site:	Three Mile Island
Issue date:	04/13/1987
From:	Shannon King, Nitti D, Snidow N BABCOCK & WILCOX CO.
To:
Shared Package
ML20214L934	List: ML20214L932 ML20214L947
References
51-1167938, 51-1167938-00, NUDOCS 8706010133
Download: ML20214L947 (35)

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1 BWNP 20440-5 (12

% "" ENGINEERING INFORMATION RECORD Document identifier 51- 1167938-00 Title Analysis of Dose Rate Under 'IMI-2 Reactor vessel PREPARED BY: REVIEWED BY:

Name N. L. Snidow and S. O. Kim Name Donald A. Nitti Signature 9/ M IthM Date 4/'3/87 Signature / I I ate FMf /# 7 N/ 14Nd?

Technical Manager Statement: Initials >

Reviewer is Independent.

h Remarks:

This document provides an analysis of the M-7 and M-9 ga:mn profiles measured with a miniature ion chamber under the 'IMI-2 reactor vessel in March of 1986. The measured profiles were adequately nutched with calculations using reasonable assumptions regarding cesium contamination source strength based on contamination information available fran other locations in the basamnt.

3706010133 870521 PDR ADOCK 05000320 P PDR Page 1 of 34

r-0 CONTENTS Page 1 INTRODUCTION . .. . . . . . . . . . . . . . . . . . . 5

2.

SUMMARY

OF RESULTS .. . . . . . . . . . . . . . . . . 6

3. MEASUREMENTS . . . .. . . . . . . . . . . . . . . . . .

7

4. QADMOD CALCULATIONS . . . . . . . . . . . . . . . . . 9 4.1. Case 1 -- Source in Ring on Wall . . . . . . . . 10 4.2. Case 2 -- Source on Wall Below Ring . . . . . . 11 4.3. Cases 3, 4, and 5 -- Source on Insulation . . . 11 4.4. Cases 6, 7,.and 8 -- Source in Water . . . . . . 12 4.5. Case 9 -- Localized Source on Guide Pipe . . . . 12 4.6. Cases 10 and 11 -- Uniform Source on Nozzle and Guide Pipe . . . . . . . . . . . . . 13 4.7. Case 12 -- 4-Inch High Ring Source on Wall . . . 13

5. TRANSPORT CALCULATIONS . . . . . . . . . . . . . . . . 14

6. RESULTS . . . . . . . . . . . . . . . . . . . . . . . 16

7. REFERENCES . . . . . . . . . . . . . . . . . . . . . . 17 51-1167938-00 Page 2 of 33

List of Tables Table Page

1. List of QADMOD cases . . . . . . . . . . . . . . . . 18

2. Calculated Dose Rate Along M-7 Withdrawal Path . . . 19

3. Attenuation in Nozzle and Guide Pipe From QADMOD . . 20

4. Dose Rate From Localized Source on Guide Pipe . . . . 20

5. Ion Chamber Sensitivity and Guide Pipe Attenuation From DOT Results . . . . . . . . . . . . 21 t

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r-Se List of Floures

. Figure Page

1. Calculated and Measured Dose Rate, M-7 Traverse . . 22

2. Primary Shield Cavity Under RPV, Plan View . . . . . 23

3. Primary Shield Cavity Under Reactor Vessel, Elevation View . . . . . . . . . . . . . . . . . . . 24

4. Path of Incore Guide Pipe #13 . .. . . . . . . . . 25

5. Current Profile Measured at Location M-7 . . . . . . 26

6. Path of Incore Guide Pipe #16 . . . . . . . . . . . 27

7. Current Profile Measured at Location M-9 . . . . . . 28

8. QADMOD Model for Case 1, Ring Source . . . . . . . . 29

9. Dose Rate From various Sources, M-7 Traverse . . . . 30

10. Dose Rate From Localized Source on Guide Pipe . . . 31

11. DOT Model . . . . . . . . . . . . . . . . . . . . . 32

12. Calculated Ion Chamber Current With Source on Insulation . . . . . . . . . . . . . . . . . . . 33

13. Calculated Ion Chamber Current With Source in Water . . . . . . . . . . . . . . . . . . . . . . 34 51-1167938-00 Page 4 of 33

1. INTRODUCTION Gamma radiation measurements below the TMI-2 reactor vessel were made in March 1986 in an attempt to characterize the gamma radiation present in this region. The measurements were made using a miniature ion chamber inserted into the calibration tube of incore instrument assemblies. The measurements are reported in Reference 1 and include a scan at position M-7 from a refer-ence plane tangent to the bottom of the reactor vessel out to approximately 168 inches withdrawn and a scan at position M-9 from approximately 103 inches withdrawn from the reference plane to about 230 inches withdrawn. Sigeg'ghe measurements were made, there have been several analyses which have attempted to explain the general shape and magnitude of the measured results as well as the peak that occurred in the M-7 profile near the air / water interface. The primary question is whether the measured results can be reasonably explained without assuming that there is fuel debris outside the reactor vessel.

In the work reported here, calculations were made to provide an independent assessment of these ion chamber measurements. This study addresses the question of whether the ion chamber profiles can be explained based on the cesium contamination known to be in the containment without assuming that there is fuel outside the reactor vessel, thus demonstrating that the profiles by them-selves do not prove that there is fuel outside the reactor vessel. It is emphasized that this study cannot prove that there is no fuel in the cavity beneath the reactor vessel. The available ion chamber measurements do not provide sufficient information to reach such a unique conclusion.

The cesium / barium gamma sources considered as contributors to the dose rate beneath the reactor vessel included contamination in a high water level ring on the cavity wall, on the remainder of the wall, on the mirror insulation across the bottom of the reactor vessel, dissolved in the water, and on the surface of the nozzle and guide pipe.

The dose rate beneath the reactor vessel resulting from the various sources was calculated using QADMOD-G, a three-dimen-sional point kernal gamma shielding code. The response of the ion chamber near the air / water interface was studied with the one-dimensional transport code ANISN and the two-dimensional transport code DOT.

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2.

SUMMARY

OF RESULTS The results are summarized in Figure 1. The curve in the f g re is the calculated dose rate for the M-7 traverse due to Cs contamination beneath the reactor vessel. The measured points are from Reference 1 with the exception that the dose rates underwater were converted from the current measurements using an underwater calibration consgt determined from the DOT calcula-tion in Section 5. The Cs source strengths, used in the calculations leading to Figure 1, were selected to be in a range considered reasonable based on contamination information avail-able from other locations in the basement and to match the measured data. The agreement between the calculated curve and the measured points in Figure 1 is not to be interpreted as proof that the assumed cesium source strengths are correct; but rather, that it is possible to match the measured data with reasonable assumptions regarding the cesium contamination source strengths without resorting to the assumption that there is fuel beneath the reactor vessel.

The calculated values for the M-7 traverse should also apply to the M-9 traverse over the range of 104 to 165 inches withdrawn.

The M-9 measured dose rate is approximately 4.0 R/hr in this range using the underwater calibration constant from DOT.

Comparing this with the calculated dose rate in Figure 1 shows that the calculated value is approximately equal to the average of the measured dose rates for M-7 and M-9 in the range of 105 to 165 inches withdrawn.

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3. MEASUREMENTS The miniature ion chamber measurements made beneath the TMI-2 reactor vessel in March of 1986 are reported in Reference 1.

Five figures from that report are reproduced here as Figures 3 through 7. Figures 3, 4, and 6 describe the geometry of the cavity beneath the reactor vessel and give the location of the ancore instrumentation guide pipes for the M-7 and M-9 locations.

An incore detector assembly (as shown in Figure 2) is located inside each guide pipe and consists of an outer Inconel wall, an inner Inconel calibration tube, and nine lead wires with Al o insulation and Inconel sheaths located i between the wall and the calibration tube.f the annular r$nh A radial traverse from the center of a calibration tube through a lead wire to the outside of the incore assembly passes through 0.057-inch of metal. For calculational purposes, the wall thickness of the nozzle and guide pipes were increased by 0.057-inch to simulate the effect of the incore detector assembly on the ion chamber current.

The gamma having measurements an 0.072-inch wereamade OD and with length sensitive a miniature ion inches.

of 1.67 chambeg The detector had a stainless steel case and was filled with 10 atmospheres of xenon. The measurements were made by inserting the ion chamber to various depths in the center calibration tube of an incore detector assembly and recording the current at each position. Position steps of 6 inches were used for the M-7 traverse and both 1- and 6-inch steps were used for the M-9 traverse. Figures 5 and 7 show the measured ion chamber current for the M-7 and M-9 traverses. Both of these figures are from Reference 1.

The gamma sensitivity of the miniature ion chamber was measurg at B&W's Lynchburg Research Center. A value of 3.47 x 10 amp /R/hr was determined a g he sensitivity in air.4 The measure-ment used a collimated Cs source with the ion chamber in a mockup of the rteel incore nozzle located at the bottom of the reactor vessel. Air filled the space between the source and nozzle. In another measurement, a spent fuel assembly with a cooling time of 14 months was used as the source. The measure-ment was made underw g r 3 feet4from the source and yielded a value of 34.8 x 10 amp /R/hr . The measured current was converted to dose rate in R/hr in Reference 1 by dividing by the ion chamber sensitivity. The measured sensitivity in air was used for the M-7 data above the air / water interface and the measured sensitivity in water was used for both the underwater M-7 data and for all of the M-9 data.

It was observed in Reference 3 that the measured underwater sensitivity was not appropriate for the specific case encountered here since the source was not distributed in the water. A calibration constant appropriate for the detector in a guide pipe 51-1167938-00 Page 7 of 34

4. QADMOD CALCULATIONS QADMOD-G is a three-dimensional point kernal gamma shielding code available from the Radiation Shielding Information Center at ORNL. The code was designed to accommodate complex source geometry configurations and to provide convenient methods of describing shielding and detector locations. A distributed source in the code is represented by a number of point sources (up to 27,000). The distance traveled in a straight line through each region from each point source to each detector position is determined. The uncollided flux and resulting dose rate at each detector point is then determined for each energy group from the attenuation coefficient in each region and the distance traveled in that region. Dose rate from scattered gammas is included through a calculated energy dependent buildup factor which is applied to the direct dose rate. The dose rate at a point is l then determined by summing over the energy groups and source points.

QADMOD calculations were made for the 12 cases listed in Table 1 and are docyted in Reference 5. The fuel inside the reactor vessel and Cs contamination on surfaces beneath the reactor vessel were considered as sources. Calculations in Reference 2 demonstrated that fuel inside the reactor vessel contributes very little to the total dose rate beneath the reactor vessel. This is due to a combination of low source strength and shielding by the reactor vessel. This result will be used in this study since, even if there is a contribution to the dose rate below the reactor vessel, it only makes it easier to explain the remaining observed dose rate with cesium contamination. That is, any relatively small contribution from the fuel inside the reactor vessel would reduce the assumed contamination on the insulation and perhaps other surfaces beneath the reactor vessel. The calculatiog7 listed in Table 1 were made to determine the dose rate from Cs contamination. The cases include:

4 l o A " bathtub ring" on the upper part of the cavity wall, l o The rest of the wall below the ring,

'l o The mirror insulation below the reactor vessel, i

{ o The 2 feet of water in the cavity, i

i o Surface of the nozzle and guide pipe, i

o Localized heavier layer on the guide pipe.

The source strength used in each case is largely arbitrary. The

calculated dose rate is proportional to the source strength used, therefore, the QADMOD results may be used for any source strength by simply multiplying by a constant. Calculated dose rates are

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underwater.' with a dissolved source is determined in the DOT calctilations reported in section 5 and was used in this report to convert current to dose rate for the underwater data.

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tt required at points along the M-7 withdrawal path as are calcu-lated in Cases 1, 2, 3, and 5. Detector locations along the '

' 1 withdrawal path can be readily modeled in QADMOD, however, a cylindrical guide pipe following the withdrawal path cannot. The

' ' guida pipe and' nozzle were omitted from Cases 1, 2, 3, and 5. A section of a vertical nozzle and guide pipe was added along the axis for Cases 4 and:7. Cases 5 and 8 are identical to Cases 4 l

' and 7 except the nozzle and guide pipe were omitted in these two cases. Case 4 compared with Case 5 then gives a measure of the attenuation due to the nozzle and guide pipe for a source on the insulation. Cases 7 and 8 were included to give the same information but for a source in water. In this case, however, 1

the attenuation due to the guide pipe was determined from the more accurate DOT calculations in Section 5. Cases 10 and 11

, were included to determine the contribution from a uniform contamination on the ~ nozzle and guide pipe . . Case 9 determines the dose rate from a localized heavier layer of contamination j over a 6-inch long section of the guide pipe. Case 12 was added to confirm that a heavier layer on the wall similar to that on the guida pipe in Case 9 would add very little.

2 4.1. Case 1 -- Source in Rina on Wall The model for Case 1 is shown in Figure 8. The geometry and dimensions were obtained from Figures 3 and 4. The source for this case is the " bathtub ring" near the top of the cavity wall. 1 Reference 6 on page 3.2-4 states that "present interpretation 4

considers the bathtub ring to extend from the upper edge of the

wall coating (approximately 5'-6" above the (basement) floor level) to the maximum level of accident water flooding (approxi-mately 8'-6" above floor level)." This corresponds to from 7'-0" (213.36 cm) to 10'-0" (304.80 cm) above the cavity floor since the cavity flooriis l'-6" below the basement floor. The M-7 path

J of detector locations starts at the reference plane tangent to the bottom of the reactor vessel (see Figure 3) at an elevation of 290'-5-7/16" (288.13 cm above the cavity floor). Detector locations were selected every 6 inches along the M-7 path to 162 inches withdrawn from the reference plane. The distance with-drawn and ' corresponding z coordinate are , listed in Table 2.

ie '

While a cogtamination level of 242.93 pCi/cm was used in QADMOD, 220 pCi/cm will be used for the comparison wiph measurements.

The initial source in QADMOD was 220 pCi/cm but due to a correction in the conversion of Ci to the number of gammgs per second, the QADMOD results are equivalent to 242.93 pCi/cm with

.the . correction. This value is consistent with the value quoted for p surfaces within the elevation range of the bathtub ring.pinted The results from QADMOD fcr Case 1 were multiplied by 0.906 to correct for the source strength (220/242.93) and by 0.84 in the nozzle-region and 0.83 in the guide pipe region to account for,the nozzle and guide pipe attenuation (see results for Cases 4'and 5 below). The results are tabulated in Table 2 and plotted in Figure 9.

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4.2. Case 2 -- Source on Wall Below Rina The QADMOD model for Case 2 is similar to that for Case 1 except the source is-on the wall below,the ring (Region 2 in Figure 3).

A source level of 55.21 LCi/cmj was used in the QADMOD calcula-tion for Case 2 and 50.0 pCi/cm will be used for. comparison with measurements.

painted walls in Reference 7.

This value is consistent with the value for The results for Case 2 were multiplied by 0.906 to correct for source strength (50.0/55.21) and by 0.83 to account for attenuation in nozzle and guide pipe.

The results are listed in Table 2 and plotted in Figure 9.

4.3. Cases 3, 4, and 5 -- Source on Insulation The QADMOD model for Case 3 is similar to the model for Case 1 shown in Figure 8 except the source is located in a disk 172 cm in radius extending from 281 cm to 289 cm a g e the cavity floor.

This source is intended to represent the Cs contamination on the mirror insulation across the bottom of the reactor vessel with perhaps some contribution from the bottom of the reactor vessel. It is known that this part of the insulation was submerged when the water was at its highest level. Although in

most cases steel surfaces have been observed to have less contamination than concrete (page 2.2-1, Reference 6), it seems highly probable that the mirror insulation under the vessel would have considerable contaminat.jon. The contamination in the water was approximately 137 pCi/cm at the time the water receded from

, the insulation (pages 4 and 9, Reference 8) and its elevation is within the range of the bathtub ring (page 3.2-4, Reference 6) .

The mirror insulation has multiple horizontal surfaces and, in general, horizontal surfaces are more contaminated than are vertical surfaces (page 2.2-1, Reference 6). For example, particulate matter has been observed on top of overhead cables and supports (page 23, Reference 8). A contamination 2 of 244.8 uCi/cm was used in QADMOD, however, only 80 pCi/cm will be used for the comparison with measurements. The results for Case 3 were multiplied by 0.327 to correct for the source strength (80/244.8) and by 0.84 in the nozzle region and 0.83 in the guide pipe region to account for attenuation in these materials (see results for Cases 4 and 5) .

Cases 4 and 5 are variations of Case 3. The gamma source was the same but the detector locations were changed to be along the vertical axis and a simulation of a nozzle and guide pipe were added coaxially to the detector points in Case 4. Case 5 is similar but with the nozzle and guide pipe removed. A comparison of Cases 4 and 5 then indicates the attenuation of gammas originating on the insulation due to the nozzle or guide pipe.

Dose rates from Cases 4 and 5 are listed in Table 3 at various heights on the axis. The results indicate an attenuation factor 51-1167938-00 Page 11 of 34

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of about - 0. 84 in the nozzle region and 0.83 in the guide pipe region.

4.4. Cases 6. 7. and 8 -- Source in Water The model for QADMOD Case 6 is similar to that for Case 1 (Figure

8) except the source is locatpd in the water. The contamination 4

in the water was 5.5 uCi/cm in December3 f 1986 (page 2.2-2, Reference 6). A souyce of 4.897 pCi/cm was used in QADMOD, however, 2.16 u ci/cm will be used for the comparison with i

measurements._ The attenuation of the gammas originating in the water by the guide pipe and incore assembly was obtained from the DOT calculations in Section 5. A factor of 0.643 was observed.

Case 6 QADMOD results were not used below the water. Some of the source points used in QADMOD were too close to detector loca-tions.

The QADMOD results under water were replgced with those from standard formulas for a semi-infinite medium . The results for both case 6 and the hand calculated values were multiplied by 0.441 to correct for source strength (2.16/4.897) and by 0.643 for attenuation in the guide pipe. The results are listed in Table 2 and are plotted in Figure 9.

The results for Cases 7 and 8 were replaced with the more accurate DOT calculations in Section 5.

4.5. Case 9 -- Localized Source '

on Guide PiDe QADMOD source on the Case guide 9 was pipe.included A

to gdy the effect of a locafized-  !

Cs source of 100 uci/cm was .

located over a 6-inch length of the surface of an essentially t infinitely long guide pipe. The DOT calculations in Section 5 show that the shift in gamma spectrum and increased sensitivity of the detector as the water is approached does not explain the peak observed at the air / water interface. The cause of the peak is more likely due to a localized source that may have been built up over time on the surface of the guide pipes just above the water level. The water level has fluctuated a number of times since the level has been near 2 feet in the cavity. Each time the water level has increased and then returned to the 2-foot level, a section of the guide pipe (6 inches for a 4-inch change in watersome rated, level) of woub7 the have been left wet. As the water evapo-during the next increase inmay Cs have water level been someleftofon thethe y g Cs face. H did not dissolve, then there would be a tendency for the contamination to buildup with each cycle. For the comparison with measurepents, the localized cont 91nation was assumed to be 220 p Ci/cm . (A value of 100 pCi/cm was used in QADMOD. ) That is, the contami-nation was made the same as that on a painted wall within the elevation range of the bathtub ring. The results are listed in Table 4 and are plotted in Figure 10.

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4.6. Cases 10 and 11 -- Uniform Source on Nozzle and Guide PiDe Cases 10 the guide and pipe11 were and added to consider uniform contaminat{onwere nozzle. on used in the calculations. Source levels of 111.29 uCi/cm Values selegted for use in the comparison with measuremepts were 5 uCi/cm below the elevation of the ring and 20 pCi/cm over the elevation range-of the ring.

As stated earlier, QADMOD results are proportional to the source strength used. Therefore, even large changes, as were made in this case, can be accommodated by multiplying by a constant. The results are listed in Table 2 and plotted in Figure 9.

4.7. Case 12 -- 4-Inch High Ring Source on Wall The fina Case 12, considered a 4-inch high ring of (3pDMOD calculation, Cs on the concrete wall just above the water level.

This calculation was made to confirm that a ring on the concrete over the same height as the localpzed source on the guide pipe and with a strength of 220 Ci/cm would only contribute a very small amount to the M-7 traverse.

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5. TRANSPORT CALCULATIONS One-dimensional ANISN and two-dimensional DOT transport calcula-tions were employed to investigate the observed peak in detector current Figure 5).

nearIt the air / water interface in the M-7 traverse (see has been_ postulated that the peak might be due to gammas originating above the water and scattering back from the water at a lower energy. Since the sensitivity of the detector increases as the energy decreases, a higher current could be expected as the ion chamber approaches the water surface. The ANISN and DOT calculations are documented in Reference 9.

Both the ANISN and DOT calculations used the P L nomial scattering approximation and Sa quadratu2'1 (egendre poly-48 scattering angles) and the CASK 23-E cross sect 1on library with 40 energy g g ps. Only the last 18 of these are used for gammas. The Ba gamma falls into energy group 34.

The first part of this task was to generate a response table for the miniature ion chamber current; that is, to determine a constant for each energy group such that the product of that constant and the gamma flux for the group yields the ion chamber current for that energy group. A similar table for dose rate was already available in the cross section library. Information available on which the current response table could be based included the theoretical variation with energy of the Compton scattering and photoelectric cross sections for xenon (gas in ion chamber) and the measured calibration constant in air and in water described in Section 3. An ANISN model was developed representing each of the two measured configurations. A trial response table base on the theoretical cross section was used initially. The table was then iteratively adjusted until the calculated ratio of current-to-dose rate matched the measured

, ratio for both the in air and in water cases.

The DOT model of the cavity beneath the reactor vessel is shown in Figure 11. An RZ cylindrical geometry was used. The R i

coordinate is along the horizontal direction in Figure 11 and the z coordinate is the vertical direction. The axis of the cylinder is along the z direction at the left of the figure. There is i symmetry in the e direction. Two DOT calculations were made. In i

one, the source was in a disk at the top gimulating the mirror i insulation and had a 9trengg of 200 poi /cm . In the other, the j

source was 4.4 pCi/cm of Cs dissolved in the 2 feet of water at the bottom of the cavity (Zone 2 in Figure 11). The calcu-

lated ion chamber current is plotted in Figure 12 for the insulation source and in Figure 13 for the source in water. In both cases the current is plotted for the ion chamber inside and outside the guide pipe. The ratio of the two gives a measure of the attenuation due to the guide pipe.

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The phenomena of scattered gammas increasing the detector current can be observed in the traverse outside the guide tube in Figure

12. The size of the peak, however, does not match that observed.

(see Figure 5). Also, the peak is greatly reduced inside the guide tube and, therefore, there is even more difference between the observed peak in Figure 5 ' and the peak due to the shift in gamma spectrum.

The DOT calculation with the source in the water provides a measure of the ion chamber sensitivity for this configuration.

The ion chamber currents and dose rates are listed in Table 5 for several points inside and outside_19e guide tube. The ratios yield a sensitivity of 5.49 x 10 amp /R/hr inside the guide tube under the water and 14.8 x 10-13 amp /R/hr outside the guide tube in the water. Also, Table 5 indicates an attenuation factor of 0.643 on the dose rate due to the guide tube.

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6. RESULTS The QADMOD results for the M-7 traverse are tabulated in Tables 2 and 4 and are plotted in Figures 9 and 10. The total dose rate obtained using the selected source strengths is compared with the measured profile in Figure 1. The agreement is sufficiently good 4

to conclude using calculations that the only M-7 measured cesium traverse sources.

contamination can be matched with Ion chamber current measurements for the M-9 traverse are plotted in Figure 7. The current is approximately constant from 104 to about 190 inches withdrawn from the reference plane. The calculated values for the M-7 traverse should also apply to the M-9 traverse over the range of 1_og to 165 inches withdrawn.

M-9 current averages 0.022 x 10 The amp in this range. Dividing by the sensitivity value calculated by DOT in Section 5 gives a measured dose rate of 4.0 R/hr. Comparing this with the calcu-lated dose rate in Figure 1 shows that the calculated value is approximately equal to the average of the measured dose rates of about 2.5 R/hr for M-7 and 4 R/hr for M-9 in the range of 105 to 165 inches withdrawn. The measured current for the M-9 traverse increases considerably from 190 to 232 inches withdrawn.

Contamination on surfaces in the back grouted wall area would be i

expected to make the radiation level increase as the 232-inch i position is approached. The observed current is within the range that could be expected particularly if there are unpainted concrete surfaces or surfaces with damaged paint. The peak and dip in the curve could be caused by either hangers or other supports providing extra localized shielding or perhaps in some way a localized source close to the guide pipe.

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7. REFERENCES

1. R. Rainisch, TMI-2 Technical Bulletin, Gamma Scanning of the Cavity Under the Reactor Vessel, May 2, 1986; B&W Records Center No. 38-1013553-00.

- 2. Letter from W. R. Cobean, Jr. to F. R. Standerfer, "QAD

' Study, TMI-2 Under Vessel Dose Rates," January 7, 1987, with Burns & Roe calculations; B&W Records Center No. 38-1013558-00.

3. Letter from R. Rainisch to G. R. Eidam, " Analysis of the M-7 Gamma Profile in the Lower Reactor Vessel Cavity," February 3, 1987; B&W Records Center No. 38-1013554-00.

4. TMI-2 Technical Planning Department, June 1985, Data Report on Analysis of Gamma Scanning of In-Core Detector #18 (L-ll) in Lower Reactor Vessel Head. ,

t. TPO/TMI-175, Rev. O, Middletown, PA, GPU Nuclear Corporation; B&W Records Center c No. 38-1013559-00.

4

5. 32-1167934-00, "QADMOD Calculations of Dose Rate Beneath TMI-2 Reactor Vessel." ,  ;

6. TMI-2 Technical Planning Department, February 1987, Data Report on Reactor Building Radiological Characterization.

TPO/TMI-125, Rev. 1, Middletown, PA, GPU Nuclear Corporation.

See 32-1167934-00, Appendix A, for copy of pages referred to in this report.

7. GPU Nuclear Letter of June 2, 1986 from C. H. Distenfeld to G. R. Eidam, " Comparison of Measured and Calculated Exposure l Rates in Two Selected RB Basement Locations," 4550-86-0196; B&W Records Center No. 38-1013555-00.

8. Thomas E. Cox, et al., Reactor Building Basement Radionuclide i and Source Distribution Studies, GEND-INF-Oll, Vol III, June 1983; B&W Records Center No. 38-1013556-00.

9. 32-1167926-00, "ANISN and DOT Calculations of Dose Rate Beneath TMI-2 Reactor Vessel."

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, Table 1. List of OADMOD Cases Guide Case Tube No, Source Present? Detector Locations 1 Ring og wall, 242.93 No Along withdrawal pCi/cm path for M-7 2 Wall other tgan ring, No Along withdrawal 55.21 pCi/cm path for M-7 3 Insulagion,244.8 No Along withdrawal uCi/cm path for M-7 4 Insulagion,244.8 Yes Along vertical path pCi/cm 5 Insulagion,244.8 No Along vertical path pCi/cm 6 Water, 4.897 pCi/cm 3 No Along withdrawal path for M-7 7 Water, 4.897 pCi/cm3 Yes Along vertical path 8 Water, 4.897 uCi/cm No Along vertical path 9 6" length on vertigal pipe, 100.0 pCi/cm Yes Along vertical path 10 Uniform contamination Yes Along vertical path on nozgle, 111.29 uCi/cm 11 Uniform contamination Yes Along vertical path on pipg, 111.29 pCi/cm 12 4" high ring on wall No Along withdrawal just above water level path for M-7 51-1167938-00 Page 18 of 34 k

l Table 2. Calculated Dose Rate Alona M-7 withdrawal Path g.l Distance Ring Wall Insulati Water Nozzle Withdrawn, 220 pCi/m 2

50 uCi/m 2

80 pCi/m 2.16 pCi/m 3 or Pipe Total inches z'm R/hr R/hr R/hr R/hr R/hr R/hr 0 288.13 2.23 0.50 5.11 0.24 1.06 9.14 6 272.89 2.28 0.54 3.97 0.26 1.06 8.11 12 257.65 2.27 0.58 2.73 0.28 1.13 6.99 18 242.41 2.25 0.63 2.09 0.31 1.13 .6.41 24 227.17 2.19 0.67 1.66 0.34 0.28 5.14 30 211.93 2.10 0.71 1.36 0.38 0.28 4.83 36 196.76 1.99 0.75 1.14 0.42 0.28 4.58 42 181.73 1.87 0.77 0.97 0.47 0.28 4.36 48 166.96 1.74 0.79 0.84 0.53 0.28 4.18

, 54 152.54 1.62 0.79 0.73 0.60 0.28 4.02 60 138.55 1.50 0.79 0.65 0.67 0.28 3.89 66 125.09 1.39 0.77 0.58 0.75 0.28 3.77 72 112.24 1.30- 0.76 0.52 0.83 0.28 3.69 78 100.09- 1.22 0.74 0.48 0.91 ~0.28 3.63 84 88.71 1.15 0.72 0.44 0.99 0.28 3.58 90 78.17 1.08 0.70 0.40 1.07 0.28 3.53 96 68.56 1.03 0.69 0.37 1.12 0.28 3.49 102 59.91 1.04 0.71 0.37 1.49 0.00 3.61 108 52.30 0.97 0.42 0.35 2.13 0.00 3.87 114 45.76 0.72 0.25 0.28 2.28 0.00 3.53 120 40.35 0.53 0.17 0.21 2.33 0.00 3.24 126 36.09 0.40 0.14 0.16 2.40 0.00 3.10 132 33.01 0.33 0.12 0.13 2.40 0.00 2.98-138 31.14 0.29 0.13 0.11 2.40 0.00 2.93 144 30.48 0.27 0.14 0.10 2.40 0.00 2.91 3

150 30.48 0.27 0.18 0.09 2.40 0.00 2.94 156 30.48 0.26 0.21 0.09 2.40 0.00 2.96 162 30.48 0.25 0.23 0.08 2.40 0.00 2.96 f

1 20 uCi/cm in region of ring, '5 pCi/m below ring, 0 uCi/cm in water.

2 See Table 4 for addition due to localized source.

51-1167938-00 Page 19 of 34

Table 3. Attenuation in Nozzle and Guide Ploe Frm QADOD Case 4 Case 5 With Nozzle, Without Nozzle Guide Pipe Guide Pipe or Ratio Receiver and Incore Incore Case 4-to-No. Z. cm Reaion R/hr R/hr Case 5 1 288.13 Nozzle 18.7 22.7 0.82 2 272.89 No zzle 13.5 15.7 0.86 3 257.65 Guide Pipe 9.31 10.6 0.88 4 242.41 Guide Pipe 7.07 8.14 0.87 5 227.17 Guide Pipe 5.62 6.53 0.86 6 196.69 Guide Pipe 3.79 4.48 0.85 7 166.21 Guide Pipe 2.68 3.24 8

0.83 135.73 Guide Pipe 1.96 2.42 0.81 9 105.25 Guide Pipe 1.48 1.87 0.79 10 74.77 Guide Pipe 1.13 1.48 0.76 Table 4. Dose Rate From Iocalized Source on Guide Ploe Dose Rate From Distance Withdrawn 220pCi/cm Over Fr a Ref Plane, Distance Relative a 6" Iength, inches to Peak. inches R/hr l 93.99 -5.01 0.31 94.83 -4.17 0.99 l 95.66 -3.34 4.20 96.50 -2.50 9.04 97.75 -1.25 11.95 98.17 -0.83 12.10 1

98.58 -0.42 12.17 99.00 0.00 12.19 99.42 0.42 12.17 99.83 0.83 12.10 100.25 1.25 11.95 101.50 2'.50 9.04 102.34 3.34 4.20 103.17 4.17 0.99 l 104.01 5.01 0.31 1

51-1167938-00 Page 20 of 34 l

Table 5. Ion Chamber Sensitivity and Attenuation Freen DCyr Ra= Hts %de Pipe Calculated Dose Rate Calculated Current Inside outside Inside outside Guide Guide Guide ~ Guide Pipe Pipe Pipe Pipe I=1 I=17~ Attenuation I=1 I=17 g R/hr R/hr Factor amo amo 6 4.17 6.45 2.26x10 -12

~

0.647 9.26x10 7 4.30 6.69 0.643 2.37x10" 9.91x10 -12 8 4.34. 10.13x10-12

~

6.77 0.641 2.40x10 9 4.30 6.70 0.642 2.37x10" 9.95x10 -12 Avg = 0.643 sensitivity I=1 I=17 J amo/R/hr amo/R/hr 6 5.42x10-13 14.4x10-13 5.51x10-13

~

7 14.8x10 8 5.53x10 -13 15.0x10 -13

'9 5.51x10 -13 14.9x10 -13 Avg = 5.49x10 -13 14.8x10 -13 h DOT case with source in water.

51-1167938-00 Page 21 of 34

FIGURE 1. CALCULATED AND MEASURED DOSE RATE, M-7 TRAVERSE n

15 -

Calculated a Measured t} l 0 10 -

h t-s 8

8 8

~

5 - -

ea g n

U 0 "00 gogg0 0 2??

gA Air r Water

~

U$ 0 I I I i l 1 l

Ra 0 2'1 '18 72 96 120 l 'i'l 168 i W8 Detector Travel From Reference Plane, Inches 1

FIGURE 2. IN-CORE DETECTOR CROSS SECTION Inconel it

• 0.042 in. Al23 0 Insulation

, Insulation Miniature Ion Chamber Probe l Inserted Through This @@ \ 0.011 in. Zircaloy 2 Leadwire Tube 1

0.062 in.

Inconel Sheath 0.093 in.

_0.125 _

in.

0.250 _

in.

0.292 =

in.

( Assembly Includes Seven Neutron-Sensitive Detectors, One Background Detector, and One Thermocouple) 51-1167938-00 Page 23 of 34

FIGURE 3. PRIMARY SilIELD CAVITY UNDER REACTOR VESSEL, ELEVATION VIEW (FROM FIG. 2 REF 1) i RPV LOWER 1

HEAD SHELL PRIMARY SHIELD  :

INSIDE SURFACE ELEV.-290*-11"

SUPPORT EL.=290*-5 7/16" SKIRT O REF.LINE r REFLECTIVE l'NSULATION

_~

i w 2 i ELEV.-289'-9 1/4"

' /

END OF NOZZLES- ,-

l '

{

3/4" PIPE h

SCH.160 ELEV.=288'-3" I

IN-CORE END OF BEND INSTRUMENT .

-3" GUIDE PIPES 1/2" SCH.80 (

/

GUIDE PIPE CHASE 7 www- -

mm BASEMENT

$[ WATER LEVEL

\

g@ ELEV. 283'-0" DIA.=150 IN' PlPE CENTERS og C O ELEV.=282*-0"

• T i

W8 FLOOR i ELEV.=281 *- 0" l

i I

FIGURE 4. PATil 0F IN-CORE GUIDE PIPE #13 (M-7)

(FROM FIG. 4 REF 1) i H-8 SCAPNED FROM REF. LIE (UNDER RPV) i R-87 1/4- TO PIPE CHASE, TOTAL TRAVEL 168" i

s M-7 REF. LINE ELEV. 290*-5 7/16" i 3/4" SCH.160 REFLECTIVE INSUL.

l NOZZLE ' 22.1" ._, START OF BEND ELEV. 288*-3" J

1/2" SCH. 80 ,; Ok R= 75" '!I j PIPE (52) l{

j gli.

( --

WATER LEVEL BASEt4NT ELEV. 283*-O" i e$ "

ELEV. 282*-0" i $4- *-- R -75 " HORIZONTAL PIPE RUN E$ $ j FLOOR, ELEV. 281*-D*

%y RPV

%8 CENTER LIE 1

l I

FIGURE 5. CURRENT PROFILE MEASURED AT LOCATION M-7 (FROM FIG. 5 REF 1 )

.040

iwi l m .035 O

w l

.030 \

Ym.

1 E .025

< )

(\

l E w .020 l [

e U

'015 (- \- -

\

y -. .._.. .

J_. . . _ . . /_ '

l .010 0 12 24 36 48 60 72 84 96 108120 132144156168 DETECTOR TRAVEL FROM REF. LINE (INCHES)

VERT. HORIZ.

p

: 90 DEG. BEtO :l: PIPE

=

! SY IN-AIR  : : UNDER WATER

%8 RPV CAVITY  : : PlPE CHASE l

l l

1 t

d FIGURE 6. PATil 0F IN-CORE GUIDE PIPE #16 (M-9)

(FROM FIG. 6 REF 1)

}

SCM4ED FROM JUST BELOW WATER LEVEL I

(ELEV. 283*) INTO PIPE CHASE i H-8 TOTAL TRAVEL 128"

R-87 1/4" 8.2" e M-9 l REF. LINE ELEV. 290*-5 7/16" 3/4" SCH.160 "

{ REFLECTIVE INSUL.

NOZZLE '

START OF BEND ELEV. 288'-3" m

I 1/2 SCH. 80 PIPE (52) #

g jili; WATER LEVEL M ELEV. 283'-0"

)3$

e._.g.75

_ - - ~

~( ELEV. 282*-0" HORIZONTAL PIPE RUN

\ $mb p 1

gg  ; .. . .;

m FLOOR, ELEV. 281*-0,,

\

\ $$ RW

\

• 9 CENT $R LINE

%8 l

4 e u _ _ _ _ . _ _ _ _ _ _ _ _ _ _

e FIGURE 7. (CURRENT PROFILE MEASURED AT LOCATION M-9

) (FROM FIG. 7 REF 1 )

! .20 a

.18 "'

.16 in

.14 a m .12 a . i

.10  ?

v .08 [ :-

E f y .06 .

.04

(

f

.02

"~

~

r ^ '

e>* _- e e u BACK GROUTED AREA

.00 f ( INNER FACE 232" )

80 100 120 140 160 180 200 220 240 ION CHAMBER TRAVEL FROM REF. PLANE (INCHES) n (Q l 90 DEG. BEND  :  : HOR Z.

p oS

["4 bO

-IN AIR :  : UMIER WATER RPV CAVITY :I; PIPE CHASE I

FIGURE 8. GADMOD MODEL FOR CASE 1, RING SOURCE i

Cylindrical Source 9 Intervals liigh a 10.16 1 Interval in Radius

, 30 Azimuthal Intervals a 12* = 1 91 .0 -

190.5 =

- 304.30

! bg 0 I

242.93 uct e

• l i

h Air l

=

g

! Ca2 l - + 3 _213.36 bki

)

I h Path of \

, @ Air Detector M h Air i Locations \

j Looking 54* \

West of Due South \

i s i

N - 60.%

l jf b ,

@ s~~ --

! 03 Water __ 0

! ^ o A Boundarles (1,2,3,4 P1 anes b \ Origin 5,6 Cylinders)

O Region Numbers All Dimensions in cm I

t i

i

, FIGURE 9. DOSE RATE FROM VARIOUS SOURCES, M-7 TRAVERSE

! 5 l

l

Source on Insulation i

4 _

1 l

Air  : : Water E

s

" 3 -

Source in Water j Source in Ring on Wall '.

E i o 1 8 2 -

! o l

l

, S 1

/

/ ource on Wal1 j l - Source on Nozzle f / and Guide Pipe

/ /

\ mw f /

i $7 e '

! d 0 i i i i\ i

^

- i

$$ 0 2'1 '18 72  % 120 l 'i'i 1 68 3

[1

.D. O Detector Travel From Reference Plane, Inches f

FIGURE 10. DOSE RATE FROM LOCALIZED SOURCE ON GUIDE PIPE 15 -

O 10 -

E s

S 8

8 5 -

l t

0 , I I I I 90 100 110 Detector Travel From Reference Plane, inches 51-1167938-00 Page 31 of 34

e FIGURE 11. DOT MODEL Vold Boundary 303 l Steel [_

l 7 l @ T4 289 281 (5) Insulation g

6 i

@ Air O i

i Reflected *h Boundary 1 Vold

@ 27 Boundary I

- T B o

i Il 60.96 - *-

~5- -

U 8

o b l)

D mB --

Water 15 T =

l 31 l I I I 2? ? 0.5149 Void Boundary 1 73 l 2 ,L 1.07 20ft i aE 1 R,5

@ ==> Zone n

. m 9 m Intervals Dimensions in cm i

4 FIGURE 12. DETECTOR CURRENT DUE TO INSULATION SOURCE x 10-13 x 10-12 8 11 . 0 7

3.0 Air

+--

Inside 6 -

Thimble E E g Water ^

g 5 / }- -+

f -

g -

2.0 f E / \ E b / '~~~~ ~_ $

g 'l -

/ '

g

$ / No Thimble y b 3

/ -

1.0

/

/

,, 2 - l 37

• M O]

R$ 1 1 1 I I I I I I I I I 0.0 wA

^

0 15 20 25 30 10 1 50 60 70 80 90 100 110 Distance Above Flcor, cm

1 .

FIGURE 13. DETECTOR CURRENT DUE TO SOURCE IN WATER l 2.6 1

2. '4 -

1.2 e

2.2 -

i 2.0 -

-- 1.0

! Alf m 1.8 a -

E

! 8 B 1.6 -

- 0.8 t J E 1 . 84 -

c 8

i t u 81.2 -

- 0.68 Water Inside Thimble S 1.0 -

b g , t

.

• 8

\

8 0.8 -

0.'48 0.6 -

Bare i

i -

j 0.li -

0.2 gy 0.2 -

l j *[

, 0.0 .I I l l I I I I I I I 0.0 l

"d Ou 0 15 20 25 30 f0 l 50 60 70 80 90 100 110

*? Distance Above Deck, cm 1

28 1

i