maine yankee final status survey release record fr-0400 ... · scan grids below water wvere 4m2....

MAINE YANKEEFINAL STATUS SURVEY RELEASE RECORD

FR-0400 FOREBAYSURVEY UNIT 7

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MAINE YANKEEFINAL STATUS SURVEY RELEASE RECORD

FR-0400 FOREBAYSURVEY UNIT 7

A. SURVEY UNIT DESCRIPTION

Survey Unit 7 is located within Survey Area FR-0400, the Forebay. The Forebay is locatedsouth of the radiologically Restricted Area of the site at coordinates 407,000 N and 623,600 E(see map FR 0400 SITE, Attachment 1). The Forebay is a large, rock-lined basin in whichcondenser cooling water collected prior to its release through the diffuser system out to theocean. During plant operation the Forebay/Diffuser System was the licensed discharge pathfor liquid, radiological effluent. After plant shutdown, stop logs were set in place at theForebay end of the diffuser to isolate the Forebay in order to prevent the release of Forebaysediment into the river during remediation activities.

Two earthen dikes make up the north-south running walls of the Forebay with concrete wallsat the extreme north and south ends to support the circulating water and diffuser pipes. Thedike walls form a V at the southern end of the Forebay (adjacent to Foxbird Island). Thediffuser discharge pipes originate at the notch of the V. A concrete dam, or weir, runs in theeast west direction at the northern end of the Forebay and creates a small, water-filled areacalled the sealpit. The sealpit maintained a water seal over the circulating water pipes toprevent loss of flow with tidal fluctuations.

Survey Unit 7 consists of the interior of the wvest dike of the Forebay. This is inclusive of arip-rap layer, sediment and ledge. The area is bounded on its southern extent by thedischarge canal, and by the weir to the north. The area includes both above water andsubmerged portions from the top to the bottom (toe) of the slope. The Survey Unit has a totalsurface area of approximately 1,550 m2.

B. SURVEY UNIT DESIGN INFORMATION

The Forebay received the liquid radioactive discharges from the plant. It was known to havebeen contaminated to levels in excess of the release limits and extensive remediationactivities including underwater dredging, underwater vacuuming, and dry surface vacuumingwere performed. Given the high probability of residual contamination, the Forebay wasclassified as Class 1.

Revision 3 of the Maine Yankee License Termination Plan (LTP)l states that the Forebaydose from residual radioactivity "is so insignificant and the probability so low that anindividual would be able to successfully place a viable well within the Forebay, surveymeasurements of the Forebay surfaces including rip-rap will be limited". As a result, thesurvey design for the Forebay is a reasonable approach to demonstrate compliance with therelease criteria while not necessarily meeting all of the requirements for a "MARSSIM"survey.

LTP, Revision 3 refers to the LTP submitted in October 2002 (Reference I) as amended by the MY's addendaof November 2002 (Reference 2). LTP, Revision 3 was approved by the NRC in February 2003 (Reference 3).

FR-0400-07, Revision 0 of 26

The survey unit design parameters are shown in Table 1. The values shown in this tablereflect those used for the design and implementation of the survey'. Changes to several keyparameters (i.e., DCGL and AF) occurred after the survey was complete. These changeswere used to evaluate the data, are discussed in Sections G and 1-1. and shown in Table 2-2.

Given a relative shift of 1.6, a minimum number of 17 direct samples were required per theSign Test. The survey design was based on 20 samples. Twventy-one actually fell within thesurvey unit. Each sample measurement location was determined using a random start pointand a square grid. These locations are presented on survey maps FR 0400-7, FR 0400-07e,and FR 0400-07f (Attachment 1). Direct measurements located above the waterlineconsisted of soil samples analyzed with laboratory gamma spectroscopy instrumentation.Measurements located below the water were obtained with in situ gamma spectroscopy(ISOCS).

In situ gamma spectroscopy was used to conduct a 100% scan of the area. The survey unitdesign used the ISOCS portable high purity germanium detector system to perform bothunderwater and above water scans. Scan grids below water wvere 4m2 . Scan grids abovewater and below the "bath tub ring" were 12m2 . Grids above the "bath tub ring" were 28 i 2 .The "bath tub ring" was the area of high water in the Forebay during plant operation. TheISOCS detector was positioned with the aid of a prefabricated track and trolley system formeasurements below water. Above water measurements were located utilizing a pre-established grid system. This scan survey ensured there were no unevaluated areasexceeding the DCGLEMC limit. The survey instruments used, their MDC values, andinvestigation levels are provided in Attachment 2.

TABLE 1

SURVEY UNIT DESIGN PARAMETERS

[ Survey Unit Design Criteria Basis

Area 1,550 miBased on an LBGR of 3.5 pCi/g

Number of Direct 17 20 d Co-60, a sigma2 of 2.18 pCi/gMeasurements Required ( used) Co-60, and a relative shift of 1.6.

Type I = Type II = 0.05Sample Area 77.5 MIn 1,550 rn' / 20 samplesSample Grid Spacings 8.5 m, (77.5)-Area Factor (AF) 10Scan Survey Area 1,550 m' 100%Background N/A In Situ gamma spec usedScan Investigation Level See Table 2-2 Less than DCGLENIC

DCGL 7.0 pCilg Co-60 Forebay Technical BasisDocument (Reference 4)

DCGLENIC 70 pCi/g Co-60 Area Factor x DCGL

2 Sigma was determined using post remediation survey results.3 Sample spacing of 8.5 was used in the final design. This is conservative and generated 21 direct points when

the grid was laid out on the SU map.


C. SURVEY RESULTS

As designed, 21 direct measurements were obtained. Thirteen measurements consisted ofsoil samples. Eight measurements were obtained in silve with the ISOCS detector. The directmeasurement data are presented in Table 2 belowv. One of the direct points was above theDCGL. This measurement (S002) was investigated as discussed in Section D.

The scan process was performed in accordance with FSS requirements using in sitir gammaspectroscopy. To achieve approximately 100% scan coverage, 221 ISOCS measurementswere obtained. One of the measurements exceeded the investigation level (i.e., > unitizedDCGL). This measurement was evaluated as discussed in Section D.

TABLE 2

DIRECT MEASUREMENTS

1Cs-137 Co-60 Unitized Value ofSample Number (pCig (Pci_____________ Unity Rl

FRO40007 I SO001 SS 1 .38E-01 + 2.43E-02 < 3.96E-02 I1.82E-03FRO40007I S002SS 3.25E+00 2.45E-01 5.89E+01 ± 2.45E+00 1.25E+00FRO4oo67ISOO3SS__ 6.71 E-01 5 .51 E-02 9._73E_+f0h ±3.43E-01 1.8913-0 IFR04OOO7 1S004SS5 4.19E-02:h 1-.79E-02 9E02 .051-03FR040007 1 SOO5S 2.29E-01~ 2.94E-02 :h6+0 1.21 E-0OI 6.1 2E-02FRO40007 I S006SS 1 .50E-01 + 2.57E-02 < 4.17 E-02 I 1.9513-03F R 040 0 07 ISUPO7SS 3.46E-01 4i 5.OOE-02 3.81E+00±~ 1.80E-01 8.18E-02FRO40007ISOO8SS- 2.69E-01 3.30E-02 6.111E-O1 ± 4.06-02 1.48E-02FR04OOO7 I SO9SS_ 2.47E-01 4.17E-02 I1.16E+00 + 7.21E-02 2.5913-021FR0400071ISO lOSS 3.36E-01 4.67E-02 1.61 E+0O + 8.65E-02 3.39E-_072FR0400071 so0II SS 2.20E-01 ~2.66E.02 1.22E-01 + 1.81E-02 4.12&E-03FRO40007 ISO I2SS 4.08E-02 1.80E-02 <33E0 .OOE-03FRO400071SO13SS < MDA 1.70E-O1 :1 2.38E-02 3.54 -03FRO400071RO14IG < MDA 1.88E+00 + 9.58E-01 3.92E-02FRO400071RO15IG < MDA 4.69E+00 + 1.25E+00 9.77E-02TFRO40007IRO16IG- < MDA 7.03E+00 :L 1.90E+00 1.46 -01F R04 0 0 07 I-RD -7-1G < MDA 1.91E+00 + 8.01E-01 3.9713-02FRO400071RO1I 8G <MA< 4.96E-t00 1 .0313-01FRO4 00071 RO19I G < MDA 9.27E+0O0± 1.91 E+0O I1.9313-0IFRO400071RO20IG < MDA <386E-6 I 8.04E-03-FR040007TRU02 hG- < MDA 2.63E+00 ! 8.41E-0O1 5.47E-02

Mean 2.83E-01 5.28E+00 1.12E-01Media15n ~4.1 9E-02 1 .88E+00 3.92 -02

Standard Deviation 7.01E-01 1 1.26E+01 2.68E-~1~Range O.OOE+00 - 3.25E+00 339E-02 - 5.89E+01 L.OOE-03 - 1.25E+00

NOTES1. All values in bold are positive detection values.2. "<" indicates MDA value for non-detect Co-60 results.3. "< MDA" indicates non-detect for Cs-137 results. Refer to Section E for additional

discussion.4. The unitized values were adjusted to account for the contamination depth used in the

excavation scenario (60 cm). Refer to Section E for additional discussion.


D. SURVEY UNIT INVESTIGATIONS PERFORMED AND RESULTS

The scan grid measurement exceeding the investigation level was evaluated to assesscompliance with the DCGLEMC unity rule criteria. This wvas done in conjunction with thedirect measurement which exceeded the DCGL. The evaluation is presented in theInvestigation Table (Attachment 3). The survey unit passed the EMC test at 32% EMCunity.

Following activity adjustment as discussed in Section E, one of the direct points in SurveyUnit 7 was above the DCGL of 12.01 pCi/g (S002 was 58.9 pCi/g). The average of the 21direct measurements wvas 5.3 pCi/g Co-60 and the survey unit passed the Sign Test usingunitized values to include the Cs-137. The one location exceeding the DCGL was evaluatedusing the EMC test.

The sample result for S002 was more than three standard deviations above the mean valuefor the survey unit direct measurements. The sample was collected from three adjacent,small sediment deposits within an area of approximately 2 feet square. S002 is considered tobe an outlier. Based on that determination, an investigation was developed for S002. Thesample location was subjected to a long in silz count using a survey area geometry of a I mby 8m rectangle 15 cm thick with gravel placed under rip-rap. The in sitll count result gave avalue of 31 pCi/g. The Area Factor for 8 m2 is 2.8. Re-evaluating the EMC test with an areafactor of 2.8 for sample S002 results in a satisfactory result for the unity calculation.

The conclusion is that Sample S002 was an outlier of small size which, when evaluated withits area factor, meets the EMC unity criteria.

E. SURVEY UNIT DATA ASSESSMENT RESULTS

The Forebay dike soil DCGL was developed assuming that a 2-foot (24") band of soilcontamination at the DCGL exists underneath the rip-rap in the Forebay dikes. This 2-footassumption was arbitrarily made based upon a minimum amount of data. In order todetermine the actual extent of contamination within this band of soil, Maine Yankeeperformed extensive characterization using samples obtained from incline core bores beneaththe rip-rap, as close to the rip-rap as possible. Overall, the Forebay dike soil coringcampaign showed that the radiological contamination had not penetrated into the Forebaydikes beyond the rip-rap to any substantial depth (likely less than several inches).

ISOCS measurements of the Forebay dike soil through the rip-rap wvere geometricallyconfigured such that the entire photon spectra was attributed to a contaminated soil band of 6inches. Thus, this activity, attributed to a 6-inch band, should be divided by a factor of four.in order to appropriately compare the results to a DCGL which was developed assuming a24-inch band of contaminated soil. This adjustment, also applicable to ISOCS measurementsabove the rip-rap and soil samples obtained at depths of 0" to 6", is justified since theForebay dike core boring campaign demonstrated that the contamination had not penetratedinto the Forebay dike beyond the rip-rap to any significant extent. Therefore, the results forFR-0400 Survey Unit 7 were evaluated as discussed above.


An analysis of the direct sample measurement results, including the mean, median, standarddeviation, and sample result range are provided in Table 2. Positively detected values arebolded in the table. Since Co-60 is the primary radionuclide of concern, non-detect valueswere assumed to be present at the MDA. Non-detect values for Cs-I 37 were assumed not bepresent.

The sampling results yielded eight measurements with both Co-60 and Cs-1 37, fourmeasurements with only Cs-137, seven measurements with only Co-60, and two sampleswith no plant-derived activity. The right hand column in Table 2 is the DCGL unity column.The survey unit mean value in this column indicates that the direct measurements were at11.2% of the DCGL limit. One direct measurement exceeded the unitized DCGL byapproximately 25%. This location (S002) was investigated and found to be acceptable.

The sigma for the direct measurements was also evaluated. If the sigma is calculated withoutthe sample outlier (S002), the result is 2.9 pCi/g as compared to a design sigma of 2.2 pCi/g.Using the new standard deviation and revised Co-60 DCGL, the revised relative shift wouldbe 2.0 verses a design value of 1.6. Therefore, the increase has no impact on the surveydesign and a sufficient number of samples were obtained.

One scan (ISOCS) location and one direct measurement were investigated/evaluated, asshown in Attachment 3, and determined to be less than 32% of the Elevated MeasurementComparison unity limit, thereby satisfying the EMC criterion.

For illustrative purposes, as indicated in LTP Section 5.9.3, a simplified general retrospectivedose estimate can be calculated from the average residual contamination level. Bysubtracting the established, mean fallout Cs-137 background value of 0.19 pCi/g (Reference5) for distributed soil from the survey unit mean (0.28/4 = 0.07 pCi/g) yields a negative valuewhich is equivalent to 0.0 mrem/y. Since there is no background value for Co-60, the annualdose contribution from this radionuclide is 1.0 mrem/y (= 5.28 pCi/g /4 x 1 /12 pCi/g x 9mrem/y). However, for the purposes of demonstrating compliance with the radiologicalcriteria for license termination and the enhanced State criteria, background activity is notsubtracted from the sample analysis activity values.


F. ADDITIONAL DATA EVALUATION

Attachment 4 provides additional data evaluation associated with this Survey Unit, includingrelevant statistical information. Based on survey unit direct measurement data, thisattachment provides the Sign Test Summary, Quantile Plot, Histogram, and RetrospectivePower Curve.

1. The Sign Test Summary provides an overall summary of design input (Table I) andresulting calculated values used to determine the required number (N) of directmeasurements (per LTP Section 5.4.2). The Sign Test Summary is a separate statisticalanalysis that also calculates the mean, median, and standard deviation of the directmeasurements.

The critical value and the result of the Sign Test are provided in the Sign Test Summarytable, as well as a listing of the key release criteria. As shown in the table, severalattributes required further evaluation. As discussed in Section E the subject releasecriteria have been satisfied.

2. The Quantile Plot was generated from direct measurement data listed in Table 2. Thedata set and plot are consistent with expectations for a Class I survey unit. All but one ofthe measurements are below the DCGL of 12.01 pCi/g Co-60 and 34.76 pCi/g Cs-137.

3. A Histogram Plot was also developed based on the direct measurement values. -This plotshows that the direct data were essentially a skewed distribution with one outlier,

4. A Retrospective Power Curve was constructed, based on FSS results. The curve showsthat this survey unit having a mean residual activity at a fraction of the DCGL has anadequate probability ("power") of meeting the release criteria. Thus, it can be concludedthat the direct measurement data support rejection of the null hypothesis, providingconfidence that the survey unit satisfied the release criteria and that the data qualityobjectives were met.

G. CHANGES IN INITIAL SURVEY UNIT ASSUMPTIONS ON TIHE EXTENT OFRESIDUAL ACTIVITY

The dose model originally assumed 24 inches of contaminated soil behind the rip-rap on thedike walls. Based on data from the core boring campaign, the depth was 2 inches or less.The ISOCS values were divided by a factor of four to adjust depth to 6 inches. In addition,the entire 10 mrem/y was assumed because there wvere no other contributing sources.


11. LTP CHANGES SUBSEQUENT TO SURVEY UNIT FSS

The FSS of Survey Unit 7 was designed and performed using the criteria of the approvedForebay Technical Basis Document (Reference 4) and LTP Revision 3 Addenda (ReferenceI and 2). Subsequent LTP changes have been evaluated and have no impact on the design,conduct, or assessment of the final status survey of this Survey Unit. However, during finaldata evaluation, Survey Unit 7 had issues related to the EMC unity rule criteria. As a resultthe Forebay soil excavation scenario was modified to increase the Forebay soil DCGL to avalue which was equivalent to the entire 10 mrem/y (9 actually used) limit allowed for soiloutside the RA. This change raised the DCGLs for Co-60, Cs-137, and Sb-125 to 12.01,34.76, and 69.52 pCi/g, respectively. These changes are documented in Reference 6.

1. CONCLUSION

The FSS of this survey unit was designed based on the LTP designation as a Class I area.The survey design parameters are presented in Table 1. The required number of directmeasurements was determined for the Sign Test in accordance with the LTP. The directmeasurement results pass the Sign Test.

A Sign Test Summary analysis demonstrated that the Sign Test criteria were satisfied. Thesample standard deviation is larger than the design sigma, however, no additionalmeasurements were required.

The Retrospective Power Curve shown in Attachment 4 confirmed that-sufficient sampleswvere taken to support rejection of the null hypothesis, providing high confidence that thesurvey unit satisfied the release criteria and the data quality objectives were met. Attachment4 also revealed that direct measurement data represented a skewed distribution with oneoutlier, with variance consistent with expectations for a Class 1 survey unit.

The scan survey design for this survey unit was developed in accordance with the ForebayTechnical Basis Document with significant aspects of the design discussed in Section B andTable 1. Scanning resulted in one verified alarm. Attachment 3 shows the elevated areasidentified and provides the results of the investigation actions. The areas under investigationwere evaluated using the appropriate area factor. Elevated measurements were evaluated anddetermined to satisfy the elevated measurement comparison unity rule per LTP methodology.

It is concluded that FRO400 Survey Unit 7 meets the release criteria of IOCFR20.1402 andthe State of Maine enhanced criteria.


J. REFERENCES

1. Maine Yankee License Termination Plan, Revision 3, October 15, 2002

2. Maine Yankee letter to the NRC, MN-02-061, dated November 26, 2002

3. NRC letter to Maine Yankee, dated February 28, 2003

4. Maine Yankee letter to the NRC, MN-03-05 1, "Forebay Technical Basis Document,"dated September 3, 2003

5. Approach for Dealing with Background Radioactivity for Maine Yankee Final StatusSurveys, Attachment E to Maine Yankee Procedure PMP 6.7.8, FSS Data Processing andReporting

6. Maine Yankee Calculation EC-041-01, Diffuser and Forebay Dose Assessment

7. Maine Yankee Calculation EC-003-04, Use of Canberra In Situ Object Counting System(ISOCS) for FSS Surveys

FR-0400 07, Revision 0Page9of26

Attachment I

Survey Unit Maps


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Attachment 2

Survey Unit Instrumentation


TABLE 2-1

INSTRUMENT INFORMATION

ISOCS Detcctors (Field Measurements)

I Detector Number I MDC (pCi/g)7605 See Table 2-27607 | See Table 2-2

HPGce Detectors (Laborary Analysis)

I Detector Number I MDC (pCilg)IlSS-l -0.151FSS-2 -0.15

TABLE 2-2

INSTRUMENT SCAN MDC, DCGL,INVESTIGATION LEVEL, AND DESIGN DCGLEAIC

| Detector I ISOCS I Comments

Scan MDC MDC < 70 pCi/g Co-60 Note I

DCGL 12.0 pCi/g Co-60 Reference 5____________________ 3 34.76 pCi/g Cs- 3 7Rernc5

Investigation Level DCGL < DCGLENIC-DCGLx 1.4 (1.4 is the

Design DCGLENIc 48.7 pCi/g Cs-o 37 actual AF for surface48.7p~ig Cs137 soil, LTP Table 6-12)

NOTE 1: The effective activity for non-detect Co-60 is 25% of the reported MDC as discussedin Section E.

FR-0400-07, Revision 0of26

Attachment 3

Investigation Table


TABLE 3-1

INVESTIGATION RESULTS

Gid | Co-60 Cs-137 (pCilg) (pCl/g) | Area m1 AFGrd(pCilg) (Pcilg) Minus Minus A c 2 Comparison

= | SU Mean SU Mean Fraction

S002 3.09E+01 + 12.38% < MDA 2.83E+01 N/A 8.OOE+00 | 2.8 < DCGL

171 5.47E+01 + 6.71% < MDA 5.21 E+OI N/A 4.00E+00 4.1 2.65E-0 1

Survey Unit Mean 5.52E-02

1 Total 3.20E-01

* FR-0400.07, Revision 0 of 26

Attachment 4

Statistical Data


Survey Package FR-0400 Unit 7 UNITY Soil Sign Test Summary

Hi E onal6 npiutValuesj , ' i- .~;~ 'a t~ - oI-

Survey Package: FR-0400 Forebay

Survey Unit: 07

Evaluator: GPDCGL.: 1.OOE+00

DCGL,.: 1.OOE+01

LBGR: 5.00E-01

Sigma: 1.82E-01 Unitized

Type I error: 0.05

Type II error: 0.05

Nuclide: UNITY

Soil Type: N/A

Z * , 1.645Z-rP- 1.645

Sign p: 0.99379

Calculated Relative Shift: 2.7

Relative Shift Used: 2.7 Uses 3.0 if Relative Shift is >3

N-Value: 12

N-Value+20%: 1 5i ' Sample DataValues -. i ;Corient At '1'' ;I':4t

Number of Samples: 21

Median: 3.92E-02

Mean: 1.122E-01

Net Sample Standard Deviation: 2.68E-01

Total Standard Deviation: 2.68E-01 SRSS

Maximum: 1.25E400

Adjusted N Value: 21

S+ Value: 20

Critical Value: 14

Sign test results: - Pass

1 ;1.'':.-..i;-,f'~teaSat'f&cj-v jm is'r i$17&mt ,,,@.

Sufficient samples collected: ! : PassMaximum value <DCGLw: Investigate See sections D & E of Release Record

Median value <DCGL,: Pass

Mean value <DCGL,: Pass

Maximum value <DCGLc,: Pass

Total Standard Deviation <=Sigma: ' lnvestigate See section E of Release Record

Criteria comparison results: ...-. Investigate See section I of Release Record

s- SW a t-tt -- .F~l S;4.A,sOtS It al;.

The survey unit passes all conditions: | :- i:investigate The SU passes.

FR-0400-SWJ-SoiISign-UNITY 12114/04 1:10 PM


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Page/Date/TimeDatabaseVariable

One-Sample T-Test Report2 12/14/04 12:57:32 PMC:\Program Files\NCSS97\FR0400SU-7.S0C2

Plots Section

Histogram of FR-0400, SU-725.

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EM

.0E

19-

13-

6-

-1-11 i,

0.o00 0.350 0.700 1.050 i.400Activity (unitized)


One-Sample T-Test Power AnalysisPage/Date/Time 2 12/14/04 1:01:43 PM

Chart Section

L_.a)~

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1.0 .

0.8

0.6

0.4

0.2

0.0 _0.1

Retrospective Power Curve

. .- . .

l

0.3 0.5 0.7

Survey Unit Mean (unitized)0.9 1.1


maine yankee final status survey release record fr-0400 ... · scan grids below water wvere 4m2....

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