ML20210H609

Special Rept:On 970717,determined Ongoing or Recent Contamination Event Could Be Source of Detected Environ Radioactivity.Collection,Analysis & Review of Results of Addl Grab Samples from North Storm Drain Outfall

ML20210H609
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	08/08/1997
From:	Wanczyk R VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-97-101, NUDOCS 9708140124
Download: ML20210H609 (5)

Text

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.. , i L.. MERMONTJYANKEE:

NUCLEARLPOwER C. ORPORATIONi 9 Ferry Road, Brattleboro, VT 05301 7002 ENGINEERING OFFICE -

580 MAIN STREET

• BoLToN. MA 01740

• '(508) 779-6711 August 8,1997 BVY 97101

- United States Nuclear Regulatory Commission ,

i ATTN: Document Control Desk Washington, D.C. : 20555 4

i

Reference:

' ' License No.- DPR 28 (Docket No. 50 271)

SUSJECT: Special Report - Radiological Environmental Sample Concentration Exceeda Reporting Level This special report is being provided in accordance with Vermont Yankee Technical Specification Section 6,7,C.2.d,~ Radiological Environmental Monitoring. Tnts report documents the occurrence of one environments.1 sample taken from Connecticut River sediment near a storm drain outfall,

, which exceeded the reporting levels specified in Table 3.9.4 of Technical Specifications. The most .

l likely source is the Turbine Building Ventilation configuration in use prior to October 1993. The 4 concentration of Cobalt-60 which requires this report does not represent a hazard to the public or the aquatic environment, in fact, the concentration of Cobalt-60 was less than the naturall/

occurring radioactivo elements in the sediment. ,

HISTORY in 1983, Vermont Yankee discovered plant related Co-60 in the outfall area of the North Storm Drain, in the Plant information Report 83-06 (Licensee Event Report 83-23/34, Vermont Yankee -

personnel concluded that low-level airborne discharges from the Turbine Building Roof Vents, which are located on the west side of the roof, could occur as a result of the original building ventilation design. The roof drains on the west side of the building drain to the North Storm Drain system. Ultimately, rain transported any cumulative particulate actMty to the turbine build!ng roof drains. In this manner, e >ortion of the particulate activity released from the Turbine Building Roof Vents could be eventually deposited in the North Storm Drain outfall area via the North Storm Drain 4

. system. As a result of this LER, Vermont Yankee initiated semiannual sampling of the North Storm

- Drain outfall which has continued to date.-

in January of 1987 Vermont Yankee added a Reporting Level for Co-60 in Individual grab samples

. taken of the North Storm Drain outfall to T. S. Table 3.9.4 with Proposed Change 131. In October, [

1993, the direct discharge from the Turbine Building Roof Vents was eliminated as a potential- /

release pathway .

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,:..= U.S. Nuclear Regulatory Commission VERMONT YANKEE NUCLEAR POWER CORPORATION I August 8,- 1997 Page 2 of 4 DESCRIPTION OF SAMPLING /ANALYe*G Grab samples of river sediment were collected at the North Storm Drain outfall on 5/12/97 as part of the regularly scheduled Radiological Erwironmental Monitoring Program (REMP) as described in Vermont Yankee Technical Specifications Table 3.9.3. and ODCM Table 4.1. The sampling area of the North Storm Drain outfall is dMded into a grid of 40 locations, each with a specific combined letter and number identifier (See Figure 1). Normandeau Associates, Inc., the contractor that collects aquatic-based REMP samples for Vermont Yankee, collected a total of 26 samples from the grid area. The final result of one of the samples collected at location U 3, approximately 40 foot out from the shoreline and 20 feet downstream of the outfall pipe, Indicates that it contained a small discrete panicle (s) of Co-60 equal to 3,820 pCI. The weight of the dried original sample of river sediment is 472.1 grams. The resulting sample concentration is calculated to be 8,092 pCl/Kg which exceeds the reporting Level requirements (3,000 pCl/Kg of Co-60) of Technical Specifications Table 3.9.4. - The other 25 grab samples collected had no detectable Co 60.

ADDITIONAL SAMPLING / ANALYSIS in response to the detected Co-60 particle in one of the 26 grab samples taken from the river sediment on 5/12/97, an in situ gamma Isotopic survey of selected site areas was performed on 7/17/97 to determine if an ongoing or recent contamination event could be the source of the detected environmental rt,dioactMty. Measurements were made of certain manholes and these were supplemented by grab samples for increased sensitMty (in progress). One in situ measurement was done six feet from the end of the North Storm Drain pipe. Two sediment samples were also collected, one from just inside the pipe outfall and the other in the same location as the in situ measurement on the river bank. The results of these measurements and the Minimum Detectable ActMty (MDA) are as follows:

Samole Description Co-60 oCl/Ka MDA oCl/Ka in situ measurement 1.22 E + 01 (*) 1.47 E + 01 6 ft from pipe (river bank)

Grab sample from inside pipe 3.92 E + 00 3.0 E + 00 Grab sample 6 ft from pipe 9.4 E + 00 7.3 E + 00 (river banlQ The in situ measurement (*) Indicated a possible Co-60 concentration near but below the detection capability of the system (see MDA above). Consequently, grab samples from the area of the in situ measurement along the river bank were taken and analyzed to special low level detection sensitMties, ~At these low detection sensitMtles, positive Co-60 was also detected. However, the

- values seen represent only about 0.3% of the required Co-60 Reporting Levelin river sediment.

Typical detection sensitMties for Co-60 are around 100 pCl/Kg. These special sample results rep esent less than 10% of tha normal minimum detetton level. This detected actMty is consistent witti the assessment that the North Storm Drain was the pathway for the release of the Cobalt det mted in the sediment sample.

In inddition, Radiation Protection (RP) Department personnel conducted a survey of the Turbine Building Roof on 7/24/97. The result of each of the 21 smears was <1000 dpm/t00cm2. A gamma lootopic analysis of all the smears Indicated no identlfled nuelldes.

'~

, ..- - U.S. Nuclear Regulatory Commission VERMONT YANKEE NUCLEAR POWER CORPORATION August 8,.1997 Page 3 of 4 -

Normandeau Associates, Inc. has subsequently collected (on 7/25/97) additional samples from 13 locations in the grid, one from the location where the particle was found and 12 from surrounding locations.- These samples are currently being analyzed at the Yankee Erwironmental Laboratory.

During the most recent radiation Site Specific Survey, which was completed in the fall of 1996, no actMty was detected on the ground in areas outside of buildings located in the Protected Area that could contribute to contamination found in the North Storm Drain system. Additionally, weekly RP surveys of the North Warehouse, which is adjacent to several of the storm drains in the North Storm Drain system, have not detected any actMty in many years.

The Vermont Public Health Laboratory is given split samples of every sample that is gathered as '(

part of the somlannual North Storm Drain outfall collection. The sample collected et location U 3, as well as the other 25 samples sent to the State Laboratory, did not indicate the presence of Co-

60. The State's sample from location U 3 is now being analyzed at the Yankee Environmental Laboratory.  ;

SOURCE OF ACTIVITY Our investigation to date Indicates that the likely source of the Co-60 found in the North Storm Drain outfall is from Turbine Building effluent releases prior to October 1993. The general downward trend in the percentage of positive samples and mean actMty support this conclusion.

The lack of detectable radioactMty in the weekly North Warehouse surveys, the annual radiation

• Site Specific Survey, and the recent Turbine Building roof survey confirm that there is no current source for transport to the North Storm Drain outfall. The lack of identified shorter lived isotopes in the sediment samples also supports the assertion that the source is not the result of an active or recent event.

As a conservative bounding assessment of the dose impact related to the detected Cobalt actMty in sediments, the Regulatory Guide 1.109 dose models for a river shoreline can be applied.

Conservatively assuming that the Co-60 actMty (8092 pCl/Kg) is uniformly spread over the entire shoreline, along with a shore width factor of 0.2 (R.G.1.109, Table A-2), the dose rate to the whole body would be 0.0011 rc. rem /hr. This would be equal to an accumulated annual dose of 0.07 mrom to the maximum hypothetical indMdual assumed to stand at this point for 67 hours7.75463e-4 days <br />0.0186 hours <br />1.107804e-4 weeks <br />2.54935e-5 months <br /> /yr per R.G.1.109, Table E 5. This bound'nj assessment is well below the annual dose objective of 10CFR50, Appendix 1 of three mrom to the whole body.

Since the detected radioactMty is actually a discrete particle, a more realistic dose impact can be assessed by assuming that a point source of 3820 pCl of Co-60 is located on the surface plane of the river sediment (no sediment or water attenuation). The exposure rate at a height of 1 meter above this point would be about 0.000005 mR/hr. If the same occupancy time is applied as above, the accumulated dose to the maximum Individual would be about 0.00034 mrom if this same IndMdual were able to stand over this point for 67 hours7.75463e-4 days <br />0.0186 hours <br />1.107804e-4 weeks <br />2.54935e-5 months <br /> in a year (no decay or energy correction for exposure to tissue vs. air taken). This is far below the three mrem annual dose objective of Appendix I and represents no significant radiological hazard to the public.

CORRECTIVE ACTIONS

1) ' Collection, analysis and review of results of additional grab samples from the North Storm Drain Outfall, another downstream area of the river, and manholes in the North Storm Drain system.

j ,

VERMONT YANKEE NUCLEAR POWER CORPORATION U.S'. Nuclear Regulatory Commission

. August 8,1997 Page 4 of 4 -

2) Evaluation of the North Storm Drain outfall and the riverbank area between the end of the North Storm Drain pipe and the river for inclusion in the file for compilance with 10CFR50.75(@.

This work la expected to be complete by the end of 1997, We trust the information provided in this report is satisfactory, however, should you desire

- additional Information, please contact this office.

' Sincerely, V ONT YANKEE NUCLEAR POWER CORPORATION Robert J. W Director of Safety and Regulatory Affairs

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USNRC Region 1 Administrator USNRC Resident inspector WNPS USNRC Project Manager WNPS 4

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