ML051650291
| ML051650291 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 06/06/2005 |
| From: | Jesse Rollins Yankee Atomic Electric Co |
| To: | Document Control Desk, NRC/FSME |
| References | |
| +KBR1SISP20050727, BYR 2005-037 | |
| Download: ML051650291 (12) | |
Text
YANKEE ATOMIC ELECTRIC COMPANY Telephone (413) 424-5261
~ANKEE 49 Yankee Road, Rowe, Massachusetts 01367 June 6, 2005 BYR 2005-037 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D C 20555
Reference:
Subject:
License No. DPR-3 (Docket 50-29)
Request for Approval of Proposed Procedures in Accordance with 10 CFR 20.2002 Yankee Atomic Electric Company (YAEC) herewith requests NRC approval of the proposed continued use of concrete blocks used as retaining walls containing very low concentrations of tritium at an off-site location in accordance with the provisions of 10 CFR 20.2002.
A description of the retaining walls that contain licensed material (tritium) is provided in. This description includes the radiological and physical properties important to risk evaluation to allowing the shield blocks to remain in place. In addition, YAEC has performed a radiological assessment of the shield blocks and determined that there is essentially no potential dose to members of the public from allowing the shield blocks to remain in place.
Should you have any questions regarding this submittal, please contact the undersigned at (413)-424-2300.
Sincerely, YANKEE ATOMIC ELECTRIC COMPANY Jack D. Rollins Regulatory Affairs Manager Attachments:
(1) Description of Retaining Wall Constructed from Reactor Support Structure Shield Blocks Containing Tritium (2) Pictures of the Retaining Wall VA Loao SS D
Document Control Desk BYR 2005-037 / Page 2 cc:
S. Collins, NRC Region 1 Administrator J. Hickman, NRC Project Manager, NMSS M. Miller, Chief, Decommissioning and Laboratory Branch, NRC Region 1 D. Howland, MADEP R. Walker, Director, MADPH C. White, Radiological Health Specialist, VT Dept. of Health 2
Docket No. 50-29 BYR 2005-037 Yankee Nuclear Power Station Description of Retaining Wall Constructed from Concrete Shield Blocks Containing Tritium
Yankee Nuclear Power Station Description of Retaining Wall Constructed from Concrete Shield Blocks Containing Tritium
1.0 INTRODUCTION
During 1999, concrete shield blocks from within the reactor support structure (RSS) which had been removed, sand blasted, and surveyed were released from radiological controls. Forty (40) of the shield blocks from the steam generator cubicles were removed from site under an approved MADEP Beneficial Use Determination (BUD) and used to construct a retaining wall on private property in Vermont. The remainder of the blocks were used for various purposes, both inside and outside of the industrial area of Yankee Rowe site.
At the time of the shield block release, analyses of the tritium content of concrete within the reactor support structure indicated values less than the minimum detectable activity.
Based on these results and surface contamination surveys, the shield blocks were determined to be free of detectable licensed radioactive material. However, the tritium analyses were performed to the specified levels for 10 CFR part 61 waste classification requirements (indicated lower limits of detection (LLD) of less than 1,000 - 2,000 pCi per gram).
In 2004, as part of preparation for demolition and plans to retain RSS concrete on-site, further volumetric sampling and analysis of radionuclides was performed. Due to the Derived Concentration Guideline Level for tritium, a lower limit of detection of 10 pCi/gm was requested for the additional volumetric sampling. An unexpected finding of this analysis was the presence of tritium in essentially all concrete within the RSS.
Levels of tritium from samples taken in proximity to where the steam generator shield blocks were located indicated tritium levels averaging approximately 200 pCi per gram.
Due to the presence of the low levels of tritium (licensed material) in the concrete shield blocks and the inherent dangers in removal of the retaining wall, a specific exemption to allow the shield blocks to remain in place is being requested.
2.0 Wall Description The retaining wall was built by the property owner atop a previous poured concrete retaining wall approximately 8 feet high along a stream. It consists of 35 interlocking blocks stacked 2 high with a nominal length of 250 feet. Gravel and soil has been back filled to the top of the additional height added by the block wall. To preclude a fall hazard, the property owner has added a chain link fence along the top of the wall. Thus the majority of the surface areas of the blocks (to all but a small 1.5' wide strip at the top) in the wall are inaccessible.
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Five (5) other blocks were used for general retaining walls, two at the extreme far end of the retaining wall, two on one side of the property's building structure and the remaining one on the opposite side of the structure. The blocks near the building structure have the greatest accessibility.
3.0 DESCRIPTION
OF BLOCKS The 40 blocks used at the off-site location varied from approximately 5 feet to over 10 feet in length, 2 feet to 3 feet thick, and 3 feet high. The total weight of the blocks (only from the reactor support structure) sent to the off-site location was 259 tons or 2.35E+8 grams. There were four (4) smaller blocks and a concrete slab, also sent to the off-site location, that were released from the turbine building. These were not included in the analysis and this request for alternate disposal because of the lack of tritium contamination in these blocks.
3.3 Radiological Characterization of Blocks 3.3.1 Background At the time of the shield block release, analyses of the tritium content of concrete within the reactor support structure indicated values less than the minimum detectable activity.
Based on these results and surface contamination surveys, the shield blocks were determined to be free of detectable licensed radioactive material. However, the tritium analyses were performed to the specified levels for 10 CFR part 61 waste classification requirements (indicated lower limits of detection (LLD) of less than 1,000 - 2,000 pCi per gram).
In 2004, as part of preparation for demolition and plans to retain RSS concrete on-site, further volumetric sampling and analysis of radionuclides was performed. Due to the Derived Concentration Guideline Level for tritium, a lower limit of detection of 10 pCi per gram was requested for the additional volumetric sampling. An unexpected finding of this analysis was the presence of tritium on and in essentially all concrete within the RSS. Levels of tritium from samples taken in proximity to where the steam generator shield blocks were located indicated tritium levels averaging approximately 200 pCi per gram.
3.3.2 Characterization Results Initial RSS sample results that first prompted further investigation indicated surface values of approximately 400 pCi per gram on lower portions of the RSS. The levels decreased to about 200 pCi per gram at one foot in depth. At 2.5 feet and greater in depth the concentrations ranged from 2-30 pCi per gram.
Additional sampling was performed on the upper portions of the RSS, where a majority of the shield blocks would have been located. Surface samples analyzed in this region indicated a range of concentration of 40-106 pCi per gram.
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A total of five (5) blocks still on site had surface samples taken and analyzed. The results ranged from a low of 25 pCi per gram to a high of 390 pCi per gram with an average of about 150 pCi per gram.
Two blocks (one on each side of the structure) at the off-site location had surface samples taken and analyzed. The lower block (and soil adjacent to it) pictured in Figure 5 of attachment 2 was sampled on February 16, 2005 in conjunction with the Vermont Department of Health. Each block indicated surface concentrations of approximately 90 pCi per gram.
A soil sample was taken at the base of the one block and initially indicated a tritium concentration of 20 pCi per gram. A second analysis of the soil sample was requested and the reanalysis found that there was no detectable tritium in the sample. The laboratory has concluded that the initial result was as a result of the short turn around requested on the sample, use of the Micro Distillation technique, and short half-life naturally occurring radioactive material causing a false positive result.
4.0 RADIOLOGICAL ASSESSMENTS Assuming an average concentration of 200 pCi per gram in the shield blocks, the total tritium would be approximately 47 mCi. The concentration of 200 pCi per gram tritium compares to an exempt concentration from 10CFR30.70 Schedule A of 30,000 pCi per gram.
Even based on the erroneous soil sample result (20 pCi per gram) from the site, the potential internal dose from this tritium is insignificant. The potential dose to a hypothetical member of the public from the tritium can be conservatively estimated using the Yankee soil DCGL of 370 pCi/g (corresponding to 25 mrem/y) and the measured soil concentration of 20 pCi/g. This application of the soil DCGL for this purpose is considered extremely conservative for this application given that:
- The DCGL is based on a resident farm that includes raising and consuming livestock and fish from the contaminated soil, which cannot be accomplished on the available soil area.
- The DCGL is based on irrigating the land with contaminated groundwater.
- The DCGL is based on a contaminated area of over 3 acres whereas the soil area available for farming activities is much smaller.
- The DCGL is based on a large fraction of consumed food products being generated from the farm.
Even given these conservatisms, the hypothetical bounding dose from this soil as calculated from the DCGL is 1.3 mrem/yr. This is well below any regulatory limits and may be considered insignificant.
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Due to the height of the wall in relation to the stream, the water flow gradient would be toward the stream. No wells are on the property where the blocks are located and none can be drilled between the blocks and the stream.
Additionally, a comparison between the tritium concentrations in the blocks and the value for tritium in the IAEA Application of the Concepts of Exclusion, Exemption and Clearance was performed. The stated value for tritium of 100 Bq/gl (about 2700 pCi per gram) is greater than 10 times the identified average level in the shield blocks.
5.0 CONCLUSION
S Based on the non-radiological safety risks to remove and relocate the shield blocks back to the Yankee Atomic Site and the preference of the property owner to keep the wall intact, the shield blocks should be allowed to remain in place. Exposures to members of the public from the tritium contained in the shield blocks is much less than one (1) millirem per year because there are essentially no credible exposure pathways.
5 Pictures of the Retaining Wall 6
Figure 1 - View of retaining wall AK
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.1 Figure 2 - Close up of retaining wall 7
Figure 3 - Owner's structure adjacent to retaining wall, two blocks visible at left of structure Figure 4 - Single block used at right of structure (lower wall portion) 8
i lIt FigureS5-Closer View of two blocks b3 side of structure 9
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