ML063320442
| ML063320442 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 10/27/2006 |
| From: | Babineau G, Carson A, Darois E Yankee Atomic Electric Co |
| To: | NRC/FSME |
| References | |
| BYR-06-094 YA-REPT-00-018-06 | |
| Download: ML063320442 (7) | |
Text
TECHNICAL REPORT TITLE PAGE Estimated Doses from Inhalation, Ingestion and Remote Exposure from Residual Discrete Particles At Yankee Nuclear Power Station Following NRC License Termination YA-REPT-00-01 8-06 Technical Report Number Azpprovpls (Prin SWR+a'mae)
Preparer:
Eric Darols 2,X\\
Date:
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Approver (Cognizant Manager);
Gregi Babineau 5-YA 6o.Qi"-.Iate: MO.?'i~
1 2
3 4
5 6
7 Table of Contents S u m m a ry.........................................................................................................................
3 In tro d u c tio n....................................................................................................................
3 B a c kg ro u n d....................................................................................................................
3 D is c u s s io n......................................................................................................................
3 R e s u lts...........................................................................................................................
6 C o n c lu s io n.....................................................................................................................
6 R e fe re n c e s.....................................................................................................................
7 YA-REPT-00-018-06 Page 2 of 7
1 Summary This technical basis document acts as a supplement to YA-REPT-00-01 6-06, "Discrete Particle Detection in the Performance of Final Status Surveys at Yankee Nuclear Power Station," which addressed effective dose equivalent from a particle on the surface and 15 cm below the soil surface. This report addresses the potential doses from ingestion, inhalation and remote exposure pathways, due to an undetected discrete particle remaining on the soil surface after performance of the Final Status Survey at the Yankee Nuclear Power Station.
2 Introduction In its request for additional information (RAI), the NRC raised questions concerning the use of In-Situ Gamma Ray Spectoscopy (ISGRS) System, as a part of final status survey in open land areas. A technical basis document, Reference 1, was developed at Yankee Nuclear Power Station to address scanning surveys in a Class 1 survey area with the ISGRS and its ability to detect discrete particles. A second technical basis document included in a subsequent response to the NRC, Reference 3, addressed the Minimum Detectable Concentration (MDC) for discrete particles and calculated the potential effective dose equivalent if a missed particle at the MDC came into contact with the skin. The NRC requested additional evaluations be performed to estimate potential doses from discrete particles if they were ingested, inhaled or were present nearby an individual. This technical basis document has been written to address those issues.
3
Background
Several evaluations of particle ingestion and inhalation have already been performed by others. This technical basis document will reference these evaluations and describe the basic concepts and assumptions of the evaluations.
The dose from a discrete particle near but not present on the skin was evaluated using techniques described in articles published in Radiation Protection Dosimetry, as discussed in Reference 6.
4 Discussion Although a final decision regarding the end use of the Yankee Nuclear Power Station has not been determined, the site will likely be set aside for land conservation purposes or use as public recreational area. Given this more plausible use of the site, the probability of any human contact with discrete particles is much less than that of the resident farmer scenario.
Regardless, this evaluation is being performed to supplement the evaluation in YA-REPT-00-016-06 and to address the dose due to other scenarios with probably of occurrence (listed in order of likelihood, least to greatest):
Inhalation: assumes exposure from an inhaled particle that is deposited in the nasal, larynx, or pharynx regions; Ingestion: assumes exposure from a particle accidentally ingested; YA-REPT-00-018-06 Page 3 of 7
Contact Skin: assumes exposure from a particle directly in contact with the skin (see YA-REPT-00-016-06); and Remote exposure: assumes exposure from a particle that is not in contact with the skin.
4.1 Inhalation Dose In the Reference 4, Pre-Filed Rebuttal Testimony of George E. Chabot, Ph.D, C.H.P in the matter of Connecticut Yankee Atomic Power Company, George estimated the dose from inhalation of a 10 micrometer (pm) particle would be less, probably far less, than 0.5 mrem.
The following assumptions and parameter values were used in the dose estimation:
The Extrathoracic Region ET2, as defined in ICRP Report 66, represents the interior posterior nasal tissues, the pharynx, and larynx tissues. It was selected as the deposition site for the inhaled 10 micron diameter particle because it represents the portion of the extrathoracic region that is most subject to cancer induction and has the highest tissue weighting factor, 0.025. The thoracic region of the respiratory tract was not selected as a deposition site because of the extremely high probability that a 10 micron particle would not penetrate to the deeper sections of the tract.
The dose equivalent to region ET2 for an adult subject was calculated by assuming an insoluble, stationary particle residing on the tissue surface for a time period equal to the mean residence time of particles in region ET2.
" The mean residence time in ET2 is equal to 0.01 days (14.4 minutes), obtained from the reciprocal of the removal rate constant of 100 day-1 as given in ICRP Report 66.
Clearance from the ET2 region is to the GI tract via swallowing.
Total surface area of ET2 region is 450 cm 2, as per ICRP 66.
" Thickness of mucous layer is 15 microns and depth of basal cell target nuclei is 45 microns below epithelial surface, as per ICRP 66. The combined thickness is 60 microns, 0.006 cm, assumed to be unit density tissue equivalent material.
No self attenuation of radiation within the source was calculated.
" The beta dose calculation was done using the VARSKIN MOD2 computer code by assuming the area of the target tissue could be represented by a disk 450 cm 2 in area (radius of 11.97 cm). Dose was evaluated at a depth of 0.006 cm, based on a 14.4 minute exposure time. The gamma dose component was evaluated, assuming no photon attenuation and a respective source position 0.006 cm above the 450 cm 2 disk.
Doses were calculated for nominal 1 microcurie sources.
YA-REPT-00-018-06 Page 4 of 7
Co-60 VARSKIN results:
Beta dose averaged over 1 cm 2 = 1.00 rads Beta dose averaged over 450 cm 2 = 0.0022 rads = 2.2 mrem Gamma dose averaged over 450 cm 2 = (7rFAT/450) In((H 2+R2)/H2) =
3.36x10-4 rem = 0.336 mrem, Where:
F = 13.2 rem h1 mCi-1 cm 2, A = 10-3 mCi, T = 0.24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, H = 0.006 cm, and R = 11.97 cm.
Total dose = 2.2 mrem + 0.34 mrem = 2.54 mrem Effective Dose = (0.025)(2.54 mrem) = 0.064 mrem.
4.2 Ingestion Dose In the Reference 5 technical support document, Connecticut Yankee evaluated the potential dose from an ingested discrete particle.
The following assumptions and parameter values were used in the dose estimation:
The particle is insoluble and does not enter the blood stream.
The particle is expected to be eliminated in 42 hours4.861111e-4 days <br />0.0117 hours <br />6.944444e-5 weeks <br />1.5981e-5 months <br /> based upon the sum of the mean residence times for each of the organs along the GI tract.
" The total number of disintegrations over 50 years was used for conservatism.
- The computer program INDOS was used to determine the number of disintegrations to the GI tract organs.
Specific Effective Energy terms from ICRP-30 were used to convert dose to target organs from disintegrations in the GI tract.
The following results were extracted from the Technical Support Document:
The absorbed dose factor for Co-60 = 1.18E+01 Mev/gram/Bq.
The dose equivalent factor for Co-60 = 1.88E-07 Rem/Bq.
4.3 Remote Exposure The effective dose from a point source not on the skin was obtained from an article published in Radiation Protection Dosimetry in 1999 by C.H.Kim et al (Reference 6). Organ YA-REPT-00-018-06 Page 5 of 7
doses were calculated with the MCNP 4A code and a mathematical anthropomorphic phantom. The maximum effective dose from a point source, 1.21E-16 Sv/photon, was taken from Table (1 b) for a 1 MeV photon at 50 cm from the center of the phantom which is 40 cm from the surface of the body.
5 Results The estimated activity of a Co-60 discrete particle that could be missed during the performance of a Final Status Survey as documented in Reference 3 was 1.7 pCi. The resulting inhalation dose based on the calculations shown in section 4.1 would be:
Inhalation Effective dose = 0.064 mrem/pCi
- 1.7 pCi = 0.11 mrem The estimated ingestion dose based upon the conversion factors in section 4.2 would be:
Ingestion Effective dose = 1.88E-07 Rem/Bq
- 3.7E04 Bq/IpCi
- 1.7 pCi Ingestion Effective dose = 0.012 Rem = 12 mrem The estimated remote exposure from a 1.7 pCi Co-60 discrete particle approximately 40 cm from the surface of the body based upon the conversion factor in section 4.3 and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> exposure would be:
Remote exposure effective dose for a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> exposure =
1.21 E-16 Sv/photon *2 photons/dis*2.22E6 dpm/pCi*1.7 pCi*60 m/hr*24 hr Remote exposure effective dose (24 hr) = 1.32E-6 Sv = 0.13 mrem 6
Conclusion As can be seen from the results in Section 5, the maximum effective dose from the three exposure scenarios (but not the most likely dose) is 12 mrem which is approximately 12 percent of the 100 mrem whole body limit for members of the public.
YA-REPT-00-018-06 Page 6 of 7
7 References Reference 1 YA-REPT-00-018-05, "Use of In-Situ Gamma Spectrum Analysis To Perform Elevated Measurement Comparisons In Support of Final Status Surveys," dated October 2006 Reference 2 Yankee (Rowe) Nuclear Power Station - Request for Additional Information Re: Final Status Surveys (TAC No. L52675), dated July 12, 2006 Reference 3 BYR 2006-071, Submittal of Responses to NRC Request for Additional Information Regarding the Use of In Situ Gamma Spectroscopy for Final Status Surveys (includes YA-REPT-00-016-06, "Discrete Particle Detection In the Performance of Final Status Surveys At Yankee Nuclear Power Company," dated August 2006)
Reference 4 Pre-Filed Rebuttal Testimony of George E. Chabot, Ph.D, CHP, In the Matter of Connecticut Yankee Atomic Power Company before the Atomic Safety and Licensing Board, filed February 28, 2003.
Reference 5 BCY-HP-0125, Dose Estimate for an Ingested Particle, December 2002.
Reference 6 Effective Dose (Equivalent) from Front-Located Point and Disc Photon Sources, Radiation Protection Dosimetry, Vol. 81, No. 3, pp.177-186 (1999), C.H. Kim, M.R. Sarder and W.D. Reece YA-REPT-00-018-06 Page 7 of 7