ML20086B932
| ML20086B932 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 06/28/1995 |
| From: | Fisher M PUBLIC SERVICE CO. OF COLORADO |
| To: | Weber M NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| P-95068, NUDOCS 9507060185 | |
| Download: ML20086B932 (14) | |
Text
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, t h Public Service-
- O" h 16805 WCR 191/2; Platteville, Colorado 80651 June 28,1995 Fort St. Vrain P-95068 U.S. Nuclear Regulatory Commission A'ITN: Document Control Desk Washington, D.C. 20555 A'ITN:
Mr. Michael F. Weber, Chief Decommissioning and Regulatory Issues Branch Docket No. 50-267
SUBJECT:
Final Survey Plan for Site Release, Revised Modifications to Classification and Investigation Criteria
REFERENCES:
1.
PSC Letter, Fisher to Weber, dated May 23,1995 (P-95059) 2.
NRC Ietter, Pittiglio to Crawford, dated Jamtary 26,1995 (G-95020)
Dear Mr. Weber:
This letter submits proposed revisions to the criteria for classification and investigation of final radiological survey areas, as previously submitted in Reference 1. In Reference 1, Public Service Company of Colorado (PSCo) proposed modifications to the criteria to be used for initial classification and for investigation / reclassification of surface and structure survey units during the final radiological survey of the Fort St. Vrain (FSV)
Nuclear Station. During subsequent discussions with Messrs. David Fauver and Clayton Pittiglio of your staff, PSCo agreed to make certain changes and to provide further justification for the proposed criteria modifications, as discussed in the attachment.
For completeness, this letter includes all of the topics addressed in the Reference I submittal; this letter and its attachment are intended to supersede Reference 1 in its ontirety.
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,P-95068 June 28,1995.
Page 2 l
ne major technical issue behind the proposed modifications involves use of the survey instrument's Minimum Detectable Activity (MDA) as the threshold above which j
measurements would require a survey area to be classified as affected, or woald require j
further investigation. PSCo agreed to include the MDA criterion in the approved Final Survey Plan (Reference 2), and we first used this criterion during final survey of the i
i Repower Area. The Repower Area nywts a very small portion of the FSV restricted i
j area and served as an excellent test case for the site survey criteria. Although all l
requirements were adequately implemented for the rather limited conditions and scope i
encountered in the final survey of the Repower Area, PSCo considers that several of the action level criteria based on the MDA and currently contained in the Plan will require an unneury level of effort when implemented on a mu::h larger scale. This is i
discussed further in the attachment.
3 The attached proposed modifications include:
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1)
Surface activity criteria to be used for initial classification of surface and structure survey units, and 2)
Surface activity action levels to be used for investigation'/ reclassification of
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surface and structure survey units.
The proposed modifications are a direct result of the information obtained and lessons learned during the Repower Area survey. These modifications are proposed to revise the action level criteria provided in the FSV Final Survey Plan, and do not alter the site j
release criteria. Implementation of the proposed modifications will streamline the implementation of the final survey and allow more flexibility in the use of engineering analysis.
These mcdifications will ensure more efficient use of decommissioning l
resources, while providing assurance that final survey criteria meet the intent of Draft l
NUREG/CR-5849 and the data obtained is representative of the radiological status of the site. Based on our experience in the Repower Area, PSCo considers that use of the i
MDA as a criteria for initial classification and investigation will increase the number of i
survey measurements and the extent of data analysis, with associated costs estimated between $1.5 and $3.5 million.
.i As stated in Reference 1, based on information and experience gathered during and after i
the Repower Area survey, other requests to modify the Plan may be submitted. For j
example, the methods to assess background exposure rates, as described in Draft I
NUREG/CR-5849 and,the Fort St.. Vrain Final Survey Plan, are being evaluated.
Preliminary results suggest that in unaffected areas such as the Turbine Building, background exposure rates are significant and highly variable, making it difficult to select one representative background value. Once this evaluation is complete, the results and any alternate method for determining background exposure rates may be submitted to the NRC.
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P-95d68.
June 28,1995 Page 3 PSCo requests NRC approval of the attached proposed modificadons by July 20,1995, to support our final survey schedule.
We plan to start final nrvey activities in unaffected amas on July 10,1995, and are delaying final data analysis until the proposed criteria for investigation and reclassification are apprmied. We appreciate your attention and timely review of this matter.
If you have any questions regarding this information, please contact kir. M. H. Holmes at (303) 620-1701.
Sincerely, Mary J.
isher Decommissioning Program Director MJF/SWC i
Attachment cc:
w/ attachment i
Regional Administrator, Region IV I
Mr. Robert M. Quillin, Director j
. Radiation Control Division l
Colorado Department of Public Health and Environment
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i ATTACHMENT 1 PROPOSED MODIFICATIONS TO FSV FINAL SURVEY PLAN Initial Cimedfication Criteria for Unaffected Surface and Structure Survey Units -
Current and Proposed The current surface activity criteria for initial classification of unaffected surface and structure survey units are as follows:
"A survey unit may be initially classified as unaffected if there is little or no potential for the presence of licensed material based upon operational history, characterization data, and routine surveillances. The presence of licensed material (in excess of MDA), or previous remediation would preclude a survey unit from being classified as unaffected." (Reference 3, Response to Comment 3, paragraph 2)
The proposed surface activity criteria for initial classification of unaffected surface and structure survey units are as follows:
"A survey unit may be initially classified as unaffected if there is little or no potential for the presence of licensed material based upon operational history, characterization data, and routine surveillances. However, radiological survey measurements indicating the presence of licensed material, or a history of contamination or l
remediation, wili preclude a survey unit from being classified as unaffected. The criteria are: for total surface activity, measurements in excess of 25% of the guideline i
value (GLV), or in excess of the MDA, whichever is larger; for removable surface activity, individual measurements in excess of 10% of the GLV, or in excess of the MDA, whichever is larger "
Justification for these proposed changes is provided on pages 9 and 10 of this Attachment.
i The following table compares the current and the proposed surface activity criteria for initial classification of surface and structure survey units.
Initial Classification Criteria Unaffected Surface and Structure Survey Units MEASUREMENT CURRE!G CRTIERIA PROPOSED CRITERIA l
Total Surface Activity Unaffected if low potential for Unaffected if low potential for
. radioactive contamination.
radioactive contamination.
l Unaffected if licensed material is Unaffected if individual expected to be < MDA.
measurements are expected to be
<25% of the GLV; or <MDA, whichever is larger.
i Removable Surface Activity Unaffected if low potential for Unaffected if low potential for
[
radioactive contamination.
radioactive contamination.
Unaffemd if licensed material is Unaffected if individual expected to be < MDA.
measurements are expected to be j
<10% of the GLV; or <MDA, whichever is larger.
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ATTACHMENT 1 PROPOSED MODIFICATIONS TO FSV FINAL SURVEY PLAN Inyestiga'tlon/ Reclassification Action I4vels for Unaffected Surface and Structure Survey Units - Current and Proposed The current surface activity action levels for investigation / reclassification of unaffected surface and structure survey units are as follows:
" Investigation surveys will be performed within an unaffected survey unit if an individual final survey measurement for removable or total surface activity indicates the presence of licensed material (in excess of MDA). If during the investigation survey, measurements for removable or total surface activity are verified to exceed 25% of the unrestricted use criteria, the survey unit will be reclassified." (Reference 3, Response to Comment 4, paragraph 2)
The proposed surface activity action levels for investigation and reclassification of unaffected surface and structure survey units are as follows:
" Investigation will be performed within an unaffected survey unit if an individual final survey measurement for removable or total surface activity indicates the presence of licensed material in excess of 50% of the GLV; or if > 10% of the measurements are >25% of the GLV. If during the investigation survey, >25% of the measurements for removable or total surface activity are verified to exceed 25% of the GLV, the survey unit, or in some instances a portion of the survey unit, will be reclassified."
l Page 2 of 11
A'ITACHMENT 1 PROPOSED MODIFICATIONS TO ISV FINAL SURVEY PLAN The follo' wing table compares the current and the proposed surface activity action levels for
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investigation / reclassification of surface and structure survey units.
i Investigation / Reclassification Action Levels Unaffected Surface and Structure Survey Units j
MEASUREMENT CURRENT ACTION LEVELS PROPOSED ACTION LEVF1S 1
Total Surface Activity Investigate an individual Investigate an individual measurement >MDA.
measurement >50% of the GLV.
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Reclassify if an individual Reclassify if verified.
measurement >25% of the GLV.
I Investigate if >10% of the j
individual measurements are>25% of the GLV.
Reclassify if >25% of the i
individual measurements are >25 % of the GLV.
l Removable Surface Activity Investigate an individual Investigate an individual 1
measurement >MDA.
measurement >50% of the GLV.
Reclassify if an individual Reclassify if verified.
j measurement >25% of the GLV.
Investigate if >10% of the i
individual measurements are >25% of the GLV.
Reclassify if >25% of the i
individual measurements are>25% of the GLV.
An investigation will be performed for instances where the results of the initial final survey measurements exceed the proposed action levels. The intent of the investigation is to verify instances where licensed material is the cause of final survey measurements in excess of the action levels. The investigation, which is typically performed by a final survey engineer, will consider such factors as the background values applied, the instrument parameters used, local influences other than licensed material, the distribution of positive results within the survey unit, and/or additional scans and fixed-point measurements. For instances where i
additional measurements are collected as a part of the investigation, it is expected that for the area of concern, the measurement frequency (initial plus investigation measurements) will exceed that which is typically required for suspect affected survey units. In the event that i
the investigation, or the additional measurements collected, verify residual activity in excess of the action levels, the area will be defined and a review will be conducted to determine the extent of the area to be reclassified. If the investigation and review indicate that a change in the classification of a portion of the survey unit is needed, supervisory review and approval will be obtained in accordance with a final survey procedure.
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'l ATTACHMENT 1 PROPOSED MODIFICATIONS TO FSV FINAL SURVEY PLAN Initial Classification Criteria for Non-suspect Affected Surface and Structure Survey Units - Current and Proposed There are no proposed changes to the initial classification criteria for non-suspect affected surface and structure survey units. A summary of the criteria that will typically be used to classify a survey unit as non-suspect affected is provided in the following table.
Initial Classification Criteria Non-suspect Affected Surface and Structure Survey Units MEASUREMENT CURRENT CRITERIA PROPOSED CRTIERIA Total Surface Activity Non-suspect affected if individual No change, measurements expected to be
<50% of the GLV; or <MDA, whichever is larger.
Non-suspect affected if average of No change.
the measurements expected to be
<25% of the GLV; or <MDA, whichever is larger.
Removable Surface Activity Non-suspect affected ifindividual No chang'e.
measurements expected to be
<50% of the GLV; or <MDA, whichever is larger.
Non-suspect affected if average of No change.
the measurements expected to be
<25% of the GLV; or <MDA, whichever is larger.
Investigation / Reclassification Action Levels for Non-Suspect Affected Surface and Structure Survey Units - Current and Proposed The current surface activity action levels for investigation / reclassification of non-suspect affected surface and structure survey units are as follows:
"The action levels to initiate investigation surveys within non-suspect affected survey units are individual final survey measurements for removable or total surface activity in excess of 50% of the unrestricted use criteria. If greater than 10% of the initial final survey measurements within a non-suspect affected survey unit are verified to exceed this action level, or if an individual measurement exceeds the guideline values, then the survey unit will be reclassified as suspect affected and resurveyed.
Conversely, if less than or equal to 10% of the initial final survey measurements within a non-suspect affected survey unit are verified to exceed this action level, and none of the individual measurements exceed the guideline values, then an investigation survey and/or reclassification will [notl be performed." (Reference 3, Response to Comment 4, paragraph 3)
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ATI'ACHMENT 1 PROPOSED MODIFICATIONS TO ESV FINAL SURVEY PLAN The proposed surface activity action levels for investigation and reclassification of non-suspect affected surface and structure survey units are as follows:
"The action levels to initiate an investigation within non-suspect affected survey units are individual final survey measurements for removable or total surface activity in excess of 75% of the GLV; or if > 10% of the measurements are >50% of the GLV.
If during the investigation survey, >25% of the measurements for removable or total surface activity are verified to exceed 50% of the GLV, the survey unit, and in some instances a portion of the survey unit, will be reclassified."
Justification for these proposed changes is provided on pages 9 and 10 of this Attachment.
The following table compares the current and the proposed surface activity action levels for investigation / reclassification of non-suspect affected surface and structure survey units.
Investigation / Reclassification Action Levels Non-suspect Affected Surface and Structure Survey Units MEASUREMENT CURRENT ACI1ON LEVELS PROPOSED ACTION LEVELS Total Surface Activity Investigate an individual Investigate an individual measurement >50% of the GLV.
measurement >75% of the GLV.
Reclassify if >10% of the Reclassify if verified.
individual measurements are verified to exceed 50% of the GLV, or an individual measurement is >GLV.
Investigate if >10% of the individual measurements are
>50% of the GLV.
Reclassify if >25% of the individual measurements are>50% of the GLV.
Removable Surface Activity Investigate an individual Investigate an individual measurement >50% of the GLV.
measurement >75% of the GLV.
Reclassify if >10% of the Reclassify if verified.
individual measurements are verified to exceed 50% of the GLV, or an individual measurement is >GLV.
j Investigate if >10% of the individual measurements are
>50% of the GLV.
Reclassify if >25% of the individual measurements are>50% of the GLV.
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A'ITACHMENT 1 PROPOSED MODIFICATIONS 'ID FSV FINAL SURVEY PLAN An investigation will be performed for instances where the results of the initial final survey measurements exceed the proposed action levels. The intent of the investigation is to identify instances where licensed material is the cause of final survey measumments in excess of the actions levels. The investigation, which is typically performed by a final survey engineer, will consider such factors as the background values applied, the instrument parameters used, local influences other than licensed material, the distribution of positive results within the j
survey unit, and/or additional scans and fixed-point measurements. For instances wherc additional measurements are collected as a part of the investigation, it is expected that for the area of concern, the measurement frequency (initial plus investigation measurements) will exceed that which is typically required for suspect affected survey units. In the event that the investigation, or the additional measurements collected, verify residual activity in excess of the action levels, the area will be defined and a review will be conducted to determine the extent of the area to be reclassified, as described on page 8 of this Attachment.
Investigation Action levels for Suspect-Affected Surface and Structure Survey Units -
Curant and Proposed The current surface activity action levels for investigation of suspect affected surface and structure survey units are as follows:
"The action levels to initiate investigation surveys within suspect affected survey units are individual final survey measurements for removable or total surface activity in excess of 75% of the unrestricted use criteria." (Reference 3, Response to Comment 4, paragraph 4)
The proposed surface activity action levels for investigation of suspect affected surface and structure survey units are as follows:
i "The action levels to initiate investigation surveys within suspect affected survey units i
are an individual final survey measurement for removable and total surface activity in j
excess of the GLV; or if > 10% of the measurements are >75% of the GLV."
Justification for thez proposed changes is provided on pages 9 and 10 of this Attachment.
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ATTACHMENT 1 PROPOSED MODIFICATIONS TO FSV FINAL SURVEY PLAN The following table compares the current and the proposed surface activity action levels for i
investigation of suspect affected surface and structure survey units.
Investigation Action Levels Suspect-Affected Surface and Structure Survey Units MEASUREMENT CURRENT ACI1ON LEVELS PROPOSED ACTION LEVELS Total Surface Activity Investigate an individual Investigate if >10% of the measurement >75% of the GLV.
individual measurements are
>75% of the GLV, or if an individual measurement >GLV.
Collect additional measurements, remediate as appropriate.
' Removable Surface Activity Investigate an individual Investigate if >10% of the measurement >75% of the GLV.
individual measurements are
>75% of the GLV, or if an individual measurement >GLV.
Collect additional measurements, remediate as appropriate.
An investigation will be performed for instances where the results of the initial final survey measurements exceed the proposed action levels. The intent of the investigation is to identify instances where licensed material is the cause of final survey measurements in excess of the i
actions levels and to provide additional confidence that licensed material does not exist in excess of the guideline values. For instances where licensed material is identified in excess of the guideline values, the surface will be remediated and resurveyed as necessary.
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ATTACHMENT 1 PROPOSED MODIFICATIONS 'IO FSV FINAL SURVEY PLAN Iny@*- @C
- 1:- Protocols
. For instances where measurement results exceed the proposed action levels for reclassification, and the investigation (which may include additional measurements) indicates that licensed material is the cause of the elevated results, the entire survey unit containing the elevated results may be reclassified. In all cases where the investigation indicates that licensed material is the cause of the elevated results and the survey unit is less than or equal to 100 square meters, the entire survey unit will be reclassified. For survey units greater 1
than 100 square meters where the investigation indicates that licensed material is the cause of i
.the elevated results, and it is apparent from a review of the distribution of the measurement l
i results, by field observation, or by other methods of evaluation that the elevated activity is i
lacali% direction may be provided to establish a new survey unit or survey subunit for reclassification. 'Ihe reclassification process will be proceduralized, and supervisory review and approval will be required for instances where the entire survey unit is not reclassified.
4 The following is a summary of the investigation and reclassification protocols and the
? designation of a survey subunit as previously submitted to the NRC.
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... If the survey unit requires remediation or reclassification, the results of the initial fixed point measurements will be archived as characterization survey data and the survey unit,'or newly-defined subunit, will be resurveyed.... " (Reference 3, Response to NRC Comment 1) j "The purpose of performing the investigation surveys is to confirm the initial final survey measurement, and if verified to exceed action levels, to define the bounds of the elevated activity. Depending on the results of the investigation survey, the survey unit may require j
remediation and/or reclassification and resurvey...." (For additional detail, please refer to l
Reference 3, Response to NRC Comment 4 and Reference 5, Section 3.8.11)
"For initial fixed point final survey measurements which exceed the maximum site-specific i
guideline value, an investigation survey will be performed to verify the presence of elevated l
activity and to define the bounds of the area of elevated activity...." (For additional detail, l
please refer to Reference 2, Response to NRC Comment 7) i.
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A'ITACHMENT 1 PROPOSED MODIFICATIONS TO FSV FINAL SURVEY PLAN Justification for Modifying Initial Classification Criteria and Investigation / Reclassification Action Levels The proposed modifications to the criteria for initial classification, and the investigation and reclassification action levels meet the intent of the recommendations in Draft NUREG/CR-5849. These modifications will streamline the implementation of the current final survey plan, and are required in consideration of the commitments made to NRC during the final phases of the survey plan approval process. These proposed modifications have been developed in the interest of optimizing the use of available decommissioning resources, and matching the level of final survey effort to the potential for residual activity.
The mod 3fication to the nitial classification criteria for unaffected survey units relative to total surface activity is reqeired because in some instances, the MDA for total surface activity measurements used for initid classification may be<25% of the guideline values for 2
unrestricted use, (i.e.,1,250 dpm/100 cm ). The use of Mi>A, for instances where the 2
MDA is less than 1,250 dpm/100 cm, as tie total surfacc activity criteria for initial classification will result in a significant number of false positives. For instances where the MDA is determined to be less than 25% of the GLV, and the results exceed the MDA, then 25% of the GLV will be used as an indication for the potential presence of licensed material, to reduce the frequency of the false-positives. For example, if the 230 total surface activity measurements collected from the Repower area had been used for initial classification, it would have been necessary to classify the Repower Area as affected which clearly would have been unwarranted. For instances where the MDA exceeds 25% of the GLV, results which exceed the MDA will be used as an indication of the potential presence of licensed material and the survey unit will be classified as affected.
The modification to the initial classification criteria for unaffected survey units relative to removable activity is required because the MDA for removable activity is typically 2 to 3 2
percent of the guideline value for release for unrestricted use, (i.e.,20 to 30 dpm/100 cm ),
Requiring an initial classification criteria for unaffected survey units relative to removable activity of less than MDA would be overly restrictive, and would penalize the licensee for using state-of-the-art counting equipment. Therefore,10% of the GLV is proposed as the initial classification criterion for removable activity, for those cases where the MDA is less than 10% of the GLV.
The use of MDA as an action level for investigation of total surface activity measurements will result in a significant number of false positives. The modification to the investigation and reclassification action levels for unaffected survey units is in part a result of the experience gained during the performance of final survey for the Repower Area. A significant number of investigations, which included additional field measurements, were required due to use of the MDA as the action level for investigation. Of the 230 total surface activity measurements included in the final report for the repower area, approximately 60 measurements (26%) were investigation measurements collected as result of using MDA as the action level for investigation. These investigations did not identify the i
presence of licensed material.
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ATTACIIMENT 1 PROPOSED MODIFICATIONS 'ID FSV FINAL SURVEY PLAN The incidence of false-positives appears to be more frequent than would be expected based solely on theory. This is likely due to background fluctuations, and not entirely due to counting statistics..It is apparent that the use of MDA for initial classification and investigation would result in a substantial drain on decommissioning resources if implemented during a large scale final survey while providing little or no benefit.
hwi on the experience gained during the final survey of the Repower Area at Fort St.
Vrain and a preliminary analysis of Shoreham final survey data, the use of MDA as a criteria for initial classification and investigation will have a significant impact on the overall cost of the FSV final survey. As discussed above, the use of the MDA will increase the number of i
survey units requiring initial classification as affected and increase the number of investigations required in unaffected areas. This will result in a significant increase in the number of survey measurements required and expend resources performing additional data analysis, revising survey packages and documenting the results in the Final Survey Report.
I It is believed that these efforts will not result in identifying licensed material above release limits. The exact cost impact is difficult to accurately assess, but initial estimates range from
$1,500,000 to $3,500,000.
l The modifications to the investigation / reclassification action levels for non-suspect affected survey units which require an investigation if > 10% of the measurements exceed 50% of the GLV, or if an individual measurement exceeds 75% of the GLV, are designed to allow for a small fraction of the measurement results to exceed 50% of the GLV without warranting an investigation. For affected rurvey units, the counting time will be selected to achieve an MDA which is less than 50% of the GLV. Allowing a small fraction of the measurement results to exceed 50% of the GLV is intended to account for statistical variation in counting, and for slight variations in the background of the area being surveyed.
The modification to the investigation action level for suspect affected survey units which requires an investigation if > 10% of the measurements exceed 75% of the GLV is intended to allow for a small fraction of the measurement results to exceed 75% of the GLV without warranting an investigation. Since these survey units are expected to contain residual activity, it is possible that individual measurements may exceed 75% of the GLV, however it is not expected that the frequency should exceed 10% of the measurements. This action level for suspect affected survey units is in addition to the recommendations contained in Draft NUREG/CR-5849.
The proposed modifications have been developed in the interest of focusing final survey efforts on those surfaces most likely to contain residual activity, and to make the most efficient use of decommissioning resources. These modifications are intended to limit the number ofinvestigations due to factors other than residual licensed material.
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I ATTACHMENT 1 PROPOSED MODIFICATIONS TO FSV FINAL SURVEY PLAN REFERENCES 1.
NRC Letter, Pittiglio to Crawford, " Response to NRC Comments on the Final Survey Plan for Site Release for Fort St. Vrain Nuclear Generating Station", January 26, 1995.
2.
PSC Letter, Fisher to Austin, " Response to Comments Regarding the Final Survey Plan for Site Release", dated January 11,1995.
3.
PSC Letter, Fisher to Austin, " Response to Comments Regarding the Final Survey Plan for Site Release", dated January 20,1995.
4.
PSC Ixtter, Fisher to Weber, " Final Survey Plan for Site Release, Proposed Modification to Classification and Investigation Criteria", dated May 23,1995.
5.
PSC Letter, Fisher to Weber, " Updated FSV Final Survey Plan for Site Release, Revision 1", dated May 25,1995.
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