ML20215J628
| ML20215J628 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/17/1986 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| NUDOCS 8610270125 | |
| Download: ML20215J628 (4) | |
Text
r Dna TENNESSEE VALLEY AUTHORITY SN 157B Lookout Place Oct
, 1986 U.S. Nuclear Regulatory Commission Region II ATTN:
Dr. J. Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Dr. Grace:
SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 - NRC-OIE REGION II INSPECTION REPORT NUMBERS 50-327/86-04 AND 50-328/86 CLARIFICATION OF SUPPLEMENTAL RESPONSE
'TO VIOLATION By my letter to you dated July 3, 1986, TVA provided supplemental responses to violations specified in NRC IE Inspection Report Nos. 50-327, -328/86-04.
The subject information had specified that "TVA has modified computer codes to include the calculation for 'MPC-hour equivalents' for similar acute exposures in the future, which could be added to MPC-hours recorded for the individual for chronic exposure in airborne areas." On October 9, 1986, during a Health Physics follow-up inspection, the NRC inspector asked if the computer code had been modified as stated above. On the following day, the inspector was informed by TVA that the computer code had not been modified. A summary of the TVA investigation is provided below.
Investigation During the initial evaluation of the circumstances involved in violation 86-04-02, it was decided that procedures should be revised to provide for calculation of "MPC-hour equivalents." This was completed on April 16, 1986, with revision to Section 5.1 of procedure WBC-1, " Internal Dosimetry overview." This procedure is included in DOS-3, " Radiation Dosimetry Procedures Manual." The revised procedure required that the calculation, or more appropriately, the results of the calculations for "MPC-hour equivalents" be included in the computerized Health Physics Dose Tracking System (HPDT) and a change to this computer code was initiated to show a more descriptive heading in the HPDT of "MPC-hour equivalents" rather than just "MPC-hour."
During the ensuing revision process, it was concluded that some misinterpretation might result from the heading changes and it was decided to list the new MPC-hour equivalent calculations under the existing heading. The proposed change was placed on hold with no revision being made to the computer code. The MFC-hour equivalent calculation results are input manually into the HPDT database. At no time was it intended that the calculation would be performed by the computer code. However, the individual providing the supplemental response was not aware of these proceedings and based his information on the assumption that the previously proposed code modification 8610270125 861017 f
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Dr. J. Nelson Grace October 17, 1986 had been completed. This assumption was carried throughout the submittal preparation and review process, resulting in the incorrect statement that "TVA has modified computer codes..." The response should have specified that TVA has modified the appropriate procedures to require calculations for "MPC-hour equivalents" and that the results be included in the HPDT. However, during subsequent review of this subject, it has been determined that there is a need to categorize the two values separately in the HPDT. Therefore, TVA is now in the process of modifying the code to explicitly display the "MPC-hour equivalent" separately from the normal MPC-hour value. The enclosed revised supplemental response corrects the erroneous statement and provides additional clarification of procedural changes involved.
l Corrective Action To preclude this from occurring in future submittals, a memorandum will be issued as a notice to all Office of Nuclear Power division directors stressing the importance of verifying, during the concurrence process, that the information to be provided to NRC is correct. This notice will be issued by October 27, 1986. This same guidance will be issued in a Nuclear Safety and Licensing Standard prior to restart.
By my letter to you dated September 4, 1986, TVA provided clarification of a response to violation 50-327, -328/86-36.
Included was a description of the cause of TVA's inaccurate statements concerning this violation. Please note that this condition was caused by a failure to properly coordinate revisions to the proposed response with the originating organization, while the cause of the inaccurate response to violation 86-04-02, as specified above, is due to a failure to ensure the accuracy of the proposed response by the originating organization.
Very truly yours, TENNESSEE VALLEY AUTHORITY R.
ridley, D rector Nuclear Safet and Licensing Enclosure cc (Enclosure):
Mr. James Taylor, Director office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Mr. G. G. Zech Director, TVA Projects U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
ENCLOSURE violation 50-327/86-04-02 and 50-328/86-04-02 i
TVA's Revised Supplemental Response:
TVA agrees that an assessment must be performed when an individual experiences an intake of radioactive material. However, it is important to recognize that the 520 MPC-hours value is a derived limit based on the fundamental quantity of dose limits (e.g., much like velocity is a derived quantity of distance and time). The relationship between MPCs and specific organ dose limits is explicitly described in ICRP-2 which, as discussed in IE Information Notice No. 82-18, is the basis of the regulations in 10 CFR 20.
The relationship I
between the NRC MPC-hour limit and specific organ dose limits in the current 10 CPR 20 is described in Table 1 of the supplementary information published with the proposed revision of 10 CFR 20 in the Federal Register on December 20, 1985. As outlined in that document, an intake of 520 MPC-hour Per quarter is calculated to result in a 50-year committed dose of:
Whole-body 1.25 rems per quarter 5 rems per year Bone, thyroid, and skin 7.5 rems per quarter 30 rems per year i
~
Other organs 3.75 rems per quarter 15 rems per year TVA performed a detailed and thorough evaluation of the bioassay results using ICRP-2 and issued a report that included a dose calculation from the quantity (microcuries) of radioactive material that entered the individual's body. The radioactivity quantity was used for the internal exposure assessment. Without such use, dose could not have been determined. The critical organ was determined to be the lower large intentine (LLI). The LLI dose was calculated to be 71 mrem. This dose is insignificant relative to the regulatory limit of 3.75 rems per quarter (520 MPC-hours per quarter) for the LLI.
TVA monitors routine exposures on the basis of airborne concentrations and
" stay times"; however, the specific case in question did not in fact follow a typical inhalation pathway. Additionally, TVA routinely operates such that if an individual's internal exposure exceeds 2 MPC-hours in a day or 10 MPC-hours in a week, a bioassay is required.
Internal dose calculations (exposure assessments) are performed for all individuals having significant positive bioassay results.
TVA believes this practice to be totally consistent with 10 CPR 20.103(b)(2) and other NRC regulations in this area.
10 CFR 20.103 endorses Regulatory Guide 8.9, " Acceptable Concepts, Models, Equations, and Assumptions for a Bioassay Program." Regulatory Guide 8.9 states that an acceptable bioassay program includes " interpretations of measurement results in terms of the location of radioactive material in the body, the quantity present, the rate of elimination, and the resulting dose or dose commitment."
n
. Regulatory Guide 8.9 also endorses ICRP-2, -10, and -10A.
Further, ICRP-2 states that " Tests should be performed to estimate the total body burden for workers who had worked with unsealed radioactive isotopes that may give rise to levels of ingestion or inhalation.
. the radiation doses delivered to the appropriate organs or tissues should be calculated and noted on the personal record..."
Thus, the philosophy of the guidance documents supporting the technical basis of 10 CFR 20 is to assess dose for the purpose of determining the significance of uptakes of radioactive materials. MPCs are based on chronic exposure. For acute uptakes like the one in question, bioassay and dose assessments are the appropriate approaches.
TVA has modified procedures to require calculations for "MPC-hour equivalents" for similar acute exposures in the future. The results of these calculations will be included in the computerized Health Physics Dose Tracking System cumulating MPC-hours. These values can then be used to assess regulatory compliance in the more direct fashion implied by the arguments put forward by NRC in support of its Notice of Violation. TVA continues to believe that such
" direct" comparison is not required by 10 CFR 20.103, but will agree to perform such calculations in the future.
DPO:CLl!
10/15/86 00791