ML24289A204

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Clarification Responses
ML24289A204
Person / Time
Site: Fort Calhoun Omaha Public Power District icon.png
Issue date: 10/09/2024
From: Pearson B
Omaha Public Power District
To: Jack Parrott
Reactor Decommissioning Branch
References
Download: ML24289A204 (1)
v • d • e


Text

ATTACHMENT 1

Response to Clarification Questions on Fort Calhoun Station Final Status Survey Final Report, Phase 1 RAJ Responses

7 Pages Follow Response to Clarification Questions on Fort Calhoun Station Final Status Sur v ey Final Report, Phase 1 RAI Responses

RAl-01-01

RAl 01 requested that instrument and sample analysis minimum detectable concentrations calculated for comparison with the DCGLs be explicitly stated in the SURRs, including calculations for a posteriori MDC.

A) Response (1)(a) indicates that the scan MDC for the 44-20 was calculated by using the TSO for the 44-10 and substituting the correct CPMR for a 44-20 with an assumed 100%

Cs-137 radionuclide mix. The ERC is discussed in the paragraph below and the value chosen was taken from the 44-10 TSO with an assumed radionuclide mix of 95% Cs-137 and 5% Co-60. The fraction used in FC-19-006 is 90% Cs-137 and 10% Co-60 allowing for some variability. Table 5-3 of the L TP applies the mixture fraction for the ABITB/RWPB for soils. In addition, Eu-152 is considered in FSS planning. Explain the use of a 95% Cs-137 and 5% Co-60 fractions given the difference in site data.

The a priori scan MDC calculated in the Phase 1 SU FSS Plans used an ERC value of 3.033E-04 mR/hr. This value represents the exposure rate with buildup for a 95% Cs-137/5% Co-60 mixture fraction with a source to detector distance of 22.86 cm (3 inches).

FCS Response:

The focus of the discussion in FC-19-006 is on the use of a 90% Cs-137 and 10% Co-60 mixture fraction, however, it also contains the MicroShield calculat ions for several other mixture fractions. Page 30 of Attachment 8.2 includes the ERC values for a 95% Cs-137 and 5% Co-60 mixture fraction at distances of 5.08, 7.62, 10.16, 12.7 and 15.24 cm (2, 3, 4, 5 and 6 inches) to the centerline of the detector active area. This is where the value of 3.033E-04 mR/hr was referenced from.

FC-19 - 006 conservatively models the source to detector distance to the centerline of the detector active area. This results in an additional inch of distance from the source term and is more conservative than the models used in NUREG-1507. NUREG-1507 models the source to detector distance to the detector end cap. The additional inch of distance used in the model provides considerable conservatism.

The RAI response compared the ERC used in the Phase 1 FSS SU plans to one using a conservative ERC value for a 100% Cs-137 mixture fraction with a 2 inch source to detector distance. This ERC value of 3.166E-04 mR/hr at distance of 2 inches was taken from Page 26 of FC-19-006 Attachment 8.2.

As part of the preparation of the new Ludlum 44-20 TSO, MicroShield calculations were performed using the L TP Table 5-3 mixture fraction (including Eu - 152) at distances of 2, 3, 4, 5 and 6 inches from the detector end cap.

The table below compares the calculated ERC values for the various mixture fractions and distances.

Page 1 of 7 Response to Clarificat ion Questions on Fort Ca lh oun Station F in al Status Survey Fi nal Report, Phase 1 RAJ Responses

Calculation Mixture Fraction & Distance ERC Phase 1 SURR plans 95% Cs - 137 & 5% Co-60 @ 3" 3.033E -04 RAI response 100% Cs-137@2" 3. 166E-04 Draft 44 -20 TSD LTP Mixture Fraction (w/ Eu-152) @2 " 3. 144E-04

As can be seen in the table, the ERC used in the Phase 1 SURR was more conservative than either of the other two ERCs. The ERC for the L TP Table 5-3 mixture fraction (including Eu-152) differs from the 100% Cs-137 ERC by less than 1 %.

1) The response, which a given background of 76, 000 cpm appear to be a priori MDC. The background range for all survey units in the Phase I submittal range from 18, 087 cpm to 36,880 cpm. Explain the use of a background rate of 76,000 cpm, particularly in the case where the background range is significantly below this value.

FCS Response:

Yes, the response provided was for the a priori MDC. The a priori MDC calculation was used in the FSS plans to calculate the max imum acceptable background that would still meet the OpDCGL.

The actual a posteriori MDCs for each SU will be provided in the revised SURRs.

2) In response (1)(a), ad ' value of 1.38 was given corresponding with a true positive of 95% and a false positive of 60%. Explain the selection of an index of sensitivity of 1. 38 based on site-specific considerations. Note that the confirmatory surveys utilize ad ' value of 2.32, which corresponds to a false positive value of 0.25 and the acceptable probability of a detection at 95%.

FCS Response:

The value of 1.38 is from Section 5.4.2.4.3 of the approved FCS L TP. It was selected based on the guidance provided in NUREG-1507 and past industry practices. The value of 1.38 for the index of sensitivity has been used in the following nuclear power plant L TPs :

  • Big Rock Point
  • Yankee Rowe
  • Rancho Seco
  • La Crosse
  • Zion
  • Humboldt Bay

Page2of7 Re s pon se to Clarification Questions on Fort Calhoun Station Final Status Surve y Final Report, Phase I RAI Responses

There were no RAls during the FCS L TP submittal process regarding the use of 1.38 for the index of sensitivity.

The FCS SER in Section 3.D states that:

OPPO may make changes to the L TP without prior approval provided the proposed changes do not meet any of the following criteria:

(e) increases the dose concentration guideline limits (OCGLs) and related minimum detectable concentrations (MOCs) (for both scan and fixed measurement methods),

FCS 's interpretation of this statement is that using an index of sensitivity of 2.32 would increase the scan MDCs and would therefore require an L TP revision.

FCS acknowledges that the NRC staff have noted that significant training is needed to ensure appropriate surveyor techniques and an appropriate sensitivity to elevations in count rate are necessary to ensure the value of 1.38 is appropriate. In response to this concern, FCS has increased management oversight to ensure appropriate survey techniques are being used dur ing the performance of FSS.

B) Response (2) states that a TSO specifically for the Ludlum 44-20 is in preparation. What additional information not currently in the RA/ response will be included in the 44-20 TSO? When would this TSO be submitted for review?

FCS Response:

The Ludlum 44-20 TSO will include the ERC value from MicroShield calculations for the L TP Table 5-3 mixture fraction. Also, a priori scan MDC calculations will be included using this ERC value for various background values.

A section documenting that the ERC values used in the Phase 1 SURRs were conservative will also be included.

The TSO will be submitted to the NRC by November 7, 2024.

RAl-01-06

A) Response (a) states that if no samples were taken in an SU, relative shift was calculated using general survey area characterization data. If samples were taken in a specific SU during this characterization, that subset of samples was used to calculate relative shift.

1) While Table 3-1 of the various SURRs reflectthis (or appear to), the calculated relative shift for those SUs using Survey Area data versus those SUs using Survey Unit Specific data are the same. Explain why this is?

Page 3 of 7 Response to Clarification Questions on Fort Calhoun Station Final Status Survey Fina l Report, Phase 1 RAI Responses

FCS Response:

Human errors exist within the SURRs for the reporting of data in the Table 3-1 s and the relative shift calculations. FCS offers the following table to clarify the relative shift issues. It should be noted that all calculated relative shifts using co rrect data were above three, and therefore adjusted to three for the determination of N for the Sign test, which is consistent with all the SURRs.

Page4of7 Response to Clarificatio n Questions on Fort Calhoun Station Fi na l Status Survey Final Report, Phase I RAI Responses

Survey Unlt j SUv. s.Area Table 3-i # of Samples SURRLBQR SURRSlg:ma SURR Relatrve Shilt Acluall.BOR Actual Sigma Ac:tual Re:.t.ative Shi.ft Random Judgment *at RandomSampOO as Judgmental Sample h Actuano t al I of Samples

8101 -* 82 0.0716 0.0360 25.8 0.0716 0.0360 25..8 A~ ~ Arl(e.:cept All 14.16. 18.31.33.37.39) 75

8102,.,.. 82 0.0716 0.0360 25.8 0.0716 0.0360 25.8 ~ "" >J:t(eAcept 75

14. 16.ta,3-1,33,31.~. All 81 0:l S1J 7 0. 0717 0.0360 25.8 0. 0~ 0.0319 28.9 3
  • 11.25. 28 -43. 44. 45. 46 7 8104 SU 10 0.0717 0.0360 25.8 o.orn; 0.0249 37.0 6
  • 3.. 21. 27. 30. 35. 38 62. 63. 64, 65 10 8106 SU 15 0.0717 0.0360 25.8 fi.0832 0.04:JG 21.0 6 9 rn. 1s. 17. 24. 29.
  • 1 52. 53, S*. 55. 56. 5&. 59. 60.61 15

8106 SU 22 0.07117 0.0549 16.8 0.07113 0.0359 25.7 10 12 l, 6. 6. 8, 9, 12,20, Zl, 40, *a. *9. 50, 5 !, 66. 67. 68. 22 42 69, 70, 71, 72, 73 8109 S!J 16 0. 0717 0. 0360 25.8 0.0504 0.0278 34.2 6 10 4, 10. lll. 26. 34, 36 47, 57, 74, ?S. 76. 77. ?S, 79.80,81 16

8110 SU 7 0.0716 0.0360 25.8 0.0436 0.0145 66.0 7 0 "'* 16, 18, 31, 33, 37, 39 NIA 7 8202 SU 8 0.0592 0.0345 27.3 0.0590 0.0;>60 36.2 *

  • 13, 14, t9.26 29, 30. 31. 32 8 820:l SU 8 o.osai 0. 0345 27.3 0.0736 0.0363 25.5 5 6 s. 8, 16, 23, 24 33. 34, 35. 36. 41, 42 11 15, lSA_ 26JJ, 42A. 43, 44, 8305 SU 16 0.0671 0.0406.23.0 0. 0664 0.0327 2 8.6
  • 15 l.S, 26, 32. 42 45,47.49. 5 1.61,62. 79. 19 80,81 8307 """' 9 3 0.0671 0.0406 2:l.O 0.069<) 0.0417 22. 3 All All All All 93

Page5of7

2) Note that sample statistics and relative shift were calculated using both random +

judgmental samples... should be calculated using just random samples.

FCS Response:

Both random and judgmental samples collected during characterization of the Phase 1 SUs are representative of residual radioactivity present in the SUs during FSS.

B) Response (b) states the licensee plans to provide a description of the survey unit specific relative shifts and the characterization samples used for the calculation of the relative shifts in a revision to the SURR. Additionally, Eu-152 data will be added to Table 3-1, to facilitate the reproducibility of the relative shift from the data contained within each SURR.

1) When do you expect to submit an updated version of the SURR with this data? If a significant delay is ex pected, in the interim, please provide a spreadsheet containing the results of the samples used to calculate the summary statistics in Table 3-1 for survey units 8101, 8106, 8202, and 8305 similar to that included in Table 2-48 of the L TP. Alternatively, for 8101, 8202, and 8305 point to the specific data in Chapter 2 of the L TP used fo r these calculat ions.

FCS Response:

The relative shift table above provides recalculated relative shifts and the sample numbers from characterization that were used in the calculations.

The revised SURRs will be submitted to the NRC by November 7, 2024.

C) Response (c) acknowledges that the LBGR is set as the mean of the characterization data set expressed as an SOF and the standard deviation as the weighted standard deviation of the characterization data set.

1) While 8101, 8103, 8104, 8105, 8109, and 8110 used different data sets with differing means and standard deviations, Equation 5-1 for these survey units applies the same mean and standard deviation. A similar situation occurs with 8202 and 8203, and 8305 and 8307. Differing data sets should not yield identical values. Please explain why this is the case.

FCS Response:

The response to A)1) under RAl-01-06 above, along with the relative shift table above, provides the necessary clarifications regarding errors in reporting relative shift.

Page6of7 The staff also notes that the licensee proposes the following revisions to the Phase I SURRs.

a. Addition of instrument and /SOCS MOCs directly comparable to the DCGLs.

b. Addition of onsite and offsite laboratory sensitivities.
c. Inclusion of a statement on how the /SOCS was applied in open land area surveys.
d. Modification of the SOF to remove /SOCS measurements.

e. Addition of the descriptions of the survey unit specific unit specific relative shifts and the characterization samples used for the calculation.

f. Addition of Eu-152 data to Table 3-1, to facilitate the reproducibility of the relative shift.

g. Figures will be provided in the SURRs to accurately display all scan areas and the location of random samples within each unit.

h. Clarity and consistency will be provided for scan area designations in Table 7-1 of the SURRs.
i. Correction of inconsistencies in the maximum OpSOF between the executive summary and Table 7-4 for Survey Units 8103 and 8109.
j. Correction of background measurement heights for the Nat detector for Survey Units 8103 and 8106.

Will these revisions be submitted with the SURR update?

FCS Response:

The list above is accurate in reflecting what FCS intends to revise within the SURRs.

Page 7 of 7

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