ML24255A842
| ML24255A842 | |
| Person / Time | |
|---|---|
| Site: | 07109975 |
| Issue date: | 09/16/2014 |
| From: | Office of Nuclear Material Safety and Safeguards |
| To: | |
| Shared Package | |
| ML24255A837 | List: |
| References | |
| Download: ML24255A842 (1) | |
Text
Comment Number Comment
Response
6.1 Provide additional justification for the determination of maximum reactivity for a single package.
The revised criticality analysis includes a single package analysis. However, the method to determine the maximum reactivity stops when the calculated keff
+2 reaches a local maximum, even though the average keff value is higher in the latter case (9 L water added). This conclusion results from a larger uncertainty in the previous calculation (8 L water added).
This phenomenon was not observed in any of the prior cases analyzed in Table Nos. 6.19, 6.20, and 6.21 of the application. The cases presented in Table Nos. 6.19 and 6.22 stop when 9 L of water are added to the Pu oxide volume. Considering the aluminum base occupies about 0.473 L, this is still about 0.227 L short of filling the SCV, even though the analysis is described as filling the SCV until it is full, as shown in Section Nos. 6.4.2.1 and 6.3.1.1 of the application.
Staff cannot reproduce the results presented in the application.
This information is required by the staff to determine compliance with 10 CFR 71.55.
At the time of the analysis, the addition of 9 L of water was judged to be conservative because the usable volume of the SCV is approximately 8.2 L (see tables below) assuming the stainless steel (SS) of the PCV remains.
Unfortunately, this detail was not provided with the submittal.
The SCALE code, a statistical modeling code, produces an uncertainty varying with the length of execution time.
Differences in the results may also vary depending on the platform (computer) that is being used. Another potential difference is the version of the installed code. Finally, another difference could be the starting random number. The results of the 8 L and 9 L cases are not statistically different.
6.2 Verify that the model represents the description in the text of the application.
The SCV flooding model still appears to retain the void space and skirt below the PCV in the application, as shown in Figure 6.3 and Appendix 6.1, Unit 6 in the sample input on pages 81-85.
With an oxide density of 10.8921 g/cm3, as provided in Table 6.1, staff calculates the corresponding volume occupied by 5 kg of Pu oxide to be 0.4591 L. Using the SCV dimensions in Table 6.4, the internal SCV height, modeled as a right, circular cylinder, is 54.508 cm.
With an internal radius of 7.703 cm, the total SCV internal volume is calculated to be 10.16 L. However, the volume of the Pu-oxide plus the water plus the aluminum spacer would then be 9.932 L, which is short of filling the cavity.
This information is required by the staff to determine compliance with 10 CFR 71.55 and 71.59.
The not-included-volume (volume of the void space and skirt below the PCV) was judged not to be a significant contributor to the neutron multiplication of the system as evaluated, as compared to assuming the PCV SS was completely absent.
The SAR Chapter 6 will be revised to incorporate a more realistic physical model that includes the material and dimensions of the PCV.
Based on a more realistic model (adding the PCV steel - but not the convenience can and/or the 3013 materials of construction), the resulting neutron multiplication is lower than the previous model (SCV without the PCV). In addition, the maximum usable volumes (using the volumes occupied by the non-stainless material inside the SCV and PCV) were used. Further conservatism was also introduced since the modeled SCV and PCV have flat bottoms which adds additional volume and therefore, potential moderation versus the ellipsoidal shape of each.
The parameters in Tables 1 and 2 represent a more realistic model with the SCV containing the PCV, with fissile solution filling the free volume of the SCV and PCV.
Neutron multiplication values will be provided in the application.
Table 1: Content Parameters 239Pu mass 4400.0 g PuO2 mass 4989.0 g Volume PuO2 + 0.5 wt.% moisture 4.603E+02 cc Volume water added 7.793E+03 cc Total Usable Volume 8.254E+03 cc Mixture Density 1.5491 g/cc Table 2: Geometric Regions Radius 1, cm Radius 2, cm Height, cm Volume, cc SCV SCV internal volume 7.703 54.512 1.016E+04 PCV PCV containment nut 3.174 1.270 4.019E+01 PCV containment top 7.445 3.505 6.103E+02 PCV cylinder 7.065 6.410 40.950 1.135E+03 PCV bottom 7.065 0.655 1.027E+02 PCV feet 5.715 5.113 0.940 1.925E+01 PCV steel volume 1.908E+03 SCV and PCV usable volume 8.254E+03 Note: Data in this table are reported as four digits. Calculations included all significant digits.