ML19263A668
| ML19263A668 | |
| Person / Time | |
|---|---|
| Site: | 07109215 |
| Issue date: | 09/04/2019 |
| From: | Ransohoff B Neutron Products |
| To: | Allen C Office of Nuclear Material Safety and Safeguards |
| References | |
| EPID L-2017-LLA-0133 | |
| Download: ML19263A668 (8) | |
Text
Document Control Desk Director Division of Spent Fuel Management.
Office of Nuclear Material Safety and Safeguards-US Nuclear Regulatory Commission Washington, D.C. 20555-0001 Mr. Chris Allen
-
- Project Manager
- Spent Fuel Licensing Branch ** : *,
Division of Spent Fuel*Managem*ent -
Office of Nu.dear Materl_pl Safety and Safeguards I
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neuTROn PRODUCTS,nc 22301 Mt. Ephraim Road, R 0. Box 68 Dickerson~ Maryland 20842
- USA 301-349-5001 FAX* 301-349-2433 e-mail: neutronprod@erols.com 4 September 2019 Re:
Clarification Teleconfer:en'"ce of 8/9/2019 regarding:second RAI Supplemental _
Information Docket.No. 71-9215
-EPID No. L.:2017-LLA~0133 -
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D_ear Mr. Allen, As we discussed by telephon_e on 9 August 2019, I am writing to provide additional information.
The principal technical questipn which was raised by NRC staff concerned the composition of material_s for the shie_ld plugs to be used in 'the various configurations contemplated in our
- Supplemental Response to the Second RAI dated 26 July 2019..
There w_a.s also a _discussion regarding the basic app'roach to the additic°n.al conditions to be added to the Certificate of Compliance for the USA/9215 package._
Technical Consideration~ *
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The discu_ssioh of the July-26 resp'onse centered around the-evaluation ofthe maxi_mum source length which*could be-shipped for a source containing the maximum activity authorized by the
- c.ertificate.. *For this evaluation, the shielding material used was tungsten alloy. Because the
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Mr. Chris Allen 4 September 2019 Page 2 certificate also authorizes the use of lead and steel for shielding, NRC staff questioned whether or not any material otherthan tungsten alloy could be used for shielding in these corifigu rations.
Figure 1 shows the -5 Drum Assembly with the proposed 9.625" long 15,000 Ci cobalt 60 source. As discussed in previous correspondence, for sources of this geometry, the highest dose rates generally occur around the steel end cap flange, either atlhe junction of the flange and the outer spherical shell, or atthe corner of the endcap just inside of the bolt.circle for the cap screws.
The shielding path shown in Figure 1 is to the endcap corner, which is the most conservative location for the purposes of this discussion. As can be seen from the, drawing, the shielding path intersects the thr?ugh hole wall at a point which is 7.54" from the through hole center.
This translates to a distance which is 3.27" from the endcap.
It is instructive to evaluate the shielding consequences of using a steel shield plug for the outside 3.27", *to see if doing so would shift the highest.package dose rates from the normal location of around the steel flange to a new location in the center of the end cap itself.
Using the same methods as described in previous correspondence, we find:
Flange Endcap Cask contact Dose rate (mR/hr) 6200
- 4000 OP contact dose rate (mR/hr) 330 250 Tl 31 The highest package dose rate would remain in t_he same location, even if a steel shield plug were used a's contemplated above. From this, we conclude tha.t the proposed use of steel (or lead) in this manner would not compromise compliance with 10 CFR 7L47. In_ order to be conservative, we suggest that the use.of material other than tungsten alloy for maximum package loadings such as this be limited to a length of 2" (as opposed to 3.27" evaluated above), at the outside end of the through hole.
Figure 2 depicts the same arrangement for the -4 Drum Assembly. In this case, the steel shield plug would begin at.a distance of 8.36" from the center of the through hole, so that it could be up to 2.46" in length.
The-4 drum assembly from drawing 240122 is authorized for activities.up to 9,SOOCi of cobait-
- 60. Perforn;:iing a *similar series of calculations on an 11.625" source in that drum assembly yields the following results:
neuTROn PRODUCTS inc
Mr. Chris Allen 4 September 2019 Page 3 Flange Endcap Cask contact Dose rate (mR/hr) 16,000 6,000 OP contact dose rate (mR/hr) 730 300 Tl 65 28 Again, this-demonstrates that the use of steel for _shielding in this manner would not compromise compliance with 10 CFR 71.47. Limiting the length of steel'to be used to 2" (as opposed to 2.46" used in the evaluation) for this configuration would also be conservative.
Figure 3 shows the same arrangement for the -2. square drum configuration.
The - 2 drum assembly from drawing 240122 is authorized for activities up to 6,000 Ciof cobalt-
- 60. Because sources shipped using the square drum are sometimes shipped radially offset, calculations were performed using both the radially offset *configuration and the radially
- centered configuration. From Figure 3, the maximum length steel plug which would not result in a reduction of shielding for the path shown is 2.24" for a radially centered source, and 1.8" for atypical configuration for a radially:offset source. Performing a similar series of *.
. calculations on an il.625" source axially centered in that drum assembly yields the following results:
- Cask contact OP contact Tl Dose rate (mR/hr) dose rate (mR/hr).
Flange 11,000 500 45 Endcap (2.24" steel) 2,600 130 13
-Endcap ~1.8" steel) 1,300 63 6
These calculations demonstrate that steel shield plugs of appropriate length and placement could be used in the -2 Drum Assen:,bly without affecting compliance with 10 CFR 71.47 for packages containing the maximum activity authorized by the current certificate.
As with the other tw*o Drum Assemblies, we propose limiting the use of steel shield plugs to 2" at the outside_ end of the through hole. In justifying this, there is a relatively minor matter which needs to be addressed*. If a 2" steel plug is used with a radially offset source, there will be a slight increase in the amount of steel (and corresponding decrease in the amount of.
tungsten alloy) in the path depi_cted in Figure 3. Using the same method*for calculation, the
- dose rates at the flange corner depicted in Figure 3 would be:
neLJTROn PRODUCTS inc
Mr. Chris Allen 4 September 2019 Page 4 All tungsten plugs u*sing 2" steel plug Cask contact Dose rate (mR/hr) 2,000 2,700 OP contact dose rate (mR/hr) 98 130 Tl 9
12 This represents a minor change, and does not affect compliance with 10 CFR 71.47 (other than to make it an exclusive use shipment), particularly in view of the fact that it would already be an exclusive use shipment because the highest dose rate point on the cask for this configuration would actually be the junction of the flange and the shell, and would not be affected at all by the use of-the steel plug. The dose rates in that location would be:
Using tungsten plugs Using 2" steel plug
. Cask contact Dose rate (mR/hr) 4,800_
-4,800 OP contc!ct dose ra'te (mR/hr) 250 250 Tl 23 23 From the above, we conclude that the use of 211 of shielding material other than tungsten alloy should be authorized for all Drum Assemblies, provided that rnaterial is used at the ends ofthe thr*ough holes.
Exception _
In our July 26 l~tter, We also discussed the shipment of very long, lower activity cesium-137 source assemblies (up to 4,000 Ci. per source as opposed to the certificate limit of 20,600 Ci).
_ We proposed reducing the required axial shield plug length to 1 inch for that configuration. For those calculations, a 1 inch tungsten alloy shield plug was used, and we do not take issue w\\th requiring the materials of construction for that configuration to be limited to tungsten alloy.
Basic Approach to Certificate Amendment During the August 9 teleconference, NRCstaff indicated thatthe modified language would not
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- specify a maximum source. length but would 1 instead, specify a minimum length of shielding material. We agree with this *approach. We propose the following language for the -5 Drum
- Assembly:
- For p_ackage loadings in which the maximum activity is contained in a single through hole, at least 6" of axial shielding is required on each side ofthe source.
- Of that_ 6", the 4" dosest to the source on each side shall be tungsten alloy. The
neLJTAo*n. PRODUCTS inc
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Mr: Chris Allen 4 September 2019 Page 5 For package loadings less than the maximum permissible activity, required axial*
shielding shall be evaluated in accordance with prior experience and Procedure R-.2014G.
And for the -2 and -4 Drum Assemblies:
For package loadings -in which_ the maximum activity is contained in a single through hole, at least 5" of axial shielding is required on each side-of the source.
Of that 5", the 3" closest to the source on each side shall be tungsten alloy. The 2" closest to.the endcap on each side shall be steel, lead or tungsten alloy.
- . For package loadings less than the maximum permissible activity, required axial shielding_ shall be evaluated in accordance with prior experience and Procedure R-2014G.
If NRC agrees with this basic approach, we will modify R-2014G in accordance with the draft language presented in our letter of 5 April 2019, as informed by NRC review. *
- Closing
- 1 believe this response fully addresses the issues raised in our August 9 teleconference. If you believe otherwise, or if you ~ave additlonal questions or concerns, please advise accordingly.
Neutro*n Products, Inc.
- President
- neLJTROn PRODUCTS inc.
2.560" drawer with 9.625" long source and 6-in plug
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