ML20245C529
| ML20245C529 | |
| Person / Time | |
|---|---|
| Issue date: | 10/16/1987 |
| From: | Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Dantonio J ENERGY, DEPT. OF |
| References | |
| REF-WM-63 NUDOCS 8711030198 | |
| Download: ML20245C529 (3) | |
Text
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o DISTRIBUTION Docket File WM-63 J
ePDR/DCS s
RGonzales
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WM-63/ROG/87/10/08/0 SGrace i
' LLW Branch, WMLU URF0 r/f ET l 6198T URF0: ROG Docket No. WM-63 040WM063601E Mr. John R. D' Antonio Operations Group Leader U.S.-Department.of Energy
. Albuquerque Operations Office P.O. Box 5400 Albuquerque, New Mexico 87115
Dear Mr. D' Antonio:
In a letter dated July 31, 1987, you requested that we review a report titled, " Evaluation of Rock for Riprap at Mexican Hat, Utah." We have completed our review of your submittal, and our comments are enclosed for your consideration.
In summary, you have not provided sufficient information to justify the use of the proposed Alhambra limestone or the oversizing methodology.
Additionally, you have not provided adequate basis for the conclusions on the other two rock sources which appear to contain better quality rock.
You conclude that the first of these sources contains gravels that are too small, and the second is too far to be economically feasible.
You should justify that the rock from the first source is too small by comparing it to the riprap size required for the top and outslopes of the pile.
In addition, if it is not economically feasible to obtain rock from the second, you should provide additional information to justify that costs are clearly excessive.
A procedure for doing this is 1
suggested in Reference No. 5 mentioned in Appendix 8 of your riprap report.
If you have questions, please contact Ray Gonzales of my staff at FTS 776-2818.
Sincerely,l Is B711030198 871016 Edward F. Hawkins, Chief PDR WASTE PDR Licensing Branch 1 i
WM-63 Uranium Recovery Field Office Region IV
Enclosure:
As stated OFC :
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l NRC REVIEW COMMENTS ON EVALUATION OF ROCK FOR RIPRAP AT THE MEXICAN HAT DISPOSAL SITE UMTRA PROJECT MEXICAN HAT, UTAH l
1.
The rock you proposed to use for erosion protection, does not meet the criteria for good quality rock.
However, you conclude that with appropriate oversizing, the rock can be used in occasionally saturated areas but not in frequently saturated areas.
The oversizing methodology you propose to use is the same as that used at the Lakeview site.
Although the NRC staff agreed to the use of marginal quality rock at Lakeview, that decision was site specific and the oversizing methodology was meant to apply only to Pepperling quarry rock at Lakeview. It was not intended to apply to all UMTRA projects.
Therefore, if an oversizing methodology is necessary at l
Mexican Hat, it should be developed specifically for that site.
In developing that methodology, you may want to consider additional and/or different durability tests, changes to the scoring methodology or changes to the oversizing factor.
2.
You state that because the Mexican Hat site is located in a semiarid desert climate and the slopes of the ditches provide adequate drainage, all of the areas requiring riprap can be considered as occasionally saturated.
Consequently the rock durability can be less than required for frequently saturated areas.
It is the NRC staff's position that aprons, natural channels and man-made diversions must be considered to be frequently saturated areas even if they are located in desert climates and are well drained.
Therefore, the rock you propose to use is not acceptable for use in diversion ditches without further justification.
3.
Oversizing marginal quality riprap by using the weight of the Dso stone as you propose, appears to be a more reasonable approach than oversizing by using the diameter of the stone.
The problem however, is that at the present time, there is no accepted procedure for oversizing using weight.
The oversizing procedure in NUREG/CR 4620 is based on rock diameter and thus is not applicable for oversizing by weight as you have proposed.
Using the procedure from the NUREG, you calculated an oversizing factor of 53 percent.
This means that the diameter of the Dso stone should be multiplied by 1.53 to obtain the oversized Dso.
You propose to increase weight instead of diameter by 53 percent.
This results in an increase in the Dso diameter of only 15 percent, because weight is proportional to the diameter cubed.
The purpose of oversizing marginal quality riprap using weight instead of diameter is so that the smaller rock is oversized by a proportionally greater amount than the larger rock to allow the smaller rock to resist weathering for a 1000 (but at least 200) year
i 2
l design life.
Oversizing by weight is not intended to allow an overall smaller increase in rock size simply to accommodate the use of the maximum rock size available, which you state is 12 inches.
Therefore, oversizing by 15 percent instead of 53 percent is not acceptable unless you can demonstrate that the rock will provide the erosien protection necessary to ensure stability of the reclaimed tailings pile for 1000 years, but at least 200 years.
4.
You identified two sources of rock that appear to be more durable than the rock you propose to use as a source of riprap.
One of these which you identify as the El Capitan source, is located about 40 miles from the Mexican Hat site and the other, identified as the Bluff Holiday Pit, is about 26 miles from the site.
You state that the El Capitan source is considered too distant to be economically feasible and the Bluff Holiday Pit contains gravels which are not of sufficient size to meet design requirements.
Of the total volume of riprap required, only about 8 percent will be used in areas where larger, more durable rock is required.
You should therefore provide additional information to show that the cost of providing 8 percent of the rock from the El Capitan source is clearly excessive.
5.
You have not provided any information on the size and gradation of the rock available at the Bluff Holiday Pit, except to say that it I
is too small to meet design requirements.
The riprap proposed for j
the pile top, which you oversized by weight using a factor of
]
15 percent, is small rock having a Dso of 2.0 inches and a 0 10o of i
3.4 inches.
For the pile outslopes, the riprap is a little larger, having a Dso of 4.3 inches and a D of 7.3 inches.
Even if the 100 riprap was to be oversized by diameter instead of by weight, using a factor of 53 percent, the required rock would still be relatively small.
You should therefore provide additional information to justify that the rock from the Bluff Holiday Pit is smaller than required for the top and outslopes of the reclaimed pile.
If it is of sufficient size, but it is not economically feasible to obtain rock from this source, then the costs of obtaining this rock should be discussed and shown to be clearly excessive.
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