ML20195J266
| ML20195J266 | |
| Person / Time | |
|---|---|
| Issue date: | 11/18/1988 |
| From: | Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Lacker D TEXAS, STATE OF |
| References | |
| REF-WM-43 NUDOCS 8812010412 | |
| Download: ML20195J266 (3) | |
Text
.
UNITO STATES Eaeog p g NUCLEAR REGULATORY COMMISSION
$ REol0N IV
\*****[,E URANIUM RECOVERY FIELD OFFICE DENVER. L DO 90225 NOV I 8 1988 URFO:ROG Docket No. WM-43 040WM043190E Mr. David K. Lacker, Chief Bureau of Radiation Control Texas Department of Health 1100 West 49th Street Austin, Texas 78756
Dear Mr. Lacker:
We have reviewed your letter dated October 13, 1988, in which you requested approval of the 5:1 embankment slopes proposed by Conoco for the Conquista tailings project.
As you know,10 CFR Part 40, Appendix A, Criterion 6, requires reasonable assurance of control of radiological hazards for a period of 1,000 years to the extent reasonably achievable, and, in any case, for at least 200 years. We generally interpret this that not only will radon-222 releases be limited to an average release rate of 20 pCi/m2sec, but also that tailings will not be exposed or transported offsite during the design life of the project. There is, however, no specified embankment slope. Accordingly, our review of your letter and its enclosures focused on the factors that could cause unacceptable erosion, since this is probably the most important factor affecting long-term stability of the mill tailings pile.
During the design period, the pile top will change due to many factors such as differential settlement, wind erosion and random flow processes. Recent studies performed for NRC, have indicated that areas of flow concentration will develop randomly even on the most carefully placed and compacted slopes. Such flow concentrations can result in the formation of rills and gullies which can threaten the erosional stability of a reclaimed pile.
Gully erosion is cumulative and progressive. Over a long period of time, the cumulative effect of smaller, more frequent flood events may exceed the effects of larger, less frequent events. Conoco considered gullying and estimated velocities using a flow concentration of 3. This evaluation indicated that velocities on the embanianent outslopes would exceed 9 feet per second (fps).
For the pile top, velocities would exceed 5 fps. The velocities in the surrounding channels would be as high as 9.5 fps. These velocities are high enough to potentially cause erosion and affect the stability of the reclaimed pile over a long period of time.
Conoco estimated a maximum permissible velocity of 7 fps for the pile top and 6 fps for the 5:1 embankment slopes. It should be pointed out that these GG12010412 GG111e 0$
10/ 1 8 1988 2
permist.Me velocities are for channels lined with uniform strands of well-mai,s.ained bermuda grass. Since active maintenance cannot be assured for a 1000 year period, it is likely that permissible velocities will be significantly lower than estimated by Conoco.
Since estimated velocities exceed the maximum permissible values, Conoco acknowledged that some gullying could occur, but concluded that the gullying should not affect the stability of the embankment or cause release of tailings.
Conoco also stated that some maintenance of the cover will be required.
Criteria 1 and 12 in Appendix A of 10 CFR Part 40, state that tailings should be disposed of such that ongoing maintenance is not required. Since the Cenoco design requires maintenance, it would not meet the requirements of Appendix A.
Before NRC could concur in your approval of the proposed embankment outslopes, Conoco would have to document that designing for 1000 years without active maintenance is clearly not practicable. This could be done by demonstrating that the cost of implementing such a design is clearly excessive. Once this has been established, Conoco should show that the plan will provide for isolation of the tailings for a minimum of 200 years. This can be done by providing evidence to show that the proposed grass cover will be self-sustaining over a long period of time. In addition, a geomorphic survey of the area should be conducted to evaluate slopes, drainage areas and gully depths which occur naturally in the vicinity of the site. Such an evaluation can be used to assess the ability of the proposed 5:1 slopes to survive over long periods of time, based on actual performance and natural occurrences in the field.
In summary, we conclude that the expected flow velocities will result in erosion which, over time. may result in exposure of tailings. In addition, consideration should be given to evaluating more frequent type events that also cause gully formation. Therefore, the licensee should modify the proposed plan to accommodate (or reduce) the excessive flow velocities.
Alternately, the licensee should demonstrate that any such modifications to the proposed plan would be clearly excessive and the proposed plan will clearly meet the minimum requirement of controlling radiological hazards for 200 years.
We hope these comments will allow you to successfully complete your review of the proposed plan. Other than the above, we did not note any "fatal flaws" in the proposed plan. We did not, however, review the entire package in great detail.
Since ely,
/^ Edw . Hawki , Chief Licensing Branch 1 Uranium Recovery Field Of fice Region IV
.- .b.
W-43/190E/ROG/88/11/16/L Case Closed DISTRIBUTION.
Docket File W-43 cPOR/DCS
RBangart, RIV LLO Branch, LLWM .
URF0 r/f DJoc.4b 3
CONCURRENCE: DATE:
EHawkins/URF0 [gg N//// TT RGorizales/URF0 h ///Ar[#f 9Jacoby/URF0 Imv M/ //////([
'