ML20126L775
| ML20126L775 | |
| Person / Time | |
|---|---|
| Issue date: | 11/30/1984 |
| From: | NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| Shared Package | |
| ML20126L767 | List: |
| References | |
| REF-WM-39, TASK-RE, TASK-WM-401-4 NUDOCS 8508010021 | |
| Download: ML20126L775 (29) | |
Text
{{#Wiki_filter:.- , - -- . ._- .- , - .-. - , - - . . - _ - _ _
- , g .e ,y -
u.s. nut,LcMM MttULAlUKf 1.UITilbb1VN *
^*
g.{ , g 8 0FFICE OF NUCLEAR REGULATORY RESEARCH , November 1984 ! r Division 3
/
ORAFT REGULATORY GUIDE AtlD VALUE/ IMPACT STATEMENT Task WM 401-4
~
***** ' ~
Contact:
J. Stewart (301) 427-4609
. AA PS q# m;~-'
DESIGN OF LONG-TERM EROSION-PROTECTION COVERS 6kT Vaftr i- FOR RECLAMATION OF URANIUM MILL SITES RECEWED . )ECO
; QUL- 9 1985 A. INTRODUCTION UMTBA S.E Urani m mill licensees are required by paragraph 20.1(c) of 10 CFR Part 20,
" Standards for Protection Against Radiation," to make every reasonable effort
) to maintain radiation exposures and. releases of radioactive materials in efflu- - '
! ents to unrestricted areas as low as is reasonably achievable. Additional cri-l teria and standards for environmental protection may be found in the Uranium j
Mill Tailings Radiation Control Act (UMTRCA) of 1978 (PL 95-604) and in 5 20.106, f "Radioactiv'ity in Effluents to Unrestricted Areas," of 10 CFR Part 20. Recently, the Environmental Protection Agency (EPA) established standards (40 CFR Part 192) for the disposal of uranium mill tailings for both inactive (Title I) sites and active (Title II) sites. These standards establish the criteria to be met in providing long-term stabilization.
! To help operators meet Federal guidelines, this regulatory guide describes design practices the NRC staff has found acceptable for providing long-term protection against erosion of stabilized uranium mill tailings. This guide focuses principally on the design of rock and vegetative covers to provide the
, necessary long-term protection.
l Any guidance in this document related to information collection activities
- has been cleared under OMB Clearance No. 3150-0014.
~
lDR50eo002g850716
*M PDR This regulatory guide and the associated value/imoset statement are being issued in draft form to involve i
the public la the early stages of the develocuent of a regulatory positten in this crea. They have not received complete staff review and de not represent an of ficial MRC staf f position. 1 ,7 Public comments are being solicited on both drafts, the guide (Including any isolementation schedule) and the value/ impact statement. Comments on the value/ impact statement should be accomeanted ny suooortino 1 data. Comments on both draf ts should be sent to the Secretary of the Commission. U.S. Nuclear Regulatory , Commission, washington. 0.C. 20555. Attention: Docketing and Service Branch, ey . . Aeovests for single cooles of draf t guides (weich may be reoroduced) or for placement on an sutoestic cistribution list for single cooles of future draft guides in specific divis6ons should be made in writing to the U.S. Nuclear Regulatory Commission. Washington, 3.C. 20555. Attention: Cir=ctor, i Otvision of Tecnnical Information and Document Control.
. __- _i_ 7 '
Z~~" ~
1_. _ _. _ _ . . . , _ _ _ , _ _ _ _ , -
1 MG'T})e, censefHentel ch ldhMf& lH$ 6 nld&tncli'est db lle C t0Non roftchen /o m ud 'Y' A &W it rf(td ll ef Y00 $, Y, Iscuss50 yo,/Co ,; pelabilty efew'*" 4 Because uranium mill tailings and byproduct materials may have potential detrimental effects on public health and safety, these hazardous materials must } be contained in accordance with EPA guidelines (40 CFR Part 192). These regula-l I tions prescribe criteria for long-term reclamation and design of protective ' covers for both inactive (Title I) sites under the UMTRCA program and active (Title II) sites currently licensed by the NRC. 1 The purpose of a protective cover is to prevent wind and water erosion of tailings, prevent biotic intrusion, and ensure the sustained functioning of the f tailings disposal system. How*ever, little information exists on the long-term j performance of such covers. Erosion due to wind and water is difficult to l assess quantitatively, and site-specific factors (such as rock durability) are difficult to factor into any long-term performance evaluation. } Because of design difficulties, the NRC staff has concluded that the goal l of any design for long-term stabilization to meet the EPA criteria should be to provide overall site stability for long time periods with no routine maintenanceN The NRC staff recognizes, however, that such designs may not be practical in some cases and that some monitoring and maintenance will proba61y be needed. i i Several long-term stability investigations (Refs. 1 through 4) have indi- 1 j I cated that the most disruptive natural phenomena affecting long-term tailings stabilization are likely to be wind and water erosion. These studies have i also indicated that wind and water erosion can be mitigated by a rock cover of l reasonable thickness (or a rock and vegetative cover) and that the size of the j rock on the protective cover will normally be controlled by the precipitation ; or flood event. Therefore, the selection of the design flood event assumes j l major importance in the overall reclamation plan. 1 In considering the selection of the flood event on which to base the reclamation plan, the NRC staff hasgied on experience and information reported in a long-term stability investigation (Ref. 1). It has been shown that, to provi e 'a level of risk corresponding to a probability of occurrence of about , the design flood for a period of 200 years wanid mania 9The conseguinar of damap du to mal &neften of de. erosan n pro tecktsn de ndjarlof
*fSee He/o Af def ofPaft. y a no 2 rmfinc. nuintenancs d'es/pt.
. - - . LL.LXX~ - . - - . . . . .- - - - - - - - - - - - - -
z ,,, # l a recurrence interval of about years . Extrapolation of limited m e unce k data bases to this time frame es ery-uncertam.in ome CAMecause the probable maximum flood (PMF) and the probable maximum precipitation (PMP) are based on site-specific physical meteorological limitations that eliminate the uncertainties associated with extensive extrapolation of limited data bases, the staff concludes that it is reasonable and prudent to use these phenomena for the long-term design of reclamation covers. MMv/-/wMe/ 47 4%#ept/f#ct/ p[ exceedQHct In general, proper site selection is needed to minimize the erosive forces producedbyaPMFNHowever,manyexistinguraniummillsitesarepoorlysited; some are located immediately adjacent to large, swiftly flowing streams with a h'igh potential for extensive erosion. For these existing sites, the PMF forces may be so large that they preclude economical long-term stabilization. In these l cases, the NRC staff has concluded that the design basis iflood event for long-
! term stability considera~tions should still be the PMF. However, if it is deter-mined that implementation of such a design would be impractical, any alternative j -
approach using a flood smaller than the PMF would have to consider increased i i levels of maintenance, repair, and environmental damage. In such cases, the staff may alto consider that certain conservatisms normally prese,nt in the l determination of design basis floods or flood velocities may be adjusted in j favor of more realistic calculations and that such reductions may not signifi-l cantly affect the overall safety and stability of the site. The staff will determine on a case-by-case basis whether there is reasonable assurance that l the site stabilization program, as designed, will be effective for a minimum i of 200 years and thus will meet EPA regulations.7 M I/SfrDcedec /T *##8 Cunierrowe & SIme ce*Mhy thenjw/Wrtcl. The suggested criteria in this guide will apply principally to existing l Title I and Title II sites. For new sites, careful consideration sho'uld be j given to siting and the various factors that must be considered following l reclamation. If it is necessary to provide above grade tailings disposal, j the sites should be located near available sources of rock and in locations where long-term erosion problems are minimal. j A serious threat to stability at any given site is likely to be gully erosion resulting from runoff from intense local precipitation. To ensure long-term stability, it is important to prevent localized erosion and the
- See x de W & WP'/* '* ,
l _. 4.-- ._.
i 7 , formation of rills and gullies. Research performed for the NRC staff (Ref.1) has concluded that if localized erosion and gu11ying occurs, damage to the cover will occur rapidly, probably in a time period shorter than 200 years. Therefore, care must be taken in the design to ensure that flat, vegetated i slopes or rock protection are provided to prevent the initiation of gullies both on the top and the sides of the pile (Ref. 4). t i At the present time, there are no known quantitative methods to determine the rock cover requirements to prevent the initiation of gullies. Because l vegetative covers may not be self-sustaining and effective over long time , i periods (Refs. 1 and 3), especially in the arid Western United States, it has j become necessary to develop a procedure to determine rock cover requirements that will prevent gullying. The NRC staff has developed a method for designing erosionprotectioncoverstopreventthedev{opmentofgullies. This method, illustrated in Appendix A to this guide, is based on staff licensing and review experienceandpertinenthydraulicengineeringprinciples.k$aNv'eNpN * ) , to provide cover design criteria that reflect an appropriate degree of conser-j vatism, taking into consideration the following:
- 1. Some degree of flow concentration will always occur as runoff progresses down an embankment slope; it is unlikely that evenly distributed sheet :
j flow will occur from top to bottom on the slope. The flow concentration 1 could be initiated by differential settlement of the tailings, normal ' ' ! settling of the rock la r, and random flow processes. M S*60tW d '#" '
- ellowe d for~ by over hat n ifreci .rtge y rEtctek. Randomfo reW*rf f/**Qrrerr.n*.7 idhe/Hn wt//
FAfNi cocesin/c N*w kIIefhj- ,
. 2. The flow over the rough rock layer will be turbulent; shear forces will be increased as a result. N Nof necerrdry k affume WMu M.
4 {,
- 3. Shear stresses, especially at the toe to the embankment, may be signifi-cantly increased by energy dissipation processes such as hydraulic jumps.
- It should be recognized that the computational procedures outlined in
- Appendix A were developed in a conservative manner based on staff experience with damage to erosion protection designs during the occurrence of relatively
- minor storm events. Of necessity, this procedure attempts to account for the limited quantitative data base available to document long-term degradation, 4
i 4 Y Yz Y N' l ---.-.- - _. - .._. _ _- - _-
k the known survivability of many rock pro'tected structures, and the questionable
- ability of vegetative covers to be self-sustaining in arid areas.
l
- TheexamplecalculationgiveninAppendixfwasselectedtorepresenta See o'~~tdf ht ATP. A typical reclaimed tailings impoundment. Based on our examination of other mill j
sites and on general rainfall / runoff relationships in other arid areas, it is 4 unlikely that the amount of rock protection required at other similar sites j will be significantly greater than that required at this " typical" site, i l provided runoff from the top of the pile is properly considered. i j , The NRC staff is currently funding efforts in those areas where quantita- > ! tive predictive methods are not available, such as estimation of gully erosion, 1 ! prediction of streambank erosion during major floods, and design of poor quality l t rock protection for longevity. Until such methods are available, it is neces-i s sary to exercise conservatism in the design of protective covers, consistent i with the needs of industry, good engineering judgment, and the health and safety of the public. , s j C. REGULATORY POSITION ; A cover layer for the protection of stabilized uranium mill tailings should l be capable of meeting the long-term stability requirements of 40 CFR Part 192. The criteria outlined below for the design of such protective covers for rec-lanation of tailings impoundments have been found acceptable by the NRC staff. P Some of these design procedures have been developed because of the unavailability of specific documented, quantitative, analytical procedures. I l These criteria are based on NRC staff experience with tailings impoundments ' l and rely extensively on experience and judgment.- If alternative methods are proposed for staff review, they will be considered on a case-by-case basis. l 1. GENERAL INFORMATION SUBMITTALS ! For the cover layer design selected, the engineering data and analyses related to the design and construction of the protective cover should be l provided for NRC staff review. These data include: 5 t
._ .- , e . m v.
_~--w
. ~e i _
7 .y ._ __ _
,p, . . ____. _ _ . _ __ .__ _ . . . __. _ . . ___..___ _ ___ _.. . __ __.
. ~ ,
~ -
a. Drainage areas of principal watercourses- and drainage features.* b. Drainage basin characteristics, including sofis, vegetative cover, local topography, and flood plains.* j c. Maps and aerial photographs showing the impoundment location and the l. upstream drainage areas.* .i d. Information regarding rock that is available, including rock types,
- l
, rock characteristics, rock availability, and rock quality.
- e. Site geomorphological characteristics.
- i f.
Drawings and photographs of impoundg nt features.
- g. Location, depth, and dimensions of tailings.
l h. Physical properties of the-radon suppression cover, tailings embank-f ment, rock cover, and foundation materials, including results of laboratory j and field tests. . !
- i.
Pertinent construction records, including construction control tests. l l construction problems, alterations, modifications, and repairs.-
- j. Principal design assumptions and analyses, including hydrologic, f hydraulic, and stability analyses. '
l j 2. DESIGN OF PROTECTIVE COVERS FOR LOCAL INTENSE PRECIPITATION The slopes of a reclaimed tailings impoundment should be desi,gned to resist the effects of local intense precipitation to prevent sheet erosion and
- Data should be mapped on 7.5-minute U.S. Geological Survey quadrangle maps i (15-minute quadrangles may be used if large-scale maps are not available).
Maps of similar scale may be substituted for U.S. Geological Survey maps if comparable levels of topography and cultural data are maintained. 6 __, - , , , , . . , . - , . - g- , . . . , m._r. , . . _ _ _ _ _ . _ __ ..__,m . ,- __._,, . . - . .__. , . _ , . _ ,-,m. ,n,m-- - - , .,, ,. ._.. . m.,, _ . , , .. .-,
subsequent formation of rills and gullies. In addition, diversion ditches and drainage features located on or near the reclaimed pile s'hould also be protected l ! from such storm events. Where practicable, erosion protection.should be ' { designe'd to resist the effects of precipitation as intense as the PMP.Nfe e- l Seced cm e d n Faye 3. 2.1 Vegetative and Soil Covers ! \ 1 ] Reference 4 provides general guidance on the design of vegetative and i soil covers. Based on the results of several studies (Refs. I and 3), it is ! unlikely that a self-sustaining vegetative cover for long-term erosion protec- l tion can be provided on steep embankment slopes in the arid portions of the
- Western United States. However, self-sustaining vegetation may provide reliable ;
l long-term stabilization in semiarid to humid climates on relatively flat slopes ! (Refs.Iand4).Ynmorearidclimateswhergself-sustainingvegetationis ! marginal (less t an 50 percent vegetative cover), rock cover should be provided
! if practica1N hye.[,n[rt[#/eW / Od / .5/ e/7 !
jforsytm ofsacrdNthl/maforto/ .r *uld h ""'N, # erora on /errfkyJar~ s'f sma//. ' i However, the staff will approve the use of vegetative covers when the f following conditions are met: - 1 4 .
- a. Suitable rock is not locally available and the cost of providing adequate protection to meet 40 CFR Part 192 requirements is excessive.
! b. The velocity produced by a concentration of PMF flows on the face of
- the embankment is less than the erodible velocity of the soils on the embankment '
- slopes or the total soil cover thickness provided is such that, if gullying j occurs and the gully. depth and the gully slopes eventually reach stable levels, i
no tailings have been eroded (see Appendix A for computations and analyses needed to document this conclusion). The latter condition would normally apply only in those cases in which it is not practicable to flatten or protect an l , existing das embankment and the tailings are located a considerable distance 1 ^ from the embankment face. t j ! 1 i l 1 l 7 I, . _ _ _ _ _ . _ _ . ____. - 1 u nn -- r =m - ; n u_ -- . - _ _ __ _ . - _ _ _ - , _ . _ . ___ _ _,
.1
- c. In general, the slopes of the reclaimed impoundment are similar to natural soil slopes currently existing in the site area (see Appendix A). )
If soil types are similar, this should provide a reasonable indication of the l l stable slope for a' given area. 1 l 2.2 Rock Covers i In the arid portions of Western United States, where the survivability ) of a vegetation is marginal, the use of a rock cover is considered by the NRC staff to be the most desirable method for satisfying the long-term stability
! requirements of 40 CFR Part 192. In arid areas where rock is locally available, i
a rock layer should be provided to prevent long-tem erosion due to wind and { surface-water runoff. i i N An acceptable analytical method for determining the stable slope of a
) vegetative cover and designing a rock cover to resist sheet erosion and thus prevent gullying may be found in Appendix A.Mec **'edt ,'* ff A . A.
Reference 3 provides guidance for the design of rock riprap protection , for ---"- diversion ditches. Because the design goal is to provide'long-term l i protection without the need for routine maintenance, appropriate conservatism t should be applied in the selection of various hydrologic input parameters, ] such as Mannings "n" values, factors of safety, times of concentration, and , l rainfall intensities. It should be noted, however, that the design of the l rock cover for an embankment will often be controlled by the velocities
! producedbyaPMFikanearbyriver(seeSectionC.3).
I'
- 3.
DESIGN OF ROCK COVERS TO RESIST FLOODING BY NEARBY STREAMS 1 Theslopesofareciaimedtailingsembankmentshouldbeprotectedfrom l the effects of flooding of nearby watercourses. Where floods impinge on the l embankment slopes with erosive velocities, erosion' protection should be pro-j vided to resist the velocities produced by a PMF.5 I l W Jee seemd med on }?oje 3 - 4 . i j 8
~ ~ ~ -
2 ::~ . T. - - ~ ~ ~ " ' ~ ~
t . Regulatory Guide 1.59, " Design Basis Floods for Nuclear Power Plants," ' provides guidance for the determination of PMF flows. Reference 5 may be used ! to compute water surface profiles and local velocities. Guidance for the
- design of riprap may be found in References 6 and 7.
i In designing the riprap layer to resist local PMF velocities, judgment W ~ must be exercised in selecting an appropriate factor of safety. A safety factor of about 1.5 times the computed shear stress should be use N The use j of less conservative safety factors will be reviewed on a case-by-case basis. The acceptability of such safety factors will depend on other considerations ! such as other conservatisms in the design, the additional cost of applying the l l recommended safety factor, expected turbulence or nonunifom flow, and the physfcal configuration of the reclaimed pile. r
- 4. SELECTION OF THE BEST AVAILABLE ROCK I L
1 .. Investigations should be conducted to identify several sources of available rock within a reasonable distance of the site. The suitability of these rocks as: protective covers should then be assessed by laboratory tests that determine i the physical characteristics of,the rocks. Several tests such as those listed j in Reference 3 should be performed to classify the rock as being of poor, fair, ;
] or good quality and to assess the expected long-term performance of the rock. I j
In those cases in which' rock is required for cover material or gully l protection and only rock of less-than good quality is available, increases in { the average rock size and riprap layer thickness may be necessary. The deter-j mination of such increases will be based largely on engineering judgment and experience taking into consideration the added safety margins and costs asso- L ciated with the increases. ' i. Where rock of good quality is available, the cover design should incor-porate this rock. { Depending on the degree of conservatism provided in the overall design, it is likely that no increase in average riprap size or layer l thickness will be necessary. In general, any increase in thickness of the rock cover layer should be based on the expected performance of the rock in resisting h Sec. Seconel eoe ee f er Ofe 3. ht{ers/loulofde)MdH ffcerk4ker. Ifry
- pre l
W Ss(e{$ud s aa y,.uye <w sc ~~cer**e fy is s a e,'n wealtu inv./,et. aelyt.:r: 4
,. , ., . _,J,' . . ,' ~ ' ' ~ ~ ~ ~' T?? ~ '? . " ~. ~' ~ ..
,_ _, -_.,n. . , _ , , ,
physical and chemical weathering. For a given ri ap ye t ness, the
. average-rock-size-{Dso) in-the. layhr[skouYd be s r"gNas ra[ticable- taking ccU"C fn[ c#onTi$eration, the: ability-of*therlaye~racaeet gradation lisits-
- 5. DESIGN OF COVERS TO RESIST WIND EROSION It has been observed in most areas of the United States, including the arid Western United States, that erosion due to surface-water runoff produces a greater potential for soil loss than does wind erosion. Consequently, if adequate protection is provided for gu ly and concentrated sheet flow erosion, losses by wind erosion will be5Nide"d N e*f! 1). *Sec / arf fenf#nc e M Af X[
ptrajraf A. However, if a protective rock cover is not provided, it will be necessary to estimate wind erosion potential. Refereqce 8 provides a method acceptable to the NRC staff for estimating wind erosion losses. If these losses are significant, it may be necessary to make design changes to reduce the erosion potential. . D. IMPLEMENTATION The purpose of this section is to provide information to applicants regarding the NRC staff's plans for using this regulatory guide. The proposed guide his been released to encourage public participation in its development. Except in those cases in which an applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method to be. described in the active guide reflecting public comments will be used in the evaluation of long-term rec-lamation and protective cover site plans for both Title I and Title II sites submitted after the implementation date to be specified in the active guide. 10
l i APPENDIX A f l SAMPLE CALCULATIONS FOR RIPRAP AND SOIL COVER DESIGNS l - STATEMENT OF PROBLEM i Determine if a vegetative and soil cover can withstand expected sheet e erosion; if not, design a protective riprap layer to resist the expected shear forces. ' l , PROPOSED DESIGN '! XYZ Uranium Co. proposes to provide an unprotected 10-foot-thick soil : t' N } cover over a reclaimed tailings impoundment located in northwestern New Mexico j ) near Farmington. The embankment slopes are 1 Vertical on 5 Norizontal; all j slopes are about 60 feet high and about 300 feet long. The soil cover will
; resist a sheet flow velocity of 4 feef, per second based on the grain size and '
I the cohesive properties of the soil. (See Note 1.) ' ? l Step 1 - Determine Flow Rate -
- i. !
i The soil cover should be designe,d to resist concentrated sheet flow at the embankment toe. For the' purposes of computing the sheet flow velocity, it should be assumed that, because of differential settlement or other phenomena, flow down the embankment slopes will be concentrated in several areas. A flow I concentrationgffourtofivetimesthenormalsheetflowrateshouldbeassumed l L $ uf. ( eNe 2.['N}CE DeJmn freeehret e
- V!!! f " *>f. Ef ock i i Sne a sa Me *ent preven +. yu// L emAwaL~en f M et vies / o V!! -
- buH b enp? tit $e e se(ffw// wo'llh f 0e f*f ser0cott neenirafro
- 1. ompute Drainage Area '
For an assumed 1-foot-wide section, the drainage' area A is computed by ' t A = (300)(1) = 300 ft2 i { l i 11 s.mm.,,. .m we= w s
. - -.y - y - - - , , ---m ,,+-y-y--- - - -
,e-e-,-s,.-,--w
- j
. l l
- 2. Comoute Time of Concentration '
i Assuming that the average sheet flow velocity down the entire length of the slope is equal to of the maximum design velocity of 4 feet per second, the time of concentration tc may be estimated by kgg f[gf. eff'pta/e/ tc = o f ayer/a d FA w 3f=150seeor2.5 min ygfogjff/rdre d*/N//$ However, use tc = 5 min. Suck af (kt S C.S (See Note 3.) gg [,,g} , f ff og,
- 3. Determine PMP and Rainfall Intensity Tf,shri/$r/
f /rer 3.t f//fer. 4 r 20 % f[e/ e m sherfjnts.rpdffure. UsingReference9he1-hourPHPise'stimatedtobeabout8.0 inches. (Other acceptable references for computing the PMP in other areas of the Western United States are listed in Ref. 10 Using Reference 10 (see Note 4), the 5-minute PMP is calculated to be 25 percent of the 1-hour PMP or 5-min PMP = 0.25 x 8 = 2.0 in. Q/Adf
.TfA/N LsCcu r/**/
#'* aM# #'clerbHO*/
usiotj Pe.raya s;f mo'd DJmr f r-The rainfall intensity, i, in inches /hr is therefore es/Thrnkoj free 9thtfloh. 60 Se / c t W o u Y a h l-i = 2 x 3 = 24 inches /hr
- 4. Determine Peak Flow Rate Using the rational formula (Ref. 9) and using a runoff coefficient C of 1.0 because of the high intensity of the rainfall, the peak runoff rate Qg for a 1-foot-wide area is calculated by Qnd grolid[r//,-[7 0[ /1edr/
Q*C'A Sdfantfr/ Mfecec{tosf reif i misf are md? Hon t 91 = (1)(24) 43,5 (fi f / acre 12 _ _, , ,,ee g asWse-ia*- -"*-a
T. . Qg = 0.165 cfs/ft . For a flow concentration factor of 5 Y See Ce ***' d #" [/* !!* , Qg = (5)(0.165) = 0.83 cfs/ft Step 2 - Compute Sheet Flow Velocity for Soil Cover und w*'dt h O PP'*b O ' Using Manning's formula and a *(ap14f4ed-rectanguleMeess-sectien-with+
-width-of-10-feet-(see-Note 4)r q . 1.486 AR 2/3 31/2 dere n
Area = unif wMfb
- A = J0y for a 10= foot-wide r:ctangul:rt .::tien, where N _
y = depth of flow Hydraulic Radius = R 3 y since width is much greater than depth of flow Bottom Slope = S = 1/s = 0:2 Manning's n = 0.025 for a cross section in earth (see Note 6)* g 7,,fg a O.f 3 or $ple (, dhit Discharge = = Me) ) =. Sri ft 3/sec
- 0. 8A= (pfy)(y)2/3 (0.2)1/2 Solving for y, y =0.12h.
Th:r:fe==. A-== = A - (10){0.12) - 1,2--ft L Velocity = V =
=$3/32=6.9ft/sec 13 e ..e,. . . * * , , e gmee-4. gm e es e+-a
.,p 4,%"' '
. t The computed velocity of 6.9 ft/sec is greater than the allowable velocity of 4 ft/sec. Therefore, it must be concluded that the soil cover will be eroded, l l
gullies will form, and,a riprap layer will be required. Step 3 - Design Riprap Layer
- 1. Compute Shear Stress Using Manning's formula with an 'n' value of 0.04 for an assumed rock flow area (see Note 6) and the other parair.eters as above:
0.3 = (10y)g)2/3(0.2) 2 (See Step 2 above.) See ce~eedr
,o .r m i .
y=0.16h. s A = 1.6 ft2 V = 8.3/1.6 = 5.2 ft/sec The shear stress (t) may be computed by* t = YRS - Reference 11 (See Note 7.) t = (62.4)(0.16)(0.2) s'ince R a y I = 2.0 lb/ft2 - 3,e pun / weed u Pp. 9 A safety factor of about 1.5 ould be included in the design (see Note 8). Therefore, the design shear stress is equal to . Y, = (1.5)(2.0) = 3.0 lb/ft2 The Dso riprap size required to resist this shear stress may be computed using page 41 of Reference 7.0For rock with a UEik weight of 165 lb/ft8 , W Wk y not use Sdely Fachrt meflo/ ? 14
- - _ _ ~ . _
r ~'- Allowable t o = (0.04)(165 - 62.4)(Dso) = 4.1 Oso l Required Dso = 3.0/4.1 = 0.7 ft. Therefore, a riprap layer with an pintmamaverage- Dso size of about 8 to 9 inches is needed to protect the face of the embankment. The thickness and gradation of the riprap layer may be determined from Reference 12, depending on the size of rock available. In this case, if a gradation is selected where the layer thickness is equal to 1.5 x Oso. the required layer thickness is approximately 1 foot. Step 4 - Determine Stable (Unaullied) Slope s
- 1. =
Using the quel 4+00iVw!1 remain unrulltra" o ocedures outlin
-( egelM ed) slopefaay b determitted for a given region and the size of , the drainage area.
n allte.r Gn-pec%r{.i, /9
% en& o, hiseT/ts,yes. 7.f y/k Blahs slopf-wdth ra hosarer s f N. E.
tidresullo%) l
- 2. .
for sff er dr/ol. . ng the procedures outlined in Steps 1.and 2 above, a slope tha't limits the velocity to the maximum permissible velocity may be directly calculated. In the example presented above, using the same input parameters to Manning's formula and solving for the slope, the stable slore 5, is S, E 0.04 or about 1V on SH E 0.0+ => l V en 2S ff, he l- L v en 5h'. The above methods may be used to estimate the final stable slope after a long period of time and should represent an upper limit of slope recession and gully potential. In the event that the two estimates vary considerably because of particular soil conditions, regional peculiarities, or lack of data, chang ~ to model input parameters may be necessary to reflect more realistic conditions. 15 _4,,, _gumm%._,a.sw** A---4WO' *
- r. .
General Notes and Considerations on Appendix A Design Procedures 1. References 7 and 11 may be used to estimate maximum permissible velocities of soils.
- 2.
A flow concentration factor of four to five times the normal sheet flow is based on Ifterature reviews and examination of gully and rill patterns (Refs.1 and 13) and provides a conservative representation of the contri-buting drainage area.* If the top of the pile contributes runoff down the slopes, this additional drainage area should be included to determine the , runoff ovei the side slopes. (Modifications to the computation of time of concentration, rainfall intensity, and rainfall distribution may be neces-sary to reflect the runoff contribution fron' the additional drainage area.) WSee Afo/e on 0. //Qu = --).- 3. A time of concentration of 5 minutes when the actual tc is less than 5 minutes was selected for convenience. Using a te of less than 5 minutes would increase rainfall intensity. In addition, the flow velocity down the slope is likely td be greater than 2 ft/sec. These factors may help to balance some of those design assumptions that may be overly conservative. WSee. AMe er f. /1(Rrsf Mir). -
- 4. Use of Reference 10 to compute rainfall distribution may not be as conser-vative as some other methods such as those in Reference 9. This too may help to balance any overly consorsative assumptionsN$re Ndes a D
'on paj e i t.
57 a .ur.;dWot section was selectedler_aase-of-computation; is ~ fact, the velocity an be-diregneputed-by-eearlaanino Manning's pf-fo any width if A is assumed to be approximately equal to y.
- 6. Values of 'n' of 0.025 for earth and 0.04 for rock were selected based on general recommendations given in Reference 11. The range of 'n' values for shallow flows over rock layers may be somewhat higher than the 'n' values assumed here. However, the NRC staff believes that a high Manning's
'n' value may not produce a velocity that properly accounts for turbulence and increased shear stresses as a result of that turbulenc Reference 7 provides guidance for direct computation of 'n' values based on velocity, NWhr t$t Je[Cl[ kC{t!! M'flkOl **Mer!Ctf4lM " ncred/tJ ih edr f frett.
i 16
-pe - mir t4 . 6 Bura W m=hu&4'- -4 se wami- .
depth of flow, and roughness factors and may be used in calculating more precise 'n' values.
- 7. The shear stress may be calculated using Reference 6 or Reference 11. For
( simplicity, no corrections need to be made for side slope effects on shear stress for slopes that are IV on SH or flatter.
- 8. The NRC staff concludes that a safety factor should be included in the design of a riprap layer. This safety factor is needed to account for turbulence, nonuniform flow, and possible errors in hydraulic computational techniques in this range of flow. A safety factor of 1.5 is nonna11y used by other government agencies in designing projects that have short design lifetimes.E For projects to remain stable for hundreds of years, 4
the design goal should be that little or no damage occurs to an engineered ! design in the event of major rainfall or' floods. It should also be pointed 1 out that high sheet flow velocities can be produced by much less intense rainfall events because of the steep slopes of the reclaimed piles. If less conservative safety factors are used, they will be considered on a case-by-case basis depending on the degree of conservatism present in the l other calculations. , i ! 9. The above analytical procedure may also be used to determine the need for rock protection for the top of a reclaimed pile. l N5ee Seced Co~~"t " Pp. 7. , era,u prdeck m Ar 1 W /foudlmtl$AH? i l i 17 p., _e--,wp- %vvm,w a- - ' - 7
REFERENCES
- 1. J. D. Nelson et al., " Design Considerations for Long-Term Stabilization of Uranium Mill Talli,ngs Impoundments,',' NUREG/CR-3397 (ORNL-5979), U.S.
l Nuclear Regulatory Commission, Washington, DC, 1983. 2. J. K. Young, L. W. Long, and J. W. Reils, " Environmental Factors Affecting Long-Tern Stabilization of Radon Suppression Covers for Uranium Mill Tailings," NUREG/CR-2564 (PNL-4193), U.S. Nuclear Regulatory Commission, I Washington, DC, 1982.
- 3. C. G.' Lindsey et al. , "Long-Tern Survivability of Riprap for Armoring Uranium Mill Tailings and Covers," NUREG/CR-2642 (PNL-4225), U.S. Nuclear i Regulatory Commission, Washington, DC, June 1982.
- 4. P. A. Beedlow, " Designing Vegetation Covers for Long-Tern Stabilization ;
of Uranium Niil Tailings," NUREG/CR-3674 (PNL-4986), U.S. Nuclear ! Regulatory Commission, Washington, DC, 1984. < 5. U. S. Army Corps of Engineers, " HEC-2 Water Surface Profiles," Hydrologic , Engineering Center, Davis, CA, 1976. ' 6. W. H. Walters, " Rock Riprap Design Methods and Their Applicability to Long-Term Protection of Uranium Mill Tailings Impoundments," NUREG/CR-2687 (PNL-4252), U.S. Nuclear Regulatory Commission, Washington, DC,1982. 7. U.S.-Army Corps of Engineers, " Hydraulic Design of Flood Control Channels," EM 111D-2-1601, office of the Chief of Engineers, Washington, DC. 1970. t
- 8. W. S. Chopil, " Soil Conditions That Influence Wind Erosion," U.S.
L Department of Ag-iculture Technical Bulletin 1185, 1958.
- 9. U.S. Bureau of Reclamation, " Design of Small Dams," U.S. Department of
- the Interior, 1973.
18 kasu hemimenph 9'E@#W"4 ' ' '
** =
- 10. U.S. Nuclear Regulatory Com.nission, " Hydrologic Design Criteria for Tailings Retention Systems," Staff Technical Position WM-8201, Uranium Recovery Licensing Branch, Washington, DC,1982.
i
- 11. V. T. Chow, Open-Channel Hydraulics, McGraw-Hill Book Company, Inc., New
! York, NY, 1964. ! i
- 12. U.S. Army Corps of Engineers, " Additional Guidance for Riprap Channel l Protection," ETL 1110-2-120, May 1971.
- 13. S. A. Schumm, The Fluvial System, John Wiley & Sons, New York, 1977. -
)
i I s l 4 e I l 4 ) - J I i 1 19-
%> .w a e 4 4 w*-95=41e ..E%,bhh *erWWNN *WW@ == '-map ** **N - * *
, BIBLIOGRAPHY i
Bander, T. S. , " Literature Review of Models for Estimating Soil Erosion from Wind Stresses on Uranium Mill Tailings Covers," NUREG/CR-2768 (PNL-4302), U.S. Nuclear Regulatory Commission, Washington, DC,1982. Barbour, M. G., and D. V. Diaz, " Larrea Plant Communities on Bajada and Moisture Gradients in the U.S. and Argentina," Vegetation, Vol. 28, 1973. 8eedlow. P. A., M. C. McShane, and L. L. Cadwell, "Revegetation/ Rock Cover for Stabilization of Inactive Uranium Mill Tailings Disposal Sites: A Status Report," PNL-4328, UMT-0210, Pacific Northwest Laboratory, Richland, WA, 1982. Brady, N. C. , The Nature and Properties of So)1s, 8th ed. , Macmillan, New York, NY, 1974.
~
California Division of Highways, " Bank and Shore Protection in California Highway Practices," Business and Transportation Agancy, Department of Public - Works, Sacramento, CA, 1970. . Chow, V. T., Handbook of Applied Hydrology, McGraw-Hill Book Company, Inc., New York, NY, 1964. Cline, J. F. , et al. , "Long-Tern Biobarriers to Plant and Animal Intrusion of Uranium Tailings," PNL-4340, Pacific Northwest Laboratory, Richland, WA, 1982. Cooke, R. U., and A. Warren, Geomorphology in Deserts, University of California Press, Berkeley and Los Angeles, CA. Douglas, G. W., " Subalpine Plant Communities of Western North Cascades, Washington," Arctic and Alpine Res., Vol. 4, 1972. Harne, R. F. , and K. T. Harper, "The Rule of Area, Heterogeneity, and Favorability in Plant Species Diversity of Pinyon-Juniper Ecosystems," Ecology, Vol. 47, 1976. 20
, . o _.. ... m _ _ _ - - . . . . _ _ . - . - . - - . _ . , +
s, <
- 1 ,
so Lindsey, J. G. , L. W. Long, and C. W. Begej, %ond .Terk: Survivability of ! Riprap for Armoring Uranium Mill Tailings and Covers: Literat'ure Keview," ' n NUREG/CR-2642 (PNL-4225), U.S. Nuclear Regulatory Co.mcission Washingt - 1982. I, i L. Simons and Associates, Inc., " Design Manual for Wter Diversions on Surface Mine Dperations," Offica of Surface Mining, U. S Department of the Interior. - l Washington, DC, 1982. t . ,
'; . J
] i L. Simons and Associates, Inc., Engineerino Analysis of Fluvial Eyste3m , Fort Collins, CO, 1982. ' i
. g ; \ l i
Mayer, D. W. , P. A. Beedlow, and L. L. Cadwell, "Moir.ture content of Analysis j } of Covered Uranium Mill Tatlings," PNL-4132,(acific I&rt.%est Laboratory, l Richland, WA, 1981. i } Mayer, D. W. , and D. A. Zimmerman, "Nadon Diffusion Through Uranium Mill -
! l Tailings and Cover Defects," NUREG/CR-2457 (PNL-4063), U.S. Nuclear Regulatory ;
i Commission, Washington, DC, 1981. ' 1 M'Closkey, R. T., " Community Structure in Sympetric U. dents," c Ecol _og , Vol. 47, i 1976. ' j i c l ! National Environmental Policy Act of 1969, 42 U.S.C. 4321 et seq., 1969. ! Nelson, R. ! l W., G. W. Gee, and C. A. Oster, " Radon Cchtrol by Multilayer Earth j Barriers, 1. Modeling of Moisture and Density Effects on Fadon utffusion from > l l i ) Uranium Mill Tailings," Uranium Mill Tailinos hanaoemerg, eroceedinos of the ( j Third Symposium, Geotechnical Engineering. Program, Civ41..En3 1 neering Departme (
- Colorado State University, Fort Collins, CD, 1980.
t # Nyhan, J. W. , and L. J. Lane, "Use of a State of_ the ArkI Hsdel in Generic l Designs of Shallow Land Repositories for Low-Level ihshes," geste Management ,l j
'82. Proceedinos of the 1982 Syroosium in Waste Mana o g Tucsoq, AZ, 1982.
j'
..' , 3) -,'
N ! .c i >. i ' _ .. _.. _. 1 [.) . - . ----- "' _ ,- r z d x-A===':==~====~=' = = ~ ~'~ ~~
~~ ~
.. g-------
O'Farrell, M. J. , "Special Relationships'of Rodents in a Sagebrush Community," Journal of Mammalogy, Vol. 61, 1900. t ( Price, M. V., "The Role of Microhabitat in\ Structuring Desert Rodent Communities," Ecology, Vol. 49, 1978.
\s L '
L - i' Schumm, S. A., and R. J. Chorley, "Geomorphic $ontrols/on the Management of i Nuclear Waste," NUREG/CR-3276, Colorado: State tiniversity, Fort Collins, CO, 1983. \ Skidmore, E. L., "A Wind Erosion Equation Development, Appilcation, and Limitations," Proceedings of the AtmospherLurface S Exchange of Particulate a_nd Gaseous Pollutants Symposium, Nationai Technical Information Service, SM ingfield, VA, 1974. q ( Thom, H. C. S., "New Distribution of Extreme Winds in the United l States," Journal of the Structural Division, Prceeedilias of the American Societ_r.af Civil _Encineers, July 1968. N - (J.S. Army Corps of Engineersg " Flood Hydrograph Analysis a d Com\putation," j 68 i 1110-2-1435, Washington,k'A , 1969. ; g t ' U.3. Army Corps of Engineers,,%ydrographic Analysis," Hydrologic Engineering MethodsforValteResources'Developement, Volume 4,HydrologicEngineering ' Center, Davis, CA, 1973. 5 U.S. Department of Agricultura (USDA), '"Jser Guide to Vegetation, Mining and Reclamation in the West," USDA Forest'Tervice General Technical Report SNT-64, Surface Environment and Mining, Washington, DC, 1979. U.S. Department of Commerce, Climath: Ati.is of the United States, Environmental Data Service, National Oceanic and AtaMpheric Administration (NOAA), Washington, i i DC, 1968. . ( ,: '
, . - s 4
[ g
\
{ + l $<# ' o 'I r '
)_
, ,f l r EE f_ .
_ _ , f i
x
,Y N
. U.S.Departmentc[ Commerce,LocalClimatologicalData-AnnualSummarywith 1
ComparativeDatalEnvironmentalDataService,NOAA, Washington,DC(published annually for all 'first-order NWS stations).
~
U.S. Department of Commerca, State Climatological Summary, Environmental Data Se:vice, NOAA, Washfr'gton, DC (published annually by state). U.S. Department of Commerce, Storm Data, Environmental Data Service, HOAA, Washington, DC (published monthly).
! i U.S. Nuclear Regulatory Commission,. Regulatory Guide 3.1L, " Design, !,
Construction, and Inspection of' Emban6ent Retention Systems for Uranium Mills," Washington, DC, 1977.
. T
'I[ .
Valentine, J. F. , Range Development and Impr'ovements, 2nd ed. , Brigham Young [ .: ! Universi.ty Press, Provo, UT, 1980. , , i
. . 'i ~
Voorhdes, L. :CL , et al. , " Guidance for Disposal of Uranium Mill Tailings: 1 , Long-Term Stabilization of Earthen' Cover Materials,". .NUREG/CR-3199, ORNL/ TM-8685, Oac Ridge. National: Laboratory, Oak Ridge, TN, 1983. I l Vories, K. C., and P. I. Sims, The Plant Information Network Vol. 1, A Users Guide, FSW/0BS-77/38, Fish and Wildlife Service, USDA, Wasnington, DC, 1977. Walters, W. H., "OverlandiE;.'osion of Uranium Mill Tailings Impoundments: Physic 6,1 Processes and Comriutational Methods," NUREG/CR-3027 (PNL-4523), . U.S. Nuclear Regulatory Commission, Washington, DC, 1983. Whicker, F. ,W. "Radioecological Invesiigations of Uranium Mill Tailings 1. t, s Systess," DOE /EV/103-5-7, Colorado Stat'e University, Fort Collins, CD, 1982. J l
.r' * -- '
,1 , ,
t, { Winsor,lTh E. , and F. W. Whicker, " Pocket Gophers and Redistribution of '
' l Plutoniuh'in. Soil,"HealthPhysics,Vol. 39, 1980. l c q ,
. l
, . i,- <
q 5 3 hi q g.
'm \
,r{'23
\1,
- 4. - . .
,e
Zellmer, J. T., " Stability of Multilayer Earthen Barriers Used To Isolate Mill Tailings: Geologic and Geotechnological Considerations," PNL-3902, UMT/02-02, Pacific Northwest Laboratory, Richland, WA, 1981. u S N l
\
e l
. l 24
L DRAFT VALUE/ IMPACT STATEMENT (IE
- 1. PROPOSED ACTION 1.1 Description The proposed action is to provide engineering practices, design criteria, ,
and analytical procedures that are considered to be satisfactory by the NRC staff for the design and construction of erosion protection systems for ! stabilized uranium mill tailing sites. 1.2 Need for Proposed Action
- The milling and processing of uranium ores produce large volumes of liquid and solid wastes that are normally stored in man-made retention structures.
When milling operations cease, the tailing disposal sites are stabilized in order to prevent the release of radiotoxic materials to the environment. It is therefore important to protect these sites from erosion due to floods, precipitation runoff, wind, or other natural phenomena. 1.3 Value/ Impact of Proposed Action - 1.3.1 NRC Operations Consistent and satisfactory engineering practices used in the design and construction of erosion protection systems, as provided by the proposed guidance, will be beneficial.to NRC license reviewers and will help NRC inspectors verify licensee adherence to requirements and commitments. This proposed action iden-tifies acceptable methods-for providing long-term erosion protection to meet 'the specific requirements of 40 CFR Part 192. These methods will facilitate licens-l ing of uranium mills and of Uranium Mill Tailings Radiation Control Act (UMTRCA) l program sites and will help NRC verify that uranium mill tailing disposal sites
\
will not pose a threat to public health and safety, in accordance with the i requirements of 10 CFR Part, 40 " Domestic Licensing of Source Material." 25 e e -'w--
m , L. '
. 1.3.2 Other Government Agencies
-l l The proposed action provides guidance to the Department of Energy, currently,
- responsible for mill tailing management under 40 CFR Part 192. The value to
[ other governmental agencies, including State and local governments, will be reflected in their comments on the guidance developed as it relates to their , programs. The guide may be of value to the Agreement States by providing
. guidance by which State and local governments may develop their own particular criteria.
1.3.3 Industry . I ! l The recommended methods for the design and construction of long-ters erosion protection have been developed using the best available technology and , engineering practices and considering the degree of erosion protection necessary, the time period over which the system must protect the tailings, the materials i .. available, and the cost to industry. The proposed action would enable industry f to adequately protect mill tailing disposal sites from erosion and in many j cases would reduce the need for extensive long-term maintenance. The proposed
- action may result in additional. cost to the industry in the near-term but may i
reduce long-term operational maintenance costs. No.overall negative impacts to the industry are expected as a result of the proposed action. j 1.3.4 Public , l The proposed guidance would provide reasonable assurance that the public j would not be subject to significant risk from the disposal of uranium mill tailings, in accordance with the requirements of 40 CFR Part 192. 1
- 1. 4 Decision on Proposed Action The proposed action should be accomplished because'of the aforementioned benefits.
- - 26
-..w c-y* --m .*- - n -=_,-4-+yvm yw e.e.--.,-my% -m3-,-g. .yyw syy -w r iei %,r- r-= yT* ww--Wr_-Wm ----wvTyvw
~
- 2. TECHNICAL APPROACH -
1 2.1 Technical Alternatives 4 i The action will provide satisfactory and consistent engineering practice for the design and construction of erosion protection systems. Alternative approaches will be reviewed by the NRC staff on a case-by-case basis. Public comments may indicate equally acceptable technical alternatives.
- 3. PROCEDURAL APPROACH 3.1 Procedural Alternatives . -
Methods that have been considered for providing necessary guidance include the following alternatives: i Amendment to the regulations, d - j - NUREG-series report Branch position - Regulatory guide , i 3.2 Discussion of Procedural Alternatives i 2 At this time, an amendment to the regulations or the issuance of a NUREG-series report is not practical for use by NRC reviewers, licensees, and applicants. At the present time, there is no branch position to provide interim i guidance until the proposed regulatory guide is developed. . l 3.3 Decision on Procedural Approach , The development and issuance of a regulatory guide for public comment would best fulfill the need for the proposed action. 27
n.
- 4. STATUTORY CONSIDERATIONS 4.1 NRC Regulatory Authority Authority for this regulatory guide is derived directly from the safety requirements of the Uranium Mill Tailings Radiation Control Act of 1978, which amended the Atomic Energy Act of 1954. This guide helps fulfill the require-ments of 10 CFR Part 40, " Domestic Licensing of Source Material," and, in particular,- the requirements of the National Environmental Policy Act of 1969 as given in 10 CFR Part 51, " Licensing and Regulatory Policy and Procedures for Environmenal Protection." This proposed guide also will be used to evaluate compliance with the EPA's proposed 40 CFR Part 192, " Enviro *nmental Protection Standards for Uranium Mill Tailings," which regulates the cleanup of open lands ,
and buildings contaminated with residual radioactive materials at inactive uranium processing sites. 4.2 Need for NEPA Statement . Issuance or amendment of guides for the implementation of regulations in Title 10, Chapter I, of the Code of Federal Regulations is a categorical exclu- i sion under paragraph 51.22(c)(16) of 10 CFR Part 51. Thus, an environmental impact statement or assessment is not required for this action.
- 5. RELATIONSHIP TO OTHER EXISTING OR PROPOSED REGULATIONS OR POLICIES 5.1 Relationship with Regulations or Policies of Other Government Agencies No potential conflicts with other governmental agencies have been iden-tified. However, Agreement States under Section 274 of the Atomic Energy Act of 1954, as amended, must consider the guide when developing decommissioning plans and protection for .long-term erosion for uranium mill tailings. Non-
, Agreement States that regulate the reclamation of uranium mill tailings may also follow the provision set forth in this guide. In addition, this guide .
will provide criteria for the implementation of 40 CFR Part 192. l 28
..g g- e+- %ee eh- ^MM+=u64^*
""'O "
---m .g-- ,--%,..--fr.7,.,&.,e,q,---p.- --,_9 ,- - . -..-m, -y ,-4 ,g. ,,. , - wyyya-., ,,_, y w ,u,e, g,-g .- ,.g , , p.- .g.'
- .. . . ~ _ - . . - _ -
+- . ", -
5.2 Relationship with Other NRC Regulations and Policies The proposed regulatory guide is intended to be used in conjunction with the following NRC' documents to the extent that the following documents affect l the erosion protection of stabilized uranium mill tailings:
- a. Regulatory Guide 3.11 " Design, Construction, and Inspection of Embankment j Retention Systems for Uranium Mills."
- b. Regulatory Guide 3.11.1, " Operational Inspection and Surveillance of Embankment Retention Systems for Uranium Mill Tailings."
- c. Regulatory Guide 3.5, " Standard Furmat and Content of License Applications
- . for Uranium Mills." '
N l . l d. " Final Generic Environmental Impact Statement on Uranium Milling," l- NUREG-0706, 1980. , ! 6: CONCLUSIONS - . ! The NRC has both the need for and the authority to implement the proposed j action. The development of a regulatory guide is the most favored procedural alternative. e I 4 29 _ . . _~ - _ _ . ~ - . _ _ _ . _ _ . , _ _ _ _ . . , . . _ . . - _ . . _ . _ . . . _ _ . _ . - - . . . _ - . ~ ~ . , - _ _ . .}}