ML20136H856
| ML20136H856 | |
| Person / Time | |
|---|---|
| Issue date: | 11/14/1985 |
| From: | Higginbotham L NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Baublitz J ENERGY, DEPT. OF |
| References | |
| REF-WM-39 NUDOCS 8601130004 | |
| Download: ML20136H856 (7) | |
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W 141985 tYna MNata raja WMEG rf JStarmer NMSS rf JBunting RBrowning M8 ell JGreeves John E. Baublitz, Director ggg> gel Mp11e Division of Remedial Action Projects Office of Terminal Waste Disposal and Remedial Action U.S. Department of Energy Washington, D.C.
20545
Dear Mr. Baublitz:
This letter responds to the EPA standards compliance issues presented by Roger Williams (DOE / TAC) at the meeting held for that purpose in our Silver Spring offices on September 27, 1985. We are responding to your positions as we understand them, based on statements made during the meeting and on clarification provided by Mr. Williams in subsequent telephone conversations with my staff.
If we have misunderstood you, please let us know.
Discussion of each of the six issues presented by Mr. Williams is provided in the enclosure. We have presented the NRC staff's understanding of the TAC /RAC/
NRC technical discussion groups' conclusions as they relate to these issues.
I believe that after you have reviewed this letter and its attachment, further discussion of these issues may be in order.
In the interim, please call me or Dan Martin of my staff if needed.
Sincerely, original signed by-Leo B. Higginbotham Leo B. Higginbotham, Chief Low-Level Waste and Uranium Recovery Projects Branch Division of Waste Management Office of Nuclear Material Safety and SafeguardyVM Record File WM Project --
Occket No.
Enclosure:
PDR /
As stated LPO R _.__ _
Distribution' cc:
J. Themelis R. Williams
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(SEE PREVIOUS CONCURRENCE *)
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- LB Higgihbotham TATE :85/10/13
- 85/10/ 14
NOV 141985 DISCUSSION OF ISSUES Two points seem to apply in general.
First, we agree that basing designs on limiting events, such as the Probable Maximum Flood (PMF) or Maximum Credible Earthquake (MCE), is definitely sufficient to demonstrate compliance with the EPA stability standard. Such designs provide the neassary reasonable assurance of stability for the maximum required design life of 1,000 years.
However, this does not mean either that designs must be based on such limiting events or that stability must be reasonably assured for at least 1,000 years.
If reasonable assurance of stability can be demonstrated using design basis events of less severity, designs need not be based on limiting events to met the EPA standard. Also, as provided for in the standard, the design lifetime may be reduced to 200 years if it is demonstrated why a longer interval is not reasonably achievable.
In either case we stand ready to work with DOE to make use of the full latitude provided for in the standard to reduce program costs.
Second, planned maintenance cannot be credited in assessing compliance with the standard.
Our reading of the standard indicates that reliance on routine, planned maintenance is not an acceptable method of compliance; this has been confirmed informally with EPA.
The consequences of potential failures may merit consideration in implementing the standard. This might be done qualitatively in judging the adequacy of assurance against failure or in determining if longer design lifetimes are reasonably achievable.
But there may be difficulties in assessing the consequences of failure.
For example, the necessary assumptions as to the extent and duration of failure, future conditions, and effectiveness of cleanup are not likely to provide a sound technical basis. Moreover, even small, localized failures may lead to significant ruptures if left unchecked.
In this regard we are unsure as to the propriety of assuming that repair work will be provided when needed in the distant future, and the extent to which such repair work could be relied upon before it must be considered planned maintenance; we will take this up directly with EPA for clarification.
A final general comment before proceeding to the main issues: We are unable to judge the accuracy of DOE's cost impact estimates without reviewing specific cost details. This aspect of the issues is therefore not addressed in this enclosure.
1.
River Flooding Protection 00E:
There is general agreement between NRC and DOE that when the incremental costs of protecting a site against a Probable Maximum Flood (PMF) increase the cost of remedial action by more than 15-20% above the cost of a baseline design, then use of a design flood less than the PMF might be appropriate. NRC and DOE have not yet agreed on how much the protection i
. from flooding can be reduced. 00E may save $13 to $21 million in the UMTRA Project by designing remaining tailings sites to withstand only a baseline flood.
NRC:
In general the NRC staff considers that the design basis flood should be selected on a site-specific basis and that it is inappropriate to designate a particular " base level flood" for comparison purposes.
There is agreement between the technical staffs, that while it is not a requirement, use of the Probable Maximum Flood (PMF) as the design basis for erosion protection will satisfy the EPA longevity standard. There is also agreement that when DOE elects, lesser design floods may be considered.
Designs based on floods smaller than the PMF will be accepted if it is demonstrated by DOE that: (1) there is reasonable assurance the flood chosen will not be exceeded during the design lifetime; and (2) if the design lifetime is less than 1,000 years, it satisfies the EPA standard, i.e., it is at least 200 years and a longer design lifetime is not reasonably achievable.
NRC and DOE have not agreed on a procedure for determining an appropriate or a specific design flood other than a PMF or for determining what cost increases constitute a basis for reduction in level of flood protection. The technology of estimating the probability of extreme floods has not been advanced to a degree that would allow establishing generic procedures for flood reduction. The basis and method for use of design basis floods less than a PMF should be addressed on a site-specific basis.
2.
Probable Maximum Precipitation (PMP)
DOE:
NRC and 00E agreed that sites should be designed to withstand the PMP.
00E believes that rock cover should be designed to withstand the PMP without considering flow concentration, unless differential settlement is anticipated.
Potential savinis are $5 to 10 M.
e NRC:
There is general agreement on this issue. NRC and DOE have agreed that erosion protection which is designed to withstand an occurrence of the PMP clearly meets the EPA longevity requirements and is therefore acceptable.
Lesser precipitation events may be used to design erosion protection if documentation is proviced as described in the previous discussion on design floods.
N'.CandDhihaveagreedthatflowconcentrationdoesnothavetobe considere7 if the following conditions are met:
, (1) a rock layer is provided to protect the earth cover, and (2) DOE analyses have documented conclusively that differential settlement will not occur, or will be mitigated usin measures (such as overbuilding or surcharge loading)g engineering If these two conditions cannot be met, NRC and DOE have agreed that the site will be designed to resist flow concentrations during an occurrence of the PMP or other design precipitation event.
In general, methods developed by the NRC staff (which have been reviewed by 00E, TAC, and RAC) will be used to determine flow concentrations, using approved DOE calculations of differential settlement.
3.
Rock Durability 00E:
NRC and DOE have agreed on the tests but not the criteria for evaluating the durability of rock riprap. DOE would like to use less durable rock when readily available and then monitor more closely for deterioration that would need repair. This could save $5 to 10 M.
NRC:
NRC and DOE have generally agreed on the tests that need to be conducted to evaluate rock durability for UMTRAP sites.
The NRC staff has work underway to develop criteria for methods for evaluating rock durability and determining the increases in rock size or thickness that may be needed to compensate for poor durability. The staff considers this the acceptable compensation for poor durability rather than reliance on planned maintenance. Based on preliminary results of the NRC work, it appears that rock of less-than-good quality may be acceptable for certain areas of a site.
In addition, it appears that the generally limited areas that will need good-quality rock can be protected with such rock at a reasonable cost, given the methodologies that have been proposed.
The methodologies under development rely heavily on actual field data collected on rock samples throughout the Western United States. Again, preliminary results of the NRC work indicate that the proposed methodology for oversizing would allow rock designs that will meet the EPA stability standard at a reasonable cost even if good quality rock is not available.
Following completion of this work, the NRC staff will work through the erosion protection technical discussion group to establish agreement on the application of criteria for durability to erosion protection design.
A
. 4.
Radon Barrier Cover Thickness DOE:
Radon barrier cover thickness is a function of the long-term moisture content of the cover material. The NRC and DOE do not agree on the method for estimating the long-term moisture content. The NRC position has been to use the wilting point as an estimate of the long-term moisture. DOE considers this estimate overly conservative. By using values other than the wilting point, DOE would be able to save $20 to $40 M.
NRC:
The NRC and 00E are not in agreement on which method should be used for estimating the long-term moisture content. As a result of the discussions between NRC and TAC /RAC personnel during the preparation of the radon attenuation sections of the NRC Standard Review Plan and the DOE Generic Design Manual, the following items have been agreed upon:
(1)
In cases where no value for the long-term moisture content has been proposed, or where justification does not technically support the value chosen, the -15 bar moisture content (wilting point) will be used.
(2) Values other than the -15 bar moisture content may be used provided that the values are justified by an acceptable technical basis.
This position will be revised if an alternate generic methodology for estimating the long-term moisture content that conservatively bounds the lower moisture retention capacities of cover materials is proposed by DOE and is found acceptable by the NRC staff.
In the interim, the NRC will continue treating this issue on a site-specific basis as described above.
Note that in the NRC's review of the Salt Lake City radon barrier, a less conservative value for long-term moisture content was approved based upon site-specific material properties and design details.
5.
Seismic Regime DOE:
NRC has agreed to use 10,000 (rather than 100,000) years as the period over which a Maximum Credible Earthquake will be established. DOE wants to use the Corps of Engineers (C0E) position to determine acceleration, that is to use 50%, while NRC wants to use 2/3. Acceptance of the 100,000 year period would increase UMTRAP costs by about $50M, by having to relocate 8 piles.
\\
. NRC:
The NRC staff has never agreed to any time period to be used as a basis for establishing a Maximum Credible Earthquake (MCE) with respect to the UMTRAP program. The NRC has adopted the definition for the MCE stated in 10CFR40, Appendix A, Criterion 4, "The term ' maximum credible earthquake' means that earthquake which would cause the maximum vibratory ground motion based upon an evaluation of earthquake potential considering the regional and local geology and seismology and specific characteristics of local subsurface material." The evaluation of earthquake potential contained in this definition is a deterministic evaluation based on interpretations of geologic and seismologic data and on professional judgement.
Members of the DOE (TAC /RAC) and NRC group on DOE's Design Manual for UMTRAP have agreed that pseudostatic analysis is acceptable if the materials in the embankment and foundation are not subject to significant loss of strength and/or development of high pore pressure under dynamic loads. The design seismic coefficient to be used in the pseudostatic analysis should be either 67 percent of the peak acceleration of the earthquake at the foundation of the embankment or 0.10, whichever is greater.
If the factor of safety by the pseudostatic analysis is slightly less than 1.0 and the seismic coefficient used in the design is greater than 0.20, alternate methods of dynamic analyses may be used to support the conclusion that the slope is safe. This option is to be evaluated on a site-specific basis. This procedure does not require any reduction in the strength parameters as is recommended in the C0E's method.
If these procedures (agreed to in the technical discussion group) are not acceptable to 00E, this issue should be elevated beyond the discussion group level.
6.
Groundwater DOE:
00E and NRC agree that institutional controls should be considered as alternative protective actions and implemented when restoration or mitigation of contaminated water is not practical or feasible at UMTRA sites. DOE recognizes quarterly water quality sampling as a desirable goal of site characterization, but states that it is not necessary in all cases.
DOE concludes that projections of long-term uses of water resources and health and environmental effects of water contamination are meaningless beyond 30 years.
4 NRC:
NRC agrees with DOE that institutional controls should be considered as alternative protective actions for water resources.
NRC staff and DOE's contractors have also mutually concluded that quarterly monitoring of l
water quality for at least one year is a desirable component of UMTRAP site characterization, provided that DOE has the option to justify reductions in the scope of ground-water monitoring programs.
NRC disagrees with DOE's statement that projections of water use and health and environmental effects are meaningless beyond ';0 years.
Based on guidance in the EPA standard and recognizing the large uncertainties associated with long-term projections of water use and health and environmental effects, NRC considers that DOE should evaluate existing and anticipated water use and contamination effects during the period that water contamination poses a potential hazard to humans and the environment. Although this period may exceed thirty years, such evaluations can be bas 2d on reasonable estimates of the duration of contamination, and on simple comparisons between estimated contaminant concentrations and appropriate exposure levels (e.g., drinking water and aquatic life criteria).
If this position is not acceptable to DOE, this issue should be elevated beyond the technical discussion group level.
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