ML20235W419
| ML20235W419 | |
| Person / Time | |
|---|---|
| Issue date: | 10/24/1988 |
| From: | Tokar M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
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| References | |
| REF-WM-3 NUDOCS 8903130035 | |
| Download: ML20235W419 (11) | |
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THE USE OF SOLIDIFICATION
-SYSTEMS AND HIGH INTEGRITY CONTAINERS FOR DISPOSAL OF LOW-LEVEL' WASTE by Dr. Michael Tokar Low-Level Technical Branch Division of Waste Management Office of Nuclear Material Safety and Safeguards U.S. Nuclear Regulatory Commission Presented at the Sixteenth Water Reactor Safety Information Meeting (16 WRSM)
National Institute of Standards and Technology Gaithersburg, MD October 24, 1988 h
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THE USE 0F SOLIDIFICATION SYSTEMS AND HIGH IMEGRITY CONTA1MER5 FOR DlSF05AL OF LOW-LEVEL. WASTE 1
by t
Michael Tokar Abstract This paper primarily addresses the 10 CFR Part 61 requirements for waste form stability and the use of solidification media and high 1 Integrity containers to provide the required stability for Class B !
and Class C waste. Tests and criteria that are provided in a Technical Position on Waste Form and the current status of NRC's waste form and HIC reviews are also discussed.
1 INTRODUCTION NRCregulaticn10CFRPart61(Ref.1) establishes,forlanddisposalof radioactive waste, the procedures, criteria, and terms and conditions upon which the Commission issues licenses for the disposal of radioactive wastes containing byproduct, source and special nuclear material received from other persors.
Section 61.55 of Part 61 establishes three categories or classes of wastes; viz., Class A, Class B, and Class C, in a generall to degree of hazard (i.e.', type and concentration)y ofascending orderClass radio-nuclides. with regard B
& Class C wastes are required to meet both minimum as well as stability requirements that are set forth in 10 CFR 61.56. Class C waste must also be protected (at the disposal facility) against inadvertent intrusion.
A.s noted in Section 61.56 of Part 31, waste form structural stability can be provided in a variety Gf ways. Two methods; viz., the use of (a) solidifica-tion agents and (b) high integrity containers (HICs) are the subject of this paper. A third approach -- the use of engineered structures has received a lot of attention recently, but a discussion of that alternative is beyond the scope of this paper. -
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2 PART 61 WASTE FORM REQUIREMENTS 2.1 Minimum Waste characteristics requirements are established in 10 CFR 61.56. There are two types or categories of requirements: (1) minimum - addressed in Section 61.56(a); (2) stability - addressed in Section 61.56(b). All classes of waste must meet the minimum requirements in 10 CFR 61.56(a). The " minimum" requirements concern: (a) a prohibition against the use of cardboard fiber-board boxes; (b) treatment, packaging and maximum quantities of liquid wastes; (c) restrictions concerning disposal of explosive or detonatable wastes; (d) restrictions against wastes containing, or capable of generating, quanti-ties of toxic gases, vapors, or fumes; (e) a prohibition against pyrophoric wastes; (f) a limit on the maximum pressure and curie content for packaged gaseous wastes; and (g) a general requirement for treatment of hazardous, biological, pathogenic, or infectious material to reduce to the maximum extent prceticable the potential hazard from non-radiological materials.
2.2 Structural Stability Requirements for stability are provided in 10 CFR 61.56(b). Stability is defined in 10 CFR 61.2 as meaning "structurai stability " While the term, structural stibility, is itself not defined anywhere in Part 61, it is indi-cated in Section 61.56(b) that " stability" (i.e., structural stability) is intended to ensure that the waste does not structurally degrade and affect overall stability of the site through slumping, collapse, or other failure of the disposal unit and thereby lead to water infiltration. Stability is also stated to be a factor in limiting exposure to an inadvertent intruder, since a stable waste form should bc recognizable and nondispersible. Therefore, in addition to recognizability and nondispersibility, the Class B & Class C waste forms are supposed to contribute to the ability of the facility to retain over-all stability and to thereby resist water infiltration. Resistance of the disposal facility to water infiltration is thus fundamentally associated with waste form structural stability. Although not explicitly so stated in Part 61, the concern about water infiltration stems from the fact that migration through groundwater is a potentially major pathway for radionuclides release to the offsite environment. The relationship of this concern, which is a thread that runs through Part 61, to the technical criteria and recommendations for immersion and leach testing will be addressed further in detail in this paper.
Further discussion of structural stability is provided in 10 CFR 61.56(b)(1),
where it is stated that "a structurally stable waste form will generally main- ,
tain its physical dimensions and its form, under expected disposal conditions !
such as weight of overburden and compaction equipment, the presence of moisture and microbial activity, and internal factors such as radiation effects and chemical changes." This section of Part 61 also indicates that structural stability can be provided in any one of three different ways: (1) by the waste form itself (as in an activated metal component); (2) by processing the waste to a stable waste form (for example, by mixing and solidifying the waste with a cementitious material such as Portland cement); or (3) by placing the waste in a disposal container or structure that provides stability after disposal (such as a HIC).
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Section 61.56(b) also provides further requirements ccncerning waste characteristics with regard to: (a) limitations on the amount of free standing or corrosive liquid (1% by volume of the waste when it is in a disposal container, or 0.5% by volume of the waste when processed to a stacle form); and (b) void spaces within the waste and between the waste and its package that must be reduced to the extent practicable.
2.3 Concepts Thcugh the basic requirements for waste form stability are provided in Section 61.56 of Part 61, the discussion of fundamental concepts or rationale is con-tained in Section 61.7, In that section is provided a fairly detailed discus-sien of stability - of the waste as well as of the disposal site. As stated there, "a cornerstena of the system is stability ...so that...[through sta-bility of the waste and site,]... access of water to the waste can be minimized (emphasisadded)." In this way, " migration of radio-nuclides is minimized...."
Implicit in these statements is a recognition of the fact that contact of waste with water can lead to extraction (i.e., " leaching") of radionuclides from the waste form. Thus, leaching of radionuclides from the waste form is the first step in' subsequent migration of the radionuclides from the waste through the groundwater and off of the site. It is clear, therefore, that, though leaching is not mentioned explicitly in Part 61, it is a phenomenon that is of funda-mental concern to low-level waste disposal. Hence, it should come as no surprise that waste form leach testing is recommended in the 1983 " Technical Position on Waste Form" (Ref. 2).
3 TECHNICAL POSITION ON WASTE FORM STABILITY
3.1 Background
Though Part 61 provides the basic licensing requirements for low level waste (LLW) Class B & Class C structural stability, the regulation does not indicate in any detail how those requirements should be demonstrated to be met. That type of detailed guidance is instead provided in a " Technical Position on Waste Form" which was issued in May 1983. For solidified waste forms, the tests (see Table 1) essentially involve subjecting the waste specimens to conditions of {
compression, irradiation, biodegradation, leaching, immersion, and thermal i cycling. Most of the tests, which were selected for their relative simplicity and reproducibility, are based on American Society for Testing and Materials (ASTM) or American Nuclear Society (ANS) standard methods of test that were originally developed for specific non-radioactive material applications.
Though it is not explicitly so stated in the TP, these methods of test are 4 ir, tended to provide confidence, by means of exposing test specimens to rela-tively short-term (minutes to weeks) conditions, that low-level radioactive waste forms will have the desired long-term (300-year) structural stability.
It is important to remember in this regard that there is a major difference in time scale between the periods of time allotted for the tests and the period of time of concern for LLW disposal. Therefore, the test conditions cannot match, and are not intended to exactly duplicate, the conditions that might actually exist in the disposal facility at the time of disposal or which might exist at 3
i some point in time following placement of the waste in the facility. For example, the irradiation test calls for the specimens to be exposed to a mini-mum of 10E+8 rads, which is the maximum level of exposure for the waste forms expected after (300 years of) disposal; this requires the test specimens to be exposed to a conditions.
real exposure much higher ganna Thus, flux than in some wayswould (someactually) of the TPbe encountered tests can be under considered to be accelerated tests, while in a more fundamental sense they are actually screening tests that are used to weed out material formulations and designs that do not exhibit sufficient assurance of long-term stability.
3.2 Test Parameters The 1983 " Technical Position on Waste Form" addresses the type of short-term testing that should be performed to demonstrate long-term (300 year) structural stability as well as the acceptance criteria for the tests. As shown in Table 1, there are eight types of tests or test conditions for solidified waste forms called out in the 1983 TP. Five of the tests are patterned after ASTM or ANS Standard Methods of Test. However, the principal acceptance criterion parameter for most of the tests is compressive strength. The compressive strength criterion and the tests are related to Part 61 through the statement (noted above) in 10 CFR 61.56(b)(1), where it is stated that "a structurally stable waste form will generally maintain its physical dimensions and its form, under expected disposal conditions, such as weight of overburden and compaction equipment, the presence of moisture [a rationale for immersion and leaching tests] and microbial activity [a rationale for biodegradation tests],
and internal factors such as radiation effects [a rationale for radiation stability tests] and chemical changes." In the 1983 Technical Position, a cover material density of 120 lbs./cu.ft. is assumed, which yields a pressure of approximately)37.5 depth at Hanford . Takingpsiinto at a burial depthpotential consideration of 45 feet (the then-naximum additional loads from burial trench compaction equipment, waste contents, etc., the compressive strength criterion was set at 50 psi, which was raised to 60 psi when Hanford increased the depth of its trenches to 55 feet. Thus, the compressive strength criterion was not established as a result of some direct correlation of an intrinsic material property to long-term structural stability, but was instead intended ,
to accommodate the environmental or in situ loads at the bottom of a disposal '
trench. Forcertaintypesofsolidificationmedia,(e.g.,Portlandcementor vinyl ester styrene), which typically have (in the unadulterated form) compressive strengths on the order of several thousand psi, a 60 psi l compressive strength criterion does not appear to have a strong correlation to long-term structural stabili1;y. Additionally, for viscoelastic media such as I bitumen, which continues to deform under load, measurements of some other property (such ais viscosity), in addition to or in place of compressive strength, might be needed to demonstrate long-term structural stability.
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' Table I Solidified product guidance
}
Tests Methods Criteria
- 1. Compressive. Strength- ASTM C39 or 01074 60 psi (a)
- 2. Radiation Stability (See 1983 TP) 60 psi comp. str.
after 10E+8 rads
- 3. Biodegradation. ASTM G21 & G22 Nogrowth(b)&
comp str._ 60 psi
- 4. : Teachability ANS 16.1 Leach index of 6
- 5. Immersion (See1983TP) 60 psi comp, str.
after 90 days
- 6. Thermal Cycling ASTM B553 60 psi comp. str.
after 30 cycles
. 7. Free liquid ANS 55.1 0.5 percent
- 8. Full-scale Tests (See1983TP) Homogeneous &
correlates to lab size test results (a) The 1983 TP calls for e minimum compressive strength of 50 psi. This '
has been raised to 60 psi to accommodate an increased maximum burial depth at Hanford of 55 feet (from 45 feet).
(b) The 1983 TP calls for a multi-steg procedure for biodegradation testing: if observed culture growth rated greater than 1"'is observed following a repeated ASTM G21 test, or any growth is observed following a repeated ASTM _G22 test, longer term testing (for at least 6 months duration) is called for, using the "Bartha-Pramer Method." Frosi this test, a total weight loss extrapolated for full-size waste forms to 300 years should produce less than a 10 percent loss of total carbon in the sample.
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3.3 Standard Methods of Te_s_t Though the 1983 TP refers to several ASTM or ANS Standard Methods of Test (see Table 1), none of the listed Standards (Refs. 3 to 9) other than-the ANS 16.1' test for teachability were developed specifically for the testing of. lowlevel waste forms. All the tests other than the leach test are adaptations of indus-try standards that were developed originally for specific nonradio active material applications. For example, the ASTM B553 thermal cycling test was developed for metalplated, plastic automobile parts, and.the ASTM D1074 ccm-pressive strength test (which is used for testing viscoelastic materials) was developed for testing road bitumens. As a result, various details of the test procedures are open to interpretation, as are the results of the tests.
3.4 Waste Solidification and HIC Problem Areas There has been considerable research and field experience obtained with HICs and wcste solidification media since the " Technical Position on Waste Form" was developed in 1983. As a result of knowledge gained through topical Report reviews and the results of tests and/or analytical calculations, the following problem areas have been identified:
o Cement - Test results (Ref. 10) from programs conducted by National Labor-atories and the cement solidification vendors, coupled with observed problems with swelling, disintegration, or incomplete. solidification of power plant cement waste forms, have led ths NRC staff to recommend that waste loading be limited to 18 percent by weight until sufficient data are presented to justify higher loadings.
o Bitumen low-level- radioactive There are two primary) waste: types of bitumen (1 " distilled" and (2) "that are usedA to solidify oxidized."
topical Report has been submitted for review on each of these materials by separate vendors. To this date, the NRC staff has not been presented with any evidence that the distilled bitumen can provide stabilized waste forms that meet the 60 psi compressive strength criterion. Therefore, in February 1988, the technical review of the topical Report on distilled bitumen was discontinued, and the topical Report was returned (Ref.11) to Inc.).
thevendor(AssociatedTechnologies(Ref.12). The topical Report for the oxidized bitumen has been approved {
l o High Density Polyethylene Containers (HPDEs) - As a result of an j allegation that HDPE HICs do not have sufficient strength to withstand the j stresses imposed by the weight of material placed above the HICs in a a burial environment, the NRC contracted with Brookhaven National Laboratory j (BNL) to analyze existing data on creep of polyethylene and to develop a q model and criteria that could be used to evaluate the structural stability )'
of the HICs. BNL recommended (Ref. 13) that the HICs be shown to be able to resist buckling, to not enter tertiary creep, and to not exceed ,
allowable membrane stresses. Preliminary calculations, using the BNL j not satisf The l model, indicate that large HDPE HICs HDPE HIC vendors have all been notified may(Ref. 14) along(y the with criteria.
the l Agreement States) and requested to show via (a) analyses, (b) testing, (c) administrative procedures, and/or (d) redesign that their HICs can satisfy the criteria. Each of the HDPE HIC vendors has submitted information that 1 is under review by NRC staff and consultants.
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1 4 THE TOPICAL REPORT REVIEW PROCESS 4.1 Eackground
- As noted earlier, the purpose of the "1983 Technical Position on Waste Form" is I
to provide guidance on an acceptable approach for demonstrating compliance with 10 CFR Part 61 requirements for LLW structural stability. Under current l
t procedures, the NRC provides a " central" review of topical Reports on waste form solidification media and HICs. The central review is intended to be -I l applicable for all disposal sites. A brief description of the evolution and t h
current status of this review process is provided below, b 4.2 Development and Evolution ,
The current process for NRC's reviews of topical Reports on waste form solidification, HICs and computer codes for classifying waste originated as a l result of several actions that occurred primarily during calendar year 1983; (the foundation for these actions and agreements, however, was laid in a series
- of earlier activities that occurred over several years, but which will not be addressed here in the interest of brevity). The 1983 " Technical Position on l Waste Form" was completed in May 1983 and made available to the public in June 1983. The NRC publicized its topical Report review process in September 1983 with a Federal Register Notice that stated that a limited waiver of fees would i be granted for Reports submitted before June 30, 1984.
The vendors responded to this by submitting eighteen topical Reports before the expiration of the fee waiver, while twelve Reports have been submitted after the June 30, 1984 expiration date.
In November 1983, NRC's Division of Waste Management (DWM) participated in a review of the South Carolina Agreement State Program. SouthCarolina(SC)had h established acceptance criteria for HICs in 1980 and had issued several CertificatesofCompliance(CsofC)toHICvendorsbeginninginMay1981, ,
based on those criteria. The DWM's examination of SC's HIC reviews was limited i to a determination that the State had used criteria that appeared to be compatible with the staff's "1983 Technical Position on Waste Form." No determination was made of the adequacy of the reviews with respect to whether '
reasonable assurance had been provided that the HICs would have 300-year structural stability. ,
InDecember1983,ameeting(Ref.15)washeldinBethesdatodiscussthe overall policy for HICs and topical Report reviews. In attendance were repre-sentatives from the States of South Carolina, Nevada and Washington, as well as NRC's Office of State Programs and DWM. At this meeting, the topical Report review process and the roles of the NRC and the States were discussed. It was recognized that the Agreement States have the licensing authority for the dis-posal sites with respect to whether specific HICs or waste forms would be acceptable for disposal at the sites. Before this meeting, the State of South Carolina had issued ten Cs of C and had under review two additional requests for approval of HICs. The State of Washington had two requests for approval.
It was at this meeting that an agreement was reached that NRC would provide a
" central" review of topical Reports that would be applicable for all the disposal sites. 4 7
4.3 Grandfathering in Dethesda concerned " grandfather-A key outcome ing." of thethat It was decided December 1983 meeting (Nevada and Washington had not ye South Carolina issued any HIC approvals) would continue to accept the use of HICs that had already been issued a C of C.
For such HICs, revocation of a C of C would take place only if a problem were identified or if new information indicated that the HICs would not meet the '
acceptance criteria. For new HICs that were described in topical Reports submitted to the NRC, the States would not issue Cs of C until the review had been completed by the NRC; (it should be noted, however, that periodic temporary approvals or " variances" for limited quantities of certain types of HICs have been granted by the State of Washington). For solidification processes, those processors who submitted information to NRC in topical Reports submitted before June 30, 1984 would still be acceptable under a grandfathering arrangement.
4.4 NRR Process Control Plans (PCP) Reviews While NMSS has been reviewing HIC designs and waste solidification media formulations in accordance with 10 CFR Part 61. requirements for structural 1 stability, the office of Nuclear Reactor Regulation (NRR) has been reviewing generic and plant-specific Process Control Plans (PCPs) requirements for reactors. The NRR reviews are intended to be focussed on the systems i interactions of the solidification equipment with the plant systems and j operation from the standpoint of reactor safety. l 4.5 Current Review Status In general the qualification of HICs appears to be a somewhat simpler process than that for solidification media, in the sense that: the HICs are finished J' products; they are produced (each HIC by a single vendor) under factory quality '
assurance procedures; they have material properties that are either well-estab-lished or that can be readily measured; and the properties can be used in j design calculations. Prototypes can then be built and tested, and the test I results can be checked against the calculations. In contrast, waste solidifi-cation media interact physically and chemically with the materials comprising the waste stream, and the resultant properties of the waste form are more difficult to predict and reproduce on a routine basis.
Four solidification media topical Reports have been reviewed and approved by NMSS (by the end of October 1988). The staff's evaluation Reports for solidi-fication media topical Reports are carefully written to clearly specify the I waste streams and concentrations and the method of preparation of the waste forms so as to ensure that the ensuing waste forms will exhibit characteristics similar to tnose held by the test specimens used in the qualifying tests.
As of October 1988, a total of 30 topical Reports has been submitted to NRC's Nuclear Material Safeguards for review. Of these, seven have been approved, six have been withdrawn, three have been returned, and fourteen are still under review. A sumary of the review status, with a breakdown of the type of product covered by each topical Report, is presented in Table II.
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SUMMARY
DISCUSSION i In summary,10 CFR Part 61 requires long-term (300 year) structural stability.
Assurance of long-term structural stability is provided.for the most part by I conducting short-term tests and meeting acceptance criteria described in a Technical Position issued in May 1983. The tests called out in the 1983 Technical Position are, in most cases, based on ASTM or ANS Standards that were l created for specific non-nuclear applications and materials. These tests, therefore, require some modification for radwaste materials, in either the methods for specimen preparation, the procedures used in the test, the inter-pretation of the test data, or the acceptance criteria used.
The most widely applied test and criterion identified in the Technical Position is the compressive strength test, which is reconnended for virgin (othemise untested) material as well as waste forms that have been subjected to various conditions of immersion, radiation, bioc'egradation, and thermal cycling. The current compressive strength criterion is 60 psi (raised from 50 psi in the 1983 Technical Position). The compressive strength test and the 60 psi criterion address the ability of the waste form to withstand the loads placed on the waste form at the bottom of a disposal trench at the time the waste is covered over. The criterion and the test do not address, except in an indirect way, the ability of the waste form to remain integral for 300 years. None of the Technical Position tests result in measurement of some intrinsic property that can be directly correlated with long-term (300-year) structural stability.
The tests are simply indirect, short-term indicators of the potential long-term stability of the waste ferms. They are intended to be generically applicable, but as evidenced by both field experience as well as laboratory tests, some waste forms have exhibited unstable behavior. In particular, there have been problems with cement-solidified wastes (notably bead resins and sludge), with low-viscosity bituminized waste, and with high-density polyethylene HICs.
There has been a rather complex evolution of the regulatory process for low-level radioactive waste forts, involving NRR, the Office of State Programs, the Agreement States, the vendors, and of HMSS. Under an agreement reached in 1983 with the Agreement States of Nevada, South Carolina, and Washington, the NRC provides centralized review of Topical Reports on waste form solidification media and HICs. Solidification media and HICs accepted by the States before this agreement continue to be accepted. In addition, variances and interim approvals have been granted to certain HICs and waste forms, while Topical Reports on the HICs and waste forms have been under review by NRC. As of October 1988, NRC has reviewqd and approved three HIC and four waste solidifi-cation media Topical Reports, while six have been withdrawn and three have been discontinued.
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, Table II TOPICAL REPORT REVIEW STATUS
SUMMARY
SOLIDIFIED WASTE FORM and HIGH INTEGRITY CONTAINERS (HICs)
September 28, 1988 Vendor Docket No. Type, Disposition Waste Chem WM-90***
General Electric Solidification (bitumen) Approved.
i WM-88 Solidification (polymer) Approved.
U.S. Gypsum WM-51*** Solidification (gypsum)* Approved.
Chichibu WM-81 HIC (poly impreg/ concrete) Approved.
Nuclear Packaging WM-45 HIC (ferralium/FL-50) Approved.
Nuclear Packaging WM-85*** HIC (ferralium/ family) Approved.
00W WM-82*** Solidification (polymer)** Approved.
ATI(U.S. Ecology) WM-91*** ' Solidification (bitumen) Discontinued.
VIKEM WM-13 Stock Solidification / oil (coment) Discontinued.
WM-92*** Solidification (cement) Discontinued.
Nuclear Packaging WM-71 Solid /Encap(cement / gypsum) Withdrawn.
LN Technologies WM-57 HIC ( Withdrawn.
Chem-Nuclear WM-47 HIC (polyethylene) fiberglass / poly) Withdrawn.
Chem-Nuclear WM-19*** Solidification (cement) Withdrawn.
Chem-Nuclear WM-96*** Solidification (cement) Withdrawn.
Hittman WM-79'** Solidification (SG-95) Withdrawn.
Chem-Nuclear WM-101 Solidification cement #1 Under review.
Chem-Nuclear WM-97 Solidification cement #2 Under review.
Chem-Nuclear WM-98 Solidification cement #3 Under review.
LN Technologies WM-20 Solidification (cement) Under review.
LN Technologies WM-99 Solidification (cement /decon)Underreview.
Hittman WM-46 Solidification (cement) Under review.
ATI(U.S. Ecology) WM-100 Solidification (bitumen) Under review. ,
Chem-Nuclear WM-18 HIC polyethylene Under review. I Hittman WM-80 . HIC polyethylene Under review.
TFC WM-76 HIC polyethylene Under review.
Nuclear Packaging WM-87 HIC (316-stainless) Under review.
LN Technologies WM-93 HIC (stainless / poly) Under review.
Bondico WM-94 HIC (fiberglass / poly) Under review.
Babcock & Wilcox WM-95 HIC (coated carbon steel) Under review.
- Approved for single waste stream for one year.
- Approved pending satisfactory completion of thermal cycling tests.
- Actions completed in Calendar Year 1988.
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