ML20196L120

Rept to Director NMSS Re Current Status & Proposed Action for Regulation of Low Level Waste Stability

ML20196L120
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Issue date:	06/21/1988
From:	NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
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ML20196L085	List: ML20196L083 ML20196L120
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REF-WM-3 NUDOCS 8807070240
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REPORT TO THE DIRECTOR OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

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REGARDING CURRENT STATUS AND PROPOSED ACTION FOR REGULATION OF-'LLW STABILITY Prepared by Division of Waste Management and Decommissioning Staff dune 21, 1988 [V 8807070240 880621 PDR WASTE WM-3 PDC ,.

. s CONTENTS CURRENT STATUS AND PROPOSED ACTION FOR REGULATION OF LOW LEVEL WASTE STABILITY Page-

1. . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2. PART 61 REQUIREMENTS 2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.2 Classes of Waste ......................... 1 2.3 Waste From Requirements . . . . . . . . . . . . . . , . . . . . 2 2.4 Concepts ............................. 3

3. TECHNICAL POSITION ON WASTE FORM STABILITY 3.1 Background ............................ 3 3.2 Test Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.3 Comments from ACRS and NUMARC . . . . . . . . . . . . . . . . . . . 4 3.4 Ctandard Methods of Test ..................... 7 3.5 Waste Solidification and HIC "roblem Areas ............ 7

4. THE TOPICAL REPORT REVIEW PROCESS 4.1 Background ............................ 7 4.2 Development and Evaluation .................... 8 4.3 Grandfathering .......................... 9 4.4 NRC Process Control Plans (PCP) Reviews . . . . .......... 9 4.5 Current Review Status . . . . . . . . . . . . . . . . . . . . . . . 10

5.

SUMMARY

DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . 11

6. CONCLUSIONS AND RECOMMENDATIONS .................. 12

7. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 APPENDIX - Waste Form Testing Discussion . . . . . . . . . . . . . . . . Al A1. Introduction to Waste Form Testing ................ Al A2. Compressiontion . . . . . . . . . . . . . . . . . . . . . . . . . . Al A3. Thermal Cycling . . . . . . . . . . . . . . . . . . . . ...... A5 a A4. Irradiation . . . . . . . . . . . . . . . . . . ......... A7 AS. Biodegradation .......................... A8 A6. Bantha Pramer Test ........... ............ A10 A7. Immarsion . . . . . . . . . . . ................. A12 A8. Leach Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . A13 A9. References ........ ................... A17 TABLES A1. Topical Report Review, Status Summary, Solidified Waste Form and High Integrity Containers (HICs) . . . . . . . . . .......... A19

. A2. Topical Report Review, Status Summary, Waste Solidification System and Process Control Program . ................... A20 A3. Solidification Media and High Integrity Containers (HICs) Accepted at Existing Sites . . . . . . . . . ................. A22

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.f CURRENT STATUS AND PROPOSED ACTION FOR REGULATION OF LOW LEVEL WASTE (LLW)

STABILITY 1 INTRODUCTION Over the past several months, there has been increasing interest in matters deal-ing with waste form stability and topical Report reviews. Concern has been expressed by several groups, including the Advisory Committee for Reactor Safe-guards (ACRS), which has identified (Ref.1) a need ta better define the scientific bases for some Technical Position (TP) criteria and recemmended tests, and the Nuclear Utilities Management and Re aurces Council (NUMMC), which has com-missioned a study and Report (Ref. 2) on the technical bases for meeting the waste form stability requirements of 10 CFR Part 61. Low-level waste generators and vendors of solidification media and high integrity containers (HICs) and state regulatory bodies and site operators have also voiced concern. The overall level of concern has increased becrJse, for some solidification media and HICs, there has been increasing evidence, from test data, from field experience and/or from analytical calculations, that some waste forms and HICs may not have the long-term stability characteristics required by 10 CFR Part 61. This paper dis-cusses: (a) the evolution and current status of the regulatory requirements and criteria for low-level waste form stability and topical Report reviews; (b) problems encountered in using the current criteria and in following the current regulatcry procedures; and (c) recommendations on ways to improve the current situation. The purpose of this discussion is to provide office of Nuclear Mat-erial Safety and Safeguards (NMSS) senior management with the information used to decide on a recommended course of action for correcting some perceived defi-ciencies in the way Classes B & C low-level radioactive wastes are regulated.

2 PART 61 REQUIREMENTS 2.1 General NRC regulation 10 CFR Part 61 (Ref. 3) establi m es, for land disposal of radio-active 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 persons.

2. 2 Classes of Waste Section 61.55 of Part 61 establishes three categories or classes of wastes; viz.,

Class A, Class B, and Class C, in a generally ascending order with regard to degree of hazard (i.e., type and concentration) of radio-nuclides. Class B &

Class C wastes are required to meet both minimum as well as stability require-ments that are set forth in 10 CFR 61.56. Class C waste must also be protected (at the disposal facility) against inadvertent intrusion.

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2.3 Waste From Requirements Waste characteristics requirements are estublished in 10 CFR 61.56. There are two types or categories of requirements: (1) minimum - addressed in Section r

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" require-ments concern: (a) a prohibition against the use of cardboard fiberboard boxes; (b) treatment, packaging and maximum quantities of liquid wastes; (c) restric-tions concerning disposal of explosive or detonatable wastes; (d) restrictions against wastes containing, or capable of generating, quantities 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 infec-tious material to reduce to the maximum extent practicable the potential hazard from non-radiological materials.

Requirements for stability are provided in 10 CFR 61.56(b). Stability is defined in 10 CFR 61.2 as meaning "structural stability." While the term, structural stability, is itself not defined anywhere in Part 61, it is indicated 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 inadverten' intrueer, since a stable waste form should be recognizable and nondispersib: Therefore, in addition to recognizability and nondispersibility, the Class , & Class C waste forms are supposed to contri-bute to the ability of the facility to retain overall stability and to thereby resist water infiltration. Resistance of the disposal facility to water infil-tration is thus fundamentally associated with waste form structural stability.

Although not explicitly so stated in Part 61' the concern about water infiltra-tion stems from the fact that migration through groundwater is a potentially major pathway for radionuclide release to the offsite environment. The relation-ship of tris concern, which is a thread that runs through Part 61, to the tech-nical criteria and recommendations for immersion and leach testing will be addressed further in detail in this paper.

Further discus structural stability is provided in 10 CFR 61.56(b)(1),

where it is sts chat "a structurally stable waste form will generally maintain its physical dimu.Sions 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).

Section 61.56(b) also provides further requirements concerning waste character-istics with regard to: (a) limitations on the amount of free standing or cor-rosive 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 stable form); and (b) void spaces within the waste and between the waste and its package that must be reduced to the extent practicable.

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. s 2.4 Concepts Though the basic requirements for waste form stability are provided in Section 61.56 of Part 61, the discussion of fundamental concepts or rationale is contained in Section 61.7. In that section is provided a fairly detailed discussion of 4

stability - of the waste as well as of the disposal site. As stated there, "a cornerstone of the system is stability ...so that...[through stability of the waste and site,]... access of water to the waste can be minimized (emphasis added)." 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 radio-nuclides from the waste form is the first' step in subsequent migration of the radionuclides from the waste through the grounowater and off of the site. It is clear, therefore, that, though leaching is not men-tioned explicitly in Part 61, it is a phenomenon that is of fundamental 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."

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" (Ref. 4), which was issued in May 1983. For solidified waste forms, the tests (see Table I) essentially involve subjecting the waste specimens to con-ditions of compression, irradiation, biodegradation, leaching, immersion, and thermal 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 appli-cations. Though it is not explicitly so stated in the TP, these methods of test are intended to provide confidence, by means of exposing test specimens to relatively 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 concitions 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 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 minimum of 10E+8 rads, which is the maximum level of exposura for the waste forms expected after (300 years of) disposal; this requires the test specimens to be exposed to a much higher gamma flux than would actually be encountered under real exposure conditions. Thus, in some ways (some of) the TP tests can be 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.

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. i 3.2 Test Parameters

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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 crite-rion 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 expec-ted 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 chemi-cal 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 psi at a burial depth of 45 feet (the then-maximum burial depth at Hanford). Taking into consideration potential additional loads fro'm 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 r.ome 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. For certain types of solidfication media, (e.g. , Portland cement or vinyl ester styrene), which typically have (in the unadulterated form) compressive strengths on the order of several thousand

. psi, a 60 psi compressive strength criterion does not appear to have a strong correlation to long-term structural stability. Additionally, for viscoelastic nedia such as bitumen, which continues to deform under load, measurements of some other property (such as viscosity), in addition to or in place of compressive strength, might be needed to demonstrate long-term structural utability.

3.3 Comments from ACRS and NUMARC The NRC staff and contractor laboratory consultants have not been alone in ques-tioning the appropriateness and applicability of the TP tests and criteria.

Critical comments have been received on this matter from other groups such as ACRS and NUMARC. In a letter dated No. ember 10, 1987, ACRS raised several issues regarding the relationship between the tests called out in the 1983 TP, and the requirements for waste form stability established in 10 CFR Part 61. The ACRS Ftated in the letter that there is a need to better define the scientific bases for the tests discussed in the TP (the basis for the leaching tests was singled out as not having a clear connection to waste form stability or to Part 61).

The ACRS also had the impression that some criteria (such as leaching) were intro-duced only "for the convenience of the Agreement States" or the operators of disposal facilities. As indicated in earlier discussion in this paper, there is a clear association between the fundamental objective of Part 61 to minimile contact of the waste with water and the need to conduct leaching and immersion tests. However, the staff has agreed (as stated in a letter dated January 11, 1988, from Victor Stello to William Kerr--Ref. 5) that there is in general a need to better define the scientific bases for the waste form TP and to provide LLW STABILITY RPT 4

Table 1 ir. vied 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 '3TM G21 & G22 No growth (b) &

comp. str.> 60 psi

4. Leachability .il:S 16.1 Leach index of 6 ,

5. Immersion (See 1983 TP) 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 (See 1983 TP) Homogeneous &

+

correlates to lab size test results (a) The 1983 TP calls 'or a 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-step procedure for biodegradation testing: if observed culture growth rated "greater than 1" is cbserved 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." From this test, a total weight loss extrapo-lated for full-size waste forms to 300 years should produce less than a 10 per-cent loss of total carbon in the sample.

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LLW STABILITY RPT 5 N --

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a clearer description of the connection between the Positions and the NRC regu-lations they are intended to support.

In a rather large-scale and comprehensive study conducted for NUMARC by the Envirosphere Company (a division of EBASCO Services, Inc.) and WMG Inc., an evaluation was performed of the technical and regulatory bases for specific recommendations for waste form criteria and stability that were provided in a draft Regulatory Guide (Ref. 6). The document that the industry group reviewed was a working draft of a Regulatory Guide that was in preparation by the NRC staff as a potential update of the 1983 TP. In addition to investigating the bases for the recommended criteria in the draft Regulatory Guide, the intent of the NUMARC study was to evaluate the "relevance" of the criteria and to recem-mend alternative criteria and test procedures. It should be noted that some of the criteria identified in the draft Regulatory Guide were new or different from those that are contained in the 1983 TP. For example, the draft Regulatory Guide addressed proposed limits on the reductions in compressive strengtn that should be allowed after exposure to test conditions for bio-degradation, immersion, etc. This approach is not followed in the current TP, where a single minimum value of compressive strength is recommended.

Some of the conclusions and recommendations reached in the NUMARC study (as pro-vided in its Report) include the following:

1. The immersion tests should use one, not two, leachants, and should run for five, not ninety days.

2. The post-immersion compressive strength test parameters should be changed to show (a) for brittle material, no greater than 20% loss of strength (mini-mum strength of 90 psi), and (b) for viscoelastic materials, no greater than 25% los- (minimum strength of 75 psi).

3. The radiation stability test should be omitted for certain waste forms and waste streams.

4. The thermal degradation test should be eliminated.

5. The biodegradation test should be replaced with an improved test.

It should be realized that one of the primary considerations involved in the NUMARC conclusions and recommendations appears to be cost. Thus, in proposing elimination of certain tests and reductions in scope of others, the costs for NUMARC contributing utilities would be reduced. (This cost reduction would presumably be indirect because the direct costs of qualifying a waste form solidification agent or HIC are borne by the vendor.) A second factor appears to be an initial assumption on the part of the investigators that the tests called out in the 1983 TP are intended to duplicate actual conditions expected in the field. As noted earlier in this discussion, this is not the case. The TP tests are instead intended merely to subject the waste form and HIC material to conditior:s that would be sufficiently challenging (in terms of physical para-meters such as stress or temperature) to provide indictions of the ability of the waste form to withstand somewhat similar (not necessarily identical) condi-tions and to remain integral for 300 years.

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3.4 Standard Methods of Test Though tid 1983 TP refers to several ASTM or ANS Standard Methods of Test (see Table 1), none of the listed Standards (Refs. 713) other than the ANS 16.1 test for leachability were developed specifically for the testing of lowlevel waste forms. All the tests other than the leach test are adaptations of industry stan-dards that were developed originally for specific nonradio active material appli-cations. For example, the ASTM B553 thermal cycling test was developed for metalplated, plastic automobile parts, and the ASTM 01074 compressive strength test (which is used for testing viscoelastic materials) was developed for test-ing road bitumens. As a result, various details of the test procedures are open to interpretation, as are the results of the tests. An appendix to this Report provides a discussion of the six primary tests { compressive strength, radiation stability, biodegradation, leachability, immersion, and thermal cycling}, along with the associated acceptance criteria that are called out in the 1983 TP.

This discussion includes: (a) the linkage of the tests to Part 61 waste form stability requirements; (b) the rationale for the acceptance criteria originally and currently in place; (c) the strengths and potential weaknesses of each test; and (d) some suggestions on ways the tests might be modified and improved or replaced.

3. 5 Waste Solidification and HIC Problem Areas There has been considerable research and field experience obtained with HICs and waste 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.14) 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 the 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 - There are two primary types of bitumen that are used to solid' /

low-level radioactive waste: (1) "distilled" and (2) "oxidized." A tv cal Report has been submitted for review on each of these materials by se .rati vendors. To this date, the NRC staff has not been presented with an-evidence that the distilled bitumen can provide stabilized waste fe as that meet the 60 psi compressive strength criterion. Therefore, in Fet ;ary 1988, the technical review of the topical Report on distilled bit nen was discontinued, and tt:e topical Report was returned (Ref.15) to ' ie vendor (Associated Tecnnologies, Inc.). The topical Report for the ' .idized bitumen has been approved (Ref.16).

o High Density Polyethylene Containers (HPDEs) - As e r- it of an allegation that HDPE HICs do not have sufficient strength to withstand the stresses imposed by the weight of material placed above the HICs in a burial environ-ment, the NRC contracted with Brookhaven National Laboratory (BNL) to analyze existing data on creep of polyethylene and to develop a model and LLW STABILITY RPT 7 l

criteria that could be used to evaluate the structural stability of the HICs. BNL recommended (Ref. 17) 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 model, indicate that large HDPE HICs may not satisfy the criteria. The HDPE HIC vendors have all been notified (Ref. 18) (along with the Agreement States) and requested to show via (a) analyses, (b) testing, (c) administrative proce-dures, and/or (d) redesign that their HICs can satisfy the criteria. Each of the HDPE HIC vendors has submitted information that is under review by NRC staff and consultants.

4 THE TOPICAL REPORT REVIEW PROCESS

4.1 Background

As noted earlier, the purpose of the "1983 Technical Position on Waste Form" is to provide guidance on an acceptable approach for demonstrating compliance with 10.CFR Part 61 requirements for LLW structural stability. Under current procedures, the NRC provides a "central" review of topical Reports on waste form solidification media and HICs. The central review is intended to be applicable for all disposal sites. A brief description of the evolution and current status of this review process is provided below.

4.2 Development and Evolution The current process for NRC's reviews of topical Reports on waste form solidifi-cation, HICs and computer codes for classifying waste originated as a result of several actions that occurred primarily during calendar year 1982: (the founda-tion for these actions and agreements, hcwever, was laid in a set tes of earlier activities that occurred over several years, but which will not bt addressed here in the interest of brevity). The 1983 "Technical Position on Naste Form" was completed in May 1983 and made available to the public in June 1383. 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 ba 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 seven Reports have been submitted after the June 30, 1984 expiration date.

In November 1983, NRC's Division of Waste Management (0WM) participated in a review of the South Carolina Agreement State Program. South Carolina (SC) had established acceptance criteria for HICs in 1980 and had issued several Certifi-cates of Compliance (Cs of C) to HIC vendors beginning in May 1981, based on those criteria. The DWM's examination of SC's HIC reviews was limited 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.

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In December 1983, a meeting (Ref. 19) was held in Bethesda to discuss the 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.

g 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.

4.3 Grandfathering A key outcome of the December 1983 meeting in Bethesda concerned "grandfather-ing." It was decided that South Carolina (Nevada and Washington had not yet '

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 ir, topical Reports submitted before June 30, 1984 would still be acceptable under a grandfatnering arrangement. A list of HICs and solidification media that are currently accepted at Barnwell, Beatty, and Hanford, respectively, can be found in the Appendix.

4.4 NRR Process Control Plans (PCP) Reviews While HMSS has been reviewing HIC designs and waste solidification media formulations in accordance with 10 CFR Part 61 requirements for structural 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 interactions of the solidification equipment with the plant systems and operation from the standpoint of reactor safety. There has been some question with respect to the scope of the NRR review and its effects relative to the NMSS review. This is discussed in the following areas:

1. While NRR reviews PCPs from the standpoint of systems effects, NMSS also reviews PCPs (and "Use Manuals, for HICs), but from the standpoint of assuring that the processes used in preparing the waste forms and HICs will produce stable products, similar in characteristics to those test +d in accordance with Part 61 and the 1983 Technical Position. The division I

of responsibilities and the distinction between the types of findings reached by the two Offices has been found to be unclear to individuals l

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within the Agency as well as to users of the praducts; e.g., the utilities.

This stems from the fact that a typical "geaeric" PCP addresses, in part, (a) process variances and ranges and (b) product acceptance criteria, which are addressed, as well, in NMSS's reviews of the topical Reports dealing with waste form stability.

2. NRR approvals of PCPs cover a period of time that began several years before the promulgation of Part 61. NRR has approved PCPs for solid-ification agents that in some cases address waste concentrations that NMSS is now finding to be unacceptable with respect to long-term structural stability. Thus, there is an apparent need to make it clear to the users (and NRC staff) that the prior (and future) NRR approvals apply to the systet only, not the waste formulation.

3. Reactor Plant Technical Specifications typically do not include the PCPs.

Inspectors, therefore, generally have no criteria or procedures to use for inspection of the waste solidification processes. From discussions with NRR and inspection staff, it appears that nuclear power plant radwaste operations receive only a few hours (4-8) inspection each year.

4. Though NRR reviews and approves plart PCPs, the utility may then implement changes in the PCP and advise NRR, or a semi-annual basis, of the changes.

NRR then has the option of reviewing the changes. NRR is, however, way behind in its review of the PCP changes because of resource limitations.

Thus, whether the procedures that were developed by the vendor to assure production of a stable waste form are in fact still being followed by a given utility user is a significant question.

5. The generic PCPs tend to be extremely general in nature, leaving consider-able latitude to the user to modify the process to specific plant conditions.

Thus, even if the plant radwaste operators follow the generic PCPs rigorously, there appears to be a fairly high possibility that the waste forms may not possess the requisite long-term structural stability because the PCP followed at the plant may not correspond to the process used in qualifying the waste formulation in laboratory tests.

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 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 design calculations. Prototypes can then be built and tested, and the test results can be checked agair.st 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 May 1988). The staff's evaluation Reports for solidifica-tion media topical Reports are carefully written to clearly specify the waste LLW STABILITY RPT 10

k 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 those held by the test specimens used in the qualifying tests.

As of May 31, 1988, a total of 25 topical Reports has been submitted to NRC's Nuclear Material Safeguards for review. Of these, seven have been approved, three have been withdrawn, two have been returned, and thirteen are still under review. A summary of the review status, with' a breakdown of the type of product covered by each topical Report, is presented in a table in the Appendix.

A similar breakdown is provided for the PCP topical Reports reviewed by NRR.

5

SUMMARY

DISCUSSION 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 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 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 NRC staff, in a draft Regulatory Guide, has proposed some modifications to the 1983 tests and criteria.

An industry group has critiqued a working draf t of the Guide and has recom-mended that certain tests be eliminated or modified, along with the associated acceptance criteria. In addition, the ACRS has raised several issues in a letter that called for a better definition of the scientific bases for the tests identified in the Technical Position and a clearer description of the connection between the tests and test criteria and the NRC regulations they are intended to support. The staff has agreed with the ACRS that those relation-ships need to be better explained. The discussion in this Report (including, in particular, the Appendix) addresses the relationships in question and may serve as a vehicle for transmitting the requa ted information to the ACRS.

The most widely applied test and criterion identified in the Technical Fosition is the compressive strength test, which is recommended for virgin (otherwise untested) material as well as waste forms that have been subjected to various conditions of immersion, radiation, biodegradation, 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 cove'ed 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 forms. They are intended to be generically applicable, but as evidenced by both field experience as well as LLW STABILITY RPT 11

laboratory tests, some waste forms have exhibited unstable behavior. In particular, there have been problems with cement-sol.idified 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 forms, 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 May 31, 1988, NRC has reviewed and approved three HIC and four waste solidification media Topical Reports, while three have been withdrawn and two have been discontinued.

While NMSS reviews topical Reports for HICs and solidification media under 10 CFR Part 61, NRR reviews related Topical Reports on process control plans.

There appears to be some question in regard to what the responsibilities of each NRC Office are and how the two Offices interface. The PCPs appear to be written in a relatively broad and general manner. Few are associated with plant Technical Specifications or are subject to audit by reactor inspectors. In addition, the plant PCPs are subject to modificatirn without NRR review or approval. Consequently, there is little assurance that the procedures developed by a solidification medium or HIC vendor are, in fact, actually followed by the reactor radwaste system operators.

6 CONCLUSIONS AND RECOMMENDATIONS Based on the considerations addressed in the discussion provided earlier in this document, the following conclusions and recommendations are provided:

1. While the presently used waste form stability tests and criteria have served well collectively as a discriminator for "good" versus "poor" waste form solidification media and formulations, none of the tests or criteria should be considered "perfect." No single test is a direct measure of a material's property that can be correlated in a quantitative way with long-term (300 year) structural stability. Therefore, one alternative approach would be to conduct a study of the need for more appropriate tests and criteria for LLW form structural stability. The study might take various forms, but one approach is to form a task force that would consist of at least one individual from NMSS, the Office of Nuclear Regulatory Research (RES) and one or more National Laboratories. The mission of the task force would be to ascertain the need for more appro- -

priate criteria and tests (or changes to the existing tests and criteria) and to develop specific recommendations in that regard. It is anticipated that the task force would require a minimum period of 15 months to conclude its work and to develop its recommendations (which would be subject to peer review). The task force should be provided with technical assistance resources to aid in accomplishing its work, if this option is pursued.

, LLW STABILITY RPT 12

2. An alternative to the attempted development of improved criteria and tests is to retain the current test and criteria with minor modifications. This approach could be justified on the grounds that (1) the current battery of j tests are working as a collective group to' eliminate the poorer waste forms i and (2) the NRC currently has limited resource:, with which to conduct or support the development of new criteria.

3. Until and unless the task force recommenda' ions are implemented, the review of waste form solidification agents and HICs would continue to be ,

carried out using the existing criteria called out in the 1983 Technical Positio1, as modified to reflect more recent information on cement cracking and disintegration, high density polyethylene container creep, buckling, and stress, and low-viscosity bitumen. The reasons for continuing the reviews are that the current tests and criteria are serving well, as a collective group, to weed out some of the poorer quality waste forms. It is necessary to continue this important work so that potential users can make informed choices regarding the types of solidification agents or HICs that can be safely used.

4. If a task forta is formed, and if it were to conclude that new or improved criteria and tests are needed and that the new tests and criteria can be readily identified (not necessarily a sequitor), implementation of the task force recommendations would be achieved through the development of a new Technical Position (or revision of the existing 1983 TP) that would specify testing procedures and criteria for demonstration of long-term stability of HICs and waste forms. Following the promulgatien of a new or revised TP, systematic review would be. conducted of the previously approved HICs and waste forms to determine whether additional qualification testing were needed. In those cases where additional data were required, the venders would be informed and granted a specified period of time in which to develop and submit their data for review.

5. The acceptance of new HICs or solidification media that are addressed in new topical Reports prior to the review and approval of the Topical Reports should be prohibited. Grandfathering of HICs or solidification media already under review should be discontinued within twelve months following the issuance of an Information Notice or Generic Letter announcing the end of grandfathering of new topical Reports.

6. NRR should examine the PCPs of the individual power plants to assure that the operators are conforming to the generic PCPs approved by NRR and the process details reviewed by NMSS. NRR should consider incorporating the PCPs into the plant Technical Specifications so that NRC inspectors can have appropriate documentation for their inspections. The PCPs should be improved so that they will provide better assurance that the waste forms will correspond to approved formulations. Revisions to the generic PCPs can be accomplished via amendments to the existing PCP Reports, which would be subject to review and approval by NRC. NRR should not issue new guidance on PCPs without NMSS concurrence and coordination.

7. For waste forms or HICs that are not approved because they are not assured of 300 year structural stability, it will be necessary to either attempt to provide some quantification of the effects of prior disposal of those LLW STABILITY RPT 13

.. i I

.- /

wastes at the existing sites or to provide at least some qualitative rationale for why such analyses are not necessary. Any conclusion that unstable wastes have been disposed of (at Barnwell, Beatty, and Hanford) will require some consideration of potential remedial-action.

o LLW STABILITY RPT 14

7 REFERENCES .

1. William Kerr, Chairman, Advisory Committee for Reactor Safeguards, Letter to V.S. NRC Chairman, Lando W. Zech, Jr. , November 10, 1987.

f 2. W. Chang. L. Skoski, R. Eng, and P.T. Tuite, "A Technical Basis for Meeting the Waste Form Stability Requirements of 10 CFR 61," Nuclear Management and Resources Council, Inc. Report, NUMARC/NESP-002, April 1988.

, 3. U.S. NRC, 10 CFR Part 61 - Licensing Requirements for Land Disposal of Radioactive Waste, Final Rule, 47 FR 57473, December 27, 1982.

4. U.S. NRC, "Technical Position on Waste Form," Rev. 0, May 1983.

5. Victor Stello, Jr. (U.S. NRC), Letter to William Kerr (ACRS), January 11,

1988.

i

6. U.S. NRC, Draft Regulatory Guide, "Low-Level Waste Form Stability," October 1986.

7. American Society for Testing and Materials, Compressive Strength of Cylindrical Concrete Specimens, ASTM C39, October 1984.

8. American Society for Testing and Materials, Com)ressive Strength of Bituminous Mixtures, ASTM 01074, ASTM D1074, Fe)ruary 1983.

9. American Society For Testing and Materials, Compressive Properities or Rigid Cellular Plastics, ASTM D1621, 1979.

10. American Society for Testing Materials, Deformation of Plastics under Load, ASTM D621, 1976.

11.- American Society for Testing and Materials, Thermal Cycling of Electoplated i

Ceramics, ASTM B553, 1979.

12. American Society for Testing and Materials, Determining Resistance of Synthetic Polymeric Materials to Fungi, ASTM G21, 1970.

13. American Society for Testing and Materials, Determining Resistance of Plastics to Bacteria, ASTM G22, 1976.

14. P.L. Piciulo, J.W. Adams, J.H. Clinton, and B. Siskind, "The Ef fect of Cure Conditions on the Stability of Cement Waste Forms after Immersion in Water," Brookhaven National Laboratory Report, WM-3171-4, August 1987.

15. Malcom R. Knapp (U.S. NRC), Letter to J.E. Day (ATI), Docket No. WM-91, 1 March 4, 1988.

l

16. Michael Tokar (U.S. NRC), Letter to William J. Klein (WasteChem), Docket

! No. WM-90, January 22, 1988.

l

17. J. Pires, "Review of the High Integrity Cask Structural Evaluation Program (HICSEP)," Brookhaven National Laboratory draft Report, April 6, 1987.

LLW STABILITY RPT 15

. 7 REFERENCES, Cont.

18. MichaelTokar(U.S.NRC),LettertoJohnChando(TFCNuclear), October 15, 1987: (identical letters to W-Hittman and Chem-Nuclear Systems).

19. Cardelia H. Maupin and Kathleen N. Schneider (U.S. NRC), "Chronology of 't Topical Reports and High Integrity Containers Review Process," memorandum for topical Reports file, February 14, 1988.

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APPENDIX WASTE FORM TESTING DISCUSSION A1. INTRODUCTION TO WASTE FORM TESTING The main body of this Report is intended to provide the basic information needed to develop a strategy for improving NRC's regulation of low-level radioactive waste long-term stability and to provide recommendations in that regard. The discussion provided in this Appendix to the Report focuses primarily on the specific test recommendations in the "1983 Technical Position on Waste Form." Items addressed in this discussion include the linkage between the tests and Part 61, rationale for the criteria, strengths and weaknesses of the tests and criteria, and ways that the individual tests and criteria might be improved.

A2. COMPRESSION Linkage between the compressivt strength test recommendations in the "1983 Technical Position on Waste Form" (Ref. A1) and 10 CFR Part 61 (Ref. A2) requirements for waste form stability is provided by 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 the expected disposal conditions such as weight of-overburden and compaction equipment...." (ernphasis added).

As noted in the discussion of "Test Parameters" in the main body of this Report, a cover material density of 120 lbs./cu.ft. was assumed in the 1983 Technical Position (TP). This yielded a pressure of approximately 37.5 psi at a burial depth of 45 feet, which was the maximum burial depth at the Hanford, .

Washington LLW disposal site at the time the TP was promulgated. Taking into consideration the potential additional loads from trench compaction equipmnt, waste concents, etc. , the compressive strength criterion was set at 50 psi.

This has been raised to 60 psi to reflect an increase in burial depth at Hanford to 55 feet. It is important to realize that it was noted in the 1983 TP that "many solidification agents will be easily capable of meeting the 50 psi limit for properly solidified wastes." For those cases, therefore, it was stated in the TP that process control parameters should be developed to achieve the "maxicum practical" compressive strengths, not simply the minimum accept-able compressive strength. In the case of cement-solidified wastes, this provision appears to have been interpreted in an extremely liberal fashion by some vendors in as much as some of the waste stream formulations for which com-pressive strength data have been provided by the vendors exhibit compressive strengths on the order of 100 to 200 psi following the immersion, irradiation, thermal cycling, and/or biodegradation tests. For those cases the position held by the vendors is that the waste forms meet the TP compressive strength criterion because the compressive strengths exceeded 60 psi.

As noted in several places in this Report, compressive strength testing is designated not only for virgin material, but also for waste form specimens that have been exposed to various test conditions (see Table 1 of the Report). The 1983 TP called for a minimum compressive strength of 50 psi (now 60 psi) after completion of the tests. However, in a working draft of a Regulatory Guide on "Low Level Waste Form Stability" (Ref. A3) that was released for informal comment, allowable reductions in strength on the order of 10 to 20 percent were considered. If adopted, this would be significant departure from the 1983 LLW STABILITY RPT A-1

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4 V

TP, where allowable reductions in strength are not addressed even in a conceptual way. In commenting on the draft Regulatory Guide, the Nuclear Utilities Management and Rescurces Council (NUMARC) Report (Ref. A4) recom-mends maximum acceptable strength reductions of 20 to 25 percent (depending on the type of test) as well as minimum post-test strengths of 75 to 90 psi ,

(depending on the type of material - bituminous vs. brittle). NUMARC's revised post-test criteria are intended to incorporate a safety factor as well as to address the variability'of test data that is inherent in the tast procedures.

Some additional information and comment on compressive testing are provided below.

A2.1 American Society for Testing and Materials (ASTM) C39: Compressive Strengtn of Cylindrical Concrete Specimens Scope: This test method (Ref. A5) covers determination of compressive strength of cylindrical concrete specimens such as molded cylinders and drilled cores.

It is intended to be limited to concrete having a unit weight in excess of 50 lbs/cu. ft., but it is currently used to test LLW specimens comprised of a variety of materials including vinyl ester styrene, gypsum, and vinyl toluene (AZTEC) solidified wastes.

Summary of Method: This test method consists of applying a compressive axial load to molded cylinders or cores, at a rate which is within a prescribed range, until failure occurs.

Significance and Use: Care must be exercised in the interpretation of the significance of compressive strength determinations by this method since strength is not a fundamental or intrinsic property of concrete made from given materials. Values obtained will depend on the size and shape of the specimen, batching, mixing procedures, the methods of sampling, molding, and fabrication and the age, temperature, and moisture conditions during curing.

Apparatus: Testing Machine - According to the Standard, the testing machine must be capable of providing rates of loading prescribed in the Standard; viz.,

0.05 in./ min. when the machine is running idle (for screw-type machines); or 20 to 50 psi /s. The machine is supposed to be power-operated and should apply the load continuously rather than intermittantly, and without shock.

Specimens: There are several prescriptions on specimen dimensional variances such as diamaters (must not vary more than 2 percent when measured in different directions), perpendicularity of the ends (must not depart by more than 0.5 degrecs), etc.

Procedure: This section of the Standard addresses moist storage and testing, permissible time for testing specimens of given test (cure) time, how to place the specimen, and rate of loading.

Calculation: The compressive strength of the specimen is calculated by dividing the maximum load carried by the specimen during the test by the average cross-sectional area. If the length-to-diameter ratio is less than 1.8, the result is adjusted using a correction factor provided in a table.

LLW STABILITY RPT A-2

A2.2 ASTM D 1074 - 83: Compressive Strength of Bituminous Mixtures Relationship to the 1983 TP: The TP says that compressive strength tests should be perforrced in accordance with ASTM D1074 (Ref. A6). Note: The August 1987 version of the draf t Regulatory Guide on "LLW Form Stability" says that "For waste forms capable of viscoelastic flow, e.g., bituminous products, stability can be demonstrated by documenting that the site ~ operator has im-plemented an administrative control procedure that ensures sufficient backfill around the waste containers to minimize the voids." In other words, com-pressive strength testing of bitumen would no longer be required. Thus, it would be up to the site operator to ensure structural stability of the waste form through proper backfilling around the waste form. However, it appears that this could be a violation of Part 61, because according to Subsection 61.56(b)(1), "Structural stability can be provided by the waste form itself, processing the waste to a stable form, or placing the waste in a disposal container or structure that provides stability after disposal." Backfill meets none of those provisions. Staff no longer supports the position that backfill alone will provide structural stability for bituminized wastes.

Scope: This method is for compacted bituminous mixtures of "the hot-mixed, hot-laid type for use in pavement surfaces and base courses...."

Sionificance and Use: This test method also describes the methods for molding, curing, and testing of specimens. Note: This test method permits the use of rehtated mixtures, but acknowledges that the resulting compressive strength va hes will be higher than for newly prepared mixtures due to the change in binder viscosity. Quest lon: Could the vendors use this to advantage by reheating the waste form test specimens before testing to jack up the com-pressive strengths?

Apparatus: The testing machine must have capacity to provide a range of accurately controllable rates of vertical deformation. The reason is that the rate of vertical deformation for the compression test is specified as 0.05 in./ min.-in. of specimen height, and it may be necessary to test specimens ranging from 2 by 2 in. to 8 by 8 in. to maintain the specified minimum ratio of specimen diameter to particle size.

Preparation of Test Mixtures: The Standard contains a lengthy section on procedures for preparing test mixtures. This section would seem to be largely irrelevant for LLW specimens, which, to be representative of the actual waste forms, should presumably have to be prepared using the type of apparatus used for solidifying LLW.

Test Specimens: The Standard states that generally the test specimens should be cylinders 4.0 in. in diameter and 4.0 in. in height and note that the size of the test specimens has an influence on the results of the compressive strength test. Specimens other than 4x4 in. may be used with the following provisions:

(a) The height must be equal to the diameter within 2.5%;

(b) The diameter must be not less than 4 times the nominal diameter of the largest aggregate particles; LLW STABILITY RPT A-3

(c) The diameter must not be less than 2 in.;

(d) The rate of deformation must be kept constant during the compression test.

Molding and Curing of Test Specimens: There is a large section in the Standerd on molding and curing of test specimens. This section would seem to be moot for LLW test specimens for reasons discussed above.

Procedure: The Standard specifies a test temperature of 77 F, which is to be attained by storing the specimens in an air bath maintained at the test temperature for not less than 4 h. Specimens 4 in. high are supposed to be tested at a rate of 0.2 in./ min. One bitumen solidification vendor has been conducting compressive strength testing at 60 F because the type of bitumen used in his process has such low strength it ha difficulty meeting the 60 psi criterion.

Calculation of Strength: The compressive strength is determined by dividing the maximum vertical load obtained during deformation by the original cross-sectional area. An average of a minimum of 3 specimens should be used as the Reported compressive strength value.

Precision: The single-operator standard deviation of a single test result (a single test result is defined as the average of a minimum of 3 separate com-pressive strengths) has been found to be 21 psi.

Remarks:_ Brookhaven National Laboratory (BNL) (in NUREG/CR-3829) (Ref. A7) points out a number of problems with this test, among them the fact that the compressive strength of bituminous materials decreases with decreasing rate of deformation, and this test was developed for road bed bitumen, which is sub-jected to very short-term load conditions, compared to a LLW form.

The TP does not specify a procedure for calculating a compressive strength in those cases where ASTM D-1074 (Ref. A6) fails to show a maximum in the stress-strain curve. In such cases, it has been suggested that the stress to provide a given strain should be determined, but at what percent--5%,10%, more?

Generally, the higher the strain value allowed, the higher the Reported strength value will be. Currently, the value of stress at a strain of 10% is used, but the basis for this is not well-documented (though one possibility (Ref. A8) is that it originated with, or was derived from, ASTM D1621, (Ref.

A9) for testing of rigid cellular plastics). In ASTM D1621, it is recommended that the strength be determined from the stress at the yield point or at a strain of 10% in the absence of a yield point. It has been customary for LLW bitumen vendors to determine the stress / strength value from the intercept on the stress / strain curve obtained by taking a vertical line from a 10% offset on the strain (i.e., "X") axis. This procedure is not the same as that used in metallurgical stress / strain testing, where an offset yield strength is obtained by taking a line parallel to the straight line portion of the stress / strain curve. A vendor of low-strength bitumen has petitioned the NRC to consider revising the method of strength calculation to allow use of the parallel offset method; this would result in a significant increase in the values of strength reported.

LLW STABILITY RPT A-4

T'e n August 1987 version of the draft Regulatory Guide on "Waste Form Stability" recommends that if the compressive strength (rather,than a leach index of 6) is used to determine stability after the other TP tests such as immersion, then ASTM D1074 should be used and that the compressive strength should not have decreased by more than 10 to 20%, depending on the type of test (e.g., immer-sion, radiation, thermal cycling), from the pretest value. The recent NUMARC study, titled, "A Technicai Basis for Meeting the Waste Form Stability Require-ments of 10 CFR 61," recommends a 25% allowable decrease. The reason for this is the high variability (see remarks on test precesion) in test results.

For viscoelastic materials such as bitumen, the fundamental question remains:

should some other mechanical / physical property, other than compressive strength, be used as an acceptance criterion and measure of long-term stabilty?

One other property that has been suggested could be used for this purpose is viscosity. Another property that has been considered is creep, which, as indicated in an early working draft of the Regulatory Guide on "Waste Form Stability," was to be determined using a creep test such as a modified ASTM D621 (Ref. A10). Using that test, stability was to be demonstrated by showing that the creep of the bituminized waste form would be less than 10 percent '

extrapolated over 300 years. However, as noted in the NUMARC Report (Ref. A4),

the 0621 test was in the process of being removed from the ASTM listing of procedures "...because the test procedure and testing equipment prescribed in the procedure are antiquated." Also pointed out in the NUMARC study was the fact that to pass the test for a test specimen one-half inch high (as recommended in the Standard), the total deformation after 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> must be less than, or equal to, approximately 20 microns. Furthermore, assuming ten data points are required to extrapolate the total deformation to 300 years, the measured deformation at each time interval has to be much less than 20 microns.

NUMARC points out, and the staff agrees, that there are serious questions on the feasibility of preparing the specimen surface with such precision for a viscoelastic material such as bitumen. Additional approaches to testing bitumen are provided in a BNL Report (Ref. A7).

A3 THERMAL CYCLING Linkage between the thermal cycling test recommendations in the 1983 TP is not as direct as it is with some of the other tests such as compression, irrad-iation, biodegradation, etc. The reason for this it that thermal effects are not called out specifically in 10 CFR 61.56(b)(1), as they are for the other factors. Section 61.56(b)(1) does, however, address "internal factors," and temperature, and temperature effects, are unquestionably internal factors, just as irradiation or chemical changes (which are specifical mentioned in Part

61) are. Some facts concerning the thermal cycling test sailed for in the 1983 TP are as follows:

A3.1 ASTM B553 - 79: Thermal Cycling of Electroplated Plastics Scope: This test method (Ref. All) covers the thermal cycling procedure and apparatus used to test electroplated plastics for evaluation of serviceability.

1 Apparatus: The apparatus should consist of a circulating air heating chamber sufficiently powered, insulated, and controlled to closely maintain the preset temperature. The controller and recorder used for chamber control and records LLW STABILITY RPT A-5 x

should be accurate to plus-or-minus one degree C. All points within the working area of the test chamber should remain within plus-or-minus 3 degrees C. The air circulation should be controlled to permit a consistent rate of heating or cooling of the parts under test.

Procedure: The parts may be introduced into the chamber unmounted, or mounted in a manner simulating assembly, if so desired. Each thermal cycle should begin by either placing the samples in a room-temperature chamber and heating the chamber up to the high limit,or by placing the samples directly into a chamber at the high limit.

The 1983 Technical Position specifically states that the test procedure should follow the following paragraphs from the Standard:

5.4.1. Expose the parts for 1 h at the high limit.

5.4.2. Allow the parts to return to 20 C and maintain at this tempe ature for 1 h. This may be accomplished by removing the parts from the chamber. Some types of apparatus are so constructed that the parts need not be removed during this step.

5.4.3. Expose the part for 1 h at the low limit teinperature.

5.4.4. Repeat 5.4.2. This constitutes one full thermal cycle.

The Standard continues with Paragraph 5.4.5 (which is not specified by the 1983 TP), which requires that the parts be inspected for coating defects produced by the thermal cycling. There is no analogous call for inspection for defects by the 1983 TP. The TP only cites the compression test and states that the specimen size should be consistent with that required for the compression test.

Remarks: The 1983 TP calls for a series of 30 thermal cycles to be carried out in accordance with Sect. ion 5.4.1 through 5.4.4 of ASTM B553. Neither the TP or the Standard, however, specify the length of time for a complete cycle. All the Standard says is that the "parts" should be "exposed" for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at the high limit and the low limit. The "parts" or specimens do not have to be thermocoupled. Thus, thermal equilibrium in the specimens is not a require-ment, except perhaps at the 20 C temperature (Section 5.4.2) where the Standard says that this temperature should be maintained for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Inasmuch as this Standard was written for electroplated parts, not for solidfied multiphase media, the Standard, as currently written, may not be fully appropriate for LLW forms.

l NUMARC has commented unfavorably on the thermal stability test. Grounds given in the NUMARC Report are that: (1) there is "...no firm technical basis ...for the test procedures, or the tests specified....." and (2) the ASTM B553 (Ref.

All) procedure is not applicable to thermal testing of waste forms. Therefore, l NUMARC recommends that the test be eliminated.

i The staff does not at this time concur with the NUMARC study with regard to the reconmendation to eliminate the thermal cycling tests. The reason for this is l

, that the test has served the staff well in distinguishing between "strong" and I

"weak" solidified waste forms. The thermal cycling test imposes a stress (due to differential thermal expansion) between the different phases and LLW STABILITY RPT A-6 l

l l

, microconstituents in the waste form. By cycling between the maximum and minimum temperatures called for in the test, cracks.that may have been initiated in the test specimen will propagate and eventually measureably weaken the form. Though the specific maximum and minimum temperatures attained during the tests may not actually be attained during disposal (or transport) of the waste forms, that point is not particulary relevant in that, as discussed in the body of this Report, the tests are not intended to duplicate actual field conditions. The test conditions are intended to provide, on a short-term basis, indications of (relative) long-term stability, and the thermal cycling test does this well by subjecting the waste form specimens to a short-term thermal stress that challenges the structural capability of the specimen.

That is not to say that the test should not be modified. As noted, this test was developed for metal-coated plastics, not low-level waste forms, and the test procedure guidance could be appreciably improved by better specifying whether the specimens should be tested bare or in containers and whether thermocouples should be used to measure the specimen temperature. Moreover, the surface and bulk condition of the test specimens with respect to the observed cracks or other defects should be considered for inclusion in the acceptance criteria. These changes in test procedure and acceptance criteria would be of a relatively minor nature, however, and could be implemented with minimal effort.

A4 IRRADIATION Linkage between the irrradiation test recommendations in the "1983 Technical Position on Waste Form" and 10 CFR Part 61 requirements for waste form stability is provided through 10 CFR 61.56(b)(1), where it is stated that "...

a structurally stable waste form will generally maintain its physical dimen-sions and form, under the expected disposal conditions...and internal factors such as r_adiation effects...." (emphasis added). The 1983 TP states that the specimens for each proposed waste stream formulation should remain stable after being exposed in a radiation field equivalent to the maximum level of exposure expected from the proposed wastes to be solidified. The TP then goes on to state, however, that specimens for each proposed waste stream formulation should be exposed to a minimum of 10E+8 rads in a gamma irradiator or equiv-alent. Though the TP also states that testing should be performed at the expected maximum accumulated dose, if the maximum level of exposure is expected to exceed 10E+8 rads, most radiation stability testing is, in fact, terminated at the 10E+8 rad level. There is no recommended Standard Method of Test for irradiation stability. The acceptance criterion applied to the radiation stability testing is a compressive strength value of 60 psi, which, as stated in the 1983 TP, is to be determined in accordance with ASTM C39 (Ref. A5) (for brittle materials) or ASTM D1074 (Ref. A6) (for viscoelastic materials such as bitumen) on irradiation test specimens after the i* radiation exposure. With regard to viwoelastic waste forms, the 1986 draft of the waste form Regulatory Guide (Ref. A3) allows the use of either a leach test or compressive strength test, after irradiation. If a compressive strength test were to be used, the draft Regulatory Guide specified that ASTM D1074 should be used and that the ccmpressive strength should not decrease by more than 10 percent from the un-irradiated compressive strength. An earlier draft of the "Low-Level Waste Form Stability" Regulatory Guide recommended use of the modified ASTM 0621 creep test (Ref. A10) with an acceptance criterion of less than 10 percent creep extrapolated over 300 years. For reasons discussed earlier in this Appendix, LLW STABILITY RPT A-7

_ _ -- _ _ _ , ~ ~ - . _ . _ _ _ . . __ _

=

the creep test recommendation has been abandoned. For reasons to be addressed later in this Report, the recommendation allowing either leach testing or compressive testing of viscoeltstic materials is also not presently end U sed by the NRC staff.

The basis for the 10E+8 rad minimum irradiation exposure test recommendation is that 10E+8 rads are approximately equivalent to the dose that would be acquired by a waste form over a 300 year period, if the waste form were loaded to a Cesiums-137 or Strontium-90 concentration of 10 Ci/cu.ft. This is the recommended (Ref. A12) maximum activity level for organic resins based on evidence that while a measurable amount of damage to the resin will occur at 10E+8 rads, the amount of damage will have negligible effect on power plant or disposal site safety. The observed degradation included acid formation, decreased ion retention capability, and hydrogen generation (Ref. A13). It is noted in the NUMARC Report that the 10E+8 rad recommended limit (which is not a requirement) is not linked to the Part 61 classification limits for Class A, B, or C wastes. As an example, for Class C Cesium-137 waste loaded to the Class C concentration limit, 10E+8 rads are achieved in about 20 years.

However, for the over-whelming majority of waste forms, the 10E+8 accumulated radiation exposure value is conservative (Ref. A14).

In the NUMARC study, it is concluded that irradiation testing to 100 megarads is reasonable for waste forms that contain orgaaic ion exchangu media, but that exposure to this dose does not have an adverse effect on other wastes or on polymer stabilized waste forms of any kind. Therefore, NUMARC recommended that such types of waste forms be specifically ex::luded from further testing.

NUMARC also recommended that safety factors of 1.5 and 1.25 be applied to the allowable minimum compressive strengths for brittle and viscoelastic materials, respectively, and that a decrease of 25 percent in compressive strength be allowed for viscoelastic materials.

At this juncture, the staff tends to agree with NUMARC's observation regarding radiation effects, or non-effects, on waste forms that do not contain ion exchange media, to the extent that this appears to be true for cement-solidified wastes and vinyl ester styrene. It does not necessarily apply to bituminous wastes, which have been shown to undergo swelling upon irradiation (Ref. A7).

This behavior of asphalts is believed to be due to internal pressurization and formation of gas bubbles caused by radiolytic gas generation, and appears to be a function of the rate of flux and type of bitumen and waste (Ref. A13). Gas generation in bitumen is a complex process, which at this point is not well understood. Because of the swelling effects, and because of the inherently low strength of bitumen at elevated temperatures (the irradiation causes tempera-ture increases in the bitumen test specimens), the bituminized waste form speci-mens are wrapped in tape during the irradiation in an attempt to retain their shape so that they can subsequently be compression-tested. Due to the complexity of the phenomena ir, bituminized low-leval waste, the NRC staff does not have any recommendations at this time regarding ways that the irradiation test might be improved for such waste forms. This is an area that requires further study.

A5 BI0 DEGRADATION Linkage between the biodegradation test recommendations in the 1983 Technical Position and 10 CFR Part 61 requirements for waste form stability is provided LLW STABILITY RPT A-8

through 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 the expected exposure conditions such as... microbial activity... " Biodegrada-tion testing is one of the more complex areas (with regard to the test pro-cedure) addressed in the 1983 Technical Position. The TP states that specimens for each proposed waste stream formulation should be tested for resistance to biodegradation in accordance with both ASTM G21 (Ref. A15) (for resistance to fungi) and ASTM G22 (Ref. A16) (for resistance to bacteria) and that "no in-dication c,f culture growth should be visible." It is further stated that speci-mens should be suitable for compression testing in accordance with ASTM C39 or ASTM D1074 and that following the biodegradation testing, specimens should have compressive strengths greater than 50 (now 60) psi.

For polymeric or bitumen waste forms, the TP provides some additional guidance.

In the expectation chat, while some visible culture growth would be encountered for such waste forms (due to contamination, additives, ar bio-degradable com-ponents on the surface of the specimens), such culture growth might not relate to overall substate integrity, the TP allows for some additional testing to be performed. In that regard, the TP discusses a procedure for re-doing the tests and provides additional acceptance criteria with respect to acceptable levels of culture growth ("level 1" for the repeated ASTM G21 test and "no observed growth" for the repeated ASTM G22 test, along with a compressive strength greater than 50 psi).

If growth is still observed after the extraction procedure, the TP recommeads longer term testing of at least six months duration. A test called the Bartha-Pramer test (Ref. A17) is listed as acceptable for such testing. The accep-tance criterion listed in the TP for the Bartha-Pramer method involves a determination of the loss in weight of the specimens and extrapolation of the loss of weight over a 300 year period to show that there would be less than a 10 percent loss of total carbon in the waste form.

Some additional information and comment on biodegradation testing are provided below.

AS.1 ASTM G21: Determining Resistance of Synthetic Polymeric Materials to Fungi Scope: This Standard Practice (Ref. A15) is intended to be used to determine the effects of fungi on the properties of synthetic polymeric materials in the form of molded and fabricated articles, tubes, rods, sheets, etc. (emphasis added). The Standard states that changes in properties, (e.g., mechanical and physical properties), may be determined by applicable ASTM methods.

Significance and Use: Although r.ot explicitly stated in the Standard, the fact that the emphasis in the text is on the effects of the test on the electrical and optical properties of plastict indicates that the Standard was primarily developed for plastic electrical components. The Standard states that the resin portion of these material is usually fungus-resistant in that it does not serve as a carbon source for the growth of fungi and that it is generally other components, such as plasticizers, cellulosics, lubricants, stabilizers, and colorants, that are responsible for fungus attack.

LLW STABILITY RPT A-9

Apparatus: The discussion of apparatus in the Standard focuses on glassware ,

and incubation equipment. -

Reagents and Materials: The Standard addresses purity of reagents and water in some detail. Also, since the procedure involves handling and working with fungi, it is recommended in the Standard that personnel trained in microbiology perform the portion of the procedure involving handling or organisms and inoculated specimens.

Test Specimens: The Standard indicates that the simplest specimen may be a 2 by 2-in. piece of the material to be tested. This is consistent with the Technical Position recommendation that the specimens should be suitable for compression testing in accordance with ASTM C39 or ASTM 01074. For visual evaluations, the Standard states that thres specimens should be inoculated.

Procedure: The pNcedure essentially consists of placing the specimens in suitable sterib Uishes, inoculating the surface of the specimens with a comporite spore suspension, incubating for a minimum period of 21 days, and observing for visible effects. Visible effects, in the form of observed growth on the specimens, is judged on a scale of 0 to 4, where 0 is no growth and 4 is ,

"heavy" growth (60 to 100% coverage).

A5.2 ASTM G22: Determining Resistance of Plastics to Bacteria Scope: This Standard Practice (Ref. A16) was developed for determining the effect of bacteria on the properties of plastics in the form of molded and fabricated articles, tubes, sheets, etc. It cover two procedures, A and B, where B providr.s more extensive contact between the test bacteria and the specimens thaa does A. Consistent with ASTM G21, the Standard indicates that changes ir properties may be determined by applicable ASTM methods.

Summary of Practice: The procedure described in the Standard consists of: (1) selection of suitable specimens; (2) inoculation of the specimens; (3) exposure of the specimens under conditions favorable to growth; (4) examination and rating for visual growth; and (5) removal, sterilization, and evaluation of specimens.

Significance: Analogous to ASTM G21, the Standard states that the resin I portion of plastic materials is usually resistant to bacteria, in that it does not serve as a carbon source for the growth of bacteria and that it is generally other components that are responsible for bacterial attack.

Apparatus: As in ASTM G21, the discussion of apparatus focuses on glassware and incubation equipment.

Reacents and Materials: The discussion of reagents and materials is similar to ASTF G21.

Test Specimens: The test specimen discussion is similar to that provided in 1

ASTM G21.

Procedure: There is considerable discussion of Procedure A and Procedure B in the Standard. The 1983 Technical Position does not indicate which is preferred.

LLW STABILITY RPT A-10

i A6 BARTHA-PRAMER TEST As noted in a BNL Report (Ref. A18) on biodegradation testing of low level waste streams, the ASTM G21 and ASTM G22 tests "... are sufficient for distinguishing between materials that are susceptible to biode gradation and those that are not," but they "... cannot be used to quantify the rate of biodegradation of a specimen." As acknowledged by BNL in another Report (Ref.

A7), the G21 and G22 tests are primarily screening tests. It has been suggested (Ref. A19) that more realistic estimates of the nature and extent of microbial attack on materials can be provided by an environmental simulation test. The so-called Bartha-Pramer (Ref. A17) method is one such test. In this test, samples are placed in soil in a flask with a side-arm containing a potassium hydroxide (K0H) solution. The KOH solution absorbs carbcn dioxide given off as a result of microbial respiration. Monitoring the carbon dioxide production with time thus provides a means of estimating the rate of blodegradation. A lengthy and comprehensive discussion and evaluation of the Bartha-Pramer method, including its limitations and applicability to low-level radioactive waste stream testing, are provided in Reference A7. Further discussion of the reasonableness cf the criteria and test methods is provided in Reference A18, In view of the extensive treatment provided in the BNL Reports, only some particular1y pertinent conclusions and recommendations are addressed in the following discussion.

Remarks: The NUMARC Report (Ref. A4) contains a recommendation that biode-gradation testing should bc eliminated for cement, gypsum and polymer types of stabilization media and that more research should be performed on bitumen for representative power plant waste stream compositions to determine their susceptibility to microbial growth. It is further recommended by NUMARC that a more realistic test procedure for biodegradation be identified and adopted "...

at a later date." NUMARC corcludes also that the G21 and G22 tests "... were not designed to evaluate the effects of strength of microbial growth on the structural strength of a material."

. The basis for NUMARC's statement that "... applying the G21 and G22 tests to

determine waste form stability is unnecessary" appears to rest on a reported conversation with the Chairman of the ASTM Section Committee responsible for the G21 and G22 procedures. According to the NUMARC Report (p.4-55), he indicated that "... no micro-organism will grow in the presence of low-level gamma radiation fields (above background)...." This is a rather curious statement in view of the times required for self-sterilization of low-level waste packages. It can be shown from BNL work (Ref. A20) that it would take only 1-2 years to acquire sufficient cumulative dose (approximately 10E+6 rads) to be lethal to microbes (assuming a waste form that is 'oaded to a Cesium-137

[

concentration of 10 Ci/cu.ft., which is the maximum rec.mmended concentration l for bead resin). However, that does not take into consideration the fact that

the dose rate declines with time or that the radionuclide concentrations in l actual waste forms will vary. Thus, at a point in time some years after disposal, and after the waste forms have been subjected to other long-term environmental effects, the dose rate could decline to a value such that bio-i logical attack could be initiated.

With regard to the effects of the biodegradation test conditions on waste form specimens, NUMARC cites data that are purported to show that the test pro-cedures "... have no effect on cement stabilized samples." NUMARC's data base, LLW STABILITY RPT A-11

___ _ ~ _ - - . _

however, evidently did not include some proprietary data submitted by the cement media vendors' in support of their topical reports. In one case involving cement-solidified bead resin, the post-biodegradation test com-pressive strength dec'reased approximately 85 percent from the pre-test value.

Changes of this magnitude cannot automatically be attributed solely to statistical variation in the ASTM C39 test procedure l though NUMARC attempts to make such attributions in its Report. It seems reasonable to conclude that, while cement as a medium would not support biological growth (since it is not itself a source of carbon), that is not to say that the waste material incorporated in a cement-solidified waste form would not support growth that could have an indirect effect on the mechanical properties and stability of the waste form. Hence, the staff is not at this time ready to endorse the idea of deleting biodegradation tecting 'for cemeat-solidified waste forms.

NUMARC's contention that the G21 and G22 tests were not designed to evaluate the effects of microbial growth on the structural strength of a material is

( also curious in view of the fact that, as noted in earlier discussion, the Standards specifically note that changes in properties, including mechanical properties, may be determined by applicable ASTM methods. Whether it is always necessary to determine the compressive strength of a specimen after a G21 or G22 test is questionable, however. The 1983 TP indicates that a compression tests should be performed after the G21 and G22 test, but if the tests do not result in growth, it is extremely unlikely that there would be any observable effect on strength of the specimens. Moreover, specimens suitable for bio-degradation testing are not necessarily of the size and shape most appropriate for compression testing. Therefore, it is the opinion of the staff that the procedures used in biodegradation testing and the type of acceptance criteria that should be used for the biodegradation tests are subjects worthy of further study. Several suggestions and comments on this matter are provided in the BNL Reports (Refs. A7 and A18) on biocegradation testing.

i A7 IMMERSION i Linkage between the immersion test recommendations in the 1983 "Technical Position on Waste Form Stability" (Ref. A1) and 10 CFR Part 61 (Ref. A2)

. requirements for waste form stability is provided by 10 CFR 61.56(b)(1), where

( it is stated that "... a structurally stable waste form will generally retain l

its physical dimensions and its form, under the expected disposal conditions such as the presence of moisture...." (emphasis added). There is no Standard l

Method of Test for immersion testing, but as indicated in the 1983 Technical Position, the immersion testing may be performed in conjunction with the leach testing. Inasmuch as both the leach testing, which is to be performed in accordance with the procedure in ANS 16.1 (Ref, A21), and the immersion testing

, are recommended to be performed for a minimum period of 90 days, there is an

! incentive to do the immersion and leach testing as one operation. The 1983 TP l called for a minimum compressive strength value of 50 (now 60) psi, as deter-mined using ASTM C39 or ASTM D1074, af ter completion of the immersion tests.

In a working draft of the Regulatory Guide on "Low Level Waste Form Stability" (Ref. A3), allowable reductions in streagth of 20 percent were proposed, along i

with a recommendation that a technical rationale justifying the decrease in strength (and/or observed surface degradation) be provided by the applicant.

LLW (TABILITY RPT A-12

In an opinion expressed in the NUMARC Report (Ref. A4), "... the immersion test is by far the most severe of all tests...." Whether that statement is in fact accurate is perhaps debatable, but it is undenisbly true that the immersion test has served well in identifying potential problems with certain waste formulations. The NUMARC Report refers to a 1978 study that resulted in catastrophic failure of bituminized sodium sulfate waste specimens. Since that early BNL work (Ref. A22), bituminized waste formulations have been success-fully immersion-tested. However, in a more recent BNL study (Ref. A23) on stabilized cement and gypsum waste forms, problems were observed, in the form of a typical cement strength behavior with time (along with cracking and spalling) and softening of gypsum-solidified waste forms. A brief summary of this more recent BNL work is provided in Reference A24.

The recent BNL work indicated that waste loading, i.e., concentration of waste material incorporated in the waste form, is a very important parameter affecting waste form stability. As noted in the NUMARC Report, vendors try to maximize the waste loading for their solidification medium to make it econom-ically attractive in comparison to competitors' systems. The immersion test (and related leaching test) has proved to be an extremely useful indicator of potential problems with excessive loading, as indicated not only by the BNL work, but also by vendor generated data. Hence, the staff agrees with the conclusion reached by NUMARC that "... the immersion test is important for determining the compatibility of the stabilizing medium to certain specific waste streams, and for determining the maximum permissible waste loading for a stabilization medium."

The staff also agrees with NUMARC's conclusion that the acceptance criteria should be reassessed (for reasons that have been addressed at length earlier in this Report). However, some of the specific recommendations provided by NUMARC in this regard appear to be unreasonable. For example, NUMARC recom-mends that either a maximum loss of less than 20 percent, or a minimum post-compression test compressive strength of 90 psi (up from Clfpsi to account for variability in the procedure) be permitted. If such an approach were followed, it would allow a reduction in compressive strength of 90% or more to occur (from 5000 psi to 100 psi, for instance), while still categorizing the result as an indication of "structural stability." In the opinion of the NRC staff, decreases in strength of such magnitude could not occur unless there were concomitant major changes in the structure of the waste form. Therefore, by

definition, the waste form would have demonstrated instability that would render it unacceptable.

l A8 LEACH TESTING l

Resistance to leaching is not specifically mentioned in 10 CFR Part 61, nor is radionuclide containment called out as a specific requirement for low-level waste packages. This is in contrast to the 300 to 1000 year substantially d complete containment" requirement for high level waste packages in NRC's regulation for geologic disposal of high level waste, 10 CFR Part 50 (Ref.

A25). As a resuit, this has led some (Ref. A26) to question the rationale for leach testing of solidified Classes B & C low-level waste forms. Though the l

relationship between the 1983 Technical Position recommendations for leach l

l l

l l LLW STABILITY RPT A-13 l

l

e testing and the requirements of Part'61 may not be as obvious as is the situation for high-level waste containment, the discussion below is intended to provide some clarification of this relationship.

As discussed in the main body of this Report (see "Concepts"), minimization of contact of waste by water is a fundamental concern (is, in fact, the

fundamental concern) of Part 61. As stated in 10 CFR 61.7, "... a cornerstone of the system is stability ...so that... access of water to the waste can be minimized (emphasis added). Migration of radionuclides is thus minimized..." In addition, in Section 61.51, it is stated that" (a) covers must be designed to minimize to the extent practicable water infiltration, to direct percolating or surface water away from the disposed waste, and to resist degradation by surface geoirgic processes and biotic activity, (b) surface features must direct surfact water drainage away from disposal units ...., and (c) the disposal site must Le designed to minimize to the extent practicable the contact of water with waJte during storage, the contact of standing water with waste during disposal, and the contact of percolating or standing water with waste after disposal."

What is the underlying reason for this preoccupation concerning the potential contact of waste by water? Though not stated specifically anywhere in the regulation, it is clear that these statements are in recognition of the fact that contact of waste with water is the first step in a potentially major pathway for radionuclide release and migration off-site. Thus, leaching, or extraction, of radionuclides through contact of waste with water is the first step in subsequent n.igration of the radionuclides from the waste through the' groundwater and off of the site. Therefore, though leaching is not mentioned explicitly in Part 61, it is a phenomenon that is of fundamental interest in low level waste disposal. The relationship of leach tetting, as called for in -

the the 1983 Technical Position, to Part 61, is thus rather straight-forward, when viewed in this context. Some further discussion of the details of the leaching tests, analyses of the results, and ways the tests might be improved is provided below.

A8.1 ANSI /ANS 16.1: Measurement of the Leachability of Solidified low-level

, Radioactive Wastes by a Short-Term Test Procedure Scope: This standard (Ref. A21) provides a uniform procedure to measure and index the release of radionuclides from waste forms as a result of leaching in demineralized water for three months.

Summary of Method: The ANS/ ANSI 16.1 leach test is a modification of an "IAEA leach test" proposed by Hespe (Ref. A2D. In the ANS/ ANSI 16.1 test, a test i

specimen is completely immersed in a measured volume of deionized water lea-chant, which is changed on a prescribed schedule. Upon removal, the leachant is analyzed for the radionuclides (or elements) of interest. The data obtained by the procedure are expressed as a material parameter of the leachability of each leached species. This parameter is called the "Leachability Index" (L), i which is the arithmetic mean of the L values obtained for each leaching intsrval (where the L value is the logarithm of the inverse of the effective diffusivity).

Specimens: Specimens are supposed to have a well-defined shape, mass, an i volume. Cylinders are preferred.

LLW STABILITY RPT A-14

Orocedure: The Standard goes into considerable detail regarding procedures for rinsing and suspending specimens and removing leachate. Basically, the lea-chate is sampled, and the leachate is completely replaced after cumulative leach times of 2,7, and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from the initiation of the test. Subsequent leachate sampling and leachate replacements are made at 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> intervals for the next four days. Three additional leach intervals of 14, 28, and 43 days each extend the entire test to 90 days.

Remarks: As specified in the 1983 Technical Position, the leachloility index, as calculated in accordance with ANS/ ANSI 16.1, should be greater than 6. The 1983 Technical Position also indicates that other leachants in addition to demineralized water should be used in the testing. The preferred leachant is listed as synthesized sea water. The draft Regulatory Guide (Ref. A3) also stated that certain radioactive tracers should be used (preferrably cobalt, cesium, and strontium) for proposed nuclear power station waste streams. As in early (circa 1982) versions of the draft ANS 16.1 Standard, the draft Regu-latory Guide addressed certain "discard criteria," which are not contained in the current (1986) version of the Standard.

In the NUMARC Report (Ref. A4), the leachability test and its basis are examined in considerable detail. NUMARC concludes that the ANS/ ANSI 16.1 procedure is "... a reasonable indicator of waste form leachability," although a 5-day test is preferred over the 90-day test and sea water is a preferred leachant over demineralized water. NoMARC contends that its study confirms the assumptions and supporting theory, as well as the intended application of the Standard. NUMARC also indicates that an applicable technical basis to support the acceptance criterion of a leachability index of greater than 6 could not be found, but concludes that the criterion is reasonable, based on, in part, "...

the demonstrated ability of the criterion to eliminate poor waste forms."

The NRC staff agrees with some of the observations made by NUMARC, in particular with respect to the need to clarify whether confidence ranges and correlation coefficients should be Reported, whether 1 or 2 leachants should be used, whether the dicard criteria should be inplemented, etc. These are matters that can and should be addressed as part of any continuing study on waste form testing and criteria. As to the recommendation that 5-day leach testing is sufficient, or whether 90-day tests should be performed, the staff currently believes that the 90-day tests should be retained (at least for the

. present). NUMARC's contention that 5-day tests are all that is needed appears to be founded on the belief that any changes in leach mechanism would be detected early and that changes during the latter stages of the test generally have little, if any, impact on the test rasults. As indicated in Appendix E of the Standard, however, several researchers have observed that some low-level waste forms (especially wastes incorporated in cement or asphalt) can undergo a dramatic increase in leachability after a few weeks or months, Therefore, if the leaching test is to be retained as an indicator of long-term stability, it is the staff's current opinion that the period of tcst shoeld continue to be 90 days.

Basic questions remain: what does leach testing (as apart from immersion testing) have to do with long-term stability, and what is the significance of or rationale for the "leach index greater than 6" acceptance criterion? A major part of the answer to these questions is provided in a Dames and Moore Report (Ref. A28) that deals with a sensitivity analysis of the effects of LLW STABILITY RPT A-15

?, .

varying (a) waste stream leaching characteristics, (b) alternative disposal site environmental characteristics, (c) alternative disposal site design characteristics, and (d) operating practices on resulting potential human exposures due to groundwater migration. The results of the analysis indicated that reducing the leaching potential of the waste streams suitable for solidification reduces the calculated exposures due to groundwater migration.

However, the relationship between the leaching potential of these solidified waste streams and the calculatad exposures, appeared to be approximately asymptotic rather than linear. Thus, as the leaching potential of the waste streams was reduced, a point was rapidly reached in which further reductions in the leaching potential had little effect on the calculated impacts. The authors concluded that there appeared to be "... no need to establish an extremely rigorous leach criteria [ sic] on waste streams suitable for solidifi-cation to assure safe disposal of low-level waste. A leach criteria (sic) which can be met by existing state-of-the-art solidification products.... would appear to be acceptable provided that the product is structurally stable (emphasis added); such a criteria would really only need to exclude extremely poor quality solidification binders from use. Experimental evidence has indicated that binders exhibiting poor structural stability have also tended to exhibit poor leaching performance."

The results of the Dames and Moore study and the conclusions quoted above thus formed the basis for the leaching recommendations in the "1983 Technical Position on Waste Form Stablity." A leach index of "greater than 6" was selected as the acceptance criterion because it was believed to be readily achievable by solidification agents such as cement, bitumen, vinyl ester styrene and synthetic polymers, even though leach indexes of such magnitude are considered to be roughly equivalent to "free ions in water." Thus, based on the results of the Dames and Moore study (and the input assumptions used in the study) the leach index value has no critical relationship to 10 CFR Part 61, and the ability of the disposal facility to meet the Part 61 off-site dose criteria. However, the greater than 6 leach index acceptance criterion, while readily achievable by "good" (i.e., "structurally stable") solidification agents, is high enough to have eliminated media such as urea formaldehyde and some gypsum-solidified waste streams. Therefore, the staff believes that the current leach index acceptarce criterion has served reasonably well to separate poor solidification agents from acceptable ones.

The fundamental relationship between leach resistance and structural stability is still rather poorly defined, however. At best, it appears that resistance to leaching of Cesium-137, Strontium-85, or Cobalt-60 has only an indirect correlation to long-term structural stability in the sense that waste forms that have very low leach indexes may have large open porosity or fairly soluble matrix phases that would eventually lead to breakdown of the waste forms if contacted by sufficient quantities of water. Therefore, in the opinion of staff, it may be possible to improve the leach test by modifying it ta include the measurement of leach indexes for the solidification agent materials as well as, or even instead of, the radionuclides currently measured. Such an approach would provide more direct indication of the relative stability of the solidification medium than does the current method. It might, however, be more difficult to perform such tests since it would probably require more chemical analyses, and it would be even more difficult to develop an acceptance criterion that would be generically applicable. This is another area that would benefit from further study.

LLW STABILITY RPT A-16 I

" o

\

A9 REFERENCES A1. U.S. NRC, "Technical Position on Waste Form," Rev. O, May 1983.

A2. U.S. NRC, 10 CFR Part 61 "Licensing Requirements for Land Disposal of Radioactive Waste," Final Rule, 47 FR 57473, December 27, 1982.

A3. U.S. NRC, Draft Regulatory Guide, "Low-Level Waste Form Stability," October 1986.

A4. W. Chang, L. Skoski, R. Eng, and P. T. Tuite, "A Technical Basis for Meeting the Waste Form Stability Requirements of 10 CFR 61," Nuclear Management and Resources Council, Inc. Report, NUMARC/NESP-002, April 1988.

AS. American Society for Testing and Materials Comaressive Strength of Cylindrical Concrete Specimens, ASTM C39, Octo)er 1984.

A6. American Society for Testing and Materials, Compressive Strength of Bituminous Mixtures, ASTM 01074, ASTM D1074, February 1983.

A7. B.S. Bowerman, et al., "An Evaluation of the Stability Tests Recommended in the Branch Technical Position on Waste Forms and Container Materials,"

Brookhaven National Laboratory Report, NUREG/CR-3289 (BNL-NUREG-51784),

March 1985.

A8. R.E. Davis and E.P. Gause, "Development of Low-Level Waste Form Criteria Testing of Low Level Waste Forms," Brookhaven National Laboratory Report, NUREG/CR-2813 (BNL-NUPEG-51556), November 1983.

A9. American Society for Testing and Materials, Compressive Properties of Rigid Cellular Plastics, ASTM D1621, 1979.

A10. American Society for Testing and Materials, Deformation of Plastics under Load, ASTM D621, 1976.

All. American Society for Testing and Materials, Thermal Cycling of Electroplated Ceramics, ASTM B553, 1979.

A12. D.R. MacKenzie, M. Lin, and R.E. Barletta, "Permissible Radionuclide Loading for Organic lon Exchange Rasins from Nuclear Power Plants,"

Brookhaven National Laboratory draft Report, BNL-NUREG-30668, January 1982.

A13. K.J. Swyler, C.J. Dodge, and R. Dayal, "Irradiation Effects on the Storage and Disposal of Radwaste Containing Organic Ion-Exchan9a Media,"

Brookhaven National Laboratory Report, NUREG/CR-3383 (BNL-NUREG-51691),

October 1983.

A14. T.J. Johnson, Personal Communication, April 26, 1988.

A15. American Society for Testing and Materials, Determining Resistance of Synthetic Polymeric Materials to Fungi, ASTM G21, 1970.

LLW STABILITY RPT A-17

'-a A9 REFERENCES, Cont.

A16. AmericanSocietyforTestingandMaterials,determiningResistanceof Plastics to Sacteria, ASTM G22, 1976.

A17. R. Bartha and D. Pramer, "Features of a Flask and Method for Measuring the Persistance and Biological Effects of Pesticides in Soils," Soil Science 100 (1), pp.68-70, 1965.

A18. P.L. Piciulo, C.E. Shea, and R.E. Barletta, "Biodegradation Testing of Solidified Low-Level Waste Streams," Brookhaven National Laboratory Report, NUREG/CR-4200 (8NL-NUREG-51868), May 1985.

A19. P. A. Gilbert and C. M. Lee, "Biodegradation Tests: Use and Value," in Biotransformation and Fate of Chemicals in the Aquatic Environment, Eds.

A. W. Maki, et al., American Society for Microbiology, Washington, DC (1980) pp. 34-45.

A20. C. R. Kempf, B. Siskind, W. E. Barletta, and D. R. Dougherty, "Character-ization of Radioactive Waste Packages of the Minnesota Mining and Manufacturing Company," NUREG/CR-3844, July 1988.

A21. American Nuclear Society, Measurement of the Leachability of Solidified Low-Lesel Radioactive Wastes by a Short-Term Test Procedure, ANS 16.1, 1986.

(22. Brookhaven National Labcratory, Properties of Radioactive Wastes and Wasta Containers, Brookhaven National Laboratory Progress Report No. 7, May 1978.

A23. P. L. Piciulo, J. W. Adams, J. H. Clinton, and B. Siskind, "The Effect of Cure Conditions on the Stability of Cement Waste Forms after Immersion in Water," Brookhaven Naticnal Laboratory Report, WM-3171-4, August 1987.

A24. Thomas L. Jungling, Keith K. McDaniel, LeRoy S. Person, and Michael Tokar, "Status of NRC's Waste Form Regulatory Guide," presented at the Ninth Annual DCE Low-Level Radioactive Waste Management Conference, Denver, CO, August 2/, 1987.

A25. US NRC, 10 CFR Part 60, "Disposal of High-Level Radioactive Wastes in Geologic Repositories."

A26. William Kerr, Letter to NRC Chairman, Lando W. Zech, Jr. , November 10, 1988.

, A27. E.D. Hespe, "Leach Testing of Immobilized Radioactive Waste Solids, A I Proposal for a Standard Method," International Atomic Energy Agency, Atomic Energy Review, [9] (1), 195-207 (1971).

i l A28. O. I. Oztunali, C. J. Pitt, and J. P. Furfaro, "Influence of Leach Rate and Other Paranieters on Groundwater Migration," Dames and Moore Report, i NUREG/CR-3130, February 1983.

i I

LLW STABILITY RPT A-18 i

C: 1 9

Table Al Topical Report Review Status Summary Solidified Waste Form and High Integrity Containers (HICs)-

May 30, 1988 Vender Docket No. Type Disposition Waste Chem WM-90 Solidification (bitumen) Approved.

General Electric 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 WM-91 Solidification (bitumen) Discontinued.

VIKEM WM-13 Solidification / oil (cement) Discontinued.

Nuclear Packaging WM-71 Solid /Encap (cement / gypsum) Withdrawn.

LN Technologies WM-57 HIC (polyethylene) Withdrawn.

Chem-Nuclear WM-47 HIC (fiberglass / poly) Withdrawn.

Chem-Nuclear WM-19 Solidification (cement) Under review.

Chem-Nuclear TBD Solidification (cement /26) Under review.

LN Technologies WM-20 Solidification (cement) Under review.

Hittman WM-46 Solidification (cemont) Under review.

Stock WM-92 Solidification (cement) Under review.

Hittman WM-79 Solidification (cement) Under review.

Chem-Nuclear WM-18 HIC (polyethylene) Under review.

Hittman WM-80 HIC (polyethylene) Under .eview.

TFC WM-76 HIC (polyethylene) Under review.

Nuclear Packaging WM-83 HIC (316-stainless) Under review.

LN Technologies WM-93 HIC (fiberglass / poly) Under review.

Bondico WM-94 HIC (fiberglass / poly) Under review.

Babcock & Wilcox TBD HIC (coated carbon steel) Under review.

• Approved fnr single waste stream for one year.

• • Approved pending satisfactory completion of thermal cycling ter,ts.

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Table A?

Topical Report Review Status Summary-for Waste Solidification System And I Process Control Program by Plant Systems Branch Office of Nuclear Reactor Regulation Vendor Report No. Type Disposition Areojet AECC-1 Fluid, Bed Dryer Approved Hittman HN-R1109 Cement Approved Wernor&Pfleiderer WPC-VRS-1 Bitumen Approved 00W DNS-RSS-001 Polymer Approved Atcor ATC-132 Cement Approved Newport News RWR-1 Fluidized Bed Approved Calcination Chem-Nuclear 4313-01354 Cement Approved JGC JGC-TR-001 Bitumen Approved Aerojet AECC-2 Fluidized Bed Approved Calcination '

Aerojet AECC-4 Incineration Approved ATI ATI-VR-001 Bitumen Approved NUS PS-53-0378 Cement Approved Chem-Nuclear CNSI-0W-11118 Dewataring Approved Atcor ATC-8019-1 Cement Approved l

I l

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i t_. . . .- -, _ , . - - - , m -- , .. -

4 .. : .

a:

Table A2 (Continued) 4 Vendor Report No. Type Disposition Nuclear Packaging TP-02 Dewatering Approved GE NEDE-30878 Azteck Approved Kock i KPS-1 Incineration iApproved Aerojet AECC-3 Fluidi:ed Bed Approved A, Calcination UNC UNC-S-8000 Cement Approved Bartlett BN-1 Cement Approved Westinghouse / STD-R-05-011 Dewatering Approved Hittman .

Stock SRS-003 Dewatering Approved Chem-Nuclear RDS-25506-1 Dewatering Under Review Duratek D-EVR/HED-1 Dewatering Under Review Nuclear Packaging TP-03 Oil / Cement Under Review Nuclear Packaging TP-04 Cement / portable Under Review Nuclear Packaging TP-06 Encapsulation / Under Review Cement Nuclear Packaging TP-01 Cement Withdrawn Nuclear Packaging TP-05 Cement Withdrawn Stock SRS-001 Cement Withdrawn

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t Table A3

^.

Certificates of Compliance State of South Carolina 4/27/88 HIC Certificates of Compliance Issued to Issued what:

• Issued when:

Adwin Equipment Company 55 gallon HIC 5/29/84 Chem-Nuclear HDPE HICs (x 14) '5/28/81 Chem-Nuclear FRP HIC 2/23/82 Chem-Nuclear Overpack HICs (x3) 4/8/83 Philadelphia Electric Comp. PECO-HIC-1 9/?8/81 Hittman Radlok-55 HIC 6/17/82 Hittman Radiok-100 HIC 6/17/82 Hittman Radlok-200 HIC 5/5/83 Hittman Radlok-500 HIC 9/31/85 LN Technologies Barrier-55 HIC 9/1/83 TFC NUHIC-120 HIC 11/1/83 NUPAC HDPE 142 H1C 8/20/84 NUPAC FL-50 HIC 9/26/85 Chichibu Concrete HICs (x2) 8/12/86 Vermont Yankee HOPE HIC 10/10/83 Approved Stabilization Media

• Vinyl Ester Styrene Cement Bitumen

• Processes shall meet and have been evaluated in accordance with the NRC "Technical Position on Waste Form" or other evaluation criteria specif-ically approved by the NRC. Other solidification media shall be accept-able for which a topical Report has been prepared and received approval from the NRC and State.

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8

,L.. . y k -g I

.. %s i

Table A3 (Continued)  :

Certificates of Compliance ,

State of Washington 4/27/88 HIC Certificates Of Compliance Issued'to: Issued what: Issued when:

Chichibu Concrete HICs (x2) 9/2'J/86 NUPAC FL-50 HIC 4/4/86 US Ecology NUPAC SOS HIC 3/23/84 Approved Stabilization Media

• Aztech (General Electric)

Bitumen (oxidized ATI and Waste Chem)

Chem-Nuclear Cement Dow Media (Vinyl Ester Styrene)

Envirostone (U.S. Gypsum Cement)

Westinghouse Hittman Cement LN Technologies Cement Stock Equipment Cement -

• 0nly those stabilization media which have been evaluated or are in the process of being evaluated and are used with the stability guidance requirements of the NRC "Technical Position on Waste Form" or are specifically approved by the Depart-ment are considered acceptable stabilization media. Other stabilization media and processes may be approved which have been reviewed and approved by the NRC and/or the Department as meeting waste form ' bility criteria.

l

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