August 25, 2009 

MEMORANDUM TO: Gregory Suber, Chief 

 Low-Level Waste Branch 

 Environmental Protection and 

 Performance Assessment Directorate 

 Division of Waste Management 

 and Environmental Protection 

 Office of Federal and State Materials 

 and Environmental Management Programs 

THRU: Christepher McKenney, Chief /RA/ by D. Esh for 

 Performance Assessment Branch 

 Environmental Protection and 

 Performance Assessment Directorate 

 Division of Waste Management 

 and Environmental Protection 

 Office of Federal and State Materials 

 and Environmental Management Programs 

FROM: David Esh, Sr. Systems Performance Analyst /RA/ 

 Performance Assessment Branch 

 Environmental Protection and 

 Performance Assessment Directorate 

 Division of Waste Management 

 and Environmental Protection 

 Office of Federal and State Materials 

 and Environmental Management Programs 

SUBJECT: TECHNICAL REVIEW: “HYDRAULIC AND PHYSICAL PROPERTIES 

OF SALTSTONE GROUTS AND VAULT CONCRETES” 

 On January 9, 2009, the U.S. Department of Energy, Savannah River Operations Office, 

provided the subject report for review by NRC staff pursuant to Section 3116(b) of the Ronald 

W. Reagan National Defense Authorization Act for Fiscal Year 2005 (ML090150297). The 

subject report is available on NRC’s Agencywide Documents Access and Management System 

(ADAMS) at accession number ML090150298. This report was reviewed in accordance with 

CONTACT: David Esh, FSME/DWMEP 

 301-415-6705 
G. Suber 2 

monitoring activities described in “U.S. Nuclear Regulatory Commission Plan for Monitoring the 

U.S. Department of Energy Salt Waste Disposal at the Savannah River Site in Accordance with 

the National Defense Authorization Act for Fiscal Year 2005.” The staff’s technical review 

summary is enclosed for your use. 

Docket No.: PROJ0734 

Enclosure: 

Technical Review Summary 
G. Suber 2 

monitoring activities described in “U.S. Nuclear Regulatory Commission Plan for Monitoring the 

U.S. Department of Energy Salt Waste Disposal at the Savannah River Site in Accordance with 

the National Defense Authorization Act for Fiscal Year 2005.” The staff’s technical review 

summary is enclosed for your use. 

Docket No.: PROJ0734 

Enclosure: 

Technical Review Summary 

DISTRIBUTION: 

DBrown CGrossman KPinkston LHoward/CNWRA 

ML092300670 

OFC DWMEP DWMEP DWMEP:BC 

NAME D.Esh AWalker-Smith D. Esh for 

C.McKenney 

DATE 08/25/09 08/27/09 08/25/09 

OFFICIAL RECORD COPY

 
Enclosure 

Technical Review Summary: TECHNICAL REVIEW: “HYDRAULIC AND PHYSICAL 

PROPERTIES OF SALTSTONE GROUTS AND VAULT CONCRETES” 

Review Completed: March 20, 2009 

Reviewer(s): D. Esh 

Document(s): Dixon, K., J Harbour, M. Phifer, Hydraulic and Physical Properties of 

Saltstone Grouts and Vault Concretes, SRNS-STI-2008-00421, 

Revision 0, Savannah River National Laboratory, WSRC. November 

2008, ADAMS accession no. ML090150298 

Evaluation

The primary focus of the report is to provide a summary of work performed to estimate the 

hydraulic and physical properties of three types of saltstone and two vault concretes. Wet 

properties measured on the saltstone formulations included yield stress, plastic viscosity, wet 

unit weight, bleed water volume, gel time, set time, and heat of hydration. Hydraulic and 

physical properties measured on cured saltstone and concrete samples included saturated 

hydraulic conductivity, moisture retention, compressive strength, porosity, particle density, and 

dry bulk density. Water retention data are presented for each material along with van 

Genuchten transport parameters determined with the RETC code. 

The report provides a summary of previous initial testing of saltstone grout that provided the 

basis for hydraulic conductivity values used in the performance assessment and subsequent 

special analysis. The report provides an adequate summary of the sample preparation and 

analysis methods for the various measurements. In appendicies, the report provides strength 

reports and materials characterization test reports provided by the contractors that performed 

the measurements. 

Note: All citations to previous work noted below are those cited in SRNS-STI-2008-00421. 

Yu et al. (1993) measured a saturated hydraulic conductivity of 5.19E-12 cm/s, whereas 

Langton (1986) reported the results of previous testing that ranged from 3E-9 to <1E-11 cm/s. 

More recent measurements by Harbour et al. (2007a) estimated the hydraulic conductivity of 

saltstone as ranging between 1.4 to 3.4E-9 cm/s. Dixon and Phifer (2007) estimated the 

hydraulic conductivity of saltstone relative to the saltstone pore fluid of 5.3E-9 cm/s. The more 

recent measurements by Harbour, Dixon and Phifer did not corroborate the previous 

measurements by Yu and Langton. The saltstone performance assessment (2005) used an 

initial saturated hydraulic conductivity for the base case of 1E-11 cm/s for saltstone and 1E-12 

cm/s for the vault concrete. In addition, the porosity measured in the most recent experiments 

described in this report was on the order of 0.6 to 0.7, much higher than used in the previous 

performance assessment of 0.42. 

The differences in the results between the older and more recent measurements highlight a 

challenge in relying on limited measurements for parameters that are difficult to measure. 

Higher than expected hydraulic conductivity for the saltstone and vault concrete and porosity for 

the saltstone would be expected to lead to higher water flow rates, faster degradation, and 

higher release rates of radionuclides than previously anticipated (DOE, 2005). Anticipated 

degradation mechanisms that may proceed more quickly would include but not be limited to 
2

sulfate attack, reinforcement corrosion (when applicable), and leaching of calcium hydroxide. In 

addition, it is likely that higher hydraulic conductivity and porosity would correlate with higher 

than anticipated diffusivity which would impact the rate at which deleterious species can be 

transported to the grout or concrete and the rate at which radionuclides would be transported 

from the grout. DOE is in the process of revising the previous performance assessment. NRC 

staff plan to evaluate the revised performance assessment to ensure that the values for 

hydraulic conductivity, porosity, and diffusivity used in the performance assessment reflect the 

recent measurements and additional uncertainties. Additional uncertainties that could impact 

the physical property data and that may not be reflected in the more recent measurements were 

discussed with DOE during the March 2008 monitoring visit (ML081290367). DOE stated that, 

as a result of that monitoring visit, they were initiating a saltstone product quality assurance 

strategy to address the additional uncertainties. NRC staff will evaluate information that is 

generated as it becomes available. In addition to impacting the performance assessment 

calculation, changes to key variables may impact the assessment of the impact of other 

processes or uncertainties. For example, the extent of sulfate attack is strongly influenced by 

the diffusivity of the material. The research process to address uncertainties in performance of 

the saltstone disposal facility should properly integrate the results of individual studies, many of 

which may be completed in parallel. NRC staff plan to evaluate future reports and information 

generated by DOE to assess whether the reports are consistent and appropriately integrated. 

This report summarizes and recommends logarithmic averages of hydraulic conductivity for use 

in future performance assessments, but does not explain why the logarithmic average is 

appropriate given the limited number of measurements and understanding about the underlying 

parameter distribution. In this case, the logarithmic average is lower than the arithmetic mean, 

and should only be used if it can be shown that the data are logarithmically distributed. 

Hydraulic conductivity measurements were performed on test cylinders that were 2.8 x 6.0 

inches that were filled, capped, and sealed. Page 4 of the report states that bleed liquid leaked 

from the hydraulic test cylinders during the cure period. It is not clear what is meant by the text, 

if the cylinders were sealed. NRC asked for additional information at the March 2009 monitoring 

visit. Adequate seals of the samples can be important in these types of measurements because 

leakage between the sample and sample holder can influence the measurements and result in 

inaccurate data for the fundamental hydraulic properties of the material. 

The hydraulic conductivity measurements discussed in the report were conducted with a 

simulated groundwater permeant for vault concrete and a permeant of similar composition as 

salt waste for saltstone grout. Due to the small volume of permeant used in these tests relative 

to the volume of simulant used to prepare the samples (i.e., a stimulant to permeant volume 

ratio of 1:150), the measured hydraulic conductivity values are considered to be representative 

of the simulant used to prepare the test materials. The report states that geochemical modeling 

was performed to assess the potential for chemical reactions between the simulants and grout 

that could impact the property testing. As the material ages, it would be expected that the grout 

would be less reactive and therefore the permeants contacting the material would be less 

concentrated because the permeants would contain less salts and other soluble components 

from reaction with the grout itself. In order for the data generated in the report to apply for 

degraded conditions, it would be necessary to derive intrinsic permeabilities that are specific to 

anticipated future groundwater compositions. However, the staff believes that this source of 

uncertainty may not be significant relative to the other sources of uncertainty. 
3

The report summarizes measurements of moisture characteristic curves for saltstone and vault 

concrete and also provides data from similar measurements completed by the Idaho National 

Laboratory (INL). Page 18 of the report discusses a fitting procedure to develop the 

parameterization of the moisture characteristic curves. The fitting procedure appears to be 

loosely constrained, which could result in non-unique solutions. The moisture characteristic 

curve measurements are difficult to perform and can be subject to considerable uncertainty. For 

example, page 32 of the report provides the characteristic curves for MCU saltstone samples as 

determined by INL. Figure 15 on page 31 of the report provides the characteristic curve 

measured for ARP/MCU saltstone in the current study. The moisture characteristic curves are 

markedly different. In simulations of facility performance, differences in the assigned moisture 

characteristic curves of dissimilar materials can sometimes have a profound effect on estimated 

release rates due to the strong non-linear relationship between saturation and relative 

permeability. NRC staff will evaluate the revised performance assessment to see if the results 

of the performance assessment are sensitive to the assigned moisture characteristic curves and 

how uncertainty in the moisture characteristic curves was evaluated in the revised performance 

assessment. 

Teleconferences or Meetings

The subject report was discussed with representatives of the Department of Energy and its 

contractors on March 25-26, 2009 at an onsite observation at the Savannah River Site (SRS). 

A summary of the discussion is provided in the onsite observation report (ADAMS accession no. 

ML091320439). The follow-up actions as a result of the discussion are: 

1) Clarify whether bleedwater was leaking from sealed containers during the hydraulic 

properties study, when the report indicated the samples were sealed; 

2) Clarify the impact of changing pore solution concentration on measured hydraulic 

properties on p. 8 of the report; 

3) Explain how uncertainty will be addressed for moisture characteristic curves that are 

fit to data reported on p. 18 of the report; 

4) Justify the use of logarithmic averages for recommended hydraulic property values 

on p. 19 of the report; and 

5) Provide an up to date copy of the PA maintenance plan. 

A follow-up action identifies an information need or request that will help NRC staff determine 

whether a technical issue is risk significant and can warrant tracking as an open issue. 

Open Issues

No open issues are identified as a result of this technical review at this time. However, as 

stated above, DOE has a number of follow-up actions resulting from the staff’s questions on the 

report. 

Conclusion

The NRC staff has not identified open issues associated with the methods and data reported in 

this report (SRNS-STI-2008-00421) at this time. However, DOE has several follow-up actions in 

response to staff questions. The staff plans to review any new information developed by DOE 

as part of these follow-up actions. 
4

This report contains data that may be relied upon in future performance assessment (PA) 

updates in support of the 2005 DOE waste determination for the Saltstone Disposal Facility. 

However, until such time as a PA update is completed and reviewed by NRC staff, the staff 

cannot fully assess the risk significance of the data. For this reason, all monitoring activities 

identified under Factors 1-3 of the NRC monitoring plan remain open at this time.