Regulatory Guide 4.25

Assessment of Abnormal Radionuclide Discharges in Ground Water to the Unrestricted Area at Nuclear Power Plant Sites.

ML16253A333
Person / Time
Issue date:	03/31/2017
From:	Thomas Nicholson NRC/RES/DRA
To:
O'Donnell E M
Shared Package
ML16253A327	List: Regulatory Guide 4.25
References
DG-4025 RG 4.25
Download: ML16253A333 (27)

U.S. NUCLEAR REGULATORY COMMISSION

March 201 7 OFFICE OF NUCLEAR REGULATORY RESEARCH

Revision 0

REGULATORY GUIDE

Technical Lead Thomas Nicholson Written suggestions regarding this guide or development of new guides may be submitted through the NRC's public Web site under the Regulatory Guides document collection of the NRC Library at http://www.nrc.gov/reading

-rm/doc-collections/reg

-guides/contactus.html. Electronic copies of this regulatory guide, previous versions of this guide, and other recently issued guides are available through the NRC's public Web site under the Regulatory Guides document collection of the NRC Library at http://www.nrc.gov/reading

-rm/doc-collections/. The regulatory guide is also available through the NRC's Agencywide Documents Access and Management System (ADAMS) at http://www.nrc.gov/reading

-rm/adams.html, under ADAMS Accession No. ML16253A333. The regulatory analysis may be found in ADAMS under Accession No. ML15237A385 and the staff responses to the public comments on DG

-4025 may be found under ADAMS Accession No. ML16253A330. The appendix to RG 4.25 may be found under ADAMS Accession No. ML16253A329.

REGULATORY GUIDE

4.25 (Draft was issued as DG

-4025, dated December 2015) ASSESSMENT OF ABNORMAL RADIONUCLIDE DISCHARGES IN GROUND WATER TO THE UNRESTRICTED

AREA AT NUCLEAR POWER PLANT SITES

A. INTRODUCTION

Purpose This regulatory guide (RG) describes an approach that the staff of the U.S. Nuclear Regulatory Commission (NRC

or Commission

) considers acceptable for use in assessing abnormal discharges of radionuclides in ground water from the subsurface to the unrestricted area at nuclear power plant sites.

Applicability This RG applies to applicants and licensees under Title 10 of the Code of Federal Regulations

(10 CFR), Part 50, "Domestic Licensing of Production and Utilization Facilities" (Ref. 1), and 10 CFR Part 52 , "Licenses, Certifications, and Approvals for Nuclear Power Plants" (Ref. 2). Applicable Regulations

10 CFR Part 20, "Standards for Protection against Radiation" (Ref. 3), provide s standards for protection against ionizing radiation resulting from activities conducted under licenses issued by the NRC: - 10 CFR 20.1406(a) requires that applicants for licenses other than early site permits and manufacturing licenses under 10 CFR Part 52, whose applications are submitted after August 20, 1997, describe in the application how the facility design and procedures for operation will minimize, to the extent practicable, contamination of the facility and the environment, facilitate eventual decommissioning, and minimize, to the extent practicable, the generation of radioactive waste.

- 10 CFR 20.1406(b) requires that applicants for standard design certifications, standard design approvals, and manufacturing licenses under 10 CFR Part 52, whose applications are submitted after August 20, 1997, describe in the application how facility design will minimize , to the extent practicable, contamination of the facility and the environment, RG 4.25, Page

2 facilitate eventual decommissioning, and minimize, to the extent practicable, the generation of radioactive waste.

- 10 CFR 20.1406(c) requires that licensees

, to the extent practical, conduct operations to minimize the introduction of residual radioactivity into the site, including the subsurface, in accordance with the existing radiation protection requirements in Subpart B , "Radiation Protection Programs,"

and radiological criteria for license termination in Subpart E, "Radiological Criteria for License Termination,"

of 10 CFR Part 20. - 10 CFR 20.1501, "General,"

requires that licensees perform surveys of areas, including the subsurface, that are reasonable to evaluate the magnitude and extent of concentrations or quantities of residual radioactivity and to determine the potential radiological hazards of the radiation levels and residual radioactivity detected.

10 CFR Part 50 provides for the licensing of nuclear power plants

- 10 CFR 5 0.3 6 a(a)(2) requires that licensee s report the quantity of each of the principal radionuclides released to unrestricted areas from liquid and gaseous effluents during the previous 12 months, including any other information as may be required by the Commission to estimate maximum potential annual radiation doses to the public resulting from effluent releases.

Appendix A, "General Design Criteria for Nuclear Power Plants," to

10 CFR Part 50 provide s general design criteria (GDC) for nuclear p ower plants. The following GDC are of importance to the radioactive releases to ground water:

- GDC 60, "Control of Releases of Radioactive Materials to the Environment," states that the nuclear power unit design shall include means to control suitably the release of radioactive materials in gaseous and liquid effluents and to handle radioactive solid wastes produced during normal reactor operation, including anticipated operational occurrences. Sufficient holdup capacity shall be provided for retention of gaseous and liquid effluents containing radioactive materials, particularly where unfavorable site environmental conditions can be expected to impose unusual operational limitations upon the release of such effluents to the environment.

- GDC 64, "Monitoring Radioactivity Releases," requires that a means shall be provided for monitoring, among other things, the facility environs for radioactivity that may be released from normal operations, including anticipated operational occurrences, and from postulated accidents.

10 CFR Part 52 provides for the licensing of early site permits, standard design certifications

, and combined licenses for nuclear power plants

- 10 CFR 52.47(a)(6) requires that the final safety analysis report (FSAR) include the information in 10 CFR 20.1406 , "Minimization of Contamination

." - 10 CFR 52.47(a)(22) requires that the FSAR include the information to demonstrate how operating insights ha ve been incorporated into the plant design.

10 CFR Part 100, "Reactor Site Criteria"

(Ref. 4), require s the NRC to consider population density; use of the site environs, including proximity to manmade hazards; and the physical RG 4.25, Page

3 characteristics of a site, including seismology, meteorology, geology, and hydrology, in determining the site's acceptability for a nuclear power reactor

- 10 CFR 100.20(c)(3) requires that factors important to hydrological radionuclide transport (such as soil, sediment and rock characteristics, adsorption and retention coefficients, ground water velocity, and distances to the nearest surface body of water) must be obtained from onsite measurements.

Related Guidance R G 1.21 , "Measuring, Evaluating, and Reporting Radioactive Material in Liquid and Gaseous Effluents and Solid Waste

" (Ref. 5), contains information on the monitoring of leaks and spills, as well as controlled releases. R G 4.1, "Radiological Environmental Monitoring for Nuclear Power Plants

" (Ref. 6), provides a method considered acceptable for use in establishing and conducting an environmental monitoring program at nuclear power plant

s. In particular

, it describes guidance on the establishment of a radiological environmental monitoring program , which involves measuring the levels of radiation and radioactive materials in the local environment (including the subsurface) during the lifetime of the facility. R G 4.21, "Minimization of Contamination and Radioactive Waste Generation:

Life-Cycle Planning" (Ref. 7), provides guidance on meeting the requirements of 10 CFR 20.1406. Regulatory Position C.2 of RG 4.21 focuses on gathering sufficient information to support the development of a conceptual site model and in planning design features for the early detection of leakage and migration of radioactivity in soils and ground and surface water.

R G 4.22, "Decommissioning Planning during Operations" (Ref. 8), provides guidance to licensees that are required to minimize contamination and radioactive waste generation, conduct appropriate radiological surveys including the subsurface, maintain records of residual radioactivity, and provide adequate funding to complete decommissioning in accordance with portions of the Decommissioning Planning Rule, namely, 10 CFR 20.1406 and

10 CFR 20.1501. In NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition" (Ref. 9), Section 2.4.12, "Ground water ," and Section 2.4.13, "Accidental Releases of Radioactive Liquid Effluents in Ground and Surface Waters," provide guidance to the NRC staff on the review of an applicant's submitted information for characterizing and assessing the ground water site conditions and scenarios for accidental releases (principally a leaking radwaste tank) at the site as well as potential offsite consequences. Section 11.2 , "Liquid Waste Management System," and Branch Technical Position

11-6 , "Postulated Radioactive Releases Due to Liquid

-Containing Tank Failures," of NUREG

-0800 are also relevant

. Design Certification (DC)/Combined License (COL) Final Interim Staff Guidance (ISG) DC/COL-ISG-06, "Evaluation and Acceptance Criteria for 10 CFR 20.1406 to Support Design Certification and Combined License Applications

," issued October

2009 (Ref. 10), provides interim guidance to DC and COL applicants and the NRC staff for their analysis o f how applicants have complied with the requirements of 10 CFR 20.1406. It provides interim guidance to supplement the evaluation and acceptance criteria found in NUREG

-0800, Chapter 2, "Site Characteristics and Site Parameters," Chapter 5, "Reactor Coolant System and Connected RG 4.25, Page

4 Systems," Chapter 9, "Auxiliary Systems," Chapter 10, "Steam and Power Conversion System," Chapter 11, "Radioactive Waste Management," Chapter 12, "Radiation Protection," and Chapter 13, "Conduct of Operations

," and the guidance in RG 4.21. DC/COL-ISG-013, "Assessing the Radiological Consequences of Accidental Releases of Radioactive Materials from Liquid Waste Tanks for Combined License Applications

," issued January 2013 (Ref. 1 1), provides interim guidance to licensees and the NRC staff for their analysis of the consequences of an accidental release

, with an emphasis on how radiological consequences are determined. It provides specific interim guidance on implementing Section 2.4.13, Section 11.2, and Branch Technical Position

11-6 of NUREG-0800. DC/COL-ISG-014, "Assessing the Radiological Consequences of Accidental Releases of Radioactive Materials from Liquid Waste Tanks in Ground and Surface Waters for Combine d License Applications

," issued January

2013 (Ref. 12), provides interim guidance to licensees and the NRC staff on analyzing the accidental releases of radioactivity in ground and surface water. It emphasizes the consideration of hydrogeologic conditi ons that control the transport of radioactive materials and provides specific interim guidance on implementing Sections 2.4.12 and 2.4.13 of NUREG-0800. NUREG/CR-6948, Volume 1, "Integrated Ground

-Water Monitoring Strategy for NRC

-Licensed Facilities and Sites: Logic, Strategic Approach and Discussion

," issued November

2007 (Ref. 13), presents a framework for assessing what, how, where , and when to monitor ground water to ensure that a licensed nuclear site or facility is within regulatory limits.

Purpose of Regulatory Guides The NRC issues regulatory guides to describe to the public methods that the staff considers acceptable for use in implementing specific parts of the agency's regulations, to explain techniques that the staff uses in evaluating specific problems or postulated events, and to provide guidance to applicants. Regulatory guides are not substitutes for regulations and compliance with them is not required. Methods and solutions that differ from those set forth in regulatory guides will be deemed acceptable if they provide a basis for the findings required for the issuance or continuance of a permit or license by the Commission.

Paperwork Reduction Act This regulatory guide contains and references information collections covered by 10 CFR Parts 20, 50, 52, and 100 that are subject to the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).

These information collections were approved by the Office of Management and Budget (OMB), control numbers 3150

-0014, 3150-0011, 3150-0151, and 3150-0093. Public Protection Notification The NRC may n ot conduct or sponsor, and a person is not required to respond to, a request for information or an information collection requirement unless the requesting document displays a currently valid OMB control numbe

r.

RG 4.25, Page

5

B. DISCUSSION

Reason for Issuance The NRC is issuing this RG

to provide guidance on acceptable methods to determine the quantity of licensed material (i.e.

, radionuclides

) in abnormal

1 discharge s into the unrestricted area through the ground water discharge pathway.

Backg round As plants began to undergo decommissioning in the late 1990s to early 2000s, instances of abnormal subsurface or ground water residual radioactivity (or both) were identified.

Several operating facilities also identified residual radioactivity in ground water resulting from spills and leaks or equipment failure s. In one instance, low levels of a radionuclide were detected in a private well located on property adjacent to a nuclear power plant. The source of these abnormal releases included a wide range of structures, systems

, and components (SSCs), such as condensate storage tanks and piping, spent fuel pools, vacuum breaker valves along steam generator blowdown lines, and other buried piping leaks. The principal radionuclide released was hydrogen-3 (tritium). Other radionuclides released sometimes included strontium-90, cesium

-137, nickel

-63, cobalt

-60, and antimony

-125 , depending upon the source. Although the releases were not a significant public health issue

, the abnormal releases need to be accounted for and reporte

d.

In March 2006, the NRC formed the Liquid Radioactive Release Lessons Learned Task Force (LLTF) to evaluate the liquid radioactive releases and to make recommendations for improvement. The LLTF summarized the result of its evaluation in September 2006 and offered recommendations for addressing the abnormal releases to the subsurface (Ref.

1 6). Among them was a recommendation in Section 3.5.4 that the NRC should consider the development of guidance for evaluati ng radionuclide transport in ground water. The LLTF report note d that American National Standards Institute/American Nuclear Society (ANSI/ANS) 2.17-1980 addressed the issue and was being extensively updated at that time. The update was released for use as ANSI/ANS 2.17

-2010, "Evaluation of Subsurface Radionuclide Transport at Commercial Nuclear Power Plants"

(Ref. 1 7). It was reaffirmed in 2016 and designated as ANSI 2.17-2010 (R2016).

The terminology and concepts used in this RG are consistent with ANSI/ANS 2.17-2010 (R2016).

The industry took action to improve utilities' management of and response to the inadvertent release of radioactive substances to subsurface soils and water. In August 2007, the Nuclear Energy Institute (NEI) issued NEI 07

-07 , "Industry Ground Water Protection Initiative

-Final Guidance Document" (Ref.

1 8). Subsequently

, all operating and decommissioning power plants adopted the initiative. The initiative involves actions to improve management of and response to instances involving

1 Normal radionuclide effluent releases that are discharged to onsite lakes or ponds may be reported as a normal effluent discharge to the unrestricted area using the reporting guidance in RG 1.21.

If leakage of licensed radioactive material occurs from the onsite lakes or ponds into a ground water discharge pathway, the release or discharge to ground water does not need to be reported (again), since the discharge has already been monitored, accounted for, and reported as a normal effluent discharge. The ground water exposure pathway should be included in the total dose evaluations if the ground water pathway contributes 10

percent or more to the total dose from all other pathways combined in accordance with RG 1.109, "Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR Part 50, Appendix I" (Ref.

14). However, at the time of decommissioning, radionuclides retained on site are residual radioactivity that must be dispositioned in accordance with the guidance in NUREG-1757, Volume

2, Revision

1, "Consolidated Decommissioning Guidance: Characterization, Survey, and Determination of Radiological Criteria," issued September

2006 (Ref. 15).

RG 4.25, Page

6 an abnormal release of radionuclides to the subsurface

. The initiative included site characterization of geology and hydrology, a site risk assessment, an onsite ground water monitoring protocol, a remediation protocol, and communications

. To determine whether industry had implemented the NEI 07

-07 ground water protection initiative (GPI), the NRC inspected licensee programs using NRC Inspection Manual/Temporary Instruction 2515/173, Revision

1, "Review of the Implementation of the Industry Ground Water Protection Voluntary Initiative," dated October

31, 2008 (Ref. 1 9), and follow-up Temporary Instruction 2515/185, Revision 1, "Follow

-Up on the Industry's Ground Water Protectio n Initiative

," dated December 19, 2011 (Ref. 20). The results of those inspections led the NRC staff to conclude that the industry had adequately implemented the GPI (Ref s. 2 1 and 2 2). The Electric Power Research Institute (EPRI) provided the nuclear power industry with supporting technical guidance for the GPI. I n September 2005 i t issued EPRI Report 1011730, "Groundwater Monitoring Guidance for Nuclear Power Plants"

(Ref. 2 3), and in November 2007 it issued EPRI Report 1015118, "Groundwater Protection Guidelines for Nuclear Power Plants

" (Ref. 2 4). In October 2009, NEI issued NEI

08-08A, Revision

0, "Generic FSAR Template Guidance for Life Cycle Minimization of Contamination" (Ref.

2 5). NEI 08-08A applies to license applicants that submit applications after August 20, 1997, under 10 CFR Part 52 , Subpart C, "Combined Licenses

." NEI 08-08A describes an operational program to minimize contamination throughout the life cycle of a facility, including provisions for minimizing facility contamination, environmental contamination, and waste generation and facilitating decommissioning.

EPRI provided the nuclear power industry supporting technical guidance for a ground water protection program.

In 2008, it issued EPRI Report 1016099 , "Ground Water Protection Guidelines for Nuclear Power Plants

Public Edition" (Ref. 2 6). EPRI Report 1016099 and the NEI 07-07 GPI provide the technical basis used in NEI 08-08A. NEI 08-08A provides an approach for an effective ground water protection program that meets the requirements of

10 CFR 20.1406 with verification of the program during the construction stage for licenses under

10 CFR Part 52 , Subpart C.

As part of the GPI

, NEI issued NEI 09

-14, Revision

4, "Guideline for the Management of Underground Piping and Tank Integrity

," issued December

2015 (Ref. 2 6). NEI 09-14 complements NEI 07-07 and describes the policy and practices that the industry uses in managing underground piping and tanks.

EPRI Technical Report 1021175 , "Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks

(1016456, Revision 1)," issued December 2010 (Ref. 2 8), provides implementation guidance for NEI 09

-14. In order to determine whether the industry implemented the NEI 09

-14 guidelines , the NRC inspected licensee programs using NRC Inspection Manual/Temporary Instruction 2515/182, "Review of the Implementation of the Industry Initiative to Control Degradation of Underground Piping and Tanks," dated August

8, 2013 (Ref. 2 9). The results of those inspections led the NRC staff to conclude that the industry had implemented the NEI 09-14 guidelines (Ref. 30). Harmonization with International Standards The International Atomic Energy Agency (IAEA) has established a series of safety guides and standards constituting a high level of safety for protecting people and the environment. IAEA safety guides present international good practices and increasingly reflect best practices to help users striving to achieve high levels of safety. Pertinent to this regulatory guide

, IAEA-TECDOC-482, "Prevention and Mitigation of Groundwater Contamination from Radioactive Releases

," issued 1988 (Ref. 3 1), discusses the characteristics of the releases (primarily for two scenarios

-an underground storage tank and a severe reactor core accident)

, modeling of radionuclide movement in the subsurface

, prevention and mitigation techniques

, monitoring and sampling

, and quality assurance and quality control. The document also includes an appendix of suggested ground water models developed in the early 1980s for both unsaturated and saturated flow conditions. A related IAEA safety standard, Safety Guide No.

WS-G-3.1, RG 4.25, Page

7 "Remediation Process for Areas Affected by Past Activities and Accidents

," issued 2007 (Ref. 3 2), briefly describes site characterization, setting remediation criteria, and establishing remediation planning and implementation. This RG is consistent with the basic safety principles provided by these two IAEA guides. Documents Discussed in Staff Regulatory Guidance This regulatory guide endorses the use of one or more codes or standards developed by external organizations, and other third party guidance documents.

These codes, standards and third party guidance documents may contain references to other codes, standards or third party guidance documents ("secondary references").

If a secondary reference has itself been incorporated by reference into NRC regulations as a requirement, then licensees and applicants must comply with that standard as set forth in the regulation.

If the secondary reference has been endorsed in a regulatory guide as an acceptable approach for meeting an NRC requirement, then the standard constitutes a method acceptable to the NRC staff for meeting that regulatory requirement as described in the specific regulatory guide

. If the secondary reference has neither been incorporated by reference into NRC regulations nor endorsed in a regulatory guide, then the secondary reference is neither a legally

-binding requirement nor a "generic" NRC approved acceptable approach for meeting an NRC requirement.

However, licensees and applicants may consider and use the information in the secondary reference, if appropriately justified , consistent

with current regulatory practice, and consistent with applicable NRC requirements.

RG 4.25, Page

8 C. STAFF REGULATORY GUIDANCE

ANSI/ANS 2.17

-2010 (R2016)

provides a method acceptable for use to evaluate the occurrence and movement of radionuclides in the subsurface resulting from abnormal radionuclide releases at nuclear power plants. The ANSI/ANS standard does not specify the use of any specific ground

-water flow and transport model. Instead, the standard provides a graded, risk

-informed approach for evaluating the effects of subsurface radionuclide transport.

1. Licensees should develop a site

-specific ground

-water flow and transport model for their sites.

The model should be based on the complexity of geologic and hydrologic conditions, the types of radioactive materials and facility design, the types and effectiveness of engineered and natural barriers, and the proximity to surface water and ground

-water receptors. A facility that has a less significant radionuclide source term, minor subsurface contamination, simple or well

-understood hydrogeology, or limited effects on ground

-water resources generally may use less extensive site characterization, mathematical modeling, and performance confirmation measures than a facility with significant residual radioactivity that has the potential to exceed national radiation protection standards.

2. The first step is to develop a three

-dimensional conceptual site model (CSM). The CSM may then be used to determine the complexity of the site's hydrogeology and determine an appropriate ground

-water flow and transport model.

3. A simple CSM is one that can be modeled with homogeneous flow and transport properties, or as a simple layering of homogenous hydrogeologic units where ground

-water flow can be represented as uniform and steady state. In contrast, a complex site may exhibit features such as highly heterogeneous hydrogeologic units, or preferential flowpaths as a result of fractured or solutioned (e.g., limestone) rock. Another feature indicating a complex site is nonuniform or transient ground water flow conditions. This may be caused by processes such as variable recharge, tidal fluctuations, or nearby water

-well pumping (or a combination).

3.1 The appendix to this RG provides a simple ground

-water flow and transport model that is acceptable for use with simple hydrogeologic conditions and geometry such as steady

-state saturated flow in homogeneous porous sand layers. The model in the appendix is similar to models described in the Interstate Technology & Regulatory Council document entitled, "Use and Measurement of Mass Flux and Mass Discharge," issued August

2010 (Ref.

33), and American Petroleum Institute Publication Number 4730, "Groundwater Remediation Strategies Tool," issued December

2003 (Ref. 34). The model is provided in a spreadsheet format to facilitate the identification of model input and output and is available at ADAMS Accession No. ML16253A329. 3.2 The simple model is basically a "flow tube" model. Development of the model begins by defining a horizontal transect perpendicular to the general ground

-water flow direction that encompasses the width of the radionuclide plume. A series of vertical cross sections are then established based upon monitoring well locations and hydrogeologic unit properties as well as ground-water flow conditions. "Modeling blocks" are then defined as having their boundaries located at the midpoints between the adjacent monitoring wells. If the subsurface is composed of layered hydrogeologic units (e.g., sand, clay, or other porous media) having different hydraulic conductivities, then smaller horizontal and vertical modeling blocks can be further defined. The total flux of radionuclides through the cross section is estimated by summing up the fluxes through the modeling blocks. These fluxes are calculated as the product of the RG 4.25, Page

9 radionuclide concentration and the specific ground water discharge rate and its cross sectional area with a conversion factor of 28.3 for liters per cubic foot (see Equation A

-3 in the appendix). The total quantity of radionuclides discharged can be determined by multiplying by the time period. Once the quantity of principal radionuclides in abnormal discharges to the unrestricted area has been determined, the abnormal discharge quantities should be reported in accordance with RG 1.21 as an abnormal discharge.

4. If the site complexity and radionuclide release scenario do not permit simple analysis, the model provided in the appendix should be adjusted or a site

-specific model should be used to account for site-specific characteristics using the guidance in ANSI/ANS

-2.17-2010 (R2016).

RG 4.25, Page

10

D. IMPLEMENTATION

The purpose of this section is to provide information on how applicants and licensees

2 may use this guide and information regarding the NRC's plans for using this regulatory guide.

In addition, it describes how the NRC staff complies with 10 CFR 50.109, "Backfitting" and any applicable finality provisions in 10 CFR Part 52, "Licenses, Certifications, and Approvals for Nuclear Power Plants

." Use by Applicants and Licensees Applicants and licensees may voluntarily

3 use the guidance in this document to demonstrate compliance with the underlying NRC regulations.

Methods or solutions that differ from those described in this regulatory guide may be deemed acceptable if they provide sufficient basis and information for the NRC staff to verify that the proposed alternative demonstrates compliance with the appropriate NRC regulations.

Current licensees may continue to use guidance the NRC found acceptable for complying with the identified regulations as long as their current licensing basis remains unchanged

. Licensees may use the information in this regulatory guide for actions which do not require NRC review and approval such as changes to a facility design under 10 CFR 50.59, "Changes, Tests, and Experiments." Licensees may use the information in this regulatory guide or applicable parts to resolve regulatory or inspection issues.

Use by NRC Staff The NRC staff does not intend or approve any imposition or backfitting of the guidance in this regulatory guide. The NRC staff does not expect any existing licensee to use or commit to using the guidance in this regulatory guide, unless the licensee makes a change to its licensing basis.

The NRC staff does not expect or plan to request licensees to voluntarily adopt this regulatory guide to resolve a generic regulatory issue.

The NRC staff does not expect or plan to initiate NRC regulatory action which would require using this regulatory guide.

Examples of such unplanned NRC regulatory actions include issuance of an order requiring using the regulatory guide, requests for information under

10 CFR 50.54(f) as to whether a licensee intends to commit to use of this regulatory guide, generic communication, or promulgation of a rule requiring using this regulatory guide without further backfit consideration.

During regulatory discussions on plant

-specific operational issues, the staff may discuss with licensees various actions consistent with staff positions in this regulatory guide, as one acceptable means of meeting the underlying NRC regulatory requirement. Such discussions would not ordinarily be considered backfitting even if prior versions of this regulatory guide are part of the licensing basis of the facility. However, unless this regulatory guide is part of the licensing basis for a facility, the staff may not represent to the licensee that the licensee's failure to comply with the positions in this regulatory guide constitutes a violation.

If an existing licensee voluntarily seeks a license amendment or change and (1)

the NRC staff's consideration of the request involves a regulatory issue directly relevant to this new or revised regulatory guide and (2) the specific subject matter of this regulatory guide is an essential consideration in the staff's

2 In this section, "licensees" refers to licensees of nuclear power plants under 10 CFR Parts 50 and 52; and the term "applicants," refers to applicants for licenses and permits for (or relating to) nuclear power plants under 10 CFR Parts 50 and 52, and applicants for standard design approvals and standard design certifications under

10 CFR Part 52. 3 In this section, "voluntary" and "voluntarily" means that the licensee is seeking the action of its own accord, without the force of a legally binding requirement or an NRC representation of further licensing or enforcement action.

RG 4.25, Page

11 determination of the acceptability of the licensee's request, then the staff may request that the licensee either follow the guidance in this regulatory guide or provide an equivalent alternative process that demonstrates compliance with the underlying NRC regulatory requirements.

This is not considered backfitting as defined in 10 CFR 50.109(a

)(1) or a violation of any of the issue finality provisions in

10 CFR Part 52. Additionally, an existing applicant may be required to comply with new rules, orders, or guidance if 10 CFR 50.109(a) (3) applies.

If a licensee believes that the NRC is either using this regulatory guide or requesting or requiring the licensee to implement the methods or processes in this regulatory guide in a manner inconsistent with the discussion in this Implementation section, then the licensee may file a backfit appeal with the NRC in accordance with the guidance in the NRC Management Directive 8.4, "Management of Facility

-Specific Backfitting and Information Collection" (Ref.

35) and NUREG-1409, "Backfitting Guidelines

," (Ref. 3 6).

RG 4.25, Page

12 GLOSSARY abnormal discharge The unplanned or uncontrolled emission of an effluent (i.e., containing plant

-related, licensed radioactive material) into the unrestricted area (RG 1.21).

abnormal release The unplanned or uncontrolled emission of an effluent (i.e., containing plant

-related, licensed radioactive material

) (RG 1.21). contamination Undesirable radiological, chemical, or biological material (with a potentially harmful effect) that is either airborne, or deposited in (or on the surface of) structures, objects, soil, water, or living organisms in a concentration that makes the medium unfit for its next intended use. A contaminant is any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil quality. controlled discharge A radioactive discharge is considered to be "controlled" if (1)

the discharge was conducted in accordance with the methods, and without exceeding any of the limits, outlined in the offsite dose calculation manual, or (2)

if one or more of the following three items is true: (1) The radioactive discharge had an associated, preplanned method of radioactivity monitoring that assured that the discharge was properly accounted and was within the limits set by 10 CFR Part 20 and 10 CFR Part 50. (2) The radioactive discharge had an associated, preplanned method of termination (and associated termination criteria) that assured that the discharge was properly accounted and was within the limits set by

10 CFR Part 20 and 10 CFR Part 50. (3) The radioactive discharge had an associated, preplanned method of adjusting, modulating, or altering the flow rate (or the rate of release of radioactive material) that assured that the discharge was properly accounted and was within the limits set by 10 CFR Part 20 and 10 CFR Part 50 (R G 1.21).

RG 4.25, Page

13 controlled release A radioactive release is considered to be "controlled" if (1) the release was conducted in accordance with methods, and without exceeding any of the limits, outlined in the offsite dose calculation manual, or (2) if one or more of the following three items is true: (1) The radioactive release had an associated, preplanned method of radioactivity monitoring that assured that the release was properly accounted and was within the limits set by 10 CFR Part 20 and 10 CFR Part 50. (2) The radioactive release ha d an associated, preplanned method of termination (and associated termination criteria) that assured that the release was properly accounted and was within the limits set by

10 CFR Part 20 and 10 CFR Part 50. (3) The radioactive release had an associated, preplanned method of adjusting, modulating, or altering the flow rate (or the rate of release of radioactive material) that assured that the release was properly accounted and was within the limits set by

10 CFR Part 20 and 10 CFR Part 50 (RG 1.21). discharge point A location at which radioactive material enters the unrestricted area. This would be the point beyond the vertical plane of the unrestricted area (surface or subsurface) (RG 1.21). flux The volumetric or mass discharge per unit cross sectional area of medium per unit of time (solids plus pores); called the Darcian flux when applied to water movement (ANSI/ANS 2.17-2010 (R2016)).

ground water All water in the surface soil, the subsurface soil, or any other subsurface water.

Ground water is simply water in the ground regardless of its quality, including saline, brackish, or fresh water.

Ground water can be moisture in the ground that is above the regional water table in the unsaturated (or vadose) zone, or ground water can be at and below the water table in the saturated zone (RG 1.21). hydrogeologic unit Any soil or rock unit/zone that, by virtue of its porosity or permeability, or lack thereof, has a distinct influence on the storage or movement of ground water (10 CFR 61.2, "Definitions"

). normal discharge The planned or controlled emission of an effluent (i.e., containing plant

-related, licensed radioactive material) into the unrestricted area.

normal release The planned or controlled emission of an effluent (i.e., containing plant

-related, licensed radioactive material

) (RG 1.21).

residual radioactivity Radioactivity in structures, materials, soils, ground water, and other media at a site resulting from activities under the licensee's control.

This includes radioactivity from all licensed and unlicensed sources used by the licensee, but it excludes background radiation.

Residual radioactivity also includes radioactive materials remaining at the site because of routine or accidental releases of radioactive material at the site and previous burials at the site, even if those burials were made in accordance with the provisions of 10 CFR Part 20.

RG 4.25, Page

14 significant residual radioactivity A quantity of radioactive material that would later require remediation during decommissioning to meet the 25 millirem per year unrestricted use criteria of

10 CFR 20.1402. site boundary The line beyond which the land is neither owned, nor leased, n or otherwise controlled by the licensee (Ref. 3 7). specific ground water discharge rate The rate of discharge of ground water per unit area of a porous medium measured at a right angle to the direction of flow (Ref. 3 8). The term is synonymous with flow velocity or specific flux.

transect A horizontal line indicating the surface locati on of the cross section that is perpendicular to the general ground water flow direction. It is subdivided in to modeling blocks based upon monitoring well locations and can be further subdivided into smaller blocks based on hydrogeologic unit heterogeneities

. uncontrolled discharge An effluent discharge that does not meet the definition of a controlled discharge.

See the definition of controlled discharge (RG 1.21). uncontrolled release An effluent release that does not meet the definition of a controlled release.

See the definition of controlled release (RG 1.21). unrestricted area An area for which access is neither limited nor controlled by the licensee (RG 1.21).

unsaturated zone The zone immediately below the land surface where the pores contain both water and air but are not totally saturated with water.

These zones differ from an aquifer, where the pores are saturated with water

. The unsaturated zone is synonymous with the vadose zone (Ref. 3 9).

RG 4.25, Page

15 REFERENCES

4 1. U.S. Code of Federal Regulations (CFR), "Domestic Licensing of Production and Utilization Facilities," Part 50, Chapter I, Title 10, "Energy."

2. CFR, "Licenses, Certifications, and Approvals for Nuclear Power Plants," Part 52, Chapter I, Title 10 , "Energy." 3. CFR, "Standards for Protection against Radiation," Part 20, Chapter I, Title 10, "Energy."

4. CFR, "Reactor Site Criteria," Part 100, Chapter I, Title 10, "Energy."

5. U.S. Nuclear Regulatory Commission (NRC), Regulatory Guide (R

G) 1.21, "Measuring, Evaluating, and Reporting Radioactive Material in Liquid and Gaseous Effluents and Solid Waste," Washington, DC.

6. NRC, RG 4.1, "Radiological Environmental Monitoring for Nuclear Power Plants,"

Washington, DC. 7. NRC, RG 4.21, "Minimization of Contamination and Radioactive Waste Generation: Life

-Cycle Planning," Washington, DC.

8. NRC, RG 4.22, "Decommissioning Planning during Operations," Washington, DC.

9. NRC, NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition," Washington, DC.

10. NRC, Design Certification/Combined License (DC/COL)

-Final Interim Staff Guidance (ISG)

-06, "Evaluation and Acceptance Criteria for 10 CFR 20.1406 to Support Design Certification and Combined License Applications," Washington, DC, October 2009. (ADAMS Accession No. ML092470100)

11. NRC, DC/COL-ISG-013, "Assessing the Radiological Consequences of Accidental Releases of Radioactive Materials from Liquid Waste Tanks for Combined License Applications," Washington, DC, January 2013. (ADAMS Accession No. ML12191A325)

12. NRC, DC/COL-ISG-014, "Assessing the Radiological Consequences of Accidental Releases of Radioactive Materials from Liquid Waste Tanks in Ground and Surface Waters for Combined License Applications," Washington, DC, January 2013. (ADAMS Accession No. ML12191A330)

13. NRC, NUREG/CR

-6948, "Integrated Grou nd-Water Monitoring Strategy for NRC

-Licensed Facilities and Sites: Logic, Strategic Approach and Discussion," prepared for the NRC by Advanced Environmental Solutions LLC, Lexington. SC, November 2007.

4 Publicly available NRC published documents are available electronically through the NRC Library on the NRC's public Web site at http://www.nrc.gov/reading

-rm/doc-collections/

and through the NRC's Agencywide Documents Access and Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html. The documents can also be viewed online or printed for a fee in the NRC's Public Document Room (PDR) at 11555 Rockville Pike, Rockville, MD. For problems with ADAMS, contact the PDR staff at 301

-415-4737 or (800) 397

-4209; fax (301) 415-3548; or e-mail pdr.resource@nrc.gov.

RG 4.25, Page

16 14. NRC, RG 1.109 , "Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR Part 50, Appendix I," Washington, DC.

15. NRC, NUREG

-1757, Volume 2, Rev. 1, "Consolidated Decommissioning Guidance, Characterization, Survey, and Determination of Radiological Criteria," Appendix F, "Ground and Surface Water Characterization," Washington, DC, September 2006. 1 6. NRC, "Liquid Radioactive Release Lessons Learned Task Force Final Report," Washington, DC, September 1, 2006. (ADAMS No. ML062650312) 1 7. American National Standards Institute/American Nuclear Society (ANSI/ANS)

-2.17-2010 (R2016), "Evaluation of Subsurface Radionuclide Transport at Commercial Nuclear Power Plants," La Grange Park, IL, reaffirmed 2016

.5 1 8. Nuclear Energy Institute (NEI) NEI 07

-07, "Industry Ground Water Protection Initiative

-Final Guidance Document," Washington, DC, August 2007.

6 (ADAMS Accession No. ML072600295)

1 9. NRC, Inspection Manual/Temporary Instruction 2515/173, Rev. 1, "Review of the Implementation of the Industry Groundwater Protection Voluntary Initiative," Washington, DC, October 31, 2008.

(ADAMS Accession No. ML082770349)

20. NRC, Inspection Manual/Temporary Instruction 2515/

185, Rev. 1, "Follow-Up on the Industry's Ground Water Protection Initiative," Washington, DC, December

19, 2011. (ADAMS Accession No. ML11342A078)

2 1. NRC, "Summary of Results from Completion of NRC's Temporary Instruction TI 2515/173, 'Industry Groundwater Protection Initiative,'" Washington, DC, April 1, 2011

. (ADAMS Accession No. ML11088A047

) 2 2. NRC, "Roll-U p Results of Temporary Instruction 2515/185, 'Follow-Up on the Industry's Ground Water Protection Initiative

,'" Washington, DC, April 11, 2014

. (ADAMS Accession No.

ML14086A644) 2 3. Electric Power Research Institute (EPRI) Report 1011730, "Groundwater Monitoring Guidance for Nuclear Power Plants," Palo Alto, CA, September 2005.

7 2 4. EPRI Report 1015118, "Groundwater Protection Guidelines for Nuclear Power Plants," Electric Power Research Institute, Palo Alt o, C A, November 2007.

5 Copies of American National Standards Institute (ANSI) standards may be purchased from ANSI, 1819 L Street, NW, Washington, DC, 20036, on its Web site at http://webstore.ansi.org/; telephone (202) 293

-8020; fax (202) 293

-9287; or e-mail storemanager@ansi.org. 6 Publications from the Nuclear Energy Institute (NEI) are available at its Web site: http://www.nei.org/

or by contacting the Nuclear Energy Institute, 1776 I Street NW, Washington DC 20006

-3708; telephone (202) 739-800 0; fax (202) 785-4019. 7 Copies of Electric Power Research Institute (EPRI) standards and reports may be purchased from EPRI , 3420 Hillview Avenue, Palo Alto, CA 94304

telephone (800) 313-3774; fax (925) 609-1310.

RG 4.25, Page

17 2 5. NEI 08-08A, Rev. 0, "Generic FSAR Template Guidance for Life

-Cycle Minimization of Contamination," Washington, DC, October 2009.

6 (ADAMS Accession No. ML093220530)

2 6. EPRI Report 1016099, "Ground Water Protection Guidelines for Nuclear Power Plants: Public Edition," Palo Alto, CA, January 2008.

7 (ADAMS Accession No. ML091171595)

2 7. NEI 09-14 , Rev. 4, "Guideline for the Management of Underground Piping and Tank Integrity," Washington, DC, December 2015

.6 (ADAMS Accession No.

ML16294A420

) 2 8. EPRI Technical Report

1021175, "Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks

(1016456, Revision 1)," Palo Alto, C A, December 2010.

7 2 9. NRC Inspection Manual/Temporary Instruction 2515/182, "Review of the Implementation of the Industry Initiative to Control Degradation of Underground Piping and Tanks," Washington, DC, August 8, 2013. (ADAMS Accession No. ML13114A318

) 30. NRC, "Summary of Results from NRC Temporary Instruction 2515/182, 'Review of the Implementation of the Industry Initiative to Control Degradation of Underground Piping and Tanks,'" Washington, DC, June 23, 2016. (ADAMS Accession No. ML16174A032

) 3 1. International Atomic Energy Agency (IAEA)

-TECDOC-482 , "Prevention and Mitigation of Ground water Contamination from Radioactive Releases,"

Vienna, Austria, 1988.8 3 2. IAEA Safety Guide No. WS-G-3.1, "Remediation Process for Areas Affected by Past Activities and Accidents," Vienna, Austria, 2007.

3 3. Interstate Technology

& Regulatory Council, "Use and Measurement of Mass Flux and Mass Discharge," Integrated DNAPL Site Strategy Team, Washington, DC, August 2010.

9 3 4. American Petroleum Institute Publication 4730, "Groundwater Remediation Strategies Tool," Regulatory Analysis & Scientific Affairs Department, Washington, DC, December 2003.

10

35. NRC, Management Directive 8.4, "Management of Facility

-Specific Backfitting and Information Collection," Washington, DC , October 9, 2013. 3 6. NRC, NUREG

-1409, "Backfitting Guidelines," Washington, DC, July 1990

. 3 7. NRC, NUREG

-1301, "Offsite Dose Calculation Manual Guidance: Standard Radiological Effluent Controls for Pressurized Water Reactors

-Generic Letter 89

-01, Supplement No. 1," Washington, DC, April 1991.

8 Copies of International Atomic Energy Agency (IAEA) documents may be obtained through their Web site:

www.iaea.org/ or by writing the International Atomic Energy Agency, P.O. Box 100 Wagramer Strasse 5, A

-1400 Vienna, Austria. 9 Publications of the Interstate Technology &

Regulatory Council are available at its Web site: http://www.itrcweb.org/

. 10 Copies of American Petroleum Institute (API) standards may be purchased through the Web site http://global.ihs.com/?RID=API1&MID=Q023 or by contacting API Headquarters at 1220 L Street, NW

, Washington, DC 20005-4070; telephone (202) 682-8000; Web site http://www.api.org/

or e-mail standards@api.org

.

RG 4.25, Page

18 3 8. Lohman, Stanley William

, "Definitions of Selected Ground

-Water Terms

-Revisions and Conceptual Refinements

," U.S. Geological Survey Water Supply Paper 1988, U.S. Government Printing [now Publishing]

Office, Washington, DC, 197 2. (see: https://pubs.usgs.gov/wsp/wsp_1988/pdf/wsp_1988.pdf

) 3 9. U.S. Geological Survey, "Water Science Glossary of Terms," Web page, Reston, VA, 2 December 2016.

(see: http://water.usgs.gov/edu/dictionary.html

)

40. CFR, "Licensing Requirements for Land Disposal of Radioactive Waste," Part 61, Chapter I, Title 10, "Energy."

Appendix to RG 4.25, Page

1 APPENDIX SIMPLE GROUND

WATER MODEL FOR ESTIMATING SUBSURFACE TRITIUM DISCHARGES FROM NUCLEAR POWER PLANTS TO UNRESTRICTED AREAS

This appendix provides a simple ground water flow and transport model for estimating subsurface tritium (hydrogen-3) discharges from nuclear power plant sites to unrestricted areas. This model is provided in a spreadsheet format to facilitate the identification of model inputs and outputs as illustrated in Figures 1 through 6 of this appendix. The spreadsheet as illustrated in this Appendix is available in the Agencywide Documents Access and Management System (ADA MS) at Accession No. ML16253A329

. The modeling process is as follows:

(1) Develop a three

-dimensional conceptual site model (CSM) for the site as specified in American National Standards Institute/American Nuclear Society (ANSI/ANS)-2.17-10 (R2016)

, "Evaluation of Subsurface Radionuclide Transport at Commercial Nuclear Power Plants."

(2) Determine whether the site hydrogeological conditions are simple or complex. Complex hydrogeological conditions (e.g., heterogeneous hydrogeologic units, sorption, preferential flowpaths) preclude the use of this simple model. Similarly, radionuclides that migrate at a rate that is different than the ground water flux (e.g., cesium-137, strontium-90, cobalt-58 , and cobalt-60) are not appropriate candidates for using this simple model. (3) Using the CSM, monitoring well locations and depths, and monitoring well data (e.g., water levels and tritium concentrations), construct a transect (see Figure 1 for a plan view of the transect and Figure 2 for a vertical view

) encompassing the tritium plume perpendicular to the approximate direction of ground water flow containing the known tritium plume leaving the site.

(4) Determine from the C SM how the hydrogeologic units are to be represented in various modeling blocks. For example, if there is hydrogeologic layering within a modeling block , then smaller modeling blocks should be defined with properties provided for each modeling block (e.g., the hydraulic conductivity (K j), where j designates the individual modeling blocks). If the hydrogeologic units are sufficiently uniform in material properties, then they can be represented as continuous hydrogeologic units with uniform hydraulic properti es (e.g., hydraulic conductivity (K) with hydraulic gradient (h) perpendicular to the transect).

(5) Construct the modeling blocks of the model. The boundaries of the modeling blocks are located at the midpoints between adjacent monitoring wells

. (6) Select the monitoring wells to be used in calculating gradients

() for estimating the specific ground water discharge rate (or flux). These monitoring wells for estimating the gradient should be as close to the site's boundary as possible given the available data (i.e.

, geologic borings and monitoring "points" or intervals). These monitoring wells should be in hydraulic communication with each other. The hydraulic gradient is determined by monitoring wells both up

- and down-gradient in the ground water flow field. Surface water bodies such as ponds, lakes, and rivers near the site boundary and hydraulically connected to the water table can also be used in calculating the hydraulic gradient

().

RG 4.25, Appendix, Page

2 (7) Review the monitoring data of trit ium concentrations to characterize the tritium plume. If tritium concentrations change significantly with depth , then determine whether there is a need to further subdivide the modeling block. If so, further subdivide the modeling block into smaller modeling blocks. If the concentrations do not change significantly with depth, no further subdivision into smaller modeling blocks is warranted. (8) Once the model definition and representation of properties are complete, do the following

a. Input hydraulic properties for each modeling block in the spreadsheet (see Figure 3). b. Calculate the specific ground water discharge flux for each modeling block using the following equation:

= x Equation A-1 where is the specific ground water discharge flux perpendicular to the modeling block , in cubic feet (ft)/day per cross sectional area measured in square feet; ultimately it is in ft/day , is the hydraulic conductivity for the modeling block , ft/day (obtained from site-specific hydraulic tests), and

is the hydraulic gradient perpendicular to each modeling block , ft/ft (dimensionless)

(i.e., change in hydraulic head over the distance to the discharge point).

c. Calculate the bulk ground-water flux , Qw j , across each modeling block , j , using the following equation:

Qw= qxA Equation A-2 where is the bulk ground-water flux for modeling block , cubic feet/day, and is the area of the modeling block , square ft.

d. Determine tritium concentrations in each modeling block in each time period (see Figure 4). e. Calculate the tritium flux across each modeling block in each time period (see Figure 5) by multiplying the tritium concentration in each block by the bulk ground water flux using the following equation:

Q=CxQwx28.3 Equation A-3 where is the tritium flux for the modeling block , pCi/day; and is the tritium concentration of modeling block , pCi/liter, and the constant 28.3 is the conversion factor f o r liters per cubic ft. f. Sum up for each time period (e.g., quarterly), the tritium fluxes in each modeling block to obtain a total tritium flux in each subarea (see Figure 6).

RG 4.25, Appendix, Page

3 (9) Multiply the tritium flux in each block by the time period to estimate the tritium discharge in that time period (see Figure 6). (10) Add up the tritium discharges in each time period to obtain the annual tritium discharge (see Figure 6). (11) To estimate the total tritium discharg ed to the unrestricted area, the distance and rate of the tritium plume travel and subsequent radioactive decay during the migration time to the unrestricted area needs to be addressed.

Appendix to RG 4.25, Page

4 Figure 1. Plan view of the transect showing location of the facility, the transect, ground water flow direction

, and location of a large body of water

RG 4.25, Appendix, Page

5 Figure 2. Vertical view of the transect illustrating the hydrostratigraphy and the location of the monitoring wells

RG 4.25, Appendix, Page

6 Figure 3. Overview of the example RG 4.25, Appendix, Page

7 Figure 4. Monitoring data showing tritium concentration for 1 year RG 4.25, Appendix, Page

8 Figure 5. Tritium flux through each modeling block (picocuries (pCi)/day)

RG 4.25, Appendix, Page

9 Figure 6. Total tritium flux and discharge quantities