ML20150C318

Draft 1 of Proposed Reg Guide 1.XX Safety Related Permanent Dewatering Sys

ML20150C318
Person / Time
Issue date:	09/09/1978
From:	NRC OFFICE OF STANDARDS DEVELOPMENT
To:
Shared Package
ML20148M845	List: ML20150C318 ML20150C321
References
REGGD-01.XXX, REGGD-1.XXX, NUDOCS 7811220163
Download: ML20150C318 (11)

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• 8 4r UNITED STATES

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, O'g NUCLEAR REGULATORY COMMISslON WASHINGTON, D. C. 20555

. ~, ,j 00T 2 31978 o 's -

MEMORANDUM FOR: Raymond F. Fraley, Executive Director Advisory Committee on Reactor Safeguards FROM: Guy A. Arlotto, Director, Division of Engineering Standards, Office of Standards Development

SUBJECT:

DRAFT 1, REGULATORY GUIDE, " SAFETY RELATED PERMANENT DEWATERING SYSTEMS" Enclosed for the use of the Subcommittee on Regulatory Activities are fifteen copies of Draft 1 of the proposed Regulatory Guide, " Safety Related Permanent Dewatering Systems," dated 9/9/78, and its associated preliminary Value/ Impact Statement.

Since the draft guide is preliminary, additional staff efforts including review and resolution of pub ic comments will be necessary prior to implementation of a regulato position. ACRS Subcommittee comments and recommendations are re sted on he proposed regulatory position.

Gu A. lotto, Director Div 'sion of Engineering Standards Off ce of Standards Development Ecclosures:

1. Draft 1 Reg. Guide (9/9/78)

2. Preliminary Value/ Impact l Statement

'781122O763

DRAFT 1 .-

Nilsen

'. 9/9/78 .

REGULATORY GUIDE X.XX SAFETY-RELATED PERMANENT DEWATERING SYSTEMS A. INTRODUCTION Section 50.34, " Contents of applications; technical information,"

requires that each application for a construction permit must include the principal design criteria for a proposed facility. General Design Criterion 2, " Design Bases for Protection Against Natural Phenomena," of Appendix A to 10 CFR Part 50, " General Design Criteria for Nuclear Power Plants," requires that structures, systems and components important to safety be designed to withstand the effects of natural phenomena such as floods, tsunami, and seiches without loss of capability to perform their safety functions. Criterion 2 also requires that design bases for these structures, systems, and components reflect (1) appropriate consideration of the most severe of the natural phenomena that have been historically -

reported for the site and surrounding region, with sufficient margin for the limited accuracy and quantity of the historical data and the period of time in which the data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena, and (3) the importance of the safety functions to be performed.

General Design Criterion 4, "Envi'ronmental and Missile Design Bases,"

requires, in part, that structures, systems, and components important to safety shall be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance, L

testing, and portulated accidents. Criterion 4 also requires that these structures, systems, and components shall be appropriately protected against dynamic effects that may result from equipment failures and from events and conditions outside the nuclear power unit.

Paragraph 100.10(c) of 10 CFR Part 10. " Reactor Site Criteria," requires that physical characteristics of the site, including seismology, meteorology, geology, and hydrology, be taken into account in determining the acceptability of a site for a nuclear power reactor.

Permanent dewatering systems lower ground water levels to reduce sub-surface water loads on plant structures, reduce inleakage, and when relied on for any safety-related function must meet the appropriate design criteria.

A safety-related designation applies when the permanent dewatering systems protect safety-related structures, systems and components from the effects of natural and man caused events.

This guide identifies acceptable geotechnical and hydrologic engineering design bases and criteria to minimize review problems common to permanent dewatering systems that are depended upon to serve safety-related purposes.

The guide applies to both active (e.g., uses pumps) and passive (e.g., uses gravity drains) dewatering systems.

B. DISCUSSION After reviewing a number of safety-related permanent dewatering systems, the staff has developed design criteria which reflect current NRC review practice. Permanent dewatering systems are not a required feature, but are a design option that several applicants have proposed to increase plant 2

operational dependability and provide a cost effective structural feature.

The systems provide an additional means over and above 11e normal waterproof-ing used on the outside of the structural foundations, for reducing rad-l waste system operating costs by minimizing the amount of drain water, from seepage, that must be treated. The structural cost effective features are the reduced anchorage and stre- asign requirements resulting from lowered groundwater level. Cost con: for underdrains, therefore, vary

• widely and are facility and ? der--bag on, (1) considerations for treating grouno water seet ted building areas and, (2) structural alternatives in cne lo sus of buildings.

Dewatering systems are geners .omposed of three components; the collector system, the drain system, and the discharge system. Water is first collected in collector drains adjacent to buildings or excavations. Inter--

ceptor drains or piping are then used to convey this water to a f'7al dis-charge system. The discharge system can be either gravity flow or a pump-ing system. Most underdrain structures, systems and components are buried alongside and under structures, although some systems employ pumping systems within larger structures (such as reactor or auxiliary buildings) to dis-charge collected water.

Many permanent dewatering systems at non-nuclear facilities, such as dams and large buildings, have functioned over the years. However, the likelihood of a portion of such a system becoming ineffective and, therefore, not performing its intended function may well be considerably greater than the probability of occurrence of a nuclear power plant design basis event such as a Probable Maximum Hurricane, Probable Maximum Flood, or Safe Shut-down Earthquake. Losses of function in the past have generally been 3

attributable to inadequate design of filters and drainage layer, inadequate hydraulic capacity, or clogging. The staff has concluded that safety analyses of such systems should consider reliability and failures of features of the system itself, as well as potentially adverse effects of failures of nearby nonsafety-related features. Underdrain systems need not be designed for design basis earthquakes if they are not intended to perform as underdrains fully during or immediately following a severe earthquake, or if the system can be expected to perform an underdrain function in a degraded condition.

Certain portions of such systems, however, may be required to regularly perform other safety functions (e.g., porous concrete base mats) and should be designed for severe earthquakes. For example, failure of a dewatering system could cause ground water levels to rise above design levels, result-ing in overloading concrete walls and mats not designed to withstand the resulting hydrostatic pressures. In addition to causing potential structural and equipment damage, ground water could enter safety-related buildings and flood components necessary for plant safety.

The staff's review evaluates the capability of the dewatering systems to perform the dewatering function and prevent structural failures and interior flooding of safety-related structures. The degree of review is directly related to the corresponding degree to which the safety of the structures and systems rely on the integrity of the dewatering system, particularly with a dewatering system in a degraded situation. For example, if structures can accommodate hydrostatic loads that would result with a total failure of a dewatering system, the review need not consider the capability of such systems to perform their functions under relatively 4

infrequent earthquake situations. If, however, such systems must remain functional (e.g., keep water levels down), whether in a degraded situation or not, to prevent structural failures and internal flooding under poten-tially frequent conditions, the detailed review includes censideration of system reliability.

In practice, many applicants have indicated that their plants can with-stand, or have been designed against, full static loadings that would occur in the absence of the underdrain systems, but not for dynamic loadings if an earthquake were to occur. If the plant is designed to withstand full hydrostatic loading, the review includes consideration of the time available for remedial action after detection of system degradation and timeliness and implementation of a backup system.

Five general areas of review are identified as follows:

1. Estimating and Confirming Permeability Values.

It is necessary to estimate the amount of water that will be collected so that system components such as strip drains, blanket drains, collector pipes, and pumps are adequately designed and sized. One of the most impor-tant and most difficult parameters to evaluate is the permeability of the soil and rock existing at a site. A permeability value could be affected significantly by conditions of concentrated flow along joints in fractured and weathered rocks, or within other aquifers affected by foundation excava-tion. In addition, geological and foundation conditions that were not detected in site explorations may affect flow conditions and cause the estimated permeability values and flow regimes to be substantially different from those assumed at the CP preliminary design stage. These conditions are 5

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often first detected during construction dewatering. Therefore, construction excavation and dewatering data must be considered in the final design of underdrain systems.

2. Operational Monitoring Requirements.

To guard against system malfunctions and to assure sufficient time is available for implementation of remedial measures before ground water could rise to an unacceptable level, provisions must be made for early detection of systems failures, and contingency measures for these failures must be well defined prior to plant operation. Since drain systems are usually buried and concealed and there may be no direct way of inspecting them, reliance must be placed on piezometers, observation wells, manholes and monitoring of collected water to detect problems or malfunctioning of the system. The details of an operational monitoring program are necessary prior to con-struction of the underdrain to assure that each of the following will be provided: (a) an early detection alarm system during normal operating conditions; (b) regularly scheduled inspection and monitoring; and (c) periodic evaluation of observations during both construction and operation.

In addition, the bases for acceptable contingency measures suitable for coping with various possible hazards must be established at the CP stage.

3. Pipe Breaks.

A dewatering system might be overloaded by such conditions as leaks or breaks in either the circulating or service water systems. A leak through a pipe break may be a very small percentage of the total flow of the cooling water system, but large enough to exceed the hydraulic capacity of drains, pipes and pumps in the dewatering system. For example, analysis of a 6

complete failure of circulating water system piping has been required in the design of the dewatering systems. ,This requirement was made to assure that such abnormal occurrences do not ad'versely affect the integrity of safety-related structures, systems, and components.

4. Sequence of Review.

Underdrain systems are usually one of the first items constructed and, after backfilling and construction of subsurface facilities, are no longer visible for regular inspection. In most cases, these systems are initially designed based on rather limited information from preconstruction field activities, and are tailored specifically for the site and facilities. By necessity then, final review and approval of the design must rely in some part on jnformation gathered during construction. Therefore, the review and approval can be accomplished in two ways: (1) design details of the permanent underdrain system, the operational monitoring program, and the plans for construction dewatering can be submitted in the PSAR, with only confirmation of the details required prior to actual construction; or (2) conceptual designs of the permanent underdrain system, the operational monitoring program, and the details of construction dewatering can be submitted in the PSAR, with a more comprehensive evaluation based on construction dewatering information to be accomplished prior to actual construction. Review and approval of design details as post-CP matters is based upon 10 CFR Part 50, Subsection 35(b) and 55(3)(1)(111). To prevent extending the review schedule, the first procedure would be the most desirable, but it is recongized that the details required may not always be available at the time the PSAR is 7

submitted. Also, it is expected that a site visit by the staff and evalua-tion of the foundation excavations will normally be required to assure that the design is sufficient.

5. Termination o'f Operating License and Decommissioning.

Recognizing future decommissioning needs, the NRC staff began an in-depth review and reevaluation of NRC's regulatory approach to decommissioning in 1975. Major technical studies on decommissioning have been initiated to provide a firm informational base on the engineering methodology, radiation risks, and estimated costs of decommissioning typical light water reactors and to provide a more specific policy on decommissioning. The present decom-missioning regulations, originally promulgated by the Atomic Energy Commis-sion, are contained in Sections 50.33(f) and 50.82 of 10 CFR Part 50. The regulations in Section 50.33(f) require applicants for power reactor operating licenses to furnish the Commission with sufficient information to demonstrate that they can obtain the funds needed to meet both operating costs as well as the estimated costs of permanently shutting down the facility and main-taining it in a safe condition. The development of detailed, specific decommissioning plans for nuclear power plants is not currently required until the licensee seeks to terminate his operating license. Should license termination be desired, Section 50.82 of 10 CFR Part 50 requires that the licensee provide the Commission with information on the proposed procedures for disposal of the radioactive material, decontamination of the site and procedures to assure public safety. Present policy, as contained in Regu-latory Guide 1.86, " Termination of Operating Licenses for Nuclear Reactors,"

considers four acceptable alternatives for retirement of nuclear reactors.

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These are mothballing or protective storage; in-place entombment; removal of radioactive components and dismantling; and conversion to a new nuclear or fossil fuel system. In this regard it is necessary that safety-relatfd permanent dewatering systems be designed to assure that the facility has adequate protection from natura) and man caused hydraulic forces and water inleakage during the period after the last shutdown from power operations but before final decommissioning is fully attained. Therefore, the staff review includes review of design considerations for the protection of public health and safety as may be affected by dewatering system operability during faci-lity decommissioning.

C. REGULATORY POSITION

1. The system should meet the appropriate criteria of Appendix A and Appendix B to 10 CFR Part 50. However, all portions of the system need not be designed to accommodate all design basis events, such as earthquakes and tornadoes, provided that such events cannot either adversely influence the system, or that the consequences of failure from such events are not important to safety.

2. All data, analyses, and estimates as requested in Sections 2.4 and 2.5 of Regulatory Guide 1.70, " Standard Format and Content of Safety Anal-ysis Reports for Nuclear Power Plants," must be provided. Guidance for structural, mechanical and electrical design criteria is also provided in related sections of the Standard Review Plan for Category I structures, systems and components.

3. Where the system is not totally redundant or is not designed for all design basis events, the bases for a technical specification should be 9

orovided to assure that in the event of system failure, necessary remedial action can be implemented before design basis conditions ara exceeded.

4. Assurance must be provided that the system as proposed can be expected to reliably perform its safety function until termination of all licensed activity.

5. In addition, the design should consider:

5.1 the potential for localized water pressure developing in areas which are not in contact with the drainage system, or seepage into the plant in areas where pipes enter or exit the structural walls or mat foundations; 5.2 uncertainty in detecting operational problems and providing a adequate monitoring system; 5.3 the pctential for entrainment and removal of foundation and fill materials by flowing ground water, and clogging of filter and drainage layers; and 5.4 the potential implications, and their resolutions, of the permanent dewatering system on decommissioning of the facility.

D. IMPLEMENTATION The purpose of this section is to provide information to license -

applicants and licensees regarding the NRC staff's plans for using this regulatory guide.

This guide reflects current NRC staff practice. Therefore, except in those cases in which the applicant proposes an acceptable alternative 10

method for complying with specified portions of the Commission's regulations, the method described herein is being and will continue to be used in the evaluation of submittals for operating license or construction permit appli-cations until this guide is revised as a result of suggestions from the public or additional staff review.

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