ML20150C321

Value/Impact Assessment on Safety-Related Permanent Dewatering Sys Concluding That Reg Guide Should Be Prepared. W/Att a Draft Staff Position

ML20150C321
Person / Time
Issue date:	09/09/1978
From:	NRC OFFICE OF STANDARDS DEVELOPMENT
To:
Shared Package
ML20148M845	List: ML20150C318 ML20150C321
References
TASK-FP-811-4, TASK-OS REGGD-01.XXX, REGGD-1.XXX, NUDOCS 7811220165
Download: ML20150C321 (22)

Text

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D VALUE/ IMPACT ASSESSMENT ON SAFETY-RELATED PERMANENT DEWATERING SYSTEMS I. The Proposed Action A. Description Permanent dewatering systems lower ground water levels to reduce subsurface water loads on plant structures and when relied on for any safety-related function must meet the appropriate design criteria. A safety-related designation applies when the perma-nent dewatering systems protect other safety related structures, systems and components from the effects of natural and man caused events. This proposed action will be to identify accept-able geotechnical and hydrologic engineering design bases and criteria to minimize review problems common to permanent dewater-ing systems that are depended upon to serve safety-related purposes. The action applies to both active (e.g., uses pumps) and passive (e.g., uses gravity drains) dewatering systems.

B. Need for the Proposed Action No dewatering system design bases or definitive design criteria have been published by NRC, nor has the practice of applicants been uniform. As a result, licensing delays have occurred from review of these systems. A definite need exists for formalized

?S11220lGF ,

criteria and guidance. A number of permanent dewatering systems have been reviewed by NRR: e.g., McGuire 1 & 2, Cherokee 1 & 2, Perkins 1 & 2, Perry 1 & 2, WPPSS 3 & 5, Douglas Point 1 & 2, and Catawba 1 & 2.

C. Value/ Impact of the Proposed Action Attachment "A" titled " Draft Staff Position Safety-Related (Category 1) Permanent Dewatering Systems" (prepared by NRR) establishes the technical position for the proposed action including a "Value Assessment." In total, attachment "A" is the Value/ Impact for the proposed action to establish dewatering system geotechnical and hydrologic criteria.

The proposed action will also include that consideration be given to the effects of the dewatering system on facility decommissioning. The action does not identify specific decommissioning criteria but requires early consideration of decommissioning. Continued operation of the system could be required to assure that the facility has adequate protection from natural and man-caused forces during the period after the last shutdown from power operations but before final decommis-sioning and termination of licensed activity.

Dewatering system engineering variations will depend on each individual licensee's process and site-related design. The 2

levels of impact therefore can be meaningfully addressed only in the detailed environmental impact statements which are prepared in connection with licensing action for individual facilities and which are based upon the license application. Early considera-tion of decommissioning, and its options, as related to permanent dewatering system design options should permit optimization of total impact.

D. Decision on the Proposed Action Guidance should be furnished on safety related permanent dewatering systems.

II. Technical Approach Attachment "A", previously referenced, includes information on how the proposed criteria were derived and evaluated to establish a branch technical position on specific design criteria.

An independent qualitative review was made of the proposed action using postulated occurrences or conditions which could affect a permanent dewatering system. It was found that the " Proposed Staff Position" would provide a basis for an in-depth safety review and evaluation of these items on facility design. For example:

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(1) Localized subsurface conditions such as sand lenses or rock fracturingLresulting from construction techniques are considered; (2) Potential problems related to individual well pump operation and/or casing degradation are detected by properly designed monitoring systems; o

(3) Conditions such as " dewatering well voids" are considerations; (4) Forty year system reliability and dewatering system capacity as might be affected by changes in local activities (e.g., irriga-tion projects man made lakes, etc.) are covered; (5) And in the final analysis if all design basis events and the redundancy of Appendix A to 10 CFR Part 50 are not met, the action requires " provide the bases for a technical specification to assure that in the event of a system failure, necessary remedial action can be implemented before design basis condi-tions are exceeded."

A major technical aspect of safety-related dewatering systems is the ground water recovery rate and associated time lag, following systen:

failure, before design basis conditions are exceeded. This is the technical basis for backup alternate systems and provides opportunity '

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for changing the reactor operating status to a condition of potentially lower safety impact (e.g., reactor shutdown, unload fuel).

An independent quantitative technical evaluation of the proposed criteria and/or alternative criteria could include the following actions:

(1) Review of licensing action for specifics of system design and conformance with proposed criteria; (2) Modeling to establish impacts from dewatering system failures for the various modes of facility operation (e.g., operation, shutdown, post-shutdown);

(3) Cost parameters for different sites and design considerations; (4) Separate consideration of active and passive systems; (5) Detailed probability analysis of concurrent occurrences (accidents) which could impact effectiveness of alternate backup systems; (6) Independent contracted study of dewatering systems.

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III Procedural Approach A. Procedural Alternatives Potential SD procedures that may be used to promulgate the proposed action and technical approach include the following:

. Regulation

. Regulatory Guide ANSI Standard, endorsed by Regulatory Guids

. Branch Position

. NUREG B. Value/ Impact of Procedural Alternatives A NUREG is not a viable alternative because the guidance provided will contain positions. No ANSI standard on the subject is under preparation. The matter is not of sufficient general importance to justify issuance of a regulation. Only a Regula-tory Guide or a Branch Position are viable alternatives.

The Draft Branch Position prepared does not include considera-tions for facility decommissioning. A Regulatory Guide on dewatering will include considerations for decommissioning and allow for formal public review and comment.

C. Decision on Procedural Approach A Regulatory Guide should be prepared.

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l IV. Statutory Considerations A. NRC Authority This guide would fall under the authority and safety require-ments of the Atomic Energy Act. In particular under General Design Criterion 2, Appendix A, 10 CFR 50, which requires in part, that structures, systems and componente important to safety be designed to withstand natural phenomena.

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8. Need for NEPA Assessment The proposed action is not a major action, as defined by 10 CFR 51.5(a)(10), and does not require an environmental impact statement. Although there is an environmental impact from permanent dewatering systems, (e.g. , local water table draw down and discharge) the criteria and guidance provided are broad and do not specifically identify methods for conformance. The impact from engineering variations for each individual licensee's process and site related design can be meaningfully addressed only in the licensee's detailed environmental impact statements.

V. Relationship to Other Existing or Proposed Regulations or Policies This proposed action is based on a Draft Branch Technical Position which is included in revised Regulatory Guide 1.70 (Standard Format and Content) and both have RRRC approval (Regulatory Guide 1.70 has been published). The specific identification of consideration for 7

facility decommissioning is not incorporated in the above documents.

If required, detailed dewatering system design criteria specific to decommissioning can be provided by revision of this guide following codification of a detailed NRC decommissioning policy.

VI. Summary and Conclusions A Regulatory Guide on safety-related permanent dewatering systems should be prepared. The proposed criteria are the same as specified in the Draft Branch Technical Position except for including considera-tion of system effect on facility decommissioning.

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. 5r Attachmeat "A" DRAFT STAFF POSITION SAFETY-RELATE.D (CATEGORY 1)

PERMANENT DEWATERING SYSTEMS I. Summary This position has been formulated to minimize review problems common to permar,ent dewatering systems that are depended upon to serve safety related purposes by describing acceptable geotechnical and hydrologic engineering design bases and criteria. A safety-related designation for permanent dewatering systems is provided since they protect other safety-related structures, systems and components from the effects of natural and man caused events such as groundwater. In addition, the level of documentation of data and studies which are considered necessary to support safety-related functions is defined. This position applies to both active (e.g., uses pumps) and passive (e.J., uses gravity drains) dewatering systems. This position does not reflect structural, mechanical and electrical criteria.

II. Background The staff has reviewed a' number of permanent dewatering' systems, including McGuire 1 &<2, Cherokee 1 & 2, Perkins 1 & 2, Perry 1 & 2, WPP55 3 & 5, Douglas Point 1 & 2, and Catawba 1 & 2' Perry, begin-ning in 1975, was'the first plant reviewed with such systems, and was

' reviewed very' late in the CP process. Only WPPS$ 3 & 5 and Douglas Point use a passive system (no pumps). -

Permanent dewatering systems lower groundwater levels to reduce subsurface ' water loads on plant structures. In addition, they can l

increase plant operational dependability and reduce costs. These effects.are accomplished by providing added means of keeping seepage water out of lower building levels during the later stages of plant life when normal waterproofing provisions may have deteriorated, and reducing radwaste system operating costs by minimizing the amount of drain water that must be treated. Benefits are, therefore, of two types, tangible (dollars) and intangible (" insurance" . We under-stand the construction costs of underdrains can vary w)idely depending on the design. Construction costs of between $125K to $1000K per.

• unit have been suggested. The costs of coping with significant ,

amounts of groundwater inleakage in safety related building areas, ,

which underdrains are expected to minimize, is estimated to be in the range of $100K to $200K per year per reactor. . The construction costs of alternatives to underdrains for structural purposes alone (exclusive of inleakage treatment,) is estimated to range upward from $300K per e

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. Attachment "A" unit and, is highly dependent on site conditions, Structural alternatives to permanent underdrains include additional concrete use of anchor and steel in the lower portions of buildings, and the

-tems to resist floatation .

Dewatering systems are generally composed of three components; the collector system, the drain system, and the discharge system.

Water or is first collected in collector drains adjacent to buildings excavations. Interceptor drains or piping are then used to convey this water to a final discharge system. The discharge system can be either gravity flow or a pumping system. Most under-drain structures, systems and components are buried alongside and under structures, although some systems employ pumping systems within larger'collected to discharge structures (such as reactor or auxiliary buildings) water.

Finally, permanent dewatering systems are act a required feature at any plant, but may be proposed as a cost effective feature. -

Many permanent dettatering 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 quake. Hurricane, Probable Maximum Flood, or Safe Shutdown Earth-Losses of function in the past have generally been attribu-table to piping of fines, inadequate' capacity, or clogging. We have '

l" concluded that safety analyses of such systems should consider reliability and failures of features of the system itself, as well ,

related features.as potentially adverse effects of failures of nearby nonsafety-earthquakes if they are not intended to perform as underdrainsS fully during or immediately following a severe earthquake, or if the system degraded can be expected to perform an underdrain function in a condition.

Certain portions of such systems, however be required to regularly perform other safety functions (e.g. , may .

porous concrete base mats) and should be designed for severe e,arth-quakes.

Failure of a dewatering system could cause groundwater levels to rise above design levels, resulting in overloading concrete walls and mats not designed to withstand the resulting hydrostatic pressures.

damage, groundwater could enter safety-related buildings a components necessary.for plant safety.

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s. <

Attachment "A' 1 .

I The basis for staff concerns over the use of such systems is whettie, I they can be expected to perform their function, and prevent struc-tural failures and interior flooding of safety related structures.

l

< The degree of concern 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 dewater-ing system in a degraded situation. For example, if structures can i

• accommodate hydrostatic loads that would result with a total failure I. of a dewatering system, our concerns have been primarily limited to the capability of such systems to perform their functions under relatively infrequent earthquake situations. If, however, such systems must remain functional (e.g. , keep water levels down),

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,! whether in a degraded situation or not to prevent structural; failures

,] and internal flooding under potentially frequent conditions, we M

have been very concerned with system reif ability. .

c 11any applicants have indicated that their plants can withstand, or have been designed against, full hydrostatic loadings that would occur in the absence of, the underdrain systems, but not if 'an earthquake were to occur.

,- If the plant can withstand full hydro-

- static loading, assuming degradation of the underdrain system, many 4

of the staff's concerns may be eliminated from further consideration

- ' of because of the time available for remedial action after detection system degradation. ,

. III. Situations Identified During Previous Reviews Four general categories of situations have been identified during

. case reviews as follows:

(a) Estimating and Confirmino Permeability Values It is necessary to estimate the amount of water that wil'1 be collected so that system components such as strip drains,

. blanket drains, designed collector pipes, and pumps are adequately and sized.

One of the most important and most diffi-cult 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 excavation. 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 substan- .

tially .diffe. rent from those assumed at the CP preliminary design stage.

These conditions are often first detected

,em b

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- , _4 Attaehment "A" during construction dewatering. Therefore, we have required a commitment to consider construction excavation and dewatering data in the final design of underdrain systems.

below.) (See situation (d)(

(b) Operational Monitoring Requirements .

To gu'ard against system malfunctions and to assure sufficient time is available for implementation of remedial measures before groundwater could rise to an unacceptable level, provi -

sions must be made for early detection of system 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 inspect-ing 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

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operational monitoring program are necessary prior to construc-tion of the underdrain to assure that each of the following will be provided: (a) an earl detection alarm system during normal operatin'g conditions;'b (y) regularly scheduled inspection and monitoring ~; and (c) competent evaluation of observations during both construction and operation. In addition, the bases for acceptable contir.gency measures suitable for coping '

with various possible hazards must be established at the CP stage. .

Pipe Breaks (c) -

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 per-centage 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, a complete failure of circulating water system piping has been required in the design of the dewatering systems reviewed to date.

This requirement was made to assure that such abnormal occur-rences do not adversely affect the integrity of safety-related '

structures,; systems, and components.

(d) Sequence of ifeview Underdrain systems are usually one of the first items construct-ed and, after backfilling and construction .of subsurface 9

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Attachment "A"

_5_

facilities, are then 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. .

necessity then, final review and approval by the staff of theBy design must rely in some part on information 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 plans for construction dewatering can be submitted in the PSAR, with only confirmation of the details required prior to actual construction; or (2) conceptuhl designs of the permanent underdrain system and the operational monitoring program and "

details of construction dewatering can be submitted in the PSAR with the more complete review and approval based on '

construction dewatering requiring review and approval prior to actual construction. Review and approval of unique designs as post-CP matters is based upon 10 CFR Part 50, Subsections' 35(b) and 55(e)(1),(iii). To prevent extending the review schedule, the first procedure would be the most desirable, but -

the staff recogr.izes that the detail. required may not a ways be available at the time the PSAR is submitted.

IV. Proposed Staff Position Wehavereviewedandapprovedthedesignofalimitednumberof permanent dewatering systems.

of these systems to plant safetyHowever, we have alwa because of the importance be designed and used in a conserv,ative manner.ys required that they list of required design provisions which are consistent withThe following is a -

requirements in recent CP reviews:

(a) if the dewatering system is relied upon for any safety-related function, A the system and Appendix 8 to 10must CFR meet the appropriate criteria of Appendix l Part 50. In addition, guidance for structural, mechanical and electrical design criteria is provided irt related sections of the Standard Review Plan for Category I structures, systems and components. However, all portions of the system need not be designed to accomodate all design basis events, such as earthquakes and tornados, provided that such events cannot either influence the system, or that the consequences of failure from such events is not important to safety; nevertheless,

.a clear demonstration of the effectiveness of a backup system and the timeliness of <its implementation must be provided; b

Attachment "A" (b) the potential for localized pressures developing in areas which are not in contact with the drainage system, or in areas where pipes enter or exit the structural walls or mat founda-tions, must be considered; (c) uncertainty in detecting operational problems and providing a suitable monitoring system must be considered; (d) the potential for piping fines and clogging of filter and drainage laye,rs must be considered; and (e) assurance must be provided that the system as proposed can be

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expected to reliably perform its fonction during the lifetime of the plant.

(f) where the system is safety-related, is not totally redundant '

or is not designed for all design basis events, provide the bases for a technical specification to assure that in the event of system failure, necessary remedial action can be implemented before design basis conditions are exceeded.

V. SAR's (Std. Format & Content Information, Sections 2.4 & 2.b) for each of the plants with permanent dewatering systems should include the following information: ,

(a) Provide a description of the proposed dewatering system, including drawings showing the proposed locations of affected structures, components and features of the system. Provide information related to the geotechnical and hydrologic design of all system components such as interceptors, drainage blankets, and pervious fills with descriptions of material scurce,

• gradation limits, material properties, special construction features, and placement and quality control measures." (Note structural, mechanical and electrical information needs described elsewhere). Where .the dewatering system is important to safety, provide a discussion.of its expected functional reliabil-ity.

The discussion of the bases for reliability should include comparisons of proposed systcc and components with the performance of existing and comparable systems and componentr.

for applications under site conditioni, similar to those proposed.

there such information is unavailable or unfavorable, or the applica-tion (design and/or site) is unique, the unusual features of the design should be supported by additional tests and analyses to -

demonstrate ~the conservative nature .of the design. In such cases the staff will meet with the applicant, on request, to establish the ba,ses for such additional tests and analyses.

,(b) Provide estimates, and their bases, for soil and rock permea-bilities, total porosity, ef fective porosity (specific yield),

storage coefficient and other related parameters-used in the

, '.' .7 - Attachment "A" design of the dewatering system. In general, these site parameters should be determined utilizing field and, if neces-sary, laboratory tests of materials representative of the entire area of influence of.the expected. drawdown of the system. Unless it can be substantiated that aquifer materials are essentially hemogeneous, or that obviously conservative estimates have been used as design bases, provide preconstruc .

tion pumping tests and other in-situ tests performed to estimate the pertinent hydrologic parameters of the aquifer. Monitoring of pumping rates and flow patterns during dewatering for the construction excavation is also necessary to verify assumed design bases relating to such factors as permeability.and .

aquifer continuity. In addition, the' final design of the system should be based on construction dswatering data and related observations to assure that the values estimated from site exploration data are ccaservative. l.astly, the final design of the dewatering system and its hydrologic and geotech-nical operational monitor.ing program should be confirmed by .

constructio,n excavation and dewatering information.

If such inf6rmation fails to' support the conservatism of the staff, the design chan'gedinformation previously~

information should reviewed be rbviewed un by' der 10 CFR Part 50, Subsections 35(b)and55(e)(1)(iii).

(c) Provide analyses and their bases for estimates of groundwater flow rates'in the various parts of the permanent dewatering

. system, the area of influence of drawdown, and the shapes of phreatic. surfaces to be expected during operation of the system.

The extent of influence of the drawdown may be especially important if a, natural or man-made water body affects, or is

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affected by, the dewatering systems.

(d) Provide analyses, including their bases, to tablish conserva-tive estimates of the time available to mitigate the consequences-of system degradation

• that. could cause groundwater levels to exceed.designgases. Document the measures that will be taken to either repair the system, or povide an alternate dewatering system that would become operational before the design basis groundwater level is exceeded.

(e) Provide both the design basis and normal operation groundwater levels for safety-ralated structures, systems and components.

The design. tfasis. groundwater level is defined as the maximum groundwater level used in: the design analysis for dynamic or See (f) for con-itra tions of differing systern types,

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• Attachment "A" s tati'c loading conditions (whichever is being considered), and may be in excess of the elevation for which the underdrain system is designed for normal operation. This level should .

consider abnormal and rare events (such as an occurrence of the Safe Shutdown Earthquake (SSE), a failure of a circulating water

' system pipe, or a single failure within the system), which can cause failure or overloading of the permanent dewatering system.

(f) A single failure of a critical active feature or component must be postulated during any design basis event. Unless it can be documented that the potential consequences of the failure will.

not result in Regulatory Guides 1.26 and 1.29 dose guidelines i being exceeded, either (1) document by pertinent analyses '

that groundwater level recovery times are sufficient to allow other forms of dewatering to be implemented before the design basis gr6undwater level is exceeded, discuss the measur'ss to be implemented and equipment needed, and identify the amount of time required to accomplish .each measure, or (2) design for all system components for all severe natural phenomena and events. For example, if the design basis ground-water level can be exceeded only as a result of a single non-seismically induced failure of any component or feature of the system, the staff may allow the design basis level of the dewatering system to be exceeded for a short period of time

• (say 2 or 3 days), provided that (1) effective alternate de-watering means can be implemented within this time period, or that (2) it can be shown that Regulatory Guides 1.26 and 1.29 guidelines will not be exceeded by groundwater induced impairments of safety-related structures, systems, or components.

(g) Where appropriate, document the bases which assure the ability of the system to withstand various natural and accidental phenomena such as earthquakes, tornadoes, surges, floods, and a single failure of a component feature of the system (such as a failure

,of any cooling water pipes penetriating, or in close proximity to, the outside walls of safety-related buildings where the groundwater level.is controlled by the system). An analysis of '

the consequences of pipe ruptures on the proposed underdrain system must be provided, and sh.ould include considerations of postulated breaks in the circulating system pipes at, in, or near the dewatering system building either independently of, or as a result <. the SSE. Unless it can be documented that the

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potential consequences will not be serious enouch to affect the safety of the plant to the extent' that Readrato~r:y Gilides l.26'and'l.29 guidelines could bs; exceeded, provide analyses ']

to document that (1) water released from the pipe '

break cannot physically enter the dewatering I ,' ..

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Attachment "A" will not be overloaded by the increased flow such that the design basis groundwater level is subsequently exceeded.

(h)

State the maximum groundwater level the plant structures can tolerate under various significant loading conditions in the absence of the underdrain system.

(i)

Provide a description of the proposed groundwater level monitoring programs forduring dewatering dewatering durimg plant construction and for permanent plant operation. Monitoring information requested includes (1) the general arrangement in plan and profile with approximate elevation of piezometers and observa-

- tion, ywells to be installed, (2) intended zone (s) of placement (3) t' pe(s) of piezometer (closed or open system), (4) screens ,

and filter gradation descriptions, (5) drawings showing typical installations showing limits of filter and seals, (6) observa-(7) plans for evaluation of recorded data, and (8) pla'n ,

. alarm action.

rective devices to assure sufficient time for initiation of cor-Provide a commitment to base' the final design ,,

of the operational monitoring program on data gathered during the construction monitoring program (if construction experienc tive or the shows assumed operational

• program bases to be nonconserva e impractical).

be documented in the FSAR. Changes to the operational program are to' *

(k)

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The information required included (1).the general lo .

and alarm procedure to identify unanticipated high o in the system and the condition of the effluent.

(1)

For OL reviews, but only if not previously reviewed by the

• . staff, provide (1) substantiation of assumed.de, sign bases us,ing information gathered during dewatering for construction excavation and (2) all other details of the dewatering system des ~ign that ,

implement design bases establishe'd during the CP review .

, (m) ,

For OL reviews, provide a Technical Specification for periods when the dewatering system may be exposed to source:, of water not considered in the design. An example of such a situation

. .o m m..,,

would be tne excavation of surface seal material for repair ,

. of piping.such'that the underdrain would be exposed to direct surface rusoff.

, .,.. In addition, where the permanent dewatering

' ,' system is safety related .. is; not completely redundant, or is

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'~. ' I ... ? ,not designed for al) design basis events, provide. the bas 9 ", koric required and the esticated time that it will tak'e' to'

' ' .'; ' ' accompl'ish the wor.k,. the sources, types of equipment'and ,

-' {

, . . poteiitially adverse conditions. manpower requ. ired and cne .j availability of the

[ See Section V(f)]'.

Attachment "A"

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Value Assessnan:

We expect the following benefits from this position -

1, .

Provide an acceptabla level of assurance that underdrain systems will be capable of performin;; their intended functions and not threaten safety-related structures and internal systems and components due to excessive loadings and flooding. As with other. safety-related facilities, considerations of redundancy

,and system failures are provided, including the potential for adversely affecting dewatering systems by the failure" of nonsafety-

'related structures, systems and components; .

2. Provide the bases for adequate monitoring programs to assure, hydrologically and geotechnically, both the conservatism of design parameters and dependability of systems that usually* . .

cannot be inspected;

3. A more timely and efficient review process due' to increased applicant 'and staff awareness of importsat issues regarding such systems; .

4.

Clearer and more timely resolution of issues, and ,

5. Assure an adequate nargin of safety by subjecting the systems to more consistent and rigorcus analyses at an early stage of the licensing process. .

A qualitative assessment of the alternatives to the recommended joint branch table. position has been made and is summarized in the accompanying Two viable alternatives are considered to exist; continue case-by-case review (No. 1), or require standard designs (No. 7).

For the former, the staff experience has been negative because of delays caused by information requests and extensive positions cnd manpower requirements.

We conclude that establishment of criteria is necessary to minimize. inconsistent and extended reviews. For the latter, the replication advantage is desirable. However, custom designs would still be allowed and the overall long-tera advantages are minimal.

We have also assessed the desirability of each general area of the joint branch position to determine (1) whether each is necessary, and (2) whether more or less stringent measures are necessary. The position may be chfracterized as incorporating six basic requiremant's as follows: ,

O e

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• - II -

., Attachment "A" UNDER0 RAIN POSITION CRITERIA SUBJECTS Subject Ranking of Iaiportance

'- Application of Appendix A and Appendix d 'to Part 50 ' ' '

, 1 Piping of Foundations and Clogging of System 6

External Hazards , .

such as Pipe Breaks -

3 System >:onitoring and Contingency Plans .

4 System Reliability 5

Information and Aryajyses 2

Eachty.subject was then ranked in terms of its relative importance to safe Further, each subject was then considered in terms of whethe'r more or less stringent criteria wap necessary or desirabic.

This review was conducted after the basic development of the position and, therefore, in reaching considered a concensus the compromises, made among staff members position.

In all cases we judge the require-ments adequate; e.g. , less stringent criteria would either not establish that theforproposed bases a thoroughdesign staffwas adequate, or not provide sufficient review..

In reviewing the' relative level '

of requiremerits developed, ue concluded that more stringent criteria could have been incorporateG into the position in terms of system redundance and monitoring.

increment in safety would rat warrant the costs.However, we concluded that the a We also reviewed the position to detemine whether there were potentially important areas that were not included. Two such positive shutoff of discharges from underdrain Based on systems. areas were the level of liquid monitoring within plant structure, we do not consider such a requirement generally necessary for routine plant operation.

However, in the event of.a major accident, it is considered possible that highly contaminated liquids and gases could.have a signi-cantly decreased pathway length and travel time through an underdrain system.

Attachment "A" ,

VAL'UE ASSESSMENT ALTERNATIVES -

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ALTERNATIVES ADVA TAGES DISADVANTAGES l.- Case-by'-Case Review .

_l . Reduced staff effort to pr'epare 1.

branch position and standard. Increased staf f review effort.

2-Potential f'or inconsistencies g' and missing areas of safetf 4 ' -

• significance.

• ' 3, Increased staff review tirce.

2

4. Potential increased costs.

2. Require Dessign f6r a71 Design ub' sis Events

_1. High' confidence in system.

2. Reduced staff effort in pr,gparing l.

Potential increased costs.

branch position and standard; 2 Still a need to identify non-

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• seismic criteria.

3. Potential for unnecessary desiga features. -

• 4.i Potential for reduced reli~abili' of system.

, , , 5.- Questionable backfit position.

3. Require Only Monitoring

1. Potential for reduedd staff; with Contingency Plans ' system review time.' -

1 Potential for reduced sa fety.

2 Potential for reduced operationc

2. Reduced cost potential.

3 dependa bi.l i ty .

- Reduced staff time in preparing 3. Questionable timeliness or branch position. ,

~ . rea.c t i on .  !

4 Allow Nd Credit for System and Require Design for 1

High degree .O structural sa'fety. 1 High costs,

2. Elimination of concerns over Full Head (Static and 2 Questi.onable backfit position. I reliability.

Dynamic)

' .3 )

Reduced 'sta ff effort in' review.

4. Elimination of staff effort in prep - .

)

aration of branch. position and .

. standard. ,

• l

~5 Ignore; Do Not Review. .

1. Min.imal staff rdview effort, .

2. No staff effort for branch 1. ' linreviewed potential safety problems.

position and standard development. ~

3. Reduced applicant costs.

- Attachment "A" .-

VALUE ASSESSMENT ALTERNATIVES (Continued)

_A_ LTERNATIVES

, ADVANTAGES DISADVAllTAGES

6. Use Other Criteria 1. Staff time for branch position and 1.

s tandard development minimized. Potential for unreviewed

,, issues. -

7 Research ahd Development of 1. Minimize staff ef. fort'in revie sing Standard Desi replication.

1. Review would have to be Std. .p,e, sign) gn (ANS or 2.

Minimize potentfal' f6r unresolved ad hoc w/o branch position safety issue.

2. . Residual problem of criter

• 3. for custom designs.

Potential for reduced costs. 3. Sta ff time <ould be increa 8 Identi fy' Acceptable 1. Mimimize applicant costs associated Criteria in. Branch 1. Staff and management time Positian and Standard with inconsistent revi'ew. -

investment in developing b

' 2. Minimize. staff review delays.

3.* positioir and standard.

Hinimize potential for unr'eviewed

~

2; Reduces latitude in design safety issues.- -

3.

. Increases applicant costs.

- 4. Increases staff review effa now nc longer ad hcc but a'

, cases.

. 9 f ,

a .

e O -

p I

. o .

1

. l

. 1

~

}

O . 9

i

f. Attachment "A"

_ 14 He concludA that such a requirement (monitoring and shutoff) may be necessary, but should consider the results of en ongoing probability assessment of such accidents.

necessary, however, it can be implemented well before all but twoShould plar.ts incorporating underdrains become operational. Those two plants could.be backfitted to meet such a requirement also.

. And, 2) the potential implications when decommissioning the plant. of a permanent dewatering system  !

i These are the subject of ongoing studies.

The pcsition cannot be considered a ratchet inasmuch as we have never

- developed standa'rds or criteria relative to such systems. On the contrary, the acceptance of s

. when ecmpared to past practicuch es, systems can be considered a de-ratchet VI.

Impact Assessment .

The criteria . outlined in this position have been developed and ~ '

implemented by the staff in our review of recent cases, and have resulted in review delays.. We expect that some additional analyses '

s'

'cosfs to applicants, but by identifying criteria and infohnation ,

need, schedule delays should not occur in the future. -

VII. Proposed Implementation Plans

. r*.... .

We request the approval of the RRRC to include the proposed position

". in the Standard Review Plan as a Technical Position and to begin

• immediate implementation in the review of new CP applications upon '

concurrence by the Director of Nuclear Reactor Regulation. We request th.d tne Office of Standards Development initiate development of a Regulatory basis. Guide on the subject, using this position as the technical When the guide is issued, the Standard Review Plan vould be .

revised Guide. to delete the Branch Technical Position and referench made in the .

VIII.

...~

Backfittino Potential - '

There are no' presently known licensed plants which would be affected .

by implementation,of this position. ~

IX. Coordination .

This posithon was developed by tiic Hydrologic Engineering Section of th ~

. the Gc' osciences Branch, DSE. Hydrology - lietcorology Branch and Geotechnica '

This position has been coordinated uith the Structural e ,,. % p .E.1gineering ..-s _Dranch, Prograa Support Bran,ch; and Auxiliary Power

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