Donald J. Danila NortheastUtilitiesEnvironmental Laboratory MillstoneNuclearPower Station P.O. Box 128 Waterford, CT06385-0128 (860) 447-1791X4538 FAX: (860) 444-5240 Email: danildj@NU.COM
June 

### 17,1999 Dr. Elizabeth 

### M. Strange Stratus Consulting Inc. PO 

### Box4059 Boulder, 

### CO 

### '80306-4059 Dear Dr. Strange: Underseparate cover, I have enclosed the reportsyou requested. Please keep us in mind 

### if your work for EPA results 

### in any publicationsor reportsthat you are free to disseminate. Thank you very much. Very truly yours,
DonaldJ. Danila Senior ScientistJ 

# FEASIBILITY

# STUDY OF 

# COOLING WATER SYSTEM ALTERNATIVES TO REDUCE WINTER FLOUNDER LARVAL ENTRAINMENT AT MILLSTONE UNITS 

# 1, 2, AND 3

I. 

## JANUARY 

## 1993



# NORTHEAST UTILITIES SERVICE COMPANY Berlin, 

# Connecticut

.

### I



# SUMMARY TABLE OF 

# CONTENTS

Section 

### Title 

### Paae ACKNOWLEDGEMENTS 

# ............................................ iii EXECUTIVE SUMMARY 

# .......................................... ES-1 INTRODUCTION.. 

# ................................................ 1-1
PART 

### I 

# - ENGINEERING EVALUATION TABLEOFCONTENTS 

# .............................................. i LISTOFTABLES 

# .................................................. v LIST

### OF FIGURES. vii


# ................................................ 1 PRESENT INTAKE DESIGNAND OPERATION 

# ....................... 1-1 2 OVERVIEW AND PRELIMINARYASSESSMENT 

### OF AVAILABLE MITiGATION MEASURES -. 

# ............................................... 2-1 

### 3 ENGINEERING DESCRIPTION

### OF SELECTED MITIGATION DESIGNS 

# ........ 3-1 4 ESTIMATED COSTS AND CONSTRUCTION SCHEDULE 

# ................ 4-1 5 ENGlNEERlNG.SUMMARY 

# ..................................... 5-1 APPENDl CES A COST ESTIMATES 

### OF ALTERNATIVE DESIGNS 

# ....................... A-i B COST ESTIMATES 

### OF PERFORMANCE PENALTIES 

# .................... B-i C COST ESTIMATES OF FORCED OUTAGES 

# .......................... C-i i 01516.WP5Cooling Water System Alternatives to Reduce Larval Entrainment 

# I SUMMARY 

### TABLE OF CONTENTS (Cont)
Section 

## Pane PART 

### li 

# - ENVIRONMENTAL/BIOLOGICALEVALUATION TABLEOFCONTENTS 

# ................................................ i LIST OF TABLES 

# . .

# . . ...

# .. .

# . .

# . ,

# .. 

# .

# . .

# .. . .. , 

# . . .

# . . ..

# . . . . . . . .

# . .. . .

# .. . . iii LISTOFFIGURES 

# ................................................. v 1 ENTRAINMENT 

### OF WINTER FLOUNDER LARVAE AT MILLSTONE NUCLEAR POWERSTATION 

# .......................................... 1-1 2 ENVIRONMENTAL CONSIDERATIONS FOR SELECTIVE ENTRAINMENT MITIGATION ALTERNATIVES 

# . .

# ... . ... . .. 

# .. . . . .. . .

# ...

# . ..

# .. . 

# . . . 2-1 3 REPLENISHMENT 

### OF WINTER FLOUNDER AS A MITIGATION ALTERNATIVE 

# . 3-1 .- 4 SELECTION 

### OF DATES USED FOR THE EVALUATION 

### OF SHUTDOWNS AS A MITIGATIONALTERNATIVE 

# . ... ,

# .. . .. .. .

# .. ... . .

# .. .

# .. .... . . .

# .

# . 4-1 5 EFFECTIVENESS OF THE MITIGATION OF LARVAL WINTER FLOUNDER ENTRAINMENT 

# .......................... 

# .................. 5-1

1 1 

# - 6 ENVIRONMENTAL AND BIOLOGICAL SUMMARY 

# . * 

# .

# .. . .

# .. .

# . ..

# .. .

# .

# .. . 6-1

ii 01 516.W5

?

# ACKNOWLEDGEMENTS

This study could not have beendone without the interest and cooperation of engineers and scientists from both Stone & Webster Engineering Corporation (Stone & Webster) and Northeast Utilities Service Company (NUSCO). We wish to acknowledge the excellent cooperation from both organizations. The following Stone & Webster engineers contributed tothe development of this report: Dr. Y.G. Mussalli Project Engineer T.A. Adams J.J. Elder R.L. Stevens P.M. Veneto R. DeConto D.R. Crouthamel R.W. Sanders P.J. Slatkavitz F. J. Trainor Principal Mechanical/Hydraulic Engineer Cooling Tower Specialist Condenser Specialist Principal CivillStructural Engineer Principal Geotechnical Engineer Geotechnical Engineer Electrical Engineer Cost Estimator -Construction Manager Thefollowing NUSCOemployeescontributedtothe developmentand/or reviewof this report: M.P. McNamara D.A. Errichetti B.W. Nichols E. Krinick A. Elms D. Danila J.D. Miller Dr. 

### E. Lorda W.A. Kramer D.A. Gilbane Project Engineer Senior Engineer, Corporate Planning Senior Engineer, Plant Engineering Senior Engineer, Nuclear Fuels Unit 3 Plant Engineering Senior Scientist, NU Environmental Laboratory Senior Scientist, NU Environmental Laboratory Principal Scientist, NU Environmental Laboratory Mechanical Engineer Attorney

01516.WP5 

### iii

## c
Cooling Water System Alternatives to Reduce Larval Entrainment The following NUSCO Departmentsprovided input and/or review of materialcontained inthis report: Mechanical Engineering Electrical Engineering Civil Engineering Balance-of-Plant Systems Engineering Plant Operations Department Plant Maintenance Department Civil and Mechanical Design Department Cost and Scheduling Generation and Environmental‘Licensing Legal Department 

### Part II, “Environmental and Biological Evaluation,” of this report was also critically reviewed 

### by Dr. C.F. Sears, Dr. 

### L.E. Bireley, and 

### P. Jacobson 

### of NUSCO Environmental Services Division and by the following members 

### of the Millstone Ecological Advisory Committee: Dr. 

### J. Tietjen (City University 

### of New York). Dr. 

### N. Marshall (emeritus, University 

### of Rhode Island), Dr. S. Saila (emeritus, University 

### of Rhode Island), and Dr. W. Pearcy (Oregon State University). c 

# n

r L

iv 0151 6.WP5

i’

# EXECUTIVE 

# SUMMARY

INTR

## 0 

# DU CTI

# ON
This report presentsthe results of a comprehensive feasibility study of cooling water system design alternatives and operational strategies to reduce the entrainment of winter flounder larvae at Millstone Nuclear Power Station (MNPS) and fulfills a condition of the recently renewed MNPS National Pollutant Discharge Elimination System (NPDES) permit. The report consists of an "Engineering Evaluation" (Part I)that provides an overview of availabletechnologies for entrainment mitigationincludingthose mitigationschemes proposed for study by the Connecticut Department of Environmental Protection (DEP). Part 

### I also includes preliminary design development of selected mitigation measures for MNPS Unit 

### 3, order of magnitude cost estimates, construction schedules, and outage durations. Part 11, "Environmental and Biological Evaluation," of this report contains a background discussion ofwinterflounder larvalentrainment, theenvironmental considerationsfor selected mitigation schemes, a discussion of replenishment of winter flounder (fish hatchery), the rationale for the selection of outage durations to mitigate entrainment, and the bases for the 

### NUSCO stochastic population dynamics model (SPDM). This numerical model was used to assess the effectivenessof mitigating winter flounder larval entrainment.

01516.WP5 

### ES-1Cooling Water System Alternatives to Reduce larval Entrainment 

### The following alternatives were evaluated asmitigation measures: Natural-Draft 

### Cooling Towers Offshore Intake Fine-Mesh Screens Wedgewire Screens Diversion Sills 

### and Curtain Walls Infiltration Systems Operational Strategies 

## - Reduced power/flow 

## - Variable-speed pumps 

# - Scheduled 

### refuel outages 

## - Forced outages Replenishment 

### of Fish /

, 

# r

PRESENT PLANT DESIGN

rc L: 

### Theexisting seawaterintakes for MNPS 

### consist of three separate, shoreline, surfaceintakes: one for each generating unit, The intakes are similar in design, having vertical wet-pit type circulating water pumps (non-nuclearsafetyrelated) and servicewater pumps (nuclear safety related). Each intake is 

### equipped with traveling water screens, coarse-bar racks, and curtain 

# @walls extending below thelowest water level. Each intake drawswater directly fromNiantic Bay. Total station withdrawal 

### of seawaterduring normal full-power operation 

### of all three units 

### is 4358 

### cubic 

### feet per 

### second 

### (cfs). Unit 3 

### withdrawal (2097

### cfs)is approximately K 

### of the total with Unit 

### 2 (1282

### cfs)and Unit 1 (979

### cfs)each using approximately % 

### of the total. c i 

## ENTRAINMENT OF WINTER FLOUNDER 

## LARVAE AT MNPS
MNPS 

### primarily affectswinter flounder by entraining larvae through the condenser coolingwater system. 

### Most (> 

### 90 percent) larvae are entrained in April and May. Since 1976, 

### operation began in 1986,

### these estimateshave exceeded 100

### million larvae eachyear. The average fecundity 

### of Niantic River females 

### is approximately 572,000 

### eggs per fish. From about ?4 

### to ?4

### of 

### theentrained winter flounder larvae were estimated 

### tohave originated from the 

### nearby Niantic River spawning stock. Based on indirect methods 

### (Le., mass-balance calculations), it was 

### determined that 

### from 8

### to 20 percent of the annual production of 

### this stock are entrained 

### at MNPS. 

### The objective of this study was to evaluate the technical feasibility and effectiveness 

### of cooling-water system alternatives with potential to

### mitigate entrainment mortality 

### ofNiantic River winter flounder larvae by 

### atleast 25 

### percent. Because annual entrainment estimates have ranged from 31 

### to 219 

### million, but since three-unit e



### ES-2 01516.WP5Millstone Units 1;2, and

### 3 half of the cooling-water flow occurs at Unit 3, engineering design efforts focused on alternatives for this unit. 

## ENGINEERING 

## EVALUATION
Each of the alternatives examined is briefly discussed below. 

### COOLINGTOWERS Cooling towers could reduce intake entrainment by reducing intake circulating water flow to only that required for cooling tower makeup, which for a full-size natural-draft cooling tower would be less than one-tenth of the current circulating water flow rate. Two salt water cooling tower alternatives for Unit 

### 3 were evaluated: a 100-percent capacitytower and a

### Vicapacity tower. 

### Withthe%-capacity tower, %of theexisting 

### Unit 

### 3 circulating water system would remain once-through. For bothalternatives, the proposedlocation for thetowerwould be in the wooded area tothe east of the switchyard. A new pump stationwould be located at the cooling tower, and piping would be routed to the 

### north and west of the station 

### in a common cut and cover trench. The condenser would be converted totwo-pass operation. The existing once-through circulating water system would remain intact and operational. Valves would be providedtooperatethe station either once-through or onthe cooling tower. A cooling tower option would reduce cooling-water demand and larval entrainment without posing insurmountable operational difficulties. However, the cooling tower option would require further environmental evaluations (e.g., chlorination to control biofouling, a waste treatment facility, dechlorinization of the blowdown, aesthetics, and noise). A full-size natural-draft cooling-towerfor MNPS would be 

### 535 feet high and, therefore, a significant visual intrusion onthecoastline nearMillstone Point. Construction would bevery challenging., given allthe present underground utilitiesthat would require re-routing or removal. A cooling tower would also pose a severe economic burden due tothe capital cost of construction and performancepenaltyresultingfrom lostgenerating capacity. Maintenanceandoperatingcosts could also be substantial; however, they were not addressed. The total estimated costfor the cooling tower is $88 million for thefull size and 

### $70million for the

### Y3 size.

01516.W5 ES-3

### pcCoo/hQWaterSystemAlternatives to Reduce Larvalfntrainment 

### OFFSHORE INTAKE
An offshore intake, placed outside of the confines of Niantic Bay, would draw a larger proportion of winter flounder larvae from Long Island Sound ratherthanfrom the Niantic River papulation. A rock tunnel design was developed which would place the Unit 

### 3 intake approximately 1 mile south into Long Island Sound. A booster pump station would be provided on the shoreward end to overcome head losses in 

### the tunnel. Cooling-water flow from the offshore tunnel and shafts would enter a sheet pile-enclosed forebay that would isolatethe existing intake structure from Niantic Bay. A separate flow bypass for the nuclear safety-related service water pumps would also be provided. Anoffshoreintake would requiresubstantial environmental reviewsand significant inputfrom regulatory agencies, such as the Connecticut Siting Council, U.S. Army Corps of Engineers, U.S. Coast Guard, US. EPA, and the National Marine Fisheries Service. Like the cooling tower, this option would be a considerable construction project and would be prone to difficulties common with tunneling. It would also be extremely expensive. The probable entrainment impact on larval populations 

### in the vicinity of the offshore intake is difficult to predict, but increased impact to some species (e.g., bay anchovy, tautog) could occur. Maintenance and operating costs could be significant, but were not addressed. The total estimated cost for this option is $117 million. 

### FINE-MESH SCREENS 

# E

c3

Fine-mesh screens can reportedly block fish and larvae from entering the intake. Fish and larvae collected on the fine-mesh screens would be transported to a sluicing system and returned to Niantic Bay. Approach flow velocities to fine-mesh screens would be limitedto 0.5 feet per second (fps) to prevent debris overloading and also to protect the larvae. This would require an approximate doubling of the screening area of the current intake. A design was developed for Unit 

### 3 which would incorporate eighteen 1 0-foot wide traveling screens. An entirely newscreen structure constructedinfront of the existing intake and connected to it bysheet pilewallswould be neededtosupport the newscreens. The new screen structure plan dimensions would be approximately 

### 270 feet long by 40 feet wide. A separate safetyrelatedbypasswould berequiredfor servicewater. Alternate fine-mesh screenarrangements, including angled screens and drum screens were evaluated, 

### but not cost estimated. While fine-mesh screen technology can be effective in reducing entrainment of certain sizes of larvae, there is little evidence that it would be successful in protecting winter flounder larvae at MNPS. Fine-mesh screens used at the Brayton Point (Mass.) Generating Station 

# 1 -I ES-4 01 516.W5 1

L/ IMillstone Units 1,’2, and3 resulted 

### in only a 

### 6.5 percent survival of winter flounder larvae. These screens were subsequently removedfrom operation. There are also significant concerns over the ability of fine-mesh screenstocontrol debris fouling, which has previously resulted in numerous plant outages at MNPS. The total estimated cost for this option is $52 million. WEDGEWIRE SCREENS Wedgewire screens could reduce or eliminate entrainment of fish and larvae by taking advantage of naturalcrosscurrentstosweep fishand larvaepastthesubmerged screen units. Screen slot width would be selected to block entry of small organisms such as fish larvae. A wedgewire ‘screen design developed for Unit 

### 3 would consist of an array of submerged wedgewire screen units extending upfrom collector conduits placed inthesea floor. Six 9-ft diameter collector conduits, each equipped with nine 84-inch diameter screen units, would extend out froma plenumstructurethatwould be constructed directly in front ofthe existing intakestructure. The array would be staggeredto promote more effectivenaturalflushing of screen units. Anautomatedair burstsystem would be requiredtobackflushthe screens, one unit at a time. An alternate bulkhead design was also developed consisting of two circular bulkheadstructurescontaining thewedgewire screenunitsthatwould beconstructed infront of the existing intake and joined to it by a plenum and inlet conduits. The bulkhead arrangementwould offer theadvantage of being abletohoistthe screen unitstoanoperating deck for cleaning. Wedgewirescreentechnology offerssome advantage inlimiting impingementandentrainment of some fish. However, the few installations currently using this technology require much smaller volumes of water than 

### Unit 3. This design is not appropriate for the flow rate at MNPS and would result 

### in new biofouling and corrosion problems. Because of their size, winter flounder larvaewould probably not besignificantly protectedusingthescreenslotsizes that would be required at MNPS. -
The total estimated cost for this option is $65 million. DIVERSION SILLS/CURTAINWALLS While there are no known installations of barriers or sills for the purpose of diverting fish larvaeawayfrom intakestructures, hydraulicdiversions are commonly usedand the principles well-understood. Diversion sills and curtain walls can possibly divert a portion of winter flounder larvaeawayfromtheintakes. Concrete sills, such as Jersey-type barriers, would be

01516.WP5 ES-5

## a L
Cooling Water System Alternatives to Reduce Larval Entrainment placed onthesea floor infront of the intakes, and offer a passive means of diverting a portion of the larvae away from the intake. 

### A design for the Unit 

### 3 intake would consist of a V-shaped barrier that would be constructed in front 

### of the intake. Additional angled vanes placed upstream of the sill would be requiredto enhance silt diversion. An alternate concept to the sill for diverting a portion of the larvae away from 

### the intake would be 

### a floating curtain wall 

### with an air bubble floatation system. The curtain wall, constructed of nonmetallic composite materials, would be supported by piles driven intothe sea floor. The floatation system would consist of multiplediffuser pipes installedonthe sea floor infront of the floating barrier. Compressedair would be supplied tothese diffuser pipes by blowers that would be located on the shore. Larvaewould be "floated" tothe surface by the rising air bubblecurtain. They couldthen bediverted awayfrom the intake bythefloating curtain wall. Becausewinter flounder larvae are planktonic, particularly at night when most entrainment occurs, it is unlikelythat a diversion sill would appreciably reduce entrainment. Further, any larvae diverted may be entrained at Units 1 and 

### 2, particularly during ebb tides. The air bubblecurtain wall is unproven technology 

### in preventing larval fish entrainment. Itshould be noted that these options would require significant additional study and modeling tovalidate the degree of effectiveness. The total estimated cost for the concrete 

### sill option is 

### $1.8 million. 

### INFILTRATION SYSTEM/BEHAVIOR BARRIERS Infiltrationsystems consist of arrays of perforated pipes installed in aquifers. Water enters the piping array by percolatingthrough the overlaying sand and collector pipe screens. These systems would prevent the entry of fish larvae, however infiltration is not 

### a viable concept for MNPS. Infiltrationsystems have not been used on large flows at the 

### MNPS intakes, and clogging and maintenance are common problemswhen a silty overlay forms on thesea floor. Therefore, infiltrative systems and behavioral barriers were not pursued beyond a preliminary evaluation. Behavioral barriers (e.g., lights, noise) were not considered credible mitigation alternatives for winter flounder larvae. 

### PLANT OPERATIONAL STRATEGIES Entrainment mitigation through reduced cooling-water flow could be accomplished by using fewer circulatingwater pumpsduring power generationor bythe installationof variable-speed

irculating water pumps. Withthe present plant design, power reduction does not result 

### in 

### ES-6 01516.W5Millstone Units 1;2, and

### 3
a corresponding reduction in cooling-water flow requirements; also flow reduction has a negative effect on plant efficiency, safety, and economics. Circulating water pump flow reductionachievedthroughtheoperationof fewer pumpsispossible but not practicalbecause itjeopardizes plant safety. Variable-speed drives for the circulating water pumps could allow reduction in circulating water flow during the spring season. Reduced flow through the condenser would promote increasedtube fouling and potentially result in an outage. A small reduction in power would also be likely. Refuelingoutages scheduled for each spring could reduceentrainment because cooling-water requirements are much reduced during outages. Many of the MNPS refueling outages have and will continue to occur during the spring season. However, fuel nucleonics, scheduled maintenance activities, unplanned outages, and other factors precludea guaranteed refueling outage each and every spring. A forced outage each spring is possible but extremely expensive. The estimated costsassociated with forced spring outages rangefrom $21 4to$519 million. The total estimated cost for conversion to variable-speed circulating water pumps is

REPLENISHMENT OF WINTER FLOUNDER Several programs established inthe United Statesand Japantoculture flatfishes were found tohave had limited or no success. Noevidence exists that large-scale production of winter flounder has successfully augmented natural wild stocks. To produce enough young winter flounder to offset entrainment mortality would require a considerable area (an estimated 

### 33.6 ha, or 

### 83 acres) for rearing ponds, which is unavailable at MNPS, and may be very expensiveelsewhere alongtheConnecticutcoast. Foodandnutritional requirements, predator anddisease control, water quality, genetic issues, productioncosts, anda meanstoascertain success of stocking remain uncertain. A conceptual engineering design for a fish hatchery wasnotdeveloped or cost estimated duetothe uncertainties associated

### with

### this alternative. 

### COST ESTIMATE SUMMARY The cost estimates prepared for the alternatives investigated, are shown in Tables ES-1 and ES-2. The costs for entrainment mitigation would most likely be shared by ratepayers, although this would require approvals by regulatory agencies such as the Connecticut Department of Public Utility Control.

01516.WP5 ES-7

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### 4 ?-+ LMiktone Units 

### I; 2, and 

### 3 TABLE ES-2 FORCED OUTAGE COST ESTIMATE 

### FOR 25 PERCENT ENTRAINMENT MITIGATION



# # Scenario 

### Unit 1 offline 4/2to 6/13 

### Unit 2 offline 4/2to 6/13 Units 1 and 

### 2 offline 4/2 to 6/13 Unit 

### 3 offline 4/2 to 6/6 Units 1, 2, and 3 offline 4/22 to 5/12 Cumulative Replacement Power Costs in Millions of 1992 $ $214 $307 $51 

### 9 $31 

### 0 $31 

### 8 NOTES: 1. Estimates are 1992 $ grossed up tofull output for each scenario. 

### 2. Some years had no replacement power cost because a scheduled refueling overlaps the time period. 

### 3. Costs estimated from 1993through 201

### 0. 4. Dates offline are approximate; Part 

### II of this report discusses rationale for date selection. 5. Maximum attainable mitigation for Unit 

### 2 is 13percent. 

## ASSESSMENT

# OFTHE EFFECTIVENESS OF

# MITIGATIONALTERNATIVES
The long-term effects

### of MNPSoperation onthe Niantic Riverwinter flounder populationhave been addressed using the SPDM. This numerical model has been used to approximate the decrease inabundance or biomass of the Niantic Riverfemalespawningstockand itseventual recovery under various scenarios 

### of plant operation. Concurrent mortality by fishing, which greatly affects winter flounder abundance, was also included 

### in the model projections. A baseline time-series was simulated that included current or projected rates of mortality from fishing, impingement, and entrainment &e., under current MNPS mode of operation). This was a reference series against which increases 

### in spawner biomass as a result of several levels of reduction in entrainment mortality (10,

### 20, 25, and 

### 50 percent) could be measured. The modelsimulations showedthat proposed reductions 

### in fishing would be of muchgreater benefit to the Niantic River female winter flounder spawning stock, than concurrent entrainment mitigation. The calculated mean gain 

### in biomass 

### as a result of a 25 percent mitigation of entrainment would be 1,274 Ib per year. The calculated cumulative total increase would only be 50,959 Ib over a 40-year period. If an average weight of 1 Ib per female spawner is assumed, biomass and numbers of fish become equivalent. These values

01516.W5 

### ES-9Coofing Water SystemAlternatives to Reduce Larval Entrainment represent 

### a modest (5 

### 4.3 percent) gain 

### inthe annual Niantic River winter flounder spawning stock biomass. Further, this would represent 

### a very small (I 

### 0.25 percent) fraction of the combined sport and commercialwinter flounder catches in Connecticut since on average, the Niantic River stock accounts for less than 

### 5 percent 

### of the Connecticut winter flounder resource. Probabilistic risk assessment was usedtoexaminethe probabilitythat the stock could fall to less than 

### 25 percent of the maximum spawning biomass (a criticalfisheries reference point) at six selected 

### points in time. The analysis indicated that 

### in 1993, before simulated reductions 

### in fishing and entrainment mitigation alternatives were put into effect, the spawning stock biomass was already (p 

### = 0.94) less than 

### 25 percent of the maximum biomass. However, once fishing was reduced, the probability of a critically reduced stock quickly fell to

### 0.02 by 

### 1998 and became zero for subsequent years. This would occur 

### with or without larval entrainment mitigation. 

### By the time the small contribution 

### in biomass attributableto 

### 25 percent mitigation 

### (0Ib for the first 

### 3 years followed by 

### 626 Ibaverage for the next 

### 3 years) became effective, the stock would no longer be depressed below a critical size. 

## CONCLUSIONS
This study has evaluated cooling-water intake designs with respect to mitigating the impact of MNPSentrainment of Niantic Riverwinter flounder larvae. Knownmitigationmethods were reviewed and some new ideas were evaluated. Some of 

### the alternatives are not technically feasible le.g., infiltrationsystems) or have safety and operability concerns (e.g., wedgewire screens, variable-speed pumps). Several alternatives (e.g., natural draft cooling tower, offshore intake) are possible toconstruct and operate, but are extremely expensive, as are forced shutdowns. Concrete sills were a simple and relatively inexpensive option, but it is highly unlikely that 

### sills could prevent the entrainment of planktonic winter flounder larvae. Mitigation of larval entrainment mortality by any technology would have minimal effects, as demonstrated 

### by the 

### SPDM simulations. Model results indicatethatthe planned reduction

### in fishingwould bethe primaryfactor responsiblefor increases

### inthe Niantic Riverwinterfemale flounder spawning stock, rather 

### than concurrent entrainment mitigation. There have been notechnological or operational strategies that have significantly advanced cooling-water intakedesignssincetheextensive reviewsperformedinthe NUSCO FinalSafety Analysis Report and the Environmental Report prepared for Unit 

### 3. The relatively small increase projected in Niantic River female winter flounder spawner biomass (mean annual increase 

### of 1,274 Ib) does not: warrant the millions of dollars required 

### for entrainment 

# a

- ES-10 01516.WP5 

# Ef L

Millstone 

### Units 7; 

### 2, ana' 3 mitigation. The projected costs that would have to be met by ratepayers are wholly disproportionate to the ecological benefits gained. Open-cycle cooling using the existing intake structures and equipment at MNPS remains the best available technology at a reasonable economic cost with respect to larval winter flounder entrainment.

Steven Scace Eric DeBarba C. Frederick Sears Vice President Vice President Vice President Millstone Station Nuclear Engineering Environmental Services Services

01516.WP5 

### ES-11

# INTRODUCTION

BACKGROUND
The Millstone NPDES Permit No, CT0003263renewalapplicationwas submittedin December 1989. The existing permit expiration was June 

### 5, 1990. The plants continued to operate under the previous permit under the Clean Water Act provision of a timely reapplication submittal. Over the past several years, staff of Northeast Utilities Service Company’s (NUSCO) Environmental Laboratory and 

### the Connecticut Department of Environmental Protection’s (DEP) Marine Fisheries Division met numerous timestodiscuss 

### the status of the Niantic River winter flounder (Pleuronectes arnericanus) population and the affect of impingement and entrainment on various flounder life stages of that population. After several meetings among personnel from DEP Water Management Bureau, DEP Marine Fisheries Division and NUSCO Environmental Services Department, the DEP directed that a feasibility study of winter flounder larval mitigation be conducted. Accordingly, in December of 1992, the Millstone station NPDES permit was renewedwith a condition that the feasibility study be completed and submitted by February 

### of 1993. The scope of the study as directed by the DEP in earlier correspondence to NUSCO was as follows: The proposed study of thefeasibility of reducing entrainment of winterflounder larvae at Millstone Nuclear Power Station should investigate several alternatives. The study should review intake structure alternatives including screening devices and physical barriers suchas sills, baffles, and curtainwalls.
01516.W5 1-1Cooling Water System Alternatives to Reduce LarvalEntrainment The study should also review cooling system design alternatives such as recirculating cooling towers and an offshore intake. Finally, the study should review operational alternatives such as reduced cooling-water flow (higher DeltaT and Maximum Delta T), reduced power generation, andthe scheduling of maintenance shutdowns. Each alternative should be reviewed with regard totechnological feasibility, effectiveness, and costs. 

## SCOPE 

# OF WORK
As a result, a project assignment was initiated andfunded for the purpose of conducting the study. A scope of work describing the study was developed and submitted to the DEP 

### on May 

### 29, 1992. This study selects and evaluates alternative mitigation measures to reduce entrainment of Niantic River winter flounder larvae into the MNPS intakes. The study consists of an engineering evaluation of existing intake technology as it could be applied at MNPS and an environmental/biological evaluation of the effectiveness of selected measures for reducing entrainment of larvae. The estimated costs for selected measures are also provided. Enaineerina Evaluation The engineering evaluation consists of an overview of existing technologies which could potentially reduce entrainment of winter flounder larvae into the station intakes. The following types of mitigation measuresfor minimizing entrainment of 

### fish larvae are included in the review:

0 Those designedtoreducethevolume of coolingwater requiredfor thestation.

e Those designed to prevent larvae from entering the plant 

### by obstructing the larvae 

### or by changing the source of cooling water.

e Those designed to reduce the number of larvae entering the plant by obstructing or diverting the flow. Under these categories of mitigation measures are the following designs: Flow Reduction T c

e Convert the Unit 3 circulating water system to a closed-loop system with cooling towers. 

# - Natural-draft 

# - Mechanical-draft 1-2 01516.wP5 

## -Millstone Units 7;2, and 

### 3

0 Convert 

### Y3 of the Unit 3 circulating water system to a closed-loop system with cooling towers.

0 Reduced flow through isolation of circulating water pumps.

0 Variable-speed circulating water pumps.

0 Scheduled and forced outages. Prevent Entrance of Larvae at Intakes Offshore intake 0 Fine-mesh screens 0 Angled screens 0 Wedgewire screens 0 Infiltration systems" Reduce Larvae Entrance at Intakes

0 0 Air bubble flotation system 0 Behavioral barriers Weir, sills, and curtain walls

ReDlenish Fish Fish hatchery Based on the initial overview, a select number of alternative measures were chosen for preliminary design and detailedevaluation. The detailed evaluations consisted of a preliminary design of major components for each selected alternative. Because Unit 

### 3 accounts for approximately 

### 50 percent 

### of the cooling-water flow at MNPS, designs were developed for Unit 3 only. The preliminary designs addressed geotechnical considerations, developed preliminary civilengineeringdesignsfor allmajor structures, sizedmajor mechanical equipment and piping, anddeveloped preliminarydesigns for electric powerand controlequipment. From these designs, quantity estimates were taken and preliminary order of magnitude cost estimates developed. Operation and maintenance costs associated with the alternatives discussed 

### inthis studycould be considerable, but have not been addressed. A constructibility review and preliminary construction and unit outage schedule was developed for each alternative. The following alternative measures were selected for preliminary design:

0 0 Offshore intake Fine-mesh screens
0 Wedgewire screens 0 Natural-draft cooling towers (1 00 and 66.7 percent capacity)

Diversion sills and curtain walls

01516.WP5 

### 1-3

# c I
Cooling Water System Alternatives to Reduce Larval Entrainment

b Operational strategies 

## - Reduced power/flow 

## - Variable-speed pumps 

## - Scheduled refueling outages Forced outages 

## ENVIRONMENTAL AND 

## BIOLOGICAL EVALUATION
The early life history of the winter flounder 

### is briefly summarized 

### in Part 

### II. Winter flounder larval entrainment at MNPS and methods of quantifying this impact are-discussed. Various mitigation alternatives were considered for environmental and biological effects that could result from their implementation. The evaluations include most of the engineering measures, and include a natural-draft cooling tower, offshore intake, fine-mesh screens, wedgewire screens, and diversion screens and curtain walls. The replenishment (Le., fish hatchery operation) of winter flounder as a mitigation alternative was also considered. The rationale for the selection of dates used for the evaluation of plant shutdowns as a mitigation assessedusingthe NUSCO stochastic populationdynamics model. The estimationor sources of information for key model parameters and rates are presented. Particularly important are the rates of mortality due to fishing, which were projected to decrease. Model output consists of the annual increase 

### in Niantic River female winter flounder spawning stock biomassforvarious reductions inentrainment mortality. The cumulative gains in biomassover time was also calculated, and probabilistic risk assessment used to investigate the effectiveness of entrainment mitigation, alternative is given. The effectiveness of various mitigation alternatives was quantitatively


### . I F 

### ti

f .i

1-4 01516.W5

# PART I ENGINEERING EVALUATION

01516.WP5 PART 1

# TABLE OF 

# CONTENTS


# . PARTI

Section 

### Paae
PART 

### I 

# . ENGINEERING EVALUATION PRESENT INTAKE DESIGNAND OPERATION 

# ....................... 1-1


### 2 OVERVIEWAND PRELIMINARY ASSESSMENT OF AVAILABLE MITIGATION MEASURES 

# ............................................... 2-1 2.1 OVERVIEW 

# .......................................... 2-1 

### 2.2 INFILTRATION SYSTEMS 

# ................................ 2-2 

### 2.3 BEHAVIORAL BARRIERS 

# ................................. 2-4 2.4 SELECTED MEASURES FOR PRELIMINARY DESIGNAND 

### COST ESTlMATiNG 

# ......................................... 2-4 2.5 REFERENCES 

# ......................................... 2-4 

### 3 ENGINEERING DESCRIPTION OF SELECTED MITIGATION DESIGNS 

# ........ 3-1 3.1 GEOLOGY AND GEOTECHNICAL CONSIDERATIONS 

# ............. 3-2 

### 3.2 NATURAL-DRAFT COOLINGTOWERS 

# ....................... 3-4 3.2.1 FULL-SIZE COOLINGTOWER SYSTEM 

# .................. 3-4 3.2.1.1 Natural-Draft Cooling Tower 

# .................. 3-5 3.2.1.2 Closed-Loop Circulating Water System 

# ........... 3-9 

### 3.2.1.3 Impact on Unit Performance 

# .................. 3-11 3.2.2.1 Two-Thirds Size Natural-Draft Cooling Tower 

# ...... 3-12 3.2.2.2 Closed-Loop Circulating Water System 

# .......... 3-15 3.2.2.3 Impact on Unit Performance 

# .................. 3-16 

### 3.2.2 TWO-THIRDS 

### SIZE COOLING TOWER 

# .................. 3-11

01516.W5 

### i PART ICooling Water System Alternatives to Reduce Larval Entrainment 

### TABLE 

### OF CONTENTS (Cont)
Section 

## . Title



### PARTI 

### 3.2.3 GEOTECHNICAL CONSIDERATIONS 

# ................... 3.3 OFFSHORE INTAKE 

# ................................... 3.3.1 DESIGN 

### BASIS 

# .................................. 3.3.2 GEOTECHNICAL CONSIDERATIONS 

# ................... 3.3.2.1 Cut 

### and Cover 

### OffshoreTwin Tube Tunnel 

# ....... 3.3.2.2 Subsurface Tunnel 

# ........................ 3.3.3 OFFSHORE INLET 

# ................................ 3.3.4 BOOSTER PUMP STATION 

# ......................... 3.3.5 OFFSHORE INTAKE EXPERIENCE AT SEABROOK NUCLEAR POWER STATION 

# ................................ 3.4 FINE-MESH SCREENS 

# .................................. 3.4.1 ENGINEERING CONSIDERATIONS 

# .................... 3.4.2 ADVANTAGES AND DISADVANTAGES OF FINE-MESH TRAVELING WATER SCREENS 

# ...................... 3.4.3 ALTERNATIVE FINE-MESH INTAKE DESIGN CONCEPTS 

# ..... 3.4.3.1 Through-Flow Fine-Mesh Screens 

# .............. 3.4.3.2 Dual-FlowKenter-Flow Fine-Mesh Screens 

# ....... 3.4.3.3 Angled Screens 

# .......................... 3.4.3.4 Fine-Mesh Drum Screen Facility 

# ............... 3.4.4 REQUIRED TESTING 

# .............................. 3.4.5 FINE-MESH SCREEN FACILITY FOR UNIT 3 

# .............. 3.4,6 GEOTECHNICAL CONSIDERATIONS 

# ................... 3.5 WEDGEWIRE SCREENS 

# ................................ 3.5.1 STAGGEREDARRAY DESIGN 

# ....................... 3.5.2 ALTERNATIVE BULKHEAD DESIGN 

# ................... 3.5.3 GEOTECHNICAL CONSIDERATIONS 

# ................... DIVERSION SILLS AND CURTAIN WALLS 

# .................... 3.6.1 SUBMERGED DIVERSION SILL 

# ....................... 3.6.2 CURTAIN WALL WITH AIR BUBBLER 

# .................. 3.7 PLANT OPERATIONAL STRATEGIES 

# ....................... 3.7.1 POWER AND 

### FLOW REDUCTION 

# ..................... 3.7.2 VARIABLE-SPEED PUMPS 

# .......................... Hydraulic 

### and Pumping Energy Requirements for '%-Speed Operation 

# ........................ 3.7.2.2 Two-Speed Electric 

### Motors 

# .................. 3.6

3.7.2.1 

### 3-16 3-17 

### 3-17 3-18 3-21 3-22 3-23 3-24 3-26 3-27 3-27 3-28 3-28 3-29 3-29 3-30 3-30 3-33 3-33 3-36 3-36 3-40 3-43 3-44 3-45 3-46 3-49 3-49 3-49 3-50 3-57 3-52 ii 01516.WP5 

# . z

ILS

s



# .



# .

## t

Millstone Units 1.’2. and 3 TABLE OF CONTENTS (Cont) Section 

## Title Pacle 3.7.2.3 Impact on Unit Performance 

# .................. 3-53 

### 3.7.3 SCHEDULED REFUELING OUTAGES 

# ................... 3-53 3.7.4 FORCED OUTAGES EACH SPRING 

# .................... 3-57 3.8 REFERENCES 

# ........................................ 3-58
4 ESTIMATED COSTS AND CONSTRUCTIONSCHEDULE 

# ................ 4-1 4.1 ESTIMATED COSTS 

# .................................... 4-1 4.2 SPECIAL EXCAVATION COST CONSIDERATIONS 

# .............. 4-10 4.2.1 NATURAL-DRAFT COOLINGTOWER EXCAVATION COSTS 

# .. 4-10 4.2.2 OFFSHORE INTAKE COSTS 

# ......................... 4-10 4.2.2.1 Tunnel ExcavationAssumptionsKosts 

# .......... 4-10 

### 4.2.2.2 

### Shaft Excavation AssumptionsKosts 

# ........... 4-12 4.2.2.3 Schedule Assumptions and Considerations 

# ....... 4-13 4.2.2.4 Total Offshore Intake Excavation Costs 

# .......... 4-13 4.3 CONSTRUCTION PERIODS ESTIMATES 

# ..................... 4-14

. 5 ENGINEERING SUMMARY 

# ..................................... 5-1 APPENDICES A COST ESTIMATES OF DESIGNALTERNATIVES 

# ....................... A-i B COST ESTIMATES OF PERFORMANCE PENALTIES 

# .................... B-i C COST ESTIMATES OF FORCED OUTAGES 

# ..........................C-i

01516.W5 

### iii 

### PARTI

# LIST OF 

# TABLES


# . PARTI

Title Paqe 1-4 Table 1-1 Millstone Nuclear Power Station Flow Withdrawal from Niantic Bay 

# ........ 3-1 MNPS Units Circulating Water Pump vs Flow Reduction 

# ............... 3-2 Millstone Station Refueling Outage Schedule 1993-2003 

# .............. 3-55 3-50

3-3 Approximate Outage Durations at MNPS for 

### 25 Percent Entrainment Mitigation 

# ............................................... 3-56 3-4 Forced Outage Cost Estimate for 25 Percent Entrainment Mitigation 

# ...... 3-57 4-1 Natural-Draft Cooling Towers Su.mmary of Order of Magnitude Cost Estimates 

# ................................................ 4-2 

### 4-2 Offshore intake Summary of Order of Magnitude Cost Estimates 

# .......... 4-3 4-3 Fish-Mesh Screens Summary of Order of Magnitude Cost Estimates 

# ....... 4-4 4-4 Wedgewire Screens Summary of Order of Magnitude Cost Estimates 

# ....... 4-5 4-5 Two-Speed Pumps Summary of Order of Magnitude Cost Estimates 

# ....... 4-6 4-6 Barrier Sills Summary of Order of Magnitude Cost Estimates 

# ............. 4-7 4-7 Total Costs Estimate Summary 

# .................................. 4-8 4-8 Relative Order of Magnitude Costs for Tunnelling 

# .................... 4-11 4-9 Construction and Outage Period Estimates 

# ........................ 4-14

01516.WP5 V 

### PARTICooling Water System Alternatives to Reduce Larval Entrainment 

### LIST 

### OF TABLES 

### (Cont)
Table 

### T& Paqe 5-1 Total Cost Estimate Summary 

# . .. . . . . . ..

# . .

# .. , 

# .

# . . .

# . .. 

# . . .

# . . .

# . ,

# . . 5-6 5-2 Forced Outage Cost Estimate

### for 25 Percent Entrainment Mitigation 

# . . .

# . .

# . . 5-7 

### 5-3 Evaluation 

### of Entrainment Mitigation Alternatives 

### for MNPS 

# . , 

# . ..

# ..

# . .

# .. . . 5-8 

# -

I 

### I I
& 

# i

PART I vi 01516.W5

# LIST OF

# FIGURES

# - PART

# I

Fiaure 

## Title Paae 1-1 Intake and Discharge Facilities for Millstone Units 1, 

### 2,and 3 

# . . .

# ...

# ..

# . . . . 1-2 1-2 3-1 3-2 

### 3-3 3-4 3-5a 3-5b 3-6 3-7 Units 1, 2, and 

### 3

# - Typical Section of Circulating Water Intake Structures 

# . .

# . 1-3 Unit 3 

## - Natural-Draft Cooling Tower Alternative 

## - 100 Percent Capacity 

# . .. . 3-7 Unit 3 

## - Natural-Draft Cooling Tower Alternative 

## - 66 Percent Capacity 

# . ,

# .. 3-13 Unit 

### 3 

## - Offshore Intake Structure Alternative 

# . 

# . . .

# . . .

# . . . .

# .. . . . 

# . . . .

# . . 3-19 Unit 

### 3 

## - Fine-Mesh Screen Alternative 

# . . ..

# . . .

# .. .

# . . .

# . .

# . ... . . .

# .

# .. . . . 3-31 Wedgewire Screen Unit 

# . .. ,

# . . . . . .

# ...

# . ..

# .. .

# . . .

# . .

# . . . ..

# ..

# .. . . .. 3-37 Unit 

### 3

# - Wedgewire Screen Alternative 

# . . ..

# ... 

# . . ... . . . .. ... . .

# . . . , 3-41 

### Unit 3

# - Sill/Curtain Wall Alternative 

# . . .

# ... 

# ..

# .. .. .. 

# . , 

# . . .. . . . . . . , 

# . , 3-47 Pump Performance Curve 

# .

# . . . .

# . . .. . .... . ,

# . . .

# . .

# . .

# ... .. 

# . . . . , , 

# .

# . 3-51

01516.WP5 vii PART 

### I

# 7

PRESENT 

# INTAKE DESIGNAND 

# OPERATION

There are two main heat dissipation systems for each of the three Millstone Nuclear Power Station (MNPS) units that draw water from Niantic Bay: Circulating Water Systems (non-nuclear safety related) Service Water Systems (nuclear safety related) The pumps for both circulating and service water systems are installed in common intake structures. Each unit has itsownseparate intake structure. Both systems draw water from Niantic Bay, pass the water through either steam surface condensers (circulating water systems) or heat exchangers (service water systems) where the water temperature is increased. The heatedwater isdischarged intothe quarry and ultimately intoTwotree Island Channel. The location 

### of the intake and discharge facilities for each 

### unit is shown on Figure 1-1. The circulating water systems condense steam by means of once-through steam surface condensers. The waste heat from the condensing process is transferred tothe circulating water as it passesthrough the condenser tubes. 

### Inthe normal operating mode, the service water system provides cooling water to numerous station facilities. Major users are the reactor plant component cooling heat exchangers and the turbine plant component cooling heat exchangers. Inthe event of anaccident, suchas a 

### loss of primary coolant 

### inthe reactor (LOCA),servicewater 

### isdivertedto thecontainment recirculation coolerstoremoveheatfrom the reactor and the emergency generator diesel engine coolers.

01516.WP5 1-1 PART ICooling WaterSystem Alternatives tu Reduce

### Larval Entrainment 

# -3

PART I 

### Figure 1-1 Intake and Discharge Facilities

### for Millstone Units 1, 

### 2, 

### and 3

1-2 01516.WP5Millstone Units 

### I, 2; and 

### 3

_ ~ The intake structures for each unit are similar in design. Each intake structure contains service and circulating water pumps in common bays. The intakes have traveling water screenswith 3/’-inch 

### (9.5mm) mesh, coarse-bar racks, and curtainwalls which extend below lowestwater level. The coarse-barrackexcludes debris andfish largerthan 2-inch insize and the meshsize of Ya-inch preventssmaller fish and debrisfrom enteringthe pumpforebay. The curtain wall prevents warm surface water, ice, and surface marine organisms from entering the intake. Each intake has lateral fish passageways installed in the bay walls upstream of the travelingscreensto

### allow fishtoescapethescreenfaces. A typical intakesection, which 

### is similar for the intake structures of Units 1, 

### 2, and 

### 3, is shown on Figure 1-2.

Figure 1-2 Units 1, 2, and 3 

# - Typical Section of Circulating Water Intake Structures

1-3 PART I 01516.W5Cooling Water System Alternatives to ReduceLarval Entrainment 

### The intake structure for Unit 1 contains four circulating water pumps which deliver 420,000 gpm (935 cfs) of cooling water to the condenser and four service water pumps, each ratedat 

### 10,000 gpm (22.3 cfs). Normalservice water flow is 20,000 gpm. The service water pumps are in the center bay of 

### the 5-bay intake structure. 

### The water velocity approaching 

### the traveling screen is 

### inthe range of 

### 0.5 to 

### 0.9 fps. The intake structure of Unit 2 contains four circulating water pumps which deliver 548,000 gprn (1,220 cfs)

### of coolingwater to

### the condensers. 

### The intake also contains three service water pumps, each rated 

### at 14,000 gpm (31 cfs) each. The normal service water flow is 28,000 gpm. The water velocity approaching 

### the traveling screen is approximately 

### 0.5 fps. The intake structure for Unit 

### 3 houses six circulating water pumps, 

### each rated at 152,000 gpm, for atotal circulating water flow of 91 

### 2,000 gpm (2,030 cfs). The intake also contains four service water pumps, each ratedat 

### 15,000 gpm. Normalservice 

### water system flow is 30,000 gpm (67 cfs). Traveling screen approach velocity 

### is in the range of 0.5 to 1

## .o fps. Table 1-1 provides a summary of station flow withdrawals TABLE 1-1 from Niantic Bay.



# - Unit Unit 1
Unit 

### 2
Unit 

### 3

PART I MILLSTONENUCLEAR POWER STATION FLOW WITHDRAWAL 

### FROM NlANTlC BAY

Svstem Circulating Water Service Water Circulating Water Service Water Circulating Water Service Water Total Station Withdrawal

1

-4 Flow Withdrawal (cfs)

935

44 

### 1,220 

### 62 2,030 

### 67 

# - 4,358

01516.WP5 .1

x

r

I

# 2
OVERVIEWAND PRELIMINARY ASSESSMENT 

# OFA VAJLABLE

# MJTJGA TION MEASURES

NUSCO extensively reviewed alternate intake structures in its Final Safety Analysis Report (FSAR) 

## (1) and Environmental Report (ER) 

## (2). This review demonstrated that open-cycle cooling using the existing intake structures was the Best Available Technology at 

### MNPS. NUSCO's basic conclusions remain accurate and valid. However, since several years have elapsed since the submittal of the FSAR and ER, it

### is usefultoprovide aninformation update, especially in regardtofish larval impingement and entrainment. 

## 2.1 

## OVERVIEW Biologists and engineers have, over the years, conducted extensive research to develop methods to protect fish and larvae at water intakes. Most of the researchthat is pertinent to

### MNPS wasconductedfromthe late 1960stotheearly 1980sandfocused on the biological effectiveness and engineering practicability of screening systems for use at steam electric stations. 

### Inthe early 1980s, the design and construction of newsteamelectric plants inthis nation came to a near standstill. From the mid-1980s to the present time, fish protection research has continued at a reduced level of effort for steam electric stations, but has increased greatly for application to hydroelectric facilities. Some of the information derived from ongoing efforts at hydroelectric facilities, however, is pertinent to the issue of fish impingement and entrainment at MNPS and is presented to provide the best information available for the evaluation of alternatives. Mostfish protection systems in usetoday are designed primarily toprotectjuvenile and adult fish from impingement. Few such systems and devices are both biologically effective in reducing entrainment, and at the same time practical to operate, cost-effective, and acceptable to regulatory agencies. 

# I)

01516.WP5 

### 2- 1 

### PARTI

# cr) Cooling Water System Alternatives to Reduce 1 

### arvai Entrainment There are several types of mitigationmeasures for minimizing the entrainment of fish larvae atcooling-water intakes. The various general categories with specific means for application are as follows: 

### Flow Reduction

0 Cooling towers 0 Variable-speed pump driver 0 Outages Prevent Entrance of Fish Larvae at Intakes

0 Offshore intake 0 Fine-mesh screens 0 Angled screens 0 Wedgewire screens 0 Infiltration systems Reduce Entrainment of Fish Larvae at Intakes

0 Weirs, sills, and curtain walls 0 Air bubble floatationsystems Behavioral barriers ReDlenish Fish

0 Fish hatchery The above mitigating measures were screened to determine 

### if they were feasible for application at MNPS. As a result of this preliminary review, the infiltration systemdesign

### and behavioral barrierswere eliminated from further analysis. The reasons for rejection are listed below: 

## 2.2 INFILTRATION SYSTEMS
Infiltration systems consist of a system of horizontal perforated water collection conduits installed inthe aquifer below or adjacent toa water body. The collector conduit system then conveysthe water toa common collector chamber where thefiltered water can be pumped tocooling systems. Thesystem utilizes

### the filtering action of 

### the bottomsoil or anengineered filter media to remove suspended solids (including biota) from the water. An infiltration system would eliminate entrainment of fish and fish larvae into an intake. Engineered filter systems placed over thefield of collector pipes can be usedto increase permeabilities thereby allow for higher flow rates.
PART I 

### 2-2 01516.WP5 a2 1 

# 3 Millstone Units 1,*2,and

### 3 .Twocompanies specializing inthe design and construction of infiltration-typeintake system, were consulted regardingtheapplicationof an infiltration-type water collectionsystem for the Unit 

### 3 intake. These companies are 

### the Ranney Division of Hydro Group, Inc., Westervilie, Ohio, and 

### M&S Systems International Ltd of Qawra, Malta. After reviewingthe geologic conditions and flow rate of the Unit 3 intake, Ranney concluded that an infiltration gallery system would be marginal and would be an extrapolation of 

### the technology to flow capacities much larger than any existing system placed by them, The limitationtoapplicationat

### MNPSis thevery highflow capacity. Thetypical yield from a radial collector can be limited to between 1000 and 3000 gallons per 

### minute (gpm). Given the normal 912,000 gpm operating flow to the Unit 

### 3 intake, 

### a large number of collector wells would be required. The 

### City of Belgrade, Yugoslavia, utilizes a series of 

### 40 collector wells installedaround an inland laketodevelop a municipalwater supply (approximately maximum system capacity 80,OO gpm); basedonthis data, approximately

### 500wells would be required for Unit 

### 3. An infiltration gallery may also be installed, consisting of horizontally oriented media as much as 2000 feet in length. However, the long-term yield of these systems appears limited to 1000to 2000 gpm, based upon years of experience with installations of this type. For both the infiltration gallery system and the collector wells, the individual wells/galleries needto be properly spaced, resulting in large seafront property requirements. I

M&S Systems InternationalLtdpresentedadesignsimilar inconcepttothe Ranney infiltration system. M&S claims it can achieve higher yields than 

### the Ranney-type system through the use of specially designed filter media systems installed around the infiltration pipes. 

### M&S claims a 40 percent capacity increase over the Ranney system. The proposed design for Unit 

### 3 would consist of an array of collector pipe screens 

### with media, covering an area of 3800 

### m2. The collectionsystem would supply cooling water to a single pumping facility. A review ofthe

### M&Sfilter media conceptindicatedthat thissystem could besubjecttoclogging in the high detrital environment of the MNPS intakes. It was concluded that 

### an infiltration system is not 

### a viable technology for the large operating flow rate of Unit 

### 3. This conclusion was based primarily on Ranney’s previous attempts to build and operate high capacity infiltrationsystems. The maintenance and screen plugging problems are likely to occur particularly during the periods of high kelp and high eelgrass loadings. The spring period of high flounder larval activity is also a period 

### of high detrital loading at the MNPS intakes. The 

### M&S system, although possibly an improvement on the Ranney design, would be subject tothe same clogging and maintenance problems. Also, there is no experience in the United States with the 

### M&S system.

01516.WP5 

### 2-3 PARTICooling WaterSystemAlternatives to

### Reduce Larval Entrainment 

## 2.3 BEHAVIORAL BARRIERS
Behavioral barriers such as lights 

### or sound devices are not considered effective measures for preventing the entrainment of early larval life stages of fish into intakes. Even if larvalfish react to lights 

### or sound, they do not have the swimming capability to overcome the flow velocities approaching or entering the intakes. 

### For this reason, behavioral barriers were eliminatedfrom further consideration as potentialmeasuresfor reducingentrainment of winter founder larvae into the MNPS intakes (3). 

## 2.4 SELECTED 

## MEASURES FOR PRELIMINARY DESIGN 

## AND COST 

## ESTIMATING
All of the alternative measures listed in Section 2.1 withthe exception of infiltrationsystems and behavioral barriers have potential for mitigating entrainment of winter flounder larvae at 

### MNPS. Preliminary designs for thefollowing alternative measuresare presented in Section 3 with cost estimates and construction schedules presented in Section 4:

e Cooling towers 0 Offshore intake e Fine-mesh screens e Wedgewire screens

0 Operational Strategies Diversion 

### sills and curtain walls 

### with air floatation



## - Reduced power/flow 

## - Variable-speed pumps 

## - Scheduled refuel outages 

## - Forced outages The fish hatchery 

### is discussed in Part 11. 

## 2.5 

## REFERENCES
1. Millstone Nuclear Power Station, Unit 

### 3; Final Safety Analysis Report; Docket NO.50-42.3. 2. Millstone Nuclear 

### Power Station Unit 

### 3, Environmental Report: Docket 

### No. 

### 50-423. 3. E.P. Taft. Assessment of Downstream Miarant Fish Protection Technoloaies for Hvdroelectric ADolication. Palo Alto, California: Electric Power Research Institute, 1986. AP-4711.

PART 

### I 2-4 01 516.W53


# ENGINEERING DESCRIPTION OF 

# SELECTED MITIGA 

# TION DESIGNS

Inthis section, preliminary designs for selected cooling system alternatives were developed for the 

### Unit 3 intake. 

### Unit 3 draws approximately 

## H of the total station intake flow. Eliminationor reduction of larval entrainment intothe Unit 

### 3 intakewould producea reduction instationentrainment. Theselecteddesignsoffer the potentialfor a reduction in entrainment of winter flounder larvae. The designsweredevelopedtoa levelof detail adequatetodevelop order of magnitude cost estimates. Previous studies evaluating cooling towers at Unit 3 were done during the initial licensing work for thestation intheearly 1970sand subsequent studies conducted during the 1 980s. The results of these evaluations were incorporated into the selection of the type of cooling tower (natural-draft)tobe usedfor preliminary design and specific system design parameters used in this study. Design criteria and construction experience for the Seabrook Nuclear Power Station offshore intake and discharge tunnels were used to develop the preliminary designforthe proposed offshore intake systemfor Unit 3. The most current U.S. andforeign design criteria were used to develop preliminary designs for fine-mesh screens, wedgewire screens, and diversion 

### sills and curtain walls. Inall casesthe nuclearsafety-related servicewater system operationwould remainthesame. The service water pumpswould remaininthe existing Unit 

### 3 intakestructure and function as they currently do. 

### In the cases of the offshore intake, fine-mesh screens and wedgewire screens, wherethe existing intakewould

### be enclosed bya forebay, a separatenuclear safetyrelated water passageway would be required. This passage system would consist of a combination of anautomatic safety-related valve or gatesystem and collapsible panels. The actual design and cost estimatefor these systems were not included in the report.

01516.W5 

### 3- 1 PART 1Coaling Water System Alternatives to Reduce

### Larval htrainment Because the service water system is nuclear safety related, the design would be nuclear safety-related Category 

### I and would be subject toNuclear Regulatory Commission review and approval. This area was not addressed in detail. 

### 3.1 

## GEOLOGY 

## AND GEOTECHNICAL CONSIDERATIONS
Much of the geology at MNPS was well documented during the licensing and construction phases of 

### the three units. The most current information is described in Section 2.5 of the Final Safety Analysis Report 

### (FSAR) (I), Boring, seismic refraction surveys, bathymetric surveys, laboratory data and geologic mapping during excavation provide information on the properties of the rock and 

### soil types expected elsewhere in the site vicinity. Bedrock at the site is overlain byglacial deposits consisting of basal

### till, ablation 

### till, stream deposits, beach sands and artificialfill. 

### All major Unit 

### 3structures, ducts and pipelines werefounded on basal till 

### or bedrock and nounusual conditions wereencountered during excavation 

### or construction. It should be notedthat the variable nature of the top of rock surface does not allow for an accurate prediction of overburden thicknesses elsewhereat Millstone Point 

### using Unit 3 data. Therefore, estimates of rock and soil quantities are difficult. The predominant site bedrock is Monson gneiss. It is a uniformly foliated (layered) metamorphic rock, composed of thin segregated layers of quartz, feldspar, and mica. The Monson gneiss is intruded by sills of younger Westerly granite, generally parallel to the foliation. The Westerly granite is most prevalent at the discharge area and near shore 

### inthe vicinity of the intakes. Both rock types are hard, dense, crystalline rocks that are mostly unweathered, except inthevicinity offault zones, and serveasexcellent foundation materials. The determined allowable bearing capacity for these rock types is 

### 200 ksf (kips per square foot) (FSARTable 2.5.4-23). According tothe site bedrock map 

### (FSAR Figure 2.5.1-1 

### 31,the Monson gneiss extends offshore into Niantic Bay, where it contactsthe Brimfield Formation. ' This rock isa garnet-mica schist and gneiss and isexpectedtohave physical propertiessimilar tothe Monson gneiss. According 

### to FSAR Figure 2.5.4-39 the rock elevation is generally highest at the eastern portion of the Unit 

### 3 site 

### (22feet) and drops to -32 feet at the Unit 

### 3 intake. Site grade is 24 feet and 

### rises gradually tothe north of the Unit 

### 3structures to

### 30 feet. Itisexpected that rock elevations pertinent to this study are similar to those found 

### in the area of 

### Unit 

### 3 (between 10 to 

### 20 feet). Offshore, the top of the rock surface is inferred from seismic refraction data which indicates highly variable elevations (0to -180 feet).

PART I 

### 3-2 01 516.W5

### -- Millstone Units 1;2, and 3 The bedrock surface is overlain by a dense basal till of variable thickness 

### (5to 40 feet). It consists of a poorly sorted mixture of clay, sand, silt and cobbles that was compacted by glacial ice. The allowable bearing capacity is 12 ksf and itsshear strength is relatively high, making

### this soil suitable for use as a foundation material in some cases. Overlying the basal till are less dense deposits consisting of ablationtill; stream deposits, which are found mainly onthe west side of the site; beach sands; and artificial fill. The physical properties of these materials were not considered well suited for foundation of major structures. Therefore, during foundation preparation, these materialswere removed until basal till or bedrock was exposed. The same general procedure

### is assumedfor foundation of the structures addressed inthis estimate. Previousexcavations indicatethe basaltill can maintaina 1H: 1 V slope while the overlying looser soils requirea 

### 2H: 1 

### V slope for stability purposes. Analysis of Unit 3 soils indicatesthat liquefaction is nota concern. However, a re-evaluation will be required ifthere are any major modificationstotheshorefront slopes and channels inthevicinity of the intake. 

# -c)

T

Geologic features which may influence design and construction include rock discontinuities, rock stress concentrations, soil deposits of poor bearing capacity, and groundwater conditions. Discontinuities that form planes of weakness that must be considered for structural stability in rock excavations and tunnels are the foliation, joints and faults. These planes of weakness canform unfavorable geometries singularly or incombinationwhen they intersect an excavation. The foliation at the site is uniform and the average orientation is N67W/48NE. The jointing (fracturing)of the rockiswell developed. The dominant orientation is N03W/63NE and two lesser sets are N02W/78NE and N48W/07NE. The joint spacing is generally 3 to 

### 5 feet and thejoint apertures are generally closed or thin. Depending on rock excavation orientations, some stabilization may be necessary through use of rock bolts. Excessive rock stress concentrations were not observed during excavation and this is not considered an issue. Elevenfault zoneswere uncoveredduring mapping asshown in FSAR (l) Figure 

### 2.5.1 -18 and more can be anticipated during future excavation. The fault zones generally trend northsouth, are nearly vertical, and can producefragmented and crushedzones a fewfeet inwidth adjacenttothefault plane. Although faultsdid notposesignificant foundation or stabilization problems during construction, they can act as conduits for groundwater flow during tunnel construction. Groundwater elevations prior to excavation at the Unit 3 site are shown in FSAR Figure 2.5.4-37. They indicate that original groundwater elevations are atelevation 20 feet and drop seaward. The overall groundwater gradient appears to be from northeast to southwest. Since the tills are relatively impervious, groundwater movement is mainly restrictedtothe more pervious materialsoverlying the till. Hydraulic conductivityfor granite

01516.WP5 3-3 PART ICooling Water SystemAlternatives to Reduce Larval Entrainment gneiss and granite typically range from 10" and cm/s and is mainly a function of the density and orientation of fracturing. Pressuretests inthe site rock indicate permeabilitiesare extremely low. construction. This was confirmed 

### by the lack of infiltration during excavation and


## 3.2 NATURAL-DRAFT COOLING TOWERS
Twocoolingtower alternativeswere addressedincluding afull-size natural-draftcoolingtower with accompanying closed-loop circulating water systemsfor Unit 

### 3 and a similar but smaller natural-draft cooling tower system for 

### Unit 3 designed to reject Y3 of the unit waste 

### heatto the atmosphere. The objective of these cooling tower alternatives was to reduce flounder larval entrainment by reducingstation saltwater withdrawal ratefrom Niantic Bay. Thesetwo cooling tower alternatives were selected to provide representative current capital cost estimates, unit performanceimpacts, andconstructionschedulesfor converting Unit 3wholly or partially to a closed-loop circulating water system. The results of studies prepared for 

### MNPS Unit 3 during the initial licensing process 

## (1) and evaluations conducted during the 1

980s addressing closed-loop cooling systems using various cooling tower configurations were used as a basis for this updated study; however, new calculations were performed to design the cooling towers. Bothcoolingtowersystemdesignswould 

### alloweither full-time 

### or part-timeoperationwiththe existing once-through cooling systemsremainingintactand operational. Performanceimpacts were estimated for both full- and part-time operation. The nuclear safety-related service water system 

### for Unit 

### 3 would remain as is 

### with both cooling tower alternatives; however, extensive regulatory approvals would be required. This area was not discussed, 3.2.1 

### FULL-SIZE COOLINGTOWER SYSTEM

\ c 4 IE;

I

P t

This alternative consists of conversion of the existing once-through circulating water system for Unit 

### 3toa closed-loop system utilizing a natural-draft saltwater cooling tower. The 

### heat rejectedbycondensing steam would be rejectedto

### the atmosphere, primarily

### by evaporation of the saltwater 

### in the cooling tower. The service water system would remain the same. 

### The objective of this alternative would 

### be to reduce total station (Units 

### I, 

### 2,and 3) intake flow from Niantic Baytoapproximately 

### K of itscurrent volume. The currentflow withdrawal 

# i) rates for Units 1, 

### 2, and 

### 3 are shown on Table 1-1. The total withdrawal rate of saltwater
PART I 3-4 01516.WP5Millstone Units 

### I; 2, and 3 from Niantic Bay is4373 cfs. The cooling tower would reducethe required Unit

### 3 circulating water flow withdrawal from 2030 cfsto 90 cfsfor cooling tower makeup resulting in a total station withdrawal of about 2430cfs. This would be a 44 percent reduction. This reduction in stationflow withdrawal from Niantic Bay would result in a corresponding reduction in the number of winter flounder larvae entrained. Bothnatural-draft and mechanical-draftcooling towerconfigurations for Unit

### 3 wereevaluated during the original licensing process, The results of these studies have been summarized in the Final Environmental Statement for Unit 3 

## (2). The results of these studies showed that thetotalcostfor mechanical-draft and natural-draft cooling tower systems were similar. The natural-draft cooling towerwas selected for this studytodevelop current representative costs for conversion of the Unit 

### 3 circulating water systemfrom once-through toclosed-loop. The advantage of the natural-draft cooling tower 

### is that .iteliminates the power requirements for fan operation. The natural-draft saltwatercooling tower alternative would consist of thetower located inthe wooded area tothe east of theswitchyard as shownon 

### Figure 3-1. The cooling tower would have a new circulating water system with the new pump station at the tower location. The existing condenser operation would be changed from the current single-pass configuration to a two-pass configuration. This change would be necessaryto maintain high condenser tube velocities for efficient heattransfer 

### with the reduced circulating water flow rate 

### inthe closedloop system. The existing condenser has adequate pressure rating (80 psi) and valving to allow operation in a two-pass mode 

### with no modifications. The proposed circulating water piping from andtothecooling tower would be routedtothe northand west ofthe station and would be manifolded into

### the existing circulating water piping on

### the west side of 

### the station as shown on Figure 3-1. Piping would be installed in a common cut and cover trench. Valving would be provided atthe tie-in point of the new closed-loop circulating water system piping and existing circulating water piping to allow operation of Unit 

### 3 either on the cooling tower or once-through. New makeup water pumps would be required 

### in the existing Unit 

### 3 intake structure. The cooling tower blowdown would be discharged tothe quarry. 

### 3.2.1.I 

### Natural-Draft Cooling 

### Tower The natural-draft saltwater cooling tower for Unit 

### 3 would be designed tooperate in summer conditions. The tower would be a massive structure, 450 feet in diameter at the base and 535 feet tall. The tower design would be the counterflow configuration with the fill located within the tower shell just above the air inlet. The fill masswould be disc-shaped covering

01516.WP5 

### 3-5 PART 

### I

# 7

Cooling Water System Alternatives to Reduce Larval Entrainment the full plan area of the tower and would be approximately 4 feet inthickness. A system of channels, pipes, and spray headerswould distribute the circulatingwater evenly over the fill area. Provisions for ice control, such as a spray curtain ring covering the circumference 

### of the air inlet and fill zoning, could be incorporated into thedesign. Special structure provisions for salt water would include galvanized or epoxy-coated rebar and Type 

### II Portland cement. The polyvinylchloride (PVC)fill is unaffected by salt water. 

# P

-- 

## I



# c i

# ! i Specific design parametersfor the cooling tower are as follows: Circulating Water Flow Cooling Range Approach Temperature Wet Bulb Temperature Dry BulbTemperature Evaporation Rate Drift Rate Concentration Factor 630,000 gpm 25 OF 14OF 

### 27OF 89 OF 2.1 

### % 0.002% 1.5
I Drift elimination technology has improved since the early 1970swhen cooling towers were originally evaluated for Unit 

### 3. Atthattime, a drift rate of 0.00375 percent of the circulating water flow was used for evaluation. Current drift eliminator designs can reduce

### the drift rate to0.002 percent of the circulating water flow. The original conclusion onthe affects of salt drift from a natural-draft cooling tower for Unit 

### 3 by the United States Atomic Energy Commission was 

### that naturally occurring levelsof salt drift from Long IslandSound would be A modern cooling tower would generate even less drift than 

### that predicted 

### by the original study. It is concluded, therefore, that salt drift from a natural-draft cooling tower at MNPS should not create an adverse environmental impact. 1 an order of magnitude higher than levels predicted for the cooling tower 

## (2). I

PART I 

### 3-6 01516.WP5

# i

,aMillstone Units 1;2, and 

### 3 

# 0
A chlorination system to control biofouling in the cooling tower fill and the condenser tubes would be required and a dechlorination system would probably also be required for the blowdown. Costs for these systems were not addressed. The required makeupwater flow tothe cooling tower to maintainthe concentration factor 

### in the closed-loop circulating water system at 1.5 or 

### less at all times would be 90 cfs (40,400 gpm). Makeup flow would be pumped intothe circulating water return line near the condenser discharge manifold as shown on 

### Figure 

### 3-1.Approximately 

### 55 feet of pumping head would be required to pump the makeup water intothe system. Required pump motor horsepower for the makeup water pump would be 720 horsepower. Two full-size makeup water pumps would be provided. A 42-inch diameter line would be required for makeup water. Blowdownwould be discharged from the cooling tower basin at an overflow weir structure thatwould belocatedonthecoolingtowerdischarge flume. The discharged blowdownwould be carried by gravity to the quarry 

### by a 60-inch line buried in a cut and cover trench. Blowdown piping would be routed tothe existing discharge flume atthe quarry. Blowdown flow would range from 27,000 to 40,000 gpm. 

### 3.2.1.2 Closed-Loop 

### Circulating Water System The circulating water systemfor thecooling tower would consist of a pumpstationcontaining six circulating water pumpsand motors locatedatthe coolingtower basin, a buried circulating water conduit w.hich would convey cooled circulating water from the cooling tower to the condenser and would return heated water from the condenser back to the cooling tower, valves, electric power, and control equipment. The proposed pipe routing istothe north of the station and then south and to the west side of the condenser as shown on 

### Figure 3-1. Flow rate for the closed-loop circulating water system would be 1,400 cfs 

### (630,000 gpml. Total system head loss and static lift to pump circulating water to the cooling tower 

### fill distribution system would be approximately 100feet, The head would include friction losses inconduit; losses

### inthetwo-pass condenser; form lossesatbends, fittings, andjunctions; and an estimated 45-foot static lift tothe cooling tower fill distribution system. To meet these flow and head requirements, six circulating water pumps would be required, rated at 105,000 gpm at 100 feet total dynamic head. This would require 3,300 horsepower per pump for a total pumping energy requirement of 19,800 horsepower. This equated to approximately 14,800 kW of electric power.

01516.WP5 

### 3-9 PART ICooling Water System Alternatives to Reduce Larval Entrainment The six circulating water pumpdischarges would be manifolded intoa single 14-footdiameter inlet conduit which would convey the circulating water to the west side of the Unit 

### 3 condenser. This piping would be manifolded to join three of the six 84-inch inlets to the condenser. Valving atthe manifoldedjunction would consist of three 84-inch motor-operated butterfly valves in thethree inlet lines from the cooling tower. These valves, 

### in conjunction with the existing pumpdischarge valves and condenser valves, would allow operation of the system either on the cooling tower or once-through. Water would maketwo passesthrough the reconfigured condenser and exit the condenser from the alternate three 84-inch lines on the west side of the condenser. These existing 84-inch lines would be cut and manifolded into a single 14-foot diameter return line 

### which would convey heated circulating water back tothecoolingtower, Pipe materialselectedfor thecirculating water pipe for this study would be fiberglass-reinforced plastic (FRP). Advantages of 

### FRP pipe as compared to concrete cylinder pipe include lighter weight for easier handling during construction, longer sections resulting in shorter placement time, and no corrosion insaltwater. Carbon steel pipe would not be considered suitable in saltwater service due to high corrosion rates. Electric power for the new circulating water pumps atthe cooling tower, the makeup water pumps to be located in the existing Unit 3 intake structure, HVAC for the cooling tower pumphouse, and cooling tower lighting would betakenfrom buses 34Aand 

### B in the existing Unit 3 pump structure. Ten new breakers would be required on buses 34A and B presently feeding the existing circulating water pumps. The breakers would feed the six new 3,500 horsepower circulating water pumps located

### inthe cooling tower pumphouse, thetwo new 750 horsepower makeup pumps which would be located in the existing circulating and service water pumphouse, anda newdouble-ended 480-Vloadcenter would be locatedinthe cooling tower pumphouse. The addition 

### of the breakersto bus 

### 348 would impair access to the switchgear room. It has been assumedthat buses 34A and

## B have adequate capacity to power the increased load. Because air blast breakers are 

### no longer manufactured, vacuum breakers would be used instead. A 2,800-foot ductline would be required for power cables running from the existing intake structure to the cooling tower. The ductline would follow the same route as the proposed new cooling.tower circulating water inlet and discharge lines.
A detailed electrical design was not performed and the information developed 

### for this study isconsidered preliminary and only conceptual in nature. Existing electrical loads and location of utilities could have a significant impact on the conceptual design.

PART I 

### 3-10 01516.WP5

### Millstone Units I;2, and 3 

## I

I 

### 3.2.1.3 Impact

### on Unit 

### Performance The 

### natural-draft cooling tower would result in 

### added power demand for operation of the 

### higher horsepower circulating water pumps and added cooling tower makeupwater pumps. Also, the 

### average circulating water temperature would be 

### higher 

### in the closed-loop cooling tower system resulting in higher average turbine back pressure and reduced turbine performance, particularly during the summermonths. The 

### existing circulating 

### water pumps 

### are 1,500 

### horsepower pumps which draw 

### a total of 

# I 

# I
i

El 

### 6,700 kW of

### electricenergy. Theclosed-loop circulating water systemwould require six 

### new circulating water pumps, each rated 

### at 3,300 

### horsepower, and 

### two makeup water pumps, eachrated at750 

### horsepower. Normally, 

### all six 

### circulating waterpumps and one

### ofthetwo makeup 

### water pumps would operate continuously. This 

### would result in a net increase in pumping energy consumption of 8,600 

### kW. The annual averagenet loss

### to

### Unit 3

### performance resulting fromthe

### higher circulating water temperatures in the 

### closed-loop system and the 

### accompanying higher turbine back pressure would be 18,500

### kW. These losses

### would occur primarily during the warm weather months of 

### May through September. This estimated performance penalty was based on the unit operating 

### on the cooling 

### tower 

### IOU percent 

### of the 

### time. Operation of the 

### full-size cooling tower only during themonths of 

### April and May

### when flounder larval activity’isgreatestwould result in reductions tounit performanceof 74,900

### kW in April and May. Switching plant operation 

### from cooling tower 

### to once-through and back to cooling tower would likely require an

### outage. Theperformance penalty associated withthis outagewas 

### not included in the estimated cost. 

### 3.2.2 TWO-THIRDS 

### SIZE 

### COOLING TOWER 

### This 

### alternative 

### is similar tothe

### full-size cooling tower exceptthat 

### four of 

### the

### six condenser paths would be converted 

### to 

### a closed-loop system integrated with 

### the natural-draftcooling tower, and theremaining two 

### condenser 

### paths would remain once-through. The 

### objective of 

### this alternative 

### is to

### provide a reductiontostation intakefiow from Niantic Bay, ata reduced capital cost and reduced performance penalty, 

### ascompared tothe full-size cooling tower. The Y3-size cooling tower would 

### reduce Unit 3 

### withdrawal 

### rate from Niantic Bay 

### from 9 12,000 

### gpm (2,030 

### cfs) 

### to 304,000 

### gprn 1677 

### cfs) plus 27,000 

### gpm I600 

### cfsf cooling 

### tower makeup. This 

### would result in 

### a net reduction in total station withdrawal from Niantic Bay 

### from 4,343 

### to 3,050 

### cfs. This would 

### be a 30 

### percent reduction.

01516.WP5 

### 3-11 PART ICooling Water SystemAlternatives to Reduce Larval Entrainment The proposed cooling tower location and circulating water pipe routing for the%-size system would be similar to that proposed for the full-size system and is shown in 

### Figure-3-2. The four condenser paths requiring conversion to closed-loop would be changed to a two-path type flow, using existing condenser valving and waterbox cross connections, In this case, aswith the full-size system, circulating water would enter and exit thecondenser onthe west side. Valves would be required at the manifolded junction to allow operation of the system with K cooling derived from the cooling tower or fully once-through. The two full-size (27,000 gpm) makeup water pumpswould be installed

### in thecirculating water pump bays 

### in the existing Unit 3 pump structure. 

### 3.2.2.1 Two-Thirds Size 

### Natural-Draft Cooling 

### Tower
A natural-draft cooling towersizedto reject 2/3 of the Unit 

### 3 heat loadwould beapproximately 400 feet indiameter atthe base andapproximately460 feet high. Specific design parameters for the %-size cooling tower are as follows: Circulating Water Flow Cooling Range Approach Temperature Wet Bulb Temperature Dry Bulb Temperature Evaporation Rate Drift Rate Concentration Factor 422,000 gpm 

### 25OF 14OF 77OF 89OF 2.1

### % 0.002% 1.5 The drift rate for the%-size tower would be anticipated to be about 2/3 of that resulting from thefull-sizetower. (Refertothe discussion of salt drift in Section 3.2.1.1 .) Requiredmakeup flow to the %-size cooling tower to maintain 

### a concentration factor in the closed-loop circulating water system at

### -1.5

### or lesswould be 

### 27,000 gpm (60cis), Makeupwater pumps would be rated at 27,000 gpm at 55-foot head. Horsepower requirements for the makeup pump would be 

### 480 horsepower. Twofull-size pumpswould be required. A 36-inch diameter makeup water line would be required. Blowdownwould be discharged from the cooling tower basin at an overflow weir structure locatedon the cooling towerdischarge flume. The discharged blowdownwould bedischarged bygravity tothe quarry by a 48-inch line buried 

### in a cut and cover trench. Blowdown piping would be routed tothe existing Unit 

### 3 discharge flume 

### atthe quarry. Blowdownflow would range from 18,000 to 27,000 gpm.

PART 

### I 3-1

### 2 01516.WP51 I! ri 

## --._- -IJ._c .. ..-

## ___



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### E

Millstone Units 1;.2, and

### 3 

### 3.2.2.2 Closed-Loop Circulating Water System The closed-loop circulating water system for the %-size cooling tower would be similar in design and layout tothat proposed for the full-size cooling tower. The circulating water pump station would be located at the cooling tower and would contain four %-size pumps, each rated at 105,000 gpm for a total circulating water flow rate of 420,000 gpm (936cfs). These four circulating water pumps would discharge to a single 12-foot diameter pipe. Both supply and return circulating water lines would be routedtothe north and tothe west Df Unit 3 in a common cut and cover trench as shown on Figure 

### 3-2.Each circulating water pump would have a motor-operated discharge valve. Existing 84-inch lines and valves at the condenser would be utilized by the new closed-loop system. Two 12-foot x '-/-foottwo-pipe manifolds would be required on the west side of the condenser to make the connection betweenthe new 1 2-foot diameter coolingtower supply, return lines, andthe existing piping. The twonortherly condenser waterboxes would beconvertedtothe closed-loop system. The twomanifolded 84-inch inlet linesfrom the cooling tower would have motor-operated valves installed. Thesevalves, in conjunctionwiththeexisting pumpdischargevalvesand condenser valves, would allow operation of the systemeither onthe cooling toweror once-through. The southerly waterbox would remain once-through. The system head losses for the %-size circulating water system would be essentially the same as that for the full-size system. The four circulating water pumps would be rated for 105,000 gpm at 100-foot total dynamic head. Pump motors rated at 3,300 horsepower would be required. Eight new breakers would be required on buses 34A and B feeding the existing circulating water pumps. The breakers would feed the four new 

### 3,500 horsepower circulating water pumpslocatedinthecoolingtowerpumphouse, thetwonew 

### 600 horsepower makeuppumps which would be located in the existing circulating and service water pumphouse, and a new double-ended 480-V load center located in the cooling tower pumphouse. The addition of breakersto bus 34Bwould impair accesstothe switchgear room. It also was assumed that buses 34A and 

### B have adequate capacity to provide power for the increased load. When obtaining estimating prices for new 4,160-V air circuit breakers and switchgear to match existing, GE stated that they no longer manufacture such equipment and they proposed vacuum breakers instead. A 2,800-foot ductline would be required for power cables running from the existing intake structure tothe cooling tower. The ductline would follow the same route asthe new cooling tower circulating water inlet and discharge lines.

01516.WP5 3-15 PART ICooling Water System Alternatives to Reduce Larval Entrainment 3.2.2.3 

### Impact on Unit Performance Four 3,300-horsepower pumps would also be required for closed-loop circulating water flow. These pumps would operate continuously ifthe cooling tower were operating. Inadditionto the higher horsepower circulating water pumps, two480-horsepower cooling tower makeup pumps would also be required. These pump changes would result in a net power increase for pumping of 5,700 kW. The annual average net 

### loss to Unit 

### 3 performance resulting from operation of 73 

### of the circulating water system closed-loop would be 12,300 kW. Operation of the %-size cooling tower only during the months 

### of April and 

### May during highest flounder larval activity would result in reduction in unit performance of 9,900 kW in April and May. Switching plant operation from cooling tower to once-through and back to cooling tower would likely require anoutage. The performance penalty associatedwiththis outage was not included in the estimated cost. 3.2.3 GEOTECHN ICAL CONS

### ID ERATlONS The topography 

### in the proposed cooling tower area is characterized by a wooded easterly sloping ground surface with elevations ranging between 15 and 

### 25 feet. No geotechnical explorations have been performed in the vicinity of the proposed cooling tower area to characterize the subsurface in that area. Some rock exposures are noted near the proposed cooling tower structure location on the 

### U.S. Geological Survey map, suggesting the top of rock surface may be near the ground surface. The overburden in that area is considered to be thin (1 0 feet 

### or less) glacial deposits of outwash and till. The ground surface in the area of the proposed cooling tower discharge and inlet lines is largelyfiat duetomodifications byconstruction activities and generally rangesfrom elevation 24 feet in the plant area to about elevation 

### 30 feet north 

### of the 

### main plant. The proposed locations of these structures are in areas where subsurface data are absent, except where boring was completed in support of the Temporary Radwaste Facility and interim Storage Facility for the SteamGenerator Replacement Project. These borings suggestthattop of rock elevation is variable, ranging from 15 to 

### 24 feet above mean sea level 

### in that area. A few feet of fill materia!wasfound atthesurface and denser glacialtill overlies the rockwhich 

### was described as granite gneiss. Since the overburden is presumed to be thin in the cooling tower area and the foundation grade may consist 

### of both rock and soil, it would be recommended that the overburden PART I 

### 3-16 01516.WP5 

## 1

a

i pMillstone Units 1; .2, and 3 materials be removed and the structure be founded entirely on bedrock to limit differential settlements. The average maximum bearing capacity of the rock based upon Unit 

### 3 field investigations is 200 ksf. The soil overburden's bearing capacity is considerably less and more variable. Thus, the overburden properties may not be sufficient to limit differential settlements for a structure of this type. The proposed conduits for the discharge and inlet lines would be constructed through a cut and cover procedure. It was estimated that 50to 60 percent of the excavation would be in rock; therefore, conduit construction would require controlled blasting methods to limit vibrations near existing structures. Some local rock support, such as rock bolts, may be necessary depending on excavation height and rock geometry. Soils would require 2H: 1 V slopes and bracing where slopes are not feasible. There could beconsiderable difficulty incoordinatingthe requiredactivities inexcavating areas adjacent to the condenserkurbine building. There are numerous buried utilities in this area, including some that are nuclear safety related. Numerous plant outages would be required. This has not been addressed in the study and could add significantly tothe cost estimate. 

### 3.3 OFFSHORE INTAKE
The offshore intake alternative would consist of extending the Unit 

### 3 intake approximately 1 mile south into Long Island Sound utilizing a submerged offshore intake, a rocktunnel, and a booster pump stationthat would be located in front of the existing Unit 3 intake structure. The proposed design is shown on 

### Figure 3-3. The objective of the offshore intake would be to placethe Unit 3 intakesouth into Long IslandSound pastthe confines of Niantic Bay such that significant numbers of Niantic Riverflounder larvae would not be entrained inthe Unit 3 intake. Those flounder larvae that would be entrained by the proposed new Unit 3 'offshore intake would come from the Long island Sound population as a whole.


### 3.3.1 DESIGN 

### BASIS The offshore intake system would be designed for a flow rate of 958,000 gpm (2134cfs) which is

### 5 percent greater than the present designflow of the Unit 

### 3 circulating water system (91 

### 2,000 gpm). The inletvelocity capstructure would be sized for aninlet velocity of 0.5 fps to minimizefish entrainment. The offshore conduit would be sized for a flowvelocity of 5 fps to minimize head losses. These criteria result in an offshore conduit I.D. (inside diameter) of 24 feet. The head 

### loss in the offshore intake system, assuming biofouling inthe tunnel and risers, would beapproximately 5 feet. The onshore booster pump facility would be designed

PART I 

### 3-1 

### 7 01516.WP5c



### Cooling WaterSystemAlternatives to Reduce Larval 

### Entrainment to provide pumping headto compensate for head losses inthe offshore intake. The booster pumps would be sized to pump a minimum of 5 percent excess flow into a newforebay that would lead to the existing Unit 3 intake. An excess flow would be provided to prevent surging between the twoin-line pumping systems. The forebay walls would be designed to spill the excess flow into Niantic Bay. Biofouling of the offshore intake, shafts, and tunnel inthe form of mussels and other marine organisms could become severe and difficult to control. A chlorination system which introduces chlorine atthe inlet and possibly at multiple locations along the tunnel would be required. Continuous chlorination during the fouling season may be required to control biofouling of thetunnel, shafts and offshore inlet. This chlorination would 

### kill flounder larvae. A dechlorination system would also be requiredfor the circulating water discharge. The cost of these systems was not addressed.


### 3.3.2 

### GEOTECHNICAL CONS

### IDERATlONS In the absence of borings along the proposed tunnel alignment and offshore intake, the geology was inferred from the nearshore boring, seismic refractionsurveys, and bathymetric surveys. The seafloor bottom along the proposed intake generally slopes seaward from the coast to about -40 feet at the proposed offshore intake. According to seismic refraction surveys, which cover approximately 4,000 feet of the initial proposed 5,000-foot tunnel, the top of rock surface along the alignment is irregular with top 

### of rock elevations ranging from -40 to -120 feet (FSAR Appendix 

### 2.5 K). 

### Thus the overburden along the alignment is expected to be between 0 and 80 feet thick.

PART I 

### 3-1 8 01516.WP5

-w

### 'I '

4 8

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# ..

I 

## I I 

## I I 0 U rn ,o mCooling Water System Alternatives to Reduce Larval Entrainment The cutand cover conduit approachwould begiven further evaluation toinclude geotechnical investigations of sea floor subsurface conditions along the proposed route prior to any final design. 

### 3.3.2.2 

### SubsurfaceTunnel The subsurfacetunnel scheme would require a vertical shaft nearthe Unit 3 intake structure, sunktoa depth of approximately 

### 300 feet below low meansea-level. The shaft must besunk 30 to50 feet deeper thanthe bottom of the tunnel to provide space for loading and storage of muck. A circular tunnel approximately 

### 270 to 250 feet below low mean sea-level 

### (minimum rock cover of 125 to 

### 150 feet), and 26.5 feet in drilled diameter (24feet inside lined diameter) would be initiated from the shaft 

### and excavated entirely in rock. The tunnel would be sloped downfromthe offshore intake structure 1 percenttowardsthe pumphouse at a descending grade to assure adequate flow and minimize ponding during scheduled shutdown. The offshore intake shaft could employ either a single or multiple "dry tap" construction scheme to intersect the tunnel. The dry tap scheme would use a circular steel caissongrouted in-place onthesea floor bottom. Water would be pumpedout of the caisson, and the shaft sinking operation initiated. Similar operations have been performed at the Oswego Steam Plant and at the Seabrook Nuclear Power Plant. The major geotechnical constraints for the tunnel scheme were determined to be: 1. Control of water seepage into the tunnel during construction. (exploratory boring in the rock may indicate that this may not be a concern). 

### 2. High costs of offshore shaft construction. 

### 3. Development of access shaft for muck transfer to the surface and a subsurface lay down area for equipment. At the surface, a temporary hoist system would be necessary to 

### lift muckfrom the shaft and lower excavation equipment. 4. Muck transfer facilities from the access shaft (barge and/or conveyor) would be necessary, as well'as a laydownarea atthesurface for underground equipment, ventilation, etc. The criteria for 

### 125 to 

### 150 feet of depth was based primarily upon estimated rock permeability, rock structure, and manageability of water inflows during construction. Based upon the above assumptions, overall tunnel seepage rates could be expected to range from less than 300 gpm to 3,000 gpm. Groundwater inflows of several hundred gpm in a short tunnel sectioncould adversely impacttunnel advance rates, even when ground support is not affected. 

### The tunnel advance rate problems are related to inefficient muck removal and


### PART I 

### 3-22 01516.WP5 

## -- 

# -

# c) Millstone Units I,. 2, and 3 production of extra fines. The extra fines would make cleanup slow (often by hand) and lengthen the drill and blast cycle. The water would also make support installation more difficult. The impact of high water conditions on grouting usage would be much higher, resulting in longer standby time, and more difficult overall machine maintenance/operation (electric drill jumbos, scaling, rock bolt and liner installation). During shaft excavation, water inflows could be expected atthe rock/soiI interface and from open joints in weathered rock below the interface. Therefore, pre-grouting would probably 

### be necessarytoreduce inflow rates atthe interfaceand in areas of high permeability. Ground freezing was not expected to be necessary and was not considered in the costs. Both drill and blast and tunnel boring machine (TBM) excavation methods were evaluated. Although the TBMadvancement rates are faster, this method would require a TBM erection chamber at both the head andtail shaft and tunnel intersections. Additionally, drill and blast would be more versatile and less risky in excavations of poor or variable ground and potentially high water inflows. This method would be recommended until a more detailed analysis 

### of other factors including equipment capital costs, labor costs and availability, machine delivery lead times, site considerations, geological considerations, and geometry/space constraints was performed. Based on available rockelevationdata, the proposedtunnel elevationatthe nearshore access shaft 

### would be 270 feet. The tunnel would slope upward at 

### a 1 percent grade towards the offshore intake structure to elevation 

### 220 feet. Preliminary layout of the offshore tunnel scheme indicates that the long axis of the tunnel would parallel the regional geological structure. Thusthe formation of unstable wedges as the tunnel face advances, prior toliner installation, would be likely. To prevent eccentric loading of the final tunnel liner due to unstable rock wedges andtoprovide for worker safety, temporary ground support would be necessary. As a preliminary estimate, patterned rock bolting may be necessary along most of the tunnel!s length. The rock bolts would be relatively light 

### in size (No. 8)and would be used primarily abovethetunnel springline 

### (60 percent utilization). Additional rock bolts would be used as necessary, as dictated by field conditions, below the springline. Because of potential environmental problems and uncertain geological conditions associated with the cut and cover offshore

### twin tube tunnel, the subsurface rocktunnel alternative was selectedtodevelop preliminarycostand schedule estimatesfortheoffshore intakealternative. The proposed tunnel design is shown on Figure 

### 3-3.

01516.WP5 

### 3-23 PART I

### Cooling WaterSystemAlternatives to Reduce Lawal 

### Entrainment 

### 3.3.3 OFFSHORE 

### INLET For preliminary design, a single riser shaft and velocity cap would be proposed. The large velocity cap could be constructed and placed in sections. An alternate approach would beto use multiple smaller riser shafts each having a smaller velocity cap. This single large riser could have cost advantages over multiple smaller shafts. A detailed evaluation of cost and construction issues would be required prior to detailed design. The offshore inlet would consist of a hexagonalvelocity cap structure supported on the sea floor by a tremie concrete matcentered over the vertical inlet shaft as shown on Figure 

### 3-3. The inlet would be 95 feet wide from point to point. The hexagon and the inlet would be 15 feet high beginning ata sill located 

### 3 feet offthe sea floor to minimize entrainment of sand and silt. The inlet entrances would be protected by bar racks. The rack spacing would be 1 foot O.C. (oncenter). These bar racks would protect the inlet from the coarsest forms 

### of debris. Inlet approach velocity would be 0.5 fps. rn 

### i;

The offshore intake would extend up 19.5 feet from the sea floor in 30-feet deep water and would create a hazard to navigation. The proper warning buoy would have to be provided with the design. 

### 3.3.4 BOOSTER PUMP STATION The 24-foot I.D. concrete-lined inlet tunnel including riser shafts on either end would be 5,400 feet 

### in length. It is anticipated that a tunnel would become significantly fouled with mussels and barnacles, causing significant hydraulic resistance. Head losseswere estimated at 5.0 feet. The existing circulating water pumps, based on the model test report 

### (31,have very little margin for degraded suction conditions. For this reason, it was considered necessarytoincludea booster pumpstation atthe onshore end oftheoffshore intake system. The booster pump station would require four low head, high flow pumps each rated at 240,000 gpm at 7.0 feet total dynamic head. Each pump would require 

### 525 horsepower. The total pumping energy requirement for the booster pump station would be 2,100 horsepower (1,600 kW). The pumps would be vertical wet pit type. Each would be located in its own pump bay. The pump bays would be 24 feet wide by52feet long with an c 

# -

invert elevation of 28 feet. The pumpswere sized todrawwater from anelevation of 

### -7 feet. The overall plan dimensions of the pump structure would be 106 feet wide by 54 feet long. 

### -



### __ The pump structure would be constructed of reinforced concrete, and would include a protective buildingwhichwouldenclosethepumps, motors, electricalequipment and controls. The pump structure would bejoined upstream by a transition structure constructed over the PART I 3-24 01518.WP5

### Millstone Units f,.2, and 

### 3 24-foot diameter riser shaft from the tunnel. This transition structure would contain a submerged weir tospread inflowingwater evenly tothe four pump bays. The pumpstructure and transition structure are shown on Figure 

### 3-3. The transition structure connecting thevertical tunnel riser shaft tothe booster pump station would also serve 

### as a surge chamber. The chamber would not be covered and thetop of the walls and would serve as an emergency spillway 

### in the event of surge. The existing Unit 3 intake structure would be joined tothe offshore intake system by sheet pile walls forming a forebay between the two structures and isolating the Unit 3 intake from Niantic Bay. A section of thetop of these sheet pile walls would be designed tofunction as overflow weirs to discharge the excess flow pumped bythe booster pumps into Niantic Bay. A 12foot x 30 foot gate would be required in each of the forebay walls designed to pass '/z of the circulating water flow in the event of failure of the offshore intake system. A separate Category 1 flow passage (not shown) would be provided for the service water pumps. The system would consist of flow passages constructed in the forebay walls with flow controlled by automatic motor-operated gates or valves. Separate openings with collapsible panels would also be required as a backup. Becausethe service water system is nuclear safety related, the design would be nuclear safety-related Category I and would be subjecttoNuclear Regulatory Commission reviewand approval. This area was notaddressed in detail. Four additional 4,160 V breakers would 

### be required for the four new pumps. The new booster pumps would be located in a new intake structure that would be located in front of the existing circulating and service water pumphouse. It was assumedthat buses 34A and 

### B have adequate capacity to provide power for the four new pump motors. When obtaining estimating prices for new 4,160 V air circuit breakers and switchgear, GE statedthat they no longer manufacture such equipment and they proposed vacuum breakers instead with a transition section to the existing switchgear. Finally, an 800-foot ductline would be required. The ductline would follow the same route as the ductline tothe existing circulating service water pumphouse. A detailed electrical design was not performed andthe information developed for this study is considered preliminary and only conceptual in nature. Existing electrical loads and location of utilities could have a significant impact on the

01516.WP5 

### 3-25 PART ICooling Water System Alternatives to Reduce Larval Entrainment 

### 3.3.5 OFFSHORE INTAKE 

### EXPERIENCE AT SEABROOK NUCLEAR 

### POWER STATION Two deep bedrock tunnels, extending into the Atlantic Ocean to provide cooling-water requirements, were constructedfor the Seabrook Nuclear Power Stationlocated in Seabrook, New Hampshire. These tunnels are similar in design to

### the rock tunnel alternative proposed for Unit 

### 3. Both an intake and a separate discharge 

### tunnel were constructed, each over 3 miles 

### in length (1 7,156-foot intake, 16,500-foot discharge) 

## (4). The design flow rate for the Seabrooktunnels is850,000 gpm at a flow velocity of 

### 6 fps. One of the primary reasons for choosing the offshore intake and discharge with deep rock tunnels at Seabrook was to minimize any damage tothe coastal environment 

### (4). Geological conditions atSeabrook necessitateddeep rocktunnels. Vertical shafts were used on bothends of thetunnels to connectthe offshore water ports and the plant cooling-water systems. At land's end, the tunnels are 

### 260 feet below sea level and 180feet below sea levelatthe seaward ends. The tunnel shafts are concrete lined. The bore diameter is 22 feet and the liner thickness is 1.5 feet with a tunnel I.D. of 19feet. Rock bolts were used as necessary along the top 

### of eachtunnei. The Seabrook intake tunnel terminates onthe seaward end withthree 9-foot 5-inch diameter shafts located approximately 7,000 feet off the Hampton Beach shoreline at a water depth of 60 feet. Mounted on each shaft at the sea floor are 

### 30.5 feet 

### in diameter velocity cap structures of similar designtothat proposed for Unit 

### 3. The velocity caps are clad over their entire exterior surfaces 

### with copper nickel sheeting to minimize marine growth. On the shoreward end the vertical shaft terminates with a surge chamber. The circulating water pump station is located 

### in an excavated chamber adjacent tothe surge chamber, The Seabrook discharge tunnel connects to the ocean by means 

### of eleven 4-fOOt 

### 1 1-inch diameter vertical shafts located approximately 

### 5,000 feet off the Seabrook Beachshoreline. The Seabrooktunnel constructionwasaccomplished bymeansoftwotunnel boring machines operating concurrently. Offshore construction was done using a jack-up barge. Offshore vertical shafts were drilled and prefabricatedsteelshaft liners installedfrom thejack up barge 

### E). Work began 

### in the summer 

### of 1978. Tunnel and vertical shaft excavation was completed in the spring of 1981. Concrete lining of the tunnels was completed by the end of 1982. The total project cost for the Seabrook tunnel was approximately $125 million.

PART I 

### 3-26 01516.WP5Millstone Units 1; 

### 2, and 3 

### 3.4 

### FINE-MESH 

## SCREENS
Mesh sizes smaller than 9.5 mm are considered to be "fine mesh" and may be effective as a barrier to the passage of fish eggs and larvae with mesh sizes in the range of 0.5 to 1

### .O mm. Various types of traveling screens, such as through-flow, dual-flow, center-flow, and drum screens, can be fitted with fine-mesh screens. Traveling screens are normally cleaned automatically by high and low pressure sprays. Wedgewire screens are also sometimes considered to be a type of fine-mesh screen and are discussed 

### in Section 3.5.
3.4.1 ENGINEERING CONSIDERATIONS Several stations have installed fine-meshtraveling water screensystems, although conditions at MNPS are generally significantly different and more severe than at these stations. The screen systems in use include:

0

0

0

0

0

0

0 Big Bend Station, Tampa Electric Company 

## - continuously traveling dual-flow screens with 0.5 millimeter screen mesh and specially designed organism troughs, buckets, and spray washes. The design flow for Units 

### 3 and 4 is about 242,000 gallons per minute each (salt water). Brayton Point Unit 4, New England Power Company 

## - 1

### .Omillimeter screen mesh, 260,000 gallons per minute with angled screens (salt water, but with much lower levels of totalsuspended solids and debris). Fine-mesh screens are no longer in service at Brayton Point. Prairie Island Nuclear Units 1 and 2, Northern States Power Company 

## - 0.5 millimeterscreenmesh, 

### 630,000 gallons per minute (MississippiRiver, with no biofouling, or salt marsh debris problems). Barney Davis Station, Central Power and Light Company, Corpus Christi, Texas 

# - 1

### .O millimeter screen mesh, 340,000 gallons per minute with heavy sea grass loading (salt water). Somerset Station, NewYork State Electric and Gas Company 

## - 1

### .O millimeter screen mesh, 195,000 gallons per minute with limited debris (Lake Ontario). Brunswick Nuclear Station, Carolina Power Company 

## - 1

### .O m.llimeter screen mesh, 

### 990,000 gallons per minute with additional barrier screens on intake canal (salt water). Danskammer Station 

## - 0.5 millimeter screen meshtested onthe Hudson River

01516.WP5 

### 3-27 PART Ic.”
. --. Cooling Water System Alternatives to Reduce Lari/al Entrainment 

### 3.4.2 ADVANTAGESAND DISADVANTAGESOF FINE-MESH TRAVELING WATER SCREENS
A fine-mesh traveling water screen intake system minimizes entrainment but increases impingement. In addition, the incorporation of rubber seals between baskets and between baskets and frame would minimize the passage of organisms around the screen. The disadvantages of the fine-mesh traveling water screen concept include:

e Effective sealing of spaces between screen baskets, screen baskets and structure, and structure and bay walls is difficult.

e Increased impingement of organisms and debris.

e Screens are subject to icing conditions including frazil ice and floe ice.

e Mesh size of 1 to 2 MM may be insufficient to block stage 3 winter flounder larvae. Additional screen wash capability may be required, and current problems with this system could be exacerbated. The growth of barnacles and mussels and the buildup of silt can clog the spray wash system. Chlorination of the screen’ wash system could help to control biofouling, butwould defeatthe purpose ofthefine-mesh screenconcept becausethechlorine could kill larvae. It could also result in existing NPDES permit violation. Periodic inspections would be necessarytomaintainthescreens, andthe use of nontoxic coatings on some screen components may reduce marine growth. Continuously operating fine-mesh screens would accumulate greater quantities of trash than coarse-meshscreens. Debris handlingsystemswould includea largecapacity sluicing system similar tothe existing system. 3.4.3 ALTERNATIVE FINE-MESH INTAKE DESIGN CONCEPTS Alternative fine-mesh intake design concepts include replacing the existing through-flow vertical traveling screens with continuously operating fine-mesh screens and constructing a new screening facility 

### in front of the existing circulating water intake incorporating new, through-flow, dual-flow, drum, or angled fine-mesh screens with a low approach velocity of 0.5 fps. Dual-flow, centerflow, and drum screens are primarily of English/European design, although some are currently in service in the United States. The angled screen is a special application of the through-flow screens where the screen units are placed at an angle tothe incoming flow todivert fish to a fish bypass system. The Electric Power Research Institute (EPRI) reviewed the performance of these screen configurations 

### (7).Facilities were visited at several utilities throughout the United States.


### PART 1 

### 3-28 01516.WP5

### Millstone Units 1; 

### .2, 

### and 3 3.4.3.1 Through-Flow Fine-Mesh Screens The existingthrough-flow traveling screenscannot be replacedbycontinuously operating finemeshscreens. The original screens at Unit 

### 3 had a 3/16-inch 

### (5mm) opening. The clogging potential of the 3/16-inch opening resulted in numerous plant outages and screen failures. The screen openings were increased to 

### YEinch 

### (9.5 mm) 

### in 1991, which has helped to eliminate the clogging potential experienced previously. The higher clogging rate of the finemesh would require that the screens be capable of operating continuously at speeds up to 50 feet or greater per minute. Also, to reduce the loading of large debris on the fine-mesh screens, the existing bar racks and mechanical rake system may require replacement with traveling trash rakes. Becausethe effective performance of fine-mesh screens issensitive to flow velocities, flow distributors and more frequent maintenance dredging may also be required to maintain approach flow velocities of 

### 0.5 fps or less tothe fine-mesh screens. 

### 3.4.3.2 Dual-FlowEenter-Flow Fine-Mesh Screens Thevertical dual-flow travelingscreen issimilar 

### in mechanismtothethrough-flow design, but the screen would be turned 90 degrees so that its faces would be parallel to the incoming water flow. Water would enter both the ascending and the descending screen faces, then flow out between the twofaces. The primary advantage of this screen configuration isthe elimination of debris carryover. This screen configuration has a possible advantage over the through-flow screen in terms of fish protection only when applied 

### in the so-called "no-well" design. In this case, the screens hang in the water from a platform and would be coupled directly to the circulating water pump, eliminating the pump bay which can form a fish trap 

### Q),(B). Because of the open platform structure supported on piles, the no-well intake configuration 

### is only suitable for warm climates where freezing is not a concern. This type of structure, therefore, 

### is not recommended for 

### MNPS. The dual-flow fine-mesh screen configuration also has beenshown

### to produce low survival rates for fish larvae, which isthe principal problemat the

### MNPS intakes. The longer impingementtime for organisms impinged on the descendingfence of thescreenmay result 

### in higher mortality rates. Forthese reasons, the dual-flow fine-mesh screen configuration was eliminated from further consideration. The centerflow screen configuration 

### isa European design and issimilar in configuration tothe dual-flow screens except the flow path is reversed. Flow would enter the centerflow screen at a key hole and pass intothe screen between the screen faces and out through the screen faces. The flow velocity entering the key hole betweenthe screen faces of the centerflow screen is usually high. whichisadisadvantagefrom afish protection standpoint 

### (5). Because of the disadvantages interms of potentialsurvival of entrained.and impinged flounder larvae, the centerflow fine-mesh screen configuration was eliminated from further consideration.

01516.WP5 

### 3-29 PART ICooling Water System Alternatives to Reduce Larval Entrainment 3.4.3.3 Angled Screens Angled screens are a special application of through-flow screens where the screen faces would be arranged atan angle of approximately 

### 25 degreestothe incoming flow. The normal through-flow screen arrangement, as discussed earlier in this section, would placethe screen faces normal or 

### 90 degrees to the incoming flow. The objective of the angled screen arrangement would be to divert fish to a fish bypass system without impinging them on the screens. Fishwould not be liftedout of thewater but would be diverted backtothe receiving water by screw-type centrifugal fish pumps. The angled screens, as proposed for MNPS, would incorporate fine-mesh, a fish and larval lifting bucket, and a standard sluicing system for handling impinged fish and larvae in addition to 

### the fish bypass system. A conceptual layout for an angled fine-mesh screen structure for Unit 

### 3 is shown on Figure 3-4. Fine-mesh angled screen facilities were formally in place at New England Power’s Brayton Point Station on Mount Hope Bay (531, are currently operating at Niagara Mohawk Power Corporation’s Oswego Steam Station Unit 

### 6 on LakeOntario

# (a), and were tested atCentral Hudson Gas & Electric Corporation’s Danskammer Point Generating Station 

## (11) on the Hudson River. 3.4.3.4 Fine-Mesh Drum Screen Facility Another type of fine-mesh screen is the drum screen that is used in Europe. A preliminary design was developed using double-entry rotating drum screens to determine if they would offer a significant cost savings as compared tothe through-flow screens. Drum screens are of British design and are similar to a ferris wheel in construction. They operate with the screen mesh mounted along the circumference of the screen. In the double entry arrangement, the drum would be installed with itsaxis normal tothe incom-ingflow with the plane of the wheel vertical. The wheel would be mounted in an enclosed chamber with all moving parts including the axle mounts above normal high water level. The operating machinery would 

### be located on the deck of the screen structure. Unscreened water would enter the screen from channels on either side and would flow intothe screen at semicircular openings oneither side of thescreenchamber. The water would bescreened bypassing from within the screen out through the screen mesh mounted on the circumference of the drum. The screened water would pass into a chamber below the drum screen and then to the pumps. Fish baskets would be mounted on the outside of the screen and would function in the same manner as with the through-flow screens.

PART I 

### 3-30 01516.WP5

# 0 Millstone 

### Units 1; 2, and 

### 3 The nature of the overburden cannot be determined from the seismic velocity data. It was assumedthata dense basaltill of varyingthickness overliesthe bedrockand looser silty sands overlie the till. The type and quality of bedrock along the alignment was assumed to be similar to those mapped at the Unit 3 intake structure. The rock types are gneiss and granite with the fractures oriented north-south and dipping near vertical. A conservative range for hydraulic conductivity of a rock mass of this type was assumed to be between 1O4 to 1 0-6 cm/s. Both cut and cover and deep rock tunnel schemes were evaluated for conveyance of water from the offshore intake.


### 3.3.2.1 Cut 

### and Cover Offshore 

### Twin Tube 

### Tunnel The cutand cover scheme would involve the fabrication of two parallel pipes, approximately 12feet 

### I.D. each, that would be placed ina single commontrench. A 5,000-foot long trench would bedredged ata constant elevationfrom the intakestructure tothe offshore intake port. The trench would be excavated to a depth of approximately 15 feet 

### (3feet deeper than the tunnel heights), 26 feet wide tat the bottom), and coveredwitha protective gravel cover after the pipes were placed. Due tothethin nature of overburden in some areas, it was estimated that 10 to 15 percent of thetrench would require underwater blasting. Based upon current offshore data, it would be expected that nearly 90 percent of the trench would be dredged in relatively dense overburden. Major technical concerns 

### of such an operation would be: 1

# . Disturbance of potentially contaminated sediments during dredging operations and their disposal plus the disturbance of marine 

### life may pose a significant environmental concern. 

### 2. Limited available construction period (late spring to early fall). 

### 3. Impact of underwater blasting on marine life and project cost. 4. Numerous regulatory reviews and approvals would be required by both state and Federal agencies. Soil tests and surveys would be necessary to verify adequate thickness of the overburden, suitability for direct pipe support, and need for structural backfill. While a cut and cover tunnelwould appear lesschallengingfrom atechnical point ofviewthansubsurface tunneling, the environmental impact during construction must be weighed in considering this scheme.

,

01516.WP5 

### 3-2 1 PART I

# i

DMillstone Units I,’ 2, and 

### 3 Having fewer moving parts, and with many moving parts located out of the water, the drum screen may offer some reliability advantages over the through-flow traveling screen. Drum screens have been used extensively at large intake facilities throughout the world 

### (6) with service records comparable tothrough-flow screens. Six 10-meter diameter by4-meter width (32.8 feet by 13.1 feet) drum screen units would be requiredtoscreenthefull design flow tothe Unit 

### 3 intake. This preliminary sizing was based on sizing charts provided by Hawker Siddeley Bracket Ltd. of Britain for a fine-mesh application 

### (3 mm or less). These drum screens would require a structure approximately 255 feet wide by 50 feet long. Deckand channel inlet elevations would be the same as for the through-flow screendesign. Thescreenedwater collection chamberwould havetoextend about 10 feet deeper under the screen to a depth of about 

### -39 feet. The top of the rock is atabout 

### -40 feet 

### in the proposed area. The structure required for drum, screens would be similar in size although different in detail to that for the through-flow screen structure. Based on the preliminary design, the drum screen arrangement does not offer major cost advantages compared to the through-flow arrangement. Pilot-scale testing for at least 1 year would also be required to confirm the effectiveness ofthedrum screenin handling flounder larvaeand returningthemtoNiantic Bay alive. 3.4.4 REQUIRED TESTING Full-scale prototype testing would be required to determine impingement and entrainment rates andthe related mortality rates for the fine-mesh traveling screens. The debris removal capability of fine-mesh traveling screens would requiretesting to. determine if an increase in debris matting or “stapling” brought about by the fine-mesh can be removed adequately. In addition, extensive testing would be required to verify the ability of fine-mesh traveling screens to perform reliably in the silty and corrosive environment of MNPS. The effects of increasing the screen travel speed 

### to over 

### 50 feet per minute would also require further evaluation and testing. 3.4.5 FINE-MESH SCREEN 

### FACILITYFOR 

### UNIT 3 For the reasons noted above, replacing the existing %-inch opening screens with fine-mesh screens, is nota reliabletechnology for MNPS. Further, it is possiblefine-mesh screens might cause as much mortality by increased impingement as they saved in entrainment.

01516.WP5 

### 3-33 PART ICooling Water

### System Alternatives to Reduce 

### Larval Entrainment The preliminary design for fine-mesh screens, as shown on 

### Figure 34, would consist of constructing an entirely newthrough-flow screen structure for Unit 

### 3 

### infront of the existing screen structure, The existing intake structure would remain functional with the existing traveling screens serving as backup screens 

### in the event the fine-mesh screens become blocked. Bypass gates would be provided to direct flow around the fine-mesh screen structure. 

# .E Fine-mesh screens, applied to Unit 

### 3 for winter flounder larvae, would be designed to block the larvaefrom entering the circulating water system andtosafelytransport impinged larvae backto Niantic Bay. The stage 

### 3 larvae, which are most susceptibleto entrainment intothe 

### MNPS intakes, are from 4.5 to

### 7.5 mm in length. The existing seasonal heavy trash loading atthe MNPS intakes of eelgrass and kelpwould require a design screen approach velocity 

### of 0.5 fps for fine-mesh screens to prevent overloading of the screens during periods of heavy trash loading. The April and Maytime frame for greatest winter flounder entrainment is also a period of heavy eelgrass influx at the Unit 

### 3 intake. Full-scale prototype testing of a fine-mesh screen facility to confirm impingement and entrainment rates andthe related mortality rates for winter flounder larvae is required before committing tothistechnology. Also the reliability 

### of fine-mesh screen operation 

### inthe heavy detrital loading environment at MNPS would have to be confirmed during this prototype testing. Design parameters for the screen structure are as follows: Deck elevation Invert elevation Design flow Approach flow velocity tofine-mesh screen 

### 0.5 fps Screen 

### unit width

. 

### IO feet 14 feet 

### 6 inches 

### -28 feet 

### 0 inches 912,000 gpm 

### (2032cfs)

The deck elevation, invert elevation, and design flow would be the same as the existing intake. The 10-foot screen 

### unit 

### width would be selected becauseexperience has shownthat wider screenwidths tendtoresult 

### in less reliableoperation and more maintenance. Throughflow screen units are available 

### in widths up to 14 feet. The number of screen units required was 'determined by calculating the required 

### crosssectional area needed to achieve a 0.5 fps approach flow velocity 

### or less tothe traveling screen. A 20 percent unscreenable area was assumed to account for the screen boot area .- d

structural metalframe area betweenscreen mesh. Flow velocity calculations were made
PART I 

### 3-34 01516.WP5Millstone Units 

### I, 2, and 3 at mean low water (0.0 feet). This would result 

### in eighteen 10-foot-wide screen units as shown 

### in Figure 3-4. The screenstructure would be40 feet wide by 

### 276 feet long. Itwould include both upstream and downstream curtainwalls extending downtoa depth of 

### -5feet for ice, cold weather and floating debris protection. Bar racks would be provided to catch large debris that could damage the traveling screens.. The structure would include open sluice fish return and a separate trash removal system. Fish would be sluiced to the west side of Bay Point and returned to Niantic Bay. Equipment included with the structure, in addition to the 18 finemeshtraveling screens, would be: Mechanical trash rake Screenwash Systems including 

### 6 screenwash pumps, each rated at 5000 gpm at 

### 200 feet total dynamic head 

### * Gantry crane Fish return sluicing system Trash sluicing system HVACfor enclosure structure Control equipment Electric supply equipment 

### The fine-mesh screen structure would bejoined 

### tothe existing Unit 

### 3 intake by double sheet pile walls with tremie concrete placed between the sheet pile. Each wall would have a 12foot by30 foot bypass gate. These bypass gates would besizedto bypass ?4 of thetotal design flow tothe Unit 

### 3 intake. The bypass system would be provided in the event that some or all of the fine-mesh screen units become blocked or inoperable and for the safetyrelatedservice water system. The forebay, formed between the new fine-mesh screen structure and the existing Unit 

### 3 intake, would have a system of flow guide vanes to create uniform flow conditions entering the existing intake. Hydraulic model studies would be required to properly design the guide vane system. The guide vanes shown in Figure 

### 3-4 are conceptual and were usedtodevelop material quantity estimates.

01516.W5 

### 3-35 PART I

# 8
Cooling Water System Alternatives to Reduce Larval Entrainment 

### 3.4.6 GEOTECHNICAL CONSlDERATlONS The geology attheintake structurewas documented bythe 

### *'P'* series boring on land and the 

### "I" series boring offshore, seismic refractionand bathymetricsurveys, andgeological mapping during construction. The intake structure isfounded directly on bedrock

### which wasexcavated where necessary to approximately elevation -40 feet after construction of a temporary offshore cofferdam. Prior to excavation, the bedrock surface was overlain by a dense basal till of approximately 20 feet in thickness. Twenty to 30 feet of glacial deposits of a looser nature and beach sands were found to overlie the till. These deposits were replaced by structural backfill around the Unit 

### 3 intake structure. In the area offshore of the intake structure, boring conducted 

### 500 feet offshore indicate bedrock elevation is variable, ranging between 

### -20 and 

### -57 feet. Bedrock immediately offshore of the intake is likely at elevation -40 feet. Most borings indicate that bedrock is overlain byseveral feet of basal till although locally thicker deposits are possible. Overlying the till is a poorly graded, micaceous silty sand which forms the seafloor bottom. The seafloor bottom in the vicinity of the intake was modified during construction of that structure, as well as by dredging after construction. Immediatelyadjacent tothe intake, the seafloor bottom elevation is at about 

### -28 feet according to soundings taken in 1990 and slopes up seaward due todredging modifications to about -1

### 6 feet. 

# Q

Nofield permeabilitytestswere conductedinany ofthe offshore overburden materials. Based on field/laboratory boring log descriptions and grain size distribution curves performed on similar soils obtained from onshore boring at the intake structure, it was estimated that hydraulic conductivity isapproximately 1

### O4 cm/secfor the siltysands comprising theseafloor bottom. 

## 3.5 WEDGEWIRE SCREENS Wedgewire screens are passive and utilize 

### "V" or wedge-shaped cross-section wire, welded toa framing system toform a slotted screening element as shownonFigure 3-5a. Where a relatively high velocity ambient current cross-flow existstocarryorganisms around and away from the screen, cylindrical wedgewire screens can reduce impingement and entrainment. Ambient currents providing highvelocity cross-flow are also necessarytoprovide continuous flushing of debris. Fixed wedgewire cylindrical screens need an open screen minimum of 40 percent, which requires slots of 1 mm or larger. Reducing the screen slot size to0.5 to 1 

### .O mm, toachievethe most effective entrainment reduction, would reducetheopen areato about 20 percent. Thus, wedgewire screens are normally less effective at reducing



### PART I 

### 3-3 6 01 516.W5

# . I 1 L ! 

### i 

## L Welded at every intersection

### of vertical 

### rod and surface wire



# u
Figure 3-5a Wedgewire Screen Unit

01516.WP5 

### 3-37 PART ICooling Water System Alternatives to Reduce Larval Entrainment entrainmentthan impingement, and ineither casetheeffectivenessishighlydependent onthe presence of the proper high velocity ambient cross-flows. The J. H. Campbell Plant Unit 

### 3 on Lake Michigan has employed a wedgewire screen intake system since November 1979 

## (12). The Campbell Plant's Unit 

### 3 withdraws 

### 340,000 gallons per minute (less than 20 percent of MNPS' total station flow) from an offshore location (3,500 feetfrom shore 

### in 35 feet of water) through 

### 28 fixed %-inch (9.5-mm) screen units. Difficultiesarose 

### inthe design and construction phases, but operating experiencetodate has beensatisfactory andthere has beennosubstantial clogging, biofouling, or icedamage. Such operating experience might be expected because of the large screen slot size and because of the relatively low debris loading in Michigan compared tothe Niantic Bay near MNPS. Even so, the Campbell Plant hasanalternate intaketosupplement flow 

### in case of severe blockage of the cylindrical screens. At the Campbell Plant's Unit 

### 3 on Lake Michigan, the stainless steelscreens haveeliminated impingement of gizzard shad, smelt, yellow perch, alewife, and shiners and have required minimal maintenance. The screens are cleaned annually bywater jets to reduce biofouling (algae) and the plant was forced to 

### shut down once (spring 1984) due toanchor ice. Philadelphia Electric Company installed a wedgewire screen intake system in June 1990 at its Eddystone Station 

### Unit 1 on the Delaware River upstream of Salem 

### (13). The Delaware River at the Eddystone Station is a relatively fresh water regime, although it 

### is under some tidal influence and can be slightly brackish. The design flow for the combined Eddystone Units 1 and 2 is440,000 gallons per minute, again only 

### 23 percentoftheflow atMNPS. The .
screen slot width is also quite large, 

### '/4 inch (6.4 mm), which would provide no significant entrainment benefitsfor Unit 

### 3. Todate, thewedgewire screenintake system has performed acceptably. The Eddystone screens are backflushed by compressed air. 

### To date, the air backflushing has maintainedthe pressuredrop across the screens ata constantvalue slightly greater than the manufacturer's design pressure drop. However, it 

### is too early to evaluate problems with biofouling. More severe problems with biofouling and corrosion would be expected at MNPS because of the higher salinities and greater tidal influence 

### in Niantic Bay. Wedgewire screens are still developmental with respect to MNPS. The flow rate at MNPS 

### is much higher than at either Campbell or Eddystone, and neither of those installations usedthe small screen mesh sizes necessary to achieve entrainment benefits. The Campbell Plant installation is not estuarine and Eddystone is in an upstream, more fresh-water environment. Total suspended solid and sand loads at MNPS are higher than at the other two plants. Detritus, eelgrass, and kelp loads are also high: MNPS has had a history of screen blockage and collapse. During the years of operation, there was a significant amount of plant outage time attributed to screen problems. Improved traveling screens were installed in the Unit 3 PART I 3-38 01516.WP5Millstone Units 1,*2,and 

### 3 

## - intake in 1991 which alleviated some of these problems. Ambient flow velocities approach zero at slack tides and currents are variable with tide, so that the high velocity cross-flows necessary for screen flushing and biological efficacy are not always assured. Further, under any tidal conditions there is a question of whether the necessary high velocity ambient crossflows can exist 

### inthe presencenearly 1 million gpm plant withdrawal flows. Salinity ishigher in the seawater environment than 

### in previous applications. Biological fouling and detritus wrapping around the screens could be resistant to cleaning 

### by compressed air backflush. Thus, biofouling and detrital loading could present very serious operating impediments. On-sitetesting and hydraulic modelingwould be necessarytodeterminewhether andtowhat extent the necessary high-velocity cross-flow currents exist, in order to obtain adequate screen cleaning action, and todetermine whether: (1 ) the necessary low velocities could be obtained, given the operating difficulties and (2)adequate ambient high-velocity cross-flow currents exist (particularly at slack tide) to achieve any reduction 

### in entrainment and impingement of aquatic life. Biological and hydraulic researchwould, in general, be needed todemonstrate the viability and effectiveness of a wedgewire screen system for MNPS. Both pilot and full-scale testing at the site would be required to determine biological effectiveness, maintainability, effectsof siltand biofoulingdeposits, andmaterial compatibility of the wedgewire screens in the water environment at MNPS. Testing would require installation of a full-scale prototype wedgewire screen intake in front of one or more of the circulating water pumps and operating it for 1 year or longer. Biological considerations, engineering performance, and cost would have to be evaluated. No amount of testing, however, could adequately predict the severity of probable siltation problems with the complete system. Twoalternateintake arrangements utilizingwedgewirescreensweredevelopedfor application to Unit 3 including the staggered array and the bulkhead design. The first alternative design concept, calledthestaggered arrayconceptwould consist of six collector conduitsthatwould be buried 

### in the sea floor in the area in front of the existing Unit 

### 3 intake. The collector conduits would be equipped with nine 'wedgewire tee screen units which would extend up from the sea floor. These collector conduits would terminate at a common plenum structure that would be constructed directly 

### infront of theexisting Unit 

### 3 intake structure. The Unit 3 intake structure would remain intact and functional. The existing traveling screens would remain in place and would provide backup screening capability in the event the wedgewire screens become blocked. Bypass gates would be provided to bypass 

### Yi of the Unit 3 circulating water flow. An automatic, compressed air system would backflush each of the tee screen units, one at a time. A separate Category Iflow passage (not shown) would be

01516.W5 

### 3-39 PART Id Cooling Water System Alternatives to Reduce LarvalEntrainment providedfor theservice water pumps. Costestimateswere developedfor thestaggered array concept. The second alternative wedgewire screen arrangement would be a bulkhead design. In the bulkhead 

### design, thetee screen assemblies would be mounted around 

### a 13-sided bulkhead structure. Two of these bulkhead structures, each having 

### 26 teescreens, would be required to handle the full Unit 3 circulating water flow. Water from the bulkhead structures would be directedthrough buriedconduitstoa common plenumstructure thatwould be constructed directly in front of the existing Unit 

### 3 intake, similar tothe plenum for the staggered array design. The bulkhead design 

### with deck above water would allow lifting, cleaning, and replacement of tee screen assemblies without divers. The bulkhead structures would also have bar racksand curtain walls similar toconventional intakes which,would protect the tee screen units from damage caused by large floating debris. The bulkhead design would also incorporate a compressed 

### air system for backflushing the tee screen units. Each bulkhead structure would be joined to the plenum structure-bya bridge capahle of supporting small vehicles for maintenance. Costs were not developed for the bulkhead concept. The large bulkhead structures would be expected toadd significantly tothe cost of this alternative as compared tothe staggered array design. These proposed conceptual designs are shown on 

### Figure 3-5b. 3.5;1 

### STAGGERED ARRAY 

### DESIGN The staggered array wedgewire screen intake systemwould besizedtohandlethefull Unit 3 circulating water flow of 912,000 gpm. The screen slot width would be selectedtoexclude thestage 3winter flounder larvae, which are 4.5 to

### 7.5 mm in length. For preliminarydesign, a screen slot width of 1 

### mm was selected. The manufacturer's sizing criteria for these wedgewire screen units was based on a through-screen-flow velocity of 

### 0.5 fps. Using this sizing criteria, a total 

### of 54 tee screen units, 

### 85 inches 

### in diameter by approximately 24 feet long, would be required to pass the 91

### 2,000 gpm circulating water pump flow to 

### Unit 3. These 54 tee screen assemblies would be arranged on six 108-inch diameter conduits with 9 tee screen units per conduit that would be buried inthe sea floor in front of the existing 

### Unit 3 pump structure. The screen arrays on the conduits would be staggered as shown

### on Figure 3-5b. The staggering would prevent crowding of the screens and would promote better natural debris flushing characteristics. The six 108-inch conduits would terminate at a plenum structure that would be constructed directly in front of the existing pump structure. Each conduit would require a sluice gate or knife gate valve at the plenum for isolation. c



### 3-40 01516.WP5 

### PART I

-.
4Millstone Units 1;

### .2, and 

### 3 The plenum structure would be a 50-foot by 125-foot reinforced concrete structure that would provide a common flow chamber to distribute flow to the existing pump bays. The plenum structure would be equipped with gates to bypass the wedgewire screen system in the event it became blocked. A separate Category 

### I bypass (not shown) would be provided for the service water pumps. Becausethe service water system is nuclear safety related, the design would be nuclear safety-related Category

### I and would be subject toNuclear Regulatory Commission review and approval. This area was not addressed in detail. The wedgewire screen unitswould be periodically backflushedwitha compressedair scouring system. The compressed air or air burst scouring system would consist of an air compressor, a compressed air tank, a compressed air piping system capable of delivering a burst of compressedair toeach individual teescreenassembly, one atatime, air-actuatedvalves, and anautomatic control system. Backflushingwould be accomplished bydischarging the entire compressed air charge in the air tank to the screen assembly to be backflushed. The compressor would then rechargethe tank tothe required pressure and the process repeated for the next screen assembly to be cleaned. The 84-inch tee screen assemblies are normally supplied with 6-inch air pipe connections. The preliminary design would use 6-inch air pipe and connections. The air compressor and tank would be sized to backflush one tee screen assembly, one ata time, with a %-hour interval. The required pressure in the compressed air tank would be approximately 150 psi. This would require a compressor size of 40 horsepower. The compressor, compressedair tank, and control system would be located on the deck of the plenum as shown on Figure 3-5b. Biofouling of the 108-inchdiameter conduits connectingthe screenunitstothe plenum would be a potential problem and a chlorination injection system could be required. This was not addressed in detail. The screen units would be fabricated of copper nickel to take advantage of the biocidal properties of the copper tocontrol biofouling. The design presented and cost estimate developed would be for a full-size installation. This design concept could be used for one circulating water pump or any combination of the six pumps. 

### 3.5.2 ALTERNATIVE 

### BULKHEAD DESIGN An alternative design concept for wedgewire screens for Unit 

### 3 would be a bulkhead structure. The tidal ebb and flow and periodic high detrital environment of the intake provide a far less 

### than optimum environment for the wedgewire screens. If a significant number of 3-43 PART I 01516.WP5Cooling WaterSystem Alternatives to Reduce 

### Larval Entrainment the tee screen assemblies of the staggered array design were severely blocked by kelp or eelgrass, the air burst backflush system may not be capable of reestablishing flow. In such case, the wedgewire screensystem would havetobe bypassed and divers employedtoclear the blocked screen units. The bulkheaddesign would incorporate standard coarse-bar racks in front of the wedgewire screen units and a mechanicaltrash raking system to handle large debris. A mechanical trash rake and trash bin would be mounted on rails along the circumference of the structure for removing debris from the bar racks. This system would provide some protection against blockage by large debris. The bulkhead structure with deck above water would also allow eachtee screen unit to be liftedindividually from thewater for draining and maintenance without the use of divers.
A preliminary bulkhead wedgewire screen structure design is shown on 

### Figure 3-5b. Two 

### '/z size structures would be proposed, each sizedtohandle ?hof the Unit 

### 3 circulating water flow. The outline of the structures would be circular with a diameter of 160 feet. The structure would mount 

### 26 tee screen units that would be arranged in double screen assemblies. The doubleteescreenassemblies would be mounted onbulkheads forming a 13- sided structure as shown on 

### figure 

### 3-5b.Eachtee screen assembly would be mounted in a set of slots which project vertically upwardtothestructure deck. Track-mounted davits with hoists would be located on the deck and could lifteach screen assembly up tothe deck for maintenance through the slots provided. Outboard of the tee screen units, the structure would include a curtain wall for protection from floating debris. Two 12-foot diameter inlet conduits would draw water from a central sump in the bulkhead structure. These unit conduits would pass under the bulkhead structures andterminate at a plenum 

### infront of the existing Unit 3 intake, similar in design to that proposed for the staggered array concept. Each-inlet conduit would have a sluice gate or valve for isolation (notshown). Each bulkhead structure would be connectedtothe plenumstructure or the adjacentshore bya bridge which would allow truck accesstothe bulkhead structure deck for maintenance.

c * Each bulkheadwedgewire screeningstructure would haveitsownair burst backflushsystem, similar in design tothat proposed for the staggered array screening system. The bulkhead wedgewire screening system would be a full-size design using two K-size bulkhead structures. This design could also be sized for a single circulating water pump. 

### 3.5.3 GEOTECHNlCAL CONSIDERATIONS 

# - The geology atthe intake structure was documented bythe 

### "P"series boring on land andthe "I" series boring offshore, seismic refractionand bathymetricsurveys, andgeological mapping during construction. Theintake structure isfounded directly on bedrockwhichwasexcavated


### PART I 

### 3-44 01516.WP5

L-Millstone Units 1;2, and 

### 3 where necessary to approximately elevation -40 feet after construction of a temporary offshore cofferdam. Prior to excavation, the bedrock surface was overlain by a dense basal till of approximately 20 feet in thickness. Twenty to 30 feet of glacial deposits of a looser nature and beach sands were found to overlie the till. These deposits were replaced by structural backfill around the Unit 3 intake structure. In the area offshore of the intake structure, borings conducted 500 feet offshore indicate bedrock elevation is variable, ranging between -20 and 

### -57 feet. Bedrock immediately offshore of the intake is likely at elevation -40 feet. Most borings indicate that bedrock is overlain by several feet of basaltill although locally thicker deposits are possible. Overlying the till is a poorly graded, micaceous silty sand which forms the seafloor bottom. The seafloor bottominthe vicinity of the intakewas modifiedduring construction of thatstructure as well as by dredging after construction. Immediately adjacent to the intake, the seafloor bottom elevation is at about -28 feet according to soundings taken in 1990 and slopes up seaward due to dredging modifications to about -16 feet. Nofield permeabilitytests wereconducted inany ofthe offshore overburden materials. Based on field/laboratory boring log descriptions and grain size distribution curves performed on similar soils obtained from onshore boring at the intake structure, it was estimated that hydraulic conductivity isapproximately 1 0-4 cm/secfor the silty sands comprisingthe seafloor bottom. 

## 3.6 DIVERSION 

### SILLS AND CURTAIN 

## WALLS
Twoalternative diversionsystem designswere developed. Thefirstwasa passivedesignthat would consist of a diversion sill on the bay bottom constructed of precast concrete Jerseybarrier units that would be placed in front of the existing Unit 

### 3 intake structure forming an angled barrier. This design would take advantage of thetendency of flounder larvaetoreside ator near the bottom of the bay during daylight hours. Itshould be noted, however, thatthis design would not prevent nighttime entrainment. This barrier would divert silt and other debris being carried along the bottom by tidal currents away from the Unit 3 intake. As part of the design, an array of diversion vanes also constructed of Jersey-barrier units would be arranged along the outboard side of the barrier toscour silt away and prevent silt from fillingin the front of the barrier. The alternative design would be a floating barrier or curtain wall, that would be constructed on piles. An air bubbler floatation system would be used for floating the flounder larvae to the surface. This diversion system would work on the principal that the rising air bubbles

01516.WP5 

### 3-45 PART ICooling Water System Alternatives to 

### Reduce Larval Entrainment could potentially float the larvae. The curtain wall, arranged at an angle tothe intake, would then divert the larvae awayfrom the intake. Preliminary designs for the submerged diversion sill and the curtain wall with air bubbler are shown on 

### Figure 

### 3-6. Both options were considered only experimental with respect to entrainment mitigation.


### 3.6.1 SUBMERGED DIVERSION 

### SILL The submerged diversion sill isa V-shaped barrier onthe bay floor that would be constructed directly in front of the Unit 3 intake as shown on Figure 

### 3-6. The barrier would be constructed of Jersey-barrier concrete units, 6 feet in height. This design could divert some portion of flounder larvae away from the intake during daylight hours when they reside at 

### or near the bottom. The V shape with an interior angle of approximately 50 degrees (or 

### 25 degrees to the flow) would be designed to divert the larvae to the sides of the intake in the incoming flow. The 50-degree angle was selected based on the experience 

### with angled screens for fish diversion @),(J-Q),{jJJ as effective for diverting fish. It is probable that the larvae would be carried up and over a straight barrier arranged normal tothe incoming flow tothe intake. Although this design is a passivesystem, dredging to remove silt build-up may be required.
A build-up of silt, if left uncorrected, would renderthe sill ineffective as a diversion barrier for flounder larvae. Toreducethis potential problem, an array of scouring vanes, arranged along the outboard sides of the diversion sill, would be required as part of the design. 

### Work by Odgaard 

## (14) has shown that arrays of submerged scouring vanes could be effective in diverting silt away from intakes. The potential effectiveness of the system in diverting winter flounder larvae 

### at MNPS could only be determined by a moredetailed analysis, hydraulic modeling and by placingthe barrier and testing it in place. There could be considerable difficulty 

### in attempts to quantify the effectivenessof thisoption andthereare noinstallations

### whichcould be used for comparative purposes. The variability of larval density 

### in the water column raises questions on attempts to quantify effectiveness. This option could also disrupt existing flow patterns and possibly increase debris loads and larval entrainment at Units 1 and 

### 2.

PART I 

### 3-46 01 516.WP5II4 

## F P 0 

# I=

# I W 

# T'?

I E t

. .......

### . 

# I



# @ NORTHb

Millstone Units 1,. 2, and 

### 3 3.6.2 CURTAIN WALL WITH AIR BUBBLER The barrier with air bubbler floatation system would be designed to float flounder larvae up to near the surface and then divert them away from the intake with an angled curtain wall. The curtain wall would consist of a barrier constructed of timber or nonmetallic synthetic material that would be supported by precast concrete piles as shown on Figure 3-6. The barrier would incorporate a float system (not shown) that would allow the barrier to slide up and down on the piles with the tide while maintaining a constant depth. The barrier would be serviceable by a walkway which would be connected to the Unit 

### 3 intake structure at either end of the barrier. The air bubbler system would consist of multiple (10 to 15) diffuser pipes that would be mounted on the sea floor on a concrete pad. Air blowers to provide air tothe diffuser pipes would be located on the shore as shown on Figure 3-6. Two air bubbler systems would be provided, one for each leg of the angled barrier. The multiple pipe air bubble diffuser arrangementwould be designedtocreate awide curtainof bubblesthatcould effectively float the flounder larvae. This multiple air bubbler diffuser pipe arrangement has been used by the Swedestofloat jellyfish. The air bubbler system would be located a distance infront of the floating barrier toallow complete floatation ofthe larvae intheapproachingflow tothe intake. The submerged position of the air bubbler system would be removable when not required for service. Both laboratory and site testing would be required to develop reliable design criteria for this systemand confirm effective performanceatthe MNPS intakes. This design concept, likethe submerged barrier, may divert a portion of floating eelgrass and kelp away from the intake. 

## 3.7 PLANT OPERATIONAL STRATEGIES
3.7.1 POWER AND FLOW REDUCTION
A reduction inthe power output of the 

### MNPS unitsdoes not have a corresponding reduction in the required cooling-water flow. Significant flow reduction can only be achieved by shutting down one or more of the circulating water pumps. Various scenarios of circulating water pump flows to achieve approximately 

### 25 percent total flow reduction are shown in Table 3-1.

01516.WP5 

### 3-49 PART I

# m Option 1 Pump from each Unit 2 Unit 3 Pumps, Cooling Water System Alternatives to Reduce Larval Entrainment

Unit 1 Unit 2 Unit 3 Total Yo of (gpm) (gpm) (gpm) (QPm) Goal 105,000 137,000 152,000 394,000 a4 1

37,000 304,000 441,000 94 TABLE 

### 3-1 MNPS UNITS CIRCULATING WATER 

### PUMP vs 

### FLOW REDUCTION

1 Unit 2 Pump, 1 Unit 1 Pump NOTE: 25 percent of Total Flow = 0.25 (1,880,000) = 470,000 gpm = Goal There are several negative aspects associated with operating one of the MNPS units during the spring season with one or more circulating water pumps isolated. The most important of these is vulnerability to an automatic plant trip if an operating pump were to trip. It also causes the condenser pressure to increase and the institute of Nuclear Power Operation 

### (INPO) thermal performance goals to degrade. Depending upon other plant factors it could also result 

### in a significant loss of power output. Other issueswhichwould require additional study are the 

### NPDES permit restriction on differential temperature between the intake structure anddischarge (whichwould be exceeded under some operating conditions) andthe impact on backflushing capability, mussel cooks, and hypochlorite injection. The challengetosafety posed bypurposefully operating an MNPS 

### unit ata state of readiness which is far less than optimum during the time of year when high energy storms have historically caused problems is not acceptable from an engineering 

### or plant management perspective. It 

### is, therefore, prudent to investigate variable/multispeed circulating-water pumps. 

### 3.7.2 VARIABLE-SPEED PUMPS Variable-speed driver for the circulating water pumps would allow reduction 

### in circulating water flow during periods of flounder larvalactivity. A two-speed drive whichwould operate the circulating water pumps either at rated flow or at %-rated flow was evaluated 

### in this section.



### PART I 

### 3-50 0157 6.WP5Millstone Units 7; 

### 2,' and 

### 3 3.7.2.1 Hydraulic and Pumping Energy Requirementsfor 

### '/7 Speed Operation Reduction in the pump speed to 

### K would result in transposition of the pump performance curve to flows equal to '/2 of the existing curve and total dynamic heads of % of the existing curve according to pump affinity laws 

## (15). The actual K-speed pump flow rate was determined by superimposing the repositioned 6-pump curve for 6 pumps operating at '/2 speed on to the circulating water resistance curve as shown on Figure 

### 3-7. Reducing 6 circulating water pumps to %-speed would result in each pump operating at a flow of 76,000 gpm at a total dynamic head of 6.5 feet. This would result in a reduced power requirement for each pump from the existing 1,500 to 170 horsepower. The 76,000 gpm was exactly K of the design pump flow of 152,000 gpm. This total reduction in pumping energy requirements for %-speed operation would be 5,950 kW.

Figure 

### 3-7 Pump Performance Curve

015 16.WP5 

### 3-5 1 PART ICooling 

### Water System Alternatives to Reduce Larval Entrainment 3.7.2.2 Two-Speed 

### Electric Motors
A circulating water flow decrease to ?4 could be achieved 

### by decreasing the motor synchronous speed from 277 to 

### 139. This could be accomplished either by a variable-speed drive or by a two-speed motor. Itwas decidedtoprovide 

### an estimate for only the two-speed motor option. The variable-speed drive was eliminated for the following reasons: 1. Only two speeds are required. 

### 2. The cost of each system was approximately equal, $275,000. 

### 3. The space requirements: Forthesysteminvestigated, eachdrivesystem would occupy an indoor area 394 inches long x 48 inches deep x 

### 90 inches high and an outdoor area 57 inches deep by 93 incheswide 

### by 100 inches high. Other systems would require comparable area. The six existing 4 kV, 1,500 horsepower, 

### 277 rpm vertical circulating water pump motors would be replaced with 2-speed, 4 kV, 1,500 horsepower, 

### 277 rpm motors. The motor would be based on the concept of pole amplitude modulation (PAM) and the license tothis design is held exclusively by Westinghouse. An estimated price was also obtained for a conventional two-speed, double winding motor. The price of this motor was in excess of $200,000 more per motor than the PAM motor. Even the PAM motor would be a large motor, approximately45,000 pounds, whichis

### 20,000 poundsmorethantheexisting motors. Power would still be provided tothe motors from the 

### six breakers located on buses 34A and 6. However, a two-speed motor starter would be required for each motor to reconnect the windings to change the motor speed. The motor starters would be controlled from control switches mounted on the main control board. The screenwell structure is neither a suitable environment nor does it have adequate space to locate this equipment. Therefore, the cost of a heatedand ventilated building, 

### 30 feet long x 25 feet wide x 12feet high, was included to house the starters. It was assumed that the existing circulating and service water pumphouse would provide power for the new building heating and ventilating, and lighting. The building would be located 

### in front of the circulating and service water pumphouse. As part of the estimate, it was also assumed that existing motor feeder cables would be pulled back to the manhole nearest the circulating and service water pumphouse. This is approximately 

### 300 feet from thatstructure. A newductline from theexisting manholetothe new starter building would be included. The existing cables would then be pulled and connectedtothetwo-speed motorstarters. Finally, newducts from the motorstarter building tothe existing circulating and service water building with new motorfeeder cables would be included. s

T

2.

PART 

### I 3-52 01516.WP5Millstone Units 

### 1,. 

### 2, and 

### 3

~~ ~ A cursory check of the existing installation indicated that the foundations were adequate. However, ifthis alternativewere pursued, anextensive investigation of thefoundations would be required. 3.7.2.3 Impact on Unit Performance Reduction 

### in circulating water flow rate to 

## YZ in each condenser tube bundle during the months of April and Maywould result in a reduction in unit performance of 32,840 kWfor each month. This reduction to unit performance would be due to the reduced flow in the condenser tubes and reduction 

### in the heat transfer efficiency of the condenser tubes due to reduced tube flow velocities. A 90 percent cleanliness factor could only be maintained with on-line ball cleaning at reduced tube flow velocities. Currently, Unit 3 does not have an online tube cleaning system. Capital cost of this cleaning system would be about one million dollars. Without on-line tube cleaning, the condenser tubes would foul. Unit 3 load would haveto be reduced toas much as % toavoid turbine trip. Because of the fouling buildup of slime 

### in the tubes during %-flow operation, condensertube cleanup could be necessaryfollowing reduced flow operation before full flow and unit'operation could be resumed. This would lead to a vulnerability similar to that described earlier for operation with one or more circulating water pumps isolated, Therefore, this alternative would require additional study of condenser vacuum imbalance and associated issues to determine if the plant could continue safe operation with significant condenser fouling and less than maximum coolingwater flow. 3.7.3 SCHEDULED REFUELING OUTAGES Refueling outagesare generallytargeted for periods of low electrical demandand, hence, most refueling outages are scheduled for the spring and fall. The outage schedule also takes into account factors such as fuel nucleonics (usable life), required upgrades to plant equipment, required inspections, regulatory commitments, safety, maintenance concerns, and available manpower. Factorsthat could influence the actual versus scheduled outage include safety, duration of a previous outage, equipment malfunctionor failure, and inspectionor surveillance failure. The scheduled refueling outages for MNPS are shown in Table 3-2. As shown, the Unit 1 scheduled refueling outages occur inthe even numberedyears and coincide with a portion of the average winter flounder larval entrainment period of April through mid-June. Unit 2's

01516.WP5 

### 3-53 PART Ii 

### Cooling Water System Alternatives to Reduce Larval Entrainment scheduled outages are also even-numbered, although the dates are subject to change based upon completion of the Steam Generator Replacement Project. Unit 3's scheduled outages occur in odd-numbered years and also coincide with a portion of the winter flounder larval entrainment period. If all plant operation and refueling outages went as scheduled, then planned outages at Unit 1 (even-numbered years) and Unit 

### 3 (odd-numbered years) could coincide with the larval entrainment period each spring. Several refueling outages have 

### in fact taken place during 

### all or portions of the larval entrainment period, and the refueling outage schedule indicates that this will probably continue. A review of past 

### MNPS refueling outages indicated that four refueling outages occurred during the dates shown in Table 3-3. There were another three refueling outages that took place for portions of the time periods shown 

### in Table 3-3. It should be noted that cooling-water flow is notterminated during refuelingoutages; however, thedurations shown in Table 3-3 compensate for continued flow and would result in 

### MNPS flow reduction of approximately 25 percent, except for Unit 

### 2 which achieves a maximum of about 13percent. For further detail in understanding how these dates were established, refer to Section 

### II, Part 4.

PART I 

### 3-54 01516.WP5r

L w

u) 0 cCooling Water System Alternatives 

### to Reduce Larval Entrainment TABLE 3-3 APPROXIMATE OUTAGE DURATIONS AT MNPS FOR 25 PERCENT ENTRAINMENT MITIGATION
PLANT(S

### 1 CALENDAR DATE 

### * ELAPSED Single Combination Start Finish Days Unit 1 April 

### 2 June 13 73 Unit 2

### * * April 2 June 13 73

Unit 

### 3 April 2 June 6 66 Unit 1 & Unit 2 April 2 June 

### 6 66 Unit 1, Unit 2, & April 22 May 12 21 Unit 3



### NOTE: * ** Maximum attainable mitigation for Unit 

### 2 is 13 percent. Rationale for date selection is described in Part 

### II of this report.
Unplanned outages are common and have a potentially significant impact on the scheduled refueling outages for a nuclear unit as well as the other nuclear units owned by NUSCO. This is due tothe nuclear fuel burn-up cycle. Interruptions 

### in plant operation during a particular fuel cycle essentially extend the life (or cycle) of the particular fuel. This could potentially postpone the required date for refueling. Changes tothe refueling schedule for one nuclear unit potentially changes the schedule for the other units. Because fuel purchases must be planned 

### in advance, there are design costs and carrying charges to consider when deciding on a refueling outage schedule change. The costs associated with nuclear fuel procurement, fuel cycle redesign, and carrying charges are significant; up to 

### SW million could be expended in cycle redesign and carrying charges. Flexibility in the refueling outage schedule 

### is obviously important. Although a detailed cost estimate and engineering analysis of all the issues associated with reschedulingthe Unit 

### 1 and Unit 

### 3 refueling outagestocoincide morepreciselywith 

### Table 

### 3-3 was not performed, preliminary indications were that a one-time adjustment to the outage schedule would not bevery difficult or costly. However, it would not be possibleto maintain that schedule every year without exception, even with extraordinary and costlyengineering and nuclear fuel procurement strategies, unless forced outages were to occur each spring.
PART 

### I 3-56 0151 6.WP5Millstone Units 1; .2, and 3 

### 9 

### 5 3.7.4 FORCED OUTAGES 

### EACH SPRING



## - A forced outage each spring to coincide with 25 percent mitigation of an average winter flounder larval entrainment year is shown in Table 

### 3-3. While this option does not significantly affectfuel nucleonics (thenext refuel outage can be extendedtoallow fuel burnup), it would be a severe economic burden to NUSCO and the ratepayers as shown on Table 3-4. 

# f

? 

# ' f 

# I

Scenario TABLE 3-4 FORCED OUTAGE COST ESTIMATE FOR 25 PERCENT ENTRAINMENT MITIGATION
Cumulative Replacement Power Costs in Millions of 1992 $ Unit 1 Offline 4/2to 6/13 $21 4 Unit 2 Offline 4/2to 6/13 $307 Unit 1 & Unit 2 Offline 4/2 to 

### 6/6 $519 Unit 3 Offline 4/2 to 6/6 $310 Unit 1, Unit 

### 2, & Unit 3 Offline 4/22 to 5/12 $31 

### 8

1. 2. 

### 3. 4. 5. 6. Estimatesare 1992$ grossed uptofull output for eachscenario. Some years hadnoreplacement power cost because a scheduled refuel overlaps the time period. Estimated costs starting in 1993 through year 2010.- Dates offline are approximate, Part II 

### of this report discusses rationale for date selection. Maximum mitigation for Unit 2 

### is 13 percent. Explanation of 

### how the cumulative replacement power costs were developed for power reduction cases using net fuel cost data included in Appendix C. e by year each case's (Case 1, Case 2, etc.) replacement costs were grossed up to full plant. dollars by discounting at 11.78 percent per year. summed. power cost for the case. e these full plant replacement power costs.were then expressed in 1992 these full plant replacement power costs in 1992 dollars were then this resulting value was then reported as the cumulative replacement e

01516.WP5 

### 3-57 PART ICooling Water System Alternatives to Reduce Larval €ntrainment 

## 3.8
1.


### 2.



### 3.

4.



### 5. 

# a 6.
7.
8.



### 9.
10.

11. 

## REFERENCES
Millstone Nuclear Power Station Unit 3, Final Safety Analysis Report (FSAR), Docket NO.50-423. Final Environmental Statement Related to the Proposed Construction of Millstone Nuclear Power Station

## - Unit 3. Millstone Point Co. et al, Docket No. 50-423, United States Atomic Energy Commission, Directorate of Licensing, February 1 974. Hydraulic Model Study 

# - Phases 

### I and 

### II; Testing 

### of the Circulating Water Pump Installation; Millstone Nuclear Power Station

### - Unit

### No. 3; Lasalle Hydraulic Laboratory Ltd; LHL-847; June 1982. A.J. Hulchizer, J.C. Stuart, R.L. Obradovic, andA.J. Stuart. Land Shaft Construction and Initial Station Development for Seabrook Station Cooling Water Tunnels. RETC Proceedings, Voi. 2, 1979. A.J. Hulchizer and J.P. Rossereau. Design and Installation of Large Diameter Sub Sea Connecting Shafts for the Seabrook Station Cooling System. RETC, San Francisco, CA, 1981. R.T. Richards. Alternative Water Screening for Thermal Power Plants. J. Hydraulic Division, ASCE Vol. 114, 

### No. 6, June 1988, pp 578-597. Electric Power Research Institute. Guidelines on Macrofouling Control Technology. 

### EPRl CS-5271, Project 1689-9, Final Report, June 1987. Y.G. Mussalli, 

### J. Williams, and J. Hockman. Engineering Biological Evaluation of a Fine-MeshTraveling Screenfor Protecting Organisms. Proceedings of theWorkshop of Advanced IntakeTechnology, held atthe Sheraton-Harbor Island Hotel, San Diego, CA, April 

### 22-24, 

### 1981. M.R. Anderson, J.A. DiVito, and 

### Y.G.Mussalli. Design and Operation of AngledScreen Intake. J. Hydraulic Division, ASCE 

### Vol. 114, No. 6, June 1988, pp598-615. 

### S.J.Edwards, J. Dimbeck, T.E. Pease, M.J. Skelly, 

### and D. Renpert. Effectiveness of Angled-Screen Intake Systems. J. Hydraulic Division, ASCE Vol. 114, No. 

### 6, June 1988, 

### pp 626-640, J.A. Matousek, T.E. Pease, 

### J.G. Holsapple, and

### R.C.Roberts. Biological Evaluation of Angled-ScreenTest Facility. J. Hydraulic Division, ASCE Vol. 114, No. 

### 6, June 1988, pp 641-650. Stefan, H., A. Tu. Collector Well Studv of the Cooiina Water Intake Svstem of James H. Camobell Electric Power Generatina Plant Unit No. 3, St. Anthony Fails Hydraulic Laboratories, University of Minnesota, Project No. 176, November 1978.

PART I 

### 3-58 01516.WP5 

# F

### Millstone Units 1,. 

### 2, and3 13.
14.
15. Veneziale, E.J. Fish Protection with Wedaewire Screens at Eddvstone Station. Proceedings of the American Power Conference 54(1):433-438. J.A. Odgaard and Y. Wang. Sediment Management with Submerged Vanes. J. Hydraulic Division, ASCE Vol. 11 7, No. 3, March 1991, pp 267-283. I.J. Karassik, W.C. Krutzsch, W.H. Fraser, and J.P. Messina. Pump Handbook, McGraw-Hill Book Co., 1976.

01516.WP5 

### 3-59 PART I

# ESTIMATED COSTS

# AND CONSTRUCTION SCHEDULE

Order of magnitude costs and estimated construction schedules were developed for each of the proposed alternative intakes for Unit 3 discussed in Section 

### 3. 

## 4.1 

## ESTIMATED COSTS
The estimated costsfor each of the seven alternatives are summarized in

### Tables4-1 through 4-6. These summary tables are based on the detailed information in Appendices A, B, and C. Appendix A provides detailed capital costs for each alternative. Appendix B providestabulated calculationsof annualcostsfor added power consumption and performance degradation resultingfrom implementationof cooling-water system alternatives for Unit 3 for the years 1993through 201

### 0. Performance penalty costs appearing 

### in

### Tables 4-1 through 

### 4-6 are the sum of total increased system annual costs for the years 1993 through 20 10. Appendix C provides net fuel cost data for the various outage scenarios evaluated to determine outage costs. 

### Table 4-7 summarizesthe direct, capital, and total costs of each alternative for comparison.

01516.WP5 4-1 PART I

### B

Cooling Water System Alternatives to Reduce Larval Entrainment TABLE 4-1



### item Cooling Tower NATURAL-DRAFTCOOLING TOWERS SUMMARY OF ORDER 

### OF MAGNITUDE COST ESTIMATES
Full-Size %-Size Tower Tower $13,000,000 $11,700,000 4,500,000 Equipment 6,500,000 Piping Main C.W. Piping Makeup and Blowdown Excavation and Backfill Cooling Tower Pump Station and Apron, and Access Road Cooling Tower Basin Electric and Control Equipment Tie-ins to Operating Plant TOTAL DIRECT COST Engineering Construction Management Allowance for Indeterminates/Contingency TOTAL CAPITAL COST Outage Cost Performance Penalty TOTAL ESTIMATED COST 12,500,000 9,600,000 1,100,000 800,000 3,100,000 2,200,000 1,700,000
3,500,000 2,600,000 100,000 44,100,000

4,400,000 3,100,000 10.500,OOO 62,100,000 12,000,000 14,700,000 $88,800,000 1,100,000
2,900,000 2,200,000 100,000 35,100,000

3,500,000 2,500,000 8,200,000 49,300,000 12,000,000

9,800,000 

### $71,100,000

IfNote: Costs were developed for relative comparison purposes and due to their conceptual nature may be considerably lower than actual. Further limitations are described in the applicable text describing the design alternative.

PART I 4-2 01516.WP5Millstone Units 1i.2,and 

### 3 TABLE 4-2 OFFSHORE INTAKE SUMMARY OF ORDER OF MAGNITUDE COST ESTIMATES I

## -- $ 

### g

r. 

### item Pumps, equipment Tunnel Shafts Concrete 

### i3 Dredging Pumphouse, Forebay, Temp. Dock Electrical Tie-ins to Operating Plant 

# e TOTAL DIRECT COSTS $4,700,000 32,700,000 11,400,000

4,700,000 6,200,000 700,000 600,000 6 1,000,000 Engineering 6,100,000 Construction Management 4,300,000 Allowance for 

### IndeterminatesKontingency 17,700,000 TOTAL CAPITAL COST 

### 89,100,000 Outage Cost 24,000,000 Performance Penalty TOTAL ESTIMATED COST 4,600,000 $117,700,000 I

Note: Costs were developed for relative comparison purposes and due to their conceptual nature may be considerably lower than actual. Further limitations are described in the applicable text describing the design alternative.

01516.WP5 

### 4-3 PART ICooling Water System Alternatives to Reduce Larval Entrainment TABLE 4-3 FINE-MESH SCREENS SUMMARY OF ORDER OF MAGNITUDE 

### COST ESTIMATES



# - item Equipment Piping & Sluicing System Concrete & Dredging Forebay, Cofferdam & Temp. Dock Electrical Tie-ins to Operating Plant TOTAL DIRECT COSTS 

### $8,600,000 500,000 4,400,000 

### 5,400,000 350,000



### 50,000 19,300,000 Engineering

, 1,900,000 Construction Management 1,300,000 Allowance for Indeterminates/Contingency 5.700.000 TOTAL CAPITAL COST 

### 28,200,000 Outage Cost 

### 24,000,000 Performance Penalty TOTAL ESTIMATED 

### COST N /A 

### $5 

### 2,200,000

Note: Costs were developed for relative comparison purposes and due to their conceptual nature may be considerably lower than actual. Further limitations are described inthe applicable text describing the design alternative.

PART I 01516.WP5

# Ir) Millstone Units I; 

### '2, and3 TABLE 4-4 WEDGEWIRE SCREENS SUMMARY 

### OF ORDER 

### OF MAGNITUDE 

### COST ESTIMATES



### item Equipment Piping Concrete & Dredging Cofferdam & Temp. Dock Electrical Tie-ins to Operating Plant TOTAL DIRECT COSTS Engineering Construction Management Allowance for 

### Indeterminates/Contingency TOTAL CAPITAL COST Outage Cost Performance Penalty TOTAL ESTIMATED 

### COST $5,500,000 1,900,000 1,200,000 3,300,000 150,000

50,000 12,100,000

1,200,000



### 800,000 3,500,000 17,600,000 

### 48,000,000 N/A $65,600,000

Note: Costs were developed for relative comparison purposes and due to their conceptual nature may be considerably lower than actual. Further limitations are described in the applicable text describing the design alternative.

01516.WP5 4-5 PART ICooling Water System Alternatives to Reduce Larval Entrainment TABLE 4-5 TWO-SPEED 

### PUMPS SUMMARY 

### OF ORDER 

### OF MAGNITUDE COST ESTIMATES



# - Item Equipment Piping Excavation/Concrete Electrical Tie-ins to Operating Plant TOTAL DIRECT COSTS Engineering Construction Management Allowance for 

### Indeterminates/Contingency TOTAL CAPITAL COST Outage Cost Performance Penalty TOTAL ESTIMATED COST $1,500,000
100,000 

### 650,000

50,000 

### 2,300.O 00 

### 200,000 200,000 500.000 3,200,000 12,000,000 16,800,000 

### $32,000,000

Note: Costs were developed for relative comparison purposes and due to their conceptual nature may beconsiderably lowerthan actual. Further limitations are described 

### in the applicable text describing the design alternative.

PART I 

### 4-6 015 16.WP5Millstone Units 1;2, and 3 TABLE 4-6 BARRIER SILLS SUMMARY 

### OF ORDER 

### OF MAGNITUDE

### COST ESTIMATES



# - Item Sill Fabrication Sill Installation Tremie Concrete Temporary Dock TOTAL DIRECT 

### COSTS Engineering Construction Management Allowance 

### for 

### Indeterminates/Contingency TOTAL CAPITAL COST Outage Cost Performance Penalty TOTAL ESTIMATED COST $400,000 

### 600,000 200,000 100,000 1,300,000 100,000 100,000 300,000 1,800,000 NIA N/A $1,800,000

Note: Costs were developed 

### for relative comparison purposes 

### and due to their conceptual nature may beconsiderably

### lower than actual. Further limitations are described inthe applicable text describing the design alternative.

01 516.WP5 4-7 PART I

# e

t

I 

### a 

## 1

9 Z 

## ? Z



## - E 0 0 N u, 

### 9 

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### 9 N u,


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### 9



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### 9

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## -

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## z 

# E m v) oc) d-Millstone Units 1, 2, and 3 The estimated costs listed in Tables 4-1 through 4-7 were based on the following general assumptions:

0 Present day prices and fully sub-contracted labor rates as of 1 1 /1/92.

e 40-hour workweek, single-shift operation

0 Dredged material can be disposed of locally; assumed to be not contaminated

0 Required construction utilities will be supplied by Owner

0 Land required for construction trailers, parking, and lay down provided by Owner

0 Allowance for interferences along pipeline trench; electrical ductbank included within trench

0 Construction management included at 7 percent of direct construction cost Detailed engineering/design included at 1

### 0 percent of direct construction cost 0 The cooling towers, the two-speed pump drives, and the concrete sills have a 20 percent AFkontingency applied to total capital costs. The fine-mesh screens, the wedgewire screens, and the offshore intake each have a 

### 25 percent AFkontingency applied to total capital-costs. Thesefactors were recommended basedonthe levelof detail of the preliminary designs and estimate pricing basis. These factors could also be referred to as budget protection factors for possible additional costs that might develop but cannot be determined at the time of preparation of the estimate. A higher factor has been applied to the more difficult marine alternatives.

. Costs associated with the following were not included in the estimate:

0 Escalation

0 Abandonment

0 Demolition/relocations

0 Sales, use, service or other taxes

0 Insurance (building all risk and other marine insurances) 

# c) 0 Severe contingency costs (e.g., those associated with adverse weather, craft strikes)

0 Startup
01516.WP5 

### 4-9 PART ICooling Water System Alternatives to Reduce Larval Entrainment Permits (including environmental)

0 Empioyee training, certifications, security work

0 Operation and maintenance Category 

### I structures Owner’s cost The total present-day capital costs consisted of the October 1992 direct, distributable, and engineering costs, and allowance for indeterminates/contingencies. 

## 4.2 SPECIAL 

## EXCAVATION 

## COST 

# CONSIDERATIONS
Relative order of magnitude cost estimates for excavation were based on preliminary excavation quantities, available site conditions and similar case histories.
4.2.1 NATURAL-DRAFT COOLING TOWER EXCAVATION COSTS 

# e Typical rockexcavation costs, utilizing pre-split blasting in rock rangefrom $10.00to $20.00 per cubic yard. This assumed that average haulage

### would be lessthan 

### 5 miles, and easy site access would be available. 4.2.2 OFFSHORE INTAKE COSTS
4.2.2.1 Tunnel Excavation Assumptions/Costs
A relative order of magnitude of tunneling costs for a 24-foot I.D., 5,000-foot long intake tunnel has been made. The following assumptions were made: 

## - 1. Thetunnel would 

### be excavated through drill and blast methodsalong its entire 5,000-foot length. 2. A single intake structure would be built offshore, requiring an offshore shaft to be constructed from the tunnel up tothe submerged structure elevation. 

### 3. The tunnel liner would be cast in place, reinforced concrete, 2-foot average thickness. 4. Tunnelcross-sectionalshapewould be nearcircular/modifiedhorseshoe.

PART i 4-1

### 0 01516.WP5Millstone Units 

### I,. 2, and 3 

### 5. The access shaft would also be located offshore, approximately 150to 200 feet from the front of the current pumphouse structure.

~ 6. One working face was assumed tobe available starting from the access shaft, and that the tunnel would be driven towards the offshore intake structure.

Mobilization 1 $5,000,000 

### $5,000,000 

### 7. The heading was assumed wet, yet withcontrollable water inflow rates; and the rock assumed competent. If the heading were to be driven under wet conditions with crushed rock 

### or unconsolidated conditions, the tunnel excavation contingency could be as high as 50 percent.



# 1 Table 4-8 describes the breakdown of 

### the tunnelling costs. In general, tunnel costs are approximately $ 6,50O/lineal foot. Total cost of the tunnel excavation and construction is estimated at $ 32,700,000 for 

### 5,000 feet of cast 

### in place concrete lined tunnel.

5000 LF 5000 LF 

### 3000 LF 106,029 cu-yd

TABLE 4-8 RELATIVE ORDER OF MAGNITUDE COSTS FOR TUNNELLING

$920 $4,600,000

$40 $200,000 $1 

### 00 $300,000 $120,000 DESCRIPTION 

# I QUANTITY 

# I UNIT COST

# 1 TOTAL COST

# 11

Final Cleanup ~~ ~ 

### 5000 LF $42 $210,000 Shaft Station Development Tunnel Excavation 

# + Temp. Support (Rock Bolts) Concrete Lining (Slip Form) Drilling in Advance of Face Pressure Grouting at 

### Tunnel Face $175,000 $350,000
5000 LF $4376 $21,880,000

GRAND TOTAL $32,700,000 or $6500/LF of Tunnel 

# 11

01516.WP5 4-1 1 PART ICooling Water System Alternatives to Reduce Larval Entrainment 4.2.2.2 Shaft Excavation AssumptionslCosts 1, The circular access shaft would be sunk through conventional drill and blast full face methods. A.gallow stage would be used toadvance, drill and muck the shaft. This platform would also allow grouting and placement of the shaft liner during construction. 

### 2. The intake shaft would be drilled by raised boreheaming methods to 26 feet in diameter. 3. Only conventional surface preparation costs and equipment were considered. Underwater preparation, offshore shaft servicing and operations were not considered and are likely to raise this estimate slightly. 4. Access shaft diameterwould be 27 feet

### O.D. (outside diameter), 24feet 

### I.D. with cast in place concrete liner. Itwould be drilled entirely through rock. 5. The rock was assumedto be competent and groundwater inflowsto be at a rate as only requiring standard grouting techniques during shaft sinking. The costs for a full-faced excavated shaft were estimated based upon 1982Army Corps of Engineers' estimates for a shaft of this diameter. The final costs were adjusted to 1992 pricesthrough the Construction Cost Index published bythe Engineering News Record. The price difference is 32 percent. The average cost per linearfoot of shaft depth is $7645/foot. This includes both capital costs and operating costs. These costs compare favorably 

### with other proposed shafts 

### in high strength granite of similar diameter in North NewJersey. The NewJersey project costestimate for a 24-foot shaftwas $6883/foot. The New Jersey costs reflect dryer conditions (little or no grouting), and little or no ground support prior to liner installation. Excavation techniques are similar. Collar development in rock for a 24-foot diameter shaft typically costs-$1 to $1.5 million. The north shaft for the outfall tunnel of the MWRA Deer island Project was not entirely comparabletothe proposed shaft of MNPS. Slurry 

### wall construction was necessary, as was a larger diameter 

### (35feet) to accommodate a TBM. Total costfor a single shaft at MNPSwould be: 350feet x $7645/foot

# + collar development ($1,500,000) = $4,175,750/shaft. This does not include underwater construction costsfor sea floor prepand caisson installation. For preparationand caissoncosts associated withthe main access shaft and the velocity cap access shaft, the allowances were $2,000,000 and Ir L



### PART I 4-12 01 516.WP5Millstone Units 1,.2, and

### 3 $1,000,000, respectively. It should be noted that shafts costs can vary considerably with respect tothe following factors: ground conditions, crew experience, quality of supervision, labor rates, and excavationtechniques. The cost estimatesfor MNPS consider that the entire length of the shaft would be excavated in competent rock under wet conditions. Ground conditions any less favorable could significantly raise the shaft excavation costs. The contingency for the shaft excavation costs was 30 percent. 4.2.2.3 ScheduleAssumptions and Considerations The schedule was based upon onsite construction requirements. It does not include engineering design, site investigation work, or other prerequisite work. The schedule also does not include the Unit 3 intake structure modifications. Both the access shaft caisson structure and the intake shaft structures would be prefabricated and floated tofinal location. The schedule was based upon similar facility experience. Variations in rock types or ground conditions could significantly impact the schedule. Excavationtechniques fortheaccessshaft andthetunnel would utilize full face drill and blast methods. The offshore intake shaft would be excavated using raised boring techniques, which would reduce shaft excavation by 1 monthand create a safer working environment. Excavation ratesfor thetunnel and access shaft were assumed at 30 feet/day and 8 feet/day, respectively. The excavation for the raised boring machinewas assumed at 30 feet/day. It was assumedthat the liner would be installed during excavation with thetunnel face at least 150feet in front of the installed final liner. Final liner installation and sealing of thetunnel floor would be performed prior to raised boring of the intake shaft.
4.2.2.4 Total Offshore Intake Excavation Costs Two offshore shafts would be necessary, one main access shaft and one intake shaft. The main access shaft would be close to shore, 350 feet deep. The offshore shaft would be 225 feet deep, yet constructedapproximately 1 mile offshore inslightly deeper water by raise bore techniques. While the raised boring schedule would be shorter than conventional shaft construction techniques, capital equipment costs were assumedto be higher. For estimation purposes, both shafts have equivalent costs of $4,175,750. The total cost for this scheme would be: Tunnel: -$ 32,500,000 Shafts (2)

## - $4,175,750 x 2: $ 8,351,500 Access Costs for Shafts: $ 3,000,000 Total: -$ 43,851,500

4-13 01516.WP5 PART ICooling Water System Alternatives to Reduce 

### Larval Entrainment 

### 4.3 

## CONSTRUCTION 

## PERIODS ESTIMATES
Construction periods and estimated outage periodsfor eachof thg alternatives are presented 

### in 

### Table 4-9. These periods do notaccount for time 

### for engineering and design, equipment procurement, or permits. The construction periods estimates were developed assumingstandard construction methods and work weeks. The periods could be scheduled totake advantage 

### of scheduled refueling outages to 

### minimize forced outage time, Estimated outage periods are total durations.



### TABLE 4-9 

### CONSTRUCTlON AND OUTAGE PERIOD ESTIMATES

Alternative Full-Size 

### Cooling Tower System Two-Thirds Size Cooling Tower System Offshore tntake Fine-Mesh Screens Wedgewire Screens Submerged Diversion Sill Curtain 

### Wall with Air 

### Bubbler Variable-Speed 

### Pumps . 

### Construction.Period (Months) 

### 24 24


### 36 18 12 

### 2 2 

### 2 Outage Period (Months) 

### 1 7


### 2-6 2-6 

### 4-6

0 0 1

PART I 4-1 4 01.51 6.WP5

# 5

ENGINEERING 

# SUMMARY

The present seawater intakes for Millstone Power Stationconsists ofthree separate shoreline surface intakes, one per each of the three units. The intakes are similar in design having vertical wet pit type circulating water pumps (non-nuclear safety related) and service water pumps (nuclearsafety related). Each intakeincorporates traveling water screens, coarse-bar racks, and curtainwalls extending below lowestwater level. Each intakedrawswater directly from Niantic Bay. Total station withdrawal from Niantic Bay during normal full power operation of all three units is 4358 cfs. Unit 3 withdrawal (2097 cfsl is approximately '/2 of the total with Unit 2 (1 282 cfs) and Unit 1 (979 cfs) each withdrawing approximately ?4 of the total. This engineering evaluation consisted of an initial overview of available mitigation measures which offered potential reductiontothe entrainment of winter flounder larvaeintothe intakes. These technologies would achieve reduction tothe entrainment into the intakes of fish and fish larvaethrough flow reduction, prevention of entrainment, and reduction of entrainment. From this overview the following alternative cooling system schemes were selected for detailed study:

0 Natural-Draft Cooling Towers
0 Offshore Intake Fine-Mesh Screens Wedgewire Screens Infiltration Systems Operational Strategies 0 Diversion Sills and Curtain Walls
Reduced power/flow Variable-speed pumps Scheduled refueling outages Forced outages

01516.WP5 5-1 PART ICooling Water System Alternatives to Reduce larval Entrainment Preliminary designs for these selected alternatives were developed for Unit 3 only. A major reduction in fish and fish larvae entrainment for Unit 3, which draws 

### '/2 of the total station flow, would represent a major reduction to station entrainment. Cooling towers would achieve reduction in fish entrainment by reducing intake flow to only that required for cooling tower makeup. Two salt water cooling tower alternatives were evaluated: afull-size natural-draft coolingtower and a2/3-sizenatural-draft cooling tower. The existing condenser crossover valving and waterbox design pressure would allow conversion to a closed-loop system with the condenser operating in a two-pass configuration. Naturaldraft cooling towers were selected based on the results of previous studies conducted for MNPS. The cooling towers would be located 

### inthe existing wooded area tothe east of the switchyard. New pumping stations would be located at the cooling towers. Piping for the newclosed-loop circulatingwatersystems would be routed in a commoncutand covertrench tothe north and east of the station and would join the existing circulating inlet piping tothe west of the turbine building. Valving would be provided to operate either the existing oncethrough systemor the closed-loop system withthecooling towers. The nuclear safety-related service water system would remain unaltered with the cooling towers. New makeup water pumps would be installed in the existing Unit 

### 3 intake structure. Cooling tower blowdown would be discharged to the quarry. A chlorination system would be required to control biofouling of the condenser tubes and tower fill. A dechlorination system would be required for the blowdown. Construction cost would be very high for a cooling tower, and there would be considerable costs associated 

### with the loss 

### in performance. Maintenance costs would probably also be high but were not evaluated. An offshore intake would place the intake outside of the confines of Nianti.c Bay. Entrained fish and larvae would be drawn from the entire Long Island Sound population 

### in lieu of the confined Niantic Bay population. The offshore intake alternative would consist of extending the Unit 3 intake approximately 1 mile south into Long Island Sound. A rock tunnel was selected to develop cost estimates. The offshore end of the tunnel would terminate with a velocity cap structure located in the bottom of the sound. A booster pump station would be locatedattheshoreward end of thetunneltoprovide added pumping headtocompensatefor hydraulic head losses in the tunnel. The offshore intake system would be joined to the existing Unit 3 pump structure by double sheet pile walls with tremie concrete filler. A nuclear safety-related flow bypass system would be provided for the service water pumps. Bypass gates for 50 percent of the circulating water flow would be provided. A chlorination system would be required to control biofouling in the inlet, shafts, and tunnel and a dechlorination system would be required for the circulating water discharge. Experience 

### at 

### 5-2 01516.WP5 

### PART IMillstone 

### Units 1,.2, and 

### 3 Seabrook Nuclear Stationandthe sewage outfalltunnel currently being constructed in Boston Harbor were utilized for design criteria and cost estimating. The construction cost for an offshore intake would be extremely high, construction time would be lengthy, and 

### the project would be difficult due to uncertainties in rock stability and permeability. Also, biofouling of the tunnel from mussels and other marine organisms could be severe and difficult to control. Chlorine 

### (CI,)will kill larvae. Fine-mesh screens prevent fish and larvae from entering the intake by intercepting them and returning them to Niantic Bay with a fish return system. The fine-mesh (1to 2 mm) screens require an approach velocity of 0.5 fps to prevent overloading of the screens by debris. A through flow fine-mesh screening system for Unit 3 would consist of eighteen 10 foot wide traveling screens, housed in a screening structure 276 feet long by 40 feet wide that would be constructed directly in front of the existing Unit 3 intake. A forebay would be created, connecting the existing intake structure to the new fine-mesh screen structure by double sheet pile walls. A nuclear safety-related flow bypass system would be included for the service water pumps and bypass gateswould be providedfor circulating water flow. Fish and larvae collected onthe fine-mesh screens would be returnedto Niantic Baytothe east of Bay Point by a sluicing system. Alternate fine-mesh screen design utilizing angled through-flow screens and double entry drums screens were also evaluated. Fine-mesh screen technology has been successful with certain species and sizes of fish and larvae; however, success with stage 3 winter flounder larvae was not found in the literature. There were also concerns with debris clogging of fine-mesh screens, which is prevalent at MNPS'during the spring season. Wedgewire screensYi3duaa $eliminate entrainment of fish and larvae by .taking advantage of natural cross currents tosweep fish and larvae past the submerged screen units and by utilizing smalt screen slot widths to block entry of small life forms and debris. A staggered array design for submerged wedgewire screen units with six collection conduits was developed for Unit 

### 3. The staggered array design 

### with alternate long and short collection conduits would promote better natural flushing of screen units. A plenum structure, constructed in front of the existing intake structure, would gat'her the flow from the collector pipes and distribute it tothe existing intake bays. An automatic air burst system would be provided to backflush the screen units. A chlorination system may be required to control biofouling inthe conduits. The plenum would be equipped with a nuclear safety-related flow bypass for the service water pumps and separate bypass gates for circulating water. An alternate bulkhead design is also presented but not costed.

5-3 01516.WP5 PART ICooling WaterSystem Alternatives to Reduce Larval Entrainment Wedgewire screens are not in use at flow rates as high as the Unit 

### 3 circulating and service water flows. There is also the strong potential for severe debris clogging, biofouling, and corrosion of the wedgewire screen units in the marine environment of Niantic Bay. Diversion sills and curtain walls can divert a portion of the flounder larvae away from the intakes. Concrete sills constructed of Jersey type barriers placed on the bottom of Niantic Bay in front of the Unit 3 intake offer the potential for diverting a portion of the flounder larvae away from the intake. A design is presented consisting of a vee shaped barrier that would be constructed in front of the existing intake. The sill has an added potential benefit of diverting silt awayfromthe intake. Additional angledvanesthat would be placed upstream of the sill are included with the design to enhance silt diversion. An alternative tothe sill is a floating curtain wall with an air bubble floatation system. The floating curtain wall would also be angled to divert larvae to either side of the intake. The curtain wall would be supported by piles driven into the sea floor. The floatation system would consist of multiple diffuser pipes installed on the sea floor in front of the barrier and would be supplied by compressed air from blowers located on the shore. There are no reported installations of divwsion barriersor sills for the purpose of diverting fish larvae and therefore no quantitative data is available for determination of effectiveness. 

### .

Infiltration systems consist of arrays of perforated pipes installed in the bottom sediments. Water enters these pipes by percolating through the overlaying sediments into the pipes. These systems would prevent the entry of fish larvae. Existing systems in the United States have capacities an order of magnitude less than the Unit 

### 3 operating flow. These systems haveclogging and maintenance problemswhen highyieldsare attempted. A Europeandesign offers potential improved performance, however, a review of this design which incorporates a patented filter media design indicated 

### it could be subject to clogging in the high detrital environment at MNPS. For these reasons, infiltration was eliminated as a nonviable technology for the high 

### MNPS intake flows. Power reductions do not result in corresponding cooling-water flow reductions; however, significant reductions in cooling-water flow could necessitate a reduction in station power production. Isolationof circulating water pumps during thespring seasonwasnot considered a viable option due to operational difficulties and a degradation of plant safety. Variable-speeddrivesforthecirculatingwater pumpsallow reductionincirculatingwater flow during periods of flounder larvae activity. Reduced circulating water flows would result in increased condenser tube fouling and would likely require a reduction in unit output or an PART I 

### 5-4 01 516.WP5Millstone Units 1,. 

### 2, and 

### 3 outage. A two-speeddrive system designwas developedwhich would operatethe circulating water system at either full-flow or 

### % flow. Refueling outages are scheduled for spring and fall seasons. Spring refueling outages will occasionally occur during some or all of the period of larval entrainment. However, it would be extremely expensive to guarantee the exact timing every year. Forced outages of one or more of the MNPS unitswould also be extremely expensive as shown in 

### Table 5-2, Cost estimates were developed 

### for the selected alternatives. Costs are order of magnitude and include direct costs, engineering, construction management, 

### AFI, contingency, outage costs, and performance penalty costs. 

### Table 5-1 provides a summary of cost estimates. A tabulated evaluation of the selected alternatives in to Unit 3, operability, maintainability, plant safety, impact, and costs is presented on 

### Table 5-3. terms of constructibility, compatibility biological effectiveness, environment

0151 6.WP5 

### 5-5 PART I

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### 3 TABLE 

### 5-2

Scenario 

### FORCED OUTAGE COST ESTIMATE FOR 25 PERCENT ENTRAINMENT MITIGATION Cumulative Replacement Power Costs in Millions of 1992 $ Unit 1 Offline 4/2 to 6/13 Unit 2 Offline 4/2 to 6/13 Unit 1 & 

### Unit 

### 2 Offline 4/2 to 6/6 Unit 3 Offline 4/2to 6/6 Unit 

### I, Unit 

### 2, & Unit 3 Offline 4/22 to 5/12 $214 $307 $51 

### 9 $31 0 $31 

### 8 NOTES: 1. 2. 3. 4. 5. 6. Estimatesare 1992$ grossed uptofull output for each scenario. Some years had noreplacement powercost becausea scheduled refuel overlaps the time period. Estimated costs starting 

### in 1993through year 2010. Dates offline are approximate, Part II of this report discusses rationale for date selection. Maximum mitigation for 

### Unit 

### 2 

### is 13 percent. Explanation of how the cumulative replacement power costs were developed 

### for power reduction cases using net fuel cost data included in Appendix 

### C. a 

### by year each case’s (Case 1, Case 

### 2, etc.) replacement costs were these full plant replacement power costs were then expressed in 1992 these full plant replacement power costs in 1992 dollars were then this resulting value was then reported as the cumulative replacement grossed up to 

### full plant. dollars 

### by discounting at 7 1.78 percent per year. summed. power cost 

### for the case. 0

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