Donald J. Danila 

Northeast Utilities Environmental 

Laboratory 

Millstone Nuclear Power Station 

P.O. Box 128 

Waterford, CT 06385-0128 

(860) 447-1791 X4538 

FAX: (860) 444-5240 

Email: danildj@NU.COM 

June 17,1999 

Dr. Elizabeth M. Strange 

Stratus Consulting Inc. 

PO Box 4059 

Boulder, CO '80306-4059 

Dear Dr. Strange: 

Under separate cover, I have enclosed the reports you requested. Please keep us in mind if 

your work for EPA results in any publications or reports that you are free to disseminate. Thank 

you very much. 

Very truly yours, 

Donald J. Danila 

Senior Scientist 
J 

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 DESIGN AND OPERATION ....................... 1-1 

2 OVERVIEW AND PRELIMINARY ASSESSMENT 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 

APPEN Dl 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 

01 51 6.WP5 i 
Cooling Water System Alternatives to Reduce Larval Entrainment I 

SUMMARY TABLE OF CONTENTS (Cont) 

Section Pane 

PART li - ENVIRONMENTAL/BIOLOGICAL EVALUATION 

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 

MITIGATION ALTERNATIVE . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 

5 EFFECTIVENESS OF THE MITIGATION OF LARVAL WINTER FLOUNDER 

ENTRAINMENT .......................... .... .............. 5-1 

1 6 ENVIRONMENTAL AND BIOLOGICAL SUMMARY . * . . . . . . . . . . . . . . . . . . 6-1 - 1 

ii 01 51 6.W5 

? 
ACKNOWLEDGEMENTS 

This study could not have been done 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 to the 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 

The following NUSCO employees contributed to the development and/or review of 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 Departments provided input and/or review of material contained in this 

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 01 51 6.WP5 

i’ 
EXECUTIVE SUMMARY 

I NTR 0 D U CTI ON 

This report presents the 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 

available technologies for entrainment mitigation including those mitigation schemes 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 of winter flounder larval entrainment, the environmental considerations for 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 effectiveness of mitigating winter flounder larval entrainment. 

01 5 16.WP5 ES-1 
Cooling Water System Alternatives to Reduce larval Entrainment 

The following alternatives were evaluated as mitigation 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 

The rc L: existing seawater intakes for MNPS consist of three separate, shoreline, surface intakes: 

one for each generating unit, The intakes are similar in design, having vertical wet-pit type 

circulating water pumps (non-nuclear safety related) and service water pumps (nuclear safety 

related). Each intake is equipped with traveling water screens, coarse-bar racks, and curtain @ walls extending below the lowest water level. Each intake draws water directly from Niantic 

Bay. Total station withdrawal of seawater during 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 affects winter 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 estimates have exceeded 100 million larvae each year. The 

average fecundity of Niantic River females is approximately 572,000 eggs per fish. From 

about ?4 to ?4 of the entrained winter flounder larvae were estimated to have 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 of Niantic River winter flounder larvae by at least 25 percent. Because 

annual entrainment estimates have ranged from 31 to 21 9 million, but since three-unit e 

ES-2 01 51 6.WP5 
Millstone 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. 

COOLING TOWERS 

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 capacity tower and a Vicapacity tower. With the %-capacity tower, % of the existing Unit 3 circulating water system 

would remain once-through. For both alternatives, the proposed location for the tower would 

be in the wooded area to the east of the switchyard. A new pump station would 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 to two-pass operation. 

The existing once-through circulating water system would remain intact and operational. 

Valves would be provided to operate the station either once-through or on the 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 -tower for MNPS would be 535 feet high and, therefore, a significant 

visual intrusion on the coastline near Millstone Point. Construction would be very challenging., 

given all the present underground utilities that would require re-routing or removal. A cooling 

tower would also pose a severe economic burden due to the capital cost of construction and 

performance penalty resulting from lost generating capacity. Maintenance and operating costs 

could also be substantial; however, they were not addressed. 

The total estimated cost for the cooling tower is $88 million for the full size and $70 million 

for the Y3 size. 

01 51 6.W5 ES-3 
p 

cCoo/hQ Water System Alternatives to Reduce Larval fntrainment 

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 rather than from 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 

isolate the existing intake structure from Niantic Bay. A separate flow bypass for the nuclear 

safety-related service water pumps would also be provided. 

An offshore intake would require substantial environmental reviews and significant input from 

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 $1 17 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 limited to 

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 new screen structure constructed in front of the existing intake and connected to 

it by sheet pile walls would be needed to support the new screens. The new screen structure 

plan dimensions would be approximately 270 feet long by 40 feet wide. A separate safetyrelated bypass would be required for service water. Alternate fine-mesh screen arrangements, 

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 51 6.W5 

1 

L/ 

I 
Millstone Units 1,’2, and 3 

resulted in only a 6.5 percent survival of winter flounder larvae. These screens were 

subsequently removed from operation. There are also significant concerns over the ability of 

fine-mesh screens to control 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 natural cross currents to sweep fish and larvae past the submerged 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 up from collector conduits placed in the sea floor. Six 9-ft 

diameter collector conduits, each equipped with nine 84-inch diameter screen units, would 

extend out from a plenum structure that would be constructed directly in front of the existing 

intake structure. The array would be staggered to promote more effective natural flushing of 

screen units. An automated air burst system would be required to backflush the screens, one 

unit at a time. An alternate bulkhead design was also developed consisting of two circular 

bulkhead structures containing the wedgewire screen units that would be constructed in front 

of the existing intake and joined to it by a plenum and inlet conduits. The bulkhead 

arrangement would offer the advantage of being able to hoist the screen units to an operating 

deck for cleaning. 

Wedgewire screen technology offers some advantage in limiting impingement and entrainment 

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 larvae would probably not be significantly protected using the screen slot sizes 

that would be required at MNPS. 

- 

The total estimated cost for this option is $65 million. 

DIVERSION SILLS/CURTAIN WALLS 

While there are no known installations of barriers or sills for the purpose of diverting fish 

larvae away from intake structures, hydraulic diversions are commonly used and the principles 

well-understood. Diversion sills and curtain walls can possibly divert a portion of winter 

flounder larvae away from the intakes. Concrete sills, such as Jersey-type barriers, would be 

01 51 6.WP5 ES-5 
a 

L 

Cooling Water System Alternatives to Reduce Larval Entrainment 

placed on the sea floor in front 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 required to 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 into the 

sea floor. The floatation system would consist of multiple diffuser pipes installed on the sea 

floor in front of the floating barrier. Compressed air would be supplied to these diffuser pipes 

by blowers that would be located on the shore. Larvae would be "floated" to the surface by 

the rising air bubble curtain. They could then be diverted away from the intake by the floating 

curtain wall. 

Because winter flounder larvae are planktonic, particularly at night when most entrainment 

occurs, it is unlikely that 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 

bubble curtain wall is unproven technology in preventing larval fish entrainment. It should be 

noted that these options would require significant additional study and modeling to validate 

the degree of effectiveness. 

The total estimated cost for the concrete sill option is $1.8 million. 

INFILTRATION SYSTEM/BEHAVIOR BARRIERS 

Infiltration systems consist of arrays of perforated pipes installed in aquifers. Water enters 

the piping array by percolating through 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. Infiltration systems have not been used on large flows at the MNPS intakes, and 

clogging and maintenance are common problems when a silty overlay forms on the sea 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 circulating water pumps during power generation or by the installation of variable-speed 

irculating water pumps. With the present plant design, power reduction does not result in 

ES-6 0 1 5 1 6.W5 
Millstone 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 

reduction achieved through the operation of fewer pumps is possible but not practical because 

it jeopardizes 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 increased tube fouling and potentially result in an outage. A small 

reduction in power would also be likely. 

Refueling outages scheduled for each spring could reduce entrainment 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 preclude a guaranteed refueling 

outage each and every spring. A forced outage each spring is possible but extremely 

expensive. 

The estimated costs associated with forced spring outages range from $21 4 to $51 9 million. 

The total estimated cost for conversion to variable-speed circulating water pumps is 

REPLENISHMENT OF WINTER FLOUNDER 

Several programs established in the United States and Japan to culture flatfishes were found 

to have had limited or no success. No evidence 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 

expensive elsewhere along the Connecticut coast. Food and nutritional requirements, predator 

and disease control, water quality, genetic issues, production costs, and a means to ascertain 

success of stocking remain uncertain. A conceptual engineering design for a fish hatchery 

was not developed or cost estimated due to the 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 
1' 

dr 

Ii 

f 

8 

0 

v) 

E 

.- 

+- 

0 

E 

m 

v) 

v) 

0 

0 

E 

c, 

a 

0 

C 

m 

E 

0) 

C 

c, 

.- 

E 

U 

C 

m 

C 

.- 0 

4- 

E 

n 

0 

- 

m 

3 

0 

m 

c 

m 

CI 

5 

v) 

v) 

W 

> 

c 

m 

V 

Lc 

C 

cp 

v) 

0) 

m 

3 

0 

0 

- 

- 

CI 

.- 

.- 

0 

4- f 

m 

C 

m 

3 

P 

0, 

0 

C 

0 

0 

W 

0 

W 

3 

U 

D 

C 

0 

4- v) 

v) 

0 

0 

W 

> 

CI 

m 

W 

O 

C 

0 

v) 

m 

- 

c, 

L .- 

5 

4- 

.- 

- 

L 

Y- 

.- 

L 

E" 

0 

0 

0 

L- 

+ 

2 

m 

v) 

+- W 

.- E 

c, 

v) 

4) 

$4 0)z 

so I-0 

4 

?-+ 

L 
Miktone Units I; 2, and 3 

TABLE ES-2 

FORCED OUTAGE COST ESTIMATE FOR 

25 PERCENT ENTRAINMENT MITIGATION 

# 

Scenario 

Unit 1 offline 4/2 to 6/13 

Unit 2 offline 4/2 to 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 to full output for each 

scenario. 

2. Some years had no replacement power cost because a 

scheduled refueling overlaps the time period. 

3. Costs estimated from 1993 through 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 13 percent. 

ASSESSMENT OF THE EFFECTIVENESS OF MITIGATION ALTERNATIVES 

The long-term effects of MNPS operation on the Niantic River winter flounder population have 

been addressed using the SPDM. This numerical model has been used to approximate the 

decrease in abundance or biomass of the Niantic River female spawning stock and its eventual 

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 model simulations showed that proposed reductions in fishing would be of much greater 

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 

01 51 6.W5 ES-9 
Coofing Water System Alternatives to Reduce Larval Entrainment 

represent a modest (5 4.3 percent) gain in the 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 commercial winter 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 used to examine the probability that the stock could fall to 

less than 25 percent of the maximum spawning biomass (a critical fisheries 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 

attributable to 25 percent mitigation (0 Ib for the first 3 years followed by 626 Ib average 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 MNPS entrainment of Niantic River winter flounder larvae. Known mitigation methods were 

reviewed and some new ideas were evaluated. Some of the alternatives are not technically 

feasible le.g., infiltration systems) 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 to construct 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 indicate that the planned reduction in 

fishing would be the primary factor responsible for increases in the Niantic River winter female 

flounder spawning stock, rather than concurrent entrainment mitigation. 

There have been no technological or operational strategies that have significantly advanced 

cooling-water intake designs since the extensive reviews performed in the NUSCO Final Safety 

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 01 51 6.WP5 

E 
f 

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, CT0003263 renewal application was submitted in 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 times to discuss 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 renewed with 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 the feasibility of reducing entrainment of winter flounder 

larvae at Millstone Nuclear Power Station should investigate several 

alternatives. The study should review intake structure alternatives including 

screening devices and physical barriers such as sills, baffles, and curtain walls. 

01 51 6.W5 1-1 
Cooling Water System Alternatives to Reduce Larval Entrainment 

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 

Delta T and Maximum Delta T), reduced power generation, and the scheduling 

of maintenance shutdowns. Each alternative should be reviewed with regard 

to technological feasibility, effectiveness, and costs. 

SCOPE OF WORK 

As a result, a project assignment was initiated and funded 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 measures for minimizing entrainment of fish larvae are included 

in the review: 

0 Those designed to reduce the volume of cooling water required for the station. 

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 detailed evaluation. 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 civil engineering designs for all major structures, sized major mechanical equipment 

and piping, and developed preliminary designs for electric power and control equipment. From 

these designs, quantity estimates were taken and preliminary order of magnitude cost 

estimates developed. Operation and maintenance costs associated with the alternatives 

discussed in this study could 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 

assessed using the NUSCO stochastic population dynamics model. The estimation or 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 

biomass for various reductions in entrainment mortality. The cumulative gains in biomass over 

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 0151 6.W5 
PART I 

ENGINEERING EVALUATION 

0 1 5 1 6.WP5 PART 1 
TABLE OF CONTENTS . PARTI 

Section Paae 

PART I . ENGINEERING EVALUATION 

PRESENT INTAKE DESIGN AND OPERATION ....................... 1-1 

2 OVERVIEW AND 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 DESIGN AND 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 COOLING TOWERS ....................... 3-4 

3.2.1 FULL-SIZE COOLING TOWER 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 

01 51 6.W5 i PART I 
Cooling Water System Alternatives to Reduce Larval Entrainment 

TABLE OF CONTENTS (Cont) 

Section . Title 

PART I 

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 Offshore Twin 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 STAGGERED ARRAY 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 01 51 6.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 CONSTRUCTION SCHEDULE ................ 4-1 

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

4.2 SPECIAL EXCAVATION COST CONSIDERATIONS .............. 4-10 

4.2.1 NATURAL-DRAFT COOLING TOWER EXCAVATION COSTS . . 4-10 

4.2.2 OFFSHORE INTAKE COSTS ......................... 4-10 

4.2.2.1 Tunnel Excavation AssumptionsKosts .......... 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 DESIGN ALTERNATIVES ....................... A-i 

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

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

01 51 6.W5 iii PART I 
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 

01 51 6.WP5 V PART I 
Cooling 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 01 51 6.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 

01 51 6.WP5 vii PART I 
7 

PRESENT INTAKE DESIGN AND 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 its own separate 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 heated water is discharged into the quarry and ultimately into Twotree 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 to the circulating 

water as it passes through the condenser tubes. In the 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. In the event of an accident, such as a loss of primary coolant in the reactor 

(LOCA), service water is diverted to the containment recirculation coolers to remove heat from 

the reactor and the emergency generator diesel engine coolers. 

01516.WP5 1-1 PART I 
Cooling Water System Alternatives tu Reduce Larval Entrainment 

-3 

PART I 

Figure 1-1 Intake and Discharge Facilities for Millstone Units 1, 2, and 3 

1-2 0 1 5 1 6.WP5 
Millstone 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 

screens with 3/’-inch (9.5 mm) mesh, coarse-bar racks, and curtain walls which extend below 

lowest water level. The coarse-bar rack excludes debris and fish larger than 2-inch in size and 

the mesh size of Ya-inch prevents smaller fish and debris from entering the pump forebay. 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 traveling screens to allow fish to escape the screen faces. A typical intake section, 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 01 51 6.W5 
Cooling Water System Alternatives to Reduce Larval 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 rated at 10,000 gpm (22.3 cfs). Normal service 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 in the 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 cooling water 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 a total circulating water flow of 91 2,000 gpm (2,030 cfs). The intake also 

contains four service water pumps, each rated at 15,000 gpm. Normal service 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 

MILLSTONE NUCLEAR 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 

01 51 6.WP5 

.1 

x 

r 

I 
2 

OVERVIEW AND PRELIMINARY 

ASSESSMENT OF A 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 useful to provide an information update, 

especially in regard to fish 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 research that is pertinent 

to MNPS was conducted from the late 1960s to the early 1980s and focused on the biological 

effectiveness and engineering practicability of screening systems for use at steam electric 

stations. In the early 1980s, the design and construction of new steam electric plants in this 

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. 

Most fish protection systems in use today are designed primarily to protect juvenile 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) 

01 51 6.WP5 2- 1 PART I 
cr) Cooling Water System Alternatives to Reduce 1 arvai Entrainment 

There are several types of mitigation measures for minimizing the entrainment of fish larvae 

at cooling-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 floatation systems 

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 system design and 

behavioral barriers were 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 in the aquifer below or adjacent to a water body. The collector conduit system then 

conveys the water to a common collector chamber where the filtered water can be pumped 

to cooling systems. The system utilizes the filtering action of the bottom soil or an engineered 

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 the field of collector pipes can be used to increase permeabilities 

thereby allow for higher flow rates. 

PART I 2-2 01516.WP5 

a 
2 

1 

3 Millstone Units 1,*2, and 3 

.Two companies specializing in the design and construction of infiltration-type intake system, 

were consulted regarding the application of an infiltration-type water collection system 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 reviewing the 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 

limitation to application at MNPS is the very high flow capacity. The typical 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 

installed around an inland lake to develop a municipal water supply (approximately maximum 

system capacity 80,OO gpm); based on this data, approximately 500 wells 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 1000 to 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 need to be properly spaced, resulting in large seafront property requirements. 

I 

M&S Systems International Ltd presented a design similar in concept to the 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 collection system would supply cooling water to a single pumping facility. A 

review of the M&S filter media concept indicated that this system could be subject to clogging 

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 infiltration systems. 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 to the same clogging and maintenance problems. Also, 

there is no experience in the United States with the M&S system. 

01 51 6.WP5 2-3 PART I 
Cooling Water System Alternatives 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 larval fish 

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 

eliminated from further consideration as potential measures for reducing entrainment 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 with the exception of infiltration systems 

and behavioral barriers have potential for mitigating entrainment of winter flounder larvae at 

MNPS. Preliminary designs for the following alternative measures are 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 51 6.W5 
3 

ENGINEERING DESCRIPTION OF SELECTED 

MITIGA TION DESIGNS 

In this 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. 

Elimination or reduction of larval entrainment into the Unit 3 intake would produce a reduction 

in station entrainment. The selected designs offer the potential for a reduction in entrainment 

of winter flounder larvae. The designs were developed to a level of detail adequate to develop 

order of magnitude cost estimates. 

Previous studies evaluating cooling towers at Unit 3 were done during the initial licensing 

work for the station in the early 1970s and 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) to be used for 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 

design for the proposed offshore intake system for Unit 3. The most current U.S. and foreign 

design criteria were used to develop preliminary designs for fine-mesh screens, wedgewire 

screens, and diversion sills and curtain walls. 

In all cases the nuclear safety-related service water system operation would remain the same. 

The service water pumps would remain in the existing Unit 3 intake structure and function as 

they currently do. In the cases of the offshore intake, fine-mesh screens and wedgewire 

screens, where the existing intake would be enclosed by a forebay, a separate nuclear safetyrelated water passageway would be required. This passage system would consist of a 

combination of an automatic safety-related valve or gate system and collapsible panels. The 

actual design and cost estimate for these systems were not included in the report. 

01 51 6.W5 3- 1 PART 1 
Coaling 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 to Nuclear 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 by glacial deposits consisting of basal till, ablation till, stream deposits, beach 

sands and artificial fill. All major Unit 3 structures, ducts and pipelines were founded on basal 

till or bedrock and no unusual conditions were encountered during excavation or construction. 

It should be noted that the variable nature of the top of rock surface does not allow for an 

accurate prediction of overburden thicknesses elsewhere at 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 in the 

vicinity of the intakes. Both rock types are hard, dense, crystalline rocks that are mostly 

unweathered, except in the vicinity of fault zones, and serve as excellent foundation materials. 

The determined allowable bearing capacity for these rock types is 200 ksf (kips per square 

foot) (FSAR Table 2.5.4-23). According to the site bedrock map (FSAR Figure 2.5.1-1 31, the 

Monson gneiss extends offshore into Niantic Bay, where it contacts the Brimfield Formation. ' 

This rock is a garnet-mica schist and gneiss and is expected to have physical properties similar 

to the 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 (22 feet) and drops to -32 feet at the Unit 3 intake. Site grade is 

24 feet and rises gradually to the north of the Unit 3 structures to 30 feet. It is expected 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 (0 to -1 80 feet). 

PART I 3-2 01 51 6.W5 
-- 

Millstone Units 1;2, and 3 

The bedrock surface is overlain by a dense basal till of variable thickness (5 to 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 its shear 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 ablation till; stream deposits, which are found mainly 

on the 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 materials were removed until basal till or bedrock was 

exposed. The same general procedure is assumed for foundation of the structures addressed 

in this estimate. Previous excavations indicate the basal till can maintain a 1 H: 1 V slope while 

the overlying looser soils require a 2H: 1 V slope for stability purposes. Analysis of Unit 3 soils 

indicates that liquefaction is not a concern. However, a re-evaluation will be required if there 

are any major modifications to the shore front slopes and channels in the vicinity 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 can form unfavorable geometries singularly or in combination when they 

intersect an excavation. The foliation at the site is uniform and the average orientation is 

N67W/48NE. The jointing (fracturing) of the rock is well 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 the joint 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. 

Eleven fault zones were uncovered during mapping as shown in FSAR (l) Figure 2.5.1 -1 8 and 

more can be anticipated during future excavation. The fault zones generally trend northsouth, are nearly vertical, and can produce fragmented and crushed zones a few feet in width 

adjacent to the fault plane. Although faults did not pose significant 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 at elevation 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 

restricted to the more pervious materials overlying the till. Hydraulic conductivity for granite 

01 51 6.WP5 3-3 PART I 
Cooling Water System Alternatives 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. Pressure tests in the site rock indicate permeabilities are 

extremely low. 

construction. 

This was confirmed by the lack of infiltration during excavation and 

3.2 NATURAL-DRAFT COOLING TOWERS 

Two cooling tower alternatives were addressed including a full-size natural-draft cooling tower 

with accompanying closed-loop circulating water systems for Unit 3 and a similar but smaller 

natural-draft cooling tower system for Unit 3 designed to reject Y3 of the unit waste heat to 

the atmosphere. The objective of these cooling tower alternatives was to reduce flounder 

larval entrainment by reducing station saltwater withdrawal rate from Niantic Bay. These two 

cooling tower alternatives were selected to provide representative current capital cost 

estimates, unit performance impacts, and construction schedules for converting Unit 3 wholly 

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. 

Both cooling tower system designs would allow either full-time or part-time operation with the 

existing once-through cooling systems remaining intact and operational. Performance impacts 

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 COOLING TOWER SYSTEM 

\ 

c 

4 

IE; 

I 

P 

t 

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

for Unit 3 to a closed-loop system utilizing a natural-draft saltwater cooling tower. The heat 

rejected by condensing steam would be rejected to 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 Bay to approximately K of its current volume. The current flow 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.WP5 
Millstone Units I; 2, and 3 

from Niantic Bay is 4373 cfs. The cooling tower would reduce the required Unit 3 circulating 

water flow withdrawal from 2030 cfs to 90 cfs for cooling tower makeup resulting in a total 

station withdrawal of about 2430 cfs. This would be a 44 percent reduction. This reduction 

in station flow withdrawal from Niantic Bay would result in a corresponding reduction in the 

number of winter flounder larvae entrained. 

Both natural-draft and mechanical-draft cooling tower configurations for Unit 3 were evaluated 

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 

the total cost for mechanical-draft and natural-draft cooling tower systems were similar. The 

natural-draft cooling tower was selected for this study to develop current representative costs 

for conversion of the Unit 3 circulating water system from once-through to closed-loop. The 

advantage of the natural-draft cooling tower is that .it eliminates the power requirements for 

fan operation. 

The natural-draft saltwater cooling tower alternative would consist of the tower located in the 

wooded area to the east of the switchyard as shown on 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 necessary to maintain high condenser tube 

velocities for efficient heat transfer with the reduced circulating water flow rate in the 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 and to the cooling tower would be routed to the north and west of the 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 at the 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 to the quarry. 

3.2.1 .I Natural-Draft Cooling Tower 

The natural-draft saltwater cooling tower for Unit 3 would be designed to operate 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 mass would 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 in thickness. A system of 

channels, pipes, and spray headers would distribute the circulating water 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 the design. 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 parameters for the cooling tower are as follows: 

Circulating Water Flow 

Cooling Range 

Approach Temperature 

Wet Bulb Temperature 

Dry Bulb Temperature 

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 1970s when cooling towers were 

originally evaluated for Unit 3. At that time, 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 

to 0.002 percent of the circulating water flow. The original conclusion on the affects of salt 

drift from a natural-draft cooling tower for Unit 3 by the United States Atomic Energy 

Commission was that naturally occurring levels of salt drift from Long Island Sound 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 01 51 6.WP5 
i 

,a 
0 Millstone Units 1;2, and 3 

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 makeup water flow to the cooling tower to maintain the 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 into the 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 into the 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. 

Blowdown would be discharged from the cooling tower basin at an overflow weir structure 

that would be located on the cooling tower discharge flume. The discharged blowdown would 

be carried by gravity to the quarry by a 60-inch line buried in a cut and cover trench. 

Blowdown piping would be routed to the existing discharge flume at the quarry. Blowdown 

flow would range from 27,000 to 40,000 gpm. 

3.2.1.2 Closed-Loop Circulating Water System 

The circulating water system for the cooling tower would consist of a pump station containing 

six circulating water pumps and motors located at the cooling tower 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 is to the 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 100 feet, The head would include friction losses 

in conduit; losses in the two-pass condenser; form losses at bends, fittings, and junctions; and 

an estimated 45-foot static lift to the 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. 

0151 6.WP5 3-9 PART I 
Cooling Water System Alternatives to Reduce Larval Entrainment 

The six circulating water pump discharges would be manifolded into a single 14-foot diameter 

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 at the manifolded junction would consist of three 84-inch motor-operated 

butterfly valves in the three inlet lines from the cooling tower. These valves, in conjunction 

with the existing pump discharge valves and condenser valves, would allow operation of the 

system either on the cooling tower or once-through. Water would make two passes through 

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 

to the cooling tower, Pipe material selected for the circulating 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 in saltwater. Carbon steel pipe would 

not be considered suitable in saltwater service due to high corrosion rates. 

Electric power for the new circulating water pumps at the 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 be taken from buses 34A and 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 in the cooling tower pumphouse, the two 

new 750 horsepower makeup pumps which would be located in the existing circulating and 

service water pumphouse, and a new double-ended 480-V load center would be located in the 

cooling tower pumphouse. The addition of the breakers to bus 348 would impair access to 

the switchgear room. It has been assumed that 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 

is considered preliminary and only conceptual in nature. Existing electrical loads and location 

of utilities could have a significant impact on the conceptual design. 

PART I 3-1 0 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 makeup water 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 summer months. 

The existing circulating water pumps are 1,500 horsepower pumps which draw a total of 

I 

I 

i 

El 

6,700 kW of electric energy. The closed-loop circulating water system would require six new 

circulating water pumps, each rated at 3,300 horsepower, and two makeup water pumps, 

each rated at 750 horsepower. Normally, all six circulating water pumps and one of the two 

makeup water pumps would operate continuously. This would result in a net increase in 

pumping energy consumption of 8,600 kW. 

The annual average net loss to Unit 3 performance resulting from the 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 the months of April and May when flounder larval activity’is greatest would 

result in reductions to unit performance of 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. The performance penalty associated with this outage was not 

included in the estimated cost. 

3.2.2 TWO-THIRDS SIZE COOLING TOWER 

This alternative is similar to the full-size cooling tower except that four of the six condenser 

paths would be converted to a closed-loop system integrated with the natural-draft cooling 

tower, and the remaining two condenser paths would remain once-through. The objective of 

this alternative is to provide a reduction to station intake fiow from Niantic Bay, at a reduced 

capital cost and reduced performance penalty, as compared to the 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. 

0151 6.WP5 3-1 1 PART I 
Cooling Water System Alternatives 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, 

as with the full-size system, circulating water would enter and exit the condenser on the 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 pumps would be installed in the circulating 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 tower sized to reject 2/3 of the Unit 3 heat load would be approximately 

400 feet in diameter at the base and approximately 460 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 Fact or 

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 

the full-size tower. (Refer to the discussion of salt drift in Section 3.2.1.1 .) Required makeup 

flow to the %-size cooling tower to maintain a concentration factor in the closed-loop 

circulating water system at -1.5 or less would be 27,000 gpm (60 cis), Makeup water pumps 

would be rated at 27,000 gpm at 55-foot head. Horsepower requirements for the makeup 

pump would be 480 horsepower. Two full-size pumps would be required. A 36-inch diameter 

makeup water line would be required. 

Blowdown would be discharged from the cooling tower basin at an overflow weir structure 

located on the cooling tower discharge flume. The discharged blowdown would be discharged 

by gravity to the quarry by a 48-inch line buried in a cut and cover trench. Blowdown piping 

would be routed to the existing Unit 3 discharge flume at the quarry. Blowdown flow would 

range from 18,000 to 27,000 gpm. 

PART I 3-1 2 0 15 16.WP5 
1 I! ri 

- -._- -IJ._c .. . .- ___ 

ga NORTH 

W 
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 to that 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 (936 cfs). 

These four circulating water pumps would discharge to a single 12-foot diameter pipe. Both 

supply and return circulating water lines would be routed to the north and to the 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 1 2-foot x '-/-foot two-pipe 

manifolds would be required on the west side of the condenser to make the connection 

between the new 1 2-foot diameter cooling tower supply, return lines, and the existing piping. 

The two northerly condenser waterboxes would be converted to the closed-loop system. The 

two manifolded 84-inch inlet lines from the cooling tower would have motor-operated valves 

installed. These valves, in conjunction with the existing pump discharge valves and condenser 

valves, would allow operation of the system either on the cooling tower or 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 

pumps located in the cooling tower pumphouse, the two new 600 horsepower makeup pumps 

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 

breakers to bus 34B would impair access to the 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 to the cooling tower. The ductline would follow the same route as the new cooling 

tower circulating water inlet and discharge lines. 

01516.WP5 3-1 5 PART I 
Cooling 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 if the cooling tower were operating. In addition to 

the higher horsepower circulating water pumps, two 480-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 an outage. The performance penalty associated with this outage was not 

included in the estimated cost. 

3.2.3 G EOTEC H N ICAL CONS ID ERATlO NS 

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 

largely fiat due to modifications by construction activities and generally ranges from 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 Steam Generator Replacement Project. These borings suggest that top of rock 

elevation is variable, ranging from 15 to 24 feet above mean sea level in that area. A few 

feet of fill materia! was found at the surface and denser glacial till overlies the rock which 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 3-1 6 0151 6.WP5 

1 

a 

i p 
Millstone 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 50 to 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 be considerable difficulty in coordinating the required activities in excavating 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 to the 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 rock tunnel, and 

a booster pump station that 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 place the Unit 3 intake south into Long Island Sound past the confines of Niantic Bay such 

that significant numbers of Niantic River flounder larvae would not be entrained in the 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 (2134 cfs) 

which is 5 percent greater than the present design flow of the Unit 3 circulating water system 

(91 2,000 gpm). The inlet velocity cap structure would be sized for an inlet velocity of 0.5 fps 

to minimize fish entrainment. The offshore conduit would be sized for a flow velocity 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 in the tunnel and 

risers, would be approximately 5 feet. The onshore booster pump facility would be designed 

01 51 6.WP5 3-1 7 PART I 
c 

Cooling Water System Alternatives to Reduce Larval Entrainment 

to provide pumping head to compensate for head losses in the offshore intake. The booster 

pumps would be sized to pump a minimum of 5 percent excess flow into a new forebay that 

would lead to the existing Unit 3 intake. An excess flow would be provided to prevent 

surging between the two in-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 in the form of mussels and other marine 

organisms could become severe and difficult to control. A chlorination system which 

introduces chlorine at the 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 the tunnel, shafts and offshore inlet. This chlorination would kill flounder larvae. 

A dechlorination system would also be required for the circulating water discharge. The cost 

of these systems was not addressed. 

3.3.2 G EOTECHNICAL CONS ID ERATlO NS 

In the absence of borings along the proposed tunnel alignment and offshore intake, the 

geology was inferred from the nearshore boring, seismic refraction surveys, 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 01 51 6.WP5 

-w 
'I ' 

4 

8 

NORTH 

'+ .. 

I U I I I I 0 m ,o rn 
Cooling Water System Alternatives to Reduce Larval Entrainment 

The cut and cover conduit approach would be given further evaluation to include geotechnical 

investigations of sea floor subsurface conditions along the proposed route prior to any final 

design. 

3.3.2.2 Subsurface Tunnel 

The subsurface tunnel scheme would require a vertical shaft near the Unit 3 intake structure, 

sunk to a depth of approximately 300 feet below low mean sea-level. The shaft must be sunk 

30 to 50 feet deeper than the 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 (24 feet inside 

lined diameter) would be initiated from the shaft and excavated entirely in rock. The tunnel 

would be sloped down from the offshore intake structure 1 percent towards the 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 

caisson grouted in-place on the sea floor bottom. Water would be pumped out 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 muck from 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 lay down area at the surface 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 section could adversely impact tunnel 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 01 51 6.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 at the rock/soiI interface and from 

open joints in weathered rock below the interface. Therefore, pre-grouting would probably 

be necessary to reduce inflow rates at the interface and 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 TBM advancement rates are faster, this method would require a TBM erection 

chamber at both the head and tail 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 rock elevation data, the proposed tunnel elevation at the near shore 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. Thus the formation of unstable wedges as the tunnel face advances, prior to liner 

installation, would be likely. To prevent eccentric loading of the final tunnel liner due to 

unstable rock wedges and to provide 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 above the tunnel 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 rock tunnel alternative was 

selected to develop preliminary cost and schedule estimates for the offshore intake alternative. 

The proposed tunnel design is shown on Figure 3-3. 

0 151 6.WP5 3-23 PART I 
Cooling Water System Alternatives to Reduce L awal 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 be to 

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 hexagonal velocity cap structure supported on the sea 

floor by a tremie concrete mat centered 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 at a sill located 3 feet off the 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. (on center). 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 losses were 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 

necessary to include a booster pump station at the onshore end of the offshore 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 by 52 feet long with an 

c 

- 

invert elevation of 28 feet. The pumps were sized to draw water from an elevation 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 building which would enclose the pumps, motors, electrical equipment and controls. 

The pump structure would be joined upstream by a transition structure constructed over the 

PART I 3-24 01 51 8.WP5 
Millstone Units f,.2, and 3 

24-foot diameter riser shaft from the tunnel. This transition structure would contain a 

submerged weir to spread inflowing water evenly to the four pump bays. The pump structure 

and transition structure are shown on Figure 3-3. 

The transition structure connecting the vertical tunnel riser shaft to the booster pump station 

would also serve as a surge chamber. The chamber would not be covered and the top of the 

walls and would serve as an emergency spillway in the event of surge. 

The existing Unit 3 intake structure would be joined to the 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 the top of these sheet pile walls would be designed to function as 

overflow weirs to discharge the excess flow pumped by the booster pumps into Niantic Bay. 

A 12 foot 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. Because the service water system is 

nuclear safety related, the design would be nuclear safety-related Category I and would be 

subject to Nuclear Regulatory Commission review and approval. This area was not addressed 

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 assumed that 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 

stated that 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 to the existing 

circulating service water pumphouse. A detailed electrical design was not performed and the 

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 

01 51 6.WP5 3-25 PART I 
Cooling 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 constructed for the Seabrook Nuclear Power Station located 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 Seabrook tunnels is 850,000 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 to the coastal environment (4). 

Geological conditions at Seabrook necessitated deep rock tunnels. Vertical shafts were used 

on both ends of the tunnels to connect the offshore water ports and the plant cooling-water 

systems. At land's end, the tunnels are 260 feet below sea level and 180 feet below sea 

level at the 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 19 feet. Rock bolts were used as 

necessary along the top of each tunnei. 

The Seabrook intake tunnel terminates on the seaward end with three 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 design to that 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 to the 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 Beach shoreline. 

The Seabrook tunnel construction was accomplished by means of two tunnel boring machines 

operating concurrently. Offshore construction was done using a jack-up barge. Offshore 

vertical shafts were drilled and prefabricated steel shaft liners installed from the jack 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 0 15 16.WP5 
Millstone 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-mesh traveling water screen systems, 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 .O millimeter screen 

mesh, 260,000 gallons per minute with angled screens (salt water, but with 

much lower levels of total suspended 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 millimeter screen mesh, 630,000 gallons per minute (Mississippi River, 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, New York 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 mesh tested on the Hudson River 

01 51 6.WP5 3-27 PART I 
. --. c.” 

Cooling Water System Alternatives to Reduce Lari/al Entrainment 

3.4.2 ADVANTAGES AND DISADVANTAGES OF 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, but would defeat the purpose of the fine-mesh screen concept because the chlorine 

could kill larvae. It could also result in existing NPDES permit violation. Periodic inspections 

would be necessary to maintain the screens, and the 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-mesh screens. Debris handling systems would include a large capacity sluicing system 

similar to the 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 to the 

incoming flow to divert 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 0151 6.WP5 
Millstone Units 1; .2, and 3 

3.4.3.1 Through-Flow Fine-Mesh Screens 

The existing through-flow traveling screens cannot be replaced by continuously operating finemesh screens. The original screens at Unit 3 had a 3/16-inch (5 mm) opening. The clogging 

potential of the 3/16-inch opening resulted in numerous plant outages and screen failures. 

The screen openings were increased to YE inch (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. Because the effective performance of fine-mesh screens is sensitive 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 to the fine-mesh screens. 

3.4.3.2 Dual-FlowEenter-Flow Fine-Mesh Screens 

The vertical dual-flow traveling screen is similar in mechanism to the through-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 two faces. The primary advantage of this screen configuration is the 

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 been shown to produce low survival rates for fish larvae, which is the 

principal problem at the MNPS intakes. The longer impingement time for organisms impinged 

on the descending fence of the screen may result in higher mortality rates. For these reasons, 

the dual-flow fine-mesh screen configuration was eliminated from further consideration. 

The centerflow screen configuration is a European design and is similar in configuration to the 

dual-flow screens except the flow path is reversed. Flow would enter the centerflow screen 

at a key hole and pass into the screen between the screen faces and out through the screen 

faces. The flow velocity entering the key hole between the screen faces of the centerflow 

screen is usually high. which is a disadvantage from a fish protection standpoint (5). Because 

of the disadvantages in terms of potential survival of entrained. and impinged flounder larvae, 

the centerflow fine-mesh screen configuration was eliminated from further consideration. 

01 51 6.WP5 3-29 PART I 
Cooling 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 at an angle of approximately 25 degrees to the incoming flow. The normal 

through-flow screen arrangement, as discussed earlier in this section, would place the 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. Fish would not be lifted out of the water but would be diverted back to the 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 Lake Ontario (a), and were tested at Central 

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 to the 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 its axis normal to the incom-ing flow 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 into the screen at semicircular 

openings on either side of the screen chamber. The water would be screened by passing 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 0151 6.WP5 
0 Millstone Units 1; 2, and 3 

The nature of the overburden cannot be determined from the seismic velocity data. It was 

assumed that a dense basal till of varying thickness overlies the bedrock and 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 1 O4 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 cut and cover scheme would involve the fabrication of two parallel pipes, approximately 

12 feet I.D. each, that would be placed in a single common trench. A 5,000-foot long trench 

would be dredged at a constant elevation from the intake structure to the offshore intake port. 

The trench would be excavated to a depth of approximately 15 feet (3 feet deeper than the 

tunnel heights), 26 feet wide tat the bottom), and covered with a protective gravel cover after 

the pipes were placed. Due to the thin nature of overburden in some areas, it was estimated 

that 10 to 15 percent of the trench 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 

tunnel would appear less challenging from a technical point of view than subsurface tunneling, 

the environmental impact during construction must be weighed in considering this scheme. , 

0 151 6.WP5 3-2 1 PART I 
i 

D 
Millstone 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 to through-flow screens. 

Six 10-meter diameter by 4-meter width (32.8 feet by 13.1 feet) drum screen units would be 

required to screen the full design flow to the 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. Deck and channel inlet elevations would be the same as for 

the through-flow screen design. The screened water collection chamber would have to extend 

about 10 feet deeper under the screen to a depth of about -39 feet. The top of the rock is 

at about -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 of the drum screen in handling flounder larvae and returning them to Niantic Bay 

alive. 

3.4.4 REQUIRED TESTING 

Full-scale prototype testing would be required to determine impingement and entrainment 

rates and the related mortality rates for the fine-mesh traveling screens. The debris removal 

capability of fine-mesh traveling screens would require testing 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 FACILITY FOR UNIT 3 

For the reasons noted above, replacing the existing %-inch opening screens with fine-mesh 

screens, is not a reliable technology for MNPS. Further, it is possible fine-mesh screens might 

cause as much mortality by increased impingement as they saved in entrainment. 

0151 6.WP5 3-33 PART I 
Cooling 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 new through-flow screen structure for Unit 3 in front 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 larvae from entering the circulating water system and to safely transport impinged larvae 

back to Niantic Bay. The stage 3 larvae, which are most susceptible to entrainment into the 

MNPS intakes, are from 4.5 to 7.5 mm in length. The existing seasonal heavy trash loading 

at the MNPS intakes of eelgrass and kelp would 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 May time 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 and the related mortality rates for winter flounder larvae is required before 

committing to this technology. Also the reliability of fine-mesh screen operation in the 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 

to fine-mesh screen 0.5 fps 

Screen unit width . IO feet 

14 feet 6 inches 

-28 feet 0 inches 

912,000 gpm (2032 cfs) 

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 because experience has shown that 

wider screen widths tend to result in less reliable operation 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 to the traveling 

screen. A 20 percent unscreenable area was assumed to account for the screen boot area 

.- 

d 

structural metal frame area between screen mesh. Flow velocity calculations were made 

PART I 3-34 01516.WP5 
Millstone 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 screen structure would be 40 feet wide by 276 feet long. It would include both upstream 

and downstream curtain walls extending down to a depth of -5 feet 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 finemesh traveling 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 

HVAC for enclosure structure 

Control equipment 

Electric supply equipment 

The fine-mesh screen structure would be joined to the existing Unit 3 intake by double sheet 

pile walls with tremie concrete placed between the sheet pile. Each wall would have a 

12 foot by 30 foot bypass gate. These bypass gates would be sized to bypass ?4 of the total 

design flow to the 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 safetyrelated service 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 used to develop 

material quantity estimates. 

01 51 6.W5 3-35 PART I 
8 

Cooling Water System Alternatives to Reduce Larval Entrainment 

3.4.6 GEOTECHNICAL CONSlDERATlONS 

The geology at the intake structure was documented by the *'P'* series boring on land and the 

"I" series boring offshore, seismic refraction and bathymetric surveys, and geological mapping 

during construction. The intake structure is founded directly on bedrock which was excavated 

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 by several 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. Immediately adjacent to the intake, the 

seafloor bottom elevation is at about -28 feet according to soundings taken in 1990 and Q slopes up seaward due to dredging modifications to about -1 6 feet. 

No field permeability tests were conducted in any of the 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 is approximately 1 O4 cm/sec for the silty sands comprising the seafloor 

bottom. 

3.5 WEDGEWIRE SCREENS 

Wedgewire screens are passive and utilize "V" or wedge-shaped cross-section wire, welded 

to a framing system to form a slotted screening element as shown on Figure 3-5a. Where a 

relatively high velocity ambient current cross-flow exists to carry organisms around and away 

from the screen, cylindrical wedgewire screens can reduce impingement and entrainment. 

Ambient currents providing high velocity cross-flow are also necessary to provide 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 to 0.5 to 

1 .O mm, to achieve the most effective entrainment reduction, would reduce the open area to 

about 20 percent. Thus, wedgewire screens are normally less effective at reducing 

PART I 3-3 6 01 51 6.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 I 
Cooling Water System Alternatives to Reduce Larval Entrainment 

entrainment than impingement, and in either case the effectiveness is highly dependent on the 

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 feet from shore in 35 feet of water) through 28 fixed %-inch (9.5-mm) screen units. 

Difficulties arose in the design and construction phases, but operating experience to date has 

been satisfactory and there has been no substantial clogging, biofouling, or ice damage. Such 

operating experience might be expected because of the large screen slot size and because of 

the relatively low debris loading in Michigan compared to the Niantic Bay near MNPS. Even 

so, the Campbell Plant has an alternate intake to supplement flow in case of severe blockage 

of the cylindrical screens. At the Campbell Plant's Unit 3 on Lake Michigan, the stainless 

steel screens have eliminated impingement of gizzard shad, smelt, yellow perch, alewife, and 

shiners and have required minimal maintenance. The screens are cleaned annually by water 

jets to reduce biofouling (algae) and the plant was forced to shut down once (spring 1984) 

due to anchor 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 is 440,000 gallons per minute, again only 23 percent of the flow at MNPS. The 

. 

screen slot width is also quite large, '/4 inch (6.4 mm), which would provide no significant 

entrainment benefits for Unit 3. To date, the wedgewire screen intake system has performed 

acceptably. The Eddystone screens are backflushed by compressed air. To date, the air 

backflushing has maintained the pressure drop across the screens at a constant value 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 used the 

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 0151 6.WP5 
Millstone Units 1,*2, and 3 

- 

intake in 199 1 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 in the presence nearly 1 million gpm plant withdrawal flows. Salinity is higher 

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-site testing and hydraulic modeling would be necessary to determine whether and to what 

extent the necessary high-velocity cross-flow currents exist, in order to obtain adequate 

screen cleaning action, and to determine 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 research would, in general, be needed 

to demonstrate 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, effects of silt and biofouling deposits, and material 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. 

Two alternate intake arrangements utilizing wedgewire screens were developed for application 

to Unit 3 including the staggered array and the bulkhead design. The first alternative design 

concept, called the staggered array concept would consist of six collector conduits that would 

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 in front of the existing 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 I flow passage (not shown) would be 

01 51 6.W5 3-39 PART I 
d 

Cooling Water System Alternatives to Reduce Larval Entrainment 

provided for the service water pumps. Cost estimates were developed for the staggered array 

concept. 

The second alternative wedgewire screen arrangement would be a bulkhead design. In the 

bulkhead design, the tee screen assemblies would be mounted around a 13-sided bulkhead 

structure. Two of these bulkhead structures, each having 26 tee screens, would be required 

to handle the full Unit 3 circulating water flow. Water from the bulkhead structures would 

be directed through buried conduits to a common plenum structure that would be constructed 

directly in front of the existing Unit 3 intake, similar to the 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 racks and curtain walls similar to conventional 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-by a bridge capahle of supporting small 

vehicles for maintenance. Costs were not developed for the bulkhead concept. The large 

bulkhead structures would be expected to add significantly to the cost of this alternative as 

compared to the 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 system would be sized to handle the full Unit 3 

circulating water flow of 91 2,000 gpm. The screen slot width would be selected to exclude 

the stage 3 winter flounder larvae, which are 4.5 to 7.5 mm in length. For preliminary design, 

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 in the 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 

PART 3-40 01516.WP5 I -. 

4 
Millstone 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. Because the service water system is nuclear safety related, the 

design would be nuclear safety-related Category I and would be subject to Nuclear Regulatory 

Commission review and approval. This area was not addressed in detail. 

The wedgewire screen units would be periodically backflushed with a compressed air 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 

compressed air to each individual tee screen assembly, one at a time, air-actuated valves, and 

an automatic control system. Backflushing would be accomplished by discharging the entire 

compressed air charge in the air tank to the screen assembly to be backflushed. The 

compressor would then recharge the tank to the 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 at a 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, compressed air tank, and control system would be located on 

the deck of the plenum as shown on Figure 3-5b. 

Biofouling of the 108-inch diameter conduits connecting the screen units to the 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 to control 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 

01 51 6.WP5 3-43 PART I 
Cooling Water System 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 screen system would have to be bypassed and divers employed to clear 

the blocked screen units. The bulkhead design would incorporate standard coarse-bar racks 

in front of the wedgewire screen units and a mechanical trash 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 each tee screen unit to be lifted individually from the water 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 sized to handle ?h of 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 double tee screen assemblies would be mounted on bulkheads forming a 13- 

sided structure as shown on figure 3-5b. Each tee screen assembly would be mounted in a 

set of slots which project vertically upward to the structure deck. Track-mounted davits with 

hoists would be located on the deck and could lift each screen assembly up to the 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 1 2-foot diameter inlet 

conduits would draw water from a central sump in the bulkhead structure. These unit 

conduits would pass under the bulkhead structures and terminate at a plenum in front 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 (not shown). Each bulkhead 

structure would be connected to the plenum structure or the adjacent shore by a bridge which 

would allow truck access to the bulkhead structure deck for maintenance. 

c 

* 

Each bulkhead wedgewire screening structure would have its own air burst backflush system, 

similar in design to that 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 at the intake structure was documented by the "P" series boring on land and the 

"I" series boring offshore, seismic refraction and bathymetric surveys, and geological mapping 

during construction. The intake structure is founded directly on bedrock which was excavated 

PART I 3-44 01 51 6.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 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. 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 -1 6 feet. 

No field permeability tests were conducted in any of the 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 is approximately 1 0-4 cm/sec for the silty sands comprising the seafloor 

bottom. 

3.6 DIVERSION SILLS AND CURTAIN WALLS 

Two alternative diversion system designs were developed. The first was a passive design that 

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 the tendency of flounder larvae to reside 

at or near the bottom of the bay during daylight hours. It should be noted, however, that this 

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 to scour 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 I 
Cooling Water System Alternatives to Reduce Larval Entrainment 

could potentially float the larvae. The curtain wall, arranged at an angle to the intake, would 

then divert the larvae away from 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 is a V-shaped barrier on the 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 to the incoming flow 

to the intake. Although this design is a passive system, dredging to remove silt build-up may 

be required. 

A build-up of silt, if left uncorrected, would render the sill ineffective as a diversion barrier for 

flounder larvae. To reduce this 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 more detailed analysis, hydraulic modeling and by placing the barrier 

and testing it in place. There could be considerable difficulty in attempts to quantify the 

effectiveness of this option and there are no installations which could 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 51 6.WP5 
II 4 

F 

P 

0 

I= 
I 

W T'? 

I 

E 

t . . .. .. . . . I 

@ NORTH 
b 

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 to the 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 

arrangement would be designed to create a wide curtain of bubbles that could effectively float 

the flounder larvae. This multiple air bubbler diffuser pipe arrangement has been used by the 

Swedes to float jellyfish. The air bubbler system would be located a distance in front of the 

floating barrier to allow complete floatation of the larvae in the approaching flow to the 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 

system and confirm effective performance at the MNPS intakes. This design concept, like the 

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 in the power output of the MNPS units does 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 issues which would require additional 

study are the NPDES permit restriction on differential temperature between the intake 

structure and discharge (which would be exceeded under some operating conditions) and the 

impact on backflushing capability, mussel cooks, and hypochlorite injection. 

The challenge to safety posed by purposefully operating an MNPS unit at a 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 larval activity. A two-speed drive which would operate 

the circulating water pumps either at rated flow or at %-rated flow was evaluated in this 

section. 

PART I 3-50 01 5 7 6.WP5 
Millstone Units 7; 2,' and 3 

3.7.2.1 Hydraulic and Pumping Energy Requirements for '/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 

0 1 5 1 6.WP5 3-5 1 PART I 
Cooling 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. It was decided to provide 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: For the system investigated, each drive system 

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 inches wide 

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 to this 

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, approximately 45,000 pounds, which is 20,000 pounds more than the existing motors. 

Power would still be provided to the 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 heated and ventilated building, 30 feet long x 25 feet wide x 12 feet 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 that structure. A new ductline from the existing manhole to the 

new starter building would be included. The existing cables would then be pulled and 

connected to the two-speed motor starters. Finally, new ducts from the motor starter building 

to the existing circulating and service water building with new motor feeder cables would be 

included. 

s 

T 

2. 

PART I 3-52 01516.WP5 
Millstone Units 1,. 2, and 3 ~~ ~ 

A cursory check of the existing installation indicated that the foundations were adequate. 

However, if this alternative were pursued, an extensive investigation of the foundations 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 May would result in a reduction in unit performance of 32,840 kW for 

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 have to be 

reduced to as much as % to avoid turbine trip. Because of the fouling buildup of slime in the 

tubes during %-flow operation, condenser tube cleanup could be necessary following 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 outages are generally targeted for periods of low electrical demand and, 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. Factors that could influence the actual versus scheduled outage include safety, 

duration of a previous outage, equipment malfunction or failure, and inspection or surveillance 

failure. 

The scheduled refueling outages for MNPS are shown in Table 3-2. As shown, the Unit 1 

scheduled refueling outages occur in the even numbered years and coincide with a portion of 

the average winter flounder larval entrainment period of April through mid-June. Unit 2's 

01 51 6.WP5 3-53 PART I 
i 

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 not terminated during refueling outages; however, the durations 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 13 percent. 

For further detail in understanding how these dates were established, refer to Section II, 

Part 4. 

PART I 3-54 0151 6.WP5 
r 

L 

w 

u) 

0 

c 
Cooling 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 Com bination 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 to the 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 to the 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 

rescheduling the Unit 1 and Unit 3 refueling outages to coincide more precisely with Table 3-3 

was not performed, preliminary indications were that a one-time adjustment to the outage 

schedule would not be very difficult or costly. However, it would not be possible to maintain 

that schedule every year without exception, even with extraordinary and costly engineering 

and nuclear fuel procurement strategies, unless forced outages were to occur each spring. 

PART I 3-56 01 51 6.WP5 
Millstone 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 affect fuel nucleonics (the next refuel outage can be extended to allow 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 4/2 to 6/13 $21 4 

Unit 2 Offline 4/2 to 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. 

Estimates are 1992 $ grossed up to full output for each scenario. 

Some years had no replacement 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 

01 51 6.WP5 3-57 PART I 
Cooling 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, and A.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-Mesh Traveling Screen for Protecting Organisms. Proceedings of the Workshop 

of Advanced Intake Technology, held at the Sheraton-Harbor Island Hotel, San Diego, 

CA, April 22-24, 198 1. 

M.R. Anderson, J.A. DiVito, and Y.G. Mussalli. Design and Operation of AngledScreen Intake. J. Hydraulic Division, ASCE Vol. 1 14, No. 6, June 1988, pp 598-61 5. 

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-Screen Test Facility. J. Hydraulic Division, ASCE Vol. 1 14, 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, and 3 

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. 

0151 6.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 costs for each of the seven alternatives are summarized in Tables 4-1 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 provides tabulated calculations of annual costs for added power consumption and 

performance degradation resulting from implementation of cooling-water system alternatives 

for Unit 3 for the years 1993 through 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 summarizes the 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-DRAFT COOLING TOWERS 

SUMMARY OF ORDER OF MAGNITUDE COST ESTIMATES 

Full-Size %-Size 

Tower Tower 

$13,000,000 $1 1,700,000 

Equipment 6,500,000 4,500,000 

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 

1 00,000 

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 

$7 1 ,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 01 51 6.WP5 
Millstone 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 

1 1,400,000 

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 

$1 17,700,000 

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. 

01 51 6.WP5 4-3 PART I 
Cooling 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 in the 

applicable text describing the design alternative. 

PART I 01 51 6.WP5 
Ir) Millstone Units I; '2, and 3 

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. 

01 516.WP5 4-5 PART I 
Cooling 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 lower than actual. Further limitations are described in the 

applicable text describing the design alternative. 

PART I 4-6 0 1 5 1 6.WP5 
Millstone 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 be considerably lower than actual. Further limitations are described in the 

applicable text describing the design alternative. 

01 51 6.WP5 4-7 PART I 
e 

t 

I 

a 

1 

9 

Z 

? 

Z 

- 

E 

0 

0 

N 

u, 

9 

- 

- 

E 

0 

0 

9 

N 

u, 

- 

E 

0 

0 

d 

N 

u, 

9 

- 

Lo 

0 

0 

N 

u, 

9 

F 

ai 

n 

E 

0 

- 

a, 

v) 

C 

0 

0 

a, 

D 

3 

I! 

8 

5 

1 

PI 

E 

Q, 

3 

0 

m 

U 

a, 

0 

3 

0 

C 

0 

C 

m 

v) 

v) 

0 

0 

a, 

V 

C 

m 

C 

W 

4- 

C 

- 5 

- 

.- 

c 

2 

c1 

.- 

E 

0 

C 

m 

C 

0 

m 

W 

P 

.- 

c1 

L 

0 

c 

- 

m 

3 

u 

m 

C 

m 

4- 

5 

v) 

v) 

a, 

>. 

C 

m 

0 

YC 

al 

v) 

W 

D 

3 

0 

0 

3 

m 

C 

m 

3 

a. 

a, 

0 

C 

0 

0 

a, 

0 

a, 

3 

U 

0 

C 

m 

c, v) 

v) 

0 

V 

al 

> 

m 

al 

0 

C 

0 

VI 

m 

- 

- 

4- 

.- 

.- 

9 

E 

4- 

- 

4- 

L .- 

5 

c 

.- 

c 

- 

L 

c 

.- 

L 

E" 

0- 

0 

0 

L 

c 

2 

m 

v) 

a, 

c 

.- z 

c 

v) 

a, 

$4 

at; 

gE 

4 

VI 

C 

5 

E 

- 

m 

0 

U 

al 

U 

al 

al 

C 

v) 

a, 

0 

Q 

C 

L 

Y- 

.- 

L 

3 

c 

E 

a, 

0 

m 

a. 

- 

E 

4- 

a. 

al 

0 

X 

a, 

- c 

a, 

0 

v) 

m 

4- 

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. These factors were recommended based on the level of 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 

01 51 6.WP5 4-9 PART I 
Cooling 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 rock excavation costs, utilizing pre-split blasting in rock range from $10.00 to $20.00 

per cubic yard. This assumed that average haulage would be less than 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. The tunnel would be excavated through drill and blast methods along 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 to the submerged structure 

elevation. 

3. The tunnel liner would be cast in place, reinforced concrete, 2-foot 

average thickness. 

4. Tunnel cross-sectional shape would be near circular/modified horseshoe. 

PART i 4-1 0 0151 6.WP5 
Millstone Units I,. 2, and 3 

5. The access shaft would also be located offshore, approximately 150 to 

200 feet from the front of the current pumphouse structure. 

~ 

6. One working face was assumed to be 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 with controllable 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 

01 51 6.WP5 4-1 1 PART I 
Cooling 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 to advance, 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 diameter would be 27 feet O.D. (outside diameter), 24 feet 

I.D. with cast in place concrete liner. It would be drilled entirely through 

rock. 

5. The rock was assumed to be competent and groundwater inflows to 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 1982 Army Corps of 

Engineers' estimates for a shaft of this diameter. The final costs were adjusted to 1992 

prices through the Construction Cost Index published by the Engineering News Record. The 

price difference is 32 percent. The average cost per linear foot 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 New Jersey. The New Jersey project cost estimate for a 24-foot shaft was 

$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 

comparable to the proposed shaft of MNPS. Slurry wall construction was necessary, as was 

a larger diameter (35 feet) to accommodate a TBM. 

Total cost for a single shaft at MNPS would be: 350 feet x $7645/foot + collar development 

($1,500,000) = $4,175,750/shaft. This does not include underwater construction costs for 

sea floor prep and caisson installation. For preparation and caisson costs associated with the 

main access shaft and the velocity cap access shaft, the allowances were $2,000,000 and 

Ir 

L 

PART I 4-1 2 01 51 6.WP5 
Millstone Units 1,.2, and 3 

$1,000,000, respectively. It should be noted that shafts costs can vary considerably with 

respect to the following factors: ground conditions, crew experience, quality of supervision, 

labor rates, and excavation techniques. The cost estimates for 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 Schedule Assumptions 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 to final location. 

The schedule was based upon similar facility experience. Variations in rock types or ground 

conditions could significantly impact the schedule. Excavation techniques for the access shaft 

and the tunnel 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 month and create a safer working environment. Excavation rates for the tunnel and access 

shaft were assumed at 30 feet/day and 8 feet/day, respectively. The excavation for the 

raised boring machine was assumed at 30 feet/day. It was assumed that the liner would be 

installed during excavation with the tunnel face at least 150 feet in front of the installed final 

liner. Final liner installation and sealing of the tunnel 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 constructed approximately 1 mile offshore in slightly deeper water by raise 

bore techniques. While the raised boring schedule would be shorter than conventional shaft 

construction techniques, capital equipment costs were assumed to 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 

4-1 3 01 51 6.WP5 PART I 
Cooling Water System Alternatives to Reduce Larval Entrainment 

4.3 CONSTRUCTION PERIODS ESTIMATES 

Construction periods and estimated outage periods for each of thg alternatives are presented 

in Table 4-9. These periods do not account for time for engineering and design, equipment 

procurement, or permits. 

The construction periods estimates were developed assuming standard construction methods 

and work weeks. The periods could be 

scheduled to take 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 Station consists of three 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 (nuclear safety related). Each intake incorporates traveling water screens, coarse-bar 

racks, and curtain walls extending below lowest water level. Each intake draws water 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 reduction to the entrainment of winter flounder larvae into the intakes. 

These technologies would achieve reduction to the entrainment into the intakes of fish and 

fish larvae through 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 

01 51 6.WP5 5-1 PART I 
Cooling 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: a full-size natural-draft cooling tower and a 2/3-size natural-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 in the existing wooded area to the east of the 

switchyard. New pumping stations would be located at the cooling towers. Piping for the 

new closed-loop circulating water systems would be routed in a common cut and cover trench 

to the north and east of the station and would join the existing circulating inlet piping to the 

west of the turbine building. Valving would be provided to operate either the existing oncethrough system or the closed-loop system with the cooling 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 

located at the shoreward end of the tunnel to provide added pumping head to compensate for 

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 

PART 5-2 01 51 6.WP5 I 
Millstone Units 1,.2, and 3 

Seabrook Nuclear Station and the sewage outfall tunnel 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 (1 to 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 gates would be provided for circulating water flow. Fish and 

larvae collected on the fine-mesh screens would be returned to Niantic Bay to the 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 screens Yi3duaa $eliminate entrainment of fish and larvae by .taking advantage 

of natural cross currents to sweep 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 to the 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 in the 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 01 51 6.WP5 PART I 
Cooling Water System 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 away from the intake. Additional angled vanes that would be placed upstream 

of the sill are included with the design to enhance silt diversion. 

An alternative to the 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 barriers or 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 

have clogging and maintenance problems when high yields are attempted. A European design 

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. Isolation of circulating water pumps during the spring season was not considered 

a viable option due to operational difficulties and a degradation of plant safety. 

Variable-speed drives for the circulating water pumps allow reduction in circulating water 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 0 1 5 1 6 .WP5 
Millstone Units 1,. 2, and 3 

outage. A two-speed drive system design was developed which would operate the 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 units would 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 

01 51 6.WP5 5-5 PART I 
I? 

r 

rir 

m 

a 

c 

w 

4 

c5 

d 

412 

:I? 0 18 0 

0 

N 

9 

.- 

412 

0 

0 

03 

aco 

(0 

ai 

E 

- 

R 

a 

U 

v) 

C 

0 

0 

a 

R 

U 

J 

0 

0 

% 

a 

.- 

- 

5 

5 - 

r 

0) 

13 

0 

m 

U 

a 

U 

3 

0 

C 

0 

C 

m 

c, v) 

v) 

- 

.- 

I-' 

2 

:: 

a 

0 

C 

m 

C 

a 

C 

I-' 

.- 

2 

U 

C 

m 

C 

.- 0 

c, 

2 

a 

0 

a 

7 

v) 

v) 

0 

0 

m 

c, 3 

0 

m 

C 

m 

c, 

- 

5 

v) 

v) 

a 

>. 

C 

m 

0 

'c 

C 

0) 

VI 

a 

0 

13 

0 

V 

- 

- 

c, 

.- 

.- 

I! 

2 

4- 13 

m 

C 

m 

3 

9. 

a 

0 

C 

0 

0 

a 

0 

a 

13 

U 

U 

C 

m 

v) 

- 

4- 

L .- 

5 

c, 

c, 

:: 

0 

a 

> 

m 

.- 

I-' 

- 

2 

Lc 

0 

C 

0 

v) 

m 

.- 

L 

2 

0 

0 

0 

L 

Lc 

2 

m 

v) 

a c, 

.- e 

I-' 

v) 

a 

a 

v) 

a 

e 

6i 

! z+ 

L1 

*: 
Millstone Units T,,2, and 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 4/2 to 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. 

Estimates are 1992 $ grossed up to full output for each scenario. 

Some years had no replacement power cost because a scheduled 

refuel overlaps the time period. 

Estimated costs starting in 1993 through year 201 0. 

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 

a 

a 

01516.WP5 5-7 PART I 
3 

m 

v) 

w 

d 

a 

tU 

0 

v) 

W 

C 

m 

W 

0 

C 

3 

.- 

4- 

.- 

Y L 

W 

a, 

Y 

- 

a 
PART I 01516.WP5 
c- I 

.. .. WW !zs 0 0' 

0 

0. 

0 

9 

0 

w 0 

0 ICc 

U 

U M 

M 

*I! i 

u 

W 

z 

c I 

c 

C* 

W Lz 

B r 

9 

-J 0 

0 0. 

0. 

9 

0 

0. 

s 

U 

U- U M M 

c 

d 

8 

8 

p: 

W 

Lz 

W 

W 

u 

2 

w 

CL 

W c 

v) 

W 

3 

z 

z 

rn 

I 

W c 

rn 

W 

z 

rn 

c 

c 

z 

W 

u 

U 

t 

3 

2 

c 

zz 

W rn 

W 

CL 

n 

az 

c 

4 

2 

WI 

-I@ 

el a e v) E! 

8 c 

u 

3 e* c 

rn 

z 

0 

u 

c 

C* 

W 

Lz 

B -I 

rn 

w 

5 

0 

2 0 

0. 

7 0 N 

0. 

0 

M 

0. 
*NN 

lnln 

NN 

\\ 

w-- 

wrr 

4 

-cq 

.. .. ww 

cc *u 

on 

z 

El 

c 

x u 

CL 

W 

W 

0 az 

W 

E 

CL 

W c 

v) 

m 

s 

an 

w ;L 

0 c 

v) 

U 

CL u an 

- 

9 

* 

n 

i2 

an 

can 

CT cc cw 

cv) * 

wan N 

-CL 

.. 

B d 

4 

v- 0 

ln 

v) 

ln 

m 

Q 

m 

.C 

n 

.r 5 

i 

-3 

2 

- 

.c 

r 

0 

c 

v) 

Q 

r L 

ln 

r 

vm L 

0 

L 

01 

c U 

Q 

I 

5 

a 

iQ 

.C 2p 

-3e 

4 0 

Y 05 

c .- 

I 

L -01 

or 

cm 

In 

-5 

E