II. Propulsion Reactors

1. Nuclear Ship

(1) Definition (International Convention for the Safety of Life at Sea, SOLAS <1960> )

“Nuclear ship is defined as a ship with the nuclear power”

The main propulsion of nuclear ship may be obtained by steam turbine,

gas turbine or electric propulsion.

★ Need of nuclear ship

☞ Need of large and rapid passenger/freight transportation due to increase of overseas trade

- The amount of freight in 2010 is expected to be doubled  as

compared with this point of time

☞  Prevention of sea pollution caused by spilled oil at marine accidents

☞ Need of a lengthened stay in the sea for deep sea probes and extraction of minerals

(2) Scheme of Nuclear Ship

○ System

• Nuclear Steam Supply System (NSSS)

• Nuclear Propulsion Plant (NPP) : NSSS an power for ship propulsion

• Auxiliary Machinery and Systems : Equipment for decontamination in the

underbody of a ship and communication system

• Electrical System

• Radioactive Waste and Management System

• Safety Enclosure : The four barriers for radiation protection

○ Sea-rescue work related with nuclear ship

• Collision

• Stranding and Grounding

• Capsizing or Sinking

• Fire

○ Environmental design standard should consider whole ship safety as well as nuclear safety, when constructing the nuclear ship.

○ The lifetime of a nuclear reactor pressure vessel = the lifetime of a ship

(3) Characteristics

Merits	Demerits
1. Small fuel weight - increase in amount of cargo 2. large transport capacity and long travel distance 3. high availability rate - refueling every 2∼4 years 4. no air for combustion(submarine) 5. free from exhaust gas 6. Low fuel cost	1. high construction and operating cost (training captain and crews) 2. Radiation protection and treatment of radioactive waste 3. Limited place for maintenance 4. Periods needed in refueling 5. Limitation of port and complicated procedure for clearance inwards 6. Noise of pump(submarine)

◈ Economical efficiency

(1) Comparison with container ship

☞ North America-Asia course ; About 600 million TEU(TEU: Conversion factor based on 20 feet's container)

☞  The expected life span of a ship : 20yr

☞  Cost to be considered : Construction cost, crew salary,  repairing expenses, insurance money, fixed cost, fuel cost, shipping cost, Scrapping cost of nuclear ship, environmental protection cost in diesel ship

■ Conclusion : advantageous on nuclear ship in high speed over 30 knots

(2) Comparison with nuclear reactor in NPP

1) Regulation requisite for design and operation ; code of Safety for Nuclear Merchant Ships

2) Safe operation during acceleration and incline

3) Rapid load following (outgoing-incoming in port, passing narrow path)

4) Preparing marine accident (vibration, shock such as collision and

stranding)

5) Residueal heat removal in case of loss of electric power

6) Extremely safe and reliabe - limited place for refueling

7) compact and light

(4) Classification

∘PWR

- excellent load following

- little change of nuclear reaction rate during rolling and pitching

- smaller size

∘BWR

∘HTGR

1) Separated type ; Mutsu, Savannah

2) Integrated type ; Otto Hanh, NSR-7, MRX

3) Semi-integrate type ; S/G connected by dual short pipe, France

(5) Main Components

1) Coolant pump

a) PWR separated type ; canned motor centrifugal pump

b) PWR integrated type ; canned motor axial flow pump

◦ Low efficiency (70%)

◦ Low inertia (depleted uranium)

◦ Outside stator cooling circuit needed

◦ Difficulty in reparing and checkup

◦ High cost

2) S/G

a) PWR separated type ; U-tube S/G

b) PWR integrated type ; Helical Coiled S/G

◦ 20% larger heat transfer area

◦ superheated steam - lower secondary pressure

◦ constant secondary pressure vs load

◦ difficulty in fabrication, repair and replacement because of the  long S/G tube

◦ feedwater purity

3) Integrated pressurizer

- self-pressurization by steam dome in the upper part of reactor vessel

◦ place for construction and reparing of S/G

◦ gas-pressurization

(6) Design and accident analysis of reactor in nuclear ship

1) Safety regulation for nuclear ship

• reactor compartment ; protection from collision, stranding, and misile

during cargo working

• safety enclosure ; physical protection ability in case of collapse of 2nd

and 3rd shield

• minimizing penetration area in reactor compartment, safety enclosure and   containment structure

• minimizing the consequence by missile

• isolate the emergency control position from reactor control room

• collision protective structure installation

• double-bottomed rear side of hull and analysis of intensity in the

direction of head-tail of hull

• equipment and barrier capable of fire protection

- assess of fire officers for easy decontamination

- limited use of ionization detectors in spaces

- iimiting or controlling hydrogen releases, origination from the process of     radislysis, or following a LOCA

2) Design features of nuclear ship

① Application to marine environments

○ The reactor placed at the center of buoyancy force of ship should    be operated in stable and safe condition in spite of various ocean    movements such as rolling and incline.

○ capable of standing against vibration and shock caused by          severely bad weather

○ ensure the reliability that nuclear reactor accident should never

occur whatever marine accident happens.

○ Residual heat should be removed and radiation must not be

released even if reactor is not controlled after sinking.

② Mobility of ship

○ Reactor power must be followed in a stable state during arrival

and departure from the port, as well as in rapid load changes.

○ Effective measure is needed to protect the exposure of radiation    as the ships come to anchor at a harbor in the city or a densely    populated district. However, unlike the nuclear reactor on land, the   nuclear ship can be isolated far away at accidents.

○ Disposal of waste liquid to outside ship should be limited since it

is difficult to detect dilution and dispersion. In addition,

appropriate facilities should be installed for this purpose.

③ Isolation in the remote ocean from the land

○ It needs enough maintenance in advance, as it is difficult to be    supported quickly by the resources from the land in the event of    accident or malfunction.

○ Residual heat in the core must be removed even when all of

the main electricity supply stop.

○ Facilites to control radiation exposure should be equipped so as

to regulate the crews' exposure dose.

○ Equipments for refueling and disposal of radioactive waste matter   must be placed in port, not in ship.

④ Propulsion power

○ The ship reactor has a small output compared with that on

land since it is limited to be installed in the hull. Thus, it is

difficult to have steady and stable power distribution

○ As the lifetime of a nuclear reactor is lengthened, the long reactivity

contol may be more difficult due to the restrictive usage of

chemical shim.

○ When the availability of reactor is lost, an auxiliary power for

propulsion is required except for operation with dual reactors.

3) Design Basis Accident of reactor in nuclear ship

4) Behavior of reactor core during rolling or incline

a) resonance in vibration of coolant or the ship body ; thermal-hydraulic instability

:  ω  ～  2 or 3 τ

b) Decrease of coolant velocity resulted from vibration ⇨ decrease of

CHFR

[eqn: & q _{CHF} `=~q _{CHF,o} `(1- TRIANGLE g/g _{o} )# # & q _{CHF} `=~q _{CHF,o} `K _{h} `K _{l}# # & H _{h} `;~ rm heaving`~~coefficient# # & K _{l} `;~ rm listing``~~coefficient]

5) Conditions of rolling, incline, load change

◦ Condition of safety system performance and maximum power operation

Mutsu                 Otto Hahn

acceleration(up and down)    [eqn: I` under{+} `0.6g]                [eqn: under{+} `0.5g]

Rolling angle	[eqn: underline + ~30 DEG ~ (underline + 60 DEG)]          [eqn: underline + 30 DEG ~(underline + 45 DEG )]

Pitching angle            [eqn: underline + 10 DEG ~(underline + 20 DEG )]           [eqn: underline + 10 DEG ~(underline + 12 DEG )]

◦ Conditions of load change

Mutsu                    Otto Hahn

Load decrease    100% -> 18% (for 1 sec)   100% -> 10% (for 1 sec)

100% -> 18% (for 30 sec)  100% -> 10% (for 22.5 sec)

Load increase     18% -> 90% (for 30 sec)  10% -> 100% (for 18 sec)

a) confirm the capability of self-control  by the appropriate negative

coefficient

b) effective operation of control rod

c) disposal of surplus steam in case of load decrease

d) sufficient margin for temperature and pressure

(7) Development of Nuclear Ship

1) Russia

◦ Focused on the icebreaker/cargo ship ; pioneer of the Arctic ocean route

a) Large power for breaking the ice

b) Supply of fuel : unnecessary  (difficulty in supplying in the coast of the Arctic Ocean )

c) No need to enter the foreign port.

◦  Present condition ; 6 icebreaker by the nuclear propulsion

◦ Support for scientific observation in the Arctic circle ; “알쿠차카호” 1977.8.17 Initially arrived at 90 degrees north latitude

◦ Nuclear cargo ship with capability of icebreaking ; “Sermorput”

◦ Development project

- Integrated type(helical-coiled S/G, RCP added, PRHR, 30 or 70MW)

- shielding and heat-sink with the water tank in the lower part of reactor operating space

- Development of unmanned and self-control nuclear propulsion using heat conversion system

- 70Mw-NPP on the sea for shipping through the North Pole ; reactor of the icebreaker loading into  barge, using natural circulation cooling system

★ Nuclear reactor of Russia

◇ Millitary ship

◇ The icebreaker and the plant ship for the desalination

◇  KLT-40 (Russian Ice-Breakers Rx)

Modular PWR

140 Reactor-Year Experience

Co-Generation Reactor

Heat for Seawater Desalination

Electric Power

Core design of KLT-40

160 MWt  Loop Type PWR

Diameter/height of core      1.212 m / 0.950 m

No. of fuel assemblyies	241

No. Fuel rods	54/Assembly

Fuel	U-Al Alloy

Life cycle of fuel	2-3yr (100% refueling)

BP	Gadolinium Base Alloy

Cladding	Zircaloy

Control rod	Boron

15 %

Control / Compensation Group - 5

Emergency Protection Group - 4

Coolant	13 MPa, 278/318 ℃

Power control	No Boron Control

Ensure Subcriticality w/o Boron at cold state

Boron Injection for beyond DBA only

Negative Temperature Feedback

High Load Following Capability

◇ AST-500 (District Heating Rx)

◇ ABV

2) Nuclear submarine

- USA, Russia, England, France, China

a) USA

◦ Nautilus ; virgin voyage by nuclear propulsion on 1955, PWR

Seawolf ; Constructed in 1957, Natrium

═⇒ Unified to PWR

◦ For the various purposes

- 2 Tritons ; Increased speed and staying ability under water, Radar Picket submarine

- Regulus(a means of attack against the lands), Halibut(for cruise missile)

- George Washington  ;  a missile warhead	charged to attack against the lands

═⇒  retirement of military submarine

◦ All of the submarines have used nuclear propulsion following Barbel in 1959

b) England

◦ Failed to construct by herself, and thus supported by USA

◦ constructed the missile charged nuclear submarine, "Resolution"

◦ Focused on nuclear-free submarine after this (Upholder in early 80's)

c) France

◦ construted Le Redoutable by herself in 1971

◦ All of the submarines have used nuclear propulsion following

squadron submarine - Rubis

◦ Turbo Electricpropulsion

d) U.S.S.R

◦ 2 power reactor, 2 Propellar

◦  Using metals that have lower melting points beside the light water, Titanium

e) Propulsion system

◦ Reduction gear ; turbine (1000rpm), Propellar (200-300 rpm)

Turbo Electric propulsion( Sturgeon), Separated from the bosf of a ship

◦ Pump ; generating noise , trying to substitute by natural circulation(Narwhal)

◦ Auxiliary propulsion ;  diesel generator, Battery

7) Nuclear Submarine for the next generation

◦ Pump jet propulsion (Cavitation removal up to 20knot), natural

circulation

◦ artificial skin

◦ man-machine interface and robotics

(8)  Present status of nuclear ship R&D in Japan

1) Present status of R&D

- The 1st nuclear ship : ‘MUTSU'

- Present R&D : MRX(Advanced Marine Reactor)

DRX(Deep Sea Reactor)

2) Introduction of Mutsu

a) reactor core and primary coolant system

- Parameters of reactor core and operation of Mutsu

- Reactor Vessel : 1.9m diameter, 5.7m height, cylindrical pressure vessel made of stainless steel of which thickness is 6mm

- Containment vessel : sphere of which diameter is 10m

- Control rod : Ag-In-Col, cruciform, No Boron

b) power control system

- constant Tav of primary coolant system load following type

- input the sum of average neutron flux and steam flow rate inputted on power control circuit

c) secondary coolant system

- S/G : U-tube type, 1.2m diameter, 5.4m height, 406 S/G tube

- designed not to be tripped but continue operating in spite of rapid change of secondary feedwater steam(Main dump system)

- main steam system, auxiliary steam system

- Feedwater control system composed of S/G water level, steam flow rate, feedwater flow rate.

- auxiliary boiler : make nuclear ship function as turbine ship when reactor cannot be operated

Parameter	Design Value
1. Reactor Power[MW(thermal)]	36
2. Pressure(MPa)	10.9
3. Core Inlet Temperature(℃)	271
4. Average Coolant Temperature(℃)	278
5. Coolant flow rate(kg/h)	1.80 x 106
6. Core effective length(m)	1.04
7. Core flow area(m2)	0.591
8. Fuel assembly Total number of fuel rods Number of burnable poison rods per assembly Number of assemblies	3584 9 32
9. Fuel rod Clad outer diameter(mm) Clad thickness(mm) Pellet outer diameter(mm)	10.53 0.4 9.6
10. Main coolant pump rated speed(rpm) / flow(m3/h)	1770 / 1165
11. Pressurizer volume(m3) / water level(m3)	2.62 / 1.12
12. Steam generator Secondary volume(m3) Secondary Pressure(MPa) Secondary temperature Steam & feed water flow rate(kg/h/steam generator) Water level(m3) Feed water temperature(℃)	4.12 4.02 250.6 3.06 x 104 1.14 160
13. Containment vessel Free volume(m3) Pressure(MPa) Temperature(℃)	480 0.098 30

d) Shielding system

- first shield around reactor core, component shield and second shield out of containment vessel

-  Power increasing test was conducted in 1974, shield repair works were performed after the operating test  on the sea failed because of the radiation leak : 1st shield in upper part of vessel in order to shield neutron leakage between reactor vessel and upper part of reactor, use concrete or Zr(OH)₄which are good at neutron absorption as the material of reactor vessel flange and the axis of vessel, installed neutron shield equipment at the lower and outer part of containment vessel made of polyethylene

- actual conditions

		Design basis dose equivalent rate
Control zone	zone I : entrance permitted within 168hr/week	≤ 5.7 μSv/h
	zone II : entrance permitted within 63hr/week	≤ 13.7 μSv/h
	zone III : Entrance is not permitted in general	Not regulated

4) R&D of advanced nuclear ship

a) Design of MRX (reactor for icebreaker)

① Design purposes and schemes

- Purpose of design

o Highly passive safety concept

o Excellent load following

o Plant design condition related with ship movement

- Design scheme

o Integrated PWR type(simplification of safety system and compactness by excluding causes of accidents in Large LOCA)

o built-in CRDM inside reactor (excluding the causes of control rod withdrawal accidents)

o passive maintenance of water and miniaturization by installing reactor vesseel in the containment vessel filled with water, especially beneficial in shielding

o PRHRS(Passive Residual Heat Removal System) Simplified safety system

o compact and light compared with general ships(Power : 3 times, volume of containment vessel : 0.8 tomes)

Design spec.	M R X	D R X
Power (MWt) Pressure (MPa) Core inlet temperature(oC) Core outlet temperature(oC)	100 12 282.5 297.5	2 6.55 270 280
Core Diameter & height(m) No. of fuel assemblies Outer diameter of fuel rod(mm) Enrichment(%) Fuel cycle(yr)	1.49/1.4 37 9.5 4 8	0.45/0.42 1 9.5 7 4
S/G tube Steam temperature(oC) Steam flow rate(t/h) Steam pressure(Mpa)	Inconel 800 289 168 4	Inconel 800 243 2.9 3

② Core design : reactor core and fuel assembly

- free toxic chemicals (Boron)

- Steering speed (20-30%) should be sustained even if the control rod is sticked into core which is located in the highest reactivity

- PWR  fuel assembly(CR Cluster included) shortened, Zr liner sticked to rod

(BWR development)

- 19 fuel assemblies : 13 assemblies contain control rod clusters(6 for

reactivity control, 7 for buck-up reactor shutdown)

- Number of control rod clusters are reduced(control rod withdrawal accidents excluded)

- Hexagonal arrangement

③ S/G design

- Helical-coiled S/G proper to the integrated reactor (Otto Hahn)

- Lowered failure rate owing to Inconel 800 that is used as the material of S/G tube.

④ Containment

- Inconvinient to repair and overhaul, but advantageous in case of nuclear ship in that extreme miniaturization and passive cooling is need

⑤ Design of Passive Residual Heat Removal System

- Highly  passive cooling in residual heat removal and maintenance of water level in the event of accident

- Natural circulation (inner water of containment vessel enters reactor vessel passively) is made when the water level is lowered by LOCA in the primary system

- Heat released into the containment vessel is emitted passively into containment vessel water cooling system

⑥ Shield design

- Water in the containment vessel

- Iron shield between core and S/G

- Air gap and thermal insulator between the Reactor vessel and the water in                     containment vessel

- Steel shield around the Reactor vessel

- Cast steel : Minimization of weight by shield, Making enough room in containment vessel

- Almost all of the weight of marine reactor shield equipment : secondary shield out of containment

shielding equipment out of containment is removed in integrated PWR such as MRX

b) Reactor for deep-water exploration vehicle(DRX)

- Conceptual investigation is on the way since 1989

- Main specification  and characteristics of design in 1991

Power    ;      0.75 MWt

Reactor type    ;      Integrated PWR   (turbine, electricity generator included)

promary coolant and circulation method and pressure ; natural circulation, 8.4 MPa, 282/298 C

Diameter/ height  of core	;  36.8/34.4 (cm)

No. of fuel assemblies and fuel rods       ;  1/336

Fuel and Enrichment	;  Zr/U02 (11 wt%)

Control rod	;  90%  B4C,  Built-in

- Self-pressurization

- Helical-coiled S/G

- Recuperator ; Heat Pipe type (Working fluid ; ammonia or freon)

steam which came from turbine is condensed in 내압각, then released into ocean through heat pipe

- PRHRS

◦ Pipes(of small diameters only) connected to reactor is ruptured -> primary coolant	is realeased into containment -> water level rises and it fills all space -> sudden pressurization in (less than 6MPa by analysis)

; Design　pressure of reactor vessel : 8.4 MPa, Design　pressure of　내압곡 安about 10Mpa

◦ PRHRS

.  Secondary loop : open loop all the time

.  S/G operation as the heat removal system

.  Natural circulation in S/G　in such a case of insufficient heat removal capability

- Dynamic properfies

◦ Analysis of LOCA, Steam Generator Tube Rupture(SGTR), etc in case of load change using RETRAN code

◦ Guaranteeing excellent load following and higher safety in accidents

◦ Confirming heat removal ability by natural circulation in S/G

(9)  Application of nuclear ship

◆ Economics

◆ Society

◆ Ocean development

◆ Environment

1) High-speed container ship

○ powerful propulsion power

○ continual long distance voyage

○ The amount of freight in 2010 is expected to be doubled  as compared with this point of time.

2) Survey ship in the polar regions

○ environment in the Arctic Ocean,

the ozone layer disruption, marine

pollutant in ocean ecosystem

○ long-range observation

○ harsh environment

3) Undersea exploration

○ difficulty in deep-sea investigation

- needing much time in going

undersea or rising

- limited working in the deep-sea

- limited mobility and space

★ Due to the limitation of

propulsion power

○ Possible to overcome such these

problems with nuclear power

- housing arrangements to survive in

long-term probe for about a month

- Easy to go undersea, rise and move horizontally

4) Other uses

◆ Nuclear power plant ship, hydrogen-producing plant at sea, extraction of minerals from the undersea