Operational Reactor Safety

22.091 /22.903

Professor Andrew C. Kadak Professor of the Practice

Spring 2008

Lecture 2 3 :

Current Regulatory Issues

Present Situation

• It doesn’t get any better than this for nuclear energy!

– Very Good Nuc lear Regulatory Commission

– Combined Construction Permit and Operating License

– Early site permits supported by DOE

– Concern about Global Climate Change

– Ris i ng and highly volatile natural gas and oil prices

– Great rhetoric from the Pres ident and Congress about need for nuc lear energy for env ironment, security and stability

– Strong Pro-nuclear congressional l egislation in the Energy Policy Act of 2005.

Congress

• P assed Energy Policy Act of 2005

– N uclear energy provisions

• P roduction tax credit - $ 200/kw – for first movers

• Loan guarantees

• Insurance protection of up to $ 500 million for regulatory delays for first 2 plants.

– E ffort to stimulate orders for new plants

• D epartment of Energy working to develop advanced reactor designs as part of Generation IV reactors - 2030

Present New Market Offerings

• AP-1000 (Westinghouse)

– 1 ,000 Mwe – P WR

• E SBWR (General Electric)

– 1390 Mwe - B WR

• E PR ( Framatome – A NP)

– 1 ,600 Mwe – P WR

• APWR – ( Mitsubisi)_

– 1 ,700 Mwe – PWR

Certified Designs

• AP-600 (Westinghouse)

• A BWR – 1250 Mwe (General Electric)

• System 80 + - 1 300 Mwe ( Westinghouse/CE)

Trends

• More passive safety features

• Less dependency on active safety systems

• Lower core damage frequencies – 10 -6

• More back up safety systems – more trains

• S ome core catchers

• Larger plants to lower capital cost $/kw

• S implification in design

• T errorist resistant features

• C onstruction time reduced but still long 4 years

ESBWR Design Features

•Natural circulation Boiling Water Reactor

•Passive Safety Systems

•Key Improvements:

– Simplification

• R educ tion in systems and equipment

• R educ tion in operator challenges

• R educ tion in core damage frequency

• R educ tion in cost/MWe

• Reduced flow restrictions

• improved separators

• shorter core

• increase downcomer area

• Higher driving head

• chimney and taller vessel

Enhanced Natural Circulation Compared to Standard BWR’s

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Differences relative to ABWR

9

2 Major Differences – N atural Circulation and Passive Safet y

Passive Safety Systems Within Containment Envelope

Decay Heat HX’s Above Drywell

All Pipes/Valves Inside Containment

High Elevation Gravity Drain Pools

Raised Suppre s sion Pool

10

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Fission Research at MIT Nuclear Science and Engineering

Tracks

CANE S

Centers

Research foci

Annular fuel Hy dride fuel Nanofluids

NGNP GFR LFR SCWR

Syste m Studies

TRU burning Economics

Projects

11

Annular Fuel for High Power Density PWRs

• L arge project lead by MIT (Westinghouse, Gamma Eng.

, Framatome ANP, AECL)

• Operates at low peak temperatures (1000  C lower than solid fuel)

• F uel allows increase of power density by 50% keeping same TH margins

• Allows achievement of burnup of 90MWd/kgHM

• Appreciably increase of rate of return (economically attractive)

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Thermal Hydraulic Performance: Fuel Temperature

‡ Very low operating peak fuel temperature

2400

2200

2000

1800

1600

1400

1200

As s u mp t i o n s :

S o l i d fuel rod 17x17 , q ' =45k W / m Annular fuel rod 1 5 x15, q'=60kW / m Annular fuel rod 1 5 x15, q'=120k W / m

1000

80 0

60 0

40 0

20 0

- H o t s p ot l i ne a r p o w e r s

-S a m e core pea k i n g of 2 . 5

-S a m e core pow e r for 45kW / m and 60kW / m ca ses

0 1 2 3 4 5 6 7

Rad i us (mm )

MIT Center for Advanced Nuclear Energy Systems 13

Nanofluids P roject

• Nano… what? A nanofluid is an ‘engineered’ c olloid = base fluid (water, organic liqu id, gas) + nanoparticles

• Nanoparticle s ize: 1-100 nm

• Nanoparticle m aterials: Al 2 O 3 , ZrO 2 , SiO 2 , CuO, Cu, Au, C

• Critical heat flux increases

Makes nanofluids appealing

for nuclear. Possibility o f significant power dens ity increase.

But large gaps in database and understanding of the

enhancement mechanisms exist.

Supercritical CO2 cycle for Gen. IV

• A chieves high efficiency at medium temperature

• H as ~25% lower cost than Rankine cycle

• C O2 abundant, cheap and does not leak as eas ily as helium

• I s extremely compact (300MWe turbine fits in home size refrigerator)

• A pplicable to reactors with outlet temperature

>500  C (most GenIV reactors)

reactors

PR EC O O L ER

8

8

1

32C

7.7 MPa

FL OW SPL I T

8

MAIN COMPRE SSO R

RE CO MPRE SSING COMPRE S SOR

6

3

FL OW ME RGE

5

3

3

TU R BI N E

650C

20MPa RE ACT OR

2

4

LOW TEM P E RATURE R E CUP ER ATOR

7

8

6

HIGH TEM P E RATURE REC U P E RA TO R

Thermal/net efficiency =51%/ 48%

250MWe steam turbine

300MW S-CO2 turbine 15

Gas Cooled Fast Reactor for Gen IV Service

Wa te r C ooling Heat E x ch an g er

Gu ard Co n t ain m en t

Eme r ge nc y / Shutdown Cooling Heat Exch an g er

Ge ne r a to r

- seal s

- be a r ings

Turbine R e c upe ra t o r

M odule

Bl o w er

C l o sed C h ec k Valve

H i gh Pre s s ure

Open C o mp resso r

C h ec k Valve

Pas siv e/A ct i ve

D eca y H eat Re moval S yst em

Ref l ect o r

600 MW t h CEA

Pl ate- T yp e C o r e

Inte r c oole r M odu le

Pre c oo ler M odule

Low Pre s s u re C o mp resso r

P o w e r Con ver sion U n it

* Not to s c a l e

R eac to r V essel

•Strives to achieve Gen IV go als – sustainability, safety and economics

•Allows management of transuranics from LWR spent fuel

•Uses combination of active and passive decay heat removal systems (passive based on natural circulation at elevated pressure)

•Direct, highly efficient S-CO2 cycle

•Innovative tube-in-duct fuel assemblies with vibropack (U,TRU)O2 fuel

•Large power rating (1200MWe)

•Breed &Burn core, which does not require reprocessing possible

LWR Pu

burner

First Ti er

Second Tier

Fast re actor or Accelerator Driven Sys.

Recycling

MA/TRU

Reproc essing

LWR

Burndo wn

burner

TRU/Pu

Recycling

Pu/TRU

Reproc essing

LWR

Once Through

Repository

Spent fuel

LWR

Fuel Cycle Options

The CONFU Assembly Concept

Co mbined N on - F ertile and U O 2 Assembly

Guide Tubes

Fert ile Free Pins : 70 v/o – Spinel ( M g A l 2 O 4 )

U O 2 Pins

18 v/o – YSZ

.2% Enrichment

12 v/o – (TRU) O 2

Total 13.2 kg of TRU/assembly

• M u l t i - r e c y c l i n g o f a l l transuranics ( T R U ) i n f e r t i l e f r e e p i n s l e a d s t o zero net TRU generation

• Preserves the cycl e l e ngth, neutronic control and safety features of all uranium cores

Courtesy of Shwageraus, E. Used with permission.

Ņ Optimization of the LWR Nuclear Fuel Cycle for Minimum Waste Production Ó , 38

E. Shwageraus , M.S. Kazimi and P. H e j z l a r , CANES, MIT (2003)

Risk Informed Design, Safety and Licensing

• Use PRA principles in design of CO2 gas reactor – avoid problems

• T echnology neutral risk informed safety standards

• “License by test” regulatory approach for innovative reactors

The “Next” Generation

• Next Generation Nuclear Plant (NGNP)

• N uclear Hydrogen Production

• P ebble Bed Reactors – H igh Temperature Gas

• R isk Informed Design, Safety and Licensing

Next Generation Nuclear Plant

• H igh Temperature Gas

• Indirect Cycle

• E lectric generation

• H ydrogen production

• P ebble bed reactor or block reactor?

• B uilt at the Idaho National Laboratory

Next Generation Nuclear Plant

Hydrogen - T hermo-electric plant

MIT Modular Pebble

Bed Reactor

Secondary HX

Hydrogen - T hermo-chemical plant

Very-High-Temperature Reactor (VHTR)

Characteristics

• Helium coolant

• 1000°C outlet t e mperature

• Water-cracking cycle

Benefits

• Hy drogen production

• High degree of passive safety

• High thermal eff i ciency

• Process heat applicat ions

U.S. Pro d u ct Team Leader: D r . Fi nis So ut hw orth (INEEL)

23

1150 MW Combined Heat and Power Station

Ten-Unit VHTR Plant Layout (Top View )

(distances in m e ters)

Ad m i n

Equip

9 A c ces s Ha tch

7

Equip

3 A c ces s Ha tch

1

T r aining

10

6

Equip A c ces s Ha tch

4

2

Contr o l Bldg.

Maintenanc e Par t s / T ools

T urbine H a ll Bo u nda ry

Pri m ary is land with r e actor and I H X

Turbo m achinery

8

0 20 40 60 80 100 120 140 1 6 0

5

Desalinization Plant

0

20

40

60

80

10 0

Oil Refinery

Hydrogen Production

24

Overview of the efficiency of nuclear hydrogen production options

• T he hydrogen production efficiency =

LHV for gaseous product/ther mal

reactors

• D eviation from ideal

efficiency values can be due to:

– heat losses

– irreversibilities in the components

• F inal comparison shou ld take the same conditions into account

Hydrogen Production Energy Efficiency

Comparison of the thermal-to-hydrogen efficiency of the HTSE, SI and WSP related technologies as a function of temperature

26

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Pebble Bed Reactor Research

• R eactor physics modeling of core - M CNP

• F uel performance model

• Safety analysis – L OCA and Air Ingress with CFD tools

• Pebble Flow modeling and experiments

• Balance of plant modularity – “ lego style”

• O verall plant conceptual design

• N on-proliferation studies

• W aste disposal studies

• I ntermediate Heat Exchanger design and testing

27

What is a Pebble Bed Reactor ?

• 360,000 pebbles in core

• about 3,000 pebbles handled by FHS each day

• about 350 discarded daily

• one pebble discharged every 30 seconds

• average pebble cycles through core 10 times

• Fuel handling most maintenance-intensive part of plant

FU E L E L E M EN T D E S I G N F O R P B M R

5m m Graphi t e l ayer

C o at ed p art ic l es imbedded i n Gr aphi te M at r i x

D i a. 60m m

Py r o l y t i c C ar bon 40 / 1 0 0 0 m m

Fu e l S phe r e

S ilic o n Ca rb it e B a r r ie r C o a t in g 35 / 1 0 0 0

Ha lf S e ct ion

I n ne r Py r o l y t i c Car bon 40 / 1 0 0 0 m m

Po ro us Ca r b o n Bu f f er 9 5/ 1 00 0m m

Di a. 0 , 92m m

Coa t e d P ar t i c le

D i a. 0,5mm U r an ium D i oxi de

Fu el

Reactor Unit

Helium Flowpath

32

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AVR: Jülich

15 MWe R esearch Reactor

HTR- 10 China

First Criticality Dec.1, 2000

China - Rongcheng Site for 19 Pebble Bed Reactors for 3600 Mwe @ 190 Mwe each

Demonstration Plant 35

Features of MIT MPBR Design

36

Current Design Schematic

28 0  C

52 0  C

12 6. 7 kg/ s

Reactor core

80 0  C

7. 75 M Pa

79 9. 2 C

HPT 52 .8M W

MPC 2

26.1 MW

HP C 26 .1M W

69 .7  C

8. 0 M Pa

90 0  C

7. 73 M Pa

6. 44 M P a

Intercool er

69.7 C

4. 67 M Pa

52 2. 5  C

7. 89 M Pa

12 5. 4 kg/ s

11 5  C

1. 3 k g/ s

Cooling RPV

50 9. 2  C

7. 59 M Pa 35 0  C

7. 90 M Pa

Circul ator

32 6  C

10 5. 7 kg/ s

69 .7  C

1. 3 k g/ s

LPT 52 .8M W

71 9.  C

5. 21 M Pa

PT 13 6. 9M W

51 1. 0  C

2. 75 M Pa

LP C

26.1 MW

30 C

2. 71 M Pa

MPC 1 26 .1M W

Bypass Valve

96 .1  C

2. 73 M Pa

Precooler

Inventory control

37

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IHX M o dule

Re a c to r Vesse l

R e c u p e ra t o r M o du l e

TOP VIEW WHOLE PLANT

Pla nt Footpr int

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For more information, see http://ocw.mit.edu/fairuse .

~77 f t .

T u r b oge ne r a to r

MP T u r b ine LP T u r b in e

HP T u rbine

Pr e c o o le r

LP C o m p re ssor

MP Compre ssor

Int e rc o o l e r # 1

~7 0 f t .

P o we r Tu rbi n e HP Compre ssor

I n te r c oo le r #2

38

PLANT MODULE SHIPPING BREAKDOWN

Tot a l M o dul e s N e e d e d F o r P l an t A s s e m b l y ( 2 1 ) : N i n e 8 x3 0 M o dule s , F i v e 8x 4 0 M o dul e s , Se v e n 8x 2 0 M o dul e s

S i x 8x 3 0 I HX M o du l e s Six 8x2 0 R e cu pe r a to r M odu le s

8 x30 Po wer T ur bin e Mo dule

8x2 0 I n ter c o o le r #2 M odu le

8 x40 Piping a nd Pr e c ooler M odu le

8x 30 Upp e r M a n i f o ld Mo dule

8x 30 L owe r Ma nif old Modu le

8x 40 Pip i ng & I n te r c ooler # 1 Mod u le