Chemical Engineering 412

Introductory Nuclear Engineering

Lecture 20Nuclear Power Plants II

Nuclear Power Plants: Gen IV Reactors

Spiritual Thought2

Typical PWR Specs

Reactor Core

Fuel Assembly

Steam Generator (Heat Exchanger)

Overall Equipment Arrangement

Pressurizer

PWR Steam Cycle

BWR Specifications

BWR Core

BWR Fuel Assembly

Generations I-IV

Generation I

• Test reactors and small-scale systems

Generation II

• Most current commercial reactors– Largely adopted from ship propulsion systems– 60s-70s technologies– Perhaps more complex than needed

Generation III/III+

• Evolutions of Generation II reactors– Safer– Less complex– More economical

The AP1000 (Gen III+) Design

Generation IV

• Future designs inspired by international agreement

• Six designs – three each of thermal and fast reactors

• Most will not be deployed until 2030 under current plans (one exception – the Next Generation Nuclear Plant, or NGNP –targeted for 2021).

Very-High Temperature Reactor

• Graphite-moderated core

• Once-through U fuel cycle

• 1000 °C steam outlet temperature

• Possible H2production

Supercritical-Water-Cooled Reactor

• SC Water (> 240 atm) for working fluid (similar to most modern coal boilers)

• 45% efficienct(compared to 33% in most current technologies)

• Combines LWR and fossil technology.

Molten Salt Reactor

• Low-pressure, high-temperature core cooling fluid

• Fuel either dissolved in salt (typically as UF6) or dispersed in graphite moderator.

• Perhaps gas-driven (He) turbine.

Gas-cooled Fast Reactor

Gas-cooled Fast Reactor

• He cooled with direct Brayton cycle for high efficiency

• Closed fuel cycle

Sodium-Cooled Fast Reactor

• Eliminates the need for transuranic (Pu) isotopes from leaving site (by breeding and consuming Pu)

• Liquid sodium cooled reactor

• Fueled by U/Pu alloy• Atmospheric pressure• Massive thermal inertia• Neutronically

transparent

Lead-cooled Fast Reactor

• Molten lead or lead-eutectic as core coolant

• Heat exchanged to gas-driven turbine

• Natural convection core cooling (cannot fail unless gravity fails)

Fast Reactors - Advantages

• Most transuranics act as fuel– Reduces waste toxicity – Reduces waste lifetime (dramatically)

• Expand potential fuel –– Thermal is primarily odd-numbered actinides (235U)– Fast is all actinides, including 238U, Th, etc.

• In waste• Depleted uranium• Actinides generated in the fuel

• When operated in breeder (as opposed to burner) mode, creates more fissionable fuel than it consumes, extending total available fuel.

Waste

0.001

0.01

0.1

1

10

100

1000

10 100 1,000 10,000 100,000 1,000,000

Years

Rel

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adio

logi

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Transuranic Elements (TRUs)

MOXSingle Pass

TRUs

TRUs with No Pu

Fission Products(same for all cases)

Natural UraniumOre

Westinghouse Approach

300 years

Traditional Fuel Cycle Approaches

© 2013 Westinghouse Electric Company LLC. All Rights Reserved.

Fast Reactors – Disadvantages

• Low response time– complicates control!– control rods less effective, other means must be used:

• Fuel thermal expansion• Doppler broadening• Absorbers• Reflectors

• Small cross sections – large critical mass– Leads to either large cores or high enrichment.

• Sodium and sodium/potassium highly reactive!– Lead, salts and gases avoid this problem, but more absorption

• Liquid metals and salts can become radioactive – (n, 𝜸𝜸) reactions – 4He avoids this problem (absorption cross section near zero).

• Potential positive void coefficient of liquids – not He.

Toshiba 4S

• Super-safe, small and simple (4S) design.

• Na-cooled fast reactor using U-Zr or U-Pu-Zrfuel, allowing operation for up to 30 years without refueling

• Uses a movable neutron reflector to adjust neutron population.

• Electro-magnetic (EM) pumps, with natural circulation used in emergencies

Traveling Wave Reactor

• Fast reactor core with fission igniter buried for entire 60 year or so lifetime.

• Reaction front propagates through core in wave fashion.• Core also is long-term containment, simplifying

decommissioning and waste storage.• Designed at both modular and utility scales

Pebble Bed Reactor

• Inherently safe (strong Doppler effect decreases fuel reactivity with increasing temperature)

• VHTGR cannot have steam explosion.

Hybrid Designs

• Hybrid of HTGR and MSR• Developed by both Chinese and US

– MIT, UW, UCB + Westinghouse and INL – US DOE NEUP IRP 2011

• Strengths: – Safety

• High thermal inertia• Atmospheric pressure• No air-ingress• Melt down-proof fuel

– Grid• Modular, small, low investment

• Weaknesses:– Economics

• Licensing, e.g. pebble locations• No data, high development costs

– Safety• Fuel handling challenges

– Waste• How to reprocess pebbles??