Chemical Engineering 412

Transcription

1 Chemical Engineering 412 Introductory Nuclear Engineering Lecture 20 Nuclear Power Plants II Nuclear Power Plants: Gen IV Reactors

2 Spiritual Thought 2

3 Typical PWR Specs

4 Reactor Core

5 Fuel Assembly

6 Steam Generator (Heat Exchanger)

7 Overall Equipment Arrangement

8 Pressurizer

9 PWR Steam Cycle

10 BWR Specifications

11 BWR Core

12 BWR Fuel Assembly

13 Generations I-IV

14 Generation I Test reactors and small-scale systems

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

16 Generation III/III+ Evolutions of Generation II reactors Safer Less complex More economical

17 The AP1000 (Gen III+) Design

18 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).

19 Very-High Temperature Reactor Graphite-moderated core Once-through U fuel cycle 1000 C steam outlet temperature Possible H 2 production

20 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.

21 Molten Salt Reactor Low-pressure, hightemperature core cooling fluid Fuel either dissolved in salt (typically as UF 6 ) or dispersed in graphite moderator. Perhaps gas-driven (He) turbine.

22 Gas-cooled Fast Reactor

23 Gas-cooled Fast Reactor He cooled with direct Brayton cycle for high efficiency Closed fuel cycle

24 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

25 Lead-cooled Fast Reactor Molten lead or leadeutectic as core coolant Heat exchanged to gas-driven turbine Natural convection core cooling (cannot fail unless gravity fails)

26 Fast Reactors - Advantages Most transuranics act as fuel Reduces waste toxicity Reduces waste lifetime (dramatically) Expand potential fuel Thermal is primarily odd-numbered actinides ( 235 U) Fast is all actinides, including 238 U, 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.

27 Waste 1000 Traditional Fuel Cycle Approaches Relative Radiological Toxicity Natural Uranium Ore Westinghouse Approach Transuranic Elements (TRUs) MOX Single Pass TRUs TRUs with No Pu Fission Products (same for all cases) ,000 10, ,000 1,000, years Years 2013 Westinghouse Electric Company LLC. All Rights Reserved.

28 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 4 He avoids this problem (absorption cross section near zero). Potential positive void coefficient of liquids not He.

29 Toshiba 4S Super-safe, small and simple (4S) design. Na-cooled fast reactor using U-Zr or U-Pu-Zr fuel, 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

30 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

31 Pebble Bed Reactor Inherently safe (strong Doppler effect decreases fuel reactivity with increasing temperature) VHTGR cannot have steam explosion.

32 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??