Fail-safe source-driven fission and fusion-fission hybrid reactor configurations

Singh, Monish

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Description

Title

Fail-safe source-driven fission and fusion-fission hybrid reactor configurations

Author(s)

Singh, Monish

Issue Date

2013-08-22T16:48:35Z

Director of Research (if dissertation) or Advisor (if thesis)

Ragheb, Magdi

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Fusion-Fission Hybrid
• Fail-Safe Reactor
• Liquid Fluoride Thorium Reactor (LFTR)
• Thorium Reactor

Abstract

A source-driven nuclear reactor configuration with a unity infinite medium multiplication factor fission core (1k), is investigated for both fission and fusion-fission hybrid systems. Suchaconfiguration is thought to offer adesirable fail-safe reactor alternative in that the loss of the fission or the fusion neutron sourceswould automatically lead to a shut-down of the system into a stable subcritical statewith an effective multiplication factor of less than unity (1effk). This is sosincethe fission core cannot sustain a chain reactionwithout the presence of the neutron source. A circulating liquid molten salt using the Th-233Ufuel cycle,where the fission products are continuously extracted,further contributes to the fail-safe characteristic by avoiding the cooling neededfor the decay heat or afterheat after reactor shut-down. Through the extraction of the 233Parelatively long-lived12( 27 )T daysprecursorisotope,and allowing it sufficient time to decay intoits 233Udaughter, breeding in either thermal orfast neutron spectrais a distinct possibility.The presence of trace amounts of 232Uand thestrong gamma-emitting 208Tldaughter isotope offers a desirable non-proliferation characteristicfor the cycle.As a proof of principle, a simplifiedanalytical one-group neutronics analysis isfirstattemptedfor the pure fission core system. This is then supplemented withnumerical one-group criticality calculationsusing an iterative finite-difference methodology. Further, amore detailed continuous energyMonte Carlo neutronics analysis of the fission core reactor driven by a 233Ufissionneutron source, Deuterium-Tritium(DT) and Deuterium-Deuterium (DD) fusion neutron sourceswas conducted usingthe MCNP5computer code.The first system studiedwas a spherical reactor core with a unity infinite medium multiplication factor (1k)and surrounded by a reflector. A 232Th and 233U FLiBe molten salt wasused as the fuel in the core. The reactor is made criticalwith the addition of a thin region of FLiBe salt with a spike of fissile material (233U). With a kin the core and total system effkof unity, the flux profile for the system becomes flat, resulting in uniform fuel burnup andpower profile. Such a configuration was found to have a conversion ratio of 1.4 in the core. However, 233U production in the core would not be able to replace the 233U consumed in the fissile source iiiregionwithout exceeding a 3-5 percent concentration. This maybe possibly achievedusing other stockpiled fissile materials such as 235Uor Pu239at higher enrichment levels.Alternatively, the fissile source region can be replaced by a fusion neutron source such as from DT or DD fusion. The systemstudiedconsisted of a cylindrical core surroundedby a fusion source. It is envisioned that the source could be provided by several cylindrical electrodynamic inertial fusion generators. A small 318 MWthsystem can be driven by a 22.3 MWDT source or a 9 MW DD source. A DT system would be able to achieve fissile breeding at the expenseof requiring an outside source of tritium. Alternatively, a DD system can use a sodium-based moltensalt and breed 233U witha doubling time of 9.2 years.The results of the investigationsuggestthat source-driven systemsassociated with a molten-saltcan be contemplatedwith substantialfail-safe benefits. Running a subcritical reactor eliminates the need for excessive reactivity control systems and providessafety in a loss of power transient situation. Furthermore, utilizing a fissile neutron source yieldsbeneficial power and flux profiles. Lastly, such systems can breed fissile material and support afuture alternative Th-233Uthorium fuel cycle.

Graduation Semester

2013-08

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http://hdl.handle.net/2142/45583

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Copyright 2013 Monish Singh

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