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On April 3, 1986 two milestone tests were conducted in Experimental Breeder Reactor-2 (EBR-II). The first test was a loss of flow without scram and the second was a loss of heat sink without scram. Both tests were initiated from 100% power and in both tests the reactor was shut down by natural processes, principally thermal expansion, without automatic scram, operator intervention or the help of special in-core devices. The temperature transients during the tests were mild, as predicted, and there was no damage to the core or reactor plant structures. In a general sense, therefore, the tests plus supporting analysis demonstrated the feasibility of inherent passive shutdown for undercooling accidents in metal-fueled LMRs. The results provide a technical basis for future experiments in EBR-II to demonstrate inherent safety for overpower accidents and provide data for validation of computer codes used for design and safety analysis of inherently safe reactor plants.
An experimental study of inherently safe characteristics of LMFBR systems is being conducted in EBR-II. Experiments have been conducted which show (1) capabilities of heat removal without the aid of active safety systems and (2) capabilities to mitigate a reduction in-core cooling flow or heat rejection to the balance of plant (BOP) without aid of active control or protection systems. Experiments involving loss of forced reactor cooling flow and loss of all heat rejection to the BOP are planned to be conducted. Purpose of this paper is to summarize the result of the test program by presenting representative test data.
Two tests of great importance to the design of future commercial nuclear power plants were carried out in the Experimental Breeder Reactor-II on April 3, 1986. These tests, (viewed by about 60 visitors, including 13 foreign LMR specialists) were a loss of flow without scram and a loss of heat sink without scram, both from 100% initial power. In these tests, inherent feedback shut the reactor down without damage to the fuel or other reactor components. This resulted primarily from advantageous characteristics of the metal driver fuel used in EBR-II. Work is currently underway at EBR-II to develop a control strategy that promotes inherent safety characteristics, including survivability of transient overpower accidents. In parallel, work is underway at EBR-II on the development of state-of-the-art plant diagnostic techniques.
EBR-II recently passed a major milestone in its operating history, 20 years of operation on August 13, 1984. The plant has gone through three major program phases during this time and is now entering a fourth. Those are: (1) demonstration of the feasibility of a complete LMFBR power plant, including on-site reprocessing of metal fuel, (2) irradiation testing of fuels and materials to support core and fuel design for CRBR and FFTF, (3) operational-safety testing to establish and demonstrate the inherent safety of LMFBRs and now, (4) the integration of this technology into demonstration of the integral fast reactor (IFR) concept. As EBR-II has progressed through these phases, much has been learned that is relevant to fast-reactor safety.
These experiments are preoperational zero-power nuclear investigations in the Experimental Breeder Reactor II (EBR-II) prior to insertion of sodium coolant. The experiments were performed with the power reactor instruments, fuel and mechanical components installed. The measured dry critical size, reactivity worth of control mechanisms and isothermal temperature coefficient of reactivity are in good agreement with predicted values. Additional measurements include neutron flux distributions in the uranium reflector and outside the reactor neutron shield.
The book has been developed in conjunction with NERS 462, a course offered every year to seniors and graduate students in the University of Michigan NERS program. The first half of the book covers the principles of risk analysis, the techniques used to develop and update a reliability data base, the reliability of multi-component systems, Markov methods used to analyze the unavailability of systems with repairs, fault trees and event trees used in probabilistic risk assessments (PRAs), and failure modes of systems. All of this material is general enough that it could be used in non-nuclear applications, although there is an emphasis placed on the analysis of nuclear systems. The second half of the book covers the safety analysis of nuclear energy systems, an analysis of major accidents and incidents that occurred in commercial nuclear plants, applications of PRA techniques to the safety analysis of nuclear power plants (focusing on a major PRA study for five nuclear power plants), practical PRA examples, and emerging techniques in the structure of dynamic event trees and fault trees that can provide a more realistic representation of complex sequences of events. The book concludes with a discussion on passive safety features of advanced nuclear energy systems under development and approaches taken for risk-informed regulations for nuclear plants.
The mission of the Experimental Breeder Reactor II (EBR-II) has evolved from that of a small LMFBR demonstration plant to a major irradiation-test facility. Because of that evolution, many operational-safety issues have been encountered. The paper describes the EBR-II operational-safety experience in four areas: protection-system design, safety-document preparation, tests of off-normal reactor conditions, and tests of elements with breached cladding.