Digital Control for Nuclear Facilities
Since 1951, fifty-two nuclear reactors have existed on the grounds of the Idaho National Laboratory (INL), which has been designated by the Department of Energy (DOE) as the lead laboratory for nuclear energy research in the United States. Like the nuclear reactor designs, the associated nuclear control systems have evolved to include computer based (digital) components that have achieved a high degree of fault tolerance and reliability.
The premier example of nuclear test reactor design is the Advanced Test Reactor (ATR), the 45th of the 52 nuclear reactors built at the INL. The mission of the ATR is to study the effects of intense neutron and gamma radiation on materials and fuels. The primary function of the ATR is to intensely bombard samples of materials and fuels with neutrons to simulate long-term exposure to high levels of radiation, as would be present in a commercial nuclear reactor. The ATR is one of only four test reactors in the world with this capability. The reactor also produces rare isotopes for use in medicine and industry.
The current experiments in the ATR are for a variety of customers – US DOE, foreign governments and private researchers, and commercial companies that need neutron irradiation testing. The ATR is considered to be among the most technologically advanced nuclear test reactors in the world. The ATR has several unique features that enable the reactor to perform diverse testing for multiple sponsors. The physical configuration of the ATR core, a 4-leaf clover shape, allows the reactor to be operated at different power levels in the corner “lobes” to allow for different testing conditions for multiple simultaneous experiments. The combination of high thermal neutron fluxes and large test volumes provide unique testing opportunities.
There are three basic types of ATR test configurations. The simplest configuration is the sealed static capsule, wherein the target material is placed in a capsule, or plate form, and the capsule is in direct contact with the primary coolant. No monitoring and temperature control are available for the static capsule configuration. The next level of test complexity is an instrumented lead experiment, which allows for real-time monitoring and control of temperature and gas conditions inside the capsule. The highest level of test complexity is the pressurized water loop experiment, in which the test sample can be subjected to the exact environment of its proposed application. Advanced instrumentation and control systems in this type of experiment generate a large amount of data, which is available to the experiment operator in real-time so that changes can be made to the experiment as required.
In April 2007, the ATR was designated a "National Scientific User Facility" to encourage use of the reactor by universities, laboratories, and industry. This status is intended to stimulate experiments to extend the life of existing commercial reactors and encourage nuclear power development. These experiments test materials, nuclear fuel, and instruments that operate in the reactors.
The original ATR control systems, installed in the mid 60s for the pressurized water loops and for ATR process control, were replaced in the early 1990s with digital distributed control systems. The digital control systems have allowed consolidation of 4 reactor control room areas into two control rooms, much greater flexibility in adjusting experiment configuration, and unlimited expansion capabilities. With each new ATR experiment there are different instrumentation and control requirements that can be realized simply by making adjustments to the field instruments that feed the digital control system. Since the inception of digital control for ATR processes and experiments in the 1990s, these systems have been upgraded to reflect technological advances. The most recent updates in 2010-2011 have included expansion of the instrumented lead distributed control system to support the National Scientific User Facility. The instrumented lead experiments have a rich history of supporting important national and international programs, such as the Very High Temperature Reactor program, life time extension of graphite used in British power reactors, and national defense programs.