The Annular Core Research Reactor rod control modification project
9th International Topical Meeting on Nuclear Plant Instrumentation, Control, and Human-Machine Interface Technologies, NPIC and HMIT 2015
The Annular Core Research Reactor (ACRR) at Sandia National Laboratories is a 2.4 MW steady state, 35,000 MW pulsing Research Reactor. In early 2013 there was an occurrence of outward rod motion of three control rods when an inward command was issued by the operator. The outward motion of the three rods resulted in a reactivity insertion of approximately $0.04. Other regulating rods were inserting considerable negative reactivity and the reactor remained well shutdown. This incident resulted in a five month shutdown period to allow two projects to progress in parallel: a Forensics Project to determine the cause of the un-commanded motion and a Rod Control Modification Project to design and implement an engineered solution to prevent further occurrences of uncontrolled outward regulating rod motion. Applying the results of the Forensics Project and a requirement to ensure more direct operator control over regulating rod motion, the Rod Control Modification Project developed a three part solution path. These solutions were divided into sub-projects; 1.0) Addition of an electronic relay between the motion controller and the rod drive motor; 2.0) Modification of the Lab VIEW software to monitor rod motion; 3.0) Modification and improvement of the motion controller code. Subsequent to these projects, a Rod Control System Upgrade Project (RCSU) was initiated to provide a long term solution and an extensive upgrade to the ACRR Reactivity Control and Instrumentation and Control Systems. The RCSU project is currently progressing.