Clean & Run

During a routine startup of the NIST reactor in early 2021, a fuel element was damaged resulting in contamination of the reactor's primary cooling loop. Following an extensive cleanup effort involving debris removal and filtering of the primary cooling water, NIST received regulatory approval to restart the reactor in March 2023.  Currently, the reactor can be operated safely and well within regulatory requirements.  However, low-power testing has revealed that a small quantity of fuel debris (~ 1-3 g) remains in the reactor vessel.   While this debris will naturally diminish through normal reactor operation, without further mitigation reactor operations will be limited. As such, NIST will undertake a follow-on cleaning effort targeting small particles and hard-to-reach areas, using techniques common in the power reactor industry.  We expect that this effort will substantially reduce the amount of debris remaining and any reduction in debris will shorten the time required to re-establish normalized reactor and scientific operations. 

We present below a high-level schedule depicting the activities planned for the next two years. This figure is based on a detailed analysis of all required activities and reflects full resource loading. 

We plan to conduct low-power operations for training and testing in the late spring of 2024, followed by reactor vessel component disassembly and cleaning preparations during the summer and fall of 2024.  Actual cleaning of the vessel in scheduled for early 2025. NCNR will also undertake other remediations intended to reduce the operational impacts of any debris remaining after cleaning. These activities include reducing gas leaks from the reactor vessel (Helium Leak Mitigation, Fall 2024) and the installation of a filtered drain for the primary system (Flange Remediation, Spring 2025).  NCNR is taking advantage of this time to upgrade neutron guides, NG5, NG6, and NG7.  We expect that the guide work will be completed by early summer of 2025 to the point that reactor confinement is restored, and reactor testing can resume.  The cold source replacement previously planned to coincide with the guide upgrade will be delayed indefinitely to avoid resource conflicts with reactor cleaning activities. 

Subsequent to cleaning, the effectiveness of the process will be assessed through an extended reactor testing period in the late summer and fall of 2025. Once new operating conditions have been characterized and established, the NCNR will resume scientific operations, planned for early 2026. As soon as the plan for scientific operations is finalized, the NCNR will issue a new call for proposals.