Tracer Technology Group

Nuclear Power Plant Control Room Testing

During an emergency, air entering the control room envelope is filtered through a charcoal system using the Control Room Emergency Ventilation System (CREVS).  The atmospheric tracer depletion (ATD) method uses perfluorocarbon tracers (PFTs) that are part of the normal background as surrogates for infiltration of unfiltered air into the Control Room Envelope (CRE).  The four PFTs are retained by the charcoal filters.  Thus, if there were no unfiltered in-leakage (UI), at steady state, the concentration of these PFTs in the CRE would be the same low level as in the outflow of the charcoal filters; a slightly higher level in the CRE would mean a slight amount of UI.  Figure 1 provides a simplified representation of the system. Through measuring of these PFTs in air outside the CRE (e.g. background concentration C_b) immediately after passing through the charcoal filters (filtered concentration C_f), and within the CRE (C_CRE), and using the known flow rate through the filter system, an accurate measure of in-leakage (Q_u) flow rate can be obtained.

Figure 1.  Control room envelope tracer mass balance.

To perform appropriate Atmospheric Tracer Depletion determinations, it is essential that measurements be made under steady state (SS) conditions – that is, the output depleted concentrations of the charcoal systems being used must be constant and the concentrations in the locations being sampled must no longer be changing. In principle, the stable performance of charcoal cells should be ascertained ahead of the actual in-leakage testing to be sure they are appropriately characterized and any portable charcoal systems used to accelerate the approach to steady-state should also be evaluated; the systems should also be checked for potential interferences from other components already on the charcoals.  In practice, these measurements are usually made at the time of actual in-leakage testing.

The schematic in Figure 1 is simplified and can be adjusted to address more complicated situations such as the potential for in-leakage into equipment rooms or other areas that are part of the CRE.   In many cases, the CRE is not a single well-mixed zone – a requirement for successful implementation of any tracer testing. This was the case for SNUPPS-designed plants – the CRE in these systems consists of 3 distinct zones.  The modeling of such situations is specified in the test design  and developed specifically for the plant undergoing testing.  For successful implementation, the mixing within such distinct zones must be demonstrated as well mixed.

It is important to note that the integrated ATD testing is a comprehensive approach to determining UI in a CRE – regardless of the pathway by which such UI arrives at the CRE.  This is especially relevant to CREs which are contained within other zones or buildings of the plant.

We have used PFT technology to measure the effectiveness of air filtration systems in several Nuclear Power Plant Control Rooms and are in the process of having our techniques certified by the Nuclear Regulatory Commission.

Last Modified: November 12, 2009
Please forward all questions about this site to: Linda Satalino

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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