Bypass Testing

1. Bypass Testing Paul Leonard

2. Background • Bypass testing establishes the quantity of material that passes through the strainer and interacts with downstream components • The significant concern is the fiber that passes through and interacts with the reactor fuel • Many licensees have performed bypass testing, but very few have had their testing reviewed by the NRC • This has left most licensees unsure as to the acceptability of previously performed testing

3. Recent History • NEI developed a generic bypass test protocol with the intent to submit it to the NRC for their review • Some licensees were concerned that this could pre-empt previously performed testing and force them to re-perform bypass testing • Some licensees that needed to perform, or re-perform bypass testing submitted bypass test protocols to the NRC for review • NRC stated that they did not have technical concerns with protocol, but could not specifically endorse the protocol due to the human actions required for it to be correctly implemented • NRC also requested that they be able to witness the testing

4. Current Status • Recently, NRC has provided (verbally) those attributes that they believe are the most important for acceptable bypass testing • Debris preparation • Concentration of debris arriving at strainer • Face velocity at strainer • Bypassed debris capture method • Test termination criteria • Interpretation of test results • These attributes are discussed in the following slides

5. Current Status • Debris Preparation • Debris is to be prepared in a method that provides for readily suspendable fibers for introduction to the test flume or test tank • NEI debris preparation protocol is an acceptable method • Concentration of Debris Arriving at Strainer • Batch addition to the test loop must be less than an equivalent 1/16” bed thickness across the test strainer OR • Must demonstrate that the concentration of fibers in the scaled batch addition(s) is representative of the concentration that would be conservatively expected to be at the strainer in the plant at the initiation of recirculation • Especially important for initial batches for a higher fiber plant in which a filtering fiber bed could quickly be formed on the strainer

6. Current Status • Face Velocity at Strainer • Test loop flow must provide a strainer face velocity that is equal to or greater than the velocity that would be expected in the plant • Bypassed Debris Capture Method • Debris capture method must be by filtration, not liquid sampling • Filtration can be either filter bags or screen capture but must be of sufficiently small size to ensure bypassed fibers are captured • Test Termination Criteria • The test duration must be sufficiently long to ensure that the quantity of fibers that would be expected to bypass the strainer would in fact be captured by the filtering media • Insignificant increases in captured fibers on the filtering media • If a significant fiber bed is established on the test strainer, the bed is stable and not passing additional fibers • The test duration can be tied to the time from initiation of recirculation to swapover to hot leg recirculation

7. Current Status • Interpretation of Test Results • The intent of bypass testing is to establish a total quantity of fibers that would be expected to pass through the strainer to interact with downstream components, e.g., reactor fuel • There is some concern by NRC in the use of the term % bypass in that this could be incorrectly applied in the determination of the total quantity of fibers that would be expected to bypass • Along with test termination criteria, similar to questions that were asked regarding strainer head loss testing, there could be questions regarding extrapolation of test results for tests that may not demonstrate an insignificant increase in fiber collection downstream of the test strainer over time

8. Conclusion • Bypass testing, if performed, will establish the quantity of fiber expected to reach the fuel • If a plant intends to use the 15g/FA limit established by WCAP-16793 to support closure of GL 2004-02, and intends to rely on previously performed bypass testing, then the attributes presented need to be considered • If a plant is going to follow the PWROG test plan that is expected to improve reactor core fiber limits, then bypass testing previously performed or planned to be performed also needs to consider the attributes presented • It is recommended that plants that are not certain of the acceptability of previously performed bypass testing • Develop the case for acceptability • Present their case to the NRC

9. Additional Information • As part of South Texas Project’s risk-informed effort, screen penetration testing is being performed • Gil Zigler will now discuss information learned from that testing