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 to support closure of GL , 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