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Prescriptive Leak Rate Testing Requirements

10 CFR Part 50, Appendix J (latest version 2010) [7] entitled, “Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors,” establishes the testing requirements for preoperational and periodic verification of the leak-tight integrity of the primary reactor containment, including systems and components which penetrate the containments of light water-cooled power reactors, and establishes the acceptance criteria for such tests. The purposes of the tests are to assure that (a) leakage through the primary reactor containment and systems and components penetrating primary containment does not exceed allowable leakage rate values as specified in the technical specifications, or associated bases, and (b) periodic testing of reactor containment penetrations and isolation valves is performed so that proper maintenance and repairs are done during the service life of the containment.

The reactor containment leakage test program includes the performance of integrated leak rate testing (ILRT), also known as Type A test, containment penetration leak rate testing — Type B tests, and containment isolation valve leak rate testing — Type C test. The Type B and Type C tests are also referred to as local leak rate tests (LLRTs). The current (1995 to 2010) Appendix J requirements provide two options for performing the tests. Option A — deterministic, and Option B — performance-based.

Option A (prescriptive) requires that after the preoperational leakage rate tests, three integrated leak rate tests (Type A tests) be performed at approximately equal intervals during each 10year service period. Option A requires Type B tests to be performed during reactor shutdown or refueling, but in no case at intervals greater than 2 years. For containments employing continuous leakage monitoring, Option A requires the Type B tests to be performed every other reactor shutdown for refueling or every 3 years, whichever is less. Air locks are required to be tested every 6 months. Option A requires Type C testing to be performed every refueling outage, or every 2 years, whichever is less.

The NRC considers the implementation of these deterministic requirements, that is, periodic inspections, (as described in Section 4.3.1) and periodic leak rate testing of containment components, will maintain the high reliability (in the qualitative sense) of the containment. The prescriptive testing procedures are described in the following paragraphs.

Some of the Appendix J definitions (most of them common to Option A and Option B) are provided below for ready reference:

  • • “Primary reactor containment” means the structure or vessel that encloses the components of the reactor coolant pressure boundary, as defined in Section 50.2(v) of 10 CFR Part 50, and serves as an essentially leak-tight barrier against the uncontrolled release of radioactivity to the environment.
  • • “Leakage rate” for test purposes is that leakage which occurs in a unit of time, stated as a percentage of weight of the original content of containment air at the leakage rate test pressure that escapes to the outside atmosphere during a 24-hour test period.
  • • “Overall integrated leakage rate” (ILRT) means that leakage rate established from a summation of leakage through all potential leakage paths including containment welds, valves, fittings, and components which penetrate containment.
  • • “Type A Tests” means tests intended to measure the primary reactor containment overall integrated leakage rate (1) after the containment construction has been completed and is ready for operation, and (2) at periodic intervals thereafter.
  • • “Type B Tests” means tests intended to detect local leaks and to measure leakage across each pressure-containing or leakage-limiting boundary for the following primary reactor containment penetrations:
    • 1. Containment penetrations whose design incorporates resilient seals, gaskets, or sealant compounds, piping penetrations fitted with expansion bellows, and electrical penetrations;
    • 2. Fitted with flexible metal seal assemblies;
    • 3. Air lock door seals, including door operating mechanism penetrations which are part of the containment pressure boundary;
    • 4. Doors with resilient seals or gaskets except for seal-welded doors;
    • 5. Components other than those listed above in 1, 2, or 3, which must meet the acceptance criteria for the combined leak rate as defined in Section III.B.3 of Option A of Appendix J.
  • • “Type C Tests” means tests intended to measure containment isolation valve leakage rates.

The containment isolation valves included are those that:

  • 1. Provide a direct connection between the inside and outside atmospheres of the primary reactor containment under normal operation, such as purge and ventilation, vacuum relief, and instrument valves;
  • 2. are required to close automatically upon receipt of a containment isolation signal in response to controls intended to effect containment isolation;
  • 3. are required to operate intermittently under post-accident conditions; and
  • 4. are in mainsteam and feedwater piping and other systems which penetrate containment of direct-cycle boiling water power reactors.

Appendix J uses the following abbreviations in defining the test parameters:

  • (1) Pa (psig or kPa) means the calculated peak containment internal pressure related to the design basis accident as specified either in the technical specification or associated bases.
  • (2) La (percent/24 hours) means the maximum allowable leakage rate at pressure Pa as specified for preoperational tests in the technical specifications or associated bases, and as specified for periodic tests in the operating license or combined license, including the technical specifications in any referenced design certification applicable new reactors.

Note: For licensing of new reactors, NRC has accepted the process of “combined licenses,” in 10 CFR Part 52. Under this regulation, once certain prerequisites are met (e.g., Early Site Permit), a licensee can apply for construction permit and operating license in a combined license application. Chapter 9 of this book provides more information on this subject.

  • (3) Ld (percent/24 hours) means the design leakage rate at pressure, Pa, as specified in the technical specifications or associated bases.
  • (4) Lam, Ltm (percent/24 hours) means the total measured containment leakage rates at pressure Pa, obtained from testing the containment with components and systems in the state as close as practical to that which would exist under design basis accident conditions (e.g., vented, drained, flooded, or pressurized).
  • (5) “Acceptance criteria” means the standard against which test results are to be compared for establishing the functional acceptability of the containment as a leakage limiting boundary.

The following paragraphs briefly describe the procedures for conducting the leakage rate testing and are based on the regulatory requirements described in Option A of Appendix J:

 
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