The Backfit Rule, 10 CFR §50.109, requires the NRC staff to produce cost-benefit evaluations to justify any changes it may make in its positions, or any new requirements it might impose on licensees, for the purpose of enhancing plant safety. The Backfit Rule also allows the NRC staff to forgo cost-benefit evaluations when it identifies errors or omissions in licensing submittals, or in its own reviews of licensing submittals. In such cases, there is no safety enhancement to be realized. Instead, the NRC staff seeks to obtain reasonable assurance that the level of safety, required by regulations, and licensees’ commitments, is maintained or, if necessary, restored. This provision in the Backfit Rule, called the “Compliance Exception”, has been proven to be very difficult to apply.
In 1998 and in 2001 two licensees had argued, in License Amendment Requests (LARs) that their pressurizer safety valves (PSVs) were qualified for water relief duty. Consequently, their PSVs were safety grade components that could be assumed to be available, in licensing basis accident analyses, to open, relieve water, and then reseat. This capability was thought to be required in order to mitigate certain accidents that caused the pressurizer to become water-solid. The 1998 LAR was withdrawn when the licensee was informed that its PSV test results did not demonstrate a capability to relieve water. However, the 2001 LAR was approved, based upon the licensee’s claim that it had acceptable PSV test results. Later, in 2013, the NRC staff realized that the PSV tests, cited in the 2001 application, did not actually exist. So, after careful consideration, over a two-year period, the NRC staff issued a compliance-based backfit order to the licensee. The licensee appealed the order, and the NRC staff denied the appeal. Then the licensee filed a second appeal, this time directly with the NRC’s Executive Director of Operations (EDO). (Such appeals are allowed by the Backfit Rule.) The EDO granted this appeal. So, the compliance-based backfit order, which was intended to address the missing PSV test results, was ultimately overturned. The PSV test results are still missing; but the licensee now has the NRC’s approval to assume the operation of water-qualified PSVs in its licensing basis accident analyses.
This paper follows the writing, issuance, and appeal of this compliance-based backfit order, and describes how difficult it is to apply the Compliance Exception of the Backfit Rule.