License Renewal Application / LTO Assessment
In the United States, in compliance with 10 CFR Part 54, an integrated plant assessment (IPA) must be performed by the utility as a part of the license renewal application (LRA) process. The IPA is an assessment that demonstrates that a nuclear power plant facility’s systems, structures, and components (SSCs) requiring aging management review (AMR) for license renewal have been identified and the effects of aging on the functionality of such SSCs will be managed. The IPA process is briefly illustrated in the following chart. In addition to IPA, utilities are required to maintain the current licensing basis (CLB) such that there is an acceptable level of safety, perform an evaluation of time-limited aging analyses (TLAA), and provide a Final Safety Analysis Report (FSAR) supplement which contains a summary description of the programs and activities for managing the effects of aging and the evaluation of TLAA for the period of extended operation (PEO).
Application Development[edit]
Licensees are required to identify and list a nuclear power plant’s SSCs requiring aging management review for license renewal (LR) through IPA as per 10 CFR 54.21 (a). The effects of aging must be managed to ensure that the SSCs can continue to perform their intended function(s) throughout the PEO.
Scoping[edit]
Reference: 10 CFR 54.4
Scoping is the process of determining which SSCs are in-scope of LR. Any SSCs meeting one or more of the following criteria are considered in-scope of LR:
- (a)(1). Safety-Related (SR) SSCs
- (a)(2). Non-safety Related (NSR) SSCs whose failure could prevent the satisfactory accomplishment of the function of any of the SR SSCs. This scoping criterion is typically very plant-specific and can be difficult to incorporate. The US NRC and the industry have agreed to additional guidance for this criterion (see NEI 95-10, R6, App. F).
- (a)(3). SSCs that are relied on in a safety analysis or plant evaluation to perform a specific function in compliance with the US NRC regulations for Fire Protection (FP) (10 CFR 50, App R for facilities operating prior to 1979), Environmental Qualification (EQ), Pressurized Thermal Shock (PTS) (10 CFR 50.61 and 50.61a), Anticipated Transients Without Scram (ATWS), & Station Blackout (SBO).
Screening[edit]
Reference: 10 CFR 54.21 a.1.i and ii
After determining which SSCs are in-scope, SSCs are further assessed to determine whether they are ‘Active’ or ‘Passive’ (See NEI 95-10, App B). While active SSCs that meet one or more of the scoping criteria above are in scope of LR, only passive, long-lived components require aging management review.
Generally, the following criteria are followed to determine which components require aging management; a passive component is a component that performs an intended function without moving parts or change in configuration or properties and requires aging management if the component is not subject to replacement based on operating lifetime or time-period.
Aging Management Review (AMR)[edit]
Reference:10 CFR 54.21 (a)(3)
The Scoping and Screening process results in a listing of SSCs that are long-lived and passive, and these SSCs then require aging management review. The material and environment of each SSC needs to be identified, and then the aging effects can be determined. The aging effects can be identified using EPRI ‘tools’ for license renewal and subsequent license renewal (Mechanical, Structural, and Electrical), and other industry guidance documents. Once the material, environment, and aging effect combinations are identified, an aging management program (AMP) is assigned to manage the effects of aging.
Aging Management Programs (AMP)[edit]
Reference: NUREG-1801, or NUREG-2191)
AMPs are created to manage the aging effects for structures and components identified in the AMR process. NUREG-1801 (for initial license renewal) or NUREG-2191 (for subsequent license renewal), commonly referred to as the GALL reports, provide a list of US NRC previously approved AMPs, including criteria for the contents of those AMPs. Some AMPs are created to manage the aging of specific components like the reactor vessel, reactor internals, or steam generators. Some AMPs could also be plant-specific, in order to manage a unique aging effect or component.
The licensee will develop AMPs or reference existing AMPs needed to demonstrate that the effects of aging will be adequately managed throughout the PEO. If the AMP meets the US NRC criteria suggested in the GALL, the US NRC review would be straightforward (i.e., AMP has been previously approved by US NRC). If a licensee uses a plant specific AMP or takes exception to suggested criteria in the GALL, additional review by the US NRC will be needed.
See Aging Management Programs (AMPs) for more detail on AMPs.
Time Limited Aging Analyses (TLAA)[edit]
Reference: 10 CFR 54.21 (c)
The License Renewal Rule, 10 CFR 54, requires that TLAA that meet the six criteria in 10 CFR 54.3 must be evaluated for the PEO and included in the LRA. TLAAs are analyses that involve systems, structures, and components within the scope of the LRA, consider the effects of aging, and involve time-limited assumptions defined by the term of the current operating license. The TLAA must be evaluated to show that the TLAA is valid through the PEO, can be projected to the end of the PEO, or the aging effects will be managed.
Environmental Report[edit]
Reference: 10 CFR Part 51, Subpart A (10 CFR 54.23)
The Environmental Report is a separate section of the application. It provides a detailed analysis of the effects of the proposed extended operation of the plant, including refurbishment activities, on the environments around the plant.
Post-Application Submission – Prior to US NRC Approval[edit]
- CLB Changes During US NRC Review of LRA (10 CFR 54.21(b))
- During the US NRC’s LRA review process, an annual update of changes to CLB is required up to at least 3 months prior to the scheduled completion of the US NRC review. This is done to ensure that the plant-specific attributes are all identified in the LRA. This process may add to the scope of LRA if changes to the CLB occur during the US NRC review process.
- A FSAR Supplement (10 CFR 54.21(d))
- Appendix A of the LRA is typically the FSAR supplement, that will be added to the FSAR after approval of the renewed license. App. A includes a summary description of all the AMPs, and a listing of all the TLAAs along with a summary evaluation of the TLAA results. Additionally, Appendix A will include a listing of all commitments related to LR. The final version of Appendix A, including the list of commitments, as agreed to by the applicant and the US NRC after changes are made during the review of the LRA, will be added to the FSAR during the next annual update of the FSAR in accordance with 10 CFR 50.71(e).
International LTO Assessment Approach[edit]
Several of the IAEA Member States follow the methodology on LTO Assessment provided in the IAEA’s SSG-48 on “Ageing Management and Development of a Programme for Long Term Operation of Nuclear Power Plants”. The NPPs following this safety guide should also address the non-physical aging (obsolescence) of SSCs. The following section addresses only physical aging of SSCs.
- Scope setting process
The objective of the scope setting process (herein referred to as “scoping”) is to verify that all SSCs of nuclear or radioactive installation are identified, selected, and prioritized using a methodology that adequately manages aging risks and that are in compliance with applicable national and international regulatory requirements.
According to the paragraph 5.16 of the IAEA’s SSG-48, “the following SSCs should be included in the scope of aging management:
- SSCs important to safety that are necessary to fulfil fundamental safety functions:
- Control of reactivity;
- Removal of heat from the reactor and from the fuel store;
- Confinement of radioactive material, shielding against radiation and control of planned radioactive releases, and limitation of accidental radioactive releases.
- Other SSCs whose failure may prevent SSCs important to safety from fulfilling their intended functions. Examples of such potential failures are:
- Missile impact from rotating machines;
- Failures of lifting equipment;
- Flooding;
- High energy line break;
- Leakage of liquids (e.g., from piping or other pressure boundary components).
- Other SSCs that are credited in the safety analyses (deterministic and probabilistic) as performing the function of coping with certain types of events, consistent with national regulatory requirements, such as:
- SSCs needed to cope with internal events (e.g., internal fire and internal flooding);
- SSCs needed to cope with external hazards (e.g., extreme weather conditions, earthquakes, tsunamis, external flooding, tornados and external fire);
- SSCs needed to cope with specific regulated events (e.g., pressurized thermal shock, anticipated transient without scram and station blackout);
- SSCs needed to cope with design extension conditions or to mitigate the consequences of severe accidents.”
IAEA’s Nuclear Safety and Security Glossary provides definitions of key words used to describe the scope of aging management.
These definitions can be used to identify detailed differences between the scoping criteria from IAEA's SSG-48 and the US license renewal scoping criteria set forth by 10 CFR 54.4.
In contrast to 10 CFR 54.21 , the IAEA’s SSG-48 considers both passive and active components in the scope of aging management.
Similar to 10 CFR 54.21, the IAEA also establishes criteria for “screening” of SSCs for aging management. SSG-48 does not explicitly use the term “screening”, however the criteria for LTO aging management scope is as follows:
“Structures and components that satisfy both of the following conditions can be excluded from the scope of aging management:
- Structures and components subject to periodic replacement or to a scheduled refurbishment plan on the basis of predefined rules (based on a manufacturer’s recommendation or other basis and not on an assessment of the condition of the structure or component, which would comprise implementation of aging management for the structure or component); and
- Structures and components that are not required by national regulatory requirements to be included in the scope.”
- SSCs important to safety that are necessary to fulfil fundamental safety functions:
- Aging management review (AMR)
The objective of AMR, according to the IAEA, is to systematically identify and assess degradation mechanisms and related aging effects of the in-scope SSCs and confirm that all of them are managed by effective plant programs and TLAAs. Those countries that follow the IAEA’s methodology on aging management assign the potential aging effects and degradation mechanisms from the IGALL Master Table.
Prior to identifying the degradation mechanisms and their aging effects, several tasks are advised to be conducted to perform a comprehensive and thorough AMR. First, it is vital that environments, materials, and operating conditions in the NPP are clearly defined and assigned to each structure, or component. When the previous task has been successfully executed, it is convenient, but not obligatory to create so-called “commodity groups” to facilitate the AMR.
A commodity group is a group of components or structures that have similar functions, materials, environment, and similar operating conditions. Structures and components within the same commodity group (e.g., all stainless steel piping in treated water) are subject to the same aging effects and degradation mechanisms.
- Aging management programs
The objective of AMPs is to ensure that for all in-scope SSCs in nuclear or radioactive installations, the aging effects and degradation mechanisms are adequately managed in compliance with applicable national and international regulatory requirements so that the structures and components do not lose their intended function during the period of operation.
- Time-limited aging analyses (TLAAs)
According to the IAEA’s SSG-48, the TLAAs should meet the six following criteria (Note: The main difference between 10 CFR 54.21(c) and IAEA’s SSG-48 is that the sixth criterion is not necessary to define a calculation as a TLAA according to the paragraph 5.65 of SSG-48 (i.e., meeting criteria 1 through 5 is enough to be considered a TLAA requiring further evaluation):
- TLAAs should involve systems, structures, and components within the scope of aging management.
- TLAAs should consider ageing effects.
- TLAAs should involve time-limited assumptions defined by the current operating term.
- TLAAs should have been determined to be relevant by the operating organization in making a safety determination as required by national regulations.
- Time limited ageing analyses should involve conclusions or provide the basis for conclusions relating to the capability of SSCs to perform their intended functions.
- Time limited ageing analyses should be contained or incorporated by reference in the current licensing basis.
Record of Revisions[edit]
Number Date Description of Changes 0 6/11/2024 Initial version