China’s approach to PLiM for LTO

The first NPP in China, Qinshan-I, was put into operation in 1991. Since then, 15 units have been built and put into operation of various reactor types, namely pressurized water reactors (PWRs), water cooled moderated power reactors (WWERs) and CANDU reactors, for a total capacity of 12 550 MW(e). PLiM LTO in Chinese NPPs was developed in the late 1990s. The 15 NPPs in operation to date are owned and operated by two groups:

the China National Nuclear Corporation (CNNC) and the China General Nuclear Power Group (CGN). Although slight differences may exist in various NPPs, the organizational structures to carry out PLiM activities are generally similar. Normally, a general manager or deputy general manager may take on the overall PLiM responsibility and a specialized group within a specific department, such as the technical support department or the equipment management department, takes charge of the AMPs.

In China, it is the technical support organizations that provide a wide range of PLiM support to NPPs. The main technical support organizations include SNERDI (Shanghai Nuclear Engineering Research and Design Institute), RINPO (Research Institute of Nuclear Power Operation), SNPI (Suzhou Nuclear Power Institute), NPIC (Nuclear Power Institute of China), CNPEC (China Nuclear Power Engineering Company) and SNPSC (State Nuclear Power Plant Service Company).

2.6.2. Licensing requirements

As shown in Fig. 10, for every NPP in China, the regulator, the National Nuclear Safety Administration (NNSA), requires that a safety review be completed as one of the preconditions for proceeding to the next step, as is done when passing from the design stage to the construction stage or from the construction stage to operations.

During operation, PSRs are required every ten years. The conclusions and recommendations of previous PSRs or FASRs are taken as input to AMP activities and the outcomes of AMPs are reviewed in preparation for the next PSR. Figure 11 shows a typical model of a systematic AMP in relation to two successive PSRs. The NPP operator is required to update the FSAR to reflect safety related modifications to essential SSCs during operation.

To date, no Chinese NPP unit has reached the end of its design life. The NNSA has not yet decided on the licensing requirements for NPP units to continue operation beyond their design life. However, the design life of the first Chinese NPP, Qinshan-I, is 30 years; only 20 years have passed and ten more years of service remain. The LTO strategy will be decided in the near future.

2.6.3. Scoping and screening method

The scoping and screening of SSCs for a PLiM study vary from plant to plant, however, the principles described in IAEA publication Methodoloy for the Management of Ageing of Nuclear Power Plant Components Important to Safety [9] are used and referred to in combination with economic considerations, which may vary from plant to plant. Figure 12 shows the typical screening steps for components under an AMP.

Design

+ decom. Safety regulation for decommission FIG. 10. Licensing steps for Chinese NPPs.

Previous PSR Overall AMP

Review of existing programme and procedure AMP organization and responsibilities

FIG. 11. Systematic AMP model and its relation to the PSR in Chinese NPP.

List all plant systems

Step 1: Preliminary screening

Step 2: System level screening

Step 3: Component level screening

List of components within scope of AMP

List of non-safety-related but lifetime significant components

FIG. 12. Typical screening steps for AMP components.

2.6.4. Evaluation of SSCs

During a PSR, ageing is reviewed in terms of 14 safety factors at the overall plant management level, as well as at the SSC level. The following elements are taken into account:

— Programme policy, organization and resources;

— A documented method and criteria for identifying SSCs covered by the AMP;

— A list of SSCs covered by the AMP, and a record that provides information in support of the ageing management methodology;

— Evaluation and documentation of potential ageing degradation that may affect the safety functions of SSCs;

— The extent of understanding the dominant ageing mechanisms of SSCs;

— The availability of data for assessing ageing degradation, including baseline, operation and maintenance history;

— The effectiveness of operation and maintenance programmes in managing the ageing of replaceable components;

— The programme for timely detection and mitigation of ageing mechanisms and ageing effects;

— Acceptance criteria and required safety margins for SSCs;

— Awareness of the physical condition of SSCs, including actual safety margins and any features that would limit service life.

For some key components in the primary loop, such as the RPV, steam generator, primary piping and cables, among other things, TLAA may be carried out to assess their actual ageing status. For example, a mid-term ageing assessment study was carried out for RPVs, steam generators and the surge line of Qinshan-1 during the period 2006–2008, and an on-line fatigue monitoring system was established on the surge line for this purpose.

2.6.5. Feasibility study

A feasibility study for LTO should be carried out by utilities from the points of view of both safety and economy. All PLiM activities related to major changes, such as power uprates, RPV head replacements and renovation of safety related digital I&C systems, among other things, usually start off with a comprehensive

feasibility study. If the feasibility study report is related to safety SSCs, it is submitted to the NNSA for review.

Only if the safety review conclusions are favourable to the proposed design change can the change be implemented under the supervision of the same nuclear safety regulatory authority.

2.6.6. Documents package structure

In China, the PSR process for an NPP begins with the submission of a PSR plan to the NNSA for review before the PSR is actually carried out. The documents package includes two levels of information, the management level and the detailed technical level. The management level documents include the PSR plan, the quality assurance programme, the overall implementation programme, as well as the implementation procedures for each individual safety factor. The technical level documents include the general PSR report, the individual PSR reports for specific safety factors, and the related supporting materials. In some cases, topical reports that are not related to safety factors are also prepared.

China has no experience in preparing documentation for the purpose of LTO or plant life extension. However, it can be assumed that the documentation system would be similar to that of a PSR with additional considerations related to ageing over and above a standard licence renewal practice.

2.7. THE REPUBLIC OF KOREA’S APPROACH TO PLiM FOR LTO