20.08.2015   Nuclear power plant life management processes: Guidelines and practices for heavy water reactors

Regulatory approach in the Republic of Korea

Korean nuclear industry follows the periodic safety review practice. In normal operating period before the plant design life, general PSR is reported to regulatory body every 10 years in accordance with IAEA safety guideline 50-SG-12 of PSR. For the long term operation beyond the design life, PSR should review plant safety including the ageing management for the continued operating period. Korea regulatory authority is trying to combine LR and PSR approach to take the synergy effect.

2.4.1. Regulatory approach in India

After completion of the safety review, the license for the nuclear power plant is issued by Atomic Energy Regulatory Board (AERB) for its design life which typically is in the range of 30 to 40 years. Within the operating license, the Regulatory Body grants initial authorization for a specified period and renewal of authorization for further specified periods after assessment of PSR. AERB requires HWR owner/ operators to conduct PSR for renewal of authorization which include the following:

• Cumulative effects of plant ageing and irradiation damage

• Results of in-service inspection (ISI)

• System modifications

• Operational feedback

• Status and performance of safety systems and safety support systems

• Revisions in applicable safety standards

• Technical developments

• Manpower training

• Radiological protection practices

• Plant management structure, etc.

Table 3. Summary of Ageing Concerns in CANDU Power Plants

SSC

Degradation Mechanisms & Effects

Safety Concern

Regulatory

Requirements

Mitigation Strategies

Pressure tube (PT)

Irradiation-enhanced deformation of PT (sag, axial creep, diametral creep & wall thinning), DHC, material property changes

Failure of PT, (small LOCA), inadequate fuel cooling

N285.4-95

FFSGs

Design/material/manufa cturing improvements (replacement PTs), chemistry control, improved leak detection, trip set-point reductions, inspection.

Calandria tube (CT)

Irradiation-enhanced deformation of CT: sag

Impairment of SDS 2 (LISS nozzles)

PROL License Condition 3.5 CSA N285.4

Monitor CT-nozzle interference, reposition nozzle, replace FC.

Feeder pipe

Wall thinning due to Flow Accelerated Corrosion, Stress Corrosion Cracking, Low-T Creep Cracking

Failure of feeder pipes (small LOCA), primary coolant leakage

CSA N285.4 FFSGs, Life cycle mgmt plan

Chemistry control, addition of chemical inhibitors, repair/replace, inspection.

Steam

generator

tube

Corrosion (SCC, IGA, pitting, wastage), fretting, denting, erosion

Tube leaking or rupture, possible releases

CSA N285.4 OP&P Limits

Inspection and tube plugging. Chemistry control, water-lancing and secondary side chemical cleaning, installing additional bar supports to reduce vibration.

PVC cable

Radiation and

temperature-induced

embrittlement

Insulation failure leading to current leaks and short circuits

R-7. R-8, R-9, L. C. 7.1

Develop effective EQ programmes, procedural controls, test plans, visual inspection.

Containmen t structure

Thermal cycling, periodic pressurizing, fabricating defects, stress relaxation, corrosion, embrittlement

Loss of leak tightness, structural integrity leading to possible releases

CSA N287 series, CSA N285.5, R-7

Pressure testing, visual inspections, concrete coating.

Reactor

assembly

Corrosion (SCC), erosion, fatigue, creep, embrittlement

Loss of moderator

containment,

shielding

CSA N285.4

Visual inspection, leak monitoring, lifetime predictions.

Battery

Oxidation of grids and top conductors

Loss of power to essential systems

L. C. 4, CSA

N286 series

Maintenance, operating experience trending, new battery designs.

Orifice

Flow erosion, material deposition

Loss of monitoring capabilities, consequent loss of control

R-8

Condition monitoring, alternative flow measurements.

This process of PSR for renewal of authorization is to be carried out every nine years within the design life of the NPPs. These PSRs are intended to further ensure a high level of safety throughout the service life of the plant. AERB has already prepared relevant guidelines in this connection as safety guides as follows:

• In-service Inspection of Nuclear Power Plants (AERB/NPP/SG/O-2)

• Surveillance of Items Important to Safety in NPPs (AERB/SG/O-8)

• Renewal of authorization for Operation of NPPs (AERB/SG/O-12)

• Operational Experience feedback for NPPs (AERB/SG/O-13)

• Ageing Management of NPPs (AERB/SG/O-14)