Regulatory oversight of nuclear safety in Finland. Annual ... - STUK

Regulation of operating plants includes
continuous safety assessment.
STUK’s regulation of operating nuclear facilities
ensures that the condition of the facilities is and
will be in compliance with the requirements, the
facilities function as planned and are operated in
compliance with the regulations. The regulatory
activities cover the operation of the facility, its systems,
components and structures, as well as the
operations of the organisation. In this work, STUK
employs regular and topical reports submitted by
the licensees, on the basis of which it assesses the
operation of the facility and the plant operator’s
activities. In addition, STUK assesses the safety of
nuclear power plants by carrying out inspections
on plant sites and at component manufacturers’
premises, and based on operational experience
feedback and safety research. On the basis of the
safety assessment during operation, both the licensee
and STUK evaluate the need and potential for
safety improvements.
Safety analyses provide tools for assessing
the safety of nuclear facilities
Safety analyses ensure that the nuclear facility
is designed to be safe and that it can be operated
safely. Deterministic and probabilistic approaches
complement each other.
Deterministic safety analyses
For the purpose of STUK’s regulatory YVL Guides,
deterministic safety analyses are analyses of
transients and accidents required for justifying
the technical solutions employed by nuclear power
plants. The licensees update these analyses in
connection with the renewal of operating licences,
periodic safety reviews and any significant modifications
carried out at the plant.
Probabilistic risk analyses
Probabilistic risk analysis (PRA) refers to quantitative
estimates of the threats affecting the safety
of a nuclear power plant and the probabilities of
chains of events and any detrimental effects. PRA
makes it possible to identify the plant’s key risk
factors, and can contribute to the design of nuclear
power plants and the development of plant operation
and technical solutions. The licensees employ
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PRA for the maintenance and continuous improvement
of the technical safety of nuclear facilities.
STUK reviews the deterministic safety analyses
and probabilistic risk analyses related to construction
and operating licences and the operation of a
nuclear power plant. When required, STUK has
its own independent comparison analyses made in
order to verify the reliability of results.
STUK oversees modifications from
planning to implementation
Various modifications are carried out at nuclear
facilities to improve safety, replace aged systems
or components, facilitate plant operation or maintenance,
or improve the efficiency of energy generation.
STUK inspects the plans for extensive or
safety-significant plant modifications and oversees
the modification work by reviewing the documents
submitted by the licensee and carrying out inspections
on site or at manufacturers’ premises.
As a consequence of modifications implemented
at the plant, several documents that describe
the plant’s operation and structure – such as the
Operating Limits and Conditions, the Final Safety
Analysis Report and the operating and maintenance
procedures – have changed. STUK oversees
the document revisions and generally follows the
updating of plant documentation after the modifications.
Operability of the plant is overseen during
operation and annual maintenance
The technical operability of nuclear facilities is
overseen by assessing the operation of the facility
in compliance with the requirements laid down in
the operational limits and conditions, and overseeing
annual maintenance outages, plant maintenance
and ageing management, fire safety, radiation
safety, physical protection and emergency
preparedness.
Operational limits and conditions
The operational limits and conditions (OLC)
of nuclear facilities lay down the detailed technical
and administrative requirements and restrictions
concerning the plant and its various
systems, equipment and structures. The licensee
is responsible for keeping the operational limits
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