1. Welcome To my Presentation
on
“An Approach to Assess the Safety Aspects of a
Nuclear Power Plant with Respect to Design Basis
Parameters”

2. Nuclear Safety
• Nuclear safety had been the central issue of nuclear reactor design since the
inception of nuclear power.
• The term “Safety” in the context of nuclear technology means the status and
the ability of a nuclear installation to prevent uncontrolled development of
fission chain reaction or unauthorized release of radioactive substances or
ionizing radiation into the environment and to mitigate the consequences of
incidents and accidents at nuclear installations.
• A nuclear power plant is assumed to be safe when its radiation impact in all
operational states is kept at a reasonably achievable low level and is
maintained below the regulatory prescribed dose limits for internal and
external exposure of the personnel and population and when in case of any
accident including those of very low frequency of occurrence, the radiation
consequences are mitigated.

3. Safety Objectives and Concepts
The nuclear safety objectives and concepts:
• establish the mandatory safety requirements that define the elements necessary to ensure nuclear
safety.
• are applicable to the design and operation of the associated structures, systems and components
as well as to procedures important to safety in nuclear power plants.
Safety Objectives
General
Nuclear Safety
Objective
Technical
Safety
Objective
Radiation
Protection
Objective
Safety
Concepts
The Concept
of Defense-in-
Depth
Consideration
of Physical
Barriers
Operational
Limits and
Conditions

4. The Concept of Defense-in-Depth
• Defense-in-Depth is an element of the safety philosophy that employs successive
compensatory measures to prevent accidents or mitigate damage if a malfunction,
accident or naturally caused event occurs at a nuclear facility.
• Application of the concept of defense in depth throughout design, construction and
operation will provide a graded protection against a wide variety of transients, anticipated
operational occurrences and accidents.
• The concept is applied in practice through the following procedures:
Prevention of Failures
Limiting The Effect of Failures
Limiting Design Basis Accidents
Severe Accident Control
Mitigation of Consequences of Significant Release

5. Design Phase
• Conservative design
approach plays a prominent
role in ensuring the safety
and integrity of a nuclear
power plant throughout its
life cycle.
• Design phase is the
transformation of a thought
to a reflection of the soon
to be built plant.
• Assessment of safety is
carried out in each and
every step of the process to
ensure the safest plant
design as practicable.
Design
Authority
General Design
Criteria
Design
Methods
Proven
Engineering
Practices
Requirement
Specifications
Quality Plans
Operational
Experience
and Safety
Research
Safety Analysis
Design
Documentatio
n
Qualification
or Quality
Assurance
Verification of
Design
Independent
Verification

6. Design Basis
• The main basis for the design of a nuclear
power plant is that the possibility of an
accident causing significant radioactive release
is eliminated .
• A necessary and adequate condition for
meeting this safety objective is that three
fundamental safety functions are provided.
• To ensure a safety level as high as reasonably
achievable through design, the following six
categories are taken into account to ensure
optimum safety of the plant.
Safety
Functions
Control of
Reactivity
Decay Heat
Removal
Containment
of
Radioactive
Release
Specific
Requireme
nts
Multiple
Protective
Barriers
Protection
and
Reactivity
Control
Systems
Fluid
systems
Reactor
Containme
nt
Fuel and
Reactivity
control

7. Design Rules and Limits
The design authority will specify the engineering design rules and limits for all
SSCs. These will comply with appropriate accepted engineering practices. The
design will also identify SSCs to which design limits will be applicable. These
design limits will be specified for normal operation, AOOs and DBAs. The design
limits will include:
• Radiological and other technical acceptance criteria for all operational states and
accident conditions;
• Criteria on protection of fuel cladding and maximum allowable fuel damage
during any operational state and design basis accidents;
• Criteria on protection of the coolant pressure boundary;
• Criteria on protection of the containment in case of extreme external events,
severe accidents and combinations of initiating events.

8. Categories of PIEs
• Postulated initiating events can lead to AOO or accident conditions and include credible failures
or malfunctions of SSCs as well as operator errors, common-cause internal hazards and external
hazards. Postulated initiating events will be grouped into different categories depending on their
frequency of occurrence per calendar year.
• Category 1: steady and transient states during normal operation;
• Category 2: anticipated operational occurrences, with frequency of 10-2 events per year;
• Category 3: accidents of low frequency of occurrence, in the range between 10-2 and 10-4
events per year;
• Category 4: design basis accident of very low frequency of occurrence, in the range
between10-4 and 10-6 events per year.

9. The Postulated Initiating Events (In Detail)
C1 (NO)
•Start up
•Power operation
•Hot standby
•Hot shutdown
•Cold shutdown
•Refueling
•Operation with an inactive loop
•Temperature increase and
decrease at a maximum
admissible rate
•Step load increase and decrease
(by 10 %)
• Load increase and decrease (at
a rate of 5 % load/minute)
within the range between 15
and100 % full power
•Switch-over to house load
operation from 100 % power
with steam dump
•Limiting conditions allowed by
the OLCs.
C2 (AOO)
•Inadvertent withdrawal of a
control rod group with reactor
subcritical
•Inadvertent withdrawal of a
control rod group with reactor at
power
•Static misalignment of control
rod or drop of a control rod
group
•Inadvertent boric acid dilution,
partial loss of core coolant flow
•Total loss of load or turbine trip
•Loss of main feed water flow to
steam generators
•Malfunction of the main feed
water system of steam
generators
•Total loss of off-site power (up to
2 hours)
•Excess increase in turbine load
•Very small loss of reactor
coolant
C3 (DBA)
•Loss of reactor coolant (small
pipe break)
•Small secondary pipe break
•Forced reduction in reactor
coolant flow
•Mispositioning of a fuel
assembly in the core with
consequent operation
•Withdrawal of a single control
rod in power operation
•Inadvertent opening and sticking
open of a pressurizer safety
valve
•Rupture of volume control tank
•Rupture of gaseous radioactive
waste hold-up tank
•Failure of liquid radioactive
waste effluent tank
•One steam-generator tube break
without previous iodine spiking
•Total loss of off-site power (up to
72 hours).
C4 (BDBA)
•Main steam line break
•Main feed water line break
•Ejection of any single control rod
•Loss of reactor coolant and
double-ended guillotine break of
the largest pipe
•Fuel handling accidents
•One steam generator tube break
with previous iodine spiking.

10. Common Cause Failures
• Common-cause failures occur when multiple components of the same type fail at the
same time.
• Failure of a number of devices or components to perform their functions may occur as a
result of a single specific event or cause.
• The event or cause may be a design deficiency, a manufacturing deficiency, an operating
or maintenance error, a natural phenomenon, a human-induced event, or an unintended
cascading effect from any other operation or failure within the plant.
• The design will provide the following remedies against common cause failures-
Physical
Separation
Diversity

11. Safety Class
• For the purpose of classification, the nuclear power plant shall be divided into structural or
operational units called systems.
• Every system that is a structural or operational entity shall be assigned to a safety class.
• When safety classification is established and applied attention shall be paid to the fact that
the ensuring of safety functions sets different requirements on equipment of different
types.
Safety
Class 1
Safety
Class 2
Safety
Class 3
Safety
Class 4

12. Nuclear Power in Bangladesh
• Bangladesh is venturing into uncharted territory by opting for nuclear
power to meet growing electricity demands.
• The first ever nuclear power plant of the country will be built at
Rooppur for producing 2000 MW(e) from two units of power.
• The Bangladesh government has signed with the Russian Government
to construct the power plant using the advanced VVER designs.
• Existing VVER nuclear power plants have demonstrated around 1500
reactor years of safe and effective operation.
• New VVER designs are the evolution of proven VVER technology by
improving plant performance and increasing plant safety.
• The viability of new passive systems implemented in new VVER design is
confirmed by extensive R&D works.

13. Safety Concept of VVER Designs
• The safety philosophy embodied in the new VVER designs is unique among reactors on the
market deploying a full range of both active and passive systems to provide fundamental safety
functions. Its safety systems can thus handle complicated situations that go beyond the
traditional design basis accidents.
•Maximum use of proven technologies.
•Minimum cost and construction times.
•Balanced combination of active and passive systems.
•Reduction in influence of human factors.
Main principles of new VVER designs
•Passivity
•Multiple train redundancy
•Diversity
•Physical separation
Concept of safety systems

14. Safety Systems
Active Safety Systems
Pressurizing
System
Emergency
Boron
Injection
System
Emergency
Feed Water
System
Residual
Heat
Removal
System
Double
Containment
Spray
System
Emergency
Power
Supply
System
Passive Safety Systems
Emergency
Core Cooling
System
(Passive Part)
Passive
Containment
Heat Removal
System
Passive SG
Heat Removal
System
Passive
Hydrogen
Removal
System
Passive
Reactor Scram
System
Passive Corium
Catcher

15. Advanced Features
• The following safety systems are provided in the
design as additional facilities aimed at severe
accident management
Severe Accident
Management
System
Core Melt
Localizing Facility
Passive System of
Heat Removal
from Containment
Passive System of
Heat Removal
from Steam
Generators
Seal Structure of
Circulation Pumps
Spray System
Fire Safety
Power Supply
Systems
Advanced
Safety
Features

16. Overview of Site Specific External Hazards
• The influence of Tsunami wave and Tornado at the specific site is practically zero with no occurrence till date and not projected for a lengthy
return period. Also there has been no incident of any aircraft crash or major external explosion at the proposed site.
• Maximum Magnitude of Earthquake: 7.6 Mw in 1918 (Epicenter
Distance - 203 km)
• Magnitude of Nearest Earthquake: 4.7 Mw (Epicenter Distance - 39
km)
• Probabilistic PGA: 0.18g-0.20g (for a return period of 2475 years)
Seismic Events
• Maximum Water Level: 15.19 m (1998)
• Predicted Maximum Water Level : 18.44m (1 of 1000 years cycles)Flooding
• Basic Wind Speed: 200 km/h
Wind Speed

17. Structural Solutions for Enhancing Protection
Seismic
•Weak soils to be avoided or
compacted .
•Length of a block be restricted
to three times of its width.
•Safety related main buildings
be designed as Seismic
category-1.
•Plant components belonging
to Seismic Category-1.
•Diverse and spatially
separated safety systems.
•Seismic detectors be installed
onto the base mat.
• Consideration of gravitational
cooling water supply or
cooling with natural
circulation.
Flooding
•Platforms of safety classified
equipment be at a level at
least equal to the MDFL
(19m).
•Elevated arrangement (>9m)
of electrical switchgears and
fuel tanks for the backup
diesel generators.
•Flood safe enclosures , Seals
against water load, Water-
tight design of penetrations
and emergency core cooling
systems, Adequate drainage
system.
•Water tight doors for the
supplementary control room
and the four diesel generator -
safety train rooms.
•Mobile flood barriers and
bilge pumps.
Wind Speed
•Increasing the thickness of
outer containment wall or
using Modular wall barrier
system.
•Plant components and safety
systems designed to
withstand Maximum Design
Load.
Aircraft Crash
•Change of construction
technique for the Shield
building from reinforced
concrete to a plate and
concrete sandwich structure.
• Separation of external fencing
structures with contraction
joint and annulus from the
building internal structures.
• Separation of safety systems
with fire-proof physical
barriers along their whole
length.

18. Comparison of Probable RNPP and VVER Design Basis Safety
RNPP Design
Basis Safety
Seismic: OBE-
0.12g, SSE-0.22g.
Flooding: DBFL:
19m
Wind Speed:
Design Wind
Velocity > 55 m/s.
Aircraft Crash:
Design Basis
Aircraft Weight-
Large Passenger
Airplane.
Tsunami:
Influence of
Tsunami Wave at
the site is
practically zero.
VVER Design Basis Safety
Seismic: OBE-0.12g,SSE-0.25g
Flooding: Mobile systems for removal of heat to the ultimate sink (engine
driven pumps, fast to assembly piping).
Wind Speed: Maximum Design Wind Velocity 56m/s.
Aircraft Crash: DBAW – 5t at a Fall Rate-120 m/s,VVER-1000 (AES-92); DBAW-
5.7t at a Fall Rate-100 m/s,VVER-1200 (AES-2006); DBAW-20t at a Fall Rate-215
m/s and BDBAW- up to 400t at a Fall Rate-150 m/s, VVER-TOI.
Tsunami: Able to Withstand Impact of Tidal Waves as High as 14m.

19. Comparison of VVER-1000 and VVER-1200
VVER 1000 VVER 1200

20. Ideal Design Characteristics of RNPP
• OBE: 0.12g, SSE: 0.22g.
• DBFL: 19m and availability of flood protection measures.
• Maximum design wind load > 200 km/hr.
• Generating units with double containment shell.
• Increased thickness of the housing building of the four trains of safety systems.
• Combination of active and passive safety systems (boron injection system, passive heat
removal systems and a molten core catcher).
• Elevated backup water tanks and large decantation ponds.
• Cooling towers.
• Outfitting of power units with hydrogen explosion, steam explosion and direct containment
heating protection systems.
• Mobile diesel generators to ensure long term safe conditions of power units in case of NPP
blackout.
• Diversity of all systems of AC emergency power.
• Separation of I&C systems.

21. Thank You
For Your Attention