Quiz 1: lec 1-3 Flashcards

Question

above supercritical on t-s diagram

Answer 1

energy loss is small (more thermal efficiency)

Answer 2

lower 32 40 30

Answer 3

use slow neutron (at <1 eV ~103 m/s) to combine with uranium 235. creates fission products and heat and fast neutron (>1 MeV ~107 m/s)

Answer 4

used in CANDU as moderator to slow neutrons

Answer 5

d has extra neutron

Answer 6

heavy water has bigger mass (2 neutrons)

Answer 7

high potential energy to low potential energy state

Answer 8

heavy water moderator modular design large heat sinks simple fuel bundle(calandria tube, pressure tube, fuel) on power fuelling

Answer 9

~7.6m 7.6m 2.5cm (1”) 5cm (2”)

Answer 10

The primary coolant flows through hundreds of individual pressure tubes, each with a feeder at either end leading to headers and steam generators. * The moderator that surrounds the pressure tubes is at ~atm pressure, so there is no need for a large pressure vessel. * Fueling is done on-line.

Answer 11

C02 - inert and wont react

Answer 12

prompt come out right away - dont want delayed can take up to 100 sec- want

Answer 13

✓adding neutron scavengers; ✓keeping below critical mass; ✓moderating the chain reaction; ✓‘delayed neutrons’

Answer 14

induce the fission reaction, which produces the heat in nuclear power reactors ✓And fission creates more neutrons that are used to sustain the chain reaction.

Answer 15

end in fission

Answer 16

(in fuel or in structural material), which do not end in fission * leakage out of the reactor

Answer 17

the very delicate balance between fission reaction, neutron capture and neutron leakage

Answer 18

is the number of ‘balls’ per sec per area: n/s/m2 or, n/(m2 s), or n/m2 s

Answer 19

spontaneous, induced

Answer 20

* The process in which an isolated nucleus undergoes fission, “splitting” into two smaller nuclei, typically accompanied by the emission of one to a few neutrons * The fission fragments are typically unequal in mass and highly radioactive * Energy is released in the form of kinetic energy of the products and as excitation energy of the (radioactive) fission fragments

Answer 21

* The process in which capture of a neutron causes a nucleus to become unstable and undergo fission * The fission fragments are similar to those of spontaneous fission

Answer 22

The total number of nucleons in the nucleus (N+Z ) is denoted A.

Answer 23

with Z protons and N neutrons, surrounded by a cloud of Z electrons

Answer 24

refers to the difference in mass between an atom and the sum of the masses of the protons, neutrons, and electrons of the atom

Answer 25

binding energy between nucleons

Answer 26

is the energy released by the formation of the atomic nucleus.

Answer 27

slide 62 and 63 and 64

Answer 28

The energy released by fission goes into the kinetic energy of the fission products (≈168 MeV), and neutrons (≈5 MeV) and gammas and betas (≈19 MeV), which ultimately becomes heat. The rest goes into neutrino energy, which does not become heat.

Answer 29

kinetic energy gained by an electron passing through an electric potential difference of 1 Volt (in vacuum). A Volt provides one Joule of energy per Coulomb of electrons (6.24 x 1018 electrons). The work done on a single electron accelerated through 1 V is given by the charge times the voltage:

Answer 30

✓ Requirement 4: Fundamental safety functions ✓ Requirement 5: Radiation protection in design; ✓ Requirement 6: Design for a nuclear power plant; ✓ Requirement 7: Application of defence in depth ✓ Requirement 8: Interfaces of safety with security and safeguards; ✓ Requirement 9: Proven engineering practices; ✓ Requirement 10: Safety assessment; ✓ Requirement 11: Provision for construction; ✓ Requirement 12: Features to facilitate radioactive waste management and decommissioning

Answer 31

Fuel * Neutron moderation * Cooling * Control and safety systems * Balance of plant systems

Answer 32

stakeholders customers public reaction / experience regulation codes + standards

Answer 33

societal attitudes and values that change with time with enough margin for human error

Answer 34

* the coolant/moderator is pressurized to15.8 Mpa; T(inlet) = 289oC, T(outlet) = 325oC

Answer 35

coolant/moderator is pressurized to 7.5 Mpa; T(inlet) = 216 oC, T(outlet) = 288 oC; Exit steam quality (wt % steam) = 14.7%

Answer 36

The coolant is pressurized in the fuel channels to 11 MPa; T(inlet)=270oC and T(outlet)=305oC; The moderator is at 70oC and roughly atmospheric pressure.

Answer 37

* There is a tremendous amount of energy produced * There is a lot of heat produced even after the nuclear reaction is terminated * The core contains a large inventory of radioactive material that is hazardous to humans and the environment * Things can happen very fast and there are also considerations over long periods of time.

Answer 38

Control * Greater than 2 billion watts at full power * Equivalent to 30 747’s at full power Cool * 5 min. after shutdown - 1 747 (all engines) * 5 hours after shutdown - 1 747 engine * 5 days after shutdown - 1 747 engine at half throttle

Answer 39

* Design should enable nuclear fission to proceed in a controlled manner CONTROL * Design should be capable to remove the heat produced and convert the heat produced to useful work (power) COOL * Design should have “a means” of ensuring that it’s functions can continue over the expected plant-life in a safe and reliable manner CONTAIN

Answer 40

Keep Fission Products Within the Fuel ✓ Control Reactor Power ▪ Control reactivity additions ▪ Shutdown reliably

Answer 41

Keep Fission Products Within the Fuel ✓ Cool the Reactor and Spent Fuel ▪ Maintain coolant inventory ▪ Maintain coolant flow ▪ Maintain coolant heat sinks

Answer 42

Keep Radioactive Material Within Reactor ✓ Maintain Containment Integrity ▪ Prevent over-pressurization ▪ Prevent over-heating ▪ Prevent containment bypass ✓ Capture Material Within Containment ▪ Scrubbing Deposition ▪ Chemical capture 88 Keep out of the Biosphere

Answer 43

Contain fission products and other radioactive species under all operating conditions, normal and abnormal. * This is the goal of public protection activities. Protect operating staff from harm. * This is the goal of radiological and conventional safety activities. Prevent damage to plant equipment. * This is the goal of financial loss control activities.

Answer 44

Nuclear design * basic design of the reactor core and required shielding Thermal and hydraulic analysis * thermal analysis of the reactor core and fuel, design of the primary coolant system Reactor control and kinetic analysis * reactor control system Mechanical design * design of the fuel elements in conjunction with the nuclear and thermal analysis; design of the primary containment system

Answer 45

Safety components and procedures area are NOT designed independently ✓the design process is interactive Exact design depends to an extent of the purpose of the design ✓examining the design of a new concept (FOAK -First Of A Kind) ✓construction of a prototype reactor of a new concept ✓examining the merits of a new feature added to a developed reactor type (NOAK - Nth Of A Kind) ✓constructing a new size or improved model of a developed reactor type (NOAK) ✓Constructing a well-developed reactor type in a size previously designed but with a minor modification needed to meet regulatory and/or customer requirements

Answer 46

core, control rods, steam to turb, water from condensor, reflector

Answer 47

* Neutron Source * The Reactor Core * Fuel Elements * Coolant * Moderator (depends on design) * Reflector * Pressurizer (depends on design) * Primary Containment * Containment * Heat Exchanger (depends on design) * Safety Systems

Answer 48

* Safety Systems * Balance of Plant Systems ✓Auxiliary Systems ✓Nuclear Steam Supply ✓Power Generating Systems ▪Turbines ▪Generator

Answer 49

The heart of any nuclear reactor system ✓The fuel must be an ideal geometry which allows nuclear fission to proceed. ✓Core geometry must allow the heat generated to be readily and economically removed by the reactor coolant system. ✓Changes in the core lifetime must maintain criticality ✓Provides for shielding of other components from core radiation. ✓Low fuel costs.

Answer 50

few use molten salts solid fuel used in all major concepts must be able to contain fuel and products in config that can be properly cooled and handled should retain integrity under expected op conditions elements- must be compatible with core design, capable of high temp op, provide minimum parasitic neutron absorption fuel fab and reprocessing costs should be low

Answer 51

uranium pellets of uranium oxide uo2 arranged in tubes to form fuel rods contained in reactor core initially u-235 and u-238 during operation other fissile nuclides, partially pu-239, u-233 produced

Answer 52

refers to a nuclide that is capable of being split by an interaction with a thermal neutron. ✓ e.g. U-233, U-235, Pu-239;

Answer 53

refers to a nuclide that may capture a neutron to form a product that eventually decays to become a fissile nucleus ✓ e.g. Th-232 which captures a neutron and becomes U-233 by double beta decay; and U-238 which similarly becomes Pu-239 (Picture a fertile material as an atom ready to be turned into useful fissile material through neutron capture. Like fertile soil, ready to be used to produce harvestable crops.)

Answer 54

In a new reactor with new fuel, a neutron source is needed to get the chain reaction going. Usually this is beryllium (Be) mixed with polonium (Po), radium (Ra) or another alpha-emitter. * Alpha particles from the decay cause a release of neutrons from the beryllium as it turns to carbon-12. * Restarting a reactor with some used fuel may not require this, as there may be enough neutrons to achieve criticality when control rods are removed.

Answer 55

Provide sufficient coolant circulation to remove the heat generated within the core and transport the energy to a prime mover or to a secondary system which also transports it to a prime mover. ✓Coolant must be capable of sustaining high temperatures ✓Must be compatible with the core design. ✓Should provide a minimum of parasitic neutron absorption. ✓Must be designed to provide adequate for all operational and shutdown states ✓Typical coolants: H2O, D2O, liquid Na (or Na-K alloy), liquid organic compounds, air, CO2 , He, boiling H2O

Answer 56

✓ In light water reactors the water moderator functions also as the primary coolant. ✓ In the PWRs, there is secondary coolant circuit where the water becomes steam. ✓ A PWR has two to four primary coolant loops with pumps, driven either by steam or electricity ✓ A BWR has no secondary coolant circuit, the water boils to steam directly

Answer 57

The reflector surrounds the core ✓ Its Purpose ▪ To reduce the loss of neutrons from the core ✓ Reflector material ▪ Determined by energy distribution of neutrons in the core ▪ Beryllium and graphite make good reflectors as they can also act as a moderator. Steel and lead also work but have less of an effect on neutron energy. ▪ Depleted Uranium oxide can also be used as U238 can absorb neutrons and become new fissile material.

Answer 58

Benefits ▪ Lowers the critical mass * Mass of fuel needed to sustain a chain reaction. ▪ Acts as thermal and radiation shield

Answer 59

✓A moderator is a material in the core that slows down neutrons released from the fission process so that they cause more fission. ✓Used to slow down high -energy fission neutrons (~to thermal energies (~0.025 eV) ✓The best moderators are elements of low mass number with small neutron capture cross sections. e.g. H2O,D2O, beryllium, beryllium oxide, graphite ✓Fast reactors don’t need a moderator

Answer 60

238U captures a neutron and forms 239U, which eventually decays to 239Pu after about 3 days. 239Pu is fissile, and contributes to CANDU reactor energy output, but we need 235U to undergo fission to keep the reactor operating, especially during start up or after refueling, where 239Pu is not yet present. 239Pu fission accounts for about half of the heat produced by a CANDU reactor during critical operation!

Answer 61

✓Pressure vessel for PWR and BWR reactors, Pressure Tubes for CANDU * The reactor core, including the fuel, and primary coolant must be contained in a leak-tight system. * The containment must also serve as a reliable barrier to the release of radioactivity: ✓From failed fuel ✓From coolant activation to the environment * Must be designed to withstand shock loading which could result from pipe severance or earthquake/seismic activity

Answer 62

* The primary containment must withstand the expected design pressures. ✓robust steel vessel containing the reactor core and moderator/coolant in some concepts ✓In others, e.g. CANDU, it may be a series of tubes holding the fuel and conveying the coolant through the surrounding moderator.

Answer 63

The structure around the reactor and associated steam generators, shown in green in the figure, is designed to protect from outside intrusion, and to protect those outside from the effects of radiation in case of any serious malfunction inside. * Newer Russian reactors, and some other reactors, install core melt localisation devices or 'core catchers' under the pressure vessel.

Answer 64

* High-pressure primary coolant brings heat from the reactor to a secondary circuit to make steam for the turbine. * From high-pressure primary circuits in some concepts, to a secondary circuit where water turns to steam. * Essentially a heat exchanger like a car’s radiator. Reactors have multiple “loops', each with a steam generator.

Answer 65

* The secondary water must flow through the support structures for the tubes. * Tubes vibration and fretting is designed out * Deposits build up impede the flow of steam and must be avoided. * Chemically maintained to avoid corrosion. * Tubes which fail and leak are plugged, and there is margin designed to allow for this. * Detection of leaks by monitoring N-16 levels in the steam as it exits the steam generator.

Answer 66

* The reactor must be capable of safely bringing the reactor to power, maintaining it there and shutting the reactor down * The control system respond to unexpected load variations and rapid reactor shutdown (scram) during an emergency * Control rods ✓ Neutron-absorbing material (poison) inserted or withdrawn from the core to control fission ✓ Control is achieved by varying neutron density. ✓ Poison materials: Boron (B), Gadolinium (Gd), Cadmium (Cd), Dysprosium (Dy).

Answer 67

✓Allows control of reactor ✓Insertion of poison results in a decrease in reactivity (or neutron multiplication) of the core, i.e., decreases neutron density. Hence, reactor power level is reduced. ✓Withdrawing the poison increases the neutron density and power level. ✓In some design concepts, special control rods are used to enable the core to sustain a low level of power efficiently. (Secondary control systems involve other neutron absorbers, usually boron in the coolant).

Answer 68

* Used for Heat Transport System inventory (liquid state) control and pressure control * The pressurizer is connected to the primary loop through a surge nozzle at the bottom. ✓ Heaters are provided at the bottom of the pressurizer internals, and ✓ a spray nozzle, relief nozzle, and safety nozzle are installed at the top of the pressurizer head. * A “positive surge” of water from the primary loop due to increasing loop pressure is compensated for by injecting cold water from the top of the pressurizer to condense steam * A “negative surge” of water empties the pressurizer, reducing steam pressure at the top of the pressurizer and thus loop pressure. * In this situation, the electrical heaters at the bottom of the pressurizer are automatically activated, converting a portion of the water into steam, resulting in a loop pressure increase

Answer 69

Auxiliary Systems ✓Removal of radioactive material and other contaminants from the primary coolant. ✓The refuelling system ✓Removal of radioactive waste from discharged air and water streams Feed water systems ✓The feedwater system supplies demineralized and preheated light water to the steam generators

Answer 70

✓The steam from the boilers is fed by separate steam mains to the turbine steam chest via the turbine stop valves, and its flow is controlled by the governor valves; ✓Excess steam can be discharged to the atmosphere or bypass the turbine by flowing directly to the condenser; ✓Over-pressure protection is as safety relief valves on each steam source

Answer 71

✓The energy transferred from the primary coolant must be transferred to a prime mover, which is always the turbine

Answer 72

✓Demonstration that no accident situation can significantly endanger the health and safety of workers and the public. ✓Systems to provide heat sink to cool under accident conditions. ✓Enclosures to retain any radioactive releases must also be provided

Answer 73

The electric power used by equipment in the plant is called the station service power. * Station service power takes 5% or so of the generator output. The rest of the electric power is delivered to the grid * It is called the unit net electrical power. Fission power (total power generated in fission)

Answer 74

see 125-133

Answer 75

* The minimum quantity of fissile material that is capable of sustaining a fission chain: ✓depends upon its nuclear material and properties ▪ nuclear fission cross-section ▪ its density, its shape, ▪ its enrichment, its purity, ▪ its temperature, and its surroundings. * Origin of issue ✓2 or 3 neutrons are liberated per fission, but only 1 is required to maintain the fission chain. However, not all neutrons resulting from fission are available to carry on the fission chain ▪ There are losses!!!!!

Answer 76

Neutron losses: non-fission reactions (e.g. radiative capture:i.e., (n, ) ) with other nuclei, but also with fissile materials; and escape from the system through its physical boundaries (leakage) Leakage: can be controlled/reduced by increasing the size, i.e., mass of the fissile material. At critical mass, the chain reaction becomes self sustaining

Answer 77

* Critical mass depends on many factors, examples are: ✓physical form of fissile material and moderator type * Examples of critical mass of 235U: ✓<1 kg for a homogeneous solution in water of uranium salt containing about 90% of fissile isotope ✓200 kg present in 30,000 kg of natural uranium embedded in a matrix of graphite

Answer 78

* Because leakage of neutrons out of reactor increases as size of reactor decreases ✓reactor must have a minimum size to work. * Below this minimum size (critical mass), leakage is too high and keff cannot possibly be equal to 1. ✓Less sustaining nuclear fission * Critical mass depends on: ✓shape of the reactor ✓composition of the fuel ✓other materials in the reactor * Shape with lowest relative leakage, i.e. for which critical mass is least, is the shape with the smallest surface-to-volume ratio: a sphere

Answer 79

* In CANDU reactors, fission neutrons travel about 50 cm before being absorbed by the fuel. The bigger the reactor, the lower the chance that the neutron will leak out before it is absorbed. * Spherical reactors are not practical, so we use a cylindrical core with a diameter slightly bigger than the length.

Answer 80

* The larger the surface area is relative to the volume, the larger the leakage. * Consider the area-to-volume ratio of a sphere. Small reactors have larger leakage and usually require higher enrichments. * Why? * What is enrichment?

Answer 81

* PWR (3400 MWTh) ✓ The vessel is ~12m high with a 4 m diameter, ✓ Core size ( 3.7 m high x 3.4 diameter) * BWR (3300 MWTh) ✓ The vessel is ~22m high with a 6 m diameter, with ✓ Core size ( 3.7 m high x 4.8 diameter) * CANDU-6 (2060 MWTh) ✓ The core is relatively “small”: ~ 7.6 m diameter, 6m length ✓ But notice the diameter

Answer 82

* Many fission products are still decaying long after the originating fission reaction. * Energy (heat) from this nuclear decay is produced in the reactor for many hours, days, even months after the chain reaction is stopped. * This decay heat is not negligible. ✓ When the reactor is in steady operation, decay heat represents about 7% of the total heat generated. ✓shutting down the fission process brings core heat down to about 7 per cent of its running temperature. ✓Even after reactor shutdown, decay heat must be dissipated safely, otherwise the fuel and reactor core can seriously overheat.

Answer 83

* 5% of fission heat goes to moderator ✓ 20% delayed ✓ 80% prompt * 95% of fission heat goes to fuel ✓ 6% delayed ✓ 93-94% prompt * 1% additional from pump heat

Answer 84

Decay heat is an issue and must be considered in two scenarios during design 1.When used fuel is removed from the reactor * Remedy is the fuel must be safely stored, to cool it and to contain its radioactivity. * Design of spent fuel bays as part of the Balance of Plant 2. During a transient when the reactor shuts down * Remedy is to obtain adequate core cooling for safe shutdown to prevent ✓ melt down of reactor and ✓ other safety issues ▪ release of radioactivity into the environment, hydrogen/steam explosions ▪ molten-concrete core interactions * Design of emergency core cooling, emergency mitigation equipment and other associated safety and auxiliary systems for safe shutdown

Answer 85

✓heat energy of the steam in the turbine (Primary mover) ✓ Flow of steam to turbine ✓Rotational energy (Rotor and Stator) ▪ which turn and drives the generator ✓Converts the mechanical energy to electrical energy

Answer 86

One double flow high pressure cylinder * three double flow low pressure cylinders with external moisture separators * live steam reheaters between the high- and low-pressure stages * Called a tandem compound * Note the size ✓ HP and LP Turbines

Answer 87

Governor valve on a steam engine * the governing system determines turbine/generator power * Design features * Reliable and fast acting governor valves * Have emergency trip systems which can detect and prevent turbine overspeed and safely unload the turbine.

Answer 88

✓Steam exiting the high pressure turbine has about 10% moisture content, which must be removed prior to admitting the steam to the low pressure stages.

Answer 89

uses mechanical means to remove much of the moisture content,

Answer 90

live steam raises the steam to superheated conditions

Answer 91

✓It is a three-phase four-pole machine directly coupled to the turbine. ✓In the case of electrical system operating at 60 Hz, the generator typically operates at 1800 rpm, ▪ 50 Hz systems at 1500 rpm. ▪ # Poles = [(120 x Freq)/#rpm] ✓The output voltage is typically 24,000 volts, and is connected via forced air cooled, ▪ isolated phase bus duct to the step-up Main Output Transformer. ✓Cooling of the rotor winding and stator core is by hydrogen

Answer 92

condensed to a pressure and temperature that is as low as practicable. can handle full steam bypass flow when the turbine is not available.

Answer 93

✓ heat removed to the environment by the condenser cooling water

Answer 94

one for each low-pressure turbine cylinder;

Answer 95

uses extraction steam to preheat the feedwater in order to optimize thermodynamic efficiency; * consists of three low pressure (LP), a deaerator, and two HP heaters; * feed pumps return the feedwater to the boilers.

Answer 96

Normal (Group 1) and Emergency (Group 2)

Answer 97

✓Class I Power ✓Class II Power ✓Class III Power ✓Class IV Power

Answer 98

than the highest in Group 1 (Class 1)

Answer 99

✓Seismic qualified – Can survive a seismic event ✓Emergency Power Supply

Answer 100

* Uninterruptible direct current (DC) supplies for essential auxiliaries are obtained from the Class 1 power supply, ✓ Three independent DC instrument buses, ✓ These buses are each supplied from a Class III bus via a rectifier in parallel with a battery ✓ Buses provide power for DC motors, switchgear operation and for the Class II AC buses via inverters. ✓ typically 50V to 250 V DC.

Answer 101

* Uninterruptible AC supplies for essential auxiliaries are obtained from Class II power supply, which comprises: ✓ Two low voltage AC three phase buses which supply critical motor loads and emergency lighting. These buses are each supplied through an inverter from a Class III bus via a rectifier in parallel with a battery. ✓ If a disruption or loss of Class III power occurs, the battery in the applicable circuit will provide the necessary power without interruption. ✓ supplies equipment and instrumentation essential to safe station operation; ✓ typically 50 V to 250 V AC.

Answer 102

* Supplied by on-site Standby Generators if cannot be supplied from Class IV; ✓ AC supplies to auxiliaries that are necessary for the safe shutdown of the reactor and turbine are obtained from the Class III power supply with a standby diesel generator ✓ These auxiliaries can tolerate short interruptions in their power supplies (may be unavailable for 3 minutes); ✓ Essentially to ensure reactor cooling is maintained ✓ typically 400 V to 5 kV AC

Answer 103

* Supplies all major loads directly and all station equipment under normal operating conditions via the other classes ✓ may be unavailable for extended periods (hrs); ✓ Essentially ensure heat sinks are operating ✓ Complete loss of Class IV power will initiate a reactor shutdown. ✓ highest distribution voltage within station(4 kV to 14 kV AC)

Answer 104

The power supplies are classified in terms of their level of reliability * The lower the number the more reliable is the power

Answer 105

✓Main Output Transformer ✓The Switchyard ✓The Station Service and Unit Service transformers

Answer 106

electrical power generated by the station and the Power Grid of the Utility that utilizes the energy. ✓It also produces the electrical power that operates the station

Answer 107

✓ The main transformer steps up the generator output voltage to the same level as the switchyard transmission voltage. ✓ The transformer is rated to meet the generator output requirements and site environment. It is equipped with all standard accessories and the necessary protective equipment.

Answer 108

✓ The switchyard, located near the turbine hall, contains the automatic switching mechanism, including the breakers and disconnects, which is the interface between the station and the power grid transmission lines. ✓ There are at least two incoming lines which are synchronized under normal conditions. ▪ However, the switchyard electrical equipment allows transmission of full station power through any one of the incoming lines.

Answer 109

✓ During normal station operation the station services power is supplied by both the unit service transformer and the system service transformer. ✓ However, either transformer can provide the total service load in the event of a failure of one supply. The transformer is fed from the output system of the turbine generator. ✓ Its operation does not require that the unit be connected to the grid

Answer 110

✓ The system service transformer is similar to the unit service transformer. Fed from the electrical grid via the switchyard ✓ It supplies half of the plant services power requirements under normal operating conditions and is able to provide the total service load when necessary. This transformer is fed from the switchyard and supplies all plant loads during the start -up of the plant, or when the turbine generator is unavailable

Answer 111

✓Digital computers are used for ▪ station control, ▪ alarm annunciation, ▪ graphical data display and logging; ✓Two independent computers, both normally running, but each capable of controlling the unit; ▪ only the 'controlling' computer's outputs are connected to the field devices; ▪ a fault in any essential part of one computer results in automatic transfer of control to the other computer

Answer 112

Because of the complex interdependence of the control systems in a CANDU unit, Digital Control Computers (DCC) perform all 5 major control functions see slide 21

Answer 113

* The two independent shutdown systems * Shut down system1 (SDS#1) and SDS#2 * The emergency coolant injection system (ECIS) and * the containment system. The plant design includes these four special safety systems to protect the public from a harmful radiation release in the event of failure, transient or accident

Answer 114

✓ These systems do not take any part in normal power plant operations, but are “poised” to act ✓ In other words, they are waiting and watching in case the processes and their control systems cannot keep key operating parameters within prescribed limits ✓ In such cases, when there is the potential for fuel failure to occur with a risk of radioactivity release, these special safety systems spring into action.

Answer 115

✓ If the control of reactor power is not assured, one or both Reactor Shutdown Systems will shut it down. ▪ SDS1 and SDS2 based on different physics a. SDS 1- Shut off Rods to absorb neutrons b. SDS 2 - liquid Poison (Gadolinium nitrate solution) to absorb neutrons

Answer 116

✓ If cooling of the fuel is judged to be insufficient, Emergency Core Cooling will be implemented; using light water to cool the core

Answer 117

✓ If there is a risk, or perhaps an actual release of radioactivity from any of the plant systems, then the Containment System will ensure that no unsafe level of radiation is released to areas outside the plant’s boundary. ▪ Called boxed-up ▪ Containment is a leak tight structure

Answer 118

SDS1 and SDS2 ✓ there are two 'full capability' reactor shutdown systems, they are functionally and physically independent of each other, and each able to shut down the reactor; * functional independence is provided by using different methods of shutdown ✓ dropping solid neutron absorbing rods into the core for SDS#1, ✓ injecting liquid poison into the moderator for SDS#2; * physical independence is achieved by positioning the shutdown rods vertically through the top of the reactor, and the poison injection tubes horizontally through the sides of the reactor; ✓ The two shutdown systems (SDS1 and SDS2) respond automatically to both neutronic and process signals

Answer 119

* ECC is initiated when the Heat Transport System pressure has dropped below 5.5 Mpa ✓Indication that Loss of coolant from the HTS has taken place ✓High reactor building pressure in case of break leaking coolant into the reactor building ✓High moderator level in case of a fuel channel break leaking into the moderator

Answer 120

* The systems provide a sealed envelope around the nuclear steam supply systems if an accidental release of radioactivity is detected: ✓ plastic lined pre-stressed posttensioned pressure-retaining concrete containment structure; ✓ Structure and supporting systems which provide the final barrier to limit radioactive releases to the environment to acceptable levels * Designed to withstand the maximum pressure which could occur following the largest possible LOCA * Containment is subdivided into: ✓ Containment envelope R/B including extensions and penetrations ✓ Containment penetrations and isolation ✓ Atmospheric Control

Answer 121

✓ automatic dousing system- ▪ Dousing system for pressure suppression ✓ R/B Air Coolers for heat removal ▪ provide a long-term containment atmosphere heat sink ✓ Filtered Air Discharge (in the long term if required) ✓ access airlocks; ✓ automatic containment isolation system that closes all reactor building penetrations open to the containment atmosphere when an increase in containment pressure or radioactivity level is detected;

Answer 122

* Multi-unit plants with vacuum building:

Answer 123

Single-unit plants with no vacuum building

Answer 124

Land area sufficient to provide the required exclusion zone (500 - 1000 meters) Source of cooling water; Large body of water Connection to the electrical grid; Geology suitable for foundations of the required structures; Known level of seismic activity; Transportation access.