The advanced heavy-water reactor (AHWR) or AHWR-300 is the latest

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

n design for a next-generation

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

that burns

thorium Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and ha ...

in its

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

core. It is slated to form the third stage in India's three-stage fuel-cycle plan. This phase of the fuel cycle plan was supposed to be built starting with a 300 MWe prototype in 2016. KAMINI is the world's first thorium-based experimental reactor. It is cooled and moderated by light water, fueled with

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

-233 metal produced by the thorium fuel cycle harnessed by the neighbouring FBTR reactor and produces 30 KW of

thermal energy The term "thermal energy" is often used ambiguously in physics and engineering. It can denote several different physical concepts, including: * Internal energy: The energy contained within a body of matter or radiation, excluding the potential en ...

at full power.

Background

The

Bhabha Atomic Research Centre The Bhabha Atomic Research Centre (BARC) is India's premier nuclear research facility, headquartered in Trombay, Mumbai, Maharashtra, India. It was founded by Homi Jehangir Bhabha as the Atomic Energy Establishment, Trombay (AEET) in January 1954 ...

(BARC) has set up large infrastructure to facilitate the design and development of advanced heavy water reactors. Things to be included range from materials technologies, critical components, reactor physics, and safety analysis. Several facilities have been set up to experiment with these reactors. The AHWR is a pressure tube type of heavy water reactor. The

Government of India The Government of India (ISO 15919, ISO: Bhārata Sarakāra, legally the Union Government or Union of India or the Central Government) is the national authority of the Republic of India, located in South Asia, consisting of States and union t ...

Department of Atomic Energy The Department of Atomic Energy (DAE) (IAST: ''Paramāṇu Ūrjā Vibhāga'') is an Indian government department with headquarters in Mumbai, Maharashtra, India. DAE was established in 1954 with Jawaharlal Nehru as its first minister and Homi ...

(DAE), is fully funding the future development, the current development, and the design of the advanced heavy water reactor. The new version of advanced heavy water reactors will be equipped with more general safety requirements. India is the base for these reactors due to India's large

reserves; therefore, it is more geared for continual use and operation of the AHWR.

Motivation

Thorium is three times more abundant in the Earth's crust than uranium, though less abundant in terms of economically viable to extract proven reserves, with India holding the largest proven reserves of any country. A lot of thorium is also contained in the

tailings In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material ...

of mines that extract

rare earth elements The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set of ...

from

monazite Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the cerium ...

which usually contains both rare earth elements and thorium. As long as demand for thorium remains low, these tailings present a chemical (thorium is a

toxic heavy metal A toxic heavy metal is a common but misleading term for a metal-like element noted for its potential toxicity. Not all heavy metals are toxic and some toxic metals are not heavy. Elements often discussed as toxic include cadmium, mercury and ...

) and - to a lesser extent - radiological issue which would be solved at least in part by use of thorium in nuclear power plants. Unlike

, which actually contains 0.72% of fissile material, thorium is composed almost only out of fertile which can be transmutated into fissile using

thermal neutrons The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...

. This allows a much larger share of the original material to be used without the need for

fast breeder reactor A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. These reactors can be Nuclear fuel, fueled with more-commonly available isotopes of uranium and Isotopes of thorium, thorium, such as uranium-238 and t ...

s and while producing orders of magnitude less

minor actinides Minor may refer to: Common meanings * Minor (law), a person not under the age of certain legal activities. * Academic minor, a secondary field of study in undergraduate education Mathematics * Minor (graph theory), a relation of one graph to an ...

. However, as thorium itself is not fissile, it has to be "bred" first to obtain a fissile material, which can then be used in the same reactor that "bred" the or chemically separated for use in a separate "burner" reactor.

Design

The proposed design of the AHWR is that of a heavy-water-moderated nuclear power reactor that will be the next generation of the PHWR type. It is being developed at

(BARC), in Mumbai, India and aims to meet the objectives of using

thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural ...

s for commercial power generation. The AHWR is a vertical pressure tube type reactor cooled by boiling light water under natural circulation. A unique feature of this design is a large tank of water on top of the primary containment vessel, called the gravity-driven water pool (GDWP). This reservoir is designed to perform several passive safety functions. The overall design of the AHWR is to utilize large amounts of thorium and the thorium cycle. The AHWR is much like that of the pressurized heavy water reactor (PHWR), in that they share similarities in the concept of the pressure tubes and calandria tubes, but the tubes' orientation in the AHWR is vertical, unlike that of the PHWR. The AHWR's core is 3.5 m long and has 513 lattice locations in a square pitch of 225 mm. The core is radially divided into three burn up regions. The burn up decreases as it moves toward the external surface of the core. Fuel occupies 452 lattice locations and the remaining 37 locations are occupied by shutdown system-1. This consists of 37 shut-off rods, 24 locations are for reactive control devices which are consisted of 8 absorber rods, 8 shim rods, and 8 regulating rods. By boiling light water at a pressure of 7 MPa, heat is then removed. The main focus with this model is to get the total power and a coarse spatial power distribution within the core to be within certain degree of accuracy. The reactor design incorporates advanced technologies, together with several proven positive features of Indian pressurised heavy water reactors (PHWRs). These features include pressure tube type design, low pressure moderator, on-power refueling, diverse fast acting shut-down systems, and availability of a large low temperature heat sink around the reactor core. The AHWR incorporates several passive safety features. These include: Core heat removal through natural circulation; direct injection of emergency core coolant system (ECCS) water in fuel; and the availability of a large inventory of borated water in overhead gravity-driven water pool (GDWP) to facilitate sustenance of core decay heat removal. The emergency core cooling system (ECCS) injection and containment cooling can act (

SCRAM A scram or SCRAM is an emergency shutdown of a nuclear reactor effected by immediately terminating the fission reaction. It is also the name that is given to the manually operated kill switch that initiates the shutdown. In commercial reactor ...

) without invoking any active systems or operator action. The reactor physics design is tuned to maximise the use of thorium based fuel, by achieving a slightly negative

void coefficient In nuclear engineering, the void coefficient (more properly called void coefficient of reactivity) is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids (typically steam bubbles) form in the reactor ...

. Fulfilling these requirements has been possible through the use of PuO₂-ThO₂ MOX, and ThO₂-²³³UO₂

MOX Mox or MOX may refer to: People * Jon Moxley (born 1985), American professional wrestler * Mox McQuery (1861–1900), American baseball player Technology * Mac OS X, a computer operating system * Microsoft Open XML, a file format * Mixed ox ...

in different pins of the same fuel cluster, and the use of a heterogeneous moderator consisting of amorphous

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

(in the fuel bundles) and

heavy water Heavy water (deuterium oxide, , ) is a form of water (molecule), water in which hydrogen atoms are all deuterium ( or D, also known as ''heavy hydrogen'') rather than the common hydrogen-1 isotope (, also called ''protium'') that makes up most o ...

in 80–20% volume ratio. The core configuration lends itself to considerable flexibility and several feasible solutions, including those not requiring the use of amorphous carbon based reflectors, are possible without any changes in reactor structure.

Some Distinctive Features of AHWR

* Elimination of high-pressure heavy water coolant resulting in reduction of heavy water leakage losses, and eliminating heavy water recovery system. * Recovery of heat generated in the moderator for feed water heating. * Elimination of major components and equipment such as primary coolant pumps and drive motors, associated control and power supply equipment and corresponding saving of electrical power required to run these pumps. * Shop assembled coolant channels, with features to enable quick replacement of pressure tube alone, without affecting other installed channel components. * Replacement of steam generators by simpler steam drums. * Higher steam pressure than in PHWRs. * Production of 500 m3/day of demineralised water in Multi Effect Desalination Plant by using steam from LP Turbine. * Hundred year

design life The design life of a component or product is the period of time during which the item is expected by its designers to work within its specified parameters; in other words, the life expectancy of the item. Engineers follow a theory to calculate th ...

of the reactor. * A design objective of requiring no exclusion zone on account of its advanced safety features.

Fuel cycle

The AHWR at standard is set to be a closed

nuclear fuel cycle The nuclear fuel cycle, also known as the nuclear fuel chain, describes the series of stages that nuclear fuel undergoes during its production, use, and recycling or disposal. It consists of steps in the ''front end'', which are the preparation o ...

because this will lead to reduction in radio-toxicity. Because of this, the AHWR has alternate fuel options, given it has diverse fuel cycles. It can do closed types and once-through types of fuel cycles. The overall aspect of the AHWR is primed for high burn up with

-based fuel (BARC, 2013). Recycled thorium that is recovered from the reactor is then sent back, and

plutonium Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...

is stored to be later used for a

. The fuel for AHWR would be manufactured by the Advanced Fuel Fabrication Facility, which is under the direction of

(BARC) Tarapur. AFFF is currently working on PFBR fuel rod production. AFFF has been associated with fuel rod fabrication for other research purposes in the past. AFFF is the only nuclear fuel production facility in the world which has dealt with uranium, plutonium and thorium.

Future plans

The Indian Government announced in 2013 it would build an AHWR of 300 MWe with its location to be decided. As of 2017, the design was in the final stages of validation.

Safety innovation

Past nuclear meltdowns such as

Chernobyl disaster On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian Soviet Socialist Republic, Ukrainian SSR, Soviet Union (now Ukraine), exploded. With dozens of direct casualties, it is one of only ...

and

Fukushima nuclear accident The Fukushima nuclear accident was a major nuclear accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan, which began on 11 March 2011. The cause of the accident was the 2011 Tōhoku earthquake and tsunami, whic ...

have made the improvement of construction and maintenance of facilities to be crucial. These accidents were with the involvement of uranium-235 reactors and the poor structures of the facilities they were in. Since then, International Atomic nuclear Association has stepped up protocols in nuclear facilities in order to prevent these accidents from occurring again. One of the top security measures for a meltdown is containment of radioactivity from escaping the reactor. The

Defence in Depth Defence in depth (also known as deep defence or elastic defence) is a military strategy that seeks to delay rather than prevent the advance of an attacker, buying time and causing additional casualties by yielding space. Rather than defeating a ...

is a method used in nuclear facilities to acquire the most effective practice of radioactive containment. The AWHR has acquired the Defense in Depth process which is used in reactors adopting provisions and required equipment in order to retain the radioactivity within the core. The Defense in Depth method establishes procedures that must be followed in order to reduce human error incidents and machine malfunctions. The procedures are the following: * Level 1: Prevention of abnormal operation and failure * Level 2: Control of abnormal operation and detection of failure * Level 3: Control of accidents within the design basis * Level 4: Control of severe plant conditions, including prevention of accident progression and mitigation of consequences of severe accidents * Level 5: Mitigation of radiological consequences of significant release of radioactive materials. The AWHR is an innovation in renewable energy safety as it will limit the use of fissile

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

to breeding fissile uranium-233 from fertile thorium-232. The extraction of

nuclear energy Nuclear energy may refer to: *Nuclear power, the use of sustained nuclear fission or nuclear fusion to generate heat and electricity *Nuclear binding energy, the energy needed to fuse or split a nucleus of an atom *Nuclear potential energy, the pot ...

from the 90th element thorium is said to have more

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

than the world's oil, coal, and uranium combined. The AHWR has safety features that distinguish it from conventional lightwater nuclear reactors. Some of these features consist of: strong safety systems, reduction of heat from core through a built in cooling system, multiple shutdown systems and a

fail-safe In engineering, a fail-safe is a design feature or practice that, in the event of a failure causes, failure of the design feature, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. ...

procedure that consist of a poison that shuts down the system in the case of a technical failure (FBR). The potential threat scientists try to avoid in reactors is the buildup of heat because nuclear energy escalates when it reacts with high temperatures, high pressures and chemical reactions. The AHWR has features that helps reduce the probability of this occurrence through: negative reactivity coefficients, low power density, low excess reactivity in the core and proper selection of material attributes built in.

Technical specifications

References

External links

Advanced Heavy Water Reactor (AHWR) now being designed in Bhabha Atomic Research Centre

Advanced Heavy Water Reactor. Sept 2008
Detailed design and diagrams *http://www.barc.gov.in/reactor/ahwr.pdf {{DEFAULTSORT:Heavy water reactor (Advanced) Heavy-water reactors Nuclear power reactor types