A decade since Fukushima

Introduction:

• The Great East Japan Earthquake of magnitude 9.0 on 11 March 2011 hit the Japanese island of Honshu. The earthquake was centred 130 km offshore the city of Sendai.
• After the earthquake, a 15-metre tsunami hit the shore and disabled the power supply and cooling of three Fukushima Daiichi reactors.
• It caused a nuclear accident beginning on 11 March 2011.
• All three cores of Fukushima Daiichi reactors largely melted in the first three days resulting into the
• Official figures show that there have been 2313 disaster-related deaths among evacuees from Fukushima prefecture.
• Disaster-related deaths are in addition to the about 19,500 that were killed by the earthquake or tsunami.

Fukushima Daiichi reactors: How a Boiling Water Reactor Works?

• In the Fukushima reactors, the radioactive element uranium is the source of the nuclear fission reaction: when one atom of the uranium isotope U-235 breaks down into smaller parts, it produces both energy and neutrons.
• The energy from the fission reaction is used to boil water into steam, which drives turbines to produce electricity.
  
• Pellets of uranium fuel are contained in long, narrow fuel rods made of an alloy of zirconium.
• Water inside the pressure vessel keeps the fuel rods from overheating, and also creates the steam for the turbines.
• Then comes the pressure chamber which is the protective steel shell called the primary containment vessel.
• Circulating the base of that containment vessel is a toroid-shaped structure called the torus, which serves a safety function: If pressure rises too high in the pressure vessel, operators can vent steam into the torus through a series of relief valves.
• The primary containment vessel and the torus are in turn encased by the secondary containment building, a large box of steel and concrete.

What went wrong?

• When earthquake hit the shore, the reactors were not badly damaged, and its emergency shutdown procedures went into effect.
• After the shut down the radioactive by-products of past fission reactions continued to generate heat inside the pressure vessel and the problem was accentuated by the tsunami that swiftly followed the earthquake.
• The tsunami swamped the coastal facility and damaged the generators and power systems that ran the reactors cooling mechanisms.
• Accumulation of heat led to the explosion and the release of radioactive nuclei in the environment.

Problems after a decade?

• Storage of more than 1,000 huge metal contains nearly 1.25 million tons of cooling water from the 2011 disaster and groundwater seepage over the years has been a major problem post disaster.
• The Japanese government wants to gradually release the water into the seaover the next three decades or more after decontamination and dilution.
• The water has been or will be cleaned with an advanced treatment system, known as Advanced Liquid Processing System, that is capable of removing almost all radionuclides present in the water, including the really dangerous ones such as strontium and caesium.
• The International Atomic Energy Agency said the release of the water is “technically feasible” and has offered to provide independent radiation monitoring to reassure the public that it would comply with international standards.

How India started generating electricity from nuclear energy?

• In 1947 when India became independent, its installed electric power capacity was only about 1.5 GW (e), which has now grown to about 298 GW(e) by 2015.
• By the late 1950's, AEC had worked out the economics of generating electricity from atomic power reactors.
• Based on this study, the Government decided to set up a series of nuclear power plants at locations away from coalmines and nearer to load centres.
• The strategy adopted by the Indian nuclear power programme is to use the country's modest uranium and vast thorium resources.
• In line with this strategy, a three-stage programme is envisaged.
  • Pressurized heavy water reactors (PHWRs): The first stage is based on setting up of pressurized heavy water reactors (PHWRs) using indigenously available natural uranium producing electricity and plutonium and is in commercial domain.
  • Plutonium fuelled fast breeder reactors (FBRs): This is being followed by the second stage by plutonium fuelled fast breeder reactors (FBRs) producing electricity and more plutonium and uranium233 from thorium.
  • Thorium cycle: The third stage of reactors will be based on thorium cycle producing electricity and more uranium233. The design of a 300 MW Advanced Heavy Water Reactor is completed and construction of a critical facility for AHWR has been built and being operated.
• The three stage process described above will enable the country to make efficient use of domestic uranium and thorium contributing significantly to attain true energy security beyond 2050.
• India is pursuing fundamental and applied research in the field of plasma physics and thermonuclear fusion and development of technologies relevant to these fields.
• The overall goal of pursuing thermonuclear fusion research is to develop it as a viable energy technology for future.
• The first indigenously designed and fabricated Tokamak ADITYA was commissioned by the Institute of Plasma Research (IPR) in 1989 and has been regularly operated. 

Post Fukushima upgrades in Indian NPPs:

Safety enhancement in Indian NPPs has been a continuous process. Immediately after the Fukushima (Japan) accident safety re-assessment of all Indian NPPs was carried out by NPCIL and AERB. These assessments brought out the requirements for further enhancement in safety, especially against severe external events.

The approach adopted for these safety enhancements is outlined below:

• Re-confirmation of capability to withstand currently defined site specific design / review basis levels of external events for individual plants. This included revisiting the results of earlier PSRs and review of need for further strengthening, as necessary.
• Assessment of margins available for beyond the design / review bases levels of external events. The objective of this assessment was to find out if cliff edges were close to the design basis /review basis levels and to suggest modifications such that minimum safety functions can be performed in such situation.
• Enhancing the capability of the plants to perform the safety functions under extended SBO / extended loss of heat sink through the design provisions. Towards this, NPCIL carried out safety assessment for extended SBO and augment the capability for continued heat removal for 7 days. The measures being incorporated based on the above assessments include:
• Alternate provisions for core cooling and cooling of reactor components including identification / creation of alternate water sources and providing hook-up points to transfer water for long term core cooling,
• Provision of portable DGs / power packs
• Battery operated devices for plant status monitoring
• Additional hook up points for adding up water to spent fuel storage pools
• Review and strengthening of severe accident management provisions particularly with respect to:
• Hydrogen Management
• Containment venting
• Creation of an On-Site Emergency Support Centre at each NPP site which should remain functional under extreme events including radiological, with adequate provisions of communication, monitoring of plant status and having capacity for housing essential personnel for a minimum period of one week.

Significant progress has been made in all the areas identified for post Fukushima upgrades for each of the operating NPP in the country.

What main lessons are learned from the Fukushima-Daiichi accident?

• The basic assumption was that the nuclear power plants safe, so there was a tendency for organizations and their staff not to challenge the level of safety and this resulted in a situation where safety improvements were not introduced promptly.
• Based on the lessons of the accident, the Contracting Parties to the Convention on Nuclear Safety, adopted the Vienna Declaration on Nuclear Safety.
• This declaration includes principles to prevent accidents with radiological consequences and to mitigate such consequences, should they occur after having reported on the implementation of safety upgrades
• It including 6 main axes:
  1. improvement of severe accident management provisions and guidelines;
  2. re-evaluation of site specific external natural hazards and multi-unit events;
  3. enhancement of power systems;
  4. additional means to withstand prolonged loss of power and cooling for the removal of residual heat;
  5. strengthening of measures to preserve containment integrity
  6. improvements of on-site and off-site emergency control centres.
• In particular, the assessment of natural hazards needs to consider the potential for their occurrence in combination, either simultaneously or sequentially, and their combined effects on multiple units of a nuclear power plant.

Way Forward:

Nuclear energy is boon for the energy prospect for the future as it is clean energy with almost zero carbon emission. The only concern is about the safety and radioactive waste disposal. Considering these two dimensions and above mentioned six parameters of Vienna Declaration on the Nuclear safety one can go ahead with the technology. Another challenge of nuclear technology of energy production is falling prey to the terror organisation and nuclear proliferation which many international treatiesseem to restrict. Thus, keeping the issue of safety and technology proliferation at the fore of the challenge nuclear energy really a game changer for the energy security.