International collaboration to improve safety

International collaboration to improve safety

There is a great deal of international cooperation on nuclear safety issues, in particular the exchange of operating experience under the auspices of the World Association of Nuclear Operators (WANO) which was set up in 1989.  In practical terms this is the most effective international means of achieving very high levels of safety through its four major programs: peer reviews; operating experience; technical support and exchange; and professional and technical development. WANO peer reviews are the main proactive way of sharing experience and expertise, and by the end of 2009 every one of the world's commercial nuclear power plants had been peer-reviewed at least once.  Following the Fukushima accident these have been stepped up to one every four years at each plant, with follow-up visits in between, and the scope extended from operational safety to include plant design upgrades. Pre-startup reviews of new plants are being increased.  See also: paper on Cooperation in Nuclear Power Industry.

The IAEA Convention on Nuclear Safety  (CNS) was drawn up during a series of expert level meetings from 1992 to 1994 and was the result of considerable work by Governments, national nuclear safety authorities and the IAEA Secretariat. Its aim is to legally commit participating States operating land-based nuclear power plants to maintain a high level of safety by setting international benchmarks to which States would subscribe.

The obligations of the Parties are based to a large extent on the principles contained in the IAEA Safety Fundamentals document The Safety of Nuclear Installations. These obligations cover for instance, siting, design, construction, operation, the availability of adequate financial and human resources, the assessment and verification of safety, quality assurance and emergency preparedness.

The Convention is an incentive instrument. It is not designed to ensure fulfillment of obligations by Parties through control and sanction, but is based on their common interest to achieve higher levels of safety. These levels are defined by international benchmarks developed and promoted through regular meetings of the Parties. The Convention obliges Parties to report on the implementation of their obligations for international peer review. This mechanism is the main innovative and dynamic element of the Convention.  Under the Operational Safety Review Team (OSART) program dating from 1982 international teams of experts conduct in-depth reviews of operational safety performance at a nuclear power plant. They review emergency planning, safety culture, radiation protection, and other areas. OSART missions are on request from the government, and involve staff from regulators, in these respects differing from WANO peer reviews.

The Convention entered into force in October 1996. As of September 2009, there were 79 signatories to the Convention, 66 of which are contracting parties, including all countries with operating nuclear power plants.

The IAEA General Conference unanimously endorsed the Action Plan on Nuclear Safety that Ministers requested in June. The plan arises from intensive consultations with Member States but not with industry, and is described as both a rallying point and a blueprint for strengthening nuclear safety worldwide. It contains suggestions to make nuclear safety more robust and effective than before, without removing the responsibility from national bodies and governments. It aims to ensure "adequate responses based on scientific knowledge and full transparency". Apart from strengthened and more frequent IAEA peer reviews (including those of regulatory systems), most of the 12 recommended actions are to be undertaken by individual countries and are likely to be well in hand already.
 

In relation to Eastern Europe particularly, since the late 1980s a major international program of assistance was carried out by the OECD, IAEA and Commission of the European Communities to bring early Soviet-designed reactors up to near western safety standards, or at least to effect significant improvements to the plants and their operation. The European Union also brought pressure to bear, particularly in countries which aspired to EU membership.

Modifications were made to overcome deficiencies in the 11 RBMK reactors still operating in Russia. Among other things, these removed the danger of a positive void coefficient response. Automated inspection equipment has also been installed in these reactors. 

The other class of reactors which has been the focus of international attention for safety upgrades is the first-generation of pressurised water VVER-440 reactors. The V-230 model was designed before formal safety standards were issued in the Soviet Union and they lack many basic safety features. Four are still operating in Russia and one in Armenia, under close inspection.

Later Soviet-designed reactors are very much safer and have Western control systems or the equivalent, along with containment structures.

Sources : Safety of Nuclear Power Reactors, from website http://www.world-nuclear.org/info/inf06.html

Nuclear Engineer

JOB SCOPE
The first Nuclear Engineer is started 1957 when the first commercial nuclear power plant (NPP) began operating.  Nuclear engineer is a part of project team where combining technical and scientific skills.  Nuclear engineering projects consist of design and construction of nuclear reactors and power plants, development and production weapons, evaluation of environmental and ecological research, health physics, or industrial safety [1].   Most of nuclear engineers are been assigned to monitor the operation of nuclear power plants to ensure efficiency and conformity to safety standards.

Nuclear engineer should provide with sufficient knowledge likes mathematics, economics, and principles of engineering.  In term of practicality, the nuclear engineer use computer for simulation in problem analysis.
The nuclear engineer tasks as below:

1. Administration
2. Projects/Technical works
3. Supervise other workers
4. Preparation of budget
5. Sales representatives
6. Consultation 
7. Advice the government 

Working hours for nuclear engineer is 40 hours a week.  However, the engineer must willing to work whatever days of shifts are necessary to meet production schedules [1].

SALARY/WAGES
The nuclear engineer salaries are depending to the location and employer.
Below are the salaries for nuclear engineer in federal civil service (California Occupational Guide) [1]:

1. Nuclear Engineer with bachelor's degree, enter at the GS-5 level ($17,686 to $22,993 a year) or at the GS-7 level ($26,000 a year)
2. Nuclear Engineer with master's degree, the beginning engineer enter at the GS-7 level ($21,900 to 28,500 yearly)
3. If three or five years experience in private industry, an engineer might enter at the GS-12 ($38,900 to $50,000 a year) or GS-13 level ($46,200 to $60,100 a year)

TABLE 1 The Median Salary and Projected Job Growth [2]

There are also few benefits as a nuclear engineer likes paid vacations, holidays, and sick leave, medical, dental, and vision insurance, and retirement plans [1].  In some cases, the employer may pay the tuition for employees who take additional job related courses.

References:

1. Nuclear Engineer.  1995.  California Employment Development Department, from World Wide web:  http://www.calmis.ca.gov/file/occguide/engnuc.htm
2. Science Careers: Nuclear Engineer.  2012.  Science Buddies, from World Wide web: http://www.sciencebuddies.org/science-fair-projects/science-engineering-careers/Energy_nuclearengineer_c001.shtml

Security of Nuclear Power Plant

Building a Nuclear Power Plant (NPP) is not an easy task.  The engineers need to concern on the security aspect of NPP.  Specifically physical security.  The incident of 9/11 gives warning to the operation of NPP that the structure must be strong enough to protect the nuclear reactor from been exploded.  In any situations, the NPP must be ready to facing with any threats.  Few factors are been highlighted for the security aspect of NPP, which are:

1. Aircraft impact on fuel housing structures
2. Effects of fire
3. Land/water delivered explosions
4. Assessment guidelines
5. Standoff distances for structures, human injury
6. Standoff distances for spent fuel casks
7. Operational prevention measures.

Below are the comparison World Trade Center (WTC) and typical NPP structures:

FIGURE 1 Comparison of WTC and typical NPP structures [1]

In Aircraft Crash Analysis, there are three types which are penetration, scabbing, and perforation.  If there is penetration crash, means the integrity containment is maintained.  However, if there are scabbing and perforation occurred, the integrity of reactor containment cannot be maintained any more.

FIGURE 2 Aircraft Crash Analysis [1]

Reference:

1. Monograph by Assoc. Prof. Dr. Nasri A. Hamid.  Reactor Safety. Universiti Tenaga Nasional (UNITEN).  Semester 3 2011/2012.

 

Nuclear Insurance

            Congress has established a system of “no-fault” insurance to provide liability coverage in the event of a major reactor accident. This insurance program, initiated under the Price-Anderson Act, combines commercial insurance and self-insurance by the nuclear industry. Large nuclear plants are required to have the maximum amount of liability insurance that is commercially available, currently $200 million. In addition, each licensed reactor is liable for a $75.5 million assessment to provide funds in the event of a major accident at a plant in the United States. (No reactor would be assessed more than $10 million in any one year.)

            With over 100 commercial nuclear power plants in the United States, the combination of commercial insurance and industry self insurance exceeds $8 billion. This is the total liability limit for an accident under the Price-Anderson Act and no claims are required to be paid in excess of this amount. Congress, however, will consider the need for providing an additional source of funds should $8 billion prove inadequate.

            The Price-Anderson Act provides for liability insurance coverage for actual damages incurred by anyone affected by a major reactor accident. Besides the coverage for offsite public liability claims, the NRC requires that utilities maintain $1 billion in onsite property damage insurance to provide funds to deal with cleanup of the reactor site after an accident.

Reference :

U.S. Nuclear Regulatory Commission from website http: /www.n / rc.gov/

External Costs

Another interesting cost to be highlighted when discussing nuclear power is the external costs. The external costs are defined as those actually incurred in relation to health and the environment and quantifiable but not built into the cost of the electricity.


The report of a major European study of the external costs of various fuel cycles, focusing on coal and nuclear, was released in mid 2001 - ExternE. It shows that in clear cash terms nuclear energy incurs about one tenth of the costs of coal. If these costs were in fact included, the EU price of electricity from coal would double and that from gas would increase 30%. These are without attempting to include the external costs of global warming.

The European Commission launched the project in 1991 in collaboration with the US Department of Energy, and it was the first research project of its kind "to put plausible financial figures against damage resulting from different forms of electricity production for the entire EU". The methodology considers emissions, dispersion and ultimate impact. With nuclear energy the risk of accidents is factored in along with high estimates of radiological impacts from mine tailings (waste management and decommissioning being already within the cost to the consumer). Nuclear energy averages 0.4 euro cents/kWh, much the same as hydro, coal is over 4.0 cents (4.1-7.3), gas ranges 1.3-2.3 cents and only wind shows up better than nuclear, at 0.1-0.2 cents/kWh average.  NB these are the external costs only. *Latest Exchange Rates: 1 Euro = 4.01580 Malaysian Ringgit.

Source: World Nuclear Association.

Comparing the Economics of Different Forms of Electricity Generation

It is important to distinguish between the economics of nuclear plants already in operation and those at the planning stage. Once capital investment costs are effectively “sunk”, existing plants operate at very low costs and are effectively “cash machines”. Their operations and maintenance (O&M) and fuel costs (including used fuel management) are, along with hydropower plants, at the low end of the spectrum and make them very suitable as base-load power suppliers. This is irrespective of whether the investment costs are amortized or depreciated in corporate financial accounts – assuming the forward or marginal costs of operation are below the power price, the plant will operate. 

US figures for 2008 published by NEI show the general picture, with nuclear generating power at 1.87 c/kW.
                                                            

 

Note: the above data refer to fuel plus operation and maintenance costs only, they exclude capital, since this varies greatly among utilities and states, as well as with the age of the plant. 

 A Finnish study in 2000 also quantified fuel price sensitivity to electricity costs:

 

These show that a doubling of fuel prices would result in the electricity cost for nuclear rising about 9%, for coal rising 31% and for gas 66%. Gas prices have since risen significantly.

The impact of varying the uranium price in isolation is shown below in a worked example of a typical US plant, assuming no alteration in the tails assay at the enrichment plant.

 

Doubling the uranium price (say from $25 to $50 per lb U3O8) takes the fuel cost up from 0.50 to 0.62 US cents per kWh, an increase of one quarter, and the expected cost of generation of the best US plants from 1.3 US cents per kWh to 1.42 cents per kWh (an increase of almost 10%). So while there is some impact, it is comparatively minor, especially by comparison with the impact of gas prices on the economics of gas generating plants. In these, 90% of the marginal costs can be fuel. Only if uranium prices rise to above $100 per lb U3O8 ($260 /kgU) and stay there for a prolonged period (which seems very unlikely) will the impact on nuclear generating costs be considerable. *Current exchange rate is 1 U.S. dollar = 3.06449537 Malaysian ringgits.

Nevertheless, for nuclear power plants operating in competitive power markets where it is impossible to pass on any fuel price increases (ie the utility is a price-taker), higher uranium prices will cut corporate profitability. Yet fuel costs have been relatively stable over time – the rise in the world uranium price between 2003 and 2007 added to generation costs, but conversion, enrichment and fuel fabrication costs did not followed the same trend.

For prospective new nuclear plants, the fuel element is even less significant (see below). The typical front end nuclear fuel cost is typically only 15-20% of the total, as opposed to 30-40% for operating nuclear plants.

Source: World Nuclear Association

The Cost of Fuel

From the outset the basic attraction of nuclear energy has been its low fuel costs compared with coal, oil and gas-fired plants. Uranium, however, has to be processed, enriched and fabricated into fuel elements, and about half of the cost is due to enrichment and fabrication. In the assessment of the economics of nuclear power allowances must also be made for the management of radioactive used fuel and the ultimate disposal of this used fuel or the wastes separated from it. But even with these included, the total fuel costs of a nuclear power plant in the OECD are typically about a third of those for a coal-fired plant and between a quarter and a fifth of those for a gas combined-cycle plant. The US Nuclear Energy Institute suggests that for a coal-fired plant 78% of the cost is the fuel, for a gas-fired plant the figure is 89%, and for nuclear the uranium is about 14%, or double that to include all front end costs.
 

In March 2011, the approx. US $ cost to get 1 kg of uranium as UO2 reactor fuel (at current spot uranium price):

Uranium:	8.9 kg U3O8 x $146	US$ 1300
Conversion:	7.5 kg U x $13	US$ 98
Enrichment:	7.3 SWU x $155	US$ 1132
Fuel fabrication:	per kg	US$ 240
Total, approx:		US$ 2770

At 45,000 MWd/t burn-up this gives 360,000 kWh electrical per kg, hence fuel cost: 0.77 c/kWh. 

*Current exchange rate is 1 U.S. dollar = 3.06449537 Malaysian ringgits.

Fuel costs are one area of steadily increasing efficiency and cost reduction. For instance, in Spain the nuclear electricity cost was reduced by 29% over 1995-2001. This involved boosting enrichment levels and burn-up to achieve 40% fuel cost reduction. Prospectively, a further 8% increase in burn-up will give another 5% reduction in fuel cost.

Uranium has the advantage of being a highly concentrated source of energy which is easily and cheaply transportable. The quantities needed are very much less than for coal or oil. One kilogram of natural uranium will yield about 20,000 times as much energy as the same amount of coal. It is therefore intrinsically a very portable and tradeable commodity.

The fuel's contribution to the overall cost of the electricity produced is relatively small, so even a large fuel price escalation will have relatively little effect (see below). Uranium is abundant.

There are other possible savings. For example, if used fuel is reprocessed and the recovered plutonium and uranium is used in mixed oxide (MOX) fuel, more energy can be extracted. The costs of achieving this are large, but are offset by MOX fuel not needing enrichment and particularly by the smaller amount of high-level wastes produced at the end. Seven UO2 fuel assemblies give rise to one MOX assembly plus some vitrified high-level waste, resulting in only about 35% of the volume, mass and cost of disposal.


Source: World Nuclear Association Website - The Economics of Nuclear Power Plant.

Recent Economics Performance of a Nuclear Power Plant

A quarter of nuclear plants in the world today have recorded capacity factors of more than 90%, with almost two-thirds of these plants recording better than 75% of capacity factors. This suggests a near-maximum plant utilisation, given that most nuclear plants have to shut down every 18 to 24 months for refuelling/maintenance. Despite this, majority of operating nuclear plants have been upgraded to increase their output. Even with fewer nuclear plants being built today compared to in the 1970s and 1980s, plants currently in operation around the world are generating more electricity than in the past, due to their upgraded output capacities.


In addition to improved economics arising from the upgraded plant capacities, the performance of most operating nuclear plants have also been further improved through better nuclear fuel design based on the use of higher uranium enrichment levels. This resulted in better nuclear fuel utilization.


In most cases, nuclear power is more cost competitive than other forms of electricity generation, except where there is direct access to low-cost fossil fuels. According to the World Nuclear Association, coal is, and will probably remain, economically attractive in countries such as China, the USA and Australia with abundant and accessible domestic coal resources as long as carbon emissions are cost-free. Gas is also competitive for base-load power in many places, particularly using combined-cycle plants, though rising gas prices have removed much of the advantage.


Nuclear energy is, in many places, competitive with fossil fuels for electricity generation, despite relatively high capital costs and the need to internalise all waste disposal and decommissioning costs. If the social, health and environmental costs of fossil fuels are also taken into account, the economics of nuclear power are outstanding.


Source: TNB Website - Think Nuclear, Think Green; and World Nuclear Association Website - The Economics of Nuclear Power 

Economics of Nuclear Power Plant

There are at least four types of costs linger around the implementation of a new nuclear power plant. These costs are basically:

1. Capital costs
2. Production costs
3. Levelised costs
4. Decommissioning and Waste Management costs

Of course there are some other additional costs, but at this point, the stated four are the most prominent.

Capital Costs

Economically speaking, nuclear plant is indeed a highly capital intensive technology. If other factors are discounted, nuclear plants do not appear as palatable as other generation sources since big bucks have to be forked out. Actual nuclear power generation & capital costs vary considerably depending on the location, country and where the plants were built.

Techno-economics studies carried out for Tenaga Nasional Berhad (TNB) - Korea Electric Power Corporation (KEPCO) Nuclear Power Pre-Feasibility Study has concluded that there is a big range of costs associated with nuclear plants. According to IEA/NEA study, typically, 1 unit of 1000MW nuclear plant’s overnight cost ranges between USD2,000/kW to USD4,500/kW. The capital cost of a coal plant ranges between USD1,000/kW to USD1,500/kW. Meanwhile, a gas plant mostly ranges between USD400 to USD800/kW. Nuclear plant has the highest overnight construction costs. Nuclear plant construction costs are generally higher, compared to coal or gas-fired plants, because of higher level of technology, sophistication of equipment, quality of material & quality assurance standards.

Production Costs

On the other hand, operation wise, nuclear plants appear to be more favourable compared to other sources due to its lower operating costs. Once the plants are commissioned, variable or operating costs are minor. Despite the highest capital cost and Operations & Maintenance (O&M) costs among other sources, overall production cost for a nuclear plant is still the lowest. In fact, nuclear power plants have achieved the lowest production costs between coal, natural gas and oil since 2001. Production costs are the O&M and fuel costs of a power plant. Fuel costs make up 26% of the overall production costs of nuclear power plants. Fuel costs for coal, natural gas and oil, however, make up more than 80% of the production costs. Observe figure below for breakdown of production costs between various generating sources.

Doubling of fuel costs will not affect the production costs due to minor percentage of fuel cost portion. As compared to gas and coal plants, nuclear plants need refuelling only once in every 15-24 months. Hence, nuclear plants are not subject to fuel price volatility like natural gas, coal and oil power plants. The graph below shows the effect of doubling the costs of fuel.

In addition, fuel costs are one area of steadily increasing efficiency and cost reduction. For instance, in Spain, nuclear electricity cost was reduced by 29% over 1995-2001. The success is attributed to boosting enrichment levels and burn-up to achieve 40% fuel cost reduction. Prospectively, a further 8% increase in burn-up will give another 5% reduction in fuel cost.

Levelised Costs

Levelised cost is another important factor in determining and comparing the economic cost of energy produced by a nuclear plant with similar base-load alternatives. Levelised cost is the minimum price at which a technology option produces electricity. It is an economic assessment of the cost of the technology over its lifetime which includes initial investment, operations and maintenance, cost of fuel and cost of capital. Levelised costs vary accordingly with figures used for discount rate, fuel price assumption, plant life, construction period as well as capacity factor. Based on the TNB-KEPCO Nuclear Power Pre-Feasibility study, by using certain assumptions for parameters mentioned above, the cost is as follows:

Economic Levelised Cost of Energy (sen/kWh)	Nuclear (Case I)	Nuclear (Case II)	Conventional Coal	Gas Combined Cycle
Without Carbon Tax	17.2	10.9	15.8	17.9
With Carbon Tax (USD 10/tCO2)	17.2	10.9	17.6	18.7

From the table, in comparison with coal and gas plants, the economic levelised cost of energy from nuclear is almost comparable to coal, and 9% lower than gas with natural gas at economic market price. Note that with added tax on carbon, the economic levelised cost of energy from nuclear plant is lower than both alternative and nuclear is economically feasible based on the assumptions in the Case I and Case II. Case I uses the nuclear capital costs of USD4,000/kW while Case II uses the nuclear capital cost of USD2,300/kW. Nuclear becomes more economically favourable when climate change mitigation method such as carbon tax is considered.

Decommissioning and Waste Management Costs

Another cost associated with nuclear plants is decommissioning costs. For nuclear power plants, any cost figure normally includes spent fuel management, plant decommissioning and final waste disposal. These costs, while usually external for other technologies, are internal for nuclear power (i.e. they have to be paid or set aside securely by the utility generating the power, and the cost passed on to the customer in the actual tariff). Decommissioning costs are about 9-15% of the initial capital cost of a nuclear power plant. But when discounted, they contribute only a few percent to the investment cost and even less to the generation cost. In the USA, they account for no more than 5% of the cost of the electricity produced. Total cost for spent fuel management and final nuclear or radioactive waste disposal, or back-end costs of the nuclear fuel cycle usually accounts for an additional 10% of the nuclear electricity cost. However, if the spent fuel is to be directly disposed of, instead of being reprocessed to extract the unused uranium and plutonium produced in routine nuclear power plant operation, the costs may be less.

Source: TNB Website - Think Nuclear, Think Green.

Safety of Nuclear Power Plant

The main component of Nuclear Power Plant (NPP) is nuclear reactor.  Nuclear reactor is an engineering device, in which nuclear fuel and structural materials are arranged such that a self-sustained fission chain reaction can occur in a controlled manner.

In term of nuclear reactor safety, there are two categories consist of :

1. Multiple Barriers
2. Defense-In-Depth.

Multiple Barriers is used to prevent the radioactive materials to the atmosphere where this particular radioactive materials causes radiological hazard to the individual, social, and environmental.

radiological hazard is adverse heath effects of radiation.

Meanwhile, Defense-In-Depth is acting to prevent accidents and mitigate the consequences.  The approaches are Multiple Physical Barriers and Multiple Level Protection.

Multiple Physical Barriers consists of five components which are fuel pellet, fuel cladding, Reactor Containment Structure (RCS) Boundary, Containment, and Exclusion Area Boundary (EAB).

[Figure 1: Multiple Physical Barriers][1]

[Figure 2: Multiple Physical Barriers][1]

Multiple Level Protection consist of five levels where from level 1 till level 5.

[Table 1: Multiple Level Protection of Nuclear Reactor][1]

Reference:

1. Monograph by Assoc. Prof. Dr. Nasri A. Hamid.  Reactor Safety. Universiti Tenaga Nasional (UNITEN).  Semester 3 2011/2012.

Nuclear Myths

Does nuclear energy offer a path away from carbon-based fuels? Or are nuclear power plants too big a threat? It’s time to separate myth from reality.

1. The biggest problem with nuclear energy is safety.

As the tragedy in Japan is making clear, safety is a critical issue. Cost and safety are not related. Concerns about safety lead to extensive regulatory approval processes and add uncertainty to plant developers’ calculations — both of which boost the price of financing new nuclear plants. It’s not clear how much these construction costs would fall if safety fears subsided and the financing became cheaper — and after the Fukushima catastrophe, we’re unlikely to find out.

2. Nuclear power plants are sitting ducks for terrorists.

It’s easy to get scared about terrorist attacks on nuclear plants. After the Sept. 11 attacks, a cottage industry sprung up around the threat, with analysts imagining ever-more horrific and creative ways that terrorists could strike nuclear facilities and unleash massive consequences

3. Democrats oppose nuclear energy; Republicans favor it.

Yes, the GOP base is enthusiastic about nuclear energy, while the Democratic base is skeptical. Moreover, many Republican politicians support assistance to the industry such as loan guarantees for nuclear developers, while many Democrats oppose them. But the politics of nuclear power have changed in recent years, mainly because of climate change.

Reference : http://www.washingtonpost.com/opinions/5-myths-about-nuclear-energy/2011

Use of Nuclear Energy in Malaysia is Safe

The use of nuclear energy to generate electricity in the country is safe and can also increase the nation's long-term energy security. It is based on the number of nuclear plants worldwide.


Director-General of Malaysian Nuclear Agency (Nuclear Malaysia) Datuk Daud Mohamad said " We know that nuclear technology is a clean and safe technology, having developed over 50years ago. Besides, it does not release the greenhouse gases".


Nuclear power was seen by the world as a future source of energy because in most places, the electricity generated by nuclear power plants was cheaper than other alternative sources. Hence, the public awareness of the importance of the use of nuclear technology to generate electricity should be enhanced.


So dear readers, you don't have to worry because the Nuclear Energy is Safe and Clean :)

Reactor Safety

What is Reactor?


Reactor is an engineering devices in which nuclear fuel and structural materials are arranged such that a self-sustained fission chain reaction can occur in a controlled manner.

multiple barriers in typical plant

Fuel container within the reactor, generally thousands of sealed metal tubes, rods, or plates, fabricated to the highest quality standards.

Closed loop of water which transport the fission energy away from the reactor. Water is converted to steam by fission.  The steam passes through a turbine-generator, is condensed and the water eventually returned to the reactor to be reheated.  Note that while this loop serves to generate steam, it also serves to cool the reactor, keeping it in thermal equilibrium.  Should one or more fuel elements fail, mechanically or due to overheating, the fission fragments would be contained in the closed cooling water loop.

Most reactors (except the Chernobyl type) have a third barrier, called a containment building.  It is a large steel lined, concrete structure completely enclosing the reactor and it’s cooling loops.  It is designed to completely contain all of the coolant should a major failure leak occur in the cooling loops, and all of the water flashed to steam.  So even if fission fragments were released into the cooling loop and the loop leaked, fission fragments would be held in the containment building.