The Chernobyl

Topics: Reliability engineering, Failure, Failure mode and effects analysis Pages: 9 (1915 words) Published: March 16, 2013



Page 597

Chapter 19

Risk management

Failure over time is often represented as a failure curve. The most common form of this is the so-called ‘bath-tub curve’ which shows the chances of failure being greater at the beginning and end of the life of a system or part of a system.

Failure analysis mechanisms include accident investigation, product liability, complaint analysis, critical incident analysis, and failure mode and effect analysis (FMEA).

➤ How can failures be prevented?

There are four major methods of improving reliability: designing out the fail points in the operation, building redundancy into the operation, ‘fail-safeing’ some of the activities of the operation, and maintenance of the physical facilities in the operation.

Maintenance is the most common way operations attempt to improve their reliability, with three broad approaches. The first is running all facilities until they break down and then repairing them, the second is regularly maintaining the facilities even if they have not broken down, and the third is to monitor facilities closely to try to predict when breakdown might occur.

Two specific approaches to maintenance have been particularly influential: total productive maintenance (TPM) and reliability-centred maintenance (RCM).

➤ How can operations mitigate the effects of failure?

Risk, or failure, mitigation means isolating a failure from its negative consequences.

Risk mitigation actions include:
– Mitigation planning.
– Economic mitigation.
– Containment (spatial and temporal).
– Loss reduction.
– Substitution.

➤ How can operations recover from the effects of failure?

Recovery can be enhanced by a systematic approach to discovering what has happened to cause failure, acting to inform, contain and follow up the consequences of failure, learning to find the root cause of the failure and preventing it taking place again, and planning to avoid the failure occurring in the future.

The idea of ‘business continuity’ planning is a common form of recovery planning.

Case study
The Chernobyl failure13
At 1.24 in the early hours of Saturday morning on 26 April
1986, the worst accident in the history of commercial nuclear power generation occurred. Two explosions in quick
succession blew off the 1,000-tonne concrete sealing
cap of the Chernobyl-4 nuclear reactor. Molten core fragments showered down on the immediate area and fission

products were released into the atmosphere. The accident
cost probably hundreds of lives and contaminated vast
areas of land in Ukraine.
Many reasons probably contributed to the disaster.
Certainly the design of the reactor was not new – around
30 years old at the time of the accident – and had been






Page 598

Part Four Improvement

Source: © Vladimir Repik/Reuters/Corbis

2.05 pm Kiev controller asked the unit to continue supplying grid. The ECCS was not reconnected (V). (This particular
violation is not thought to have contributed materially to the disaster, but it is indicative of a lax attitude on the part of the operators toward the observance of safety procedures.)
11.10 pm The unit was released from the grid and continued power reduction to achieve the 25 per cent power level planned for the test programme.

26 April 1986

conceived before the days of sophisticated computercontrolled safety systems. Because of this, the reactor’s emergency-handling procedures relied heavily on the skill
of the operators. This type of reactor also had a tendency
to run ‘out of control’ when operated at low power. For this reason, the operating procedures for the reactor strictly prohibited it being operated below 20 per cent of its maximum power. It was mainly a combination of circumstance and

human error which caused the failure, however. Ironically,
the events which...
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