Ricardo Videla ValdebenitoRadiological and Nuclear Safety Department

Chilean Nuclear Energy Commission

The Radiological Accident in Nueva Aldea

Introduction

• The accident occurred on December 14, 2005 during the construction of the Cellulose plant in Nueva Aldea, VIII Region.

• In one of towers under construction, the staff of a contractor company inadvertently lost control of the radioactive source of Ir-192 of 3.33 [TBq] (90 [Ci]) from the operating gamma radiography equipment.

• The operator did not notice the situation because he kept off his ionizing radiation detector.

• The incident occurred on a platform of 22 meters high. • The next day the radioactive source was found by a

group of scaffolding workers. One of them took the radioactive source even though he was indicated that he did not.

Taking account of the Accident• Phone call on 15/12/2005, by responsible for

radiation protection Cellulosa Plant, indicating that there had been a radiological accident, in Nueva Aldea near Concepcion. He indicated that the radioactive source was safe but that they had several irradiated people.

• We were given a phone number to make appropriate inquiries to the industrial radiography company.

• We tell the operators and people who were in contact with the radioactive source were taken urgently to Santiago, in order to make biological dosimetry and analysis of personal dosimeters.

• The inspection mission is prepared.

Prevailing Conditions

• Authorized installation and Radiographer.• Radiography assistant with little experience (6

months in the company) • Night job available starting 20:00.• Low lighting. • Excessive workload. • Near Christmas time. • Nearest overall completion time of the work.• Only 4 radiographs would be made:

“A pain in the neck”, because they would work all night in another structure, also under construction.

Evaporators on contruction

Tower N° 3

(first four radiographies of the shift)

Hour: aprox. 20:00 hrs.

Then from 22:15 they would move to Boiler also in construction

(where it was worked all night after work in Tower N° 3)

General scheme of cellulose plant

• The work team was composed by an Radiographer and three radiography assistants.

• The operator had an ionizing radiation detector kept off.

• The gamma radiography equipment was operated by an unauthorized assistant (only 6 months of experience) Meanwhile, the authorized Radiographer was allocated inside the structure that was going to be radiographed, in order to accelerate the process .

• The assistant did not have adequate training regarding to industrial radiography, equipment safety, radiation protection and the procedure to be performed.

The Accident Root Cause

Failed to assemble source connector

Source assembly connector

The Radiographer allowed an inexperienced person operate the gamma radiography equipment!

Right

Wrong

8

View of where the accident occurredTower N°3, shows the level where the radioactive source remained

Ionizing radiation detectors

Monitor 4EC Rados RDS-110

• The operation was finished (22:15 hrs.) the guide pipe is disassembled, time at which it is estimated that the radioactive source fell on platform.

• Workers could not disconnect the telecommand, the security mechanisms locked that component when the radioactive source is missing or is not in final safety position inside the projector.

• The operator did not consider important the situation and indicated to keep working and check it the next morning.

• The equipment was tied up and dropped to the ground, in order to continue the work, in the power boiler under construction.

The Accident

Post accident inspection on 16 and 17 December 2005

• Equipment and accessories were inspected to verify the conditions in which the accident occurred.

• Statements were taken from each one of the operators involved.

• A met was assembled to gather information from all staff and the Companies involved.

The gamma radiography storage facility

Gamma radiography equipment involved in accident

Manufacturer : Amersham

Model: 660

Nº serie: 5657

Source: Iridio-192

Model source: T-5

Nº serie: MK0807

Activity: 3,33 TBq

or 90 Ci to 12/15/05

Operational test made with “connector gage” to the equipment connections and remote control during the inspection.

Verification of the connection between the conductor cable and the source

Verification of the connection between the conductor cable and the source

16

Dummy model of the Iridium sourceholder used in Amersham equipment

Source assembly connector

Back Sealed Source

Inside Ir-192

Front

Stop ballFlexible leader

17

Scaffold structure where the radioactive source is found

Height, 22 meters above ground level.

Presumably place where it would have fallen Iridium 192 source.

Dummy model of the Iridium sourceholder used in Amersham equipment

In gamma radiography storage facility, some tests were conducted with equipment involved in the accident

Another night view of the storage facility

Test preparation to equipment involved in the accident

Test to ionizing radiation detectors

Operational testing of gamma radiography equipment

Another view of the test

Projector

Telecommand

Connected guide pipe

Ionizing radiation detector

• Although the radiography company had procedures in place and had identified the individual’s responsibilities, they were not strictly followed and their implementation was not supervised.

• A safety culture was practically absent.• The prime responsibility for the radiation

safety lies with the licensee. A safety culture needs to be introduced, fostered and maintained by the management.

Lessons Learnedoperating organization

• The failure to monitor dose rates during the whole radiography operations decisively contributed to the accident consequences.

• Safe operation of industrial radiography depends crucially on proper implementation of radiation protection and safety, for example, regular use of alarm dosimeters and dose rate meters.

Lessons Learnedoperating organization

• The radiography workers involved complained that they were overloaded and working under time pressure. The operator assistant who assembled the radiography equipment was not trained, not qualified (unlicensed) and unskilled.

• On-site safety in industrial radiography depends vitally on the radiographers’ knowledge and skills, and their correct implementation of procedures. Overload and time pressure may hinder safety.

Lessons Learnedoperating organization

• There was no evidence that the gamma radiography company had in place any preventive maintenance programme for the radiography equipment.

• Preventive maintenance programmes may reveal technical incompatibilities or problems that can be corrected in time to eliminate possible causes of mishaps.

Lessons Learnedoperating organization

• The regulatory authority (the CCHEN) granted the gamma radiography company a license and performed annual inspections.

• Formal licenses and inspections by themselves cannot prevent accidents from occurring. The use of specific practical regulations and comprehensive national guidance can provide additional support in the assessment of information submitted with license applications and in the performance of regulatory inspections.

Lessons LearnedNational Authority

• The frequency of inspections should depend on a threat assessment of the practice. An additional way to prevent or to minimize the occurrence of these types of accidents would be to widely distribute posters with photographs of pigtails and instructions on what actions to take should such an object be found at sites where gamma radiography is to be carried out.

Lessons LearnedNational Authority

• After the accident, and on the basis of the accident evaluation, the regulatory body reviewed the technical and administrative requirements for the operators, equipment and training, and introduced additional requirements to fill the gaps existing and to improve the system (a new policy, more resources, enhanced procedures and stricter inspections).

Lessons LearnedNational Authority

• A process of continuous reviews and improvement of the regulatory system by amending the requirements and regulations and by assigning appropriate resources should be instituted.

Lessons LearnedNational Authority

• Due to their having and maintaining basic dosimetry knowledge and capabilities, the Chilean authorities were able to assess the risks and make early knowledge based decisions.

• For any radiation emergency, at least basic capabilities for initial dose assessment should exist in a country.

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Lessons LearnedNational Authority

Corrective Actions• A series of workshops to awareness to the

Radiographers and Radiography assistents on the radiological protection in the field.

• The radiographer and radiography assistent have to do regular use of personal dosimeters, alarm dosimeters and dose rate meters.

• Increase in inspections according to verify the status of the equipment and the control of these by the Companies.

• It pulled out all equipment that no longer met the safety requirements (Amersham 660 and SPEC 2T)

Emergency Cases• The companies are required to have an

emergency plan for natural disasters and radiological emergencies.

• That plan should be tested in simulations throughout the institution staff operating gamma radiography equipment.

• The simulation should be evaluated and approved by the authority.

• The institution must have a record of the date of completion of the simulations, the participants of the tests performed and the staff that gave the instruction.

Workers affected by the accident

By directly manipulating the radioactive source, 3 workers were irradiated.

Two workers were discharged after a few days in the Hospital of the Mutual Security in Santiago.

1 worker was transferred to France to Percy Hospital. He received a specialized treatment for first level.

Another worker, discovered in the investigation process of the Prosecutor, a radiation injury resulted on a foot and had to travel to France.

A total of 35 workers were subjected to tests of biological dosimetry.

Worker ANot related with a Gamma radiography Company

Physical dose reconstruction whole body 1.3-1.5 GyLocal dose to left buttock 940-1600 Gy

Radiography assistant E

Radiography assistant

Estimated dose

whole body < 0.10 Gy