Our national safety standards for design and operation of industrial gamma radiography exposure devices (IGRED) prescribed by the Atomic Energy Regulatory Board (AERB) in AERB SS-1 are largely based on the requirements specified in ISO 3999 and ANSI N432. Quality assurance which lays down how the prescribed standards are fulfilled is applied to the four phases, viz., design, testing, manufacture and operation and to the various components of the IGRED. These components are source capsule, source holder assembly and coupling, source housing, control unit, guide tube and collimator. The QA requirements do not constitute an upgradation of the stringency of safety standards. They are only a means of effectively ensuring that such standards are indeed met.

Source capsules and coupling:

The source capsules, classified as C43515, be designed to the standards prescribed in AERB SS-3 which are based on ISO-2919.The capsule, for example, is designed to withstand class 4 thermal environment, a thermal shock from 400°C to 20°C and the stipulated external pressure, impact and puncture tests. The coupling between the driving unit and source holder assembly are designed for a tensile load of 1000 N.

Source housing:

The source housing satisfies the shielding and containment standards and the requirements of vibration, horizontal shock, vertical shock and endurance tests.

Control unit, guide tube and collimator:

The control unit which consists of a cranking unit and a teleflex cable is designed and subjected to kinking, crushing and tensile tests.

The teleflex guide tube is to be designed and tested just as the drive cable is. Collimator itself is a QA device in industrial radiography, as it reduces scattered radiation. Its design, manufacture and use are subjected to QA so that it indeed serves the intended purpose effectively.

Operation:

QA in the operation of IGRED is based on proper work practice and frequent checking of the components of the devices for wear and tear. Check lists specific to each type of IGRED have been drawn up for this purpose.

QA procedure:

The QA procedure demands that the various components of the device be designed, reviewed and approved by qualified persons. Design modification introduced at any stage are routed again through design, review and approval phases. The manufacturer process, material selection, inspection, tolerances, techniques of inspections, qualifications of inspectors and acceptance criteria are to be specified prior to manufacture. Each stage of design and manufacture should be documented.

In order to assure that the test parameters are indeed as per specifications, the tests are witnessed by the representatives of the competent authority and the proceedings are documented.

Verification and documentation:

It is important to ensure that the qualifications of person involved in the design, manufacture, testing and operation of IGRED and the specifications of equipment are according to the prescribed standards, these facts are to be verified by authorized persons and documented.

Efforts of RPhD:

The Radiological Physics Division of BARC is bringing out a QA manual for IGREDs. This manual addresses the procedures in design, manufacture and use of various components of IGREDs. For example, the QA requirements for the drive cable include resistance to crushing, uniformity of internal diameter, brittleness of cable, sheathing, tensile strength of the cable wire, and coupling. QA organization and documentation of each activity are key to assuring quality in the design, manufacture and use of industrial gamma radiography exposure devices.