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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrilling and Well Services software such as casing design, directional collision avoidance scans and well control applications were introduced as Safety Critical Systems in the paper SPE 73893. A serious, undetected failure in the development or use of one of these products could result in loss of life or catastrophic environmental damage. It was concluded that safety-critical software should only be used within the strict confines of a controlled management system, where software integrity, change, data, process and people competency are all tightly managed. Audits were used to identify best practice and areas for improvement.The paper describes aspects of the controlled management environment developed over the last 18 months in response to the audit's recommendations. The first step was to introduce a series of principles covering software development, implementation, fault tracking and use. These principles are now incorporated as standards, supporting the BP Wells Policy. Both safety and business critical components are now formally incorporated in the vendor's, Landmark Graphics development process. Major reviews involving other operators have been conducted on the casing design and well control applications. A complete listing of the principles is provided in the paper. Their application is illustrated using examples from the casing design, well control, pore pressure, fracture gradient and directional applications. Simple procedures used to track both progress and adherence to the principles are also presented.

LN·l LEGAL NOTICEThis report was prepared as an account of Government sponsored work. Neither the United Slates, n(!r the Commission, nor any pe,.son a~ting on behalf of the Commission: A. Makes any warranty or representation, .expressed or implied, with respe~t to the at~ura~y, completeness, or usefulness of the information ~ontained in this report, or thallhe use of any information, apparatus, method, or pro~ess disclosed in this report may not infringe privately owned-rights; (!r B. Assumes any liabilities with respe~t io the use of; or for damages resulting from the use of any information, apparatus, method, or pro~ess dis~losed in this report.· As used in the above, "person acting on behalf of the Commission" includes any employee or contra~tor of the Commission, or em· ployee of such contractor, to the extent that such employee or contractor of the Commission, or employee of su~h contractor prepares, disseminates, or provides a~cess to, any information pursuant to his employment or ~ontract with the Commission, or bis employment with su~h contractor. y I -:• GEAP-4013 ABSTRACT Control rod materials, designs, and fabrication processes are compared for their relative economies. Control rod lifetime data are calculated with a simple approximation of nuclear worth depreciation.These data are used in conjunction with the estimated fabrication costs to determine the cost of using several absorber materials in a typical power reactor on a cost-per-year basis. The effect the control system has on core power density and fuel lifetime is included. ACKNOWLEDGMENTThe authors are indebted to A. J. Alexander for his help in estimating the costs for the various fabrication processes evaluated in this study.

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