Frequency of Regulatory Inspections. Hernández, D.G.; Tellería, D.M. and Jordan, O.D.

Transcription

1 Frequency of Reguatory Inspections Hernández, D.G.; Teería, D.M. and Jordan, O.D. Presentado en: Internationa Conference on the Safety of Radiation Sources and the Security of Radioactive Materias. Dijon, Francia, setiembre 1998

2 FREQUENCY OF REGULATORY INSPECTIONS Hernández, D.G.; Teería, D.M. and Jordan, O.D. Nucear Reguatory Authority Argentina ABSTRACT The efficacy of a reguatory system to contro radiation sources is determined by its appropriated impementation considering the resources avaiabe. The avaiabe resources are usuay imited and, therefore, the effectiveness of the system can be considered as a probem of optimum assignment of resources. The frequency of inspections coud be estabished considering a "safety indicator" for different practices, as we as from each registrant records. In this work, how to determine the frequency of inspections to registrants controed by a Reguatory Authority is anaysed. The methodoogy presented incudes use of Decision Anaysis techniques and experts' opinion. 1. SAFETY DEGREE OF THE PRACTICE To authorise a practice, the Authority imposes requirements, through egisation and pertinent reguations. Naturay, they are the east according to the Authority necessary to carry on safey the practice. We have defined "safety indicator" as a mutiatribute quantity reated with the nature of practices. Different practices have different vaues of the safety indicator, which coud be used to estabish inspection frequencies to verify compiance with requirements. To assess the vaue of the safety indicator, each practice characteristics shoud be considered. Besides safety systems, protection measures, probabiity, and consequences of potentia exposures shoud aso be taken into account. In particuar the foowing items shoud be considered: Requirements imposed to authorise the practice. Leve of standardisation of the practice. Compexity of the practice. Risk of interna contamination or externa irradiation. Typica radioactive inventory. Probabiity and consequences of the potentia exposures. 2. THE SAFETY INDICATOR FOR REGISTRANTS BEHAVIOUR One of the main toos to evauate the safety indicator of each registrant is the reguatory inspection. Inspections shoud be panned to obtain the required information; in particuar "performance indicators" shoud be considered. Radiation protection aspects are considered as appropriated performance indicators, for instance: Leve of compiance with reguations. Radioactive inventory. 581

3 Training and retraining eve of the personne. Safety systems impemented. Doses distribution. Monitoring data from inspections. Accidents occurred. 3. EVALUATION OF SAFETY INDICATOR The safety indicator of a practice and for a registrant in particuar can be evauated by means of appropriate Decision Anaysis techniques, using experts' opinion [1], [2]. The muti-attribute utiity anaysis uses a scoring scheme or muti-attribute utiity function, U, to rank the practices or instaations, considering the reevant radioogica factors. This cassification is carried out through utiity function for each factor, u that indicates the reative desirabiity of the possibe outcome for the factor. Usuay the vaue one is adopted for the best outcome and the vaue of zero for the worst one. The muti-attribute utiity function is given by: U = k u where k represents scae constants that express the reative importance assigned to each attribute. These constants are generay normaized in such a form that k = THE FREQUENCY OF INSPECTION FOR PRACTICES Experts' opinion can be used to carry out a forma Decision Anaysis or, in a simper manner, it can be used to rank the practices according to the vaue of its safety indicator. For exampe, the foowing categories coud be used: EXTREMELY LOW UNACCEPTABLE PRACTICES VERY LOW SAFETY LOW INDICATOR MIDDLE ACCEPTABLE HIGH VERY HIGH With practices ranked in categories, according to the safety indicator, a reative inspection frequency can be estimated. Let us suppose that the categories have been seected in such way that it is assigned an inspection frequency equa to zero to practices of higher vaue of the safety indicator, whie to that of smaer acceptabe vaue of the safety indicator it corresponds an inspection frequency of one. In these circumstances, the inspection frequency can be interpreted as a utiity function that represents a scaing of the subjective vaues assigned by the decision-maker (DM) to the consequences of a decision. The utiity function captures the attitude toward risk of the decisionmaker and it refects his wiingness to take chances. These attitudes can express risk neutraity, risk aversion or risk proneness. See Figure

4 U P VERY LOW LOW MEDIUM HIGH VERY HIGH Practice Safety Indicator Figure 1. Possibe shapes of the utiity function for the Practice Safety Indicator There are severa techniques to construct the utiity function of the DM [3], [4]. If it is estabished the maximum inspection frequency for the practices of smaest acceptabe vaue of the safety indicator, M, and the minimum inspection frequency for the practices with the highest vaue of the safety indicator, m, the inspection frequency for each practice can be determined with the utiity function. For the practice i, the basic frequency of inspection is given by: BFi = U Pi ( M m) + m The inspection frequency is caed by us "basic inspection frequency by practice". 5. THE FREQUENCY OF INSPECTION EACH REGISTRANT The anaysis of the records on radioogica safety of each registrant carrying out a practice aows the deduction of the vaue of its safety indicator. In this paper, the safety indicator of each registrant is used as a modifier of the basic inspection frequency for the practice. In order to determine how much the basic inspection frequency shoud be modified, due to the radioogica safety record of each instaation, the Decision Anaysis technique previousy presented can be used. In that sense, the registrants can be ranked taking into account their own safety indicator, in simiar way to the categorisation carried out for the practices. Assuming that the modifier of the basic inspection frequency varies between 0 and 1 and choosing an arbitrary vaue of 0.5 for registrants with a safety indicator considered norma, the utiity function can take the forms schematised in Figure

5 U I VERY LOW LOW MEDIUM HIGH VERY HIGH Registrant Safety Indicator Figure 2. Possibe shapes of the utiity function for the Registrant Safety Indicator In that sense, the inspection frequency for a registrant j that carries out the practice i is: F ij BF + k ( U 0.5) = i Ij Being for a new instaation U Ij =0.5. The constant k indicates the reative weight that is assigned at the safety indicator of the practice and the safety indicator of the registrant, and can be determined considering the preferences of the DM [3]. In a ess rigorous but much simper way, the constant k can be determined considering how much it coud be accepted that the basic inspection frequency per practice is modify by the registrant records. 6. CONCLUSIONS The proposed method aows determining the inspection frequency to different registrants, considering the vaue of a safety indicator of the practice, and the records of each registrant. In such way, it is possibe to achieve a simpe, ogica and systematic assignment to the avaiabe resources in a compex framework. REFERENCES 1. RAIFFA, H., Decision Anaysis, Addison-Wesey, Reading, (1969) 308 pp. 2. COVELLO, V.T. Decision Anaysis and Risk Management Decision Making: Issues and Methods, Risk Anaysis, Vo. 7, No. 2 (1987) WINKLER, R.L. and HAYS, W.L., Statistics, Hot, Rinehart, Winston (1975) 783 pp. 4. DeGROOT, M.H., Reaching a Consensus, Journa of the American Statistica Association, Vo. 69 No. 345 (1974) Vover a Contenido 584