A Worker Safety Assessment Methodology has been developed to assess the risks to workers from radiological accidents at non-reactor nuclear facilities. The methodology utilizes Process Hazards Analysis, proposed risk goals, and Quantitative Risk Analysis. The first phase of a trial application of the methodology to a nuclear facility has been completed and is being reports

Marchese, A.R.

Neogy, P.

UNT Digital Library

BNL-62 7 2 7 CofiF-qS I l l  3+- y Trial Application of the Worker SaMy Assessment Methodology' Andrew R. Marchese' and Partha Neogy 'U.S. Department of Energy EH GTN Germantown, Maryland 20585 ABSTRACT A Worker Safety Assessment Methodology has been developed to assess the risks to workers from radiological accidents at non-reactor nuclear facilities. The methodology utilizes Process Hazards Analysis, proposed risk goals, and Quantitative Risk Analysis. The first phase of a trial application of the methodology to a nuclear facility has been completed and is being reported. 1. INTRODUCTION It has been generally recognized for some time that the primary recipients of risks fiom radiological accidents at non- reactor nuclear facilities are the facility workers. In order to assess these risks, the U.S. Department of Energy's (DOE) Office of Nuclear and Facility Safety developed a Worker Safety Assessment Methodology (WSAM)  as described in a DOE report dated June 3, 1994. Subsequently, a trial application of the methodology to a DOE plutonium facility was initiated. The first phase of the trial application has been completed, and preliminary results are being reported in this paper. 2. METHODOLOGY WSAM essentially augments the results of the Process Hazards Analysis @HA) element of the Process Safety Management (PSM) assessment, required for all DOE nuclear facilities, for those cases where PSWrHA results do not provide adequate assurance that DOE worker risks are acceptable. WSAM is a focused analysis of risks to workers from radiological accidents. It conserves resources by first Saeening and then analyzing in detail those selected accident scenarios which approach or exceed a preset threshold risk level. It achieves these results by utilizing three key elements: (1) the Process Hazards Analysis (PrHA) which identifies the various accident scenarios and provides semiquantitative esthaks of their frequencies and consequences, (2) proposed goals which provide metrics against which the risks of the accident scenan'os can be measured. and (3) Quantitative Risk Analysis (QR4) which refines the risk estimates for selected scenarios that approach or exceed the threshold risk level. 'Work pcrformcd undcr the auspices of thc U.S Dcpnrciiiciit of Ejiagy uiidn ConlnflNo. DEACO2-76CH00016. Brookhaven National Laboratory Department of Advanced Technology Bldg. 130, P. 0. Box 5000 Upton, New York 11973-5000 O S T f  The most significant of the proposed goals is a threshold risk level of 10'' fatality per year. This is the average fatality risk from accidents in American industries, and provides the primary benchmark against which the accident scenario risks a! the facility are compared. A maximum dose of 250 rem for all accident scenarios at all credible frequencies constitutes a second proposed goal, and guards against a non-negligible likelihood of prompt fatality. A risk level of lVs fatality per year (i.e., 10% of the average fatality risk from accidents in American industries) constitutes a third proposed goal - one to aspire to. Since WSAM deals with radiological risks, accident scenarios are represented on a risk matrix defined in terms of the scenm'o frequencies and maximum individual doses (Figure 1). The proposed goals are transferred on to the risk matrix by utilizing the appropriate latent fatal cancer risk coefficients applicable to workers (4x10'' per rem for doses below 20 rem, and 8x10'' per rem at doses exceeding 20 rem). Frequency (evenWycaf) R - W W > o a O i r -  C-ZSIIp>Dao>LSlJw A-Doc>2.50- D - U l c ~ > D a c  ' Figure 1 Risk matrix with proposed goals 2 ConWqUCnCC cltcgory (PrHA) A WSAM has been developed to enable its implementation within the Prows Safety Management (PSM) h e w o r k  being considered by DOE for all worker hazards. Process Hazards Analysis (PrHA) forms an important element of PSM as well as of WSAh4. PrHA involves systematic procedures to identify the processes at a facility, select an assessment technique, and perform‘ a systematic hazards analysis. PrHA is utilized in WSAh4 as a first step to provide semiquantitative estimates of risks. In many cases. the semi- quantitative estimates are adequate to demonstrate that the risks are below proposed goals. In some cases. the risks estimated with PrHA may be sufficiently close to the threshold risk level to require more refined estimation involving quantitative analysis. Quantitative Risk Analysis (QRA) is performed by using standard techniques such as fault tree analysis for frequency quantification, and applying an accident analysis approach for consequence evaluation. . Msxiinuin Possible Maximum Individual con?xqucncc @rHA) Dosc Range (CEDE) LotsorLirc > 250 ran 3. APPLICATION B C D One of the recommendations resulting from the development of the Worker Safety Assessment Methodology was that trial applications of the method should be performed in order to: (1) determine the feasibility of performing the assessment, (2) assess the expected resources needed for the assessment, and (3) evaluate whether the expected benefits from the assessment can be realized. Preliminary results from the first of the recommended trial applications are presented below. Dose> MPBB Uptake 250 mn>Dosc>25 mn Dorc CIusing 25 rcm>Dosc~2.5 rem Temporary Work Restriction MinororNo Injuly <25 ran The fhality investigated utilizes a number of processes including plutonium metal production and fabrication, radioisotope heat source development, fabrication of uranium and plutonium based ceramic fuel, and recovery of plutonium and tritium. It incorporates a large number of glove boxes to cany out these processes while providing containment of airborne contaminants. Airborne contaminants are also contained within a four-zone ventilation system that maintains progressively lower pressures from uncontaminated areas to those with the potential for contamination, ensuring air flow from areas of lower contamination to those with higher contamination. The intake and exhaust of the ventilation system are provided with High Efficiency Particulate Air (HEPA) Fiitas to reduce rdease of particulate radioactivity to the environment. The facility is housed in a reinforced concrete building designed to withstand a 0.38g seismic event. The PrHA team had identified and recorded 1435 scenarios having potential consequences to workers, the public and the environment. Each of these scenarios was reviewed as part of this study to determine if the risk is due to a radiologid hazard, and if the risk recipient is a worker. Of the total number of scenarios. 533 were identified as posing radiological risks to workers. The PrHA had assigned fiequency ranges and consequence categories A (loss of life), B (dose greater than maximum permissible body burden uptake), C (dose causing temporary work restriction). and D (dose causing minor or no injury) to each of the scenarios. The consequences categories in the PrHA represent effects differing by orders of magnitude as can be seen when expressed in dose ranges as illustrated in the table below. Table 1 Relationship Between PrHA Consequence Categories, Maximum Possible Consequence, and Corresponding Dose Ranges 3 CIII for which the risk level of 1 0 '  per year is exceeded. The much smaller number of scenarios applying to the ex-facility worker for which a risk level of 1 0 '  fatality per year is exceeded indicates that at a facility with a robust confinement structure and effluent filtration systeN the in-facility worker is the primary risk recipient. Frequency Bins . v  N Ill IO4 IO' IO4 IOJ lo5 lo" loo Frequency (events/year) Figure 2 In-facility worker risk matrix 4. LIMITATIONS OF APPLICATION In this phase of the study. only scoping quantitative risk estimates have been performed for a few selected scenarios. In alater phase. the scenarios with risk which may 5. CONCLUSIONS The present study shows that the WSAM provides a feasible methodology for assessing worker risks at DOE facilities. The cost of this phase of the present study was a modest fiaction of the cost of peworming the PrHA. A second phase involving QRA would be more resource intensive; however, QRA may be applied in a graded fashion to promote cost efficiency. The present study also'indicates that WSAM has the potential to provide significant benefits in terms of facility risk characterization, and cost-effective prioritization of risk reduction measures. DISCLAIMER . -  exceed Or approach 10" fatality per Year would be subjected mj report was prepared as an account of work sponsored by an agency of the United States to firlher detailed to better quantify their frequencies, Government. Neither the United States Government nor any agency thcreof, nor any of their consequences, and the uncertainties in the frequencies and employees, makes any warranty, express or implied, or assumes any legal liability or responsi- consequences. bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- me &sting p r m  ofthe facility, partially motivated ence herein to any specific commercial product, process, or service by trade name. trademark, detailed fisk manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- asset for evaluating worker mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the by the analysis, proved to be a results, however, have limitations as well. They do not provide a dc ien t ly  narrow range of risks to the workers; the Scenario risks are not measured against objective criteria; and the risk discrimination provided may be insufficient to make informed decisions. These limitations can be removed by util'lzing the results of the PrHA in a study like this, and extending it by performing QRA of the higher risk scenarios identified in this study. A follow-up QRA will have other benefits such as determining the importance of preventive and mitigative systems in reducing risk. ofpro,,iding the bases ofa risks and comparing them to Proposed goals' The prHA United States Government or any agency thereof. . 

Trial application of the worker safety assessment methodology

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Trial application of the worker safety assessment methodology

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