ML20127L540
| ML20127L540 | |
| Person / Time | |
|---|---|
| Issue date: | 11/18/1992 |
| From: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| References | |
| SECY-92-389, NUDOCS 9211240364 | |
| Download: ML20127L540 (4) | |
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POLICY ISSUE November 18, 1992 SECY-92-389 (Informat. ion) o Lo_t: The Commissioners From: James M. Taylor Executive Director for Operations Sub.iect: SECY-91-241 -- ADEQUACY OF RADI0 ACTIVE MATERIALS USED UNDER TiiE GENERAL LICENSE OF 10 CFR 31.5
Purpose:
To respond to the staff requirements memorandum (SRM) dated October 25, 1991, which requested the staff to provide periodic updates, including specific milestones, of the plans for improved oversight of general licensees.
Backoround: The SRM contained six specific issues that were to be addressed. Five of those issues depended directly on the peer review of an Oak Ridge Association Universities (0RAU) report. The ORAU study was conducted under a Nuclear Regulatory Commission contract to address safety questions related to the improper transfer or disposal of certain devices authorized under general license. The ORAU report postulated scenarios and estimated probabilities that a device would follow certain pathways if not properly controlled (e.g., loss of control th?.t results in a device '
being discarded as trash and being processed in a metal recovery operation). In response to some observed problems with the control of these devices, the Commission published a proposed rule, for a registration and response system (SECY-91-275), that should better ensure that generally licensed devices are not inadvertently or improperly discarded. The ORAU report also postulated scenarios involving the removal of the sources from generally licensed CONTACT:
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- The Commissioners 2 gauges, the subsequent rupture of the sealed sources, and the intake of radioisotopes in ways that lead to very high dose estimates for gauge accidents. No probabilities were-assigned to these scenarios. If the-postulated dose .
scenarios were credible, they would-indicate a need to change some licensing requirements, most' likely the -
engineered-safety design of gauging devices authorized'under both general and specific licenses. However, the staff believed that the assumptions leading to high doses were associated with probabilities so low that changes to licensing requirements, on the basis of the ORAU report, were not justified. The staff's belief was based on its experience with the actual safety performance of the gauges involved in accidents.
In order to provide a better foundation for the ORAU report or to better support the staff views about some of the assumptions and conclusions in the report, the SRM dated August 13, 1990, required a peer review'of the report. The staff contacted the Idaho National Engineering Laboratory (INEL), to conduct the peer review. However, the staff terminated the INEL contract when INEL was either unable or unwilling to provide an acceptable review panel.
. The sixth issue deals with followup action on general licensees that responded to the mail survey, but could not-account for their sources. The one gauge that was not' located during the survey was reported by the licensee under 10 CFR 20.402 and followup actions were taken in accordance with existing policy and procedures. .No resources were expanded to followup on other devices such as tritium exit-signs and static eliminators, because of the-low risk involved.
Discussion: The staff takes issue with the scenarios in the ORAU report involving the destruction of sealed sources used in generally licensed gauges and the subsequent intake of radionuclides which result in very-large' doses. There are about 100,000 generally licensed gauges in use in the-United
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States, under 10.CFR 31.5. .These gauges _'are used for measuring quantities such as levels, thicknesses, and density. The majority of radioisotopes.used in the gauges include: cesium-137, americium-241, .or strontium-90, in quantities ranging from a few millicuries to about 500' millicuries and about I curie of krypton-85, all een - , y 1 ,- < + , --
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incorporated in sealed sources. -Because-of past regulatory
- efforts, many of the radioisotopes used in sealed sources are in- forms that are as far as practicable, both insoluble and non-dispersable,- i.e.,- a cerami.c matrix. Although the ORAU report was limited to a study of. generally licensed devices, it should be noted that there are in' excess of - 1 20,000 gauges used by NRC's specific I?:ensees with similar safety design requirements, where the consequences of an .
extraordinary accident would be about the same. Both sealed sources and gauges are designed and manufactured in accordance with American National Standards Institute and other applicable standards and receive _an independent safety.
review by either NRC or an Agreement State. !
A few million gauge years of exper ence.have been i
accumulated during the past four decades. During that time, the Atomic Energy Commission, and later, the NRC, have.
reviewed numerous reports of gauges, which by design,_could be either specifically or generally licensed, subjected to severe fires, explosions, crushing by industrial equipment, and submerging in molten metals. These. types of-accidents rarely have resulted in a break.of.the sealed source, and to-the best of the staff's knowledge, have not resulted in.
doses above occupational limits ar i probably not above the public dose limit basis for the current 10 CFR Part ~ 20.
During the 1960's, gauges that were involved in severe accidents were subsequently examined by Oak Ridge National Laboratory and Underwriters Laboratories, Inc., to determine safety performance. Records of these examinations indicate that most devices retained their integrity during these events, although some gauges lost lead shielding, Even so, doses remained within regulatory limits. One report examined the. sources from five devices involved in an industrial fire that completely demolished-.the building in which they were located. Only two sources failed, and there was only a minor amount of contamination in the building rubble.
To the best of the staff's knowledge based on its review effort and collective recollection, none of the reports received from general or specific licensees over the years, about gauges involved in industrial and transport accidents, has indicated substantial exposure, if any. The staff believes that it is unlikely that other documented events,
- which substantiate a basis for concern about potential high exposures in the ORAU' report, are likely to surface, during a peer review, to lend credibility to the ORAU-assumptions-at issue. Although, scenarios and assumptions that form the bases for high internal doses in the ORAU report might be possible, experience with the consequences of real . accidents makes them seem highly unlikely.
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- The Commissioners 4 The severe scenarios and consequences presented in the ORAU report represent a sort of bounding analysis that does not demonstrate evident safety but instead indicates a substantial potential risk for certain ingestion pathways.
The staff analysis and experience with these sources indicates that the ORAU scenarios and consequences may be far too conservatively drawn. It would not be simple to deal with the potential risk by some regulatory initiative to avert it. There would be substantial costs associated with regulatory initiatives that require engineering design changes for gauges utilizing radioisotopes. It would be difficult to justify any such changes in current design requirements, given our years of good safety experience with both generally and specifically licensed gauges. Al s o , -
since publication of the ORAU report, a proposed rule that aimed at improved maintenance and control of generally licensed gauges has been published. Nevertheless, the potential risk indicated by the ORAU report must be addressed. The staff is resuming the peer review study of the ORAU report that will be conducted by Pacific Northwest Laboratories and will focus on appropriateness of assumptions and scenario modelling. We presently estimate that it will cost $252,000 and will be completed in about ten months.
Coordination: The Office of the General Counsel has reviewed this paper and has no legal objection.
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aes M. T lor
'ecutive irector for Operations L/
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