Resolution of Generic Safety Issues: Item B-60: Loose Parts Monitoring Systems (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–34 )
The presence of a loose (i.e., disengaged and/or drifting) object in the primary coolant system can be indicative of degraded reactor safety resulting from failure or weakening of a safety-related component. A loose part, whether it be from a failed or weakened component or from an item inadvertently left in the primary system during construction, refueling, or maintenance, can contribute to component damage and material wear by frequent impacting with other parts in the system. A loose part can pose a serious threat of partial flow blockage with attendant departure from nucleate boiling (DNB) which in turn could result in failure of fuel cladding. In addition, a loose part increases the potential for control rod jamming and for accumulation of increased levels of radioactive crud in the primary system.
The primary purpose of the loose part detection program is the early detection of loose metallic parts in the primary system. Early detection can provide the time required to avoid or mitigate safety-related damage to, or malfunction of, primary system components.
Applicants for construction permits and operating licenses are required to commit to a loose-part detection program. The NRC has developed hardware criteria and programmatic (operational) criteria for loose-parts detection programs. These criteria are contained in Regulatory Guide 1.133146 which was issued in May 1981 after consideration of comments received from the industry.
Loose-parts detection programs are also in effect at most PWR operating facilities. For those programs which are generally consistent with the criteria contained in the proposed Regulatory Guide, operating experience has been very good.
The purpose of this NUREG-04713 task is to resolve any outstanding issues related to implementation of the Regulatory Guide, including the development of staff positions and guidance with respect to upgrading loose parts detection systems at operating facilities.
All CPs and OLs reviewed after January 1, 1978 were required to meet the provisions of the existing Regulatory Guide 1.133,146 Revision 1. In addition, Regulatory Guide 1.133146 recommended that owners of reactors licensed to operate prior to January 1, 1978 review their systems to determine if they were in compliance. Thus, this issue was RESOLVED and no new requirements were established.670