Aging Management of Reactor Coolant System Mechanical Components in Pressurized Water Reactors for License Renewal

2002 ◽  
Author(s):  
M. Subudhi ◽  
R. Morante ◽  
A. D. Lee
Keyword(s):  
Reactor Vessel ◽  
Pressurized Water Reactors ◽  
Pressurized Water ◽  
Reactor Coolant ◽  
Management Review ◽  
Mechanical Components ◽  
Water Reactors ◽  
Effects Of Aging ◽  
License Renewal ◽  
Coolant System

The reactor coolant system (RCS) mechanical components in pressurized water reactors (PWRs) that require an aging management review for license renewal include the primary loop piping and associated connections to other support systems, reactor vessel, reactor vessel internals, pressurizer, steam generators, reactor coolant pumps, and all other inter-connected piping, pipe fittings, valves, and bolting. All major RCS components are located inside the reactor building. Based on the evaluation findings of recently submitted license renewal applications for pressurized water reactors, this paper presents the plant programs and/or activities proposed by the applicants to manage the effects of aging. These programs and/or activities provide reasonable assurance that the intended function(s) of these mechanical components will be maintained for the period of extended operation. The license renewal application includes identification of RCS subcomponents that are within the scope of license renewal and are vulnerable to age-related degradation when exposed to environmental and operational conditions, determination of the effects of aging on their intended safety functions, and implementation of the aging management programs and/or activities including both current and new programs. Industry-wide operating experience, including generic communication by the NRC, is part of the aging management review for the RCS components. This paper presents a number of generic issues, including the time-limited aging analyses, associated with RCS components that require further review by the staff.

Generic Aging Management Programs for License Renewal of PWR Reactor Coolant System Components

2002 ◽  
Author(s):  
V. N. Shah ◽  
Y. Y. Liu
Keyword(s):  
Extended Period ◽  
Nuclear Regulatory Commission ◽  
Lessons Learned ◽  
Aging Effects ◽  
Pressurized Water ◽  
Reactor Coolant ◽  
Water Reactors ◽  
Regulatory Commission ◽  
License Renewal ◽  
Coolant System

The paper reviews the existing aging management programs (AMPs) for the reactor coolant system (RCS) components in pressurized water reactors (PWRs), including the reactor pressure vessel and internals, the reactor coolant system and connected lines, pressurizer, reactor coolant pumps, valves, and steam generators. These programs have been evaluated in the U.S. Nuclear Regulatory Commission (NRC) report Generic Aging Lessons Learned (GALL), NUREG-1801, for their use in the license renewal process. These AMPs include both generic and plant-specific programs. The generic AMPs are acceptable for managing aging effects during an extended period of operation and do not require further evaluation; the plant-specific AMPs require further evaluation. The use of the GALL report should facilitate both preparation of a license renewal application and timely and uniform review by the NRC staff.

Evaluation of Laser Peening for Mitigation of Primary Water Stress Corrosion Cracking in Pressurized Water Reactors

2019 ◽  
Author(s):  
Stephen Marlette ◽  
Stan Bovid
Keyword(s):  
Surface Stress ◽  
Reactor Vessel ◽  
Pressurized Water Reactors ◽  
Laser Peening ◽  
Alloy 600 ◽  
Test Results ◽  
Pressurized Water ◽  
Performance Requirements ◽  
Primary Water ◽  
Water Reactors

Abstract For several decades pressurized water reactors have experienced Primary Water Stress Corrosion Cracking (PWSCC) within Alloy 600 components and welds. The nuclear industry has developed several methods for mitigation of PWSCC to prevent costly repairs to pressurized water reactor (PWR) components including surface stress improvement by peening. Laser shock peening (LSP) is one method to effectively place the surface of a PWSCC susceptible component into compression and significantly reduce the potential for crack initiation during future operation. The Material Reliability Program (MRP) has issued MRP-335, which provides guidelines for effective mitigation of reactor vessel heads and nozzles constructed of Alloy 600 material. In addition, ASME Code Case N-729-6 provides performance requirements for peening processes applied to reactor vessel head penetrations in order to prevent degradation and take advantage of inspection relief, which will reduce operating costs for nuclear plants. LSP Technologies, Inc. (LSPT) has developed and utilized a proprietary LSP system called the Procudo® 200 Laser Peening System. System specifications are laser energy of 10 J, pulse width of 20 ns, and repetition rate of 20 Hz. Scalable processing intensity is provided through automated focusing optics control. For the presented work, power densities of 4 to 9.5 GW/cm2 and spot sizes of nominally 2 mm were selected. This system has been used effectively in many non-nuclear industries including aerospace, power generation, automotive, and oil and gas. The Procudo® 200 Laser Peening System will be used to process reactor vessel heads in the United States for mitigation of PWSCC. The Procudo® 200 Laser Peening System is a versatile and portable system that can be deployed in many variations. This paper presents test results used to evaluate the effectiveness of the Procudo® 200 Laser Peening System on Alloy 600 material and welds. As a part of the qualification process, testing was performed to demonstrate compliance with industry requirements. The test results include surface stress measurements on laser peened Alloy 600, and Alloy 182 coupons using x-ray diffraction (XRD) and crack compliance (slitting) stress measurement techniques. The test results are compared to stress criteria developed based on the performance requirements documented in MRP-335 and Code Case N-729-6. Other test results include surface roughness measurements and percent of cold work induced by the peening process. The test results demonstrate the ability of the LSP process to induce the level and depth of compression required for mitigation of PWSCC and that the process does not result in adverse conditions within the material.

Situation of the Baffle-Former Bolts in Belgian Units

2009 ◽  
Author(s):  
Robert Ge´rard ◽  
Fre´de´ric Somville
Keyword(s):  
Stress Corrosion ◽  
Water Flow ◽  
Stress Corrosion Cracking ◽  
Structural Integrity ◽  
Operating Time ◽  
Reactor Vessel ◽  
Pressurized Water Reactors ◽  
Pressurized Water ◽  
Fuel Assemblies ◽  
Water Reactors

The baffle to former bolts are used in Pressurized Water Reactors to attach the baffle plates to the former plates in the reactor vessel lower internals. The resulting structure forms a boundary for the flow of coolant and provides lateral support to the fuel assemblies. Some edge bolts are also present, assembling together the baffle plates. After an operating time of the order of 120 000 hours, some bolts exhibit cracking at the junction of the head and the shaft of the bolt. Examinations of failed bolts have made it possible to identify the cause of cracking as irradiation assisted stress corrosion cracking (IASCC). Up to now, baffle bolt cracking has been detected in units older than 15 years, where the baffle bolts are not cooled (no holes in the former to allow a water flow on the bolt shaft). In Belgium the concerned unit are Tihange 1 and Doel 1–2. The paper summarizes the experience with baffle bolts cracking in Belgian units and the strategy implemented to mitigate this problem, consisting of structural integrity analyses, baffle bolts inspections and replacement, and research programs in the field of IASCC, including examinations of highly irradiated replaced bolts.

Safety Evaluation of the Hydrogen Flaking Damage in the Doel 3 and Tihange 2 Reactor Pressure Vessels

2016 ◽  
Author(s):  
Guy Roussel
Keyword(s):  
Safety Evaluation ◽  
Pressure Vessels ◽  
Reactor Vessel ◽  
Pressurized Water Reactors ◽  
Pressurized Water ◽  
Significant Safety ◽  
Nuclear Control ◽  
Safety Case ◽  
Water Reactors ◽  
Reactor Pressure

In the summer of 2012, the detection of a large number of quasi-laminar flaw indications in the reactor vessel beltline ring forgings of two Belgian pressurized water reactors (Doel Unit 3 and Tihange Unit 2) posed a significant safety threat that led the licensee to shutdown both plants. Those indications were identified by the licensee as hydrogen flakes that developed during the fabrication of the forgings. As a prerequisite for a potential restart of the units, the Belgian Nuclear Safety Regulator, the Federal Agency for Nuclear Control (FANC), requested the licensee to provide, for each unit, a safety case demonstrating the acceptability of the reactor pressure vessel for continued operation. As the technical subsidiary of the FANC, Bel V performed a safety evaluation of the condition of the reactor pressure vessels. The paper documents the approach Bel V used in his safety evaluation and the criteria he defined to evaluate the acceptability of the hydrogen flaking damage in the reactor pressure vessels.

Modeling and Phenomenological Aspects of Severe Accidents in Integral Pressurized Water Reactors

2011 ◽  
Author(s):  
I. K. Madni ◽  
M. Khatib-Rahbar
Keyword(s):  
Computer Code ◽  
Severe Accident ◽  
Pressurized Water Reactors ◽  
Modeling Framework ◽  
Pressurized Water ◽  
Product Release ◽  
Severe Accidents ◽  
Water Reactors ◽  
Accident Conditions ◽  
Coolant System

This paper focuses on modeling and phenomenological issues relevant to analysis of severe accidents in integral Pressurized Water Reactors (iPWRs). It identifies relevant thermal-hydraulics, melt progression and fission product release and transport phenomena, and discusses the applicability of the MELCOR computer code to modeling of severe accidents in iPWRs. Areas where the current MELCOR severe accident modeling framework has limitations in the representation of phenomenological processes are identified and examples of possible modeling remedies are discussed. The paper identifies modeling and phenomenological issues that contribute to differences in the calculated reactor coolant system and containment response for iPWRs as compared to traditional PWRs under severe accident conditions.

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