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According to the US NRC, during planned inspection of Indian Point Nuclear Power Station “Entergy identified baffle/former bolts with either visual anomalies or ultrasonic indications. All vessel internal examinations have been successfully completed with no anomalies other than the baffle/former bolts.http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2016/20160330en.html

Entergy offered more details in a Press Release: “Engineers identified missing bolts, and bars meant to hold them in place, and other degradation requiring replacement of the bolts. Each bolt, about two inches long and made of stainless steel, holds plate inserts together inside the reactor.http://www.prnewswire.com/news-releases/hundreds-of-inspections-completed-on-indian-point-unit-2-replacement-of-reactor-liner-bolts-planned-300242845.html
Core baffle diagram US NRC
There are many bolts because there are many plates. Although there were “only” 11% damaged, the damage maybe concentrated because loss of one bolt could increase stresses in the surrounding areas. Thus, one suspects that there may have been plate failure or almost failure. [1] Apparently, even without total failure it can cause serious damage to the fuel rods, as explained below. The document below suggests that a failure could block coolant, as well.

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.” “Situation of the Baffle-Former Bolts in Belgian Units” Robert Gerard and F. Somville: http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1627939

How long were the bolts and bars missing? Where did they go? It’s apparently not a good idea to lose things in a nuclear reactor core: http://allthingsnuclear.org/dlochbaum/perils-of-new-nuclear-fuel-part-2-grand-gulfs-mighty-pen

Some of these bolts remain difficult to inspect: http://www.ndt.net/article/jrc-nde2012/papers/106.pdf

How many more nuclear power stations are missing bolts? Did inspection catch all near failed bolts, since inspection can be difficult? What about the reactor pressure vessel? What is found may depend on the sensitivity of measuring instruments and the methodological assumptions. In Belgium “…Electrabel has increased the sensitivity of the ultrasonic detection device MIS-B to ensure that all flaw indications were detected. In May and June 2014, the operator conducted new ultrasonic inspections in Doel 3 and Tihange 2 with these adapted detection parameters. The results of these inspections were then interpreted using the aforementioned new measurement method./ The combination of these two improvements has resulted in the detection of about 60% more flaw indications in the steel walls of the reactor pressure vessels of Doel 3 and Tihange 2. The new method implies that signals with a very low amplitude, which is characteristic for small flaw indications that wouldn’t be detected with the detection threshold of 2012, are being regrouped. This regroupment leads to an increase of the average and maximum length of the flaw indications.http://www.fanc.be/fr/news/doel-3/tihange-2-clarifications-regarding-the-detection-the-position-and-the-size-of-the-flaw-indications/753.aspx

Description of Circumstances
Reactor vessel internals are structures located within the reactor vessel that support and orient the reactor fuel assemblies and direct coolant flow through the core. The core baffle is part of the internals structure, which consists of vertical plates that surround the outer faces of the peripheral fuel assemblies. The baffle directs coolant flow through the core. The vertical plates are bolted to the edges of horizontal former plates that are bolted to the inside surface of the core barrel. There are typically eight levels of former plates located at various elevations within the core barrel. The bolts that secure the baffle plates to the former plates are referred to as “baffle former bolts.”

European plants identified the cracking of baffle former bolts as early as 1988 and this problem continues to occur. Although this cracking is not fully understood, testing of cracked bolts suggests an age-related intergranular stress-corrosion cracking process influenced by bolt material, fluence, stress, and temperature. The reported cracking occurred in 316 cold-worked stainless steel bolts. Most of the cracking reported has been in four French 900-MWe (megawatt electric) PWRs
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1998/in98011.html

Baffle plate gaps have been known to cause fuel damage since at least the 1970s:
May 6, 1982, Portland General Electric submitted a Licensee Event Report (LER) 344/82-06, describing abnormal fuel clad degradation identified during a pre-planned fuel inspection to locate suspected leaking fuel assemblies. Fuel rod damage involved 17 fuel assemblies examined at the end of Cycle 4 operation. Portions of fuel rods were found missing and loose fuel pellets were discovered and retrieved from reactor vessel internals and the refueling cavity. Visual inspections revealed severe perimeter fuel rod failures in 8 fuel assemblies. Failures in the remaining 9 assemblies were detected by sipping operations, but did not exhibit visual damage./ This general type of fuel rod damage has been encountered previously. In April 1980, fuel rod failures were found in two fuel assemblies at the end of Cycle 2 for the Trojan reactor (LER 344/80-06. Similar events were also reported for the Point Beach 1 reactor during the years 1975 and 1977. These occurrences are delineated in LER 266/75-18 and 76-12, respectively. IE Circular No. 80-17 likewise has cited fuel rod failures for foreign plants. / The aforementioned fuel rod damage, involving 10 of the 17 assemblies, can be attributed to the water-jetting-induced motion of fuel rods in fuel assemblies that are adjacent to baffle plate joint locations with enlarged gaps. Two mechanisms for baffle gap-related rod failures have been determined. The first of these is the outside corner or center-injection jetting failure that is similar to clad degradation as described in LER 344/80-06. (See Figure 1.) In this case, the water jet impacts on the third rod from the corner and causes its failure in the lower axial regions from direct water impingement, combined with induced rod whirling and vibration. The second type of baffle gap-related failure is the inside corner or corner-injection jetting failure, whereby a jet of water flows parallel to the fuel bundle perimeter face between the fuel and the adjacent baffle plate. This flow also causes fuel rod whirling and vibration to occur at the first few rod locations. Such water-jetting parallel to these fuel rods ultimately results in failure of the rods and in the likelihood of failure propagation to adjacent rods. In general, the water-jetting-induced rod motion causes fuel rod fretting because of abnormal clad wear against the Inconel grid assemblies, which consist of slotted straps interlocked in an “egg-crate” arrangement.” Read in detail at link or in the bottom of this blog post. http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1982/in82027.html
Irradiation-Assisted Stress Corrosion Cracking has resulted in cracking at the head of a baffle bolt ornl. gov
According to Oak Ridge National Lab: “Nuclear power plant operating environments create material degradation mechanisms that may be unique or environmentally exacerbated. In this figure, Irradiation-Assisted Stress Corrosion Cracking has resulted in cracking at the head of a baffle bolt.”
http://www.ornl.gov/science-discovery/nuclear-science/research-areas/reactor-technology/light-water-reactor-sustainability (Link now dead: rearrangement of web site or a hiding of useful info?)

Engineers identified missing bolts, and bars meant to hold them in place, and other degradation requiring replacement of the bolts. Each bolt, about two inches long and made of stainless steel, holds plate inserts together inside the reactor.http://www.prnewswire.com/news-releases/hundreds-of-inspections-completed-on-indian-point-unit-2-replacement-of-reactor-liner-bolts-planned-300242845.html There are many bolts because there are many plates. The damage could be concentrated. Loss of one bolt could increase stresses in the surrounding areas leading to more failures. Missing bolts and bars sounds really bad: “Inspections of more than 2,000 bolts in the reactor’s removable insert liner revealed issues with approximately 11 percent that require further analysis. Issues were identified on bolts on the face of the removable liner, not on bolts along the liner’s edges.http://www.prnewswire.com/news-releases/hundreds-of-inspections-completed-on-indian-point-unit-2-replacement-of-reactor-liner-bolts-planned-300242845.html

Long-term exposure degradation mechanisms are a concern of nuclear power plants as they exceed 40-years of service life. Degradation for reactor internals may include irradiation assisted stress corrosion cracking (IASCC), which has been a suggested mode of failure for baffle former bolts (from herein called baffle bolts) in pressurized water reactors (PWRs). The first identification of failed bolts was an outcome of the investigation of flow-induced vibration of fuel rods in elements on the core periphery observed in French 900 MW plants in the 1980’s. This abnormal condition was created by water flow through gaps between baffle plates as a result of the failure of baffle bolts [1]. These bolts, made from 10 to 30% cold worked 316-grade stainless steel, were determined to have failed through intergranular cracking following destructive examinations of removed bolts. The location of these bolts being in a high irradiation flux position near to the bottom of the fuel core suggests that crack development was related to IASCC as 316 steel is not prone to intragranular stress corrosion cracking in the hydrogenated primary water of the PWR environment.

Baffle bolts secure the baffle plates to the former plates in the lower internal assembly of the reactor vessel. The baffle plates are the vertical internal structure around periphery of the fuel core, with the former plates being the horizontal structural components distributed along the height of the fuel core separating the baffle plates from the core barrel (see Figure 1). For two-loop PWR designs, such as in the R.E. Ginna PWR (from here on, Ginna), there are thirty-six baffle plates and seven former plates [2]. In addition to the baffle bolts, there are bolts between the core barrel and former plates (barrel bolts), and bolts that pin the baffle plate to baffle plate on the ends (edge bolts). For a two-loop Westinghouse design, there can be up to 728 baffle bolts with up to 104 bolts at each height elevation in the lower internal assembly. The bolts can experience varied neutron flux based on the location of the bolt within the assembly as well as a fluence distribution along the length of the bolt.

In 1997, the Westinghouse Owners Group created a task force to evaluate the integrity of baffle bolts in U.S. and international PWR’s and determined that IASCC was an issue with significant regulatory risk [2]. Baffle bolt cracking can still remain an issue in plants that have not been modified to an up-flow design in which the direction of the water flow between the core barrel and baffle plates has been changed from the traditional downward direction. This results in lower temperatures of the baffle bolts even after gamma heating is accounted for [1]. Plants with the modified flow direction have shown little baffle bolt cracking as compared to the unconverted down flow designs. However, other factors such as improved bolt and replacement bolt designs minimizing stress concentrations between the bolt head and shank could also mitigate crack development.http://info.ornl.gov/sites/publications/files/Pub55536.pdf

Indian Point is a Westinghouse PWR 4 loop https://en.wikipedia.org/wiki/Indian_Point_Energy_Center

In “A Probabilistic Approach to Baffle Bolt IASCC Predictions
Timothy J. Griesbach, George J. Licina, Peter C. Riccardella, Joe R. Rashid, Robert E. Nickell explained: “In PWRs, the reactor core is surrounded by a series of vertical baffle plates that form a boundary for coolant flow to the core. These plates also provide lateral support for the fuel assemblies. The baffle plates are supported by horizontal plates (typically seven or eight) called formers or former plates that are bolted to the outside of the cylindrical core barrel. The baffle plates are in turn bolted to the former plates. The bolts that connect the baffle plates to the formers are called the baffle-former bolts. The overall arrangement of the baffle-former bolt configuration at the plane of a former plate is shown in Figure 1. In one of the PWR examples evaluated in this paper, there are a total of 832 baffle-former bolts, 104 bolts around the periphery of the baffle plates in each octant; 13 bolts at each of the 8 former levels in each octant as noted by the designations A through M Figure 1.
http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/43/070/43070864.pdf

The core baffle forms the boundary of the core, and it also directs and guides the coolant flow through the core region./ The core baffle is made of vertical baffle plates and horizontal former plates (also known as baffle radial support plates). The horizontal former plates are bolted to the inside surface of the lower part of the core barrel. The vertical plates are bolted to the inner edges of the horizontal plates, forming the boundary of the core. The bolts are made of type 316 stainless steel. Holes in the horizontal former plates provide a flow path for the bypass cooling flow in the region between the core barrel and the vertical baffle plates. A cross section of the core showing the core baffle and other components of the lower core support structure is shown in Fig. 2.3.http://pbadupws.nrc.gov/docs/ML0403/ML040340653.pdf

Almost 34 years ago, in 1982:
NRC Library > Document Collections > Generic Communications > Information Notices > 1982 > IN 82-27

SSINS No.: 6835 IN 82-27

UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555

August 5, 1982

Information Notice No. 82-27: FUEL ROD DEGRADATION RESULTING FROM BAFFLE WATER-JET IMPINGEMENT

Addressees:

All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP).

Purpose:

This information notice is provided as a notification of an incident that may have safety significance. It is expected that recipients will review the information for applicability to their facilities. No specific action or response is required at this time.

Description of Circumstances:

On May 6, 1982, Portland General Electric submitted a Licensee Event Report (LER) 344/82-06, describing abnormal fuel clad degradation identified during a pre-planned fuel inspection to locate suspected leaking fuel assemblies. Fuel rod damage involved 17 fuel assemblies examined at the end of Cycle 4 operation. Portions of fuel rods were found missing and loose fuel pellets were discovered and retrieved from reactor vessel internals and the refueling cavity. Visual inspections revealed severe perimeter fuel rod failures in 8 fuel assemblies. Failures in the remaining 9 assemblies were detected by sipping operations, but did not exhibit visual damage.

This general type of fuel rod damage has been encountered previously. In April 1980, fuel rod failures were found in two fuel assemblies at the end of Cycle 2 for the Trojan reactor (LER 344/80-06. Similar events were also reported for the Point Beach 1 reactor during the years 1975 and 1977. These occurrences are delineated in LER 266/75-18 and 76-12, respectively. IE Circular No. 80-17 likewise has cited fuel rod failures for foreign plants.

The aforementioned fuel rod damage, involving 10 of the 17 assemblies, can be attributed to the water-jetting-induced motion of fuel rods in fuel assemblies that are adjacent to baffle plate joint locations with enlarged gaps. Two mechanisms for baffle gap-related rod failures have been determined. The first of these is the outside corner or center-injection jetting failure that is similar to clad degradation as described in LER 344/80-06. (See Figure 1.) In this case, the water jet impacts on the third rod from the corner and causes its failure in the lower axial regions from direct water impingement, combined with induced rod whirling and vibration. The second type of baffle gap-related failure is the inside corner or corner-injection jetting failure, whereby a jet .

IN 82-27 August 5, 1982 Page 2 of 4

of water flows parallel to the fuel bundle perimeter face between the fuel and the adjacent baffle plate. This flow also causes fuel rod whirling and vibration to occur at the first few rod locations. Such water-jetting parallel to these fuel rods ultimately results in failure of the rods and in the likelihood of failure propagation to adjacent rods. In general, the water-jetting-induced rod motion causes fuel rod fretting because of abnormal clad wear against the Inconel grid assemblies, which consist of slotted straps interlocked in an “egg-crate” arrangement.

For the Trojan design, holes in the core barrel provide pathways for bypass flow which is diverted from the annulus between the vessel and the core barrel walls, to a downward direction through holes in the horizontal “former” plate segments. (See Figure 2.) This small portion of the coolant flow between the baffle plates and the core barrel, provides additional cooling for the barrel. However, most of the coolant flow from the vessel cold-leg inlet nozzles is downward through the annulus between the core barrel and the vessel walls, then into a plenum at the bottom of the vessel. It then reverses direction and flows upward through the core. A pressure differential is thereby established between the downward coolant flow in the vessel-barrel annulus and through the “former” plates, and the reversed upward flow through the core inside the .

IN 82-27 August 5, 1982 Page 3 of 4

barrel. Coolant cross-flow through the enlarged baffle gaps results in high velocity jetting because of this pressure differential. The baffle water-jet then impinges on fuel rods and induces excessive rod motion, producing severe clad degradation.

One fix of the baffle joint is to peen the entire joint to reduce the gaps between baffle plates. However, as noted in the most recent Trojan Event Report (82-06) relating to the problem, the gaps in the corner-injection baffle joints were apparently enlarged during the peening of the center-injection baffle joints at the end of Cycle 3 operation (1981). In addition, peening did not entirely dispose of the problem with the center-injection assemblies, since damage was found in three fuel assemblies of this type. A more successful interim solution includes the use of modified fuel assemblies to replace those damaged assemblies adjacent to baffle plate joints. Such modified fuel assemblies which utilize stainless steel fuel rods have been licensed and used previously. Two fuel assemblies were modified for Cycle 3 operation at

IN 82-27 August 5, 1982 Page 4 of 4

Trojan, as a result of the baffle jet problem described in LER 344/80-06. Three Zircaloy-clad rods in each of two assemblies were replaced with solid stainless steel rods of the same diameter and length as the fuel rods. Damage was not observed in the modified assemblies at the end of Cycle 3 or at the end of Cycle 4. These assemblies were located adjacent to baffle corners where water-jetting-induced fuel rod degradation had occurred. LER 344/82-06 cites the continued use of modified fuel assemblies with stainless steel rods, in addition to inserting partial grids that will provide midspan support to fuel rods adjacent to corner-injection baffle joints. The partial grids serve to increase the frequencies and decrease the amplitudes of the fundamental modes of vibration for fuel rods, and thus raise the threshold for rod vibration, which causes clad damage. With regard to the center-injection assemblies, the most vulnerable fuel rod (the one nearly aligned with the baffle plate gap) and the two adjacent fuel rods in the first row are to be replaced with stainless steel rods to minimize the possibility of additional baffle-jet-induce failures. Westinghouse is presently evaluating proposed permanent fixes for the baffle water-jetting problem.

Although the baffle water-jetting problem has been experienced in a limited number of Westinghouse PWRs, this information notice is being distributed to all licensees and construction permit holders, including PWRs whose core baffle designs may have features which contribute to fuel rod failures as previously described. Such fuel degradation may result in relatively high primary coolant activity and thereby impede periodic maintenance-related functions and/or pose radiological hazards to personnel.

Edward L. Jordan, Director Division of Engineering and Quality Assurance Office of Inspection and Enforcement

Technical Contact: R.M. Young 49-29672

Attachment: List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Friday, May 22, 2015
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1982/in82027.html
Why was it reviewed-updated? Why are the pictures so often missing?

According to Chopra, 2010, for the US NRC: “Austenitic stainless steels are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods changes the microstructure and microchemistry of these steels and degrades their fracture properties. This report presents a critical assessment of the susceptibility of LWR core internal materials to irradiation effects such as irradiation-assisted stress corrosion cracking (IASCC), neutron embrittlement, void swelling, and irradiation-induced stress relaxation.” (http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr7027/: “Degradation of LWR Core Internal Materials Due to Neutron Irradiation (NUREG/CR-7027)“, Prepared by: O.K. Chopra (2010)

https://miningawareness.wordpress.com/2014/08/15/neutrons-in-nuclear-reactors-bombs-make-non-radioactive-materials-radioactive-accelerate-reactor-degradation/

https://miningawareness.wordpress.com/2014/12/01/fire-at-belgian-nuclear-reactor-cracks-in-pressure-vessels-oil-leak/

The US NRC Event Notification offers few details: http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2016/20160330en.html

IAEA report on PWR internals: http://www-pub.iaea.org/MTCD/publications/PDF/gnppa-cd/PDF-Files/SpecGuide/te_1119_prn.pdf

EMPHASIS OUR OWN THROUGHOUT. There is less emphasis than there would be because WordPress did not save our draft and there are other urgent things to do.

Note 1: The best picture is probably the one in the Entergy Press Release. What would the repercussions of total failure of these bolts be? Is total plate failure possible or would other parts prop it up? The baffle and lower core plates appear to be a sort of basket which supports, or helps to support the fuel rods. One hopes that those more directly involved have access to better information than we were able to find in a timely manner. Do some bolts receive more radiation than others? Then these would be more at risk for failure. Once again, where did the bolt and bars go?