Limerick: Information On Testing US Reactor Vessels and Belgium Cracks

It is basically the blind leading the blind with my understanding this???

Big questions:

1) What does this mean and is it going on in the USA?  

"In carrying out tests related to theme 2 during the spring of 2014, a fracture toughness test revealed unexpected results, which suggested that the mechanical properties of the material were more strongly influenced by radiation than experts had expected."

Alliance for a Clean Environment response from NRC

May 5, 2015

Dr. Lewis Cuthbert

President

Alliance for a Clean Environment

1189 Foxview Road

Pottstown, PA 19465

Dear Dr. Cuthbert:

May 5, 2015

On behalf of the U.S. Nuclear Regulatory Commission (NRC), I am responding to your e-mail dated March 16, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML 15076A480), expressing concerns primarily about cracking, due to embrittlement, of the reactor pressure vessels at Limerick Generating Station, Units 1 and 2. I have included answers to your specific concerns in the enclosure to this letter. Thank you for contacting the NRC with your concerns.

'NRC Response to Concerns in March 16, 2015, E-Mail From the Alliance for a Clean Environment Regarding Limerick Generating Station, Units 1 and 2'

Background

This enclosure provides the U.S. Nuclear Regulatory Commission's (NRC's) response to concerns regarding Limerick Generating Station, Units 1 and 2 (Limerick), as discussed in the March 16, 2015, e-mail from the Alliance for a Clean Environment (ACE) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML 15076A480). ACE previously raised some of the same concerns in an e-mail dated November 9, 2014(ADAMS Accession No. ML 14321A054). The NRC staff provided a response in an e-mail dated December 8, 2014 (ADAMS Accession No. ML 14345A078).

Destructive Testing

ACE raised concerns regarding embrittlement of the Limerick reactors and asked if destructive testing of the reactors had been performed.

When a nuclear plant is operated, neutron radiation from the reactor core causes embrittlement of the reactor pressure vessel (RPV). Embrittlement refers to a decrease in the fracture toughness of RPV materials and affects the vessel materials in the section closest to the reactor fuel, referred to as the vessel's "beltline."

Section 50.60 of Title 10 of the Code of Federal Regulations (10 CFR), "Acceptance criteria for fracture prevention measures for lightwater nuclear power reactors for normal operation," requires compliance with the

Basically this is saying a plant is licensed with a vessel with these kinds of metallurgical properties based on 1960s technology and knowledge. No other inspections is necessary throughout the life of the plant.  

fracture toughness and material surveillance program requirements set forth in Appendices G and H to 1 O CFR Part 50. Compliance with the requirements of this rule, and the associated appendices, provides assurance regarding the structural integrity of the reactor coolant pressure boundary (RCPB) and, specifically, the RPV.

Appendix H to 10 CFR Part 50, "Reactor Vessel Material Surveillance Program Requirements," requires nuclear power plant licensees to implement RPV surveillance programs to monitor changes in the fracture toughness properties of ferritic materials in the RPV beltline region which result from exposure of these materials to

For a host of reasons, I don't think the coupon specimen surveillance is representative of the properties of the vessel. Basically a crack in the reactor vessel bypasses all the safety designs of the plant and a accident could be so severe, we need actual ultrasonic testing of the vessel. A stand in coupon testing is no longer a guarantor of safety. 

neutron irradiation. The RPV surveillance programs require destructive testing of material test specimens that are representative for the materials in the reactor. Two specific alternatives are provided for the design of a facility's RPV surveillance program to address the requirements of Appendix H to 10 CFR Part 50.

The first alternative, provided in Appendix H to 1 O CFR Part 50, is the implementation of a plant specific RPV surveillance program consistent with the requirements of American Society for Testing of Materials (ASTM) E 185, "Standard Practice for Conducting Surveillance Tests for Light-Water Cooled Nuclear Power Reactor Vessels."

The second alternative, provided in Appendix H to 10 CFR Part 50, is the implementation of an Integrated

You get it, always a stand in type testing, never inspection the real deal. Basically it is too expensive and disrupting the capacity factor.  

Surveillance Program (ISP). When a licensee uses an ISP, representative materials chosen for surveillance of a reactor are irradiated in one or more other reactors that have similar design and operating features.

As discussed in the NRC staff's safety evaluation for a Limerick amendment dated November 4, 2003 (ADAMS Accession No. ML032310540), Limerick, Units 1 and 2, have implemented the Boiling Water Reactor Vessel and Internals Project (BWRVIP) ISP as the basis for demonstrating compliance with the requirements of Appendix H to 1 O CFR Part 50.

To comply with Appendix H to 10 CFR Part 50, the entire fleet of operating U.S. reactors, including the Limerick RPVs, contain material specimens, representative of the materials in RPV beltline region, in surveillance capsules. These surveillance capsules are removed for

So they got specimens designed to be remove for testing from the vessel, but are never required to be tested. 

destructive testing of the material specimens as necessary. None of the surveillance capsules in the Limerick RPVs have been removed to date. In addition, as discussed in a Limerick license amendment dated April 8, 2011 (ADAMS Accession No. ML 110691095), based on the BWRVIP ISP, Limerick is not scheduled to remove any surveillance capsules in the future. 

Instead, the limiting weld and plate materials for the Limerick RPVs are monitored through representative material specimens that are exposed to irradiation in other boiling water reactors, as part of the BWRVIP ISP. The BWRVIP ISP was found acceptable by the NRC staff to satisfy the requirements of Appendix H to 10 CFR Part 50, during the period of extended operation for Limerick, as discussed in the Section 3.0.3.1.11 of NUREG-2171, "Safety Evaluation Report Related to the License Renewal of Limerick Generating Station, Units 1 and 2" (ADAMS Accession No. ML 14276A156).

In summary, destructive testing has not been performed on the material specimens in the Limerick RPV surveillance capsules. Destructive testing has been and will continue

Ultrasonic like I want is not destructive and the destructive testing of drilled out specimens  I want is from permanently  shutdown plants.  Further I want ultrasonic testing of the permanently shutdown vessels...if no defects are discovered then no further inspection are needed.  

to be performed, for material specimens representative of the materials in the Limerick RPV, to meet the requirements in Appendix H to 10 CFR Part 50, as part of the BWRVIP ISP.

Material Fatigue Testing

ACE requested that the NRC "require independent 'material fatigue' testing of both Limerick Nuclear Plant reactors, with the results of testing immediately reported to the public."

All U.S. nuclear RPVs are designed and fabricated for operational cyclic stresses caused by all postulated loadings, including startup, shutdown, and scram events. Fatigue is explicitly evaluated as a part of the design

Based on 1960s technology and knowledge!!! 

process. Once the RPV is designed and fabricated and placed into service, licensees are required to track operational events, such as startups and shutdowns, to ensure they remain within their design bases with respect to fatigue. The NRC staff found that Limerick's fatigue program satisfied these requirements for the extended period of operation, as discussed in Section 4.3 of NUREG-2171, "Safety Evaluation Report Related to the License Renewal of Limerick Generating Station, Units 1 and 2" (ADAMS Accession No. ML 14276A 156). As a result of satisfying these requirements, there is no demonstrated need for material fatigue testing at Limerick.

The NRC's regulations in 10 CFR 2.206 describe the

At least I got this right... 

petition process, which is the primary mechanism for the public to request enforcement-related action by the NRC in a public process. This process permits anyone to petition the NRC to take enforcement-related action associated with NRC licensees or licensed activities. Depending on the results of its evaluation, NRC could-modify, suspend or revoke an NRC-issued license or take any other appropriate enforcement related action to resolve a problem.

Although ACE's e-mail dated March 16, 2015, did not specifically cite the 10 CFR 2.206 process, it did request enforcement-related action (i.e., ACE's request to require material fatigue testing at Limerick). The NRC staff has previously offered the use of the petition process to address concerns where enforcement-related action was requested by ACE (e.g., NRC e-mail dated April 23, 2014 (ADAMS Accession No. ML 14129A184)). However, ACE has previously rejected use of the NRC's petition process to address its concerns (e.g., letter dated July 25, 2014 (ADAMS Accession No. ML 14216A339)). Nevertheless, the NRC staff considers the 10 CFR 2.206 petition process to be the appropriate process to address requested enforcement-related action. The NRC's petition process is available if ACE disagrees with the NRC's findings and has information the NRC did not consider in making its findings.

Belgium Reactor Operating Experience

ACE cited issues with cracking that had been reported in two reactor vessels in Belgium.

The NRC staff is well aware of this issue. Evaluations in Belgium and the U.S. demonstrated that because these many flaws are oriented nearly parallel to the direction of stress in the reactor vessel shell, they do not pose a significant safety concern. Additionally, it should be

Suggest isn't proof it is safe. Again this is a inference a vessel is safe, not acceptable proof it is safe. 

It is generially a new kind of corrosion/ hydrogen process...hydrogen collecting deep into the vessel leading to crack and flaws.

As far as I can see, nobody has taken a sample and cut into metal, thus nobody really what is going on.  

noted that information available from Belgium suggests that the flaws occurred as part of the initial fabrication process (i.e., flaws are not service-induced). As such, there is no indication that the flaws in the Belgium reactors are in any way related to fatigue damage.

Notes:

*** At least one reactor in Switzerland, another in Belgium and two in Spain have components produced by the same Dutch firm, Rotterdam Drydock Company, which has gone bankrupt since producing the equipment. The U.S. Nuclear Regulatory Commission said Friday it has been informed that 10 American reactors may have used the component in question, but it hasn't yetverified that information with U.S. nuclear operators.

***Doel 3/Tihange 2: new update

After a large number of flaw indications was discovered in the walls of the reactor pressure vessels (RPVs) of Doel 3 and Tihange 2 during a scheduled maintenance in the summer of 2012, the Belgian nuclear safety authorities (FANC and Bel V) decided that Electrabel had to submit a Safety Case to justify the restart of both reactors. Electrabel had to demonstrate specifically and convincingly in its Safety Case that the flaw indications in the walls of the RPVs do not compromise its structural integrity. 

After an analysis of the safety cases of both reactors, the FANC and Bel V decided on May 17, 2013 that Doel 3 and Tihange 2 could be restarted. Linked to this agreement, however, was the condition that Electrabel had to perform a series of medium-term actions to consolidate the hypotheses of its Safety Case. These actions were divided into three major themes:

1. The ultrasonic inspection technique of the RPVs: detection and measurement of hydrogen-induced flaw indications
2. Material properties of steel containing hydrogen flakes
3. Structural integrity of a rpv containing hydrogen flakes

The results of the actions on issues 1 and 2 provide the input for theme 3. 

"In carrying out tests related to theme 2 during the spring of 2014, a fracture toughness test revealed unexpected results, which suggested that the mechanical properties of the material were more strongly influenced by radiation than experts had expected." As a precaution both reactors were immediately shut down again.

Electrabel launched a test campaign to find an explanation for the unexpected test results.
At the same time, the licensee continued the execution of the medium termed-action plan. In the mean, this has led to the following results:

More accurate information about the flaw indications 

In February 2015, Electrabel completed the actions related to the theme of the ultrasonic inspection technique. 

This technique was originally designed for the control of the welding and the cladding of the RPV, but it also proved to be able to detect flaw indications in the wall of the RPV. Electrabel had to qualify the technique, i.e. prove that all hydrogen-induced flaw indications can be found and can be measured correctly using the ultrasonic inspection. By doing so, Electrabel found that the inspection procedure had to be slightly modified and that the detection threshold of the probes had to be lowered to ensure the proper detection of all flaw indications.
In 2014, a further inspection was carried out based on the improved procedure and the modified settings of the machine, resulting in the detection of a greater number of flaw indications than was measured in 2012 and 2013. This means that Electrabel now has to take into account 13 047 flaw indications for Doel 3 and 3149 flaw indications for Tihange 2 in its calculations. These additional flaw indications are similar to those which were previously considered and are located in the same area of the RPV. 

New sequence of material testing 

At the same time, Electrabel also continues its research on the material properties of the RPV and the unexpected results of the previous fracture toughness test. 

Currently a 4th irradiation campaign is being executed in the research reactor BR2 of the SCK, where, next to hydrogen-flaked samples of the French VB395 test material, other hydrogen-flaked samples of another test material of German origin are also being irradiated. The results of this irradiation campaign and of the subsequent material tests are expected by April 2015. 

New meeting of the international review board 

Electrabel provides the FANC and Bel V with results of ongoing tests and analyses on a regular basis. The Belgian security authorities need time to look into this new information and will continue their analysis during the first months of 2015. Therefore, they call in the help of international experts who are specialized in damage mechanisms caused by radiation and in mechanical resistance tests. This international expert panel (International Review Board) met for the first time in Brussels at the start of November 2014. The main conclusion of this meeting was that the methodology used by Electrabel was not yet sufficiently developed to make a well-grounded judgment. The international experts have formulated some suggestions for further actions and studies. Based on these suggestions and on the documents already analyzed, the Belgian security authorities have passed a series of additional demands and suggestions to Electrabel, so that the licensee can adjust its methodology and validate the underlying hypotheses of its arguments. 

In April 2015, the FANC will organize a new meeting of the international panel of experts to obtain their advice on the results of the new material tests and on the new data provided by Electrabel.

***Good Back Ground info: Report Activities in WENRA countries following the Recommendation regarding flaw indications found in Belgian reactors