Dec 14
WAM-E.1 08:30 Tungsten Shield Vest Barbara Thompson*, Dominion - North Anna Power Station Abstract: This paper will discuss the evaluation and implementation of the tungsten shield vest as an ALARA measure to reduce personnel exposure. The tungsten shield vest was invented in 2009 by an industry veteran from Entergy Arkansas Nuclear One. The form-fitting shield vests are similar to lead vests worn to protect dental and medical patients from radiation exposure – but much lighter. Tungsten shielding reduces the amount of radiation to the parts of the body that are most sensitive to ionizing radiation and is flexible enough to move with the worker. In 2010, the North Anna Power Station became the first nuclear facility in the Dominion Fleet to test and use tungsten shielding vests. Due to the non-uniform radiation field created by the vest, the Radiological Protection group utilized Effective Dose Equivalent (EDE) monitoring of individual whole body compartments. The tungsten shield vests have been used for fuel manipulator roller replacement, pressurizer spray valve repairs, and transfer canal upender sheave replacement. Initial test results showed up to a 30 percent reduction in personal radiation exposure for workers doing outage maintenance tasks within the containment building at North Anna. The use of tungsten vests has allowed the benefits of shielding to become mobile with the worker and their tasks, thus reducing the overall radiation exposure to the worker.
Fuel Reliability: How it affects the industry, and one fuel vendor's journey to flawless fuel performance
http://www.power-eng.com/articles/npi/print/volume-7/issue-4/nucleus/fuel-reliability-how-it-affects-the-industry-and-one-fuel-vendor-s-journey-to-flawless-fuel-performance.html
https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML14338A739
Trait Talk: A questioning Attitude
For example, ten years after
removal from a reactor, the surface dose rate for a typical spent fuel
assembly exceeds 10,000 rem/hour, whereas a fatal whole-body dose for humans is
about 500 rem (if received all at one time). Furthermore, if constituents of
these high-level wastes were to get into ground water or rivers, they could
enter into food chains.
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1993/in93082.html
Information Notice No. 93-82: Recent Fuel and Core Performance problems in Operating Reactor
These fuel failures have been attributed to high cross flows, caused, in part, from mixed fuel designs which induced fuel rod vibration with fretting wear at the lower grids. The mixture of standard and VANTAGE 5H fuel (with debris filter bottom nozzles) resulted in axial mismatches between the bottom nozzles and the grid spacers of the two fuel types.
Although the staff recognizes that it is impossible
to avoid all fuel rod failures and that cleanup systems are installed to handle a
small number of leaking rods, the review must ensure that fuel does not fail as a
result of specific causes during normal operation and AOOs.
The allowable fretting wear should be stated in
the safety analysis report, and the stress and fatigue limits in items (i)
and (ii) above should presume the existence of this wear.
2.3 Fuel Dispersal
Fuel dispersal is the ejection of fuel fragments or particles through a rupture or opening in the
cladding. For the purpose of this report, fuel dispersal is said to have occurred if any fuel
material is found outside of the fuel rod. Even if the fuel material is small in quantity, the finding
will be noted and qualified by the nature of the dispersal (e.g., “only a small black powder on the
test chamber wall was observed”).
3.14. Fuel fragmentation and fuel dispersal
In this chapter, fuel fragmentation refers to situations for which the fuel
cladding breaks into pieces and fuel dispersal to situations for which fuel particles
escape from the cladding following a rupture.
Although fuel fragmentation is traditionally considered to exist only in
conjunction with highly energetic events such as the reactivity-initiated accidents
(RIA), recent results from the Halden test reactor show that fuel fragmentation can
also occur during the loss-of-coolant accident (LOCA).
1981: US. NUCLEAR REGULATORY COMMISSION
STANDARD REVIEW PLAN
OFFICE OF NUCLEAR REACTOR REGULATION
4.2
"Fuel rod failure" means that the fuel rod leaks and that the first fission product barrier (the cladding) has,
therefore, been breached.
Fuel rod failure is defined as the
loss of fuel rod hermeticity.
007
In a “fuel rod failure,” the fuel rod leaks and the first fission product barrier (the cladding) is breached.
Definition
1. (General Physics) sealed so as to be airtight
2. hidden or protected from the outside world
Fuel Vendor
PWR
Fuel Failure Management
Handbook
The tendency of grid-rod fretting
increases with increased cross flow, e.g. due to different pressure drops of
different fuel assembly designs sitting adjacent to each other. Baffle jetting will
also increase the risk of getting grid-rod fretting. To reduce the risk of getting
grid-rod fretting, appropriate loop tests should be performed to verify the
fretting performance of a new grid design.
The ultimate solution is the conversion of down-flow design to up-flow
design.
These above mentioned corrective actions have successfully reduced the
number of plants and fuel assemblies that are affected by this failure
mechanism. Very few fuel failure as the result of baffle jetting has been
observed in recent years.
Brief Description: This 10 CFR 50.59 evaluation is being performed to support the
transition to RFA-2 fuel at North Anna.
Reason for Change: ETE-NAF-2011-0173 implements the analyses supporting the
RFA-2 fuel transition at North Anna. UCR-2010-007 is a UFSAR change request that
encompasses the changes related to the RFA-2 fuel transition at North Anna. Three
License Amendment Requests (LARs) were submitted to the NRC for approval in
support of the RFA-2 transition at North Anna. The LAR for Optimized ZIRLO has been
approved and the LARs for VIPRE-D and Westinghouse's Best Estimate Large Break
LOCA evaluation were being tracked and were subsequently approved by the NRC.
http://pbadupws.nrc.gov/docs/ML0631/ML063110095.pdf
BAFFLE JETTING RESULTS IN FUEL ROD DEGRADATION AT VIRGIL C. SUMMER
Examination of two previous cycle fuel assemblies from the same location showed indications of baffle jetting (shiny areas) on the same fuel rod location as P1.
https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML14316A338
November 10, 2014
Mr. David A. Heacock
President and Chief Nuclear Officer
Virginia Electric and Power Company
Innsbrook Technical Center
5000 Dominion Boulevard
Glen Allen, VA 23060
SUBJECT: NORTH ANNA POWER STATION – NRC INTEGRATED INSPECTION
REPORT 05000338/2014004 and 05000339/2014004
The inspectors reviewed the Outage Safety Review (OSR) and contingency plans for the
Unit 2 refueling outage, which began September 7, 2014, to confirm that the licensee
had appropriately considered risk, industry experience, and previous site-specific
problems in developing and implementing a plan that assured maintenance of defense in-
depth.
1998:
North Anna Unit 1 Fuel Failures
During the present refueling outage, it was determined that there were 19 failed (leaking) fuel rods in 9 assemblies in the completed cycle at North Anna
Unit 1. Coolant activity had indicated fuel failures, but the number was unknown until the outage. These failures were all in third-cycle, ZIRLO clad fuel,
located near the baffle. The root cause investigation is underway, with the most likely cause being grid to rod fretting at the mid grids. These failures
appear to be similar to vibration related failures that were experienced in the 1993 time frame at two other plants. The North Anna fuel had incorporated
the rotated grids which was the fix for the previous problem. All affected assemblies were scheduled for discharge during this outage. Virginia Power has
installed vibration suppression devices on all peripheral locations for the upcoming cycle. The Reactor Systems Branch (SRXB) will continue to follow this
issue.
https://www.nukeworker.com/forum/index.php?action=printpage%3Btopic=38257.0
Title: Re: North Anna Fuel Failure
Post by: cheme09 on Sep 18, 2014, 05:39
Has been Areva, but we're in the process of going to W fuel. I think the last Areva bundles come out next outage.
https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML060200275
G45 Fuel Assembly Clad Damage
The G45 assembly has been ultrasonically and visually inspected and the failure is in a high power IFBA rod and is believed to have occurred during the initial power ascension for Cycle 6. This is evident by the secondary hydriding of the failed rod and the high Iodine concentrations experienced in the Reactor Coolant System (RCS) during R Cycle 6.
The existence of a cladding leak was initially established during Cycle 6 operation through sampling of the Reactor Coolant System (RCS) that identified elevated levels of Iodine 131 (1-131) and Xenon 133 (Xe-133).
This condition was documented in TVA's corrective action program as Problem Evaluation Report (PER) 9174. A limit for the concentration of 1-131 is defined in Limiting Condition for Operation (LCO) 3.4.16, "Reactor Coolant System (RCS) Specific Activity." In order to ensure this limit was closely monitored during Cycle 6, the RCS was sampled three times a week and reviewed by site management.
At the time a fuel leak was initially identified in October 2003, Operations personnel notified appropriate site
management of the problem and ensured the problem was documented in TVA's corrective action program.
When the cladding defect in rod G45 was identified in November 2005, the Operations staff ensured the
required notifications were made to NRC in accordance with 10 CFR 50.72.
http://www.orau.org/ptp/PTP%20Library/library/NRC/Info/in87039.pdf
August 21, 1987
NRC INFORMATION NOTICE NO. 87-39: CONTROL OF HOT PARTICLE CONTAMINATION
AT NUCLEAR POWER PLANTS
In a recent study for the NRC (Reference 3), it was reported that a plant
operating with 0.125 percent pin-hole fuel cladding defects showed a
general five-fold increase in whole-body radiation exposure rates in some
IN 87-39
August 21, 1987
Page 4 of 5
areas of the plant when compared to a sister plant with high-integrity
fuel (<0 .01="" around="" certain="" degraded="" leakers="" p="" percent="" plant="" systems="" the="">fuel may elevate radiation exposure rates even more.
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1982/in82027.html
Information Notice No. 82-27: FUEL ROD DEGRADATION RESULTING FROM BAFFLE WATER-JET IMPINGEMENT
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.
2010: CR319099, “North Anna 2 confirmed single fuel rod failure” (subsequently
determined to result from unidentified debris)
Just in Time Training Presentation, Response to Recently Identified Fuel Failures, dated 09/22/2014
| 09/06/2014 | REFUELING OUTAGE |
LER 2014-002-00: Failed Fuel Assembly
Nov 12, 2014
05000338/340
05000338/340
On September 15, 2014, with Unit 2 defueled, debris that had
the potential to be fuel fragments was located on the core plate directly below
the B131 core location, where fuel assembly 4Z9 resided during Cycle 23. Video
inspection of fuel assembly 4Z9 identified that the top springs of two fuel
pins were dislodged.
Due to the fact that the fuel damage exceeded expected conditions, at 1454 on September 15, 2014, this event was reported as an eight
hour report as per 10 CFR 50.72(b)(3)(ii)(A), any event or condition that
results in the condition of the nuclear plant, including its principle safety
barriers, being seriously degraded. Detailed video inspections estimated that
15 fuel pellets were dislodged from fuel assembly 4Z9. During efforts to
identify and recover the fuel pellets, 7 fuel pellets worth of material were
not found and have already or are expected to granulate into fine particles
that will dissolve in low flow areas of the primary plant systems, or be
removed by normal purification processes. Since the specific location of the 7
fuel pellets is undesignated and because those pellets contain licensed
material in a quantity greater than 10 times the quantity specified in App. C
of 10 CFR 20, a report was made at 1227 on September 30, 2014, pursuant to 10
CFR 74.11(a) and to 10 CFR 20.2201 (a)(ii). The health and safety of the public
were not affected by this event.
At 0900 on September 15, 2014,
with Unit 2 defueled, debris that had the potential to be fuel fragments was
located on the core plate (EIIS System - AC) directly below the B1 1 core location.
Ten pieces of material, approximately 1/8" in diameter, were found. The material
was near the edge of the outer flow hole and partially under the gap between the
baffle plate and the core plate. Fuel assembly (ElIS System -AC) 4Z9 was
located at the B131 location during Cycle 23. Video inspection of fuel assembly
4Z9 identified that the top springs of two fuel pins were dislodged.
Due to the fact that the fuel
damage exceeded expected conditions, at 1454 on September 15, 2014, this event
was reported as an eight hour report as per 10 CFR 50.72(b)(3)(ii)(A), any
event or condition that results in the condition of the nuclear plant,
including its principle safety barriers, being seriously degraded.
Detailed video inspections
estimated that fifteen (15) fuel pellets were dislodged from fuel assembly 4Z9.
For reference, the reactor core contains approximately 15 million fuel pellets.
During efforts to identify and recover the fuel pellets, debris fragments estimated
to represent five (5) fuel pellets were found in the damaged fuel assembly that
is currently in the Spent Fuel Pool (SFP) (EIIS System - DA). In
addition, an estimated three (3) pellets worth of material was retrieved by the
foreign object search and retrieval (FOSAR) efforts in the reactor vessel and are
now located in the SFP. The remaining seven (7) fuel pellets have already or
are expected to granulate into fine particles that will dissolve in low flow
areas of the primary plant systems or be removed by normal purification
processes. However, since the specific location of the seven (7) fuel pellets
is undesignated, a report was made at 1227 on September 30, 2014, pursuant to
10 CFR 74.11 (a) for the loss of special nuclear material (SNM). At that same
time, a report was made pursuant to 10 CFR 20.2201 (a)(ii) because the seven
(7) fuel pellets contain licensed material in a quantity greater than 10 times
the quantity specified in Appendix C of 10 CFR 20. 10 CFR 20.2201(b) requires a
written report after the initial notification for the occurrence of any lost,
stolen, or missing licensed material that was reported under 10 CFR 20.2201
(a)(ii) for licensed material in a quantity greater than 10 times the quantity specified
in Appendix C of 10 CFR 20. The following topics are required to be addressed:
Fuel Pellet Description - Based on the review of the video of the recovered material, the possibility that these fuel pellets have remained intact is very low.
Type of Special Nuclear Material Uranium dioxide pellets initially enriched to 4.45%
Length of fuel pellet 0.4 inches nominal Pellet diameter 0.3225 inches
Total Uranium in the 7 fuel pellets 32.3 grams (Sept 2014)
Total Uranium 235 in the 7 fuel pellets 0.4 grams (Sept 2014)
Total Plutonium in the 7 fuel pellets 0.4 grams (Sept 2014)
Total Fissile Plutonium in the 7 fuel pellets 0.3 grams (Sept 2014)
Activity Level 266 Ci
Average Burnup of Assembly 4Z9 46733 MWD/MTUEffective Full Power Days (EFPD) of Assembly 4Z9 1160 EFPD
(ii) A description of the
circumstances under which the loss or theft occurred:
The fuel pellet loss occurred as
a result of baffle jetting on the fuel assembly. The affected fuel rods had
their top springs dislodged and fuel pellets were able to escape the fuel rod.
Fragments of fuel pellets were found within the associated fuel assembly and on
the core plate. However, about seven (7) fuel pellets worth of material were
not located and have already or are expected to granulate into fine particles
that will remain in low flow areas of the primary plant systems or be removed
by normal purification processes. The possibility of theft is not plausible because
of the plant's radiation monitoring instrumentation, physical security measures,
and the size and type of container required for transporting nuclear material
of this nature.
(iii) A statement of disposition,
or probable disposition, of the licensed material involved:
During efforts to identify and recover
the fuel pellets, debris fragments estimated to represent five (5) fuel pellets
were found in the damaged fuel assembly that is currently in the SFP. In
addition, an estimated three (3) pellets worth of material was retrieved by the
FOSAR efforts in the reactor vessel and are now located in the SFP. The
remaining seven (7) fuel pellets have already or are expected to granulate into
fine particles that will dissolve in low flow areas of the primary plant
systems or be removed by normal purification processes.
(iv) Exposures of individuals to
radiation, circumstances under which the exposures occurred, and the possible
total effective dose equivalent to persons in unrestricted areas:
No unauthorized exposure to
radiation occurred to the plant staff or members of the public because the fuel
pellet fragments either remain in the SFP or granulated into fine particles
that will dissolve in low flow areas of the primary plant systems or be removed
by normal purification processes.
(v) Actions that have been taken,
or will be taken, to recover the material: During efforts to identify and
recover the fuel pellets, debris fragments estimated to represent five (5) fuel
pellets were found in the damaged fuel assembly that is currently in the SFP.
In addition, an estimated three (3) pellets worth of material was retrieved by
the FOSAR efforts in the reactor vessel and are now located in the SFP. The
remaining seven (7) fuel pellets have already or are expected to granulate into fine particles
that will dissolve in low flow areas of the primary plant systems, or be
removed by normal purification processes.
(vi) Procedures or measures that
have been, or will be, adopted to ensure against a recurrence of the loss or theft of licensed material:
Westinghouse fabricated and
delivered a low-enrichment RFA-2 fuel assembly armored with seven (7) stainless
steel rods in place of fuel rods which could be affected by jets from baffle
gaps for core location B1 1 in cycle 24. A similar modification to that of the
reactor vessel upflow conversion design change that was performed on Unit 1, DC
NA-95-001, will be developed and implemented on Unit 2.
2.0 SIGNIFICANT SAFETY CONSEQUENCES
AND IMPLICATIONS
No significant safety
consequences resulted from this event because the reactor coolant system
activity levels during Unit 2 Cycle 23 were well within the requirements of Technical
Specification (TS) 3.4.16, Reactor Coolant System Specific Activity. After Cycle
24 startup, the activity remains well within the requirements of TS 3.4.16. The
health and safety of the public were not affected by this event.
3.0 CAUSE
The direct cause of the event was
due to baffle jetting. Baffle jetting is the process by which water on the
outside of the core baffle plate is forced through small openings in the baffle
seams and onto the fuel assemblies. During Unit 2 Cycle 23, baffle jetting caused
two rods in assembly 4Z9, located in core position B11, to begin rotating and vibrating.
This movement resulted in fuel rod wear and eventual mechanical failure and rod
separation. Once separated, a maximum of 15 fuel pellets were released from the
two affected fuel rods. The Root Cause of the failed fuel assembly was the
change in material properties of the baffle plates and bolting due to aging
mechanisms resulting in the gap widening at the baffle joint. Stress,
temperature, and irradiation since initial plant start-up have resulted in
relaxation, creep, and loss of pre-load in the bolting and baffle plates. The
changes in material properties allowed the gap in the corner baffle joint, adjacent
to location B1 1, to widen when subjected to the relatively high differential pressure,
approximately 25 psi, associated with the baffle-barrel downflow configuration in
North Anna Unit 2.
4.0 IMMEDIATE CORRECTIVE
ACTION(S)
Westinghouse fabricated and
delivered a low-enrichment RFA-2 fuel assembly armored with seven (7) stainless
steel rods in place of fuel rods which could be affected by jets from baffle
gaps for core location B1 1 in cycle 24. Visible debris on the core plate from 4Z9
was found and retrieved. An inspection of the baffle was performed with no anomalies
noted. An inspection of the fuel assembly that was previously located at B1i1 for
fuel cycle 22 was performed and no indications of baffle jetting were noted. An
inspection was performed of other cycle 23 fuel assemblies in other baffle
locations for baffle jetting damage. Ten of the other assemblies exhibited some
indications at the center injection locations ranging from slight marks on a
mid-grid adjacent to rod 15 or rod 3 to some slight surface erosion or buffing
of the grid at the same locations. Other than being in the proper location for
where center injection would be expected to occur, it was not clear whether the
indications were due to baffle jetting or to some other interaction such as
fuel handling or wear from a bowed assembly rubbing against the baffle plates.
The indications were reviewed by Dominion's Nuclear Analysis and Fuel (NA&F)
Fuel Performance Analysis (FPA) group, and it was determined that no further action
was required. Both AREVA and Westinghouse reviewed the video of 4Z9 and concluded
that the cause was baffle jetting. A revised Reload Safety Evaluation (RSE) incorporating
the replacement fuel assembly for location B1 1 was completed and approved. An
Operability Determination, OD000600, was completed for baffle jetting.
5.0 ADDITIONAL CORRECTIVE ACTIONS
No additional corrective actions
were identified by the Root Cause Team.
6.0 ACTIONS TO PREVENT RECURRENCE
A modification similar to the
reactor vessel upflow conversion design change that was performed on Unit 1, DC
NA-95-001, will be developed and implemented on Unit 2.
7.0 SIMILAR EVENTS
Unit 2 has operated without
indications of baffle jetting for 34 years and Unit 1 has operated without
baffle jetting since 1996 when the upflow conversion was performed. While Unit
1 did have baffle jetting issues prior to 1996, the baffle jetting issues were from
the center joints. Whereas the Unit 2 baffle jetting was from a corner joint. Additionally,
Unit 2 has a different bolting configuration that made it less susceptible to the
baffle jetting experienced on Unit 1.
8.0 ADDITIONAL INFORMATION
Unit 1 continued operating in
Mode 1, 100 percent power during this event.
