ML20247R196
| ML20247R196 | |
| Person / Time | |
|---|---|
| Issue date: | 06/13/1989 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2643, NUDOCS 8908070382 | |
| Download: ML20247R196 (9) | |
Text
.-.
L 0 0 3 4 6 9'S N8 M CERTIFIED COPY DATE ISSUED:'Uune 13, 1989 QT.
.11s.$ I[;
i, i
- ' : ; :.Il h bE N b O b N $bObc: -.
eg y i
. r.
g
SUMMARY
/ MINUTES OF THE ACRS SUBCOMMITTEE ON MATERIALS AND METALLURGY APRIL 27, 1989 BETHESDA, MD The ACRS Subcommittee on Materials and Metallurgy met on April 27, 1989 at Bethesda, MD., to be briefed on 1) water chemistry, 2) radiation assisted stress corrosion cracking, 3) Erosion / corrosion in piping systems, 4) full plant decontamination and its effects on materials, 5) valve body erosion, 6) boric acid corrosion, and 7) service water system fouling and corrosion. The meeting was requested by P. Shewman and C. Michelson of the subcommittee on Materials and Metallurgy.
Notice of the meeting was published in the Federal Register on April 17, 1989. The schedule of items covered in the meeting and a list of handouts are kept with the office copy. There were no written or oral statements received or presented from members of the public at the meeting.
E. G. Igne was cognizant ACRS Staff member for the meeting, Principal Attendees o
m c)
ACR5 7; '
P. G. Shewman, Chairman g
Cy Michelson, Member o
D. Ward, Member T. Kassner, ACRS Consultant n$
^
$oo NRC S"g/
C. McCracken F. Witt
$g K. Parczewski (q3or 1
i A. Taboada
'I Others R. Cowan, GE
- h ;
a }f inghouse 1
cert $nc3 37
[gg
[Yb b $y 1,iy '.;
g
' b3
~
Minutes / Materials & Metallurgy 2
o
~
Subcommittee Mtg., April 27, 1989 B..Chexal, EPRI J.-Parry, Consolidated Edison R. Hess, Philadelphia Electric C. Welty, EPRI Highlights 1.
R. Cowan, GE, presented an update on BWR water chemistry technology.
He stated that BWR water chemistry of U.S. plants have improved since the water chemistry guideline was available for industry use in 1985.
About 78% of all GE-BWRs operated at 90% of the time below 0.3 ps/cm (reactor water conductivity; below 0.3 pS/cm is normal water chemistry) during 1988.
Similarily, foreign plants did much better. Sulfates and chlorides are most harmful impurities and should be controlled to less than 20 and 15 ppb respectively.
Water quality guideline for makeup and condensate storage water are controlled based on total organic carbon in order to. reduce inpurities.
EPRI guideline is 400 ppb while INP0 has proposed 100 ppb.
It was stated that organic contaminants include refrigerants, oil, solvents, lab drains, etc.
These organics are non-ionic and can not be removed by ion exchange.
In the reactor they form organic acids or hydrogen halides that can cause failure of components. Study shows that ultra-violet ozone organic removal systems developed by GE exceeded performance expectations; 90-95 per cent of the organic carbon can be removed.
Radiation buildup in BWR reactor coolant loop is essentially caused by.
Co-60 deposition on the inner surface of the loop.
It has been observed that increasing mpurity level reduces the dose rate. Hypothesis was i
developed based on these observations and laboratory tests verified the I
hypothosis.
It was stated that zine reduces CP-60 film binding, which w- - _a
Minutes'/ Materials & Metallurgy 3
Subcommittee Mtg., April 27, 1989 in turn reduces dose rate significantly.
It was also mentioned that i
j.
zinc has no degradation effects on reactor pressure boundary components.
Fitzpatrick and Perry nuclear power plants have implemented zinc injection or GEZIP recently.
BWR hydrogen water chemistry guidelines issued in 1985 maintain requirements of normal water chemistry to a conductivity value of less than0.3pS/cm,andestablishelectrochemicalpotentialofstainless steel to a value of below -0.230V.
If hydrogen water chemistry (HWC) conditions are established both IGSCC initiation and growth are inhibited.
R. Cowan stated that feedwater injection amounts required to establish HWC conditions may vary from plant to plant and region to region with a plant. A significant portion of BWR nuclear power plants now are implementing HWC.
2.
G. Gordon, GE, presented an update on irradiation assisted stress corrosion cracking (IASCC). Efforts are underway to assess generic implications of the IASCC phenomenon.
IASCC constant strain rate tests at 288C on irradiated 30455 (annealed) in pure water results in an observed IASCC threshold fluence level ranging from about SE20 to 2E21 nyt depending on the application of either high or low applied stresses.
It was stated that in-core (most susceptible to IASCC) non-sensitized 4
stainless steel undergoes fluence induced chromium depletion plus segregation of deleterious alloy impurities; also radiation hardening occurs.
l Minutes / Materials & Metallurgy 4
Subcommittee Mtg., April 27, 1989 These conditions (in-core) are more severe than in pipes because radiolysis leads to highly oxidizing conditions from oxygen, peroxide, etc. and IASCC is accelerated by the presence of trevices. Cracking can occur at lower stresses because irradiation defects allow material flow j.
(creep) at low stresses.- Solutions to this problem involve operation with low conductivity water, use of HWC and high purity steels, and post irradiation annealing.
Some top guide components of BWRs are potentially susceptible to IASCC, although recent examination of two in-plant show no evidence of IGSCC.
3.
G. Gordon, GE, discussed pipe cracks recently reported at Dresden-2.
Since this plant was operating on HWC, concern was raised regarding HWC benefits.
GE preliminary evaluation are as follows:
Lack of change in known previously detected cracks indicates that some degree of HWC protection in recirculation system existed.
Data suggests that "new" axial cracking may have been present as early as 1983, but was below the detection threshold for prior in-service inspection techniques.
Many new circumferential cracks in the recirculation water cleanup (RWCU) system obviously occurred since this type of cracks are not likely to have been previously missed during in-service inspection.
l L' -
Minutes / Materials & Metallurgy 5
Subcommittee Mtg., April 27, 1989 Future degree of protection for plant will be monitored by current water chemistry measurements and use of crack arrest verification L
system.
1 The RWCU system may require higher hydrogen injection rate for l-protection than recirculation system.
Better water chemistry data is necessary in order to quantify HWC effectiveness.
4 B. Chexal, EPRI, presented an update in EPRI's erosion - corrosion technology.
He stated that cavitation erosion is not included in the study. The problem is the potential deterioration of piping from flow assisted corrosion due to either high velocity single phase water flow or two phase steam / water flow.
He stated that two computer programs CHEC and CHECMATE have been developed to handle single and two phase flows problems. These programs will predict erosion-corrosion in various piping systems that account for water chemistry, material chemistry and hydrodynamics (i.e., velocity, geometry and steam quality). Comparison with plant data indicate that the code can predict erosion-corrosion degradation within a 120% error band. Technology transfer to the industry has been satisfactory and on-going.
. Minutes / Materials & Metallurgy 6
)
Subcommittee M29., April.27, 1989 1
5.
C. Welty, Jr., EPRI, discussed EPRI-managed water chemistry guidelines for PWR primary and secondary systems. Water chemistry j.
guidleines for.PWR secondary loop were available in 1981 and the latest revision was completed in 1988. On the primary loop the guidelines were l
l.
available in 1986 and revised in 1988.
It was stated that the guidelines are industry concensus documents and not regulatory requirements.
The secondary loop chemistry is to provide for material integrity, primarily to prevent steam generator degradation due to corrosion, while the primary loop chemistry provides for continued material and fuel integrity and radiation field control.
It was stated that according to INP0, every PWR nuclear power plant must have water chemistry guidelines. These guidelines contain action level (AL) responses indicatin9 that long term reliability will be significantly worse at or above a specified value. AL-2 indicate that system damage could be done in the short term, thereby warranting a prompt corrective action.
AL-3 indicates that is it inadvisable to continue to operate the plant, thereby warranting a prompt shutdown Action levels in PWR secondary circuit and in BWR's are progressive leading to power reduction to plant shutdown; while the PWR primary are not progressive, requires engineering review and no power reduction.
The action level control parameter is the concentration; normal value being less than 0.8 pS/cm, and action levels 1, 2 and 3 being greater than0.8,2.0,and7.0pS/cm. The intent is to provide an indication of what has been achieved at several plants by application of good operat-ing practices.
It was stated that these values are not an appropriate basis for regulatory or evaluation purposes, a--___-__-._
Minutes / Materials & Metallurgy 7
Subcommittee Mtg., April 27, 1989 s
6.
J. Parry, Consolidated Edison, dibrassed the full reactor coolant system chemical decontan nation program. This is a three phase program, Phase
-I, initial parametric studies, is now nearing completion; Phase II, decon procc,s qualification, engineering evaluations and safety analysis; and Phase III,detaileddesign and implementation. The program assumes removal of nuclear fuel from the reactor pressure vessel. Ten utilties make up the Westinghouse Owners Group (WDG) decontamination subgroup.
It was stated that information generated from the program is for members only. Phase II is the major phase of this program entail ng materiai corrosion and compatibility tests, fluid systems and RCS equipment ' evaluations, waste and radiological evaluations, nuclear evaluations and cost / benefit studies.
In reply te a question it was stated that surface decontamination factor of about five, and work area decontamination factor of about three can be readily achieved.
7.
P. Miller, Westinghou:e, discussed in more details Phase II aspects of the full decontamination program including reasons for the process qualification program. Two processes, CAN DECON and LOMI, will be tested and evaluated. A topical report on the full RCS chemical decontamination program is due in March of 1991.
It is expected that a successfbl decontamination program will significantly reduce personnel exposure at older plants.
8.
R. Hess Philadelphia Electric, presented the status of the BWR valve body erosion matter. A BWROG was recently formed (March 1989) to determite if the Brunswick valve body erosion phenomenon may be a generic concern. The valve erosion at Brunswick is attributable to cavitation. The erosion was extensive although the minimum ASME code thickness requirement was nat violated. The NRC staff has an on-going
--__m m_._.
_mm
____m
Y
.g'.
. Minutes /Moterials & Metallurgy 8
Subcommittee Mtg., April 27, 1989
[t
- 9. - K. Karczewski, NRR, presented an update of Doric acid corrosion of carbon steel components of PWR reattor coolant system. Many incidents of degradation of carbon steel components ie., reactor vessel head, fasteners, reactor vessel nozzles, etc., have teen reported.
IE otices, Bulletins.and NUREG reports on this matter have been issued since 1979. On March 17, 1988 Generic Letter 88-05, " Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants," was issued. This generic letter essentially specifies corrective actions in order to prevent recurrence of this type of corrosion. Auditing of licensees programs is enderway.
10.
F. Witt, NRR, discussed the status of service water system fouling and corrosion.
Flow blockage of cooSing water systems can be caused by clams, mussels, and/or debris, Many generic communications i.e.
Bulletins 81-03 (causes of flow birckage), 81-20 (causing loss of direct s
access to ultimate heat sink), and Generic Issue 51 (improving the reliability of open-cycle service water systems) have been issued on this matter. Generic Letter 89-XX (service water system problems affecting safety-related equipment) currently being developed request licensees and applicants to perform an extensive surveillance and
.1
- Minutes / Materials & Metallurgy 9
Subcommittee Mtg., April >27, 1989 4-control program in order to ensure that service water systems are in compliance with current regulations.
It was stated that Generic Letter 89-XX when released will be reviewed by the ACRS Subcommittee on Auxiliary and Secondary Systems on May 25, 1989 (tentative).
It was also stated that EPRI has an extensive on-going program on service water system reliability improvement which will provide utilities a technical basis and support for improving the overall reliability and performance of service water systems.
Action:
No planned subcommittee action was discussed at the meeting.
(Note: after the meeting the subcommittee chairman stated that a subcommittee report to the full ACRS is not planned).
- r****
NOTE:
A transcript of the meeting is available at the NRC Public Document Room, Gelman Bldg. 2120 "L" Street, NW., b ahington, D.C. Telephone (202) 634-3383 or can be purchased from Heritage Reporting Corporation, 1220 L Street, N.W.,
Washington, D.C. 20005, Telephone (202) 628-4888.
l
_ _ - _ - _ - - - _ _ - _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _