ML20151A226
| ML20151A226 | |
| Person / Time | |
|---|---|
| Issue date: | 07/08/1988 |
| From: | Sniezek J Office of Nuclear Reactor Regulation |
| To: | Jordan E Committee To Review Generic Requirements |
| Shared Package | |
| ML20150F860 | List: |
| References | |
| IEIN-87-044, IEIN-87-44, NUDOCS 8807190289 | |
| Download: ML20151A226 (13) | |
Text
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UNITED STATES
[
g NUCLEAR REGULATORY COMMISSION 7,
s WASHINGTON, D, C. 20555
's,.....
l MEMORANDUM FOR:
Edward L. Jordan, Chairman Comittee to Review Generic Requirements FROM:
James H. Sniezek, Deputy Director Office of Nuclear Reactor Regulation l
SUBJECT:
RE0 VEST FOR REVIEW OF A DRAFT BULLETIN ON THlMBLE TUBE THINNING IN WESTINGHOUSE REACTORS 1
On September 16, 1987 and March 28, 1988, the NRC issued Information Notices 87-44, "Thimble Tube Thinning in Westinghouse Reactors," and 87-44 Supplement 1, 1
"Thimble Tube Thinning in Westinghouse Reactors," respectively. These infor-I mation notices alerted addressees to a potentially generic problem regarding thinning of the incore neutron monitoring system thimble tubes as a result of flow-induced vibration. Thimble tubes, over most of their length, constitute l
a portion of the reactor coolant system (RCS) pressure bouncary. Thus, wear of the thimble tubes results in degradation of the RCS pressure boundary and 7
can also create a potentially non-isolable leak of reactor coolant.
Further-more, thimble tube thinning could result in multiple thimble tube failures beyond a facility's design basis following a seismic or reactor coolant system overpressure event.
The staff is aware that many licensees (including North Anna Units 1 and 2 Salem Units 1 and 2, Farley Units 1 and 2, Surry Units 1 and 2, trairie Island l
Units 1 and 2. Kewaunee Beaver Valley Unit 1. Millstone Unit 3. Haddam Neck, South Texas Unit 1, and D. C. Cook Unit 2) have detected thimble tube wear.
There have also been instances of thimble tubes experiencing leaks (for example, Salem Unit 1 and D. C. Cook Unit 1). Thus, we believe that Westinghouse-designed nuclear power reactors that utilize bottom mounted instrumentation may not comply entirely with General Design Criterion (GDC) 14 "Reactor Coolant Pressure Boundary" of 10 CFR 50, Appendix A, which requires that the reactor coolant pressure boundary be designed to have an extremely small probability of abnormal leakage, of rapidly propagating failure, and of gross rupture.
e The enclosed draft bulletin would ensure that compliance with GDC 14 is achieved, and would also minimize (through early detection of thinble tube thinning) the likelihood of a potentially non-isolable leak of reactor coolant. Addressed to all holders of operating Itcenses or construction permits for Westinghouse-l designed nuclear power reactors that utilize bottom mounted instrumer.tation, r
Y CONTACT: Jack Ramsey, NRR 492-1167 Pd 0.7 f3 M
R08e Edward L. Jordan.
it would request that they 1) establish an inspection program to menitor thimble tube integrity and 2) implement this program by inspecting the thimble tubes at the next (or first) refueling outage that begins 90 days after the receipt of the bulletin.
The proposed bulletin and background infomation required by the CRGR Charter are enclosed.
In addition, to ensure that NRC bulletins and generic letters remain in corpliance with the recently (53 FR 16618) amended Paperwork Reduction Act, we are in the process of developing, with the assistance of OGC, the pare-l graph regarding the OMB Clearance. Additional modifications to this pa,agraph i
may be made, as necessary, prior to issuance of the bulletin.
We request that review of this package be scheduled at CRGR's earliest conve-nience. The bulletin is sponsored by Charles E. Rossi, Director, Division of Operational Events Assessment, t
J.%46t hM VL aines H. Snierek Deput Director Of rice of Nuclear React Regulation
Enclosures:
2.
NRC Bulletin No. 88-XX. Thimble ube Thinning in Westinghouse i
Reactors 2.
CRGR Item IV.B.
Contents of Packages Submitted to CRGR l
l
OMB No.: 3150-0011 NRCB 88-XX UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C.
20555 July xx, 1988 NRC BULLETIN NO, 88-XX:
THIMBLE TUBE TitiNN!NG IN WESTINGHOUSE REACTORS Addressees:
All holders of operating licenses or censtruction permits for Westinghouse (W)-designed nuclear power reactors that utilize bottom mounted instnmenta-tion.
Purpose:
The purpose of this bulletin is to request that addressees 1) establish an inspection program to monitor incore neutron monitoring system thimble tube integrity and 2) im the next (or first)plement this program by inspecting the thimble tubes at refueling outage that begins 90 days after the receipt of this bulletin.
Description of Circumstances:
The incore neutron monitoring system thimble tubes extend fron a 10-path transfer device, through the seal table, through the botton of the reactor vessel, and into selected fuel assemblies. *The thimble tubes are sealed at the leading (reactor) end, but are open at the 10-path transfer device to allow insertion of an incore neutron detector during flux napping.
By design, the thimble tubes, over most of their length, serve as a portion of the reactor coolant systen (RCS) pressure boundary.
(A description of a typical incore neutron monitoring system is contained in NRC Information Notice No. 87-44,)
i "Thimble Tube Thinning in Westinghouse Reactors," dated September 16, 1987.
Thus, wear of the thimble tubes results in degradation of the RCS pressure boundary and can also create a potentially r.on-isolable leak of reactor conlant.
Furthemore, thimble tube thinning could result in multiple thimble tu w failures beyond a facility's design basis following a seismic or reactor coolant system overpressure event.
As discussed in NRC Infomation Notice No. 87-44 Supplement 1. "Thimble Tube Thinning in Westinghouse Reactors," dated March 28, 1988, thimble tubes are experiencing thinning as a result of flow-induced vibration.
Thimble tube wear has generally been detected at locations associated with geometric discontinut-ties or area changes along the flow path (such as areas near the lower core plate, the core support forging, the lower tie plate, the upper tie plate, and
NRCB 88-XX July xx, 1988 Page 2 of 3 i
the vessel penetration). Many licensees have detected thimble wear. There have also been several instances (both foreign and domestic) of thimble tubes 3
experiencing leaks.
In addition, a review of the available data indicates that most leaks have occurred during f1tix mapping (while either inserting or re-tracting the probe).
L Discussion:
The amount of vibration the thinble tubes experience is determined by such plant-specific factors as the gas distance from the lower core plate to the fuel assembly instrument tube, tie amoult of clearance between the thinble tube and the guide or instrument tube, the axial component of the local fluid velocity, the thickness of the thimble tube, and the moment of inertia of the thimble tube.
A review of the available data indicates that it is not possible to accurately predict thimble wear rates. Thus, it appears that the only effective method for determining thimble tube integrity is through plant-specific inspections and periodic monitoring.
3 There are currently no inservice inspection or testing requirements for thimble l
tubes.
The NRC staff believes that this may have resulted in significant i
thimble tube degradation having gone undetected, creating a conditicn that may i
be adverse to safety.
To ensure that addressees are in compliance with G$rcral Design Criteria 14 "Reactor Coolant Pressure Boundary" of 10 CFR 50, Appendix A and to minimize (through early detection of thimble tube thinning) the likeliheed I
of a potentially non-isolable leak of reactor coolant, the NetC staff requests that addressees perfom the actions described below.
Actions pequested:
1)
Each addressee is requested to establish an inspection program to monitor thimble tube performance.
This inspection program should include:
the establishment, with technical justification, of an appropriate thimble tube wear acceptance criterion (for example, percent through-wall loss).
This acceptance criterion should include allowances for such items as inspection methodology and wear scar geometry uncertain-ties.
the establishment, with technical justification, of an appropriate inspection frequency (for example, every refueling outage).
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the establishment of an inspection methodology that is capable of I
adeouately detecting wear of the thimble tubes (such as eddy current testing).
2)
Addressees are requested to implement the inspection program established by item 1) above by performing inspections of the thimble tubes at the next for first) refueling cutage that begins 90 days after the receipt of this bulletin.
In addition, addressees are requested to take appro-l priate corrective actions (such as isolation or replacement) should a thimble tube fail to reet the acceptance criterion established in Item 1) above.
o NRCB 88-XX July xx, 1988 Page 3 of 3 l
1 Reporting Requirements:
i 1)
Records generated during the development of the inspection program re-questedbyItem1)above,aswellastheresultsoftheinspections t
requested in Item 2) above, shall be documented and maintained in accor-l l
dance with plant procedures.
l 2)
Addressees are required to, within 30 days of the completion of the next (or first) refueling outage that begins 90 da bulletin, provide a written response that a) ys after the receipt of this j
confims that the inspection program requested in Item 1) abnve has been established and b) confirms that inspections requested in Item 2) above have been performed.
j
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Although not required by this bulletin, addressees are encouraged to work
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collectively to address this issue.
i The written reports required above shall be addressed to the V. S. Nuclear l
Regulatory Comission, ATTN: Document Control Desk, Washington, D.C.
- 20555, i
j under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended.
In addition, a copy shall be submitted to the appro-j; priate Regional Administrator.
l This request is covered by Office of Management and Budget Clearance Number 3150-0011 which expires December 31, 1989. The estimated average burden as l
defined in 5 CFR 1320.7 is approximately 3000 man-hours per licensee response.
Coments on the accuracy of t11s estimate and suogestions to reduce the burden may be directed to the Office of Management and Budget. Room 3208, New l
l Executive Office Building Washington, D.C.
20503, and to the U. S. Nuclear Regulatory Comission, Records and Reports Management Branch. Office of Administration and Resources Management, Washington, D.C.
20555.
If you have any questions abbut this matter, please contact one of the techni-cal contacts listed below or the Regional Administrator of the appropriate regional office.
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Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation I
Technical Contacts: Jack Ramsey, NRR (301) 492-1167 Shou-Nien Hou, NRR (301)492-0904
Attachment:
List of Recently Issued NRC Bulletins i
i i
CRGR Item IV.B.
Contents of Packages Submitted to CRGR (Rev. 4, Stello to List 042387, des 41860 342 ff)
The following requirements apply for proposals to reduce existing requirements I
or (regulatory) positions as well as proposals to increase requirements or (regulatory) positions.
Each package submitted to the CRGR f,e review shall include fifteen (15) copies of the following infomation:
SUBJECT:
BULLETIN REGARDING THIMBLE TUBE THINNING IN WESTINGHOUSE REACTORS Question:
The proposed generic requirement or staff position as it is proposed to be sent out to licensees.
I-
Response
The proposed requirements are set forth in the bulletin (Enclosure 1).
i Ouestion:
Draft staff papers or other underly(A copy of all materials referenced in ing staff documents supporting the requirements or staff positions.
l the document shall be made available upon request to the CRGR staff. Any comittee member may request CRGR staff to obtain a copy of any referenced material for his or her use.)
Response
1.
NRC Information Notice No. 87-44, Supplement 1, "Thimble Tube Thin-
[
ning in Westinghouse Reactors," March 28, 1988 1
2.
NRC Infomation Notice No. 87-44, "Thimble Tube Thinning in Westing-house Reactors," September 16, 1987 i
3.
Memorandum from T. Novak to E. Rossi, "Thimble Tube Wear and Other Results of Flow-Induced Vibration in Westinghouse Reactors,"
i December 31, 1987.
4 Memorandum from W. Hodges to T. Marsh, "Flux Thimble Wear in Westing-house Plants," February 24, 1988.
l S.
Hemorandum from S. Hou to T. Marsh, "Trip Report - European Experi-
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ence on BMI Thimble Wear," December 8, 1987.
6.
NRC Inspection Reports 50-272/86-11 and 50-311/86-11 (Salem Units 1 and 2).
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7.
NRC Inspection Peports 50-338/87-10 and 50-339/87-10 (North Anna i
Unit 1).
8.
NRC Inspection Reports 50-338/87-29 and 50-339/87-29 (North Anna Unit 2).
2 9.
NRC Inspection Report 50-213/87-31 (Haddam Neck),
i 10.
NRC Inspection Report 50-423/87-33(MillstoneUnit3).
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11.
NRC Inspection Reports 50-334/88-01 and 50-412/88-01 (Beaver Valley i
Unit 1).
12.
NRC Inspection Peports 50-282/88001(ORP)and 50-306/88001 (DRP)
(Prairie Island Unit 2).
I Ouestion:
III. Each proposed requirement or staff position shall contain the sponsoring office's cosition as to whether the proposal would increase staff require-I ments or staff positions, would implement existing staff requirements or positions, or would relax or Wuce existing requirements or staff positions.
Response
I General Design Criterion (GDC) 14 "Reactor Coolant Pressure Boundary" of 1
Appendix A to 10 CFR Part 50 requires that the reactor coolant system j
(RCS) pressure boundary be designed to have an extremely low probability 1l of abnormal leakage, of rapidly propagating failure, and of gross rupture.
Thirtle tubes, over most of their length, constitute a portion of the RCS 4
pressure boundary.
The staff is aware that thimble tube wear has been l
I detected at a number of facilities in this country (including North Anna l
j Units 1 and 2, Salem Units 1 and 2. Farley Units 1 and 2. Surry Units 1 1
and 2, Prairie Island Units 1 and 2, Kewaunee, Haddam Neck, Millstone Unit 3. Beaver Valley Unit 1. South Texas Unit 1, and D. C. Cook Unit 2),
and that there have been instances where thimble tubes are known to have i
experienced leaks (for example, Salem Unit 1 and D. C. Cook Unit 1).
In 1
addition, there are currently no inservice inspection or testing require-i ments for thimble tubes. The staff believes that this may have resulted j
in significant thimble tube degradation having gone undetected, possibly creating a condition that is adverse to safety.
Thus, we conclude that I
the action items in the proposed bulletin implement existing regulatory
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requirements by ensuring that addressees comply and renain in compliance with GDC 14 and by minimizing (through early detection of thinble tube l
thinning) the likelihood of a potentially non-isolable leak of reactor l
- coolant, i
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l Question:
!Y. The proposed nethod of implementation with the concurrence (and any comments) of OGC on the method proposed.
Res ponse:
The method of implementation will be the proposed bulletin (Enclosure 1).
A copy of this, bulletin has been forwarded to OGC. Any comments received
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will be incorporated prior to issuance.
t Question:
l Y.
Regulatory analyses generally conforming to the directives and guidance of L
NUREG/BR-0058 and NUREG/CR-3568.
Response
This is a compliance issue. No value/ impact analysis was made, i
Ouestion:
i VI.
Identification of the category of reactor plants to which the generic require-l ments or staff position is to apply (that is, whether it is to apply to new plants only, new OLs [cperating licenses] only. OLs after a certain date, all Ols, all plants under construction, all plants, all water reactors, all PWRs [ pressurized water reactors] only, some vendor types, some vintage types such as CWR 6 and 4. jet pump and nonjet pump plants, etc).
Response
I 1
The proposed bulletin would apply to all holders of operating licenses or
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construction permits for Westinghouse (W)-designed nuclear power reactors that utilize bottom mounted instrumentation.
l Question:
l VII. For each such category of reactor plants, an evaluation which demonstrates l
how the action should be prioritized and scheduled in light of other ongoing regulatory activities. The evaluation shall document for consid-eration infonnation available concerning any of the following factors as i
may be appropriate and any other information relevant and material to the l
proposed action, I
A.
Statement of the specific objectives that the proposed action is designed to achieve...
i l
Response
i The objectives of the proposed action are to ensure that addressees comply and remain in compliance with GDC 14 and to prevent (through l
early detectiva of thimble tube thinning) the creation of a potentially
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l non-isolable leak of reactor coolant, j
1
t 4
Question:
B.
General description of the activity that would be required by the licensee or applicant in order to complete the action...
Response
i To complete the action, addressees would have to establish an inspection program to monitor thimble tube performance, implerent this program by inspection of the thinble tubes at the next (or first) refueling outage that begins 90 days after the receipt of the bulletin, L
and take appropriate corrective actions (such as isolation or replace-ment) should the requested inspections identify thimble tubes that do not satisfy the established acceptability criterion.
Question:
C.
Potential change in the risk to the public from the accidental
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offsite release of radioactive material...
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Response
At present, the risk to the public from the accidental offsite release of radioactive material would be due to the loss of reactor coolant through failed thinble tubes.
GDC 14 and the design bases of the Final Safety Analysis Report (FSAR) do not account for such a scenario. Thus, the proposed actions (by ensuring compliance with GDC 14 and by minimizing [through early detection of thir.ble tube thinning 1 the likelihood of a potentially non-isolable leak of reactor coolant) would ensure that the rfsk to the public from the l
accidental offsite release of radioactive material is consistent j
with that intended by the promulgation of GDC 14 and the design bases
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of the FSAR.
Furthemore, thimble tube thinning could result in
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multiple thinble tube failures beyond a facility's design basis following a seismic or overpressure event.
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hestion:
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D.
Potential impact on radiological exposure of facility employees and other onsite workers...
Response
During refueling, the area in which these inspections are usually performed (the seal table) does not normally exhibit high radiation l
fields (typically, 2 to 3 millirem / hour). Thus, cumulative addi-j tional radiological exposure of facility employees and other onsite 4
w;rkers is expected to be minimal (on the order of 100 person-(
milliren per inspection).
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Question:
E.
Installation and continuing costs associated with the action, includ-ing the cost of facility downtime or the cost of construction delay...
Response
Thinble tube inspections have typically been performed over a 2 to 3 day period during a facility's refueling outage.
Thus, the proposed i
I actions will not result in forced plant outages or forced extended plant outages. Licensees that have voluntarily performd thirble tube inspections have indicated that the cost of these inspections has been on the order $30,000 per inspection. An estimate of addi-tional cost to industry by the proposed actions is:
1.
The 7 affected 2-loop Westinghouse facilities have an average operating history of approximately 17 years. Assuming an effective 40 year lifetime, an average 2-loop facility will be operational for an additional 23 years.
Assuming a 12 month operating cycle and a 1 month refueling outage, an average 2-loop facility will have an additional 21 refueling outages.
Assuming that inspections are done at the next 2 refueling outages and then at every third refueling outage, an average 2-loop facility will perform approximately 8 inspections over the remaining life of the plant. Thus, an additional cost to licensees of these facilities is ($30,000 per inspection)(8 I
inspections per plant)(7 plants) or approximately $1.fP0,000, 2.
The 39 affected 3-loop or 4-loop Westinghouse facilities have an average operating history of approximately 8 years.
Assuming an effective 40 year lifetime, an average 3-loop or 4-loop facility will be operational for an additional 32 years. Assuming an 18 i
renth operating cycle and a 2 month refueling outage, an average 3-loop or 4-loop facility will have an additional 19 refueling outages. Assuming that inspections are done at the next 2 refueling outages and then at every other refueling outage, an average 3-loop or 4-loop facility will perforni approximately 10 inspections over the remaining life of the plant. Thus, an additional cost to licensees of these facilities is ($30,000 per inspection)(10 inspections per plant)(39 plants) or approxi-mately $11,700,000, 3.
The 7 affected facilities under construction or not yet operat-ing (Comanche Peak Units 1 and 2. Watts Bar Units 1 and 2. South Texas Unit 2 Vogtle Unit 2, and Seabrook Unit 1), assuming an effective 40 year lifetime, will (assuming an 18 month operating cycle and a 2 month refueling outage) have approximately ?4 refueling outages each. Assuming that inspections are done at
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the first 2 refueling outages and then at every other refueling outage, each facility will perform approximately 12 inspections i
l over the life of the plant.
Thus, an additional cost to licensees of these facilities is ($30,000 per inspection)(12 inspections per plant)(7 plants) or approximately $2,520,000.
i Thus, the staff has estirated that the additional cost'to industry i
(over the next 40 years) associated with the proposed actions is approximately $15,900,000, t
Question:
t i
F.
The potential safety impact of changes in plant or operational complexity, including the relationship to proposed and existing i
regulatory requirements and staff positions...
I Response-l A slight increase in operational complexity may result from inopera-l
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ble thimble tubes (due to actions taken (such as isolation) should a thimble tube fail to rreet the established acceptability criterion).
l However, this increase in operational complexity is not as signifi-l 1
cant as the operational problems that can arise shonid a thimble tube j
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fail and create a non-isolable leak of reactor coolant.
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Ouestion:
)
G.
The estimated resource burden on the NRC associated with the proposed action and the a'ailability of such resources...
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Response
j i
Licensees would be required to submit letters confiming that the requested actions have been taken. NRR would identify a lead project i
manager to coordinate the review of licensees' responses. The r
estimated staff effort to complete the review of licensees' responses is approximately 50 person-hours. No requirement for regional review
)j will be necessary; however, licensee's actions in response to this bulletin may be selected for audit by the regions.
Ouestion:
\\
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H.
The potential frpact of differences in facility type, design, or age on the relevancy and practicality of the proposed action...
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Response
Thimble tube thinning problems are relevant to all Westinghouse designed facilities that utilize bottom mounted instrumentation.
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7 All Westinghouse designed bottom mounted instrurentation systers are essentially identical.
In addition, the staff is not aware of other reactor types (such as those designed by CE, MW, or GE) that have experienced similar problems.
This appears to be due to the unique design features of the Westinghcuse intore neutron monitoring system.
Thus, with regard to Westinghouse facilities that utilize bottom rounted instrumentation, type, design, and age are not errected to be significant factors with regard to the practicality of the proposed action.
Question:
Whether the proposed action is interin or final, and if interim, the justification for imposing the proposed action on an interim basis.
1
Response
The proposed actien is final.
Ouestion:
VI!!. For each evaluation conducted pursuant to 10 CFR 50.109, the proposing Office Director's determination together with the rationale for the detemination based on the considerations of paragraph (!) through l
(VII) above that:
A.
there is a substantial increase in the overall prctection of public health and safety or the comon defense and security to be derived fror the proposal; and B.
the direct and indirect costs of irplementatien, for the facilities affected, are justified in view of this increased protection.
Response
Thimble tube thinning problems are believed to be generic to all Westinghouse designed facilities that utilize bottom mounted instru-rentation.
Since there are currently no inservice inspection or testing requirerents for thimble tubes, the staff believes that significant thirble tube degradation ray have gone undetected, creating a condition that nay be adverse to safety.
In addition, staff review of the available data indicates that it is not possible to accurately predict thirble tube wear rates, and that the only effective rethod for determining thinble tube integrity is through plant-specific inspections and periodic monitoring.
Thus, we believe that an expenditure by the industry of an additional $15,900,000 over the next 40 years is reasonable for the increased protection that would result from the proposed bulletin.
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Ouestion:
!X.
For each evaluation conducted for proposed relaxations or decreases in current requirements or staff positions, the proposing Office Director's determination, together with the rationale for the determination based on the considerations of paragraphs (!) through (VII) above, that:
A.
the public health and safety and the cormon defense and security would be adequately protected if the proposed reduction in require-rents or positions were implemented, and I
B.
the cost savings attributed to the action would be substantial enough to justify taking the action.
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Response
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Relaxations or decreases in current requirements or staff positions 1
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are not proposed, i
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