ML20215N222
| ML20215N222 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 10/24/1986 |
| From: | Haynes J ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | Kirsch D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| REF-PT21-86-344-000 ANPP-38840-JGH, DER-86-26, PT21-86-344, PT21-86-344-000, NUDOCS 8611050024 | |
| Download: ML20215N222 (8) | |
Text
vs O
!Oc, _
Arizona Nuclear Power Project
" Q pg
[/@
P.O. BOX 52034 e PHOENIX, ARIZONA 85072-2034 '
October 24, 1986 OlCN pp, ANPP-38840-JGil/DJU/DRL-92.11 0
U. S. Nucicar Regulatory Commission Region V 1450 !! aria Lane - Suite 210 Walnut Creek, California 94596-5368 Attention:
lir. D. F. Kirsch, Acting Director Division of Reactor Safety and Projects Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2, 3 Docket Nos. 50-528, 529, 530
Subject:
Final Report - DER 86-26 A 50.55(e) and 10CFR21 Condition Relating to Sof t Nuts on Steam Generator Upper Supports File: 86-006-216; D.4.33.2
Reference:
.(A) Telephone Conversation between R. C. Sorenson and D. R. Larkin on August 27, 1986 (Initial Notification -
(E) ANPP-38430, dated September 25,1986 (Interim Report -
Dear Sir:
Attached, is our final written report of the deficiency under 10CFR50.55(e) referenced above. The 10CFR21 evaluation is also included.
Very truly yours, AUW J. G. Ilaynes Vice President-Nuclear Production JGil/DRL:kp cc: See Page 2 8611050024 961024 PDR.ADOCK 0000 B
S
.,TE-A 7
e F
f.
DER 86 Final Report Mr.~ D. F. Kirsch Acting. Director Page Two October 24, 1986 ANPP-38840-JGH/DJW/DRL-92.11 cc:
J. M. Taylor Office of Inspection and Enforcement U. S.. Nuclear Regulatory ' Commission Washington, D. C.
20555 A. C. Gehr (4141)
R. P. Zimmerman (6295)
Records Center Institute of Nuclear Power Operations 1100 circle 75 Parkway - Suite 1500 Atlanta, Georgia 30339
5..,
FINAL REPORT - DER 86-26 DEFICIENCY EVALUATION 50.55(e)
ARIZONA NUCLEAR POWER PROJECT (ANPP)
PVNGS UNITS 1, 2, 3 I.
Description of Deficiency The upper steam generator supports consist of.three parts; the upper keyways, lever supporte and snubber support assemblies.
The upper keyways (located north and south of each steam generator) are composed of two ASTM A336 forgings located on either side of the steam generator key. Each forging is bolted by twelve, 2-1/2 inch diameter, preloaded ASTM AS40 Crade B23 Class 1 studs and nuts. These forgings resist the thermal, seismic, primary loop and main steam line pipe break loads tracomitted by the key.
The lever support assemblies also utilize 2-1/2 inch diameter preload ASTM A540 Grade B23 Class 1 studs and nuts.
Whereas, the snubber assemblies use 1-1/4 inch diameter bolting of the same material.
During Equotip hardness testing to resolve DER 86-23, six 2-1/2 inch diameter heavy hex nuts were found to have hardness 'less than the minimum specified for ASTM A540 Crade B23 Class 1 bolting material. These nuts were six of twenty-four total, required to hold the Unit 3 Steam Generator Number 1 canal wall keyway forgings to the embed. Hardness of the six nuts ranged from 200 to 220 Brinell (HB) whereas the minimum required by the material specification is 321 HB.
Bechtel Drawing 13-C-ZCS-606, Revision 7, " Containment Internals, Steam Generator Upper Supports, Sections and Details", specified high strength anchor bolts, heavy hexagon nuts and washers meeting ASTM Specification AS40, Grade, B23, Class 1 (E-4340-H).
The Palo Verde Project purchased the nuts from Marathon Steel Company, Phoenix, Arizona. Marathon Steel Company in turn used several subtier suppliers as sources for the nuts. A review of the Certified Material Test Reports (CNTR) revealed that Custom Bolt Manufacturing Company supplied the nonconforming nuts under heat trace code 5C.
Evaluation Investigation of 2-1/2 inch Diameter Nuts, Heat Trace Code SC As part of DER 86-23's resolution plan, a review of Certified Material Test Reports (CMTR) of ASTM A540 material was conducted. The purpose of the review was to identify bolts, studs and nuts in which the CKIR indicated that material hardness was 41 Rockwell C or greater. This review identified 2-1/2 inch diameter heavy hex nuts of heat trace code SC used for the steam generator upper support.
P Visual examination of all exposed Unit 3 steam generator upper support 2-1/2 inch diameter nuts located only eleven nuts of heat trace code SC.
Visual, hardness and ultrasonic testing of the SC nuts did not provide any evidence of stress corrosion cracking. However, Equotip hardness testing revealed that six of the eleven nuts had hardness less than required by the ASTM material specification.
Subsequent to the testing listed above, all eleven SC nuts were subjected to in-situ chemical analysis using the Texas Nuclear Alloy Analyzer. The chemical analysis revealed that the six nonconforming nuts were carbon steel. The analysis confirmed that the remaining five nuts were of the appropriate material.
Investigation of All ASTM AS40 Material Supplied By Custom Bolt Manufacturing Company A review was made to identify the ASTM A540 material supplied by Custom Bolt Manufacturing Company to Bechtel through Marathon Steel Company.
The review established that Custom Bolt supplied the following material:
a.
2-1/2 inch diameter A540 Grade B23 Class 1 heavy hex nuts for the steam generator upper support (heat trace code SA, 5B, and.5C). A total of 480 nuts were supplied for all three units.
In Unit 3 positive identification has been made of 90 keyway nuts (43 nuts from heat trace code 5A, 36 nuts from heat trace code 5B and 11 nuts from heat trace code SC). The heat trace code of six keyway nuts was not identified.
b.
1-1/4 inch diameter A540 Grade B23 Class 1 studs for the steam generator upper snubber support assembly anchorage (heat numbers 46014 and 88078). A documentation review determined that only 26 studs were supplied by Custom Bolt and all 26 are installed in Unit 1.
c.
1-1/4 inch diameter A540 Grade B23 Class 1 heavy hex nuts for the steam generator upper snubber support assembly anchorage (heat trace 8071070). A documentation review determined that 96 Custom Bolt supplied nuts were installed. An equal number of nuts (i.e. 32) were installed in each unit and embedded in concrete.
To determine if carbon steel nuts had been mixed within the heat trace Code 5A and SB, 2-1/2 inch diameter nuts, ten from each heat, were randomly selected from those identified in Unit 3.
Equotip hardness testing of the randomly selected nuts identified three nuts from heat 5B that had hardnesses less than required. The hardness of the nuts tested from heat 5A met specification requirements. Thus a total of nine 2-1/2 inch diameter nuts (six from 5C and three from 5B) had hardness less than the specification requirement. Hardness of the nine carbon steel nuts ranged from 199 to 220 HB.
Subsequent to the Equotip hardness testing, the randomly selected nuts from heat trace codes 5A and 5B were subjected to in-situ chemical analysis using the Texas Nuclear Alloy Analyzer. The chemical analysis determined that the nonconforming nuts from heat 5B were carbon steel.
P The Custom Bolt 1-1/4 inch diameter studs or nuts were not visually examined or Equotip hardness tested since they were not accessible.
Visual examination of the Unit 3 steam generator snubber support assembly anchorage verified that the 1-1/4 inch diameter nuts were not Custom Bolt material. However, review of CIP's has established that at least 10 of the 26 Custom Bolt 1-1/4 inch diameter studs were preloaded by the direct tension method. Drawing 13-C-ZCS-606 requires the snubber support studs to be pretensioned to 90 + 5 kips. Upon applying the required preload, carbon steel studs would yield preventing the nut from being run down.
Thus it has been demonstrated that at least 10 of the studs would satisfy design requirements and it is unlikely that any of the 26 studs would be carbon steel.
Engineering Calculation An engineering calculation (Calc. No.13-CC-AC-141, Rev. 8 CCN No. 2) concluded that carbon steel nuts with a minimum hardness of 156HB (80 Ksi tensile strength) would meet strength requirements. The calculation addressed both the 2-1/2 inch diameter bolting for the upper steam generator keyway forgings and the 1-1/4 inch diameter bolting for the steam generator snubber support assembly anchorage. The 1-1/4 inch diameter snubber support bolting was included since none were available for testing in Unit 3.
The calculation assumed for both the keyway and the snubber support assembly anchorage that all nuts were carbon steel with a tensile strength of 80 Ksi and the studs were A540 material. This assumption allows for the full preload to be applied.
Because the relationship between hardness and tensile strength is approximate, a 20% margin was applied in the calculation. The association between tensile strength and hardness is shown in Table 3 of ASTM Specification A370.
As a part of the engineering evaluation, a statistical analysis of the nine hardness values for the carbon steel nuts was made. The purpose of this analysis was to determine the potential for having nuts with a hardness less than 156 HB.
The statistical analysis (Calc. No.
13-CC-ZC-141, Rev. 8, CCN No. 3) revealed that with a 95 percent confidence icvel no more than 0.1 percent of the total population (480 nuts) of 2-1/2 inch diameter nuts would have a hardness less than 163 HB.
Thus it is expected that none of the 2-1/2 inch diameter nuts would have a hardness less than 156 HB.
Investigation of Other Material Supplied by Custom Bolt Manuf acturing Company A documentation review was conducted to identify additional material supplied by Custom Bolt.
In addition to the 1-1/4 inch and 2-1/2 inch diameter bolting material supplied under Purchase Order (P.O.) 13-CM-125, it was determined that Custom Bolt had supplied ASTM A307, ASTM A193 Grade B7, /STM A194 Grade 2H, ASTM A354 Grade BD and ASTM A449 bolting material under P.O. 13-CM-131. A review of drawings concluded that the Custom Bolt material, except ASTM A307 material, was required to be s
pretensioned with calibrated torque wrenches using torque values specified on the design. drawings. Thus, the bolting material supplied by -
Custom Bolt, except ASTM A307 material, has been subjected to a proof test at11ts greatest possible-load. The ASTM A307 material'is not of concern because it is carbon ~ steel and not quench and tempored high.
strength material.
Review of Custom Bolt Manufacturing Company In addition to the above investigation, ANPP Quality Assurance visist J the Custom Bolt Manufacturing company facility. Review of present operations and shop practices,'would not provide information for material processed during t he subject purchase order time period.
ANPP' Quality Assurance reviewed supporting documentation to Custom Bolt-certificates of analysis / test for material-supplied to ANPP. Mill Test Reports, heat treatment certificates and magnetic particle inspection reports were examined. Custom Bolt's files were in order-and contained all the required documentation. Custom Bolt has not supplied nuclear grade material since 1982.
Root Cause The root cause of the problem appears to be the inadvertent mixing of materials prior to shipment from Custom Bolt. This material mix-up resulted in a number of carbon steel 2-1/2 ' inch diameter nuts' being represented as ASTM AS40 Grade B23 Class 1 material.
The material mix-up did not occur at PVNGS since, the nuts had the appropriate supplier heat trace code stamped.on them.
Units 1 and 2 Operations Although carbon steel nuts were represented as ASTM A540 Grade B23 Class 1-material, the operatibility of Units 1 and 2 is not adversely affected. Hardness testing and/or chemical analysis of nuts from Unit 1 and 2 is not required because:
a.
Engineering caluclations for the 1-1/4 inch and 2-1/2 inch nuts shows that carbon steel nuts with a 156 HB Brinel1~ hardness have sufficient strength to meet design requirements.
b.
The engineering calculations assumed that all nuts were of the lowest strength of carbon steel found instead of an average. In fact a majority of the nuts are the correct A540 material.
c.
There is a 95% confidence of not having material with a Brinell hardness less than 163.
d.
Review of C1P's determined that the studs have been successfully pretensioned. With pretensioned loads, the studs and nuts would be subjected to the greatest possible load. Therefore, the studs and nuts have been proof tested.
. c Transportability The hardness testing and in-situ chemical analysis has determined that carbon steel material has been mixed with at least two heats of ASTM A540 nuts supplied by Custom Bolt. However, calculations have demonstrated
' that.the design requirements are satisfied with carbon steel nuts.
Safety Assessment Calculation No. 13-CC-AC-141, Revision 8, CCN No. 2 was performed considering that all of the 1-1/4 inch and 2-1/2 inch diameter nuts for the upper steam generator supports (snubber support _and keyway forgings) were of carbon steel. The calculation determined that material with a Brinell hardness of 156 HB (80 Ksi) would meet strength requirements.
Actual hardness values, determined by the Equotip hardness tester, ranged from 199 to 220 HB.
In addition, the carbon steel nuts are acceptable for services provided they can withstand a proof load without " stripping or. rupturing." When preloading, each bolt / nut receives a proof test at the greatest load which 'it will experience. The Custom Bolt 2-1/2 inch nuts were preloaded to between 515 and 550 Kips, which is equivalent to 124 Ks1 minimum L(using 4.44 square inches for the stress area).
Evaluation of the Equotip hardness and the in-situ chemical analysis concluded that the nonconforming nuts would meet ASTM A194 Grade 2 or A563 Grade D specification requirements. Carbon steel 2-1/2 inch
~
diameter nuts meeting ASTM A563 Grade D or A194 Grade 2 are required to pass a 666 Kip (150 Ksi) proof test. Since the 2-1/2 inch diamete'r nuts were preloaded'to only 550 kips, carbon steel nuts would not strip or rupture. Thus carbon ' steel 2-1/2 inch diameter nuts of 199 to 220_ HB would be adequate for the steam generator upper support.
For Palo Verde Project, the mixing of 2-1/2 inch diameter carbon steel nuts with nuts conforming to ASTM AS40 Grade B23 Class 1 does not constitute a safety significant deficiency.
II.
Reportability Assessment This condition is evaluated as not reportable under the requirements of 10CFR 50.55(e), since if this condition were to remain uncorrected it would not represent a safety significant condition. This project has l
also evaluated this condition as not reportable under 10CFR21 with respect to PVNGS.
i Since there is a potential that nonconforming material could have been suppiled to other nuclear power projects, it may be reportable under 10CFR21 by Custom Bolt Manufacturing Company. A copy'of this report will be sent to Custom Bolt for their use in evaluating reportability.
l t l t
r-
~
)
III. Corrective Action The corrective action, required to preclude recurrence of the material deficiency, has already been addressed by the project's-implementation of specification 13-PM-414, " User Test Requirements for Quality Class Q Bolting Materials." Project Specification 13-FM-414 was issued for project use on June 24, 1985. However, ' the carbon steel 2-1/2 inch diameter nuts were received prior to the implementation of this specification. The carbon steel nuts. which have already been installed, will not be replaced.