RBG-47400, Request for Relief RBS-R&R-2013-001, Request for Relief from ASME Boiler & Pressure Vessel Code
| ML13295A421 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 10/17/2013 |
| From: | Clark J Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-47400 | |
| Download: ML13295A421 (14) | |
Text
River Bend Station
-- Entervy 5485 U.S. Highway 61N St. Francisville, LA 70775
- Tel 225-381-4177 Joseph A Clark Manager, Licensing RBG-47400 October 17, 2013 U. S. Nuclear Regulatory Commission Attn.: Document Control Desk Washington, DC 20555-0001
SUBJECT:
Request for Relief RBS-R&R-2013-001 Request for Relief from ASME Boiler & Pressure Vessel Code River Bend Station, Unit 1 Docket No. 50-458 License No. NPF-47 Reference 1 Entergy letter; Request for Relief from ASME Boiler & Pressure Vessel Code Section III, Dated August 19, 2013 (RBG-47386) 2 NRC Letter; UNACCEPTABLE WITH OPPORTUNITY TO SUPPLEMENT INFORMATION NEEDED FOR ACCEPTANCE OF REQUEST FOR RELIEF (TAC NO. MF2733), Dated October 7, 2013
Dear Sir or Madam:
In the Reference 1, Entergy requested relief from 10 CFR 50.55a, "Codes and Standards,"
paragraph. (3)(i). This request proposed an alternative to the postweld heat treatment exemption of Table ND-4622.7 that will provide an acceptable level of quality and safety.
As a result of discussions with the NRC Staff on September 30, 2013, Entergy requests a modification to the referenced American Society of Mechanical Engineers (ASME) Code from Section III to ASME Section Xl. Specifically, Entergy proposes an alternative to the Construction Code requirements of IWA-4221 (c).
In addition to the change from ASME Section III to Section Xl, Entergy accepts the NRC suggestion to revise the request from an alternative under 10 CFR 50.55a, "Codes and Standards," paragraph (3)(i) to a hardship under paragraph (3)(ii). Additional information supporting hardship is included in Attachment 3 to this letter. Note, the attachment numbering/identification was chosen for consistency with the initial submittal.
RBG-47400 Page 2 of 3 The previous Attachment 1 requires a revision to page 3, the revised Attachment is included.
The previous Attachment 2 to Reference 1, remains as submitted without need for revision.
This letter contains no new regulatory commitments.
As identified in the initial Attachment 1 submittal, a request was approved by the NRC to require replacement of the Division II valves during refueling outage 18 (RF-18) scheduled for early 2015. To support this action the construction of the replacement valves is currently estimated as 52 weeks. Your review is requested by the end of 2013 to avoid the cost of ordering the replacement valves.
If you have any questions regarding this request or require additional information, please contact me at (225) 381-4177.
Respectfully, (W. J. Fountain for)
JAC/bmb Attachments: - Request for Alternative - (No Change - See Reference 1) - Basis of Hardship LAR 2013-16 RBF1-13-0131 cc: U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.
Arlington, TX 76011-4511 NRC Sr. Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 Central Records Clerk Public Utility Commission of Texas 1701 N. Congress Ave.
Austin, TX 78711-3326
RBG-47400 Page 3 of 3 Department of Environmental Quality Office of Environmental Compliance Radiological Emergency Planning and Response Section JiYoung Wiley P.O. Box 4312 Baton Rouge, LA 70821-4312 U.S. Nuclear Regulatory Commission Attn: Mr. Alan Wang Mail Stop MS 0-8 B1 Washington, DC 20555-0001
Attachment I RBG-47400 Request for Alternative
RBG-47400 Page 1 of 5 Entergy Operations, Inc.
River Bend Station Request No. RBS-R&R-2013-001 COMPONENTS Component Various Size ASME Class 3 Valves:
Number and E12-MOVF068A, Residual Heat Removal Heat Exchanger
Description:
Service Water Return E12-MOVF068B, Residual Heat Removal Heat Exchanger Service Water Return SWP-MOV506A, High Pressure Core Spray Diesel Generator Engine Water Heat Exchange Service Water Header Isolation SWP-MOV506B, High Pressure Core Spray Diesel Generator Engine Water Heat Exchange Service Water Header Isolation SWP-MOV501A, Reactor Closed Cooling Water Heat Exchanger Service Water Supply Header Isolation Valve SWP-MOV501 B, Reactor Closed Cooling Water Heat Exchanger Service Water Supply Header Isolation Valve SWP-MOV51 1A, Normal Service Water Return Isolation SWP-MOV51 1 B, Normal Service Water Return Isolation SWP-MOV55A, Standby Service Water Cooling Tower 1 Inlet SWP-MOV55B, Standby Service Water Cooling Tower 1 Inlet Code Class: 3
References:
- 1. ASME Section Xl, 2001 Edition through 2003 Addenda
- 2. ASME Section III, 1974 Edition / Summer 1975 Addenda
- 3. ASME Section III, 1992 Edition / No Addenda
- 4. ASME Section III, Code Case N-804, Alternative Preheat Temperature for Austenitic Welds in P-No. I Material without PWHT Unit: River Bend Station (RBS) Unit 1 Inspection Third ( 3 rd) 10-Year Interval Interval:
RBG-47400 Page 2 of 5 II. CODE REQUIREMENTS IWA-4221 (b)(1) states, "When replacing an existing item, the new item shall meet the Construction Code to which the original item was constructed."
IWA-4221(c) states in part, "As an alternative to (b), the item may meet all or portions of the requirements of different Editions and Addenda of the Construction Code, or Section III when the Construction Code was not Section III... Construction Code Cases may also be used."
ND-4600 of ASME Section III, 1992 Edition contains the following requirements regarding postweld heat treatment of ASME Class 3 welds:
" ND-4622.1 states that all welds, including repair welds, shall be postweld heat treated within the temperature ranges and holding times of Table ND-4622.1-1 except as otherwise permitted in ND-4622.7.
- ND-4622.7 states that postweld heat treatment is not required for nonferrous materials and welds exempted in Table ND-4622.7(b)-1.
- Table ND-4622.7(b)-1, Exemptions to Mandatory PWHT, states that all welds in P-Number 1 material over 1 11/2 inch thick with a nominal thickness of %"or less are exempt from postweld heat treatment provided a minimum preheat of 200OF is applied.
II. PROPOSED ALTERNATIVE
Background
Entergy River Bend Station (RBS) purchased sixteen (16) ASME Class 3 valves from Weir Valves and Controls Company USA, Inc. All 16 valves were stamped and certified to be in compliance with ASME Section II1. Ten of these valves, listed in Section I, have been installed at RBS. Of the remaining 6 valves, 5 are in warehouse storage at RBS, and 1 was sacrificed for destructive testing to support this request. Only the installed valves are applicable to this request.
On 8/2/2011, a letter was received from Weir Valves and Controls Company USA. The letter indicated that, during fabrication, the welding process used to install stainless steel (P-Number 8) seats to carbon steel (P-Number 1) bodies of the subject valves did not fully comply with Table ND-4622.7(b)-1 of the ASME Code.
The condition noted was that the base material was not preheated to 200°F (minimum) as required by Table ND-4622.7(b)-1 for exemption from post weld heat treatment. The Weir welding procedure required a minimum preheat of 60°F instead of 200 0 F. These seat rings are attached to the valve body wall by a 3/16 or 1/4 inch fillet weld on both sides of the ring using GTAW or SMAW process.
Weir indicated in the letter they performed testing and submitted a proposed code case (N-804) to the ASME committee based on these findings. The testing Weir conducted was performed on wrought material only, both plate and production valves. The proposal was approved by the ASME committee however, was not approved for use by the NRC. Entergy submitted relief request in December 2011, based on this Code Case and the Weir test results but subsequently withdrew it June 2012.
Entergy considered several options to address the above condition including replacement of the subject valves and performance of postweld heat treatment of the
RBG-47400 Page 3 of 5 valve seat ring welds. With regard to postweld heat treatment, this option is not practical since a postweld heat treatment at 1100 - 1250 0 F, as required by Table ND-4622.1-1, would adversely affect the metallurgical properties (sensitize) of the austenitic stainless steel.
To replace the Standby Service Water (SSW) valves on-line, the affected piping section would require the divisional loop of SSW to be secured and drained. While the RBS Technical Specifications (TS) provides 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to effect repairs to the system, doing so would result in the loss of an entire train of emergency core cooling components during the repair window. In addition, isolation and draining of a Service Water (SW) loop during power operation is complex and would expend a significant portion of the 72-hour allowed outage period.
Replacing the valves during a refueling outage requires draining a divisional loop of SSW which typically extends the system outage window making emergency core cooling system components unavailable for longer periods of time. It also removes a source of cooling for other systems and components.
RBS has previously requested relief to allow the replacement of the Division II valves (5) during RF18 and the remaining Division I valves (5) in RF19. This request was approved by the NRC Staff on February 20, 2013.
Proposed Alternative As a result of additional evaluation this request was developed. It is important to note this request is based on testing and evaluation performed on a cast carbon steel product form and is not taking any credit from information developed on wrought material.
Although not the basis for this request, a connection has been made between the similar Chemical compositions of wrought and cast material and the material properties produced. As described in Attachment 2 the omission of an elevated pre-heat or postweld heat treatment (PWHT) of the valve seat welds will not hinder the valves from performing their Safety Function.
Pursuant to 10CFR50.55a(3)(ii), Entergy requests relief from American Society of Mechanical Engineers (ASME) Section Xl requirements. Specifically, Entergy proposes an alternative to the Construction Code requirements of IWA-4221 (c). As permitted by IWA-4221 (c), replacement components may comply with a later Edition/Addenda of the original Construction Code (e.g., ASME Section III). However, contrary to IWA-4221(c),
sixteen (16) replacement ASME Class 3 valves that were certified as complying with ASME Section 11, Subsection ND requirements were later found to be in noncompliance with the postweld heat treatment exemptions of Table ND-4622.7. More specifically, the postweld heat treatment exemption applicable to fillet and partial penetration welds in base materials over 1-1/2" and with nominal thicknesses %" or less in table ND-4622.7 was not met. Structural Integrity Report No. 1300615.401, Attachment 2, was developed to address the conditions at River Bend Station and provides a technical basis that demonstrates the valves installed at RBS are capable of satisfactory performance without the application of elevated preheat or postweld heat treatment.
RBG-47400 Page 4 of 5 IV. BASIS FOR ALTERNATIVE As discussed in Attachment 2 the basis for relief features metallography and test results measured on samples removed from a production valve of the same lot and welded using the same weld procedure. The testing included metallography, hardness mapping, and Automated Ball Indenter (ABI) testing.
In addition to the as-received condition, additional test welds were prepared to examine effects of preheating and for multiple pass welding. All testing focused on E-309-L fillet welds joining the SA240 Type 316-L stainless steel seat ring to the SA-216 Grade WCB casting valve body material so that the test weld data would be directly applicable to the valves installed at RBS.
The Electric Power Research Institute (EPRI) performed the required welding, metallography and hardness mapping evaluations and provided technical support on the findings. The ABI testing was performed by ABI Services, LLC The attached study examined applicable characteristics of the material including;
- chemistries,
- likelihood for forming brittle transformation products,
- weld heat affected zone metallurgy,
- stress analysis of the valves,
- welding procedure and techniques,
- hardness mapping, and
- ABI testing for mechanical properties plus estimates of fracture toughness of the Heat Affected Zone (HAZ) material.
The results of the study support the position that the valve body HAZs provide sufficient ductility and toughness to perform satisfactorily without PWHT without the application of the welding preheat requirement.
V. CONCLUSION 10 CFR 50.55a(a)(3) states:
"Proposed alternatives to the requirements of (c), (d), (e), (f), (g), and (h) of this section or portions thereof may be used when authorized by the Director of the Office of Nuclear Reactor Regulation. The applicant shall demonstrate that:
(ii) Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Entergy believes that this hardship request does provide a technical basis showing a low level of risk and a sufficient level of quality and safety. The studies and tests conducted in support of this request, coupled with the findings discussed in Attachment 2, show that the expected HAZ (Heat Affected Zone) properties would be adequate to meet the requirements for the installed valves; thus proving their continued use is acceptable and that replacement is an unnecessary hardship. Therefore, Entergy requests that the NRC
RBG-47400 Page 5 of 5 staff authorize the requested hardship and allow continued use of all (10) installed valves in accordance with 10 CFR 50.55a(a)(3)(ii).
Augmented Inspection of the valve internals is not proposed due to the hardship of implementation and the low level of impact and unlikelihood a crack under the seat ring will occur. External inspections would serve no value as there is no viable failure path to the outer surface.
Attachment 3 RBG-47400 Basis of Hardship
RBG-47400 Page 1 of 4
Background
As discussed in Attachment 1 to the Reference, River Bend Station (RBS) currently has 10 valves installed which have not been heat treated in accordance with ASME Code requirements of IWA-4221 (c). Attachment 2 of Reference 1, a technical evaluation of the effects of the non-compliance provides evidence that the effect of the non-compliance should not impact the ability of the valves to perform as required.
As discussed in this letter Entergy requests NRC approval to allow the valves to remain in service for the life of the valve seat based upon the technical evaluation and the significant difficulties involved with obtaining and installing replacements.
Additional details on the difficulties involved with obtaining and installing replacements are provided below.
Basis of Hardship Entergy reviewed various options to resolve this issue as described below.
The valves are installed in the Standby Service Water (SSW) system. The system configuration will not allow isolation of the valves without the use of freeze seals or other alternative isolation methods, isolation during power operations involves significant risk.
Without the ability to resolve the issue through code case N-804, Entergy reviewed the information available and the option to replace all of the valves in question. After consulting with industry experts and with the additional information developed to support Attachment 2 of the initial submittal letter in the Reference, Entergy determined there is a technical basis for allowing the valves to remain in service.
The issues involved with the replacement are in three areas, 1) construction impacts, 2) Risk impacts and 3) radiation dose impact. Each of these will be discussed below. Note, the discussion below is on a "per division" basis with the total impacts expected to be twice the individual division impact.
Also the final detail planning for the valve replacements will not be conducted until summer 2014. The estimates below are based upon similar efforts in the past and have been reviewed for consistency with current practices.
Construction The valve locations are at low elevations in the plant, at or below the grade level of about 95 ft elevation. Therefore, each division (subsystem) will need to be essentially or completely drained to facilitate the removal of the valves. As a result, replacement of the valves will require a significant outage to allow the draining of the system.
To drain the system has taken approximately 2 days in past outages and the refill operation was a similar period. The actual replacement work will be approximately 3 days. As a result, replacement of a single or multiple valves will require a division of the safety related SSW system to be out of service for about 7 days.
RBG-47400 Page 2 of 4 Note, a week is the normal out-of-service time for any single division during an outage.
As a result, during the installation of the valves and recovery of the system, this work is expected to be critical path on the affected division.
The effect of this outage on risk will be discussed below.
The effort to replace the valves will total about 2300 manhours (mhrs) and with a total cost of about 2 million dollars of which about 1.2 million dollars will be for the replacement valves.
The dose resulting for this effort is discussed below.
Risk An evaluation of the risk to replace the valves while in power operation was performed.
This evaluation determined the risk to replace any one or multiple valves will place the plant at significant risk per the RBS procedure for on-line maintenance risk assessment.
Risk assessments of this activity were conducted for the shutdown conditions per plant risk assessment procedures. One of the functions of the valves being replaced is to isolate the SSW from supported systems. With the valves being removed, the isolation function is not available through alternative valves currently installed. To allow 3 of the supported systems to continue to be available temporary barriers are expected to be installed. The 3 systems are; 1) the plant component cooling system (CCP) which supports a number of other plant systems, 2) the High Pressure Core Spray (HPCS) diesel, and 3) the Alternate Decay Heat Removal (ADHR) system used during shutdown. The availability of these systems has a positive impact on risk.
The risk assessment is based upon the previous outage (RF-17). The results indicate an increase in risk of about 2 to 3 E-9 for each division.
The assessment also identifies the following;
- When the Division II SSW is out of service the ability to inject fire protection water into the vessel is disabled,
- The Reactor Plant Component Cooling Water (RPCCW) system will be out of service with cooling to the spent fuel pool provided through normal service water,
- The spent fuel pool cooling Key Safety Function risk would be coded as "YELLOW" or acceptable risk, vice "GREEN" or minimal risk for the extended period of time that Standby Service Water trains are assumed unavailable.
The increase in risk is considered acceptable within current guidance.
RBG-47400 Page 3 of 4 Dose As noted previously the locations of the valves are in low dose areas and the total dose currently estimated at 290 mrem (milli-rem).
Inspection of Valves Entergy considered inspection of valves using Non-Destructive methods, however, Inspections would also require the same system configurations as replacement, resulting in the need for the system to be drained. This would result in similar risk, dose and outage impacts as replacement. In addition, in the unlikely event of an indication valve seat failure replacement valves must be available.
With the technical information included in Attachment 2 of the Reference and with much of the cost, dose, risk and outage impacts similar to replacement, this option was not pursued further.
Other In-Service testing will be maintained. This includes stroke time testing and position indication verification testing.
FLEX Installation Impact Current plans are to modify the Division II SSW in support of the FLEX initiative. This modification would also require the draining of the system. If the common work is removed from the discussion above, the effect is estimated as a reduction of about 120 mhrs and a total cost reduction of about $29,000.
These modifications are not planned to affect the Division I SSW system.
This work is expected to have negligible impact on dose and risk.
Summary of Total Impacts As noted above the estimates are on a "per division" basis with the scope in each division very similar and therefore the total impact very similar. The following is a table of the resulting impacts with the FLEX initiative also identified.
Division I (RF-19) Division II (RF-18) Total Construction 2300 mhrs / 2300 mhrs / 4600 mhrs /
[ mhr/cost ] $2 million $2 million $4 million FLEX removed No change 2180 mhrs / 4480 mhrs /
$2 milion $4 million
RBG-47400 Page 4 of 4 Division I (RF-19) Division II(RF-18) Total Dose 290 mrem 290 mrem 580 mrem Risk 2 E-09 / yr 3 E-09 / yr Conclusion As provided in the technical evaluation of the effects in Attachment 2 of the Reference, the effect of the non-compliance should not impact the ability of the valves to perform as required.
In addition to the information developed in support of code Case N-804, an RBS specific valve was subjected to additional testing in support of Structural Integrity Report No. 1300615.401, . The results of the study support the position that the valve body HAZs provide sufficient ductility and toughness to perform satisfactorily without PWHT without the application of the welding preheat requirement. The report explains that the slightly elevated hardness resulting from the lack of PWHT or preheat was offset by the multi-pass welds used during valve fabrication.
While the risk associated with the replacement of the identified valves would be acceptable, when evaluated with the high confidence that the valves can perform the originally specified service without restriction, as identified in Attachment 2 of the Reference, the replacement of the valves does not appear to support a corresponding increase in reliability.
In addition to the quantitative impacts identified above, there will be a loss of flexibility on the affected SSW system during installation. This loss can impact the outage including restrictions on the ability to respond to unplanned events.
The increase in outage dose is not excessive but the resulting dose to replace the valves when they can perform their function without restriction, as supported by the evaluation performed in Attachment 2 of the Reference, would not be consistent with the 10 CFR 20; As Low As Reasonability Achievable principles.
With the reduction in outage flexibility/planning, unnecessary increase in risk, dose and cost, Entergy believes the requested action is appropriate.
Reference; Entergy letter; Request for Relief from ASME Boiler & Pressure Vessel Code Section III, Dated August 19, 2013 (RBG-47386)