ML12181A442
| ML12181A442 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 06/29/2012 |
| From: | Office of Nuclear Reactor Regulation |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| Shared Package | |
| ML12181A438 | List: |
| References | |
| RAS 22867, 50-247-LR, 50-286-LR, ASBLP 07-858-03-LR-BD01 | |
| Download: ML12181A442 (6) | |
Text
RIV000115 Submitted: June 29, 2012 NRC: Bulletin 88-11: Pressurizer Surge Line Thermal Stratification Page 1 of 6
[an error occurred while processing this directive]
Home > NRC Library > Document Collections > Generic Communications > Bulletins > 1988 > BL 11 OMB No. 3150-0011 NRCB 88-11 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 December 20, 1988 NRC BULLETIN NO. 88-11: PRESSURIZER SURGE LINE THERMAL STRATIFICATION Addressees:
All holders of operating licenses or construction permits for pressurized water reactors (PWRs).
Purpose:
The purpose of this bulletin is to (1) request that addressees establish and implement a program to confirm pressurizer surge line integrity in view of the occurrence of thermal stratification and (2) require addressees to inform the staff of the actions taken to resolve this issue.
Description of Circumstances:
The licensee for the Trojan plant has observed unexpected movement of the pressurizer surge line during inspections performed at each refueling outage since 1982, when monitoring of the line movements began. During the last refueling outage, the licensee found that in addition to unexpected gap clo-sures in the pipe whip restraints, the piping actually contacted two re-straints. Although the licensee had repeatedly adjusted shims and gap sizes based on analysis of various postulated conditions, the problem had not been resolved. The most recent investigation by the licensee confirmed that the movement of piping was caused by thermal stratification in the line. This phenomenon was not considered in the original piping design. On October 7, 1988, the staff issued Information Notice 88-80, "Unexpected Piping Movement Attributed to Thermal Stratification," regarding the Trojan experience and indicated that further generic communication may be forthcoming. The licensee for Beaver Valley 2 has also noticed unusual snubber movement and significantly larger-than-expected surge line displacement during power ascension.
The concerns raised by the above observations are similar to those described http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1988/bl88011.html 6/25/2012
NRC: Bulletin 88-11: Pressurizer Surge Line Thermal Stratification Page 2 of 6 in NRC Bulletins 79-13 (Revision 2, dated October 16, 1979), "Cracking in Feedwater System Piping" and 88-08 (dated June 22, 1988), "Thermal Stresses in Piping Connected to Reactor Coolant Systems."
8812150118
. NRCB 88-11 December 20, 1988 Page 2 of 6 Discussion:
Unexpected piping movements are highly undesirable because of potential high piping stress that may exceed design limits for fatigue and stresses. The problem can be more acute when the piping expansion is restricted, such as through contact with pipe whip restraints. Plastic deformation can result, which can lead to high local stresses, low cycle fatigue and functional im-pairment of the line. Analysis performed by the Trojan licensee indicated that thermal stratification occurs in the pressurizer surge line during heatup, cooldown, and steady-state operations of the plant.
During a typical plant heatup, water in the pressurizer is heated to about 440øF; a steam bubble is then formed in the pressurizer. Although the exact phenomenon is not thoroughly understood, as the hot water flows (at a very low flowrate) from the pressurizer through the surge line to the hot-leg piping, the hot water rides on a layer of cooler water, causing the upper part of the pipe to be heated to a higher temperature than the lower part (see Figure 1).
The differential temperature could be as high as 300øF, based on expected conditions during typical plant operations. Under this condition, differential thermal expansion of the pipe metal can cause the pipe to deflect significantly.
For the specific configuration of the pressurizer surge line in the Trojan plant, the line deflected downward and when the surge line contacted two pipe whip restraints, it underwent plastic deformation, resulting in permanent deformation of the pipe.
The Trojan event demonstrates that thermal stratification in the pressurizer surge line causes unexpected piping movement and potential plastic deformation. The licensing basis according to 10 CFR 50.55a for all PWRs requires that the licensee meet the American Society of Mechanical Engineers Boiler and Pressure Vessel Code Sections III and XI and to reconcile the pipe stresses and fatigue evaluation when any significant differences are observed between measured data and the analytical results for the hypothesized conditions. Staff evaluation indicates that the thermal stratification phenomenon could occur in all PWR surge lines and may invalidate the analyses supporting the integrity of the surge line. The staff's concerns include unexpected bending and thermal striping (rapid oscillation of the thermal boundary interface along the piping inside surface) as they affect the overall integrity of the surge line for its design life (e.g., the increase of fatigue).
Actions Requested:
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1988/bl88011.html 6/25/2012
NRC: Bulletin 88-11: Pressurizer Surge Line Thermal Stratification Page 3 of 6 Addressees are requested to take the following actions:
- 1. For all licensees of operating PWRs:
- a. Licensees are requested to conduct a visual inspection (ASME,Section XI, VT-3) of the pressurizer surge line at the first available cold shutdown after receipt of this bulletin which exceeds seven days.
. NRCB 88-11 December 20, 1988 Page 3 of 6 This inspection should determine any gross discernable distress or structural damage in the entire pressurizer surge line, including piping, pipe supports, pipe whip restraints, and anchor bolts.
- b. Within four months of receipt of this Bulletin, licensees of plants in operation over 10 years (i.e., low power license prior to January 1, 1979) are requested to demonstrate that the pressurizer surge line meets the applicable design codes* and other FSAR and regulatory commitments for the licensed life of the plant, consider-ing the phenomenon of thermal stratification and thermal striping in the fatigue and stress evaluations. This may be accomplished by performing a plant specific or generic bounding analysis. If the latter option is selected, licensees should demonstrate applicability of the referenced generic bounding analysis.
Licensees of plants in operation less than ten years (i.e., low power license after January 1, 1979), should complete the foregoing analysis within one year of receipt of this bulletin. Since any piping distress observed by addressees in performing action 1.a may affect the analysis, the licensee should verify that the bounding analysis remains valid. If the opportunity to perform the visual inspection in 1.a does not occur within the periods specified in this requested item, incorporation of the results of the visual inspection into the analysis should be performed in a supplemental analysis as appropriate.
Where the analysis shows that the surge line does not meet the requirements and licensing commitments stated above for the duration of the license, the licensee should submit a justification for continued operation or bring the plant to cold shutdown, as appropriate, and implement Items 1.c and 1.d below to develop a detailed analysis of the surge line.
- c. If the analysis in 1.b does not show compliance with the requirements and licensing commitments stated therein for the duration of the operating license, the licensee is requested to obtain plant specific data on thermal stratification, thermal striping, and line deflections. The licensee may choose, for example, either to install instruments on the surge line to detect temperature distribution and thermal movements or to obtain data through collective efforts, such as from other plants with a similar surge line design. If the latter option is selected, the licensee should demonstrate similarity in geometry and operation.
- d. Based on the applicable plant specific or referenced data, licensees are requested to update their stress and fatigue analyses to ensure http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1988/bl88011.html 6/25/2012
NRC: Bulletin 88-11: Pressurizer Surge Line Thermal Stratification Page 4 of 6 compliance with applicable Code requirements, incorporating any observations from 1.a above. The analysis should be completed no later than two years after receipt of this bulletin. If a licensee
- Fatigue analysis should be performed in accordance with the latest ASME Section III requirements incorporating high cycle fatigue.
. NRCB 88-11 December 20, 1988 Page 4 of 6 is unable to show compliance with the applicable design codes and other FSAR and regulatory commitments, the licensee is requested to submit a justification for continued operation and a description of the proposed corrective actions for effecting long term resolution.
- 2. For all applicants for PWR Operating Licenses:
- a. Before issuance of the low power license, applicants are requested to demonstrate that the pressurizer surge line meets the applicable design codes and other FSAR and regulatory commitments for the licensed life of the plant. This may be accomplished by performing a plant-specific or generic bounding analysis. The analysis should include consideration of thermal stratification and thermal striping to ensure that fatigue and stresses are in compliance with applicable code limits. The analysis and hot functional testing should verify that piping thermal deflections result in no adverse consequences, such as contacting the pipe whip restraints. If analysis or test results show Code noncompliance, conduct of all actions specified below is requested.
- b. Applicants are requested to evaluate operational alternatives or piping modifications needed to reduce fatigue and stresses to acceptable levels.
- c. Applicants are requested to either monitor the surge line for the effects of thermal stratification, beginning with hot functional testing, or obtain data through collective efforts to assess the extent of thermal stratification, thermal striping and piping deflections.
- d. Applicants are requested to update stress and fatigue analyses, as necessary, to ensure Code compliance.* The analyses should be completed no later than one year after issuance of the low power license.
- 3. Addressees are requested to generate records to document the development and implementation of the program requested by Items 1 or 2, as well as any subsequent corrective actions, and maintain these records in accor-dance with 10 CFR Part 50, Appendix B and plant procedures.
Reporting Requirements:
- 1. Addressees shall report to the NRC any discernable distress and damage observed in Action 1.a along with corrective actions taken or plans and schedules for repair before restart of the unit.
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1988/bl88011.html 6/25/2012
NRC: Bulletin 88-11: Pressurizer Surge Line Thermal Stratification Page 5 of 6
- If compliance with the applicable codes is not demonstrated for the full duration of an operating license, the staff may impose a license condition such that normal operation is restricted to the duration that compliance is actually demonstrated.
. NRCB 88-11 December 20, 1988 Page 5 of 6
- 2. Addressees who cannot meet the schedule described in Items 1 or 2 of Actions Requested are required to submit to the NRC within 60 days of receipt of this bulletin an alternative schedule with justification for the requested schedule.
- 3. Addressees shall submit a letter within 30 days after the completion of these actions which notifies the NRC that the actions requested in Items 1b, ld or 2 of Actions Requested have been performed and that the results are available for inspection. The letter shall include the justification for continued operation, if appropriate, a description of the analytical approaches used, and a summary of the results.
Although not requested by this bulletin, addressees are encouraged to work collectively to address the technical concerns associated with this issue, as well as to share pressurizer surge line data and operational experience. In addition, addressees are encouraged to review piping in other systems which may experience thermal stratification and thermal striping, especially in light of the previously mentioned Bulletins 79-13 and 88-08. The NRC staff intends to review operational experience giving appropriate recognition to this phenomenon, so as to determine if further generic communications are in order.
The letters required above shall be addressed to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, D.C. 20555, 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 appropriate Regional Administrator.
This request is covered by Office of Management and Budget Clearance Number 3150-0011 which expires December 31, 1989. The estimated average burden hours is approximately 3000 person-hours per licensee response, including assessment of the new requirements, searching data sources, gathering and analyzing the data, and preparing the required reports. These estimated average burden hours pertain only to these identified response-related matters and do not include the time for actual implementation of physical changes, such as test equipment installation or component modification. The estimated average radiation exposure is approximately 3.5 person-rems per licensee response.
Comments on the accuracy of this estimate and suggestions to reduce the burden may be directed to the Office of Management and Budget, Room 3208, New Execu-tive Office Building, Washington, D.C. 20503, and to the U.S. Nuclear Regula-tory Commission, Records and Reports Management Branch, Office of Administration and Resource Management, Washington, D.C. 20555.
. NRCB 88-11 December 20, 1988 Page 6 of 6 If you have any questions about this matter, please contact one of the techni-http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1988/bl88011.html 6/25/2012
NRC: Bulletin 88-11: Pressurizer Surge Line Thermal Stratification Page 6 of 6 cal contacts listed below or the Regional Administrator of the appropriate regional office.
Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: S. N. Hou, NRR (301) 492-0904 S. S. Lee, NRR (301) 492-0943 N. P. Kadambi, NRR (301) 492-1153 Attachments:
- 1. Figure 1
- 2. List of Recently Issued NRC Bulletins Page Last Reviewed/Updated Thursday, March 29, 2012 http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1988/bl88011.html 6/25/2012