ML20216H226
| ML20216H226 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/10/1998 |
| From: | Wetzel B NRC (Affiliation Not Assigned) |
| To: | Richard Anderson NORTHERN STATES POWER CO. |
| References | |
| GL-96-06, GL-96-6, TAC-M96854, TAC-M96855, NUDOCS 9804210088 | |
| Download: ML20216H226 (4) | |
Text
April 10, 1998 Mr. Roger O. Anderson, Dir;ctor -
Nuclear Energy Engineering Northern States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION RELATED TO THE PRAIRIE
]
ISLAND RESPONSE TO GL 96-06 (TAC NOS. M96854 & M96855)
Dear Mr. Anderson:
In a letter dated September 15,1997, Northern States Power Company (NSP) responded to the staffs request for additional information pertaining to the analysis for Prairie Island Nuclear Generating Plant for waterhammer and two-phase flow conditions associated with Generic Letter 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions." The NRC staff has completed its review of NSP's response and has concluded that NSP has not adequately evaluated and addressed the waterhammer and two-phase flow concerns that were expressed in GL 96-06 and additional evaluation should be performed.
)
The staff is concerned with NSP's use of engineering judgment in evaluating these issues. The staffs specific comments are enclosed. Please review and evaluate our enclosed comments and take immediate actions to ensure that the existing operability determinations applicable to these issues are conservative and continue to be valid. Additionally, please address these concerns relative to the final resolution of GL 96-06 issues for Prairie Island Nuclear Generating Plant Units 1 and 2. The staff requests that it be kept informed of these activities and any 3
revisions to NSP's response to GL 96-06 be submitted to the NRC, as appropriate.
Sincerely, ORIGINAL SIGNED BY Beth A. Wetzel, Senior Project Manager Project Directorate ill-1 Division of Reactor Projects lil/IV Office of Nuclear Reactor Regulation Docket Nos. 50-282, 50-306
Enclosure:
Staff Comments cc w/ encl: See next page DISTRIBUTION:
Docket File PUBLIC
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Mr. Roger O. Anderson, Director Prairie Island Nuclear Generating Northem States Power Company Plant I
cc:
J. E. Silberg, Esquire Site Licensing Shaw, Pittman, Potts and Trowbridge Prairie Island Nuclear Generating 2300 N Street, N. W.
Plant Washington DC 20037 Northem States Power Company 1717 Wakonade Drive East Plant Manager Welch, Minnesota 55089 l
Prairie Island Nuclear Generating Plant Tribal Council Northem States Power Company Prairie Island Indian Community 1717 Wakonade Drive East ATTN: Environmental Department Welch, Minnesota 55089 5636 Sturgeon Lake Road i
Welch, Minnesota 55089 i
Adonis A. Nebiett j'
Assistant Attomey General l
Office of the Attomey General l
455 Minnesota Street i
Suite 900 l
St. Paul, Minnesota 55101-2127 l
l U.S. Nuclear Regulatory Commission Resident Inspector's Office 1719 Wakonade Drive East Welch, Minnesota 55089-9642 l
Regional Administrator, Region lll U.S. Nuclear Regulatory Commission l
801 Warrenville Road L
Lisle, Illinois 60532-4351 l
Mr. Jeff Cole, Auditor / Treasurer i
Goodhue County Courthouse Box 408 l
Red Wing, Minnesota 55066-0408 l
Kris Sanda, Commissioner Department of Public Service 121 Sevmth Pk;,ce East Suite 200 St. Paul, Minnesota 55101-2145 November 1996
a COMMENTS PERTAINING TO RESOLUTION OF GL 96-06 ISSUES AT PRAIRIE ISLAND UNITS 1 AND 2 Generic Letter 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," dated September 30,1996, included a request for licensees to evaluate cooling water systems that serve containment air coolers to assure that they are not vulnerable to waterhammer and two-phase flow conditions. Northem States Power Company (the licensee) provided its assessment for Prairie Island Units 1 and 2 in a letter dated January 28,1997. Part 1 of the licensee's submittal addressed waterhammer and two-phase flow conditions. The licensee provided additional information in a letter dated September 15, 1997, in response to a request for additional infonnation dated August 14,1997. Brookhaven National Laboratory (BNL), under contract to the NRC, reviewed the licensee's analysis of waterhammer and two-phase flow conditions and has provided the results of its review in a letter report dated January 23,1998. The following comments are based on the results of BNL's review:
1.
The licensee has concluded that column separation and rejoining is the bounding scenario for the waterhammer issue. While the analysis that was performed for the column separation and rejoining scenario is adequate for a " nominal" treatment of this event, the licensee has not established that the assumptions that were used are appropriate for the worst-case scenario. For example, the value for the speed of sound that was used in the analysis has not been adequately justified and the effects of potential single failure scenarios have not been addressed.
2.
Except for evaluation of the column separation and rejoining scenario, the licensee has not completed a rigorous analysis of the various types of waterhammer that can be encountered. The licensee credits experimentation that has been done to show that the column separation and rejoining scenario is the bounding case, but the experiments are very limiting and much more work is needed to establish the worst-case scenario for the licensee's plant-specific application. Also, the licensee's assumption that a Froude (Fr) number of 0.5 is sufficient to demonstrate that piping lines run full during refill is not consistent with Fr21.0 as suggested in NUREG/CR-5220 [' Diagnosis of Condensation -
Induced Waterhammer"] and must be justifed.
3.
The licensee's evaluation indicated that the piping and pipe supports were evaluated by inputting the expected dynamic loads due to waterhammer into the pipe stress program PIPEPLUS. However, the licensee did not describe the method used to bench mark the computer code for this type of loading condition (see Standard Review Plan Section 3.9.1),
4.
The licensee's evaluation of the hydrodynamic loads due to two-phase flow discharge from the fan coil units is qualitative and does not include analysis of the effects of two-phase flow on components and piping (e.g., flow-induced vibration, erosion, and cavitation effects). Also, the licensee's two-phase hydraulic analysis with initial pressure and flow corresponding to the cooling water pump operating at 93% of the inservice testing (IST) pump curve had not been completed.
ENCLOSURE
R. O. Anderson 2
During a workshop that was held at the Gaithersburg [ Maryland] Marriott on December 4,1997, the NRC staff discussed future plans to review licensee resolution of GL 96-06 issues. Review considerations pertaining to waterhammer and two-phase flow were discussed during the moming session of the workshop and, since this information is also applicable to the licensee's evaluation of waterhammer and two-phase flow for the Prairie Island units, it is repeated here for completeness:
1.
Licensees using a methodology to analyze waterhammer that is different from that discussed in NUREG/CR-5220, " Diagnosis of Condensation-Induced Waterhammer,"
must demonstrate (typically through rigorous plant-specific modeling, testing and analysis) that the approach is applicable and provides conservative results.
2.
Assumptions and input parameters such as amplification due to fluid-structure interaction, cushioning, speed of sound, and force reductions must be justified and selected to provide conservative results (e.g., the use of engineering judgment must be supported by research and test data applicable to the specific system design and configuration).
3.
All parameters within the licensing basis envelope (e.g., temperatures, pressures, flow rates, load combinations, and single failures), event scenarios, and waterhammer types must be considered such that the worst case is identified.
4.
Similar to waterhammer analyses, assumptions and input parameters used for two-phase flow analyses must be justified and selected to provide conservative results (e.g., the use of engineering judgment must be supported by research and test data j
applicable to the specific system design and configuration), and all parameters and event scenarios within the licensing basis envelope must be considered such that the worst case is identified. The following elements, for example, should be addressed in two-phase flow analyses:
a.
effects of void fraction on flow balance and heat transfer; b,
consequences of steam formation, transport, and accumulation; c.
cavitation, resonance, and fatigue effects; and d.
erosion considerations.
Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves," helpful in addressing some aspects of the two-phase flow analyses.