ML17191A622
| ML17191A622 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/27/1998 |
| From: | Rossbach L NRC (Affiliation Not Assigned) |
| To: | Kingsley O COMMONWEALTH EDISON CO. |
| References | |
| GL-96-06, GL-96-6, TAC-M96806, TAC-M96807, NUDOCS 9805040077 | |
| Download: ML17191A622 (5) | |
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Mr. Oliver D. Kingsley, President Nuclear Generation Group
- Commonwealth Edison Company EXecutive Towe rs West Ill 1400 Opus Place, Suite 500 Downers Grove, IL 60515 April 27, 1998
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION FOR GENERIC LETTER 96-06 FOR DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3 (TAC NOS. M96806 AND M96807)
Dear Mr. Kingsley:
Generic Letter (GL) 96-06, "Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," dated September 30, 1996, included a reque$t for licensees to evaluate cooling water ~ystems that serve containment air coolers to ass_ure that they are not.'vulnerable to water hammer and two-phase flow con_ditions..
Commonwealth Edison Company (ComEd) provided its assessment for the Dresden Station, Units 2 and 3, in letters dated Ja~uary 28, March 28, and May 30, 1997. The staff has reviewed ComEd's submittals and has determined that additional information, as discussed in.the enclosure, is necessary to complete its review. We ask that this additional information be
- provided within 90 days in order to support our review schedule. for GL 96-06.
Docket Nos. 50-237 and 50-249
Enclosure:
RAI cc w/encl: See next-page DISTRIBUTION:
--. Docket file.
- PUBLIC S. Richards C. Moore Sincerely, ORIG. SIGNED BY:
Lawrence W. Rossbach, Project Manager Project Directorate 111-2 Division of Reactor Projects - Ill/IV Office of Nuclear Reactor Regulation 1.:*.
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UNITED STATES
. NUCLEAR REGULATORY COMMISSION Mr. Oliver D. Kingsley, President Nuclear Generation Group Commonwealth Edison Company
. Executive Towers West Ill 1400 Opus Place, Suite 500 Downers Grove, IL 60515 WASHINGTON, D.C. 20555-0001 Apri 1 27, 1998
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION FOR GENERIC LETTER 96-06 FOR
.DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3 (TAC NOS. M96806 AND M96807)
Dear Mr. Kingsley:
Generic Letter (GL) 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 water hammer and two-phase flow conditions.
Commonwealth Edison Company (ComEd) provided its assessment for the Dresden Station, Units 2 and 3, in letters dated January 28, March 28, and May 30, 1997. The staff has reviewed ComEd's submittals and has determined that additional information, as discussed in the enclosure, is necessary to complete its review. We ask that this additional information be provided within 90 days in order to support our review schedule for GL 96-06.
Docket Nos. 50-237 and 50-249
Enclosure:
RAI cc w/encl: ~ee next page Sincerely,
~.:_______ i,._,, K~
Lawrence W. Rossbach, Project Manager Project Directorate 111-2 Division of Reactor Projects.;. Ill/IV Office of Nuclear Reactor Regulation
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- 0. Kingsley Commonwealth Edison Company cc:
Michael I. Miller, Esquire Sidley and Austin One First National Plaza Chicago, Illinois 60603 Commonwealth* Edison Company Site Vice President - Dresden 6500 N. Dresden Road Morris, Illinois 60450-9765
. Commonwealth Edison Company Dresden Station Manager 6500 N. Dresden Road Morris, Illinois 60450-9765 U.S. Nuclear Regulatory Commission Dresden Resident lnspeciors Office 6500 N. Dresden Road Morris, Illinois 60450-9766 Regional Administrator U.S. NRC, Region Ill 801 Warrenville Road Lisle, Illinois 60532-4351 Illinois Department of Nuclear Safety Office of Nuclear Facility Safety 1035 Outer Park Drive Springfield, Illinois 62704 Chairman Grundy County Board Administration Building 1320 Union Street Morris, Illinois 60450 Document Control Desk-Licensing Commonwealth Edison Company 1400 Opus Place, Suite 400 Downers Grove, Illinois 60515 Mr. David Helwig Senior Vice President Commonwealth Edison Company Executive Towers West Ill 1400 Opus Place, Suite 900 Downers Grove, IL 60515 Dresden Nuclear Power Station Units 2 and 3 Mr. Gene H. Stanley PWR's Vice President Commonwealth Edison Company Executive Towers West Ill 1400 Opus Place, Suite 900 Downers Grove, IL 60515 Mr. Steve Perry BWR's Vice President
.Commonwealth Edison Company Executive Towers West Ill 1400 Opus Place, Suite 900 Downers Grove, IL 60515 Mr. Dennis Farrar
. Regulatory Services Manager Commonwealth Edison Company Executive Towers West Ill 1400 Opu.s Place, Suite 500 Downers Grove, IL 60515 Ms. Irene Johnson, Licensing Director Nuclear Regulatory Services Commonwealth Edison Company Executive Towers West Ill 1400 Opus Place, Suite 500 Downers Grove, IL 60515 Commonwealth Edison Company Reg. Assurance Supervisor-Dresden 6500 N. Dresden Road Morris, Illinois 60450-9765 Mr. Michael J. Wallace Senior Vice President Commonwealth Edison Company Executive Towers West Ill 1400 Opus Place, Suite 900 Downers Grove, IL 60515
REQUEST FOR ADDITIONAL INFORMATION FOR RESOLUTION OF GL 96-06 ISSUES AT THE DRESDEN STATION, UNITS 2 AND 3 (TAC NOS. M96806 AND M96807)
Generic Letter (GL) 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 water hammer and two-phase flow conditions. Commonwealth Edison Company (the licensee) provided its assessment for Dresden Station, Units 2 and 3, in letters dated January 28, March 28, and May 30, 1997. The licensee's response indicates that the Drywell Cooling System at Dresden is not safety-related and is not assumed to operated under postulated accident conditions. However, the Reactor Building Closed Cooling System (RBCCW), which provides cooling water to the drywell coolers, is not automatically isolated during a loss-of-coolant accident (LOCA) or a main steam line break and water continues to flow through the drywell units until RBCCW is manually isolated from the control room due to RBCCW pump trip or low RBCCW expansion tank water level. The following three scenarios were discussed in the licensee's response:
- a.
The RBCCW system continues to operate. Heat will be removed by the RBCCW system following the accident and steam pockets should not form.
- b.
The RBCCW system isolation valves are manually closed by the.control room operators following the accident. Water hammer is not a concern unless RBCCW flow is reinitiated.
For this scenario, the licensee indicated that all applicable post accident operating procedures wo*uld be reviewed and updated as needed to include a warning on the potential for water hammer in the RBCCW system if cooling water flow is reinitiated after a LOCA.
- c.
The RBCCW pumps trip during the initial phase of the accident and the isolation valves are not manually closed. *The licensee expects that steam formation would be minimal because the RBCCW system is a closed loop system and the expansion tank is at least 50 feet above the RBCCW piping in the drywell.
In order to adequately assess the licensee's resolution of the water hammer and two-phase flow issues, the following additional information is requested:
- 1.
The scenarios that were discussed do not specifically include LOCA with loss of offsite power, unless (c) above is meant to be representative of this case. Explain.
- 2.
For the scenario discussed in (b), above, explain under what specific circumstances operators will be allowed to reinitiate flow through the RBCCW system and how this will be accomplished such that complications due to water hammer and two-phase flow are avoided.
- 3.
Confirm that a complete failure modes and effects analysis (FMEA) for all components (including. electrical and pneumatic failures) that could impact performance of the RBCCW system has been performed for the various scenarios and confirm that these FMEAs are documented and *available for review, or explain why complete and fully documented FMEAs were not performed: Confirm that these scenarios re*main valid even when "worst-case" conditions and failure modes are assumed.
ENCLOSURE
2
- 4.
For all scenarios that include the possibility of water hammer or two-phase flow, provide the following additional information:
- a.
If a methodology other than that discussed in NUREG/CR-5220, "Diagnosis of Condensation-Induced Water hammer," was used in evaluating the effects of water hammer, describe this alternate methodology in detail. Also, explain why this methodology is applieable and gives conservative* results for Dresden units (typically accomplished through rigorous plant-specific modeling, testing, and analysis).
- b.
Identify any computer codes that were used in the water hammer and two-phase flow analyses and describe the methods used to bench mark the codes for the specific loading conditions involved (see Standard Review Plan Section 3.9.1).
- c.
Describe and justify all assumptions and input parameters (including those used in any computer codes) such as amplifications due to fluid structure interaction, cushioning, speed of sound, force reductions, and mesh sizes, and explain why the values selected give conservative results. Also, provide justification for omitting any effects that may be relevant to the analysis (e.g., fluid structure interaction, flow induced vibration, erosion).
- d.
Provide a detailed description of the "worst case" scenarios for water hammer and two-phase flow, taking into consideration the complete range of event possibilities, system configurations, and parameters. For example, all water hammer types and water slug scenarios should be considered, as well as temperatures, pressures, flow rates, load
. combinations, and potential component failures. Additional examples include:
the consequences of steam formation, transport, and accumulation; cavitation, resonance, and fatigue effects; and erosion considerations.
Licensees may find NUREG/CR-6031, "Cavitation Guide for Control Valves," helpful in addressing some aspects of the two-phase flow analyses.
- e.
Determine the uncertainty in.the water hammer and two-phase flow analyses, explain how the uncertainty was determined, and how it was accounted for in the analyses to assure conservative results for the Dresden units.
- f.
Confirm that the water hammer and two-phase flow loading conditions do not exceed any design specifications or recommended service conditions for the piping system and components, including those stated by equipment vendors; and confirm that the system will continue to perform its design-basis functions as assumed in the safety analysis report for the facility.
- g.
Explain and justify all uses of "engineering judgement."
- 5.
Provide a simplified diagram of the RBCCW system, showing major components, active components, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions.