ML020020108
| ML020020108 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/16/2002 |
| From: | Kim T NRC/NRR/DLPM/LPD3 |
| To: | Nazar M Nuclear Management Co |
| Kim, TJ, NRR/DLPM/LPD III-1, 415-1392 | |
| References | |
| TAC MB1855, TAC MB1856, TIA 2001-04 | |
| Download: ML020020108 (7) | |
Text
January 16, 2002 Mr. Mano Nazar Site Vice President Prairie Island Nuclear Generating Plant Nuclear Management Company, LLC 1717 Wakonade Drive East Welch, MN 55089
SUBJECT:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 -
OPPORTUNITY FOR COMMENT ON TIA 2001-04, "DESIGN BASIS RELIANCE ON NON-SEISMIC AND NON-SAFETY RELATED EQUIPMENT" (TAC NOS. MB1855 AND MB1856)
Dear Mr. Nazar:
The Nuclear Regulatory Commission (NRC) staff has completed its review of the subject Task Interface Agreement (TIA) request, dated April 26, 2001, from the NRCs Region III office.
This TIA requested the Office of Nuclear Reactor Regulation (NRR) staffs assistance in resolving issues related to design-basis assumptions for the service water system operations at the Prairie Island Nuclear Generating Plant. The purpose of this letter is to provide you with the opportunity to respond to the NRR staffs preliminary conclusions made in the enclosed draft TIA response. In developing the enclosed TIA response, the NRR staff considered your letter dated September 17, 2001, as well as other relevant licensing basis documents.
Our internal procedures encourage the input of licensees or other external stakeholders in order to ensure all relevant information has been considered in responding to a TIA. While you are not required to respond to this letter, your staff has previously indicated a desire to review and comment on the staffs draft TIA response.
If you decide to respond to this letter, we request that your response be provided within 60 days of receipt of this letter. Please feel free to contact me at (301) 415-1392 if you have any questions.
Sincerely,
/RA/
Tae Kim, Senior Project Manager, Section 1 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306
Enclosure:
Response to TIA 2001-04 cc w/encl: See next page
ML020020108 OFFICE PDIII-1/PM PDIII-1/LA PDIII-1/SC(A)
NAME TKim RBouling WReckley DATE 01/15/02 01/15/02 01/16/02
Prairie Island Nuclear Generating Plant, Units 1 and 2 cc:
J. E. Silberg, Esquire Tribal Council Shaw, Pittman, Potts and Trowbridge Prairie Island Indian Community 2300 N Street, N. W. ATTN: Environmental Department Washington, DC 20037 5636 Sturgeon Lake Road Welch, MN 55089 Site Licensing Manager Prairie Island Nuclear Generating Plant Mr. Roy A. Anderson Nuclear Management Company, LLC Executive Vice President and 1717 Wakonade Drive East Chief Nuclear Officer Welch, MN 55089 Nuclear Management Company, LLC 700 First Street Adonis A. Neblett Hudson, WI 54016 Assistant Attorney General Office of the Attorney General Nuclear Asset Manager 455 Minnesota Street Xcel Energy, Inc.
Suite 900 414 Nicollet Mall St. Paul, MN 55101-2127 Minneapolis, MN 55401 U.S. Nuclear Regulatory Commission Resident Inspector's Office 1719 Wakonade Drive East Welch, MN 55089-9642 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532-4351 Mr. Stephen Bloom, Administrator Goodhue County Courthouse Box 408 Red Wing, MN 55066-0408 Commissioner Minnesota Department of Commerce 121 Seventh Place East Suite 200 St. Paul, MN 55101-2145 May 2001
OFFICE OF NUCLEAR REACTOR REGULATION STAFFS RESPONSE TO TASK INTERFACE AGREEMENT 2001-04, "DESIGN BASIS RELIANCE ON NON-SEISMIC AND NON-SAFETY RELATED EQUIPMENT"
1.0 BACKGROUND
By memorandum dated April 26, 2001, Region III requested that the Office of Nuclear Reactor Regulation (NRR) resolve two issues related to design-basis service water system operations at the Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2. The specific issues involve the Nuclear Management Companys (the licensees) assumption that (1) only a single seismically qualified or adequate flow path is required to demonstrate ongoing operability of the cooling water line (CL) system and (2) nonsafety-related equipment (air-operated valve and associated air supply) may be relied upon to demonstrate operability of the CL system. The requested actions in Task Interface Agreement (TIA) 2001-04 are as follows:
Issue (1)
From a licensing basis perspective for system functional capability, is the Prairie Island Plant design required to include two independent, seismically adequate discharge flow pathways for the preferred service water system? Also, if the plant design is required to include two independent, seismically adequate discharge flow pathways, what criteria should the regional staff use to determine that the pathways are seismically adequate (e.g., SQUG, etc)?
Issue (2)
From a design and licensing basis perspective for system functional capability, may the licensee rely upon the post-accident, automatic closure of the spring-to-open, air-to-close non-safety related turbine building hydrogen cooler service water control valve to preclude the service water pumps from operating beyond the run-out region of the pump curve and to ensure adequate cooling of safety-related loads?
By letter dated September 17, 2001, the licensee submitted to NRC its response to the issues identified in TIA 2001-04. The NRR staff has reviewed TIA 2001-04 and the licensees associated submittal. The NRR staffs safety assessment of TIA 2001-04 is below.
2.0 NRR STAFFS RESPONSE TO ISSUE (1)
The design-basis requirements that were established for the PINGP service water system are discussed in the Final Safety Analysis Report (FSAR) that was in effect at the time of licensing of the plant. As discussed in FSAR Section 1.2.8, Engineered Safety Features (ESF), the cooling water system (a.k.a., service water system) is considered to be an ESF. The following criterion listed in FSAR Section 1.3, Principal Design Criteria, is among those that apply to the cooling water system:
FSAR Section 1.3.1, Overall Plant Requirements (GDC 1-GDC 5)
All systems and components of the facility are classified according to their importance. Those items vital to safe shutdown [among other things] are designated Class I. Class I systems and components are designed so that no loss of function will result from the Design Basis Earthquake (DBE).
Appendix B of the FSAR, Special Design Procedures, Table B.2-1, Classification of Structures, Systems, and Components, identifies the cooling water system as Class I up to the Class I system isolation valves, and classifies those areas of the Turbine Building that house cooling water system pipes as Class I. Section B.5, Protection of Class I Items, states that Class I items are protected against damage from earthquakes by having the ability to sustain seismic accelerations without loss of function. Section B.7.2(a), Design Criteria for Class I Vessels, Piping, and Supports, provides that in the case of the DBE, it is necessary to ensure that critical components do not lose the ability to perform their safety function (i.e., shut the plant down and maintain it in a safe condition). The FSAR also states that for the simultaneous occurrence of a DBE and a reactor coolant pipe rupture, the design of Class I piping and components (excluding the broken leg) is checked for no loss of function (i.e., the capability to contain fluid and allow fluid flow). Therefore, based on the FSAR design criteria, those elements of the cooling water system that are relied upon for accident mitigation, including discharge flow paths, should satisfy the Class I criteria as set forth in Appendix B of the FSAR.
This does not preclude the licensee from crediting other flow paths in response to Generic Letter (GL) 87-02, Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety Issue (USI) A-46, in addition to those that are required for accident mitigation.
GL 87-02 specified that licensees determine the systems, subsystems, components, instrumentation, and controls required during and following a design-basis seismic event using the following assumptions:
- 1. The seismic event does not cause a loss-of-coolant accident (LOCA), a steam-line-break accident (SLBA), or a high-energy line break (HELB). In addition, a LOCA, an SLBA, or an HELB does not occur simultaneously with or during a seismic event. However, the effects of transients that may result from ground shaking should be considered.
- 2. Offsite power may be lost during or following a seismic event.
- 3. The plant must be capable of being brought to a safe shutdown condition following a design-basis seismic event.
The equipment to be included is generally limited to active mechanical and electrical components and cable trays. Piping, tanks, and heat exchangers are not included except that those tanks and heat exchangers that are required to achieve and maintain safe shutdown must be reviewed for adequate anchorage.
Seismic system interaction is included in the scope of review to the extent that equipment within the scope must be protected from seismically induced physical interaction with all structures, piping, or equipment located nearby.
GL 87-02 also specified that each licensee must show practical means of staying at hot shutdown for a minimum of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If maintaining safe shutdown is dependent on a single (not redundant) component whose failure (either due to seismic loads or random failure) would preclude decay heat removal by the identified means, the licensee must show that at least one practical alternative for achieving and maintaining safe shutdown exists that is not dependent on that component.
Based on the above, the licensee for PINGP was required, for the implementation of USI A-46, to ensure that the plant would be capable of being brought to a safe shutdown condition following a design-basis seismic event by verifying the seismic adequacy of a success path with the assumption of a failure of a single active component. Although piping is not included in the scope of USI A-46, piping functionality must be assured (to ensure the viability of the success path in order) for the licensee to demonstrate that PINGP can be shut down safely following a design-basis seismic event.
On pages 4 and 5 of NUREG-1211, the staff provided its rationale for excluding piping and piping supports within the accident-mitigation systems from the scope of the USI A-46 program.
Central to the staffs position is that the seismic adequacy of safety-related piping and piping supports has been addressed within the scope of several IE bulletins (e.g., IE Bulletins 79-02, 79-07, and 79-14). It was never the staffs intent or position to endorse the acceptability of nonseismically designed piping within the safe shutdown system without an engineering evaluation to establish its seismic adequacy consistent with other seismically adequate in-line components within these systems. The staff, therefore, finds the licensees arguments on pages 4 and 5 of its September 17, 2001, letter unacceptable for nonsafety-related piping within the CL system.
To satisfy the provisions of GL 87-02, the licensee should demonstrate the seismic adequacy of a chosen safe shutdown path with the assumption of a failure of a single active component.
Since piping is part of the safe shutdown path, its functionality should be demonstrated during a safe-shutdown earthquake (SSE) event.
If the licensee has incorporated the Seismic Qualification Utility Groups (SQUGs) Generic Implementation Procedure (GIP), Revision 2 (GIP-2), in the FSAR, then a successful (seismically adequate) safe shutdown path (while considering the failure of a single active component) would be required in accordance with the GIP-2 provisions. If the discharge flow pathways are required to be seismically adequate, an acceptable approach may include:
(A) Use of SQUG GIP-2 to demonstrate the seismic adequacy of equipment.
(B) Use of either the licensing basis criteria to demonstrate the seismic adequacy of safety-related piping systems, or specific criteria to be proposed by the licensee and approved by the staff for demonstrating the seismic adequacy of piping in the CL system.
The staff notes that having a success flow pathway with the assumption of a failure of a single active component is not the same as having two independent flow pathways. In Supplement 4 to GL 88-20, Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities," seismic adequacy stipulates the identification of two independent safe shutdown paths. However, IPEEE was established to address Severe Accident Vulnerabilities, which are beyond the licensing basis.
3.0 NRR STAFFS RESPONSE TO ISSUE (2)
As stipulated in Section 1.3.1 of the FSAR, All systems and components of the facility are classified according to their importance. Those items vital to safe shutdown and isolation of the reactor or whose failure might cause or increase the severity of an accident or result in an uncontrolled release of substantial amounts of radioactivity are designated Class I (i.e., safety related). Reliance on non-Class I equipment in the manner described does not satisfy the plant design-basis requirements as set forth in the FSAR, and is therefore unacceptable. The licensees response of September 17, 2001, to the TIA request speculates that the NRC was aware that non-Class I equipment was being relied upon in the manner described. However, the staff has found no explicit recognition or acknowledgment of this during plant licensing by either the licensee or the NRC. It was the staffs expectation during licensing, as it is the staffs expectation now, that the licensee comply with the plant design-basis requirements.