ML003776828
| ML003776828 | |
| Person / Time | |
|---|---|
| Site: | Boiling Water Reactor Owners Group |
| Issue date: | 12/12/2000 |
| From: | Richards S NRC/NRR/DLPM |
| To: | Kenny J BWR Owners Group |
| Pulsifer R ,NRR/DLPM, 415-3016 | |
| References | |
| TAC MA8545 | |
| Download: ML003776828 (8) | |
Text
December 12, 2000 Mr. James M. Kenny, Chairman BWR Owners Group PPL, Inc.
2 North Ninth Street M/C A6-1 Allentown, PA 18101
SUBJECT:
BWR OWNERS GROUP APPENDIX R FIRE PROTECTION COMMITTEE POSITION ON SRVS + LOW PRESSURE SYSTEMS USED AS "REDUNDANT" SHUTDOWN SYSTEMS UNDER APPENDIX R (TOPICAL REPORT GE-NE-T43-0002-00-03-R01) (TAC NO. MA8545)
Dear Mr. Kenny:
In a letter dated September 1, 1999, the Boiling Water Reactor Owners Group (BWROG) submitted its position on the use of safety relief valves (SRVs) and low pressure systems (LPS) as "redundant" post-fire safe shutdown systems under 10 CFR Part 50, Appendix R. The staff subsequently reviewed the BWROG position, conducted a number of meetings and conference calls with the BWROG Appendix R Committee, and received a number of additional documents from the BWROG Appendix R Committee, as discussed below.
Technical, Licensing, and Regulatory Analysis On September 21, 1999, the staff stated that the SRV/LPS "depressurization path is the least preferred path because of the potential for core uncovery and reactor vessel thermal shock,"
but concluded that "the current Appendix R requirement to keep the reactor coolant level above the top of the core for BWRs during a fire is unnecessarily stringent and should be changed,"
"the short term uncovery of the core of a BWR is acceptable during a fire event," and "the depressurization path is equally capable of maintaining core cooling during a fire, and therefore should be considered a redundant safe shutdown method for fire protection." Further, on July 14, 2000, the staff determined by computer code analysis that an SRV/LPS shutdown directly to a cold shutdown condition would not damage the core. This analysis predicted a
("full ADS" worst case) peak cladding temperature of approximately 800 degrees Kelvin (980.3 degrees F) during the SRV/LPS shutdown evolution. The staff finds this acceptable for a fire event.
On April 25, 2000, the staff met with the BWROG Appendix R Committee. During that meeting it was determined that certain additional information was required by the staff. That additional information was either received from the BWROG on July 20, 2000 (ADAMS ML003734575),
August 25, 2000 (ADAMS ML003745185), and September 28, 2000 (ADAMS ML003776421),
or was developed independently by the staff. The information, the subsequent staff/BWROG interactions, and related staff conclusions are as follows:
James M. Kenny December 12, 2000 ÿ Hot Shutdown. Appendix R requires the existence of a functional capability to achieve and maintain hot shutdown capability (Section III.G.1.a). The staff requested a narrative discussion regarding how a BWR reactor plant can redundantly meet this requirement using SRVs and low pressure systems. On July 20, 2000, August 25, 2000, and September 28, 2000, the BWROG forwarded versions of a narrative discussion of how SRVs and low pressure systems can be used to achieve and maintain hot shutdown using generic technical procedures; in this case BWR Emergency Procedure Guideline, Revision 4. The following information shows how, from this information, the staff was able to reach a conclusion regarding the hot shutdown functional capability of SRV/LPS.
Upon review of a July 20, 2000, BWROG "hot shutdown" procedure narrative discussion, the staff noted that Emergency Procedure Guideline (EPG), Revision 4 (from which BWR emergency operating procedures (EOPs) are derived), in its alternate level control section, requires immediate depressurization below the shutoff head of the low pressure injection system when indicated level falls below the top of the active fuel (TAF). It was not immediately clear in the narrative whether it was the BWROG position that the operators were being directed to go to cold shutdown (<200 degrees F average coolant temperature), or whether the operators could maintain the reactor in a hot shutdown condition (as required by Sections III.G.1.a and III.G.2 of Appendix R). This issue was the topic of a phone call to the BWROG on August 2, 2000, during which the BWROG committed to send amplifying information.
On August 25, 2000, the BWROG submitted an amplifying post-fire SRV/LPS shutdown discussion (a revision of Attachment 1 to the original SRV/LPS submittal). This amplifying information made the following salient points:
ÿ When using SRVs and low pressure systems for achieving safe shutdown, the equipment required for cold shutdown is the same equipment used to achieve hot shutdown.
ÿ Appendix R,Section III.G.1.b does not require hot shutdown to be maintained for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Rather, it puts a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> upper bound on the time allowed for making repairs to the cold shutdown equipment.
ÿ Once scram has been achieved in a BWR, the remaining challenges to the reactor are limited to reactor vessel inventory loss due to boil-off and decay heat removal. This is achieved through a controlled SRV depressurization at a rate of less than the operational limit of 100 degrees F/hr, followed by residual heat removal system (RHR) normal or alternate shutdown cooling initiation below the RHR system pressure interlock.
ÿ Reactor level is likely to reach top of active fuel, due to boil-off, prior to reactor pressure reaching the level at which low pressure coolant injection (LPCI) mode of the RHR system can inject. At that time, the reactor pressure vessel (RPV) Level Control Section of the RPV Control Guideline of EPG 4 would instruct the operator to rapidly depressurize
James M. Kenny December 12, 2000 the reactor at a rate greater than 100 degrees F/hr, to allow injection using the available low pressure system. This results in short-term core uncovery during which steam cooling of the fuel operates to maintain fuel integrity. As stated in the BWROG submittal of August 25, 2000, "cooldown in excess of 100 degrees F/hr will not have adverse consequences on the integrity of the RPV or attached piping. The possibility of an automatic depressurization system (ADS) blowdown is included in the design basis of the reactor coolant system." An ADS blowdown, which uses the automatic opening of (typically) six SRVs is a much more severe transient than depressurization using one or two SRVs.
ÿ After depressurization, the reactor average coolant temperature will be near 212 degrees F, and the reactor can remain in hot shutdown (>200 degrees F average coolant temperature) for an extended period of time
[the duration of which is strongly related to core power history] unless RHR is purposely used to remove significant amounts of decay heat.
Although use of RHR may momentarily result in an average coolant temperature below 200 degrees F, decay heat will quickly raise the temperature to maintain hot shutdown conditions.
In the BWROG submittal of September 28, 2000, the following amplifying information related to SRV/LPS hot shutdown was noted:
ÿ The BWROG considers "one train" of systems to consist of, for example, the number of pumps necessary to reach maximum required flow. Since only one RHR pump is required to provide maximum RHR heat exchanger flow, "one (redundant) train" consists of one protected RHR pump. The staff concurs in this interpretation of the term "one train."
ÿ Core spray components can be used in an adequate SRV/LPS post-fire safe shutdown system. Specifically, in terms of thermal shock, core spray is within fuel design limits.
ÿ Core spray can be used in combination with the RHR system: core spray is used to flood up the vessel, reactor coolant flows out of the SRVs to the suppression pool, and RHR removes the heat in the suppression pool cooling mode. A non-core spray lineup would be as follows: RHR/LPCI is used to flood the vessel, reactor coolant flows through the SRVs to the suppression pool, and the suction source for RHR/LPCI is from the suppression pool through the RHR heat exchanger. The staff expects that licensees will perform plant specific shutdown analyses to verify that these methods are feasible at each plant.
James M. Kenny December 12, 2000 ÿ In Section III.L.4 of 10 CFR 50, Appendix R, for Section III.G.3 alternative shutdown capability, the rule states that "if the capability to achieve and maintain cold shutdown will not be available because of fire damage, the equipment and systems comprising the means to achieve and maintain the... hot shutdown conditions shall be capable of maintaining such conditions until cold shutdown can be achieved." This passage can be reasonably interpreted as not requiring hot shutdown capability when undamaged alternative cold shutdown systems will exist. Therefore, the staff reiterates its longstanding position that SRV/LPS is an appropriate means of satisfying Section III.G.3 of Appendix R (regardless of whether SRV/LPS can be considered to be a means of redundant hot shutdown capability). However, the staff emphasizes that reactor licensees should note that Section III.G.3 of Appendix R contains additional requirements regarding the provision of detection and suppression capabilities in fire affected areas for which alternative shutdown capabilities are provided.
ÿ Number of SRVs. On September 28, 2000, in a further revision to Attachment 1 of the original BWROG SRV/LPS submittal, the BWROG stated that the minimum number of SRVs required for depressurization for an Appendix R fire event at a specific reactor plant is determined either (1) by the minimum number of SRVs specified in the licensees plant specific EOPs (derived from the EPG Revision 4 discussed above), or (2) by the number of SRVs used in the licensees plant-unique analysis specifically addressing the Appendix R fire scenario. The staff finds either of these approaches to be appropriate, and notes that NRC inspectors may review such analyses during the post-fire safe shutdown phase of future fire protection inspections.
ÿ Applicability of Section III.L. Requirements. The staff considered whether licensees who designate SRV/LPS as a redundant means of post-fire safe shutdown need to meet the Appendix R,Section III.L. requirement that "reactor coolant process variables be maintained within those predicted for a loss of normal a.c. power," and other Section III.L. performance criteria. The staff concluded that Section III.L. performance criteria are applicable only to alternative or dedicated shutdown capability, and need not be met for redundant post-fire safe shutdown capability. Rather, licensees who designate SRV/LPS as a redundant means of post-fire safe shutdown must show that SRV/LPS can achieve and maintain hot shutdown in accordance with Sections III.G.1.a and III.G.2 of Appendix R (see above).
ÿ Single Failure Criteria. The staff considered whether protected trains of redundant means of post-fire safe shutdown need to meet single failure criteria. The staff concluded that the single failure criteria of the GDC 34 (Residual Heat Removal) applies to the "system safety function" overall, and that the wording of Section III.G.2 in addressing the preservation of the capability of only a single train of safe shutdown equipment, does not contain the expectation that each protected train must meet the single failure criterion in GDC 34. However, it should be understood that the fire protection requirements in Section III.G.2 must be met for each train of safe shutdown
James M. Kenny December 12, 2000 equipment, so that at least one train of a safe shutdown system remains free of fire damage.
Licensing Precedents Review The BWROG has made the point that there are past licensing precedents under which SRV/LPS has been considered as a redundant means of post-fire safe shutdown under Section III.G.2 of Appendix R. Citations from plant specific licensing documents were provided to the staff on July 20, 2000. The BWROG stated that these citations represent past staff approvals of SRV/LPS as a redundant means of post-fire safe shutdown. The BWROG licensing document citations related to a number of NUREG 0800 Standard Review Plan (SRP) plants and one 10 CFR Part 50, Appendix R plant.
ÿ For Perry, an SRP plant, the cited SER approves a combination of pressure relief system (ADS/SRV) and the RHR makeup for "hot shutdown" (among other methods),
although the same SER indicates that the use of SRV/LPS would actually result in cold shutdown. Another passage in the SER explicitly states that "a combination of pressure relief system (Automatic Depressurization System, ADS) and Residual Heat Removal (RHR) system is a means of redundant safe shutdown." For this plant, the staff appears to have approved SRV/LPS as redundant means of post-fire safe shutdown.
ÿ For Clinton, an SRP plant, the cited SER discusses redundancy in the context of its hot shutdown and cold shutdown requirements. Among the systems discussed as capable of achieving hot shutdown are ADS/SRV and LPCI. For this plant, the staff appears to have approved SRV/LPS as a redundant means of post-fire safe shutdown.
ÿ For WNP-2, an SRP plant, the cited SER approves only low pressure systems for post-fire safe shutdown (ADS/SRV and LPCI). The SER quotes the licensee that "a fire in any fire area will not require an alternative safe shutdown capability, except for the control room." For this plant, the staff appears to have approved SRV/LPS as a redundant means of post-fire safe shutdown.
ÿ For Peach Bottom, an Appendix R plant, three redundant shutdown methods are listed including "either the low pressure coolant injection (LPCI) mode of the residual heat removal (RHR) systems or the core spray (CS) system in concert with the automatic depressurization system (ADS)." For this plant, the staff appears to have approved SRV/LPS as a redundant means of post-fire safe shutdown.
ÿ Separate from the BWROG citations, the staff has identified an additional citation for Browns Ferry, an Appendix R plant, wherein a staff SER states that the HPCI system is assumed to be lost due to the fire event, and the RHR system in LPCI mode "is used to inject water from the suppression pool into the vessel to maintain the reactor coolant inventory after manual depressurization of the RCS is achieved using the MSRVs.
Decay heat removal and suppression pool (SP) cooling are accomplished by the RHR system in conjunction with the MSRVs and RHR Service Water (RHRSW) system." For
James M. Kenny December 12, 2000 this plant, the staff appears to have approved SRV/LPS as a redundant means of post-fire safe shutdown.
The staff concludes that in at least five instances, it has previously approved SRV/LPS as a redundant means of post-fire safe shutdown.
Regulatory Burden Reduction Analysis The BWROG has stated that up to 20 boiling water reactors have already established SRV/LPS to varying degrees as a designated means of redundant post-fire safe shutdown. The selected staff interpretations that SRV/LPS is not a redundant means of post-fire safe shutdown have been used in the development of post-fire safe shutdown inspection findings during recent fire protection functional inspections and the more recent triennial baseline fire protection inspections, as well as during the consideration of various BWR licensing submittals. According to the BWROG, depending on the extent of existing redundant use of SRV/LPS at each plant, re-analyzing and reconfiguring these reactor plants would represent a regulatory burden of between $.2M and $20M at each reactor plant. Staff endorsement of the BWROG "redundant" SRV/LPS position would therefore represent a significant regulatory burden reduction for those plants which have already established the redundant configuration. For those reactor plants which use SRV/LPS alternatively, which would not be required to re-analyze or reconfigure their post-fire safe shutdown capability, there would be no regulatory burden increase resulting from a staff endorsement of the BWROG position.
Conclusion The staff, for the reasons stated above, has concluded that the September 1, 1999, BWROG SRV/LPS position, as revised, establishes that SRV/LPS meets the requirements of a redundant means of post-fire safe shutdown under Section III.G.2 of 10 CFR Part 50, Appendix R.
If you have any questions, please call Robert M. Pulsifer at (301) 415-3016.
Sincerely,
/RA by Robert A. Gramm for/
Stuart A. Richards, Director Project Directorate IV and Decommissioning Division of Licensing Project Management Office of Nuclear Reactor Regulation Project No. 691 cc: See next page this plant, the staff appears to have approved SRV/LPS as a redundant means of post-fire safe shutdown.
James M. Kenny December 12, 2000 The staff concludes that in at least five instances, it has previously approved SRV/LPS as a redundant means of post-fire safe shutdown.
Regulatory Burden Reduction Analysis The BWROG has stated that up to 20 boiling water reactors have already established SRV/LPS to varying degrees as a designated means of redundant post-fire safe shutdown. The selected staff interpretations that SRV/LPS is not a redundant means of post-fire safe shutdown have been used in the development of post-fire safe shutdown inspection findings during recent fire protection functional inspections and the more recent triennial baseline fire protection inspections, as well as during the consideration of various BWR licensing submittals. According to the BWROG, depending on the extent of existing redundant use of SRV/LPS at each plant, re-analyzing and reconfiguring these reactor plants would represent a regulatory burden of between $.2M and $20M at each reactor plant. Staff endorsement of the BWROG "redundant" SRV/LPS position would therefore represent a significant regulatory burden reduction for those plants which have already established the redundant configuration. For those reactor plants which use SRV/LPS alternatively, which would not be required to re-analyze or reconfigure their post-fire safe shutdown capability, there would be no regulatory burden increase resulting from a staff endorsement of the BWROG position.
Conclusion The staff, for the reasons stated above, has concluded that the September 1, 1999, BWROG SRV/LPS position, as revised, establishes that SRV/LPS meets the requirements of a redundant means of post-fire safe shutdown under Section III.G.2 of 10 CFR Part 50, Appendix R.
If you have any questions, please call Robert M. Pulsifer at (301) 415-3016.
Sincerely,
/RA by Robert A. Gramm for/
Stuart A. Richards, Director Project Directorate IV and Decommissioning Division of Licensing Project Management Office of Nuclear Reactor Regulation Project No. 691 DISTRIBUTION:
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