ML041330526
| ML041330526 | |
| Person / Time | |
|---|---|
| Site: | Boiling Water Reactor Owners Group |
| Issue date: | 05/10/2004 |
| From: | Stephen Dembek NRC/NRR/DLPM/LPD4 |
| To: | Putnam K Nuclear Management Co |
| Dembek S,NRR/DLPM,415-1455 | |
| References | |
| TAC MB9642 | |
| Download: ML041330526 (7) | |
Text
May 10, 2004 Mr. Kenneth Putnam, Chairman BWR Owners Group Nuclear Management Company Duane Arnold Energy Center 3277 DAEC Rd.
Palo, IA 52324
SUBJECT:
DRAFT SAFETY EVALUATION FOR LICENSING TOPICAL REPORT (LTR)
NEDO-33091, "IMPROVED BPWS CONTROL ROD INSERTION PROCESS" (TAC NO. MB9642)
Dear Mr. Putnam:
On June 6, 2003, the Boiling Water Reactors Owners Group (BWROG) submitted LTR NEDO-33091, "Improved BPWS Control Rod Insertion Process," to the staff for review. Enclosed for the BWROGs review and comment is a copy of the staffs draft safety evaluation (SE) for the LTR.
Twenty working days are provided to you to comment on any factual errors or clarity concerns contained in the SE. The final SE will be issued after making any necessary changes and will be made publicly available. The staffs disposition of your comments on the draft SE will be discussed in the final SE.
To facilitate the staffs review of your comments, please provide a marked-up copy of the draft SE showing proposed changes and provide a summary table of the proposed changes.
If you have any questions, please contact Bo Pham at (301) 415-8450.
Sincerely,
/RA/
Stephen Dembek, Chief, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Project No. 691
Enclosure:
Draft Safety Evaluation cc w/encl: See next page
May 10, 2004 Mr. Kenneth Putnam, Chairman BWR Owners Group Nuclear Management Company Duane Arnold Energy Center 3277 DAEC Rd.
Palo, IA 52324
SUBJECT:
DRAFT SAFETY EVALUATION FOR LICENSING TOPICAL REPORT (LTR)
NEDO-33091, "IMPROVED BPWS CONTROL ROD INSERTION PROCESS" (TAC NO. MB9642)
Dear Mr. Putnam:
On June 6, 2003, the Boiling Water Reactors Owners Group (BWROG) submitted LTR NEDO-33091, "Improved BPWS Control Rod Insertion Process," to the staff for review. Enclosed for the BWROGs review and comment is a copy of the staffs draft safety evaluation (SE) for the LTR.
Twenty working days are provided to you to comment on any factual errors or clarity concerns contained in the SE. The final SE will be issued after making any necessary changes and will be made publicly available. The staffs disposition of your comments on the draft SE will be discussed in the final SE.
To facilitate the staffs review of your comments, please provide a marked-up copy of the draft SE showing proposed changes and provide a summary table of the proposed changes.
If you have any questions, please contact Bo Pham at (301) 415-8450.
Sincerely,
/RA/
Stephen Dembek, Chief, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Project No. 691
Enclosure:
Draft Safety Evaluation cc w/encl: See next page DISTRIBUTION:
PUBLIC JWermiel PDIV-2 Reading FAkstulewicz HBerkow (RidsNrrDlpmLpdiv)
SLu BPham (RidsNrrPMBPham)
RidsOgcMailCenter EPeyton (RidsNrrLAEPeyton)
RidsAcrsAcnwMailCenter ACCESSION NO.: ML041330526 NRR-106
- SE Input OFFICE PDIV-2/PM PDIV-2/LA SRXB*
PDIV-2/SC NAME BPham EPeyton FAkstulewicz SDembek DATE 5/7/04 5/7/04 4/26/04 5/10/04 File: C:\\ORPCheckout\\FileNET\\ML041330526.wpd OFFICIAL RECORD COPY
BWR Owners Group Project No. 691 cc:
Mr. Joseph E. Conen Vice Chairman, BWR Owners Group DTE Energy - Fermi 2 200 TAC 6400 N. Dixie Highway Newport, MI 48166 Mr. J. A. Gray, Jr.
Regulatory Response Group Chairman BWR Owners Group Entergy Nuclear Northeast 440 Hamilton Avenue Mail Stop 12C White Plains, NY 10601-5029 Mr. H. Lewis Sumner Southern Nuclear Company 40 Inverness Center Parkway P.O. Box 1295 Birmingham, AL 35242 Mr. Carl D. Terry Vice President, Nuclear Engineering Nine Mile Point - Station OPS Building/2nd Floor P.O. Box 63 Lycoming, NY 13093 Mr. Thomas G. Hurst GE Nuclear Energy M/C 782 175 Curtner Avenue San Jose, CA 95125 Mr. Thomas A. Green GE Nuclear Energy M/C 782 175 Curtner Avenue San Jose, CA 95125 Mr. James Meister Exelon Cornerstone II at Cantera 4300 Winfield Road Warrenville, IL 60555 Mr. William A. Eaton ENTERGY Grand Gulf Nuclear Station P.O. Box 756 Port Gibson, MS 39150 Mr. Mark Reddeman Vice President Engineering Point Beach Nuclear Plant 6610 Nuclear Road Two Rivers, WI 54241 Mr. Richard Libra DTE Energy Fermi 2 M/C 280 OBA 6400 North Dixie Highway Newport, MI 48166 Mr. James F. Klapproth GE Nuclear Energy M/C 706 175 Curtner Avenue San Jose, CA 95125
DRAFT SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION LICENSING TOPICAL REPORT NEDO-33091, "IMPROVED BPWS CONTROL ROD INSERTION PROCESS" BOILING WATER REACTOR OWNERS GROUP (BWROG)
PROJECT NO. 691
1.0 INTRODUCTION
1 By letter dated June 6, 2003, the BWROG requested the NRC to review its licensing topical 2
report (TR) NEDO-33091, "Improved BPWS [Banked Position Withdraw Sequence] Control 3
Rod Insertion Process." Both the original BPWS process previously approved by the staff and 4
the proposed improved process, are designed to minimize reactivity insertion during a 5
postulated design basis control rod drop accident.
6 Throughout its operating cycle, a boiling water reactor (BWR) experiences various startup, 7
normal, and shutdown operations. Control rods are also moved due to fuel burn-up, power 8
maneuvers, and normal operational occurrences. This rod movement could potentially result in 9
a decoupled control rod thats stuck in the core, followed by a subsequent control rod drop, 10 which would lead to a high reactivity insertion in a small region of the core. For large loosely 11 coupled cores, a significant shift in the spatial power generation could occur during the course 12 of this excursion. Utilizing rod pattern control systems, i.e., rod worth minimizer, rod sequence 13 control system or rod pattern controller, the BPWS was developed to reduce the maximum 14 control rod worth during the startup and shutdown processes. The current BPWS process 15 requires control rods to be moved in banked positions, even during the shutdown process after 16 the low power set point (LPSP) is reached. This requirement results in the control of rod 17 movement through many steps, when there is an extremely low possibility for the control rod to 18 drop out of the core. Therefore, the improved BPWS proposes the one-step full insertion of 19 control rods without banking after the reactor power is below LPSP.
20 2.0 REGULATORY BASIS 21 Control rod drop accident (CRDA) is the design basis accident for the subject LTR. In order to 22 minimize the impact of a CRDA, the BPWS process was developed to minimize control rod 23 reactivity worth for BWR2-6. The proposed improved BPWS further simplifies the control rod 24 insertion process, and in order to evaluate it, the staff followed the guidelines of Standard 25 Review Plan Section 15.4.9, and referred to General Design Criterion 28 of Appendix A to 26 10 CFR Part 50 as its regulatory requirement.
27
3.0 TECHNICAL EVALUATION
1 The original BPWS was developed to minimize the control rod worth and prevent a CRDA from 2
occurring during startup, because of frequent control rod movements. This procedure also 3
directly applied to the control rod insertion sequence during the shutdown routine, after power is 4
lower than the LPSP. The BWROG and GE Nuclear Energy (GENE) found that this approach, 5
while conservative, requires unnecessary control rod movements during the shutdown process.
6 The procedural requirements on the operator also increases the risk of incorrect control rod 7
movement, and causes additional wear on the rod and rod drive hardware systems. Since the 8
possibility of having a decoupled control rod extremely low during the shutdown process, GENE 9
is proposing the improved BPWS, which allows control rods to be fully inserted in a single step 10 during the shutdown process.
11 The improved BPWS proposes the following changes to the operational procedures:
12
- 1.
Before reducing power to the LPSP, operators shall confirm control rod coupling 13 integrity for all rods that are fully withdrawn. Control rods that have not been confirmed 14 coupled and are in intermediate positions must be fully inserted prior to power reduction 15 to the LPSP. No action is required for fully-inserted control rods.
16 If a shutdown is required and all rods, which are not confirmed coupled, cannot be fully 17 inserted prior to the power dropping below the LPSP, then the original/standard BPWS 18 must be adhered to.
19
- 2.
After the reactor power drops below the LPSP, rods may be inserted from notch position 20 48 to notch position 00 without stopping at intermediate positions. However, GENE 21 recommends that operators should insert rods in the same order as specified for the 22 standard BPWS as much as reasonably possible. If a plant is in the process of shutting 23 down following improved BPWS with the power below the LPSP, no control rod shall be 24 withdrawn unless the control rod pattern is in compliance with standard BPWS 25 requirements.
26 All other control rod operational requirements are unchanged and continue to apply. The 27 proposed changes may alter the technical specifications of certain plants; GENE has identified 28 the potentially affected areas in the standard technical specifications. The specific changes for 29 each plant implementing the improved BPWS will be determined on a case-by-case basis.
30 The basis of the improved BPWS is the assumption that a CRDA can only be caused by a 31 stuck rod which is decoupled from the control rod drop (CRD). No single failure of a BWR CRD 32 mechanical or hydraulic system can cause a control rod to drop completely out of the reactor 33 core during the reactor shut-down process. In its April 21, 2004, response to the staffs request 34 for additional information (RAI), the BWROG/GENE referred the staff to Final Safety Analysis 35 Report (FSAR) sections, isometric drawings, and hydraulic schematics describing CRD 36 hydraulic unit design, control rod assembly configuration, and postulated CRD failure modes 37 and effects scenarios from the FSARs for Oyster Creek (BWR/2), Monticello (BWR/3), Limerick 38 (BWR/4), LaSalle (BWR/5), and Perry (BWR/6). The staffs review considered CRD hydraulic 39 systems from plants of various BWR designs, and found that the CRD systems of BWR/2 40 through BWR/6 designs are very similar with respect to the mechanisms for rod insertion, 41 withdrawal, and locking. The staff found that during a reactor shutdown process for all 1
operating BWRs when each control rod is given an insert signal, there exists no single failure of 2
the CRD hydraulic or mechanical system that could result in a control rod withdrawal out of the 3
core of more than six inches (equivalent to one CRD index tube drive notch length). Therefore, 4
the staff agrees with the BWROG/GENEs assessment regarding the possible cause of a 5
CRDA during the shutdown process after reactor power reaches below the LPSP since the 6
technical basis, as cited above, is sound and acceptable.
7 Implementation of the improved BPWS requires two major operating procedure changes. The 8
requirement for operators to confirm control rod coupling integrity for all rods fully withdrawn will 9
assure proper coupling during the control rod insertion process and any possible rod withdrawal 10 after reactor power drops below LPSP. The proposed procedure for the full insertion of all 11 unconfirmed control rods prior to LPSP will prevent the possibility of a decoupled control rod 12 dropping out during the control rod maneuvers. If all unconfirmed control rods cannot be fully 13 inserted prior to the LPSP, the use of the standard BPWS will become the conservative fall 14 back position, since the risk of a CRDA occurring using the improved BPWS will be no different 15 than the standard BPWS using this procedure.
16 After reactor power drops below the LPSP, the improved BPWS allows the full insertion of each 17 control rod without banking. This simplification of the control rod insertion process helps to 18 reduce the number of control rod insertion steps. Since all unconfirmed control rods have been 19 inserted, it is highly unlikely for a CRDA to occur while confirmed rods are being inserted 20 without banking. Therefore, the improved BPWS will have the same level of safety assurance 21 as the previously approved standard BPWS process. Should the operator decide to reverse the 22 shutdown process, the improved BPWS does not allow for the withdrawal of any control rods, 23 unless the control rod pattern meets the standard BPWS requirements. This ensures that all 24 control rods are always banked for withdrawal.
25 The improved BPWSs single step full insertion also reduces the insertion time of each rod, 26 which may induce a necessary increase in other procedures or processes to accommodate this 27 rapid change. During telephone conferences, the staff requested additional information from 28 the BWROG/GENE regarding the impact of the accelerated shut-down process on other 29 procedures. The BWROG/GENE examined its process and requirements, and concluded in its 30 RAI response on April 21, 2004, that the improved BPWS process does not adversely affect the 31 normal shutdown processes, since the operating procedures will remain to be bounded by the 32 most limiting (fastest negative reactivity) control rod insertion scenario (RAI #3). In addition, 33 pressure-temperature effects, as in the cooldown process for example, are accounted for and 34 controlled by controlling reactor dome pressure, coolant flow and coolant temperature.
35
4.0 CONCLUSION
S 36 The BWROG/GENE has proposed an improved BPWS process which allows for the single step 37 full insertion of control rods during shutdown, when the reactor power is lower than the LPSP.
38 The staff has completed its review of the subject LTR, and concluded that the proposed change 39 is acceptable and applicable to BWR/2-6 with standard BPWS already implemented. Plants 40 electing to implement the improved BPWS must reflect the changes in their operating 1
procedure. If the technical specification of a plant is impacted or needs to be updated, an 2
amendment submittal to the NRC will be required.
3 Principal Contributor: Shanlai Lu 4
Date: May 10, 2004 5