ML032330211
| ML032330211 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point, Boiling Water Reactor Owners Group  |
| Issue date: | 08/15/2003 |
| From: | May M BWR Owners Group, Exelon Corp |
| To: | Office of Nuclear Reactor Regulation |
| Wang A,/NRR/DLPM/415-1445 | |
| Shared Package | |
| ML032320424 | List: |
| References | |
| Download: ML032330211 (16) | |
Text
BWR Owners' Group Nine Mile Point 2 Instability Event Briefing Presentation to USNRC Mike May, Exelon Corp.
August 15, 2003
4fI M Agenda
- Event Description NMP-2 Design
- Event Analysis August 15, 2003 Nine Mile Point 2 Instability Event Briefing Slide 2
Event Description At 05:50:36 on July 24, 2003 while operating at 100%
power / 94% core flow, the loss of a power supply causes an unexpected plant transient Recirculation pumps auto-downshift from high to low speed Reactor power lowered to 45% and flow to 35%
After -3 minutes, operators manually tripped one of two feed pumps due to rising water level Reactor Recirculation flow control valve run-back occurred Reactor power lowered to 35% and flow to 28%
Auvst 1.5,2003 Nine Mile Point 2 Instability Event Briefing Slide 3
Event Description After -7 minutes, decreasing feedwater temperature raised power to -45% and 28% flow prior to scram At 05:57:13-17 OPRM Pre-trip Alarmed At 05:57:17 OPRM Channel 4 PBA Tripped At 05:57:19 OPRM Channel 1 PBA Tripped (Reactor scram)
August IS, 2003 Nine Mile Point 2 Instability Event Briefing Slide 4
.I I
NMP-2 Design BWR-5 3467 MWth (104.3% Uprate)
Currently in Cycle 9 started in spring 2002 Full core GE-1 1 fuel 24 month cycles OPRMs enabled since BOC-8 in 2000 Cycle 9 OPRM PBA Amplitude Setpoint calculated with plant specific DIVOM Cycle 9 OPRM PBA Amplitude Setpoint at 1.12 @ 14 counts August 15, 2003 Nine Mile Point 2 Instability Event Briefing Slide 5
40 Event Analysis The rapid flow reduction and accompanying feedwater temperature transient led to power and flow conditions in the upper left corner of the power/flow map which are typically susceptible to coupled neutronic thermal-hydraulic oscillations.
The MCPR immediately prior to oscillations was calculated at greater than 1.8. Based on bounding analysis, the transient MCPR was never less than 1.3 and there was significant margin to the 1.06 SLMCPR during the event.
August 15, 2003 Nine Mile Point 2 Instability Event Briefing Slide 6
Event Analysis Based on a preliminary plant data analysis, a core-wide mode instability event occurred The instability event lasted for about 40 seconds and terminated by the PBDA in a reactor scram The plant data indicates that several OPRM cells reached the PBDA confirmation count trip setpoint (14) and that the relative amplitude of the leading OPRM cells reached the PBDA amplitude trip setpoint (1.12) immediately before the scram Further analysis of the event is in progress August 15, 2003 Nine Mile Point 2 Instability Event Briefing Slide 7
BWR Owners' Group Stability Option III DIVOM Part 21 Closure Plan Presentation to USNRC Mike May, Exelon Corp.
August 15, 2003
4 1 A
Agenda
- Background
- BWROG Decisions
- Proposed Closure Plan
- Open Discussion - NRC Feedback Augmt 15, 2003 Stability Option Im DIVOM Part 21 Closue Plan Slide 2
=
Background===
Current D&S methodology defines cycle-specific calculation to ensure MCPR safety limit protection Current reload method relies on generic DIVOM curve (fractional change in CPR vs. oscillation magnitude)
- June 2001: GE reported that generic DIVOM curve may be non-conservative, resulted in Part 21 notification
- BWROG D&S Committee re-formed to develop new generic DIVOM correlation August 15, 2003 Stability Option m DIVOM Part 21 Closure Plan Slide 3
.4 Background
Concluded that generic DIVOM approach not viable for Option HI plants (good correlation of DIVOM with plant parameters not achieved)
Pursued generic setpoint approach that uses TRACG event simulation to demonstrate MCPR SL protection Pursued new stability limit instead of MCPR SL to increase long-term viability and range of applicability Analysis successfully identified key PCT parameters Appears technically feasible, but wide margins not demonstrated To proceed, need to better quantify uncertainties in analysis and the acceptance criteria August 15, 2003 Stability Option m DIVOM Part 21 Closure Plan Slide 4
BWROG Decisions
- Not pursue generic setpoints with new stability limit Large work scope / scope uncertainty High cost / cost uncertainty Long schedule (years to accomplish)
Recognized that separating departure from nucleate boiling from fuel damage would be major shift in philosophy for fuel protection
- Use next best alternative:
Plant-specific DIVOM August 15,2003 Stability Option m DIVOM Part 21 Closure Plan Slide 5
.a Plant-Specific DIVOM
- proposed approach
- Methodology described in NEDO-32465-A:
Establish initial MCPR prior to oscillation (IMCPR)
Calculate hot channel oscillation magnitude (HCOM)
Use fractional change in CPR vs. oscillation magnitude (DIVOM)
Follow process in NEDO-32465-A to develop plant-specific DIVOM No change to NEDO-32465-A and no planned generic submittals August 15, 2003 Stability Option HI DIVOM Part 21 Closure Plan Slide 6
-r I
Plant-Specif ic DIVOM - advantages/disadvantages Plant/cycle specific DIVOM is technically appropriate Addresses changes in core loading, fuel designs, and operating strategies not accounted for by generic DIVOM Follows NRC approved methodology (NEDO-32465-A)
Consistent with interim approach
- Advantages Closes Part 21 on setpoint methodology Allows for relatively quick OPRM arming of Option HI plants Reduces BWROG and NRC resource requirements
- Disadvantages Requires plant-specific analysis (TRACG or equivalent)
Setpoints may be too low for some plants (unnecessary scrams)
August 15, 20M Stability Option m DIVOM Part 21 Closure Plan Slide 7
Proposed Closure Plan Develop technical procedure for plant-specific DIVOM Provide consistency with NEDO-32465-A approach Provide consistency for all fuel vendors Continue to work with non-GE fuel vendors to perform plant-specific DIVOM analyses Plant implementation Select plant-specific DIVOM or DSS-CD MELLLA+ plants use DSS-CD Develop schedule Interim stability protection used until LTS implemented August 15, 2003 Stability Option Em DIVOM Part 21 Closure Plan Slido 8
N 'C NRC Comments and Feedback August 15, 2003 Stability Option III DIVOM Part 21 Closure Plan Slide 9