ML060400058
| ML060400058 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 12/31/2005 |
| From: | Nuclear Management Co |
| To: | Office of Nuclear Reactor Regulation |
| spaulding D, NRR/DORL, 415-2928 | |
| References | |
| Download: ML060400058 (12) | |
Text
Duane Arnold..
Safe - Reliable - Predictable -
NRC Briefing HPCI December 2005
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Duane Arnold NR HPCI Operability Determination f C Briefing Interim Corrective Actions & Results vRoot Cause Evaluation
- Further Analysis VI co 2.K NMC Nuclear Excellence 2.
Operability Determination ssues Identified:
- Existence of a steam void at the top of the discharge pipe.
^ Identified non-conformances associated with T-TPflT A ;
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- Discharge piping should not have been insulated.
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- September 29 venting done at lower CAT eve
Operability Determination ctions Taken:
- Established Event Response Team
- Around-the-clock Engineering support.
- Obtained additional resources from Monticello and MPR.
- Successfully vented HPCI several times with higher CST level.
- Completed OE review:
- Internal
- External
- Operating Modes 7
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to Nu( JMC
,Iear Excellence 4
Operability Determination Actions Taken:
Evaluated Non-Conformances (insulation and high pipe temperatures).
Reviewed Transient Recorder data.
- Completed thorough system walkdown.
Note: Operations performs quarterly leakage detection walkdowns.
Static and dynamic testing performed.
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- Static - with pressure transducer.
- Dynamic - with accelerometer.
- Conducted three NMC challenge-boards('
NM Comtdto Nuclear ExceS 5
Operability Determination Potential Causes of Steam Void Formation:
- Valve leakage.
- Heat conduction from feedwater line.
- Lower CST water level.
NMC Nuclear Excelenc 6
==
Conclusions:==
- HPCI was capable of performing its safety function.
- Non-conformances do not impact system operability.
Steam volume near MO-23 12 disc does not cause ladetrimental later hammLer.
- Steam volume does not affect HPCI start times.
- Void size collapse similar for both surveillance and injection modes.
- No current or past evidence of water hammqr.
- HPCI declared Operable, but degraded & nod<
conforming on 10/12/05.
NMC to Nuclear Excellence 7 '
Interim Corrective Actions &
Results Interim Compensatory Actions:
1I. HPCI suction lined up to CST with water level of 15 ft or greater, otherwise HPCI keep fill system in service.
- i2.
Periodic venting of HPCI discharge piping.
- - Started at an increased frequency then extended out to TS SR frequency based on results.
- - Performed to validate conclusions of OPR.
- 3.
Shiftly monitoring of HPCI discharge piping temperatures.
Performed to verify void size does not change.
//
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Interim Actions & Results
-0Results:
Discharge pipe temperatures monitored shiftly.
Acceptance criteria: < 115 'C.
Results: Upper pipe temp steady @ - 113 'C.
Table below summarizes venting and temperature monitoring results:
ate Oct 14 Oct 17 Oct 21 Oct 26 Nov I Nov 8 Nov 22 Dec 6 ent 24 sec 8 sec 11 sec 28 sec 21 sec 15 sec 6.3 se seQc pe 113 0 C 1130 C 113 0 C 1130 C 113 0C 113 0C 114 0C emp Results support original conclusions i N
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Root Cause Evaluation Root Causes Ie effects of "turbulent penetration" were not taken into account in the original HPCI system design.
<- Unknown to the site, thermal energy was being delivered to MO-23 12 via the nhenornenon of turbulent penetration.
Thermal energy is being conducted through MO-2312's valve disc.
Steam is being produced on the low-pressure sice of the MO-2312 valve disc due to higher than designed temperature existing.
- Root Cause Evaluation
'urbulent Penetration:
- Previously un-recognized phenomena.
- Discussed in:
- IAEA-TECDOC-1 36 1, Assessment and management of aging of major nuclear power plant components important to safety, dated Juy20
- EPRI MRP-32, Thermal Fatigue Monito ing Guidance, dated April 2001.
NMC I to Nuclear Excellence I11I
Further Analysis Analysis to be performed:
- Determine bounding void size.
- Determine minimum CST water level to assure
- Determine effects of pipe movement with determined void size and collapse underma.
and automatic start scenarios.
Complete a past operability determin iŽ Current Schedule.,