ML19199A275
| ML19199A275 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 07/24/1978 |
| From: | Metropolitan Edison Co |
| To: | |
| Shared Package | |
| ML19199A270 | List: |
| References | |
| TASK-TF, TASK-TMR TM-0848, TM-848, NUDOCS 7904100179 | |
| Download: ML19199A275 (4) | |
Text
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SPECIAL REPORT CONCERNING TdE YMI-2 ECCS ACTL'ATION OF 4/23/78 79041001T1 13'Of1
s At 1651:23 en L-23-78, TMI, Unit 2, experienced a reacter trip while at 30%
Rated Thermal Power with 3 reactor ecolant pumps in operation (ROP-2A secured) due to a noise epike on HIS power range detecter.
The reactor tripped because RP3 Channel C was already in the tripped state as required by Technical Specifi-cation 3.3.1.1 due to the inoperability of NI-7.
When the reactor tripped, the turbine tripped causing a very rapid pressure increase in the B stea: generator and a slightly slover pressure increase in the A generater. Four of the cix =ain stes= relief valves lifted en the B stea generator and very rapidly blev B side steam pressure down. One main steam relief valva " the A stea: generator lifted and also caused a rapid pressure blevdova buo e ;ut h0 seconds delayed frc the 3 stes: generator.
The 3 Our-bine Bypass va Ave received a signal to go full cpen but n'
ost inmediately received a signal to go full closed due to the rapid depressurizat'en in the 3 stean generator.
The A Turbine Eypass valve received a signal to open at the proper pressure but the signal to cpen the bypass valve vaa lover in mag-nitude than it should have been.
The four 3 side nain steam safety valves and the one A siie valve failed to properly reseat. The safety valves on the E side st1rted to reseat just prdor to two minutes into the event with the remainder cf the 3 safety valves and the A safety valve reseating almost four minutes into the e'ert.
The steam gener-ator pressures were between 550 and 600 psig when all safety valves reseated.
The operator teck the proper irrediate acticn in manually cutting back feedvater demand, shutting the letdcyn isolation valve, starting a seccnd makeup pump, and opening the high pressure injecticn valves en the side of the cperating takeup pumps. The operater failed ta initially recognize that the feed pump was in manual and did not run the feed pump speed back until'apprcxirately 1 minute and 20 seconds had elapsed.
Th6 Integrated Centrol of the feedvaner valves had not yet teen initially tuned at the time of the event.
Integral vice proportional centrol was the dominating signal of the feedvater valves and although the valves responded in the proper direction, they respended much sicver than the traditionally expected response. Thus, the feedvater valves sicvly going shut, rapidly decreasing stes: generator pressure and a ecnstant feed pump speed, too much water was fed into the steam generators.
The safety valves failing to reseat at the proper pressure ccupled with cverfeedir-the stea: generators caused a rapid depressurizaticn and eccidown of the reanter coolant syste:. The reacter ecolant temperature varied frca 583 F to h6hcF in 3 U
minutes. The RCS rhrinkage frc: the coc1down caused the pressurizer volume to drop below the minicus indicated level range approximately one minute after the reactor trip. D.e to the rapid depressurization of the R.C.S. SFAS safety injection eccurred % prcx cately cne minute after the trip.
Ey present design this injected NaOH into tle r, actor cooltat systen through the high pressure injection lines.
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? Prec:mrizer level was restored two minutec into the event as a result of safety injection, the Turbine 3ypass valve going shut and sene of the B side Main Steam Eelle-r Valves going shut. Feedvater latch occurred 2h =inutes into the event and terminated feedvater flov to the steam generators.
Feedvater latch was the key event in terminating the transient.
The rupid depressurizatica and cocidevn event caused violatiens of the following Technical Specificaticns.
1.
ECS Cooldcun limit of 100 ? in any cne hour was exceeded (rctual 13h in one heur) T.S. 3.L. 9.1.
2.
Fressurizer cooldown limit of 100 F in any one hcur was 2ceeded (actual 136CF in ene hc 2) - T.S. 3.k.9.2 3.
Fressurizer velune was less than that required c' y Technical Specificatien 3.h.L.
Calculaticns vere performed irrediately 1fter the event and subsequent chemistry analysis showed that the
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-as throughcut the tran-sie-t.
Evalus'icns of the excercive cccidcun rates cn the reacter vessel, reactor ecolant piping, pressurizer and steam generators h17e teen perferred by Esbecek and 'rlilecx and have teen reviewed by Metrcpolitan Ediscn. These evaluations conclude that the structural integrity of these reactor ecclant systen ec penents is acceptable
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In additicn, evaluaticns have teer perferred en the reactor ecolant pumps, control red drive rechanic s, and fuel cladding.
It has been concluded that these cct-ponents should centinue to perfcr= as designed.
13 013
e Areas of Corrective Action 1.
Prior to criticality, the relief valves vill be tested for proper lift pressure and also to ensure that blevdown is not excessive.
2.
NI-7 power range detecter has been replaced.
The source of the noise fron NI-8 is teing investigated. Tests vill continue in order to deter =ine the cause of the intercittent noise.
3 Discussions are undervey with the Cc==1ssien to change the SFAS logic to prevent innediate injection of NaCH through DE 'ISA & 3 cpen receipt of a safety injection signal.
h.
?aning of the Integrated Centrol Systen vill centinu: throughcut initial plant startup to achieve balanced tuning fer transient cperation.
l 5.
Plant cperating proced2res will te changed to reflect experience gained f
as a result of the transient.
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