ML19249D340
| ML19249D340 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/07/1979 |
| From: | Minners W NRC - TMI-2 LESSONS LEARNED TASK FORCE |
| To: | Mattson R NRC - TMI-2 LESSONS LEARNED TASK FORCE |
| References | |
| NUDOCS 7909240178 | |
| Download: ML19249D340 (2) | |
Text
_ ff, AUG 0 71079 Docket No. 50-320 EMORANtw FOR: Roger J. Mattson, Director, lessons Learned Task Force FROM:
Warren Minners. Lessons Learned Task Focce.#
Sth1ECT:
JAPANESE RESPONSE TO TMI The recommendations of NUREG 0578 were discussed with Mr. K. Aisaka. Director.
Division of Nuclear Power Examination Safety. Agency of Natural Resources and Energy. Ministry of International Trade and Industry (MITI) in Bethesda on July 30 & 31.1979. The proposed changes to Japanese plants as a result of the TMI accident and an incident at the Oh11 plant were also discussed.
Proposed Changes All operating PWRs in Japan are of Westinghouse design and the only proposed change resulting fram the TMI-2 accident is the modification of the pressurizer pressure / level coincident signal for ECCS initiation. The coincident low pres-sure and low level signal (which is a 1/3 logic) will be retained but a partial-ly independent low pressure ECCS initiation signal will be added. This signal will have indMendent logic (2/4 in two loop plants and 2/3 in three loop plants) but will use tw same pressure transmitters as and will be set 100 psi lower than the pressure in the coincident circuit.
The Japanese have more concern than we that EECS will unnecessarily actuate and subja:t the system to a themel cycle. Therefore the Oht 1 & 2 units will not have the additional pressure signal because they are ice condenser plants with a very low setting of the containment pressum ECCS signal. Following a FW trip with a stuck open relief valve. the containment h$gh pressure safety injection signal occurs relatively early (600 sec) and the core quality is always low (21).
They apparently feel that the possible consequence of this event does not justify the possible increase in the frequer4y of unnecessary ECCS actuations.
In the other plants the containment signal is late (1367 to 4000 sec) and quality in the core is greater (ep to 71). These other plaats will be modified to include the independent pressure signal.
In plants with the added fadopendent pressure signal, taterlocks will also be added to prevent unnecessary ECCS actuation fier two possible events. If the pressurizer pressure control logic caused the spray vllve to fall opet, the h
coincident signal would not be actuated because the pressurizer level would no i
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- ,,- AUG 0 7 B79 reach the set yoint, but the pressure would go below the independent pressure set point. Therefore an interlock will added to the spray valve control to prevent opening the valve below 154 kg/
(2193 psig).
If a reactor coolant pump starts at a pressure below 140 kg/cm2 (1993 psig) when ECCS actuation is blocked, the pressure will rise above this pressure and then fall below the independent pressure signal set point. To prevent ECCS actuation in this case the independent peessure, but not the coincident pressure signal, will be interlocked with the intenaldiate neutron flux.
i Two other events were analyzed, but no changes were judged to be necessary. Loss of the pressurizer heaters would also result in the pressure falling below the in-dependent pressure signal set point. However this would not occur until after one hour, which is considered sufficient time for the operator to take cot;rective ac-tion. The-final event analyzed was continued FW flow after a reactor trip which would reduce pressure but not low enough to actuate the independent pressure sig-nal.
Oh1 1 Incident A recent incident at Ohi 1 was interpreted by the operators to be a TMI-2 type event. A short caused by twisted wires at a connector initiated a low flow reac-tor trip signal. (The circuit hhd a 1/1 logic.) The resulting transient caused the secondary system relief valve to open 2 minutes after the reactor tripped be-cause the valve set point was inddvertently set too low. The blowdown through the valve caused the steamline differential pressure (between steamlines) to trip and actuate ECCS. During the transient the RCS pressure fell and returned rapidly to near the initial valve. The high rete of pressure change xcesed the pressuri-zer relief valve to open. The operator checked the pmssure control system and primary to secondary leakage. After 9 minutes the operators plotted the'RCS pres-sure and temperature to assere adequate subcooling, checked pressurizer level (in-creased to 75% from normal 605) AFW pump operation. SG 1evel, pain steamline valves closed, and containment supp level and then reset safety injection after 13 minutes.
About two tons of water were added by the HpIS during the incident.
DISTRIBUTION:
Watten Minners Docket Files 50-320 Z. Rosztoczy Lessons Learned Task Force Central Files E. Case NRR Rdg. File D. Vassallo LLTF Rdg. File PDR V. Stello LPDR D. Eisenhut j
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NRC Form 3188 (4 79) NRCM 0240 e.
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