ML19225C892
| ML19225C892 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/15/1979 |
| From: | Counsil W NORTHEAST UTILITIES |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NUDOCS 7908030196 | |
| Download: ML19225C892 (4) | |
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June 15,1979 Docket No. 50-245 Mr. Boyce H. Grier Director, Region L Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406
Dear Sir :
Northeast Nuclear Energy Company (NNECO) responded to ISE Bulletin 79-08 on April 24, 1979, regarding the review of operational errors and system mis-alignments identified during the Three Mile Island incident. Following that submittal, conversations were held with SRC Staff members wherein it was deemed necessary to submit clarifying information. The attachment provides those clarifications. The paragraph numberc correspond to the numbers in the April 24, 1979 letter, and the changes are indicated in the margins.
Should you have any further questions, please contact us.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY
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The primary containment isolation design has been reviewed and it has been confirmed by this review that the required containment isolation does occur in parallel with the automatic initiation of any of the safety injection systems. This is because containment isolation and safety injection utilize the same water level sensors as shour in P&ID 719E553. The BWR design provides containment and reactor coolant pressure boundary (RCPB) isolation (excluding emergency core cooling and make-up systems). The isolation occurs upon reactor vessel low water level or high drywell pressure prior to or simultaneous with initiation of emergency core cooling and saf ety inj ec _ ion systems.
The isolation valves will remain closed until operator action is taken, even if the initiating signal clears.
(A detailed description of the containment and system isolations can be found in the Millstone 1 FSAR and they are su2marized in the hillstone 1 Technical Specifica-tions.)
4.
Reactor vessel water level in the BWR is continuously monitored by seven indicators or recorders for normal, transient a::1 accident conditions. Those monitors used to provide automatic safety equipment initiation are arranged in a redundant array with two instruments in each of two or more independent electronic divisions. Thus, adequate information is provided to automatically initiate safety actions and provide the operator with assurance of the vessel water level at all times.
In addition to this, the operating procedures reflect the requirements for the operators to also rely upon the information provided by the instrumentation discussed in (5b) below.
These water level measurement devices have operated in BWR plants for twenty years. Tests of EWR water level instrumentation under simulated steam and water line breaks have been conducted showing satisfactory performance; reference GE topical report NEDE-13117, Transient Testing of Yarway Level Instrumentation, April, 1970.
The range of reactor vessel water level from below the bottom of the active fuel area up to the top of the vessel is covered by a combina-tion of narrow and wide-range instruments.
Level is indicated and recorded in the control room.
A separate net of narrow-range level instrumentation on separate condensing chambers prosides reactor level control via the reactor feed water system. This set also indicates and records in the control room.
The safety-related systems or functions served by safety-related reactor water level instrumentation are :
408 144
i Reactor scram Feedwater coolant injection system (FWCI)
Core spray system (CS)
Low pressure coolant injection system (LPCI)
Automatic pressure relief system (APR) bbin steam isolation valve closure Primary containment isolation All systems automatically initiate on low reactor water level. The FWCI system will control in level control mode if and when level is restored to the normal operating range. The core spray and LPCI systems will continue to operate until manually shutdown.
In the unlikely event that vessel level indication were in doubt, the operators would continue to allow the FWCI, core spray and LPCI systems to operate, overflowing the vessel to the torus via the APR valves.
Existing procedures have been modified to clarify this operation.
5.
a.
The Millstone 1 plant 's procedures and traini-2 currently are in agreement with the NRC 's position on not ove-
.ing automatic safety functions.
b.
Over a dozen other types of instrumentation in the BWR provide the operator with indirect indication of reactor vessel coolant inventory changes and could inform the reactor operator of the need to take corrective actions. A review of operating and emergency procedures shows that various parameters are monitored for each type of accident.
Operators are required to first confirm that automatic functions have occurred.
Operator actions, as required in the procedures, are based upon a number of symptoms for each potential accident, and upon the monitoring of many redundant parameters; one of which is vessel water level.
Some of the instrumentation which the operator can use to determine changes in reactor coolant inventory or other abnormal conditions are:
Drywell high pressure-Drywell high radioactivity levels Suppression pool high temperature Safety relief valve (SRV) discharge high temperature High feedwater flow rates High main steam flow High containment and equipment area temperatures High differentisl flow-reactor water clean up system Abnormal reactor pressure High suppression pool water level High drywell and containment sump fill and pumpout rate An example of the use of this additional information by the operator is as follows: Drywell high pressure is an indirect indication of coolant loes.
Coincident high suppression pool temperature further verifies a loss of reactor coolant.
High SRV discharge temperature would pinpoint loss of coolant via an open valve.
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. Other instrumentation that can signal abnormal plant status, but not necessarily indicative of loss of coolant are:
High neutron flux High process monitor radiation levels Main turbine ster s instrumentation Abnormal reac*
recirculation flow High el e-"
.1 current (Amperes) to pump motors 6.
We have reviewed our procedures which relate to periodic surveillance of safety-related valve positions. These procedures have been revised to make them more inclusive. We have also reviewed the administrative procedures governing surveillance testing, maintenance and system / plant startup relative to safety-related valve position verification. The existing procedures for surveillance testing are adequate. The proce-dure for control of maintenance on safety-related equipment have been revised to specifically assure correct positioning of valves which were worked on or were used for isolttion purposes. As a normal practice required by Technical Specifications, the valve line-up lists are reviewed by the onsite operating review committee (PORC) to ensure proper valve positionlag prior to operation, any time modifications are made that could affect valve line-ups.
Simulated or actual auto-matic actuation and functional system testing is also required per Technical Specifications each refueling cycle on the ECCS systems:
core spray, LPCI, FWCT, Isolation Condenser, and APR.
In addition, the Millstone Station Administrative Control Procedures and the NUSCO Quality Assurance Program Topical Report require that system drawings including P&ID 's be updated any time modifications are made to af fected systems.
8.
c.
A licensed operator is required to authorize all maintenance, tests, or surveillance which affect plant systems. Prior to releasing the controlling document, the operator ensures he is aware of the effect of the activity on the system or equipment. Upon completion of the item, the document is returned to the operator for acceptance or tive procedures which control these evolutions provide the required explicit notification of operational personnel whenever a safety-related system is removed from and returned to service. The control room procedures assure that during shift changes, the oncoming shift is fully informed of any abnormalities in the plant, the equipment running, and other pertinent facts about the plant status.
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