ML20052B287
| ML20052B287 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Arkansas Nuclear |
| Issue date: | 03/19/1980 |
| From: | Hunter D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML18043A232 | List: |
| References | |
| FOIA-82-122 NUDOCS 8204300258 | |
| Download: ML20052B287 (3) | |
Text
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UNITED STATES 8%
NUCLEAR REGULATORY COMMISSION E
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MAR 19 ESQ MEMORANDUM FOR:
E. L. Jordan, Assistant Director for Technical Program, Division of Reactor Operations Inspectors, IE THRU:
J. E. Gagliardo, Acting Branch Chief, PAB, RCI FROM:
D. R. Hunter, Inspector Specialist, PAB, RCI
SUBJECT:
PROTECTION SYSTEMS ENVELOP TO ENCOMPASS CONTROL SYSTEM FAILURES
REFERENCE:
ELJ TO DGE, FEBRUARY 26, 1980 - SMALL BREAK LOCA RCP MANUAL TRIP.
8 HWW TO ELJ, FEBRUARY 5, 1980 - ANO-2 TRIP, JANUARY 29, 1980.
The possibility of a loss of Coolant Accident (LOCA) is small; but the safety valves, located on the pressurizer at the Pressurized Water Reactors (PWR) provides a finite possibility of a 4-inch LOCA, particu-larly following a severe plant transient similar to those which occur routinely at the facilities.
The PWR engineered safeguards systems (ESS) are not presently designed to cope with a water-break LOCA. The HPI systems are designed to provide core, decay heat / cooling by conversion of 100 F water to steam at 550*F (@
1000 BTU /lb of water), which requires " steaming the break." Consequently 1) the RCP's must be tripped automatically via the ESS protection systems or 2) the PWR plants must be provided with a high pressure cooling injec-tion system (HPCI) and/or an automatic depressurization system (ADS) similar to a boiling water reactor (BWR).
Core cooling at high and low pressure conditions could then be assured under the portulated accident conditions.
The overcooling transient, as occurred at the ANO-2 plant, demonstrated that the plant could and does survive this event without RCP's operating.
l Furthermore the continuing plant cooldown, due to a safety valve being stuck open on the steam generator secondary side or similar steam line rupture, does not appear to be non-conservative.
The "as-installed" high pressure injection system and emergency feedwater systems will and does, maintain core cooling. There is no need for natural circulation while the HPI is discharging to the reactor core / reactor coolant system (RCS) and " refilling" the reactor coolant system (RCS).
The core is being cooled and the HPI system flow (minimum considering a single failure) will return the plant to a sub-cooled system temperature and pressure condition, at which time the natural circulation will recommence and l
Attachment A
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maintain the reactor coolant system at hot shutdown (HSD) (S/G secondary safety valve setpoint - 554*F) conditions or intermediate shutdown (ISD),(depending upon the steam break size, availability of the secondary power operated relief valves / atmospheric dump valves, and specific operator actions performed) conditions.
The high pressure decay heat removal. system will maintain the plant at the above conditions for an analyzed period of time in preparation for plant cold shutdown for repairs, if necessary.
The emphasis of the NRC analysis should be directed at providing auto-matic interlock systems on the spray valves, atmospheric dump valves, and other non-essential equipment to prevent an overcooling incident from occurring at the PWR facilities.
This~, of course, includes adequate Class IE, redundant and separate features as appropriate.
Examples include:
Pressurizer power operated relief valves interlocks /permissives.
Pressurizer spray valves interlocks /permissives.
Steam generator atmospheric relief / power operated relief valves interlocks /permissives.
Decay heat removal valves (Main Steam System)-interlocks /permissives.
Condenser steam dump systems interlocks /permissives.
Main feedwater systems interlocks /permissives.
Consideration should be given to review of the generic and plant specific systems utilized for control purposes, such.as preventing the opening of g
code safety valves and normal plant cooldown, to determine the specific need for safety grade interlocks /permissives to prevent a malfunctioning control system from causing an incident.
&s D. R. Hunter Inspector Specialist, PAB, RCI
Attachment:
As stated
Contact:
D. R. Hunter 384-2657 M
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