ML19329E391
| ML19329E391 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 05/26/1978 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Howell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| NUDOCS 8006120706 | |
| Download: ML19329E391 (1) | |
Text
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"r-d 8 OT f2. A L F I L. E.'
MAY 2 61978 Docket No. 50-329 Docket No. 50-330 Constners Power Company ATTN: Mr. Stephen H. Howell Vice President 1945 West Parnall Road Jackson, MI 49201 Gentlemen:
The -1ased IE Circular No. 78-05, is forwarded to you for infor-nation. No written response is required. Should you have any questions
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related to your understanding of this matter, please contact this offica.
Sin - ely, James G. Keppler Director
Enclosures:
1.
IE Circular No. 78-05 2.
List of IE Circulars Issued in 1978
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THIS DOCUMENT CONTAINS
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POOR QUALITY PAGES
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U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT i
REGION III May 26, 1978 IE Circular No. 78-05 INADVERTENT SAFETY INJECTION DURING C00LDOWN Salem-1, a four-loop (cold shutdown) on JanuaryWestinghouse PWR, was being cooled f standby) to Mode 5 23, 1978. With one reactor cooling pump operating, the atomospheric relief valves on all four steam genarators were used to remove heat from the reactor coolant system. When reactor coolant pressure and average temperature were at 1500 psig and 403 degrees fahrenheit, an inadvertent safety injection occurred due to low pressure in the steamline from one of the steam generators. Water at 61 degrees f ahrenheit was transferred from the refueling water storage tank to the reactor coolant system resulting in thermal shock to the safety injec-tion nozzles. Operator action limited the duration of the safety injection to 2 to 4 1/2 minutes.
The nuclear steam system supplier had informed the licensee that 50 safety injections using refueling water at 40 degrees fahrenheit would not result in excessive stress at the safety injection nozzle. Because Salem-1 has had an unexpectedly large number of inadvertent safety injections, the licensee is taking action to reduce the frequency with which they occur.
There are a number of contributing factors which land to inadvertent safety inject' ion when the reactor is being cooled from Mode 3 to Mode 5.
These factors include: (1) operation of a single reactor coolant pump instead of reactor coolart pumps in opposed cooling loops, (2) lack of pressure recording instruments for the steamlines, and (3) use of atmos-pheric relief valves instead of steam dump valves.
The reactor vessel inlet nozzles for the four reactor cooling loops are not equally spaced on tha circumference of the reactor vessel. Two pairs of inlet nozzles are located on opposite sides of the vessel. The azimuthal separation between the inlet nozzles of each pair is approxi-mately 45 degrees. With one reactor coolant pump in operation, backflow occurs in the other three cooling loops and is expected to be greatest in the loop with the nearest adjacent inlet nozzle. Because of the different flow rates in the four cooling loops, the task of controlling the cooling di rate in each steam generator is difficult. If the atmospheric relief 3
y gt/ valves on each steam generator are positioned alike, the cooling rate will f[i\\g
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IE Circular No. 78-05 May 26, 1978 i
be greatest in the steam generator receiving the least reactor coolant aflow and thus the least heat. Therefore, the saturation pressure in that steam generator falls more rapidly than in the other steam generators.
When the pressure in any steamline is 100 psi less than the pressure in any two of the other three steamlines, a safety injection occurs.
So that the flow rates will be more nearly equal in the four reactor cooling loops, the licensee has changed the procedure for cooling from Mode 3 to Mode 5.
The revised procedure requires that two reactor coolant pumps in opposic; reactor cooling loops be in operation when available.
While cooling from Mode 3 to Mode 5, the Salem-1 operator acaitors the pressure in each steamline and adjusts the position of each atmospheric relief valve as necessary to maintain an equal rate of pressure decrease.
The operator's task is more difficult than necessary because steam genera-tor pressures are indicated but not recorded on the control panel.
I The steam generators can also be cooled using the steam dump valves when the condenser is available. The steam dump valves are in steamlines connecting the mixing bottle to the condenser. The mixing bottle is a large diameter manifold which receives steam from all four steam generators.
Use of the steam dump valves and the mixing bottla, instead of the atmos-pheric relief valves, causes heat transfer in each steam generator to be essentially self regulating and to tend to maintain the same pressure in each steamline. For this reason the licensee has changed the procedure for cooling from Mode 3 to Mode 5 to require that the steam dump valves l
be used when the condenser is available.
Holders of Operating Licenses for PWRs which have experienced problems with inadvertent safety injections during cooldown and holders of construction i
permits for PWRs should consider actions which would minimize the frequency of those occurrences.
No written response to this circular is required. If additional informatica is needed regarding this matter, please contset the Director of your NRC Regional Offica.
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IE Circular No. 78-05 May 26, 1978 LISTING OF IE CIRCULARS ISSUED IN 1978 Circular Subject Data Issued To No.
of Issue 78-01 Loss of Well Logging 4/5/78 All Holders of Well Logging Source Source Licenses 78-02 Proper Lubricating Oil 4/20/78 All Holders of for Terry Turbines Reactor Operating Licenses (OL) or Construction Permit (CP) 78-03 Packaging Greater Than 5/12/78 All Holders of Type A Quantities of Reactor Operating Licenses (OL),
Few Specific Activity Radioactive Material Construction Permits (CP), Fuel for Transport Cycle, Priority I Material and Waste Disposal Licenses 78-04 Installation Error That 5/15/78 All Holder of an NRC Could Prevent Closing of Operating License (OL) or Construction Fire Doors Permit (LT) l Enclosure Page 1 of 1
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