ML20027C437
| ML20027C437 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 10/13/1982 |
| From: | Toner K CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-05-11.A, TASK-05-11.B, TASK-5-11.A, TASK-5-11.B, TASK-RR NUDOCS 8210150533 | |
| Download: ML20027C437 (4) | |
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Consumers Power Company oeneral offices: 1946 West Pernell Road. Jackson, Mt 49201 * ($17) 788 0650 October 13, 1982 Dennis M Crutchfield, Chief Operating Reactors BrancL s' 5 Nuclear Reactor Regulation US Nuclear Regulatory Commissist Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - SEP TOPICS V-11.A, REQUIREMENTS FOR ISOLATION OF HIGH AND LOW PRESSURE SYSTEMS AND V-11.B, RHR INTERLOCK REQUIREMENTS The purpose of this letter is to provide Consumers Power Company comments regarding the NRC's August 12, 1982 final Safety Evaluation Report (SER) concerning SEP Topics V-11.A, Requirements for Isolation cf High and Low Pressure Systems, and V-11.B RHR Interlock Requirements for the Big Rock Point Plant. Consumers Power Company has reviewed the Big Rock Point Shutdown Cooling System (SDCS) and the Core Spray System (CSS), against appropriate Branch Technical Positions (BTP) and Standard Review Plans (SRP) and oncludes that further modifications are not warranted.
Consumers Power Company assessment of the SDCS and CSS is provided in the following discussions:
Shutdown Cooling System (SDCS)
Although the staff is correct in concluding that the existing interlocks for the isolation valves are not diverse, as recommended by BTP RSB-5-1, it should be noted that if one pressure switch or auxiliary relay were to fail one MOV in the suction line and one MOV in the discharge line would remain closed.
Also, the Big Rock Point System Operating Procedure SOP-5 provides for proper system operation and Technical Specifications require that breakers for the isolation valves be checked "open" when reacto pressure is greater than 300 psig. These breakers are also caution tagged while in the open position.
I Furthermore, the NRC safe j evaluation of triis to,ic (NRC letter dated August i
14, 1981) states:
"The staff does not recommend.nedification of the SDCS because the present design satisfies the single failure criterion and further modifications will not provide significant improvement in the protection of the public health and safety."
ON oc1082-0053bl42 8210150533 821013 PDR ADOCK 05000155 P
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D M Crutchfield, Chief 2
Big Rock Point Plant SEP Topics V-11.A & V-11.B October 13, 1982 Core Spray System (CSS)
As part of Enclosure 2 to its August 12, 1982 SER, the NRC concludes that CSS control should be' modified to satisfy the interlock provisions of SRP 6-3 and BTP RSB 5-1.
As described in the Enclosure, the NRC bases its conclusion on the following two assertions:
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- 1) the CSS has no interlocks to prevent opening the isolation valves from the local control station when Reactor Coolant System (RCS) pressure exceeds CSS design pressure and i
- 2) the CSS does not satisfy the single failure criterion because a check valve failure alone may result in a loss of the CSS during accident conditions since there are no suitable provisions to augment adminis-trative controls over the operator's actions when valve action is desired.
In the opinion of Consumers Power Company, the design and operation of the CSS i-meets the intent of the single. failure criterion and, therefore, does not require modification. The opinion of Consumers Power Company is described in the paragraphs that follow.
Regarding CSS valve interlocks, it should be noted that letter R A Vincent to D M Crutchfield dated November 12, 1981 (refer to page 5, paragraph 4 of the subject letter) stated that neither of the four isolation valves (M0/7051, M0/7061, M0/7070 nor M0/7071) feature interlocks to prevent opening the valves from the control room when RCS pressure exceeds the CSS design pressure.
In addition, the letter states that valves M0/7070 and M0/7071 can also be opened from the local control station when the RCS pressure exceeds the CSS design pressure. As documented in the August 12, 1982 SER, the NRC is particularly concerned about the ability to open CSS isolation valves-from the local control station. As perceived by Consumers Power Company, this concern was generated since the NRC believes that local control stations are areas where plant activities are generally less controlled than those in the main control room. Therefore, it is the opinion of the NRC that the likelihood of opening the valves when RCS pressure is greater than CSS design pressure is greater at the local control station than in the main control room.
Overpressurizing the CSS by opening the CSS isolation valves from the local control station is very unlikely. First of all, it should be noted that only the backup CSS consists of isolation valves that feature local control. As shown in Attachment #6 (see schemes #B163 and B152) of the Consumers Power Company November 12, 1981 submittal, isolation valves M0/7070 and M0/7071 feature pushbuttons at local control stations N63 and N52, respectively, which can be used to open the valves. Attachment #7 (see schemes #5601 and 5602) of the Consumers Power Company submittal reveals that neither of the primary CSS isolation valves, namely M0/7051 nor M0/7061, features local control circuitry. The NRC concern of opening the valves from the local control station, therefore, does not apply to the primary CSS. Although the backup CSS isolation valves can be opened locally, inadvertent overpressurization of oc1082-0053bl42
D M Crutchfield, Chief 3
Big Rock Point Plant SEP Topics V-11.A & V-11.B October 13, 1982 the CSS by operator error is very unlikely since both isolation valves (namely M0/7070 and M0/7071) would have to be opened concurrent with a failure of the backup CSS isolating check valve VPI 303 (see Attachment #5 of the Consumers Power Company submittal) which by design unseats only when the RCS pressure decreases below the CSS pressure.
Although it could be argued that an operator could make an erroneous decision at the system level to initiate either CSS when the RCS pressure exceeded the CSS design pressure (regardless of whether action is taken in the main control room or at the local control station), overpressurization of the CSS remains very unlikely. Overpressurization of the CSS is highly unlikely primarily due to the isolating check valve in each CSS line (ie, VPI 303 in the backup CSS and VPI 304 in the primary CSS). Consumers Power Company confidence in the ability of each of the check valves to isolate the RCS from the CSS is a result of frequent on-line testing. Such testing verifies that each of the check valves is properly seated and is preventing RCS pressure from entering the CSS.
Technical Specification Surveillance Test T30-22 " Emergency Core Cooling System Valve Tests" Rev. 17 is performed monthly.
The test requires that for each CSS the motor-operated isolation valve on the reactor side of the isolating check valve (ie, M0/7061 and check valve VPI 304 in the primary CSS and M0/7071 and check valve VPI 303 in the secondary CSS) be opened. When the reactor-side motor-operated isolation valve is opened, check valve leakage can be detected through the normally open telltale line which is installed adjacent to the check valve on the side opposite the RCS (see Attachment #5 of the Consumers Power Company submittal) by an operator who is stationed inside containment during this portion of the test.
It should be noted that each telltale valve is normally open and a small hole is drilled into the bottom of a pipe cap which is screwed onto the end of the telltale line.
The drilled cap effectively provides a permanent vent to atmosphere for the telltale line and is located in an area which is readily observable by an operator. Also, Consumers Power Company has recently take,n action to modify procedure T30-22 to specifically require that each telltale line be observed for leakage when l
its associated reactor-side motor-operated isolation valve is opened.
Such frequent on-line verification provides more than an adequate measure of the ability of each check valve to remain seated and isolate the RCS from the CSS.
Regarding the single-failure criterion, it is the opinion of Consumers Power Company that the design and operation of the CSS meets the intent of such i
criteria. This opinion is based on the fact that overpressurization of the CSS can only occur if two independent failures occur simultaneously:
the failure of the isolating check valve which is monthly tested while at power and an operator error which results in opening both in-series motor-operated I
isolation valves.
In conclusion, both the Consumers Power Company review of the CSS and the fact that the Big Rock Point ECCS was given a lifetime exemption from 10 CFR 50.46 and Appendix K by the NRC for the specific case of a LOCA caused by a break in either core spray line (NRC letter dated May 26, 1976) serve to collectively oc1082-0053bl42 j
D M Crutchfield, Chief 4
Big Rock Point Plant SEP Topics V-11.A & V-11.B October 13, 1982 demonstrate that the CSS is designed to perform its function and provide the necessary protection for the health and safety of the public.
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Kerry A Toner Senior Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point oc1082-0053bl42
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