ML20003A041
| ML20003A041 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 01/26/1981 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| IEB-80-17, NUDOCS 8101290231 | |
| Download: ML20003A041 (11) | |
Text
s
-o y_%
u V
F 6 CORSum8f5 g
w n
J
%w
} Power l
Company y
4s a
a J
D o
N h
General Offices: 212 West Michigan Avenue, Jackson, MI 49201 * (517) 7884550 C
b-E
+
January 26, 1981 Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Branch No 5 US Nuclear Regulatory Commission Washington, DC 20535 DOCKET 50-155 - LICENSE DPR BIG ROCK
."0 INT PLANT - BWR SCRAM SYSTEM - LONG-TERM EVALUATION OF SCRAM DISCHARGE VOLUME SYSTEM Consumers Power Company letter dated October 27, 1980, provided our commitment to perform an evaluation of the scram discharge volume system (SDVS) as re-quested by NRC letter dated October 1, 1980. As a member of the BWR Owners Group and its subgroup for the scram discharge volume, Consumers Power elected to use for the Big Rock Point long-term evaluation " Attachment 1 - Long-Term Evaluation Criteria for Scram Discharge System" developed by the subgroup as modified by " Attachment 2 - Clarifications of Applicability of Attachment 1 to the Big Rock Point Scram Discharge System Long-Term Evaluation." The clarifications of Attachment 2 are required because the subgroup criteria (Attachment 1) developed as a generic document for all BWRs do not directly apply to Big Rock Point in all cases because of significant design differences from the later model BWR designs used as the generic plant basis. Consumers Power submittals to the NRC in response to IE Bulletin No 80-17 and its supplements provided information to show that the Big Rock Point SDVS is of a significantly different design than that of the more recent BWRs (such as Browns Ferry 3).
To date, the only modification incorporated into the Big Rock Point SDVS to assure its operability involved the addition of an atmos-pheric scram dump tank vent which was required by IE Bulletin No 80-17, Supplement No 2.
The long-term evaluation of the Big Rock Point SDVS has been completed.
No significant deficiencies with respect to the evaluation criteria (Attachment 1 as modified by Attachment 2) were noted. Consumers Power was not able to I
complete the evaluation with appropriate reviews nor develop required correc-tive actions by December 15, 1980 commitment date. The preliminary results of this evaluation were completed and discussed with the NRC staf f on December 15, 1980. At that time, an extension was granted by the NRC staff based on our findings which indicated that no modifications wauld be required.
oc0181-0318a-71 b1O)
,f h f
Mr lDannis M Crutchfield 2
Big Rock-Point Plant January 26, 1981 Results'.of this evaluation are provided by " Attachment 3:- Results of Long-Term Evaluation for the Big Rock Point Scram Discharge Volume System." This attachment only addresses those criteria that have specific items where cor-rective actions or special clarifications are deemed necessary in order to show compliance with the intent of Attachment 1 as modified by Attachment 2.
In addition to the long-term evaluation, the acceptable operating history (in excess of 17 years), special scram tests and the differences in the Big Rock Point SDVS design from more recent BWRs indicate that only minor changes in-surveillance programs are required as corrective actions. The corrective actions that are identified in Attachment 3 will be implemented by May 1, 1981.
David P Hoffman (Signed)
David P.Hoffman Nuclear Licensing Administrator CC Director, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachments - 8 pages References (Associated with IE Bulletin No 80-17.and its supplements):
Subject NRC Letter Date Response Date IE Bulletin No'80-17 7/03/80 Item 1 - 7/10/80 (Af-firmation - 7/16/80).
Item 7 - 7/14/80 Items 4 & 6 - 7/23/80 Items 2, 3 & 5 - 7/31/80 Supplement 1 7/18/80 8/8/80 Supplement 2 7/22/80 7/25/80 Supplement 3 8/22/80-9/2/80 Supplement 4 12/18/80 1/16/81 oc0181-0318a-71 s
CONSUMERS POWER COMPANY-Big Rock Point Plant F
BWR SCRAM "YSTEM Response to NRC Letter Dated October 1, 1980 Docket No 50-155 License No DPR-6 At the request of the ~ Commission and pursuant to the Atomic Energy Act of'
-1954,.and the Energy Reorganization Act of 1974, as-amended,'and the Commission's Rules and Regulations thereunder,' Consumers Power Company submits results of our Long-Term Evaluation of the Scram Discharge Volume System in response to NRC letter dated October 1, 1980, entitled, "BWR Scram System,"
Consumers Power Company's response is dated January 26, 1981.
CONSUMERS POWER COMPANY By R C Youngdahl (Signed)
R C Youngdahl, Executive Vice President Sworn and subscribed to before me this 26th day of January 1981.
Linda K Carstens (Signed)
Linda K Carstens, Notary Public (SEAL)
Jackson County, Michigan My commission expires June 10, 1981.
nu0181-0318a-43
1 l
A'ITACHMENT 1 LONG-TERM EVALUATION CRITERIA FOR SCRAM DISCHARGE SYSTEM The utilities have reviewed General Electric's evaluation and are following the ongoing INP0/NSAC study on failure of the control rods to fully insert on a scram signal at Browns Ferry. The utilities agree that at Browns Ferry there was an undetected accumulation of water in the scram discharge volume.
Subsequent testing at some plants has also indicated that under certain conditions'the instrumentation may not give consistent level indication due to the piping configuration as it ties into the instrument volume.
Scope The following is a listing of design and operational criteria that shall be followed by the' utilities in formulating individual design changes. The criteria has taken into consideration the original system criteria, problems experienced in the operation of the system and concerns regarding operability and reliability. Criteria which have been.added or changed as a result of this evaluation are denoted by an asterisk (*).
For the purpose of this discussion, the work " system" includes all components downstream of the scram exhaust valves. The philosophy for evaluation of the design is that the safety function is of prime concern. The safety boundaries are whatever affects the scram function of the system. The evaluation must show that the safety boundaries considered meet this philosophy.
Functional Criteria
- The scram discharge volume shall have sufficient capacity to receive and contain water' exhausted by a full reactor scram without adversely affecting control rod drive scrsm performance.
Safety Criteria
- l.
No single active failure of a component or service function shall prevent a reactor scram under the most degraded conditions that are operationally acceptable.
- 2.
No single active failure shall prevent uncontrolled loss of reactor coolant.
- 3.
The scram discharge system instrumentation shall be designed to provide redundancy, to operate reliably under all conditions, and shall not be adversely affected by hydrodynamic forces or flow characteristics.
4.
System operating conditions which are required for scram shall be continuously monitored.
- S.
Repair, replacement, adjustment or surveillance of any system component shall not require the scram function to be bypassed.
.nu0181-0318b-43 i
e 2
ATTAC10fENT 1 Operational Criteria 1.
Level instrumentation shall be designed to be maintained, tested or calibrated during plant opr ation without causing a scram.
2.
The system shall include sufficient. supervisory instrumentation and alarms to permit surveillance of system operation.
3.
The system shall be designed to minimize the exposure of operating personnel to radiation.
- 4.
Vent paths shall be provided to assure adequate drainage in preparation for scram reset.
- S.
. Vent and drain functions shall not be adversely affected by other system interfaces. The objective of this requirement is to preclude water backup in the scram instrument volume which could cause spurious scram.
Design Criteria
- 1.
The scram discharge headers shall be sized in accordance with GE OER-52 and shall be hydraulically coupled to the instrumented volume (s) in a manner to permit operability of the scram level instrumentation prior to loss of system function. The analysis should show no need for vents or drains. Each system shall be analyzed based on a plant specific maximum inleakage to ensure that the system function is not lost prior to initiation of automatic scram. Maximum inleakage is the maximum flow rate through the scram discharge line without centrol rod motion summed over all control rods.
- 2.
Level instrumentation shall be provided for automatic scram initiation while sufficient volume exists in the scram discharge volume.
- 3.
Inst.umentation taps shall be provided on the vertical instrument volume and not on the connected piping.
- 4.
The scram instrumentation shall be capable of detecting water accumulation in the instrumented volume (s) assuming a single active failure in the instrumentation system or the plugging of an instrument line.
- 5.
Structural and component design shall consider loads and conditions including those due to fluid dynamics, thermal expansion, internal pressure, seismic considerations and adverse environments.
- 6.
The power-operated vent and drain valves shall close under loss of air and/or electric power. Valve position indication shall be provided in the control room.
nu0181-0318b-43 l
r I
I t
J ATTACH)1ENT 1
- 7; Any reductions in the system' piping flow path shall be analyzed to assure system reliability and operability under all modes of. operation.
- 8.
System piping geometry _(le, pitch, line size, orientation) shall be.such that the system drains continuously during normal plant operation.
- 9.
Instrumentation shall be provided to aid the operator in the detection of water accumulation in the -instrumented volume (s) prior to scram initiation.
- 10.
Vent and drain line valves shall be provided to.contain the scram discharge water with a' single active failure and to minimize operational exposure.
Surveillance Criteria
- 1.
Vent and drain valves shall be periodically tested.
- 2.
Verifying and level detection instrumentation shall be periodically tested in place.
- 3.
The operability of the entire syst i as an integrated whole shall be demonstrated periodically and during each operating cycle by demonstrating scram instrument response and valve function at pressure and temperature at approximately 50* control rod density.
[
nu0181-0318b-43
1 NITACE!ENT 2 CLARIFICATIONS OF' APPLICABILITY OF ATTACm!ENT 1 TO THE BIG ROCK POINT SCRA.! DISCHARGE SYSTEM LONG-TERM EVALUATION The design of the Big Rock Point scram discharge system is significantly different-from the BWR-2 and later designs. A scram dump tank, capable of accumulating discharge water from more than one scram, is provided with both level monitoring and automatic scram instrumentation to assure adequate scram
' discharge volume. Consumers Power Company's previous submittals in response to IE Bulletin No 80-17 and its subsequent supplements have provided a detailed description of the system and the results of scram tests which prove the system operates as designed in a safe and reliable manner. The long operating history, in excess of seventeen (17) years, of Big Rock Point and the numerous satisfactory operations of the scram system indicate system modifications are probably not warranted and could prove counterproductive.
The following provides clarifying positions, with respect to Attachment 1, that Consumers Power Company will use in its formal long-term evaluation of the Big Rock Point scram dischcrge system to assure its continued safe and reliable operation. The clarifying positions are identified in accordance with the format and. numbering scheme used by Attachment 1.
Safety Criteria 2.
The ability of the scram valves and scram dump tank vent and drain valves shall be evaluated to assure the consequences of any single active failure is bounded by previously analyzed accidents.
3.
The scram discharge system instrumentation redundancy shall be evaluated to assure automatic scram capab.'lity with sufficient scram dump capacity in accordance with the Functiona. Criteria of Attachment 1.
5.
The input of a trip signal for a rsmoved component is acceptable to meet this criteria.
Operational Criteria 1.
The clarification for Safety Criteria 5 applies.
Design Criteria 1.
This criteria shall be applied to the scram dump tank which provides the same function as the scram discharge headers in more recent BWR designs.
3.
This criteria is currently met by the Big Rock Point design which provides instrumentation taps on the scram dump tank that act as both the scram discharge and instrument volumes of more recent BWR designs.
4.
The absence of plugging of it.strument lines shall be verified by periodic testing which may be accomplished without degradation of system function nu0181-0318c-43
e.
2 ATTACHMENT 2 because of the instrumentation and large scram dump tank capacity provided in the Big Rock Point design ~.
3.
Structural and component design as affected by seismic considerations and adverse environments will be considered under the ongoing Systematic Eval
- 11>n Program (SEP) in which Big Rock Point is involved.
10.
The uarification for Safety Criteria 2 applies.
Surveillance Criteria 2.
The clarification for Safety Criteria 5 applies.
3.
It-is believed that the intent of this criteria is to perform testing in accordance with Item 2 of IE Bulletin No 80-17, and as such, will not be applied to Big Rock Point because of its design differences and the potential deleterious effects-it can have on the rest of nuclear steam supply system. The scram. dump tank design provides a continuously monitored and sufficiently large discharge volume to assure scram system operability. This criteria is only considered necessary tur mere recent BWR designs which utilize scram discharge header piping that do not provide direct measurement capability for the entire scram discharge volume.
nu0181-0318c-43 l
t
P 1
ATTACHMENT 3 RESULTS OF LONG-TERM EVALUATION FOR THE BIG ROCK POINT SCRAM DISCHARGE VOLUME SYSTEM Significant differences exist between the Big Rock Point and later BWR designs with_ respect to the scram discharge volume system (SDVS) as described previously in Consumers Power Company submittals in response to IE Bulletin No 80-17 and its supplements and the introductory paragraph to " Attachment 2 -
Clarifications of Applicability of Attachment 1 to the Big Rock Point Scram Discharge System Long-Term Evaluation." The most significant of these differences involve the following:
1.
A small core design requiring only 32 control.ods which travel approximately six feet from the fully withdrswn to the fully inserted position, thereby resulting in a significantly smaller scram water discharge to the SDVS than for larger core design plants.
2.
The amount of scram water discharge as described in 1 above allows the use of a scram dump tank (SDT) to receive the entire volume of water dis-charged during a scram. The Big Rock Point design uses a continuously monitored SDT which incorporates tank level annunciation and automatic scram (prior to inadequate remaining v nume in the SDT to accept a full scram of all drives from the fully withdrawn position) instrumentation.
The results of the long-term evaluation provided herein only address specific items where corrective actions or special clarifications are deemed necessary to show compliance with the intent of the BWR Owners Group evaluation criteria (Attachment 1 as modified for application to Big Rock Point by Attachment 2).
Detailed results of the entire evaluation are available for review on site.
The results of the evaluation indicate that modifications to equipment and system design are unnecessary and that corrective actions involve testing and surveillance program modifications. The following provides a summary of those corrective actions which Consumers Power Company has or is in the procces of implementing and special clarifications showing compliance with evaluation criteria:
(NOTE: Corrective actions and clarifications are identified in accordance with the format and numbering scheme used by Attachment 1).
Safety Criteria 3.
The evaluation indicated a need to demonstrate that adequate volume exists in the SDT to allow a full automatic scram (resulting from SDT high-level scram circuitry) of all rods from the fully withdrawn position. This action was determined necessary in view of the clarification for this criteria by Attachment 2 and the inability to find sufficiently documented information on this subject.
It should be noted that original design and acceptance test information implied that this position could be met, but it was determined prudent to verify this information by test and/or calcu-lation. Therefore, a special site test was conducted on December 19, 1980 (during a refueling outage with no fuel in the reactor) which verified that adequate volume exists in the SDT to accept a full automatic scram of nu0182-0318d-43
?
6 2
ATTACHMENT 3 all control rods. Also, calculations were made to determine how many full scrams could be discharged into an empty SDT. These calculations were based on vendor instructions GEI-56217 because GE OER-54 (incorrectly stated as GE OER-52 in Attachment 1 - Design Criteria 1) is only applica-ble to BWR 2 through BWR 6 plants.
It was concluded from the calculations that two full scrams of-all control rods could be accommodated by an empty SDT. Therefore, no additional action is proposed with respect to this criteria.
5.
The reactor protective system design (including the SDT high-level scram sensors) is such that if a sensor is disconnected for maintenance it will automatically cause a trip on the safety channel to which the sensor is connected (Technical Specifications, Section 6.1.1).
Therefore, the scram function cannot be bypassed during the performance of maintenance activi-ties. The good operational history (in excess of 17 years) and the redun-dancy provided in the SDT high-level scram sensors makes the replacement of the sensors unnecessary during reactor operation. Therefore, our maintenance practice involving repair, calibration and testing of the sensors will continue to be performed during refueling outages.
Operational Criteria 1.
Clarification for Safety Criteria 5 - Attachment 3 applies.
NOTE: Our response dated August 8, 1980 (to Supplement 1 of IE Bulletin No 80-17) incorrectly stated the model number and rating for level switches RD 08A through RD 08E. The model number should be 402-X and not 102. The units are rated for a working pressure of 1700 psig at 615'F and not 1668 psig at 800 F.
Design Criteria 1.
Discussion for Safety Criteria 3 - Attachment 3 applies.
5.
The evaluation indicates a need to add the 3/4" equalization line vent piping (from the 26" loop seal, on the inlet header just prior to the SDT, to the reactor - Drawing No 0740G40122) to the Inservice Inspection Program. This line was installed in 1966 to prevent control rod drift after a scram by equalizing pressure between the SDT and reactor. During its service life (in excess of 13 years), no degradation has been noted in this 3/4" equalization line. The evaluation review was unable to locate specific design information for this line; therefore, this line will be added to our Inservice Inspection Program to assure continued satisfactory performance.
6.
SDT vent and drain valve position indication is provided in the Control Room by a single set of lights for both valves.
If the system shows a malfunction, the valve positions are physically checked (access to these valves is available during reactor operation). Drain valve closure may also be indicated by the SDT high-level alarm resulting from water nu0181-0318d-43
f
^
^
3 ATTACHMENT 3
- accumulation in the SDT. Therefore, existing valve position indication in the Control Room is considered satisfactcry.
Surveillance Criteria
- 1. and 2.
.SDT vent and drain valves' operability and the.SDT level detection instrtmentation are tested at each refueling outage under the current surveillance test program. The evaluation identified a conflict between the surveillance test designations (each refueling) and the alternate test interval (12 months) specified by the Technical Specifications. The Technical Specifications require that' reactor safety system scram circuits (requiring plant shutdown to check) shall be conducted during each major refueling shutdown, but no less frequently than once every 12 months.
This conflict has not resulted in a Technical Specifications violation, but it is considered prudent to modify the surveillance test program to eliminate such an occurrence. Therefore, the test status boards will be changed to identify both the primary test interval (each refueling) and the alternate test interval (12 months).
3.
As discussed in Attachment 2, these criteria are not considered applicable to-Big Rock Point. The acceptable operating history (in excess of 17 years); scram tests conducted pursuant to Item 2 of IE Bulletin No 80-17; and,.the scraz test discussed by Attachment 3 for Safety Criteria 3 and Design Criteria 1 demonstrate the acceptability and dependability of the scram discharge system.
nu0181-0318d-43