ML16342A619
| ML16342A619 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 12/30/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16342A620 | List: |
| References | |
| NUDOCS 9901050166 | |
| Download: ML16342A619 (10) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&4001 EVALU E
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The Code ofFedera/ Regulations, 10 CFR 50.55a, requires that inservice testing (IST) of certain American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 pumps and valves be performed in accordance with Section XI of the ASME Boilerand Pressure Vessel Code (the Code) and applicable addenda, except where alternatives have been authorized or relief has been requested by the licensee and granted by the Commission pursuant to Sections (a)(3)(i), (a)(3)(ii), or (f)(6)(i)of 10 CFR 50.55a.
In proposing alternatives or requesting relief, the licensee must demonstrate that (1) the proposed alternatives provide an acceptable level of quality and safety; (2) compliance would result in hardship or unusual difficultywithout a compensating increase in the level of quality and safety; or (3) conformance is impractical for its facility. Section 50.55a authorizes the Commission to approve alternatives and to grant relief from ASME Code requirements upon making the necessary findings. Guidance related to the development and implementation of inservice testing (IST) programs is given in Generic Letter (GL) 89-04, "Guidance on Developing Acceptable Inservice Testing Programs," issued April 3, 1989, and its Supplement 1 issued April4, 1995. Additional guidance can be found in NUREG-'1482, "Guidelines for Inservice Testing at Nuclear Power Plants," NUREG/CR-6396, "Examples, Clarifications, and Guidance on Preparing Requests for Relief from Pump and Valve Inservice Testing Requirements," and "Summary of Public Workshops Held in NRC Regions on Inspection Procedure 73756, 'Inservice Testing of Pumps and Valves,'nd Answers to Panel Questions on Inservice Testing Issues."
The 1989 Edition of the ASME Code is the latest edition incorporated by reference in Paragraph (b) of Section 50.55a.
Subsection IWP of the 1989 Edition, which gives the requirements for IST of pumps, references Part 6 of the American National Standards Institute/ASME Operations and Maintenance Standards (OM-6) as the rules for IST of pumps.
OM-6 replaces'specific requirements in previous editions of Section XI, Subsection IWP of the ASME Code.
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2.0 By letter dated December 12, 1997, Pacific Gas and Electric Company (PG&E), submitted a new pump relief request P-RR5 for the second ten-year interval for Diablo Canyon Power Plant (DCPP), Units 1 and 2 Inservice Testing (IST) Program.
P-RR5 would allow auxiliary saltwater pump (ASWP) testing using an evaluation of pump performance compared to pump curves in lieu of Operation and Maintenance (OM) Part 6, "Inservice Testing of Pumps in Light-Water Reactor Power Plants," paragraph 5.2(b). PG&E states that compliance with OM Part 6 requirements for ASWP performance testing is impractical due to varying flow rates based on tide level (suction pressure) and heat exchanger differential pressure (system resistance),
which cannot be readily controlled. The NRC staff issued a request for additional information (RAI) related to pump relief request P-RR5 on June 2, 1998.
PG&E responded to the RAI by letter dated August 31, 1998.
As stated in the licensee's December 29, 1995, submittal, the start date for Unit 1's second interval IST progr'am is January 1, 1996, which corresponds approximately with the completion of Unit 1's seventh refueling outage.
The start date for Unit 2's second interval is June 1, 1996, which corresponds approximately with the completion of Unit 2's seventh refueling outage.
[These start dates constituted a change from PG&E's original plan to place both units on a concurrent testing interval starting in November of 1995 as stated in PG&E letter DCL-94-231, dated October 18, 1995.] The DCPP IST program was developed to the requirements of ANSI/ASME Operations and Maintenance (OM) Standard OM-1987 with addenda through OMa-1988. [Reference PG&E second 10-year IST program submittal for DCPP dated December 29, 1995 (DCL-95-288), and NRC safety evaluation dated June 24, 1997.]
DCPP utilized pump curves for evaluation of ASWP performance during the first 10-year interval as identified by a note in the IST Program Plan. PG&E did not apply for a relief request for the second 10-year. interval. PG&E is currently testing using a reference flowvalue in accordance with OM Part 6; however, as described in the relief request [and elaborated on in the licensee's August 31, 1998, response to the staffs RAI],the configuration required to achieve thiscondition is highly undesirable.
This undesirable configuration was noted in NRC Design Inspection Report Nos. 50-275/97-202 and 50-323/97-202, dated November 13, 1997 (Section E1.2.1.2.f).
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-R NGE P-RR5 pertains to the four ASWPs for DCPP Units 1 & 2 (ASW Pump 1-1, 1-2, 2-1, and 2-2)
The licensee requests relief from Section 5.2(b) of OM-6 for the four ASWPs. This section of the ASME Code requires that "Pressure, flow rate, and vibration (displacement or velocity) shall be determined and compared with corresponding reference values.
Alldeviations from the reference values shall be compared with the limits given in Table 3 and corrective action taken as specified in para. 6.1."
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~f The auxiliary saltwater (ASW) system supplies cooling water from the ultimate heat sink, the Pacific Ocean, to the component cooling water (CCW) heat exchangers.
The CCW system, in turn, removes heat from nuclear primary plant equipment and components during normal plant operation, plant cooldowns, refueling and accident conditions, including a loss-of-coolant accident.
Each DCPP unit is provided with two redundant ASW trains.
Each of these trains consist of a full capacity ASWP and associated piping to supply the tube side of one of the CCW heat exchangers with cooling water.
Each pump may also be cross-connected so as to supply the opposite train heat exchanger.
3.1 Licensee's Basis for Request The licensee provided the following basis for the relief request:
Adjustment to a specific reference value for the ASWP test is not practical because the pump flow rate varies based on tide level (suction pressure) and heat exchanger differential pressure (system resistance), which cannot be readily controlled. The CCW heat exchanger outlet throttle valves are the only valves which can be adjusted to set ASWP flowat the desired test flow. These valves are sealed in a throttled position which ensures the train can perform its required safety function under worst case conditions. A CCW heat exchanger is considered inoperable after its outlet valve is adjusted until a flowveriTication test is performed.
The fiow verification test requires that the system alignment with the most system resistance i.e., ASW pump ¹1 to CCW heat exchanger ¹2 (or ASW pump ¹2 to CCW heat exchanger ¹1) be used.
This realignment, test and subsequent data analysis takes several hours, during which time the CCW heat exchanger is inoperable.
Diablo Canyon Technical Specifications require that the second vital CCW heat exchanger be placed in service whenever ultimate heat sink temperature is greater than 64'F.
In order to meet the Technical Specification LCO, ASW pump tests performed when ultimate heat sink temperatures are above 64 F must be performed with two CCW heat exchangers in service and result in test flows of up to 14,000 gpm. When the test is run with only one CCW heat exchanger in service (normal test alignment),
reference pump flow is between 11,500 and 12,500 gpm. Relief is requested per 10 CFR 50.55a(f)(5)(iii).
3.2 Proposed Alternate Testing The licensee proposed the following:
Perform inservice tests on ASWPs using guidance from NUREG-1482,-
paragraph 5.2. A reference pump curve (flow rate vs. pump head) willbe developed for each of the four ASWPs.
The following elements willbe performed in developing the pump curves for testing the ASWPs:
Pump reference curves willbe developed when the pumps are known to be operating satisfactorily.
Instrumentation used to develop pump curves is at least as accurate (accuracy and range) as required by OM Part 6, Table 1.
3.
4, These pump curves willbe constructed using a minimum of five points.
Points used to construct the curves are beyond the flat portion (low flow rates) of the pump curve in a range which includes the design bases flow rate.
5.
Acceptance criteria for flow rate and differential pressure willbe established by taking the more conservative of curves based on the limits of OM Part 6, Table 3b, or the operability criteria in TS or Safety Analysis
'eport.
6.
Vibration levels will be measured over the range of pump conditions, and appropriate vibration acceptance criteria based on OM Part 6, Table 3a, will be assigned for regions of the pump curve.
7.
A new reference curve will be prepared, or the previous curve willbe
. validated, ifthe pump curve is affected by replacement, repair, or routine service.
3.3 Evaluation The Code requires that either the resistance of the system be varied until the flow rate equals the reference value or the flow rate be varied until the pressure equals the reference value.
Then either pressure or flow is recorded and compared with the Code pump acceptance criteria. The licensee has stated that it is impractical to establish repeatable reference values.
Section 5.2 of NUREG-1482, "Guidelines for Inservice Testing at Nuclear Power Plants," states that the use of reference curves is not currently addressed by the Code and relief is required.
Section 5.2 provides guidance for the use of variable reference values for flow rate and differential pressure during pump testing (i.e., reference curves).
NUREG-1482 states that if the licensee implements this guidance, it must demonstrate the impracticality of achieving reference conditions for IST. The licensee states that adjustment to a. specific reference value for the ASW pump test is not practical because the pump flow rate varies based on tide level (suction pressure) and heat exchanger differential pressure (system resistance), which cannot be readily controlled. The CCW heat exchanger outlet throttle valves are the only valves which can be adjusted to set ASW pump flow at the desired test flow. These valves are sealed in a throttled position which ensures the train can perform its required safety function under worst case conditions. As indicated by the licensee, system realignment and flowverification
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4 following any adjustments to these valves can take several hours and is further complicated when both CCW heat exchangers are required to be in service (i.e., when ultimate heat sink temperature is above 64'F).
In its August 31, 1998, response to the staffs RAI, the licensee elaborated on the impracticality of testing the ASW pumps when both CCW heat exchangers are required to be in service.
Ifan ASWP test were required to be performed in this configuration, the outlet valves for both CCWHXs would be required to be throttled to achieve the ASWP reference flow and pressure.
Since throttling the outlet valves of the CCWHXs renders them both inoperable, both trains of CCW would be rendered inoperable and the action statement of TS 3/4.7.12 could not be satisfied.
Either both CCW trains inoperable or failure to meet the action statement TS 3/4.7. 12 requires application ofTS 3.0.3, which requires initiation of a shutdown within one hour.
The staff finds that CCWP testing in accordance with the Code, while practical, imposes a hardship on the licensee, particularly when Pacific Ocean temperature is above 64 F.
The licensee has proposed to use pump reference curves to determine compliance with the Code requirements.
NUREG-1482 states that to obtain approval to use pump reference curves, the licensee must demonstrate that the acceptance criteria are equivalent to the Code requirements in Table 3b of Part 6 for allowable ranges using reference values. The guidance provides a list of seven elements that the licensee must perform in preparing pump curves for the IST pump relief request.
The licensee has committed to these seven elements in their proposed alternative testing. Adherence to this guidance provides assurance that the proposed reference curves satisfy the Code requirements and willdetect degradation in the pump over the range of the curve bounded by reference points. Therefore, the proposed alternative provides reasonable assurance of operational readiness of the pump.
Moreover, approval of the licensee's request to use pump curves when testing the ASWPs willeliminate the need for certain valve manipulations of the ASW system.
This is an enhancement to plant safety and reliability by eliminating the potential for operator errors and plant transients, e.g., potential entry into Technical Specification 3.0.3, which requires initiation of a shutdown within one hour.
4,
~L The staff concludes that the licensee's proposed alternative to the pump test requirements of OMa-1988, Part 6, Paragraph 5.2(b) for.the four ASWPs is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) based on the determination that compliance with the specified requirement would result in a hardship or unusual difficultywithout a compensating increase in the level of quality and safety.
Consistent with'the Code test requirements', the alternative proposed by the licensee willprovide reasonable assurance of the operational readiness of the ASWPs.
Principal Contributor: D. Fischer, EMEB Date:
December 30, 1998