ML20012B525
| ML20012B525 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 02/26/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20012B524 | List: |
| References | |
| GL-85-16, NUDOCS 9003150188 | |
| Download: ML20012B525 (4) | |
Text
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UNITED STATES
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i
R_ ELATED TO AMENDMENT NO. 51 TO FACILITY OPERATING LICENSE NO. DPR-80 E
AND AMENDMENT NO. 50 TO FACILITY OPERATING LICENSE NO. DPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT. UNIT NOS 1 AND 2
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DOCKET NO. 50-275 AND 50-323 j
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1.0 INTRODUCTION
By letter dated May 15, 1989 September 15, and November 36,as modified by letters dated July 31989(Refere l
and Electric Company (PG&E or the licensee) requested amendments to the combinedTechnicalSpecifications(TS)appendedtoFacilityOperating License Nos. DPR-80 and DPR-82 for the Diablo Canyon Power Plant (DCPP) i l
Unit Nos. I and 2, respectively. The amendments change the TS to allow the removal of the boron injection tank (BIT).
Specifically, the license amendment request proposed to:
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i (1) Limit the applicability of Technical Specification (TS) 3/4.5.4
" Boron Injection System" and the associated bases to Unit 1 Cycle 4 and Unit 2 Cycle 3 operation. After those cycles. TS 3/4.5.4 and the associated bases will no longer apply, (2)
Revise TS Table 3.3-5, " Engineered Safet by increasing the safety injection (SI) y features Response Times,"
response times to 25 and 35 seconds for the offsite power available and unavailable cases, respectively, to be consistent with the BIT removal program, and (3) Revise TS Table 3.8-1, " Motor-Operated Valves Thermal Overload ProtectionandBygassDevices,"andTSTable3.6-1," Containment l
Isolation Valves, by changing the functional description of the BIT inlet and outlet valves and other valves to charging injection valves.
l-The staff evaluation of these changes is given below, 2.0 EVALUATION i
The NRC staff has evaluated the proposed changes and finds them i
acceptable, based on its review of the analyses and evaluations given by the licensee. A discussion of each of the specific technical specification changes made by these amendments is presented below.
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The BIT was originally incorporated into Westinghouse-designed plants as a means of mitigating the consequence of accidental depressurization of the main steam system events. The sole purpose of the BIT, as a component of the Safety Injection System is to provide concentrated boricacid(20,000ppe)andthusanegatIvereactivityinsertionduring accidents.
Problems and safety concerns associated with the 81T were identified in NRC Generic Letter 85-16, 'High Boron Concentrations,*
August 23, 1985. The use of high concentration boric acid imposes operational and maintenance problems such as minimum volumes and concentrations in boric acid system tanks, heat tracing malfunctions,ich BIT valve testing, and recovery from inadvertent safety injection, wh adversely affect plant availability. The high boric acid concentrations also cause safety concern involving boric acid solidification which may render the emergency core cooling inoperable. Therefore, many plants such as Beaver Valley, Byron /Braidwood, Turkey Point, McGuire and Catawba have removed the BITS. For these reasons PGAE also decided to remove the BIT and the associated heat tracing sys,tems from Diablo Canyon during the next refueling outage of Units 1 and 2.
The proposed change to limit the applicability to Unit 1 Cycle 4 and Unit 2 Cycle 3 operations for TS 3/4.5.4 is necessary to reflect the planned removal of the BIT and associated heat tracing systems. Since the BIT removal can only be implemented during a refueling outage, the cycle-specific TS changes reflect the differences between Units 1 and 2 that will exist between the Unit 2 third refueling outage and the Unit 1 fourthrefuelingoutage. Thereafter, TS 3/4.5.4 can be completely deleted.
Revisions o' the functional description of certain valves in TS Tables 3.6-1 and 3.8-1 is necessary to properly reflect the removal of the BIT.
The proposed BIT removal also requires a change in the safety injection response times. The increase of the SI response times is due to the interlock logic between the refueling water storage tank (RWST) and volume control tank (VCT) outlet isolation valves which ensures a water source to the suction of the centrifugal charging pumps, but delay the delivery of borated water to the RCS by the valve stroke time of the VCT outlet isolation valves.
Since the BIT is downstream of the charging pumps, borated water from the BIT would be delivered to the RCS regardless of where the charging pump suction source was coming from, and no TS changes were required as long as the BIT boron concentration requirement was in effect. However, the proposed elimination of the BIT boron concentration requirement necessitates the revision of the safety injection response times. The extra safety injection response times are included to account for the sequential operation of the refueling water storage tank and the closing of the Volume Control Tank valve.
Therefore the response times for delivery of the 2300 ppm borated water to the primary system in TS Table 3.3-5 are increased to 25 seconds and 35 seconds, respectively, for the off-site power available and unavailable situations.
Both the BIT removal and the SI response time increase are supported by the safety analysis using the new response times for the cases where the offsite power is available and not available to ensure compliance with the safety limits and other acceptance criteria, m-
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The licensee, by letter dated September 15, 1989, submitted WCAP.11938, Volume 1, ' BIT Elimination Study for Diablo Canyon Units 1 and 2," which provides safety analysis with the removal of the BIT. The safety analysis was performed for (1) the hypothetical steamline break, with and without offsite power available, for the largest double ended rupture of a steam pipe, and (2) credible steamline break, with and without offsite power available, for the largest single failed open steam generator relief safety and dump valve. The credible steamline break is an ANS Condition II event with the acceptance criteria that the specified acceptable fuel design limits should not be violated. The hypothetical main steamline break is an ANS Condition IV event with the criteria that the radiological release should not exceed the limits set forth in 10 CFR 100.
The steamline breaks were analyzed using the NRC approved method and computer code LOFTRAN.
Conservative assumptions and initial conditions were used in the analyses.
For example the analysis was set up to conservatively account for a low steam 1Ine pressure setpoint of 15 psia.
l Even though the BIT recirculation lines between the BIT and the boric acid tanks along with the isolation valves and flow instrument will be i
cut out and removed, the BIT and associated piping are conservatively modeled as being in place and full of water having 0 ppm boric acid.
l The safety injection (SI) response time for delivering the 2300 ppm borated water to the primary system was modeled as a 22 second pure delay followed by a 10 second linear ramp in the SI flow for the cases with the offsite power available. This is different from the 25 seconds l
in the proposed TS changes. However, since the SI delay time in the TS p
is defined as the durat< on between the time when the )rocess parameters l
being measured reach the setpoint and the time when tie charging pumps are at full flow, the assumed 22 second pure time delay and a 10 second linear ramp of $1 flow in the safety analysis is considered adequate.
The steamline break analysis used the W 3 critical heat flux correlation l-with an approved minimum departure from nucleate boiling ratio (DNBR) limit of 1.45 for the pressure below 1000 psia. Since a homogeneous core was used in the analysis for the transitional mixed core of the j
standard fuel and the Vantage 5 fuel, a mixed core penalty calculated i
with approved method was assigned to the Vantage 5 fuel which has higher i
hydraulic resistance than the standard fuel and would divert flow into the standard fuel if a true mixed core was modeled in the analysis. No mixed core penalty was assigned to the standard fuel because of its lower hydraulic resistance.
The resulting DNBRs in all cases analyzed never fall below the minimum DNBR limit. Therefore, there is a 95 percent probability at 95 percent confidence level that DNB will not l
occur and there is no fuel failure.
Even for the ANS Condition IV main steamline break event, no fuel failure is anticipated and the radiological consequence complies with the 10 CFR 100 criteria.
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,... In sumary, the staff has reviewed the safety analysis performed to support the proposed TS changes for removal of BIT and the associated heat tracing systems, as well as the increase in the SI response time.
Since approved methods were used for the analysis and the results conform to the acceptance criteria, the proposed TS changes are acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
These amendments involve changes in the installation or use of facility components located within the restricted area as defined in 10 CFR Part 20 and a change in surveillance requirements. At Diablo Canyon. the restricted area coincides with the site boundary. We have determined that the amendments involve no significant increase in the amounts, and no si nificant change in the types maybereleasedofgsite,andthatthereisnosIgnificantincreaseinof any effluents that individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10CFR51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of these amendments.
4.0 CONCLUSION
We have concluded, based on the consideraticns discussed above, that:
i (1) there is reasonable assurance that the health and safety of the p(2) such activities will be conducted in compliance with theublic will not b Commission'sregulationsand(3)theissuanceoftheseamendmentswill not be inimical to the common defense and security or the health and safety of the public.
Principal Contributors:
Y. Hsii Harry Rood Dated: February 26, 1990 t
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