ML19305C224

Forwards Technical Evaluations & Proposed Tech Spec Changes Reflecting New Max Average Planar Linear Heat Generation Rate Limits & Incorporating Isolation Condenser Sys Into ECCS Sys.Class III Fee Encl

ML19305C224
Person / Time
Site:	Millstone
Issue date:	03/19/1980
From:	Counsil W NORTHEAST UTILITIES
To:	Ziemann D Office of Nuclear Reactor Regulation
Shared Package
ML19305C225	List: ML19305C224 ML19305C230
References
NUDOCS 8003260365
Download: ML19305C224 (8)

Text

{{#Wiki_filter:-, nourrunnsnmtmas ] =$N2SU* N R FORD. CONNECTICUT 06101 ll::"":::.:.:'llll':."l :' "~" ammsen L L J C".*: :::m l=',2% March 19, 1980 Docket No. 50-2145 Director of Nuclear Reactor Regulation Attn: Mr. D. L. Ziemann, Chief Operating Reactors Branch #2 U. S. Nuclear Regulatory Commission Washington, D. C. 20555 11, 1980.

References:

(1) W. G. Council letter to D. L. Ziemann dated February 4 (2) A. D. Vaughn (GE) letter to M. P. Hills (NUSCO) dated February 8,1980 (attached to Reference (1)). (3) A. D. Vaughn (GE) letter to R. L. McGuinness/W. C. Mihal (NUSCO) dated March 12, 1980. Gentlemen: Millstone Nuclear Power Station, Unit No. 1 Small Break Loss of Coolant Accident Analysis Proposed Technical Specification Changes for Isolation Condenser In Reference (1), Northeast Nuclear Energy Company (NNECO) described the impact of the LPCI loop selection logic insensitivity to small treak accidents. Reference (1) also explained the interim corrective actions: administrative MAPLHGR reduction and ADS timer setback. This letter now proposes Technical Specification changes for the long term, which conservatively bound the more limiting small break accident results. The proposed changes analytically incorporat' the Isolation Condenser System into the ECCS systems. The proposed Specification changes and our technical evaluations are attached. The safet, evaluation and rcview by the offsite Nuclear Review Board have concluded this change reflects new MAPLHGR limits based on taking credit for the isolatior. condenser during certain small break scenarios. The addition of the isolation condenser reduces the inventory loss during depressurization, increases the depressurization rate, and decreases the depressurization time. The above improvements result in earlier hot node recovery and lower peak clad temperature. The addition of the isolation condenser to the ECCS scheme does not increase the probability of an accident, does not create the possibility of an accident of a different nature and does not reduce the margin of safety of any Technical Specifications. The change does not present any unreviewed safety questions when reviewed with respect to 10CFR50.59 P 30 800s280

.. During the interim, until these changes are approved by the NRC, the plant will administratively maintain a MAPLHGR multiplier of 0.86. The proposed change is a 0 91 multiplier. Reference (2) explains that the 0.86 multiplier provides sufficient margin under low core flow conditions such that the " Low Core Flow Multiplier" in Specification 3.ll.A.1 does not need to be applied. It is, therefore, proposed to be deleted. Upon learning of the LPCI loop selection togic insensitivity, the plant also administratively instituted an interim ADS timer setback of 45 seconds as described in Reference (1), which is within Specification limits. Inasmuch as the 120 second ADS timer is the preferred delay to enhance high pressure ECCS capability, the timer will be administratively returned to the 120 second Specification limit. The schedule for returning the 120-second ADS involves the availability of automatic initiation features on the Isolation Condenser system as described in the following paragraph. The Isolation Condenser initiation logic is being augmented with an ability for automatic initiation upon reactor vessel low-low level ECCS signal. This is in addition to the high pressure automatic initiation currently installed. Plant reviews of the attached Technical Specification changes concluded that operator action or Safety Relief Valve action may maintain vessel pressure low enough following a nmall break that sustained high pressure would not exist to automatically start the Isclation Condenser. Therefore, the low-low level feature is being added. This is further discussed in the attached technical evaluation. Until the low-low trip is added, it is concluded by NNECO that the 0 91 MAPLHGR multiplier, Isolation Condenser credit, and associated 120 second ADS should not replace the current 0.86 MAPLHGR multiplie and associated 45 second ADS. It is expected that the low-low trip of the Isolation Condenser will be installed by the end of March,1980. At that time, NNECO vill administratively return the timer to 120 seconds, but will recain the more restrictive.86 multiplier until Staff approval of the proposed Specification changes herein. NNECO has reviewed the proposed License Amendment pursuant to the requirements of 10CFR170, and has determined that the proposal constitutes a Class III amendment. Accordingly, enclosed herewith is payment in the emount of $4,000 (four thousand dollars). Although Reference (1) indicated this letter would be submitted by March 15, 1980, the delay (resulting from operator feedback on the need for a low-low level trip) was discussel with the NRC Project Manager, and an extension of several days was granted via telephone. Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY f (fLd1/ /. 'G. Counsil Vice President Attachment

~. STATE OF CONNECTICLT ) ');bg, /9 / Q fd ) ss. Berlin 3 COUNTY OF HARTFORD ) Then personally appeared before se W. G. Counsil, who being duly sworn, did state that he is Vice President of Northeast Nuclear Energy Company, a Licensee herein, that he is-authorized to execute and file the foregoing information in the name and on behalf of the Licensees herein and that the statements contained in said information are true and correct to the best of his knowledge and belief, bAJ hr. Oakb Notary Public My Commission Exp!res March 31,1981 9 i

e TECHNICAL REVIEW Revised MAPLHGR Limits Based on Small Break Accident / Gas Turbine Failure / IPCI' Injection _into Broken Recire. Discharge Loop / Isolation Condenser Credit-In Addition to ICS/2LPCI/3 ADS (120 Sec. Timer)- ~ PHENOMENON ~ The effects of adding the isolation condenser (IC) to the ECCS small break systems that are assumed to remain after gas turbine failure (1CS + 2LPCI + 3 ADS) are twofold: (1) depressurization performed by the IC prior to ADS reduces reactor inventory loss compared to depressurization only by ADS;. therefore, reflonding time is accelerated and uncovery time reduced; and (2) more rapid depressuriza- . tion causes the rated core spray pressure (105 psia) to be achieved approximately 40 seconds before hot. node recovery; this spray cooling credit helps to reduce lthe heatup rate and, therefore, reduces peak clad temperature. 1 METHODS j t New analyses using approved codes (SAFE, REFLOOD, CHASTE) in accordance with 10CFR50.46'and Appendix K have been performed (by General Electric (GE) to address the subject small break accident scenario, Reference (3)). Two analytical methods changes 'have been incorporated in the subject scenario. 4 l To accommodate the LPCI injection into the broken loop (LPCI loop selection 4 ' logic assumed to fail for breaks less than 0.1 ft ), GE calculates a flow

split -between LPCI flow to the vessel and out the break.

Conservative assump-tions are used to determine the a.,unt of cooling water which gets to the vessel. GE is in the process of documenting the assumptions and sensitivity of the flow split calculation. To determine the IC heat removal pcrformance, GE has calculated the appropriate . values for several pressures and uses a linear approximation to evaluate heat removal during depressurization. ( All other' analytical methods are consistent with the SAFE, REFLOOD, and CHASTE codes. ASSUMPTIONS ~(1) Worst break location for the LPCI loop selection logic failure is in . the discharge' side of the recire. loop. This' causes the flow split. l and reduction of LPCI' cooling flow to the vessel. Loop B was analyzed since IC return is to the suction side of Loop B. However, the IC condensate return flow is isolated from the break by the automatic closure of the discharge valve. A break spectrum from O'.07 - 0.12 ft2 i 2 was analyzed, with 0.10 ft being most' limiting. 4 4 a- ~,, = 4 s

2- -(2) ADS timer'is set at 120 seconds. (3)-' Credit was taken for the design heat transfer rate for the IC of '2.06 x 108 BTU /hr. This is conservative since the most recent sur-8 veillance showed a 2.79 x 10 BTU /hr capability. Actuation was based on the high pressur a signal (1085 psig for 15 seconds) which - occurs after'MSIV closure on low-low water level and subsequent re-pressurization. This corresponds to IC system initiating at approximately 110 seconds after the accident. High' pressure actuation vill be a backup to direct activation of IC on l low-low level, similar to other ECCS systems. Low-low level occurs at approximately 30 seconds, compared to the backup pressure actuation at 110 seconds. In all cases, an additional 30 second time delay is added to the analysis before IC is at rated conditions. Considering that the conden-sate line valve (IC-3) opens within 3.5 seconds, this is considered conserva-tive. 1 OTHER IC FEATURES I The activation of _the IC requires only the opening of normally closed valve IC-3 in the condensate return line. This valve.is powered by the safety-grade DC_ battery. All valves in the system are powered by safety-grade AC or DC ~ power and are also used for containment isolation. All are nonnally in i the open position (other than IC-3). r The IC system is safety Class 2 and is seismically qualified. The shell side water volume is sufficient for 30 minutes of operation at rated conditions without makeup. Two sources'of makeup are available. For small break mitigation, less.than 10 minutes of operation is required, and generally at less than rated conditions. RESULTS AND CONCLUSIONS The results of. the analyses are summarized in References (2) and (3) and are shown in the attached. Table 1 and Figures 1 and 2. Based on the analyses performed and documented by GE, the conservative assump-tions with respect to the IC capacity and actuation time, and the extremely - limiting conditions assumed regarding break location, break size, single failure, and loop selection logic failure, the resulting modification to MAPLHGR limits - (namely, a10 91 multiplier)- is considered acceptable for the remaining Cycle T operation. l-ew- -t c myr.-v-- _v = y ,_m.,.r<,w ..y,y- ,e-+

e 4 TABLE 1 - MILLSTONE EFFECT OF ISOLATION CONDENSER MAPLHGR MULTIPLIER =.91* 4 i Break Size Uncovery Time Reflooding Time Total Uncovered Time (ft ) SAFE (sec) REFLOOD (sec) (Sec) 2 0.07 229 509 280 0.085 205 502 297 0.10** 183 507 324 0.12 179 501 322

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