ML20010A372
| ML20010A372 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 08/07/1981 |
| From: | Wells R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 13399, NUDOCS 8108110367 | |
| Download: ML20010A372 (6) | |
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COPSumBIS Power u,n w co.
l Vice President - Projects, Engineering and Construction General offices: 1945 West ParnaH Road, Jackson, MI 49201 * (517) 788-0453 August 7, 1981 b) e y\\
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missa Harold R Denton, Director
'.h Y, D Office of Nuclear Reactor Regulation US Nuclear Regulatory Commission
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Washington, DC 20555 iG MIDLAND PROJECT MIDLAND DOCKET NOS 50-329, 50-330 RESPONSE TO OPEN ITEMS OF DRAFT SER SECTION 5.4.7 FILE:
0505.805 SERIAL:
13399 ENCLOSURE: RESPONSE TO OPEN ITEMS OF DRAI'T SER SECTION 5.4.7 We have reviewed draft sections of the NRC Staff Safety Evaluation Report 5.4.1, 5.4.2, 5.4.3, 5.4.7 and 5.4.10.
Enclosed are our responses / comments to the open items contained in draft section 5.4.7.
.It should be noted that, as a result of our Design Review Board on Cold Shutdown, most of the open items identified in the draft SER were already being addressed.
With the reponses provided in this letter, Open Item 1 can be closed out by the Staff and the remainder of the open items should be classified as confirmatory issue; with respect to the final SER.
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a A ells Executive Manager For: J W Cook JWC/JRW/fs
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l CC RJCook, Midland Resident Inspector DSHood, US NRC TPSpeis, US NRC DBMiller, Midland hWHuston, Washington 8108110367 810807 oc0881-0165a131 hDRADOCK 05000329 PDR
1 DECAY HEAT REMOVAL SYSTEM - DRAFT SER SECTION 5.4.7 RESPONSE TO OPEN ITEMS The draft SER on the Decay Heat Removal System (5.4.7) received by Consumers Power Company contains the following NRC Reactor Systems Branch open items.
MANUAL ACTION OUTSIDE THE CONTROL ROOM Open Item 1(a) Manual action outside the control room in the absence of a postulated single failure of a safety grade system is not consistent with BTP 5-1.
The present design requires that the operator leave the control room to open DHR suction valves, restore power to the DHR heat exchanger bypass valves, align the Emergency Boration System and actuate the Auxiliary Pressurizer Fpray. Provide modifications so that these actions can be performed within the control room or propose alternate qualified paths by which these functions can be performed from the control room.
Response
This position summarizes the requirements for full compliance with BTP RSB 5-1.
However, for the purpose of implementation, this BTP divides plants into three classes. Class 2 plants are defined as "all plants (custom or standard) for which CP or PDA applications are docketed Letore January 1,1978 and for which an OL issuance is expected on or after January 1, 1979," and thus include the Midland Plant. For such plants, only partial implementation is required. Recommended implementation for Class 2 plants is addressed in Table 1 of the BTP RSB 5-1, which we have interpreted to allow local manual actions in cases other than recovery from a single failure if such manual actions are found to be acceptable.
We have completed our review of manual action outside the control room mentioned on page 8 of the draft SER for the various conditions described below. The Midland design would require local manual alignment for portions cf three processes within the scope of BTP RSB 5-1:
- 1) boration using the makeup and purification system, emergency boration system (EBS), and borated water storage tank or boric acid addition tanks (BAAT), 2) depressurization using the auxiliary pressurizer spray, and 3) long-term cooling using the decay heat removal drop line. As discussed below, these manual actions are performed in accessible areas and within acceptable time frames.
Regarding boration, table 1 of BTP RSB 5-1 does not give any specific system design as a possible solution for full compliance.
Instead, the BTP requires that boration be performed using only safety grade systems which can operate with either onsite or offsite power and with a single failure. Boration without letdown is mentioned as an acceptable example of such safety grade boration. The BTP also requires monitoring the boron concentration. For full compliance, " limited operator action inside or outside containment if justified" is allowed.
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The recommended implementation for Class 2 plants states:
Compliance will not be required if a) dependence on manual actions inside containment after SSE or single - failure or i
b) remaining at hot standby until manual actions or repairs are complete are found to be acceptable for the individual
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plant.
The Midland design provides a safety-grade EBS which can provide sufficient boration for hot standby with onsite or offsite power. Local manual actions i
are required to align the EBS and-for reactor coolant system sampling. These i
actions are performed in the auxiliary building. The earliest manual action outside the control room is alignment of the EBS. For the scenario requiring-the earliest EBS injection, this alignment is required approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> i
af ter a reactor trip. Thus, relying on operator actions is justified in terms of access and time available, as allowed by the BTP for full compliance. Use of the EBS is required only in the event of a reactor trip with.a stuck l
control rod and assuming loss of letdown capability. Since the frequency of a stuck control rod is comparable with that of a single failure, manual 4
alignment should be allowed in this case. The Midland design exceeds the-recommended implementation for Class 2 plants, which allows for nonsafety-grade boration with manual actions in containment.
Regarding depressurization, Table 1 of the BTP provides the following possible solution for full compliance:
Provide upgrading and additional valves to ensure operation of auxiliary pressurizer spray using only safety-grade
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subsystem meeting single failure.
Possible alternative may I
involve using pressurizer power-operated relief valves j
wnich have been upgraded. Meet SSE and single failure without manual operation within containment.
l The recommended implementation for Class 2 plants states:
l Compliance will not be required if a) dependence on manual l
actions inside containment. after SSE or single failure or b) remaining at hot standby until manual actions or repairs i
are' complete are found to be acceptable for the individual plant.
The Midland design provides a safety grade auxiliary pressurizer. spray which
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requires local manual alignment. This alignment is not required until after 1
EBS injection, -thus giving the operator sufficient time to take action. The manual action for the alignment-is performed in the auxiliary building. The 2
auxiliary pressurizer. spray is required only in the event of a loss of offsite power resulting in the loss of all reactor coolant flow. A safety-grade PORV 4
is also available and operable from the control room. The-Midland design meets the proposed solution for full compliance and exceeds the recommended implementation for Class 2 plants, which could be a nonsafety-grade auxiliary-l.
pressurizer spray with manual actions in containt t.
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i For long-term cooling, BTP RSB 5-1 provides the following possible solution 4
for full compliance:
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Provide double drop line (or valves in parallel) to prevent I
single valve failure from stopping RHR cooling function.
The recommended implementation for Class 2 plants states:
Compliance will not be required if it can be shown that correction for single failure by manual actions inside or outside of containment or return to hot standby until manual actions (or repairs) are found to be acceptable for the individual plant.
i The Midland design provides a single decay heat removal (DHR) drop line with a series / parallel motor-operated valve arrangement in containment. Local manual actions in the auxiliary building are required for alignment. Local manual actions inside containment are not required for alignment or control.
Because the plant can be maintained at hot standby, sufficient time is available for the operator to perform these actions. Manual actions are not required outside the control room to recover from single active failures that could interrupt decay heat removal cooling. The Midland desf 7 meets or 3
exceeds the recommended implementation for Class 2 plants, which allows for the possibility of a single drop line inside containment as well as outside.
Elimination of local manual actions to align the Decay Heat Removal System was evaluated.
Cooldown rate can be controlled from the control room through use of the cooler discharge valves rather than the cooler bypass valves. Several options exist involving the DHR suction valves:
- 1) leave the valves closed which would require local manual action for alignment, 2) leave either of the valves open, or 3) provide remote operation for either of the valves from the control room.
Leaving one valve open will affect reliability of the ECCS train with the open valve and expand the boundary of piping which could contain. post-accident radioactivity. Providing remote control of the DHR suction valves is not practical due to the tight piping configuration involved and inability to perform modifications in support of the scheduled fuel load date. Thus, local alignment of the DHR suction valves should be allowed given the dr:rb3cks of the other options and the previously stated justification.
With the single exception noted above, Midland would have an ultimate capability to reach cold shutdown from the control room. Given the long time frames involved and the safe shutdown design basis for Midland (hot standby) disallowance of manual actions outside the control room is not justifiable under GDC-19. Plant procedures are currently being developed which require i
manual actions outside the control room.
Open Item 1(b) Confirm that core floodtank isolation during the cooldown process can be
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accomplished from the control room.
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Response
The core floodtank isolation valves (IMO-1001A, IMO-1001B, 2MO-1101A, 2MO-1101B) are currently electrically locked open at the motor control centers for the valves. Closure of the valves would require power restoration at the breakers in the auxiliary building. The valves are then operable from the control room.
The valves are operated in this fashion to prevent spurious closure of the valves. As an alternative to isolating the core floodtanks, the capability exists to bleed the nitrogen from the tanks through the emergency vents from the control room.
NATURAL CIRCULATION C00LDOWN ANALYSIS Open Items 2.
Provide analyses of boron mixing in the reactor system during the approach to cold shutdown under natural circulation.
IncluC3 calculations of boron concentration and shutdaen margin as a function of time during cooldown. Address the possibility of boron injection into an inactive reactor coolant loop.
3.
Provide a time dependent calculation of reactor's system pressure and temperature for natural circulation cooldown. The calculations should include both two steam generator and single steam generator cooldown.
Response
The scheduled completion for the development of the code and for completion of the cooldown analyses is June 1982. Several options for a mathematical code tc evaluate single loop natural circulation cooldown are presently being evaluated. Single loop natural circulation cooldown is considered a limiting case and should bracket a two loop natural circulation cooldown. The analysis will include the potential for reverse flow in the idle loop. A description of the code can be provided by December 1981.
NATURAL CIRCULATION TEST PROGRAM Open Items 4.
Provide the details of a natural circulation test program which will demonstrate that the Midland Plants can be brought to cold shutdown without offsite power. Discuss provisions for demonstrating steam voids will not form in the p;1 mary system during cooldown.
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Provide the details of a test program designed to demonstrate that boron injected into the primary system during natural circulation cooldown will be adequately mixed within the primary system.
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Response
A natural circulation test program will be performed which is consistent with the guidance contained in the NRC leter from R L Tedesco to J W Cook, dated April 22, 1981, and the recent natural circulation test programs at NTOL
.fa cilities. The natural circulation test program will be documented in Chapter 14 of the FSAR by June 1982 and will include boron mixing and cooldown capability. Strict control of cooldown rate and water subcooling limits should prevent void formation.
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