Reactor 2 – Short and bitter.

Revision:

50.46 Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors US NRC.

Paragraph 5: (5) Long-term cooling. After any calculated successful initial operation of the ECCS, the calculated core temperature shall be maintained at an acceptably low value and decay heat shall be removed for the extended period of time required by the long-lived radioactivity remaining in the core.
http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0046.html
This requirement has existed in essence as a requirement for the ECCS since Ergen et al, AEC, 1967. The time ground was first turned at Fukushima Diiachi.

American Nuclear Society, “Fukushima Diiachi : ANS Committee Report”

http://fukushima.ans.org/report/accident-analysis

II.B.2. Fukushima Daiichi Unit 2
As with Unit 1, a scram occurred, and the MSIVs were closed after the earthquake. The RCIC system was manually started a couple of times and automatically tripped because of a high water level in the RPV. After the tsunami, some DC power was also lost, just as in Unit 1; therefore, the HPCI system was lost. However, the RCIC system operated for ~70 hours. In general, one should not expect the RCIC system to run much beyond 8 hours in a station blackout (SBO).

At 1:25 p.m. on March 14, it was determined that the RCIC system of Unit 2 had stopped because the reactor water level was decreasing, and operators began to reduce the RPV pressure in order to be able to inject seawater into the reactor using fire-extinguishing-system lines. There were problems depressurizing due to lack of electricity for the solenoid valves and lack of pressurized nitrogen supply to force the SRVs open. These issues caused significant time delays in achieving a low-enough reactor pressure to allow the low-pressure emergency pumps to add water to the RPV. Therefore, the fuel was uncovered while the RPV was without any water injection for ~6.5 hours. The fuel heated up, with significant damage and hydrogen production. Longer term, the water level in the RPV has not recovered to higher than core midplane, indicating a low-elevation leak in the RPV pressure boundary.
The containment pressure rise at first was much slower than should be expected if all the decay heat is delivered to the suppression pool, which is an indication of a leak in the containment boundary. The wetwell venting line configuration had been completed by 11:00 a.m. on March 13, but the containment pressure had not reached the rupture disk setpoint, so no venting occurred. After core damage, the containment pressure increased more rapidly, probably because of hydrogen production. At 6:00 a.m. on March 15, an impulsive sound that was initially attributed to a hydrogen explosion was confirmed near the suppression chamber of the containment. Later reviews suggested that sound was not due to hydrogen burn. In any case the containment pressure did sharply decrease. It is not clear whether the designed vent path was ever in service; however, longer term, the containment pressure has remained low, around the level of atmospheric pressure.” end quote.

They guarantee from 1967 that the ECCS is self powered and regulate that the ECCS must remove decay heat for as long as it takes. Regardless of the state of the primary cooling circuit, regardless of the state of the primary heatsinks.

Then, they power the ECCS valving from batteries which fail during a frequently encountered natural event. After 70 hours of the RCIC (Reactor Core Isolation Cooling) operating because the HPCI (High Pressure Core Coolant Injection) system lost its control and battery power due to water damage.

It was apparently impossible to change or charge the RCIC valve batteries within the 70 hours. And the RCIC is described in part by the ANS as follows:

“The primary purpose of the RCIC system (Fig. 2) is to provide makeup water to the RPV when the
RPV is isolated from the turbine-condenser. The RCIC system uses a steam-driven turbine-pump unit
and operates automatically in time and with sufficient coolant flow to maintain adequate water level in
the RPV for the following events:

• RPV isolated and maintained at hot standby
• complete NPP shutdown with loss of normal feedwater before the reactor is depressurized to a
level where the shutdown cooling system can be placed in operation
• loss of AC power. ”

(ANS, Appendix F Safety System Descriptions for Station Blackout Mitigation: Isolation Condenser, Reactor Core Isolation Cooling, and High-Pressure Coolant Injection, ANS committee Report, Fukushima Diiachi Disaster)

The response to the performance the “steam powered” RCIC performance by the ANS is this:

“the RCIC system operated for ~70 hours. In general, one should not expect the RCIC system to run much beyond 8 hours in a station blackout (SBO).”

“50.46 Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors US NRC.

Paragraph 5: (5) Long-term cooling. After any calculated successful initial operation of the ECCS, the calculated core temperature shall be maintained at an acceptably low value and decay heat shall be removed for the extended period of time required by the long-lived radioactivity remaining in the core.

He who owns the gold maketh the rules I guess.

Besides the primary coolant circuit loop heat exchangers, which were destroyed by the tsunami (recorded in Japan in writing at least as far back as the 1700s) there are three right next to each reactor: two isolation cooling system heat exchangers and associated cooling fans located in each reactor building and the Torus itself which is a multipurpose device.

And, after all that has happened the ANS doggedly states that “one should not expect the RCIC system to run much beyond 8 hours in a station blackout (SBO)” The contribution of the earthquake to the reactor failures

That is a value judgement the enfranchised should make. Ask the Japanese people.

I wouldn’t buy one.

One Response to “Reactor 2 – Short and bitter.”

  1. Blog de serge angeles » Blog Archive » Japon 2012 Apres le déluge/153 Says:

    […] fonctionne à l’aide de batteries prévues pour offrir une autonomie maximale d’environ 72 heures. Le 13 mars, ce système de secours fonctionnait déjà depuis 48 heures […]

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