Tokyo Electric Power Co. release video footage is its completion of steel pipe sheet piles for a coastal wall designed to protect Fukushima No. 1 nuclear plant, which was damaged after the 2011 Tohoku earthquake and tsunami.
Tokyo Electric Power Co. release video footage is its completion of steel pipe sheet piles for a coastal wall designed to protect Fukushima No. 1 nuclear plant, which was damaged after the 2011 Tohoku earthquake and tsunami.
A new plan has recently been worked out for rehabilitating Tokyo Electric Power Co. Holdings Inc. (TEPCO), the embattled operator of the crippled Fukushima No. 1 nuclear power plant.
The plan is centered on a bold management reform for enhancing the utility’s earning capacity so it can cover the ballooning expenses related to the Fukushima nuclear disaster of 2011, including the payment of damages and the cost of scrapping the hobbled nuclear reactors.
TEPCO obviously has the duty to fulfill its responsibility to the people and communities affected by the disaster. But the plan has set profit targets that are anything but easy to achieve, and some of the components of the plan appear unlikely to be realizable any time soon.
There is a need to continue reviewing the plan so it will not end up as simply pie in the sky.
TEPCO came under de facto government ownership after it could no longer keep operating on its own as a result of the Fukushima nuclear meltdowns. The utility has since been paying damages and otherwise dealing with the aftermath of the disaster while receiving aid in various forms under government supervision.
It was learned late last year that post-disaster processing would cost twice as much as the previous estimate. The government worked out a framework, wherein about 16 trillion yen ($141 billion), out of the total expense of some 22 trillion yen, would be covered either by TEPCO or with profits from the sale of the government’s share in TEPCO.
The rehabilitation plan, which was revised in response thereto, envisages that TEPCO can come up with 500 billion yen in necessary expenses annually over the coming three decades. It also sets the goal of substantially increasing TEPCO’s profits.
Many questions linger, however.
A restart of the idled Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture, which is expected to be the key instrument for TEPCO’s turnaround, is unlikely to be feasible any time soon. The governor of Niigata Prefecture and others are growing increasingly distrustful of TEPCO, as it recently came to light that the company had failed to inform the government’s Nuclear Regulation Authority that one key building on the nuclear plant site is not sufficiently anti-seismic.
The first order of business is to take thorough safety measures. TEPCO should come up with ways for generating the necessary financial resources without relying on a restart of the nuclear plant.
The centerpiece of new measures for enhancing TEPCO’s earning capacity is a prospective reorganization of its operations along segment lines, such as in the field of power transmission and distribution and in nuclear power operations, which would also involve other utilities. That apparently came against the backdrop of the industry ministry’s hopes that TEPCO’s realignment will trigger a reform of the entire energy industry.
Other major electric utilities, however, are wary of the risk of having to play a part in TEPCO’s response to the nuclear disaster. It therefore remains uncertain whether the reorganization will actually take place as envisaged.
The framework for sharing the burdens of post-disaster processing, which the government has worked out as a precondition for the new plan, is in the first place ridden with problems.
The framework envisages that new entrants to the power supply market, who operate no nuclear reactors, will also have to pay part of the disaster response costs. Critics continue to argue such a plan is about passing the bill on to irrelevant parties.
The 4 trillion yen in radioactive cleanup fees are designated for being covered by profits on the sale of TEPCO shares. But that plan could fail unless TEPCO’s earnings were to expand and its share price were to grow significantly.
Using taxpayers’ money to fill the hole would then emerge as a realistic option.
TEPCO was allowed to stay afloat at the expense of taxpayers on the sole grounds that it bears heavy responsibility to the people and communities affected by the Fukushima disaster.
The government would have to take another step forward if TEPCO were unable to fulfill that responsibility. That would also fuel the argument for dismantling the embattled utility.
TEPCO is expected to soon make a fresh start under a reshuffled management. The utility and the government should not forget about the exacting eyes of the public.
Former Hitachi Ltd. chairman Takashi Kawamura, left, who will take the post of the next chairman of Tokyo Electric Power Company Holdings Inc., and Tomoaki Kobayakawa, who has been tapped to be the next TEPCO Holdings president, are pictured here in Tokyo’s Chiyoda Ward on April 3, 2017.
Six years since the outbreak of the nuclear disaster at Tokyo Electric Power Company (TEPCO) Holdings Inc.’s Fukushima nuclear plant, the utility still faces massive challenges. And yet, what I’ve come to see through my reporting is that efforts meant to help revitalize the company’s finances in order to secure the funds needed to bring the nuclear crisis under control and compensate victims, have been overshadowed by petty feuds over personnel appointments between executives dispatched by the central government — which effectively owns the company — and dyed-in-the-wool TEPCO employees. Rebuilding TEPCO will be impossible if such squabbles are not put to rest.
In March of this year, TEPCO announced an outline of its revitalization plans, with a restructuring of its nuclear power business as a central pillar, as well as a reshuffling of executive personnel. According to the announcement, chairman Fumio Sudo, 76, will be replaced by Takashi Kawamura, 77, the previous chairman at Hitachi Ltd., and president Naomi Hirose, 64, will be replaced by 53-year-old board director Tomoaki Kobayakawa.
After the nuclear crisis began in March 2011, TEPCO was effectively nationalized. The plan has been for TEPCO to increase its earning power by rebuilding its finances under the central government’s management, so that it could secure the funds necessary to decommission the reactors at Fukushima No. 1 Nuclear Power Plant and compensate victims of the disaster.
With the nationalization of TEPCO, the government swept the utility clean of all its old executives and in addition to placing bureaucrats from the Ministry of Economy, Trade and Industry (METI) on the company’s board, in 2014 it put Sudo, formerly of major steel corporation JFE Holdings, in the position of TEPCO chairman. However, when Sudo, with the backing of the government, implemented cost-cutting measures, grumblings were heard within the company that Sudo was seeking too many results too fast and that staff evaluations were changing too dramatically. Sudo’s clashes with TEPCO president Hirose, who had worked up the ranks and was initially considered pro-reform, grew increasingly serious.
There was an incident in the spring of 2016 that could be considered a prelude to current conflicts. Sudo and METI, unhappy with the fact that Hirose would not cut his ties with former management, tried to re-appoint him to the post of deputy chairman. Hirose resisted and, according to multiple sources involved with TEPCO, was able to get the support of a former TEPCO executive who had close ties with the prime minister’s office. As a result, Hirose stayed in his post as company president, but his relationship with Sudo deteriorated beyond the point of repair. “It wasn’t uncommon for the two to criticize each other openly at management meetings,” a senior TEPCO official said.
At the end of 2016, METI announced that the amount of money necessary to deal with the nuclear crisis would be about 21.5 trillion yen, almost twice the amount of an earlier estimate. Because of the need to secure more funds, the government set up an expert panel, which then offered “recommendations” to TEPCO on how to rebuild its finances. When it was revealed that “the passing of authority down to the next generation” was one of the pieces of advice offered by the panel, industry insiders saw it as another government attempt at bringing Hirose down from his post, a source close to the case said.
Hirose is said to have resisted strongly to such renewed efforts. However, Sudo vowed that he would step down if Hirose did, forcing Hirose to bow to the pressure to resign. Some in the electric power industry have described the latest personnel reshuffle a “tie” in that both “camps” made concessions, but discontent is already spreading among career TEPCO employees. According to a senior TEPCO official, new executives, including Kobayakawa and the new president of a subsidiary company, are “all drinking buddies of outside board members who are former METI bureaucrats.”
TEPCO can’t afford to waste time on personnel feuds. In order to come up with the money needed to bring the troubled reactors under control, TEPCO must earn 500 billion yen per year for the next 30 years. The amount goes up further when taking into account the funds needed for capital investment. Meanwhile, TEPCO’s consolidated financial results for fiscal 2016 stood at just 258.6 billion yen in operating income.
TEPCO’s outline of its latest reorganization plan shows that it is aiming to raise earning power by realigning its various businesses, such as nuclear power, as well as the transmission and distribution of power, with other utilities. However, this plan is a carbon copy of the recommendations given by the government-established expert panel. Some long-time TEPCO employees have said the company only included the recommendation into its reorganization plan because the government has been on its back to do so, and that because other utilities will find no benefit to them in restructuring with TEPCO, the plan will never come to fruition. If people in the company remain this divided, TEPCO will never be able to follow through with rigorous reforms.
If TEPCO drops the ball on management reform and is unable to come up with the money it needs, it could lead to further burdens on the public in the form of higher electricity prices. TEPCO, under normal circumstances, would have gone under following the onset nuclear disaster. So if things go further south, not just the utility, but the central government, which allowed the utility to survive by pumping 1 trillion yen from national coffers into the company, will be held accountable.
Kawamura, who will be appointed TEPCO’s new chairman at the company’s general meeting of shareholders in late June, has the experience of having accomplished Hitachi’s v-shaped turnaround through fundamental management reforms. While his appointment was initiated by the government, many TEPCO employees welcome Kawamura’s pending appointment. The latest personnel change may be the last chance for TEPCO and the government to put its differences aside toward the goal of rebuilding the troubled power company.
Looking back at the latest personnel power struggle, a senior TEPCO official said, “I’m embarrassed when asked if any of the people involved (in the debacle) had ‘our responsibility toward Fukushima’ in mind.” The government and TEPCO must not forget its responsibility toward the victims of the nuclear disaster. If they focused on the fact that there are people out there whose peaceful lives in their beloved hometowns were taken away from them, they could refrain from feuds over personnel appointments. (By Daisuke Oka, Business News Department)
Japan passes bill requiring TEPCO to save money for decommissioning Fukushima plant
TOKYO, May 10 (Xinhua) — Tokyo Electric Power Company Holdings Inc. will be required to raise funds for the decommissioning of the crisis-hit Fukushima nuclear power plant following the passing of a bill in parliament on Wednesday.
Under the law revised with the passage of the newly-passed bill, the government-backed Nuclear Damage Compensation and Decommissioning Facilitation Corp. will be involved in the decommissioning of the stricken plant in a bid for the government to assert more control over the utility hemorrhaging its profits.
The cost of decommissioning the facility that went through multiple meltdowns in the wake of an earthquake-triggered tsunami knocking out its key cooling functions in March 2011 has surged from previous estimates of 2 trillion yen (17.56 billion U.S. dollars) to 8 trillion yen (70.24 billion U.S. dollars) and a state panel has called for funds to be raised without affecting the embattled utility’s performance.
The government forecasts that the plant’s decommissioning work, as well as compensation payouts and costs related to ongoing decontamination work, will amount to some 21.5 trillion yen (188.77 billion U.S. dollars) in total.
The new bill will require TEPCO, under the supervision of the government-backed organization, to set aside an annual sum each business year to be approved by the industry minister.
The amount eyed by the industry ministry required each year to be banked by the utility is around 300 billion yen for a period of 30 years.
The use of reserve funds for decommissioning work will also have to be signed off by the industry minister under the new scheme.
Private think tanks have put estimates for decommissioning the plant at being far higher than the government’s estimates.
TEPCO is also eyeing the restarting of four of its seven reactors at its Kashiwazaki-Kariwa power plant in Niigata Prefecture from April 2019 as means to secure more finances.
The local governor, however, is skeptical about the reactors going back online.
The Diet passed a bill Wednesday requiring Tokyo Electric Power Company Holdings Inc. to put aside extra funds to decommission its crisis-hit Fukushima nuclear power plant, as the state seeks to gain more financial control over the utility.
Under the revised law, the state-backed Nuclear Damage Compensation and Decommissioning Facilitation Corp. will also be involved in the decommissioning process.
Currently, Tepco has been using profits to pay for scrapping the Fukushima No. 1 plant, which was destroyed after a 2011 earthquake and tsunami triggered a triple meltdown.
The revised law is expected to take effect later this year. With the estimated cost of the decommissioning work already surging to ¥8 trillion from the previously forecast ¥2 trillion, a government panel has called for setting up a funding system that is not dependent on the company’s financial health.
The government projects the total cost to deal with the Fukushima nuclear disaster will reach ¥21.5 trillion, including decommissioning costs, compensation and decontamination work.
Under the new program, the state-backed organization will decide on the amount Tepco should store away each business year and the industry minister must approve it.
The utility must also formulate a financial plan and obtain the minister’s approval when it uses the reserve fund for its decommissioning work.
The new law will strengthen the monitoring power of authorities as well, enabling the industry ministry and the organization to conduct on-site inspections to check whether Tepco is putting aside the money.
The government has a major say in the utility’s operations after acquiring 50.1 percent of the company’s voting rights. Tepco faces huge compensation payments and decommissioning costs among other problems due to the 2011 disaster.
The industry ministry has projected roughly ¥300 billion will be needed annually for the next 30 years to complete the scrapping of the power plant, which involves the difficult procedure of extracting nuclear debris.
The costs could grow further. A study by a Tokyo-based private think tank has shown the bill for the decommissioning could balloon to between ¥11 trillion and ¥32 trillion assuming materials from the No. 1 to 3 reactors, which suffered core meltdowns, need to be specially treated for radioactive waste.
The Japan Center for Economic Research estimated the total cost of managing the disaster could reach ¥70 trillion, more than three times the government calculation.
« …Researchers still believe the overall exposure to have been negligible in the grand scheme of things… » A nicely turned lie in the grand scheme !
« …Of course, the robots sent in to do the dirty work haven’t been nearly as lucky… » Yes, no joke !
Japan’s nuclear disaster gave everyone on Earth extra radiation
It’s been over half a decade since Japan’s Fukushima-Daiichi nuclear plant suffered a catastrophic meltdown due to the effects of a tsunami which struck the island nation, but scientists are only just now confirming its far-reaching effects. After conducting the first worldwide survey to measure the ultimate radiation exposure caused by the reactor meltdown, researchers at the Norwegian Institute for Air Research finally have a figure on exactly how much extra radiation humanity was exposed to.
According to the group’s data, over 80 percent of the radiation that was released by the meltdown ended up in either the ocean or ice at the north and south poles. Of the remaining radiation, each human on the planet received roughly 0.1 millisievert, which equates to about “one extra X-ray each,” according to the team.
That amount of radiation isn’t likely to have much of an effect on humanity, however, and in comparison to the normal amount of radiation each of us receives over the course of a year, which can be as high as 3.65 millisieverts on average, it’s hardly anything. In fact, as NewScientist notes, a typical CT scan exposes you to 15 millisieverts on its own, and radiation sickness doesn’t occur until you reach the 1,000 millisievert threshold.
Obviously, those living the the vicinity of the reactor, especially in the immediate aftermath of the meltdown, can expect to have received a good deal more radiation as a result, but the researchers still believe the overall exposure to have been negligible in the grand scheme of things. Of course, the robots sent in to do the dirty work haven’t been nearly as lucky.
We have developed an Electron Tracking Compton Camera (ETCC), which provides a well-defined Point Spread Function (PSF) by reconstructing a direction of each gamma as a point and realizes simultaneous measurement of brightness and spectrum of MeV gamma-rays for the first time. Here, we present the results of our on-site pilot gamma-imaging-spectroscopy with ETCC at three contaminated locations in the vicinity of the Fukushima Daiichi Nuclear Power Plants in Japan in 2014. The obtained distribution of brightness (or emissivity) with remote-sensing observations is unambiguously converted into the dose distribution. We confirm that the dose distribution is consistent with the one taken by conventional mapping measurements with a dosimeter physically placed at each grid point. Furthermore, its imaging spectroscopy, boosted by Compton-edge-free spectra, reveals complex radioactive features in a quantitative manner around each individual target point in the background-dominated environment. Notably, we successfully identify a “micro hot spot” of residual caesium contamination even in an already decontaminated area. These results show that the ETCC performs exactly as the geometrical optics predicts, demonstrates its versatility in the field radiation measurement, and reveals potentials for application in many fields, including the nuclear industry, medical field, and astronomy.
Following the accident in Fukushima Daiichi Nuclear Power Plants on 11 March 2011, a huge amount of radionuclides was released to the atmosphere. As in 2016, 137Cs and 134Cs, which radiate gammas mainly from 600 keV to 800 keV, still remain in Fukushima, and many areas are still contaminated as a result1. Operations of decontamination are called for in a wide area in Fukushima and its surroundings to satisfy a legal limit for the maximum exposure of 0.23 μSv/h at any publicly-accessible open spaces2. An effective method to measure and monitor gamma-ray radiation is essential for efficient decontamination work, and as a result there has been a surge of demand for gamma-ray instruments with a wide field of view (FoV) which quantitatively visualize Cs contamination.
Many gamma cameras have been developed to make imaging observations to help decontamination, based on the Compton camera (CC)3,4,5,6,7, pin-hole (PHC)8, and coded-mask technologies. However, none of them has detected more than a limited number of hot spots, or has reported any quantitative radiation maps, let alone imaging spectroscopy. The CC is the most advanced among these three, yet has an intrinsic difficulty in imaging spectroscopy, which is related to its Point Spread Function (PSF)9,10.
So far, the most successful evaluations for the environmental radiation in contamination areas have been made by backpacks11 and unmanned helicopters12,13. Although these methods are, unlike gamma cameras, non-imaging measurements, in which measurements at each point are made with either a spectrometer or conventional dosimeter, quantitative and reliable 2-dimensional distributions of radiation have been successfully obtained after several measurements with overlapping fields of view are combined. The downside is that they require a considerable amount of time and efforts, and thus are not practical to be employed in a wide area.
Another fundamental problem with all these methods is that they do not directly measure the radioactivity on the ground, but measure the dose at 1 metre high from the ground (hereafter referred to as “1-m dose”) instead, and hence require complex analyses to convert the measured dose to the actual radioactivity on the ground. Indeed, we show that the 1-m dose does not always agree well with that measured immediately above the ground, which suggests an intrinsic difficulty in obtaining an accurate radioactivity distribution on the ground from the 1-m dose.
After a few pilot experiments of decontamination were conducted in Fukushima, it turned out that the amount of reduction of the ambient dose by decontamination was limited. The reduction ratios, defined by the dose ratio compared between before and after decontamination, were approximately 20% only in lower ambient-dose areas (<3 μSv/h)2, while >39% in higher ambient-dose areas (>3 μSv/h). When a (high) dose is measured at a point, gammas that contribute to the dose can originate anywhere a few radiation lengths away (~100 m) from the point. The goal of decontamination is to somehow identify and remove those radiation sources. However, none of the existing instruments can identify them, i.e., none of them can tell where or even in which direction the radiation source is located. To untangle the sources of a dose of contamination, the directions of all the gammas, as well as their energies if possible, must be determined. It means that the brightness distribution around the point must be obtained.
To address these issues of existing methods and visualize the Cs contamination, we have developed and employed an Electron-Tracking Compton Camera (ETCC). ETCCs were originally developed to observe nuclear gammas from celestial objects in MeV astronomy14, but have been applied in wider fields, including medical imaging15 and environmental monitoring16,17. An ETCC outputs two angles of an incident gamma by measuring the direction of a recoil electron and hence provides the brightness distribution of gammas with a resolution of the PSF9,10. The PSF is determined from the angular resolutions of angular resolution measure (ARM) and scatter plane deviation (SPD)9,18. The ARM and SPD correspond to a resolution of the polar and azimuthal angles of an incident gamma, respectively. Since a leakage of gammas from their adjacent region to the measured point is correctly estimated with the PSF, quantitative evaluation of the emissivity anywhere in the FoV is attained.
The most remarkable feature of the ETCC is to resolve the Compton process completely; the ETCC does not only provide the direction of a gamma, but also enables us to distinguish correctly reconstructed gammas from those mis-reconstructed9. Thus, the ETCC makes true images of gammas based on proper geometrical optics (PGO), as well as energy spectra9 free of Compton edges10. The PGO enables us to measure precise brightness (or emissivity) at any points in an image using an equi-solid-angle projection, such as Lambert projection, without the information of the distance to the source, as shown in Fig. 1. The obtained emissivity can be unambiguously converted into the dose on the ground (hereafter the E-dose), of which the procedure is identical with that described in the IAEA report19, but without need of the fitting parameters. We find the E-dose to be consistent with the dose independently measured by a dosimeter, and thus confirm that remote-sensing imaging-spectroscopy with the ETCC perfectly reproduces the spatial distribution of radioactivity10.
We performed the field test of gamma measurement in October, 2014 in relatively high-dose locations with the averaged ambient dose ranging from 1 to 5 μSv/h in Fukushima prefecture, using the compact 10 cm × 10 cm × 16 cm ETCC with a FoV of ~100°ϕ17. The SPD and ARM of the ETCC were measured to be 120° and 6° (FWHM), respectively, for 662-keV 137Cs peaks, which correspond to the PSF (Θ~15°), i.e., the radius of the PSF of 15° for the region that encompasses a half of gammas emitted from a point source9. It uses GSO scintillators and has an energy resolution of 11% (FWHM) at 662 keV. We chose the three different kinds of locations for measurements: (A) decontaminated pavement surrounded with not-decontaminated bush, (B) not-decontaminated ground, and (C) decontaminated parking lot. Figure 2a,c and d show their respective photographs.
We have found that the doses at 1-m and 1-cm measured with a dosimeter do not agree with each other, as demonstrated in Fig. 2a and b in the location (C). The 1-m dose, which is practically the emissivity averaged over the adjacent region of ~10 m, is the standard in the radiation measurement, presumably because it is useful to estimate potential health effects to the human body. The 1-cm dose, on the other hand, better reflects the emissivity on the ground at each grid point, of which the size is likely to be similar to the spatial resolution of the ETCC, and hence is useful to locate radioactivity on the ground for decontamination work. For these reasons, we adopt the 1-cm dose to compare with the emissivity measured with the ETCC in this work.
Figure 3a shows the photograph of FoV, overlaid with 1-cm dose at nine points and the E-dose map by ETCC, where the brightness (equivalent to the E-dose) is defined as the count rate of reconstructed gammas per unit solid angle (here 0.014 sr), corrected for the detection efficiency including the angular dependence of the ETCC9. Figure 3b shows the energy spectrum accumulated for the entire FoV, whereas Fig. 3c–e display those accumulated for the sky, the decontaminated pavement, and the not-decontaminated bush, respectively. The E-dose at the maximum brightness in Fig. 3a is estimated to be 2.6 μSv/h, which is consistent with the average of the 1-cm dose (0.9–4.3 μSv/h) around the centre of the FoV.
The spatial distribution of the E-dose is found to be consistent with that of the 1-cm dose, which was independently measured. The spectrum in Fig. 3e shows prominent peaks of direct gammas of Cs, which implies the contamination from the bush area, whereas the spectrum of the decontaminated pavement (Fig. 3d) shows much weaker Cs peaks, which implies the effect of the decontamination. The latter is dominated with low-energy scattered gammas, which emanate from inside of the ground and the adjacent areas. The spectrum of the sky (Fig. 3c) is clearly dominated with Compton-scattered gammas from Cs peaks (with the expected energy ranging from 200 to 500 keV) in the air. We should note that the spectra free of Compton scattering components enable us to make the unambiguous identification of the sources of radiation.
The results of imaging-spectroscopy in the two contrasting locations (B and C), in which no and thorough decontaminations, respectively, have been conducted, are shown in Figs 4 and 5. The exposure times are 80 min and 100 min, respectively. The ETCC gives spatially-resolved spectra, and accordingly the detailed condition of contamination at each point, similar to Fig. 3. In the contaminated location (B), although the energy spectrum of the FoV shows strong and direct gamma emission from Cs, Cs is found to be concentrated in the limited area of spot 1 (Fig. 4e), whereas little Cs is found in the other regions in the FoV (Fig. 4f). As such, imaging-spectroscopic measurement is a reliable method to unravel the state of contamination quantitatively. Even in the decontaminated location (C), both the image (Fig. 5a) and spectrum (Fig. 5f) reveal the existence of a “micro hot spot”, where some Cs remains on the ground and the spectrum has the dominant Cs peak (Fig. 5f), whereas the spectra for other regions (Fig. 5e) show that the main component is scattered low-energy gammas. Both the maps of 1-cm dose (Fig. 5a) and E-dose (Fig. 5b) show a hint of a small enhancement originating from a micro hot spot, although it is at a similar level to the fluctuation of the scattered gammas. The E-doses at the points of the maximum brightness in (B) and (C) are 5.0 and 1.3 μSv/h, respectively, which are also consistent with the 1-cm dose at the corresponding points.
Finally, we check consistency about a couple of properties of the ETCC and conventional dose measurements. First, we plot the total gamma counts obtained with the ETCC as 1-m doses at the position of the ETCC in Fig. 6a, and confirm a good correlation. Then, we plot the correlation between the 1-cm dose measured by the dosimeter and by the ETCC (E-dose) at the locations (B) and (C) in Fig. 6b. Except ~3 points adjacent to the hot spots in (B), the discrepancy between them is limited within ± ~30%. Considering the difference in the conditions, such as the size of the measured areas (~100 cm2 for a dosimeter and ~1 m2 for ETCC) and the energy range (>150 keV for a dosimeter and 486–1000 keV for ETCC), as well as the fact that a large dispersion in the accuracy of commercial dosimeters (±several 10%) has been reported, this amount of discrepancy is more or less expected. We conclude that good consistency between them is established for the wide range of the dose (0.1–5 μSv/h), and this is another proof that the ETCC achieves the PGO. In addition, the PGO gives the brightness of the sky over the hemisphere, and we find it to be comparable with that from the ground, after the difference in their solid angles is corrected (see the bottom row in Table 1). This means that roughly a half of the 1-m dose at any points originates from the sky. It then implies that the wide-band energy balance of gammas between the ground and the sky is in equilibrium and contribute to the ambient dose, presumably because the air is thick enough to scatter most of gammas emanating from the ground. It is consistent with the fact that the spectra of the sky (Figs 3c, 4c and 5c) are dominated with Compton scattering for Cs gammas (200–500 keV). This could not have been identified without spectra free of Compton edges. Our results also explain the reason why the amount of the reduction of the ambient dose was limited to often no more than 50% after decontamination work2 had been conducted in Fukushima, it is because a significant amount of radiation still comes from the sky in equilibrium.
Firstly, let us convert the emissivity to the 1-cm dose, using only the brightness measured by the ETCC. Figure 1b schematically shows the dosimeter configuration for the measurement of 1-cm dose. Since the top and the upper sides of the dosimeter are shielded with tungsten rubber, it detects gammas emanating from the ground to the lower hemisphere only. The count density of the gammas which pass through the plane of the dosimeter (indicated as P in Fig. 1b) is estimated to be approximately 2πΣ · (1 − cos(θ = 80°)) = 5.2Σ, where Σ is emissivity on the ground. Then we convert the count density of gammas at the dosimeter position into doses in units of μSv/h with the conversion factor of 1 μSv/h = ~100 counts · sec−1 · cm−2 for 662-keV gammas in the dosimeter, based on the IAEA report19 (in page 85).
In the not-decontaminated location (B), 135 gammas were observed with the ETCC (dB) at the maximum brightness point in Fig. 4a, where the unit solid angle is 0.014 sr. The brightness of the gamma is calculated to be 135 counts · sec−1/(0.014 sr · 100 cm2) = 96 counts · sec−1 · sr−1 · cm−2, and then we get, from the relation Σ = dB, 5.2Σ = 500 counts · sec−1 · cm−2, which corresponds to the dose of 5.0 μSv/h (the two points indicated as 5.0 and 5.7 [μSv/h] in Fig. 4a). For the location (C), 35 gammas were observed at the maximum brightness point in Fig. 5a, and then dB (=Σ) = 35 counts · sec−1/(0.014 sr · 100 cm2) = 25 counts · sec−1 · sr−1 · cm−2 and 5.2Σ = 130 counts · sec−1 · cm−2, which corresponds to 1.3 μSv/h. The 1-cm dose at this point is found to be roughly equal to the average of 1.0–2.2 μSv/h in Fig. 5a. For the location (A), dB is calculated in the similar manner to be dB = 70 counts · sec−1/(0.014 sr · 100 cm2) = 50 counts · sec−1 · sr−1 · cm−2 and 5.2Σ = 260 counts · sec−1 · cm−2, which corresponds to the dose of 2.6 μSv/h. The 1-cm dose at this point is ~3 μSv/h, and is roughly equal to the average of 1–4.3 μSv/h in Fig. 3a.
For comparison, we also applied the simple method described in pages 96–101 in the IAEA report19, calculating the doses with a conversion coefficient of 8.7 × 10−3 (μSv/h)/(Bq/cm2) for θ~80° for the 1-cm dose, which is estimated by accumulating gamma-flux at each point from the ground with the tungsten rubber shield. This method is the one described in pages 96–101 in the IAEA report19. For the location (A), a gamma flux on the ground is calculated to be 2πΣ/0.85 = 369 (Bq/cm2) and then the dose is 369 × 8.7 × 10−3 = 3.1 μSv/h. For the locations (B) and (C), the doses are estimated to be 5.9 and 1.6 μSv/h, respectively. Thus, we confirmed that the results deduced by the two independent methods are consistent with each other.
Decontamination work in Fukushima faces serious difficulty; it is hard to pin down which region is badly contaminated from which radiation source without investing massive resources like wide-scale backpack measurements. The capability of the ETCC to measure the emissivity (or dose) independently of the distance would enable us to propose a novel approach to it. If a mapping of the brightness of 137Cs on the ground was carried out over the wide area with the ETCC by aircraft with the similar way conducted in 20122, we could visualize variation of the doses across the area, and could tell where decontamination work would be required most and how much.
As a different application, if multiple ETCCs are installed at various places in a nuclear plant to carry out a continuous three-dimensional brightness monitoring, we could not only detect, for example, a sudden radiation release by accident, but also make a quantitative assessment of where and how the release has happened. This would provide vital initial parameters to computer simulations to estimate the later dissemination of radioactivity over a wide area after an accident. In fact, simulations for this purpose faced a great difficulty in the past due to lack of reliable observed parameters of radio activity, because radiation monitoring was performed solely by repeated simple dose measurements. These simple dose measurements are unable to provide sufficient information over the wide area where the gamma radiation comes from, unless a huge amount of resources of manpower and hence budget are invested. Given that governments in many countries are confronted with the reactor dismantling issue, detailed and quantitative mapping of the radiation emissivity on the surfaces of reactor facilities, which would be well achievable with the ETCC, would be beneficial. The ETCC has immense potentials for immediate applications to various radiation-related issues in the environment.
Some scientists assert that the detection efficiency of gas-based gamma detectors would be too low. However, we have found that some types of gas have sufficient Compton-scattering probability with the relevant effective areas of 110 cm2 and 65 cm2 at 1-MeV gammas with a 50-cm-cubic ETCC using CF4 gas and Ar gas at 3 atm, respectively9. Our prototype 30 cm-cubic ETCC with the effective area of a few cm2 at 300 keV was proved to perform expectedly well in MeV gamma-ray astronomy.
Now, we are constructing two types of more advanced ETCCs: one is a compact ETCC with the similar size and weight to the current model, but having a 20 times larger effective area (0.2 cm2 at 662 keV; type-A) and the other is a large ETCC aimed to be completed in 2018, which has a 1000 times larger effective area (10 cm2 at 662 keV; type-B). The details of Type-B are described elsewhere10.
Type-A has the similar size to the current ETCC, but has an increased TPC volume from 10 cm × 10 cm × 16 cm (rectangular solid) to 20 cm ϕ (in diameter)× 20 cm (cylinder), installed in the similar-sized gas vessel. It has a 5 times larger gas volume and 2.5 times wider detectable electron energy band with the TPC than the current model. In addition, if the mixed gas with Ar and CF4 (50%: 50%) at 2 atm is used, as opposed to the current Ar gas (~90% and some cooling gases) at 1.5 atm, the detection efficiency will be improved by a factor of 29. Then, the resultant detection efficiency (or effective area) will become 20 times larger than that of the current model, while keeping the similarly compact size and weight. The development of Type-A will be completed in 2017.
Type-B will provide the same detection limit for 6 sec exposure. If we perform a survey with Type-B from some aircraft at the altitude of 100 m, we will be able to make a spectroscopic map of a 1 km2 area with a 10 m × 10 m resolution for 1200 sec exposure to achieve the same detection limit, taking account of the absorption of the air. An unmanned airship is a good candidate for the aircraft, it flies slowly for an extended period and hence would enable us to do the precise imaging-spectroscopic survey. Then, the whole contamination area in Fukushima prefecture (roughly 20 km × 50 km) can be mapped with the same resolution as mentioned above in a realistic timescale of ~2 months, assuming 8 hours of work per day. Some of the spectra obtained in our aircraft-based survey might be found out to be generated by the gammas scattered by something, such as trees in woods, within the grid. Our survey will efficiently detect a hint for those areas, which can be then studied in more detail with on-site measurements, such as ones by backpacks11. No successful large-scale survey has been yet performed to monitor the radioactivity in Fukushima. Our upgraded ETCC will be capable of revolutionizing the decontamination work and more. We summarized the specifications of the current ETCC, type-A and type-B in Table 2.
The ETCC was mounted at 1.3 m high from the ground at its centre, tilted 20° downwards beneath the horizontal plane. The average distance to the ground in the FoV is ~4 m, which corresponds to the spatial resolution of ~1 m at the ground for its PSF. As a reference, we also made a mapping measurement of the dose at two heights of 1 m and 1 cm with every 1-m square grid in the FoV (except for the location (A), where the points of the measurements were sparser and irregular) with the commercial dosimeter (HORIBA, Radi PA-1100, http://www.horiba.com). In the dose measurement at the latter height (~1 cm), the top and four sides of the dosimeter were covered by tungsten rubber to shield it from the downward radiation (Fig. 1b).
We have developed a compact ETCC with a 10 cm × 10 cm × 16 cm gas volume, based on the 30-cm-cubic SMILE-II for MeV astronomy9. The ETCC is, like CCs, equipped with a forward detector as a scatterer of nuclear gammas and a backward detector as a calorimeter for measuring the energy and hit position of scattered gammas. The forward detector of the ETCC is a gaseous Time Projection Chamber (TPC) based on micro-pattern gas detectors (MPGD), which tracks recoil electrons. The TPC of the ETCC is a closed gas chamber, and thus can be used continuously for about three weeks without refilling with the gas5. The backward detector is pixel scintillator arrays (PSAs) with heavy crystal (at present we use Gd2SiO5: Ce, GSO). It is noted that, at the time of writing in 2016 after the survey work presented in this paper, we have been developing the Ethernet-based data handling system to replace the existing VME-based system. The latest ETCC available for field measurements is much more compact, which is built in the 40 cm × 40 cm × 50 cm base frame with the weight of 40–50 kg, and operated with a single PC with 24 V portable battery.
The contamination area in Fukushima is the similar environment to the space in the background dominated condition, where the radiation spreads ubiquitously. It is understandable that gamma cameras with the Compton method became the first choice to be employed for the decontamination work in Fukushima, following the precedents in MeV astronomy, even though it is clearly not the ideal instrument especially in the background-dominated environment.
Here, we explain how we measure the emissivity (or brightness) based on the proper geometrical optics (PGO) by the ETCC and how we estimate the dose on the ground from the emissivity measured by the ETCC. The following are the reason why no gamma camera but the ETCC can take a quantitative nuclear gamma image with the similar principle to that of optical cameras. According to the well-known formulas in PGO, the relation between emissivity Σ on the ground and detected brightness of the gamma in ETCC (dB) for solid angle Ω is given as Σ · A1 · dΩ1 = dB · A2 · dΩ2. and the relations dΩ1 = A2/D2, dΩ2 = A1/D2 hold, where A1 and A2 are the observed areas on the ground and the detection area in the ETCC (A2 = 100 cm2), respectively, and D is a distance between the ground and the ETCC. Figure 1a gives a schematic demonstration of it. These relations are then reduced to Σ = dB, which means that the emissivity is equal to the obtained brightness and is independent of the distance D in this optics. In practice, dB is calculated simply from the number of the detected gammas per unit solid angle corrected for the detection efficiency9. We should note that when the distance between a source and the ETCC (L) is comparable with, or longer than, the radiation length in the air (~70 m), dB in a unit solid angle must be corrected for the expected absorption, using the absorption coefficient (α) in the air for gammas with the relation dBcorrect = dB/(1 − exp(−L/α)).
We estimate the detection limit using the sensitivity from the calibration data with a point source (137Cs, 3 MBq) in the laboratory17. We detected 662-keV gammas from the point source with a significance of 5σ at a distance of 1.5 m with the exposure time of 13 min. The point source increases the dose at the detector front by 0.015 μSv/h from a background dose. If the same amount of gammas entered the ETCC over the whole FoV, the significance would decrease by = 0.5σ, assuming that the background gamma increases proportionally from 1 to 100 to the number of pixels. The current ETCC comprises 100 pixels and one pixel is defined as an area of the unit solid angle in the FoV. In the case of a 100 min observation under the dose of 2 μSv/h at the detector front (assuming the case of Location (C), i.e., low dose), the total number of gammas increases by . The expected significance per pixel is then calculated to be 16σ/ = 1.6σ, which is consistent with the observed significances of (1.2–2.5σ) in the low-dose area (see the error bars in Fig. 6b). Similarly, the expected significance for the high-dose area is calculated and is found to be also consistent with the observed values of (3–5σ). Thus, our results of the on-site measurements are well consistent with the expected significances estimated from the calibration in the laboratory.
We also estimate the emissivity within the PSF and the detection limit to check consistency with the calibration data. As shown in Fig. 7 the covered area by the PSF for the distance L between a target and the ETCC is given by L · sinΘ. Since the number of gammas (brightness) within the PSF is conserved along the line of sight, the sensitivity in the PSF is independent of the distance L if absorption in the air is not taken into account. For example, for the distances L of 10 m and 100 m, the sizes of an area corresponding to a detector pixel are estimated to be 1 m and 10 m, respectively, when the same detection limits for both the distances are used. The detection limit for the ~2σ level of the ETCC is 0.5 μSv/h at a unit solid angle for an exposure of 100 min (see the distribution of red points in Fig. 6b). Note that the limit is proportional to , and hence can be easily scaled for different exposures and effective areas.
How to cite this article: Tomono, D. et al. First On-Site True Gamma-Ray Imaging-Spectroscopy of Contamination near Fukushima Plant. Sci. Rep. 7, 41972; doi: 10.1038/srep41972 (2017).
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Takeda, S. et al. A portable Si/CdTe Compton camera and its applications to the visualization of radioactive substances. Nucl. Instr. Meth. Phys. Res. A 787, 207–211 (2015).
Cresswell, A. J. et al. Evaluation of forest decontamination using radiometric measurements”. Journal of Environmental Radioactivity. 164, 133–144 (2016).
Mizumoto, T. et al. A performance study of an electron-tracking Compton camera with a compact system for environmental gamma-ray observation. J. Instrum. 10, C01053 (2015).
Hero: Masao Yoshida disregarded orders to abandon the Fukushima No. 1 nuclear power plant. The actions of him and his team are credited with averting further disaster.
Disaster response, even at its most heroic, can fall to people who would rather be somewhere else.
So it was for Masao Yoshida, who, while helming the Fukushima No. 1 nuclear power plant during the disaster in 2011, gave the groan, “Why does this happen on my shift?”
But in some ways Yoshida, an industry veteran of 32 years, was the right man to handle the crisis. His leadership during those days on the edge, at times in defiance of orders from the top of the utility that employed him, is at the center of Rob Gilhooly’s new book “Yoshida’s Dilemma: One Man’s Struggle to Avert Nuclear Catastrophe.”
Gilhooly writes from the eye of the storm, putting the reader in the plant’s control room with almost claustrophobic immediacy. One of his challenges was to render the emergency in real-time. How much can prose, moving forward in measured steps, convey a lethal technology unraveling in extremis? How do you convey the breakdown of machinery without getting mired in technical detail?
“It was difficult,” says Gilhooly, who spent almost four years researching and writing the book. “What struck me about the plant workers — it sounded like complete chaos. My decision was not to make it sound orderly. I wanted it to appear chaotic, without the writing becoming chaotic itself. I tore my hair out over the technical details, because I wanted the book to be readable.”
In the end, the book is a cumulative experience — an intense ride that rewards endurance. Gilhooly weaves in the history of nuclear energy in Japan, interviews with experts and re-created conversations among the plant workers.
“Yoshida was a straight talker from Osaka — a larger-than-life personality,” says Gilhooly, who interviewed the superintendent off the record. “He was different from the other superintendents, more prepared to stick his neck out. He was sharper, more bloody-minded. When tipping his hat to authority, he may have done so with a quietly raised middle finger.”
This attitude might have saved lives, when, after a hydrogen blast at the No. 1 plant, Tepco HQ in Tokyo ordered staff to evacuate. Yoshida knew that the executives had little idea of what was actually happening at the plant. Going behind the backs of his superiors, he contacted then-Prime Minister Naoto Kan, insisting that leaving the plant would be reckless. The utility also ordered that seawater not be pumped through the reactor as coolant, since that would render it useless for energy generation in the future. Exposed to life-threatening levels of radiation, Yoshida and his team defied the order, scrambling to cool the overheating reactor with seawater.
The desperate move worked. The team managed to cool the reactor, and later the Fukushima Nuclear Accident Independent Investigation Commission, which was authorized by the Diet, concluded in its report that “(Yoshida’s) disregard for corporate instructions was possibly the only reason that the reactor cores didn’t explode.”
In Western media coverage of the Fukushima disaster, much was made of Japanese groupthink. A culturally ingrained obedience and a reluctance to question authority was blamed in part for the disaster. Still, the responses vary, and some staff put safety concerns over company loyalty.
“I didn’t want to editorialize,” says Gilhooly, who writes with a calm, thoughtful voice, avoiding the temptation of melodrama. “But yes, Yoshida — and others — refuted the stereotype that was used to explain parts of the disaster.”
Gilhooly is talking to a Japanese publisher, but thinks a translated version may prove difficult: His sources spoke freely about the events at the plant assuming the interviews wouldn’t be published in Japanese. Still, Gilhooly, who takes a stand in the book against using nuclear energy, hopes to fuel the ongoing debate in his adopted home.
“I just wanted to know the truth,” he says. “There is a discussion that needs to happen about nuclear power — about disaster un-preparedness in Japan. I wanted to contribute to that argument. It’s six years on and already we are airbrushing some things out.”
The book points out the gulf between rural Fukushima and the large cities consuming the energy it produced. Gilhooly talked to Atsufumi Yoshizawa, Yoshida’s deputy at the plant, who recalled the first home leave with his boss, a month after the disaster:
“Tokyo was … as though nothing had happened. They were selling things as usual, women were walking around with high heels and makeup as usual, while we didn’t even have our own clothes (which had been contaminated). I remember thinking, ‘What the hell is this? How can it be so different?’ I realized just how useless it would be to try and explain the situation at the plant to these people, what we had been through and the fear we had faced.”
It is a punch in the gut, then, to read about Yoshida’s death from esophageal cancer at age 58, just two years after his exposure to radiation. It’s one of the many elements of the Fukushima crisis that stirs anger, demanding a change that honors the lessons and sacrifice.
Gilhooly points out that, unlike Yoshida in the stricken plant, Japan has the chance to make positive choices about the future, choices that should be informed by the suffering in Fukushima.
“We should think more about how we use energy,” he concludes. “There are things we can do better, with small changes in lifestyle.”